-this does not help #3719, likely diagnosis was wrong as well, undo
[oweals/gnunet.git] / src / transport / plugin_transport_udp.c
index 925159a76cc9b777dbdd5bc225b4dd0b5526f63c..4db28b45c11f48f9a6d8bb0b7d6ed4fa8e20f0c4 100644 (file)
@@ -1,22 +1,22 @@
 /*
    This file is part of GNUnet
    (C) 2010, 2011 Christian Grothoff (and other contributing authors)
-
    GNUnet is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published
    by the Free Software Foundation; either version 3, or (at your
    option) any later version.
-
    GNUnet is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    General Public License for more details.
-
    You should have received a copy of the GNU General Public License
    along with GNUnet; see the file COPYING.  If not, write to the
    Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.
-*/
+ This file is part of GNUnet
Copyright (C) 2010-2015 Christian Grothoff (and other contributing authors)
+
+ GNUnet is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published
+ by the Free Software Foundation; either version 3, or (at your
+ option) any later version.
+
+ GNUnet is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with GNUnet; see the file COPYING.  If not, write to the
+ Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ Boston, MA 02111-1307, USA.
+ */
 
 /**
  * @file transport/plugin_transport_udp.c
 
 #define LOG(kind,...) GNUNET_log_from (kind, "transport-udp", __VA_ARGS__)
 
-#define PLUGIN_NAME "udp"
+/**
+ * After how much inactivity should a UDP session time out?
+ */
+#define UDP_SESSION_TIME_OUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 60)
 
 /**
  * Number of messages we can defragment in parallel.  We only really
 /**
  * We keep a defragmentation queue per sender address.  How many
  * sender addresses do we support at the same time? Memory consumption
- * is roughly a factor of 32k * UDP_MAX_MESSAGES_IN_DEFRAG times this
+ * is roughly a factor of 32k * #UDP_MAX_MESSAGES_IN_DEFRAG times this
  * value. (So 128 corresponds to 12 MB and should suffice for
  * connecting to roughly 128 peers via UDP).
  */
 #define UDP_MAX_SENDER_ADDRESSES_WITH_DEFRAG 128
 
+
+/**
+ * UDP Message-Packet header (after defragmentation).
+ */
+struct UDPMessage
+{
+  /**
+   * Message header.
+   */
+  struct GNUNET_MessageHeader header;
+
+  /**
+   * Always zero for now.
+   */
+  uint32_t reserved;
+
+  /**
+   * What is the identity of the sender
+   */
+  struct GNUNET_PeerIdentity sender;
+
+};
+
+
 /**
- * Closure for 'append_port'.
+ * Closure for #append_port().
  */
 struct PrettyPrinterContext
 {
+  /**
+   * DLL
+   */
+  struct PrettyPrinterContext *next;
+
+  /**
+   * DLL
+   */
+  struct PrettyPrinterContext *prev;
+
+  /**
+   * Our plugin.
+   */
+  struct Plugin *plugin;
+
+  /**
+   * Resolver handle
+   */
+  struct GNUNET_RESOLVER_RequestHandle *resolver_handle;
+
   /**
    * Function to call with the result.
    */
   GNUNET_TRANSPORT_AddressStringCallback asc;
 
   /**
-   * Clsoure for 'asc'.
+   * Clsoure for @e asc.
    */
   void *asc_cls;
 
   /**
-   * Port to add after the IP address.
+   * Timeout task
    */
-  uint16_t port;
+  struct GNUNET_SCHEDULER_Task *timeout_task;
 
   /**
-   * IPv6 address
+   * Is this an IPv6 address?
    */
-
   int ipv6;
 
   /**
    * Options
    */
   uint32_t options;
-};
 
+  /**
+   * Port to add after the IP address.
+   */
+  uint16_t port;
 
-enum UDP_MessageType
-{
-  UNDEFINED = 0,
-  MSG_FRAGMENTED = 1,
-  MSG_FRAGMENTED_COMPLETE = 2,
-  MSG_UNFRAGMENTED = 3,
-  MSG_ACK = 4,
-  MSG_BEACON = 5
 };
 
+
+/**
+ * Session with another peer.
+ */
 struct Session
 {
   /**
@@ -113,12 +158,15 @@ struct Session
    */
   struct GNUNET_PeerIdentity target;
 
-  struct UDP_FragmentationContext * frag_ctx;
+  /**
+   * Plugin this session belongs to.
+   */
+  struct Plugin *plugin;
 
   /**
-   * Address of the other peer
+   * Context for dealing with fragments.
    */
-  const struct sockaddr *sock_addr;
+  struct UDP_FragmentationContext *frag_ctx;
 
   /**
    * Desired delay for next sending we send to other peer
@@ -133,7 +181,12 @@ struct Session
   /**
    * Session timeout task
    */
-  GNUNET_SCHEDULER_TaskIdentifier timeout_task;
+  struct GNUNET_SCHEDULER_Task *timeout_task;
+
+  /**
+   * When does this session time out?
+   */
+  struct GNUNET_TIME_Absolute timeout;
 
   /**
    * expected delay for ACKs
@@ -145,72 +198,41 @@ struct Session
    */
   struct GNUNET_TIME_Relative last_expected_msg_delay;
 
-  struct GNUNET_ATS_Information ats;
-
-  size_t addrlen;
-
-
-  unsigned int rc;
-
-  int in_destroy;
-
-  int inbound;
-};
-
-
-struct SessionCompareContext
-{
-  struct Session *res;
-  const struct GNUNET_HELLO_Address *addr;
-};
-
-
-/**
- * Closure for 'process_inbound_tokenized_messages'
- */
-struct SourceInformation
-{
   /**
-   * Sender identity.
+   * Our own address.
    */
-  struct GNUNET_PeerIdentity sender;
+  struct GNUNET_HELLO_Address *address;
 
   /**
-   * Source address.
+   * Number of bytes waiting for transmission to this peer.
    */
-  const void *arg;
+  unsigned long long bytes_in_queue;
 
-  struct Session *session;
   /**
-   * Number of bytes in source address.
+   * Number of messages waiting for transmission to this peer.
    */
-  size_t args;
-
-};
-
+  unsigned int msgs_in_queue;
 
-/**
- * Closure for 'find_receive_context'.
- */
-struct FindReceiveContext
-{
   /**
-   * Where to store the result.
+   * Reference counter to indicate that this session is
+   * currently being used and must not be destroyed;
+   * setting @e in_destroy will destroy it as soon as
+   * possible.
    */
-  struct DefragContext *rc;
+  unsigned int rc;
 
   /**
-   * Address to find.
+   * Network type of the address.
    */
-  const struct sockaddr *addr;
-
-  struct Session *session;
+  enum GNUNET_ATS_Network_Type scope;
 
   /**
-   * Number of bytes in 'addr'.
+   * Is this session about to be destroyed (sometimes we cannot
+   * destroy a session immediately as below us on the stack
+   * there might be code that still uses it; in this case,
+   * @e rc is non-zero).
    */
-  socklen_t addr_len;
-
+  int in_destroy;
 };
 
 
@@ -227,28 +249,44 @@ struct DefragContext
    */
   struct GNUNET_DEFRAGMENT_Context *defrag;
 
+  /**
+   * Reference to master plugin struct.
+   */
+  struct Plugin *plugin;
+
+  /**
+   * Node in the defrag heap.
+   */
+  struct GNUNET_CONTAINER_HeapNode *hnode;
+
   /**
    * Source address this receive context is for (allocated at the
    * end of the struct).
    */
-  const struct sockaddr *src_addr;
+  const union UdpAddress *udp_addr;
 
   /**
-   * Reference to master plugin struct.
+   * Who's message(s) are we defragmenting here?
+   * Only initialized once we succeeded and
+   * @e have_sender is set.
    */
-  struct Plugin *plugin;
+  struct GNUNET_PeerIdentity sender;
 
   /**
-   * Node in the defrag heap.
+   * Length of @e udp_addr.
    */
-  struct GNUNET_CONTAINER_HeapNode *hnode;
+  size_t udp_addr_len;
 
   /**
-   * Length of 'src_addr'
+   * Network type the address belongs to.
    */
-  size_t addr_len;
-};
+  enum GNUNET_ATS_Network_Type network_type;
 
+  /**
+   * Has the @e sender field been initialized yet?
+   */
+  int have_sender;
+};
 
 
 /**
@@ -259,27 +297,27 @@ struct UDP_FragmentationContext
   /**
    * Next in linked list
    */
-  struct UDP_FragmentationContext * next;
+  struct UDP_FragmentationContext *next;
 
   /**
    * Previous in linked list
    */
-  struct UDP_FragmentationContext * prev;
+  struct UDP_FragmentationContext *prev;
 
   /**
    * The plugin
    */
-  struct Plugin * plugin;
+  struct Plugin *plugin;
 
   /**
-   * Handle for GNUNET_FRAGMENT context
+   * Handle for fragmentation.
    */
-  struct GNUNET_FRAGMENT_Context * frag;
+  struct GNUNET_FRAGMENT_Context *frag;
 
   /**
    * The session this fragmentation context belongs to
    */
-  struct Session * session;
+  struct Session *session;
 
   /**
    * Function to call upon completion of the transmission.
@@ -287,7 +325,7 @@ struct UDP_FragmentationContext
   GNUNET_TRANSPORT_TransmitContinuation cont;
 
   /**
-   * Closure for 'cont'.
+   * Closure for @e cont.
    */
   void *cont_cls;
 
@@ -306,11 +344,28 @@ struct UDP_FragmentationContext
    */
   size_t on_wire_size;
 
-  unsigned int fragments_used;
-
 };
 
 
+/**
+ * Function called when a message is removed from the
+ * transmission queue.
+ *
+ * @param cls closure
+ * @param udpw message wrapper finished
+ * @param result #GNUNET_OK on success (message was sent)
+ *               #GNUNET_SYSERR if the target disconnected
+ *               or we had a timeout or other trouble sending
+ */
+typedef void
+(*QueueContinuation) (void *cls,
+                      struct UDP_MessageWrapper *udpw,
+                      int result);
+
+
+/**
+ * Information we track for each message in the queue.
+ */
 struct UDP_MessageWrapper
 {
   /**
@@ -319,64 +374,72 @@ struct UDP_MessageWrapper
   struct Session *session;
 
   /**
-   * DLL of messages
-   * previous element
+   * DLL of messages, previous element
    */
   struct UDP_MessageWrapper *prev;
 
   /**
-   * DLL of messages
-   * previous element
+   * DLL of messages, next element
    */
   struct UDP_MessageWrapper *next;
 
   /**
-   * Message type
-   * According to UDP_MessageType
-   */
-  int msg_type;
-
-  /**
-   * Message with size msg_size including UDP specific overhead
+   * Message with @e msg_size bytes including UDP-specific overhead.
    */
   char *msg_buf;
 
   /**
-   * Size of UDP message to send including UDP specific overhead
-   */
-  size_t msg_size;
-
-  /**
-   * Payload size of original message
+   * Function to call once the message wrapper is being removed
+   * from the queue (with success or failure).
    */
-  size_t payload_size;
+  QueueContinuation qc;
 
   /**
-   * Message timeout
+   * Closure for @e qc.
    */
-  struct GNUNET_TIME_Absolute timeout;
+  void *qc_cls;
 
   /**
-   * Function to call upon completion of the transmission.
+   * External continuation to call upon completion of the
+   * transmission, NULL if this queue entry is not for a
+   * message from the application.
    */
   GNUNET_TRANSPORT_TransmitContinuation cont;
 
   /**
-   * Closure for 'cont'.
+   * Closure for @e cont.
    */
   void *cont_cls;
 
   /**
-   * Fragmentation context
+   * Fragmentation context.
    * frag_ctx == NULL if transport <= MTU
    * frag_ctx != NULL if transport > MTU
    */
   struct UDP_FragmentationContext *frag_ctx;
+
+  /**
+   * Message timeout.
+   */
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * Size of UDP message to send, including UDP-specific overhead.
+   */
+  size_t msg_size;
+
+  /**
+   * Payload size of original message.
+   */
+  size_t payload_size;
+
 };
 
 
+GNUNET_NETWORK_STRUCT_BEGIN
+
 /**
- * UDP ACK Message-Packet header (after defragmentation).
+ * UDP ACK Message-Packet header.
  */
 struct UDP_ACK_Message
 {
@@ -386,9 +449,9 @@ struct UDP_ACK_Message
   struct GNUNET_MessageHeader header;
 
   /**
-   * Desired delay for flow control
+   * Desired delay for flow control, in us (in NBO).
    */
-  uint32_t delay;
+  uint32_t delay GNUNET_PACKED;
 
   /**
    * What is the identity of the sender
@@ -397,112 +460,258 @@ struct UDP_ACK_Message
 
 };
 
+GNUNET_NETWORK_STRUCT_END
+
+
+/* ************************* Monitoring *********** */
+
+
 /**
- * Address options
+ * If a session monitor is attached, notify it about the new
+ * session state.
+ *
+ * @param plugin our plugin
+ * @param session session that changed state
+ * @param state new state of the session
  */
-static uint32_t myoptions;
+static void
+notify_session_monitor (struct Plugin *plugin,
+                        struct Session *session,
+                        enum GNUNET_TRANSPORT_SessionState state)
+{
+  struct GNUNET_TRANSPORT_SessionInfo info;
+
+  if (NULL == plugin->sic)
+    return;
+  if (GNUNET_YES == session->in_destroy)
+    return; /* already destroyed, just RC>0 left-over actions */
+  memset (&info,
+          0,
+          sizeof (info));
+  info.state = state;
+  info.is_inbound = GNUNET_SYSERR; /* hard to say */
+  info.num_msg_pending = session->msgs_in_queue;
+  info.num_bytes_pending = session->bytes_in_queue;
+  /* info.receive_delay remains zero as this is not supported by UDP
+     (cannot selectively not receive from 'some' peer while continuing
+     to receive from others) */
+  info.session_timeout = session->timeout;
+  info.address = session->address;
+  plugin->sic (plugin->sic_cls,
+               session,
+               &info);
+}
 
 
 /**
- * Encapsulation of all of the state of the plugin.
+ * Return information about the given session to the monitor callback.
+ *
+ * @param cls the `struct Plugin` with the monitor callback (`sic`)
+ * @param peer peer we send information about
+ * @param value our `struct Session` to send information about
+ * @return #GNUNET_OK (continue to iterate)
  */
-struct Plugin * plugin;
+static int
+send_session_info_iter (void *cls,
+                        const struct GNUNET_PeerIdentity *peer,
+                        void *value)
+{
+  struct Plugin *plugin = cls;
+  struct Session *session = value;
+
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_INIT);
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_UP);
+  return GNUNET_OK;
+}
 
 
 /**
- * We have been notified that our readset has something to read.  We don't
- * know which socket needs to be read, so we have to check each one
- * Then reschedule this function to be called again once more is available.
+ * Begin monitoring sessions of a plugin.  There can only
+ * be one active monitor per plugin (i.e. if there are
+ * multiple monitors, the transport service needs to
+ * multiplex the generated events over all of them).
  *
- * @param cls the plugin handle
- * @param tc the scheduling context (for rescheduling this function again)
+ * @param cls closure of the plugin
+ * @param sic callback to invoke, NULL to disable monitor;
+ *            plugin will being by iterating over all active
+ *            sessions immediately and then enter monitor mode
+ * @param sic_cls closure for @a sic
  */
 static void
-udp_plugin_select (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc);
+udp_plugin_setup_monitor (void *cls,
+                          GNUNET_TRANSPORT_SessionInfoCallback sic,
+                          void *sic_cls)
+{
+  struct Plugin *plugin = cls;
+
+  plugin->sic = sic;
+  plugin->sic_cls = sic_cls;
+  if (NULL != sic)
+  {
+    GNUNET_CONTAINER_multipeermap_iterate (plugin->sessions,
+                                           &send_session_info_iter,
+                                           plugin);
+    /* signal end of first iteration */
+    sic (sic_cls,
+         NULL,
+         NULL);
+  }
+}
+
+
+/* ****************** Little Helpers ****************** */
 
 
 /**
- * We have been notified that our readset has something to read.  We don't
- * know which socket needs to be read, so we have to check each one
- * Then reschedule this function to be called again once more is available.
+ * Function to free last resources associated with a session.
  *
- * @param cls the plugin handle
- * @param tc the scheduling context (for rescheduling this function again)
+ * @param s session to free
  */
 static void
-udp_plugin_select_v6 (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc);
+free_session (struct Session *s)
+{
+  if (NULL != s->address)
+  {
+    GNUNET_HELLO_address_free (s->address);
+    s->address = NULL;
+  }
+  if (NULL != s->frag_ctx)
+  {
+    GNUNET_FRAGMENT_context_destroy (s->frag_ctx->frag,
+                                     NULL,
+                                     NULL);
+    GNUNET_free (s->frag_ctx);
+    s->frag_ctx = NULL;
+  }
+  GNUNET_free (s);
+}
 
 
 /**
- * Start session timeout
+ * Function that is called to get the keepalive factor.
+ * #GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT is divided by this number to
+ * calculate the interval between keepalive packets.
+ *
+ * @param cls closure with the `struct Plugin`
+ * @return keepalive factor
  */
-static void
-start_session_timeout (struct Session *s);
+static unsigned int
+udp_query_keepalive_factor (void *cls)
+{
+  return 15;
+}
+
+
+/**
+ * Function obtain the network type for a session
+ *
+ * @param cls closure (`struct Plugin *`)
+ * @param session the session
+ * @return the network type
+ */
+static enum GNUNET_ATS_Network_Type
+udp_get_network (void *cls,
+                 struct Session *session)
+{
+  return session->scope;
+}
+
+
+/* ******************* Event loop ******************** */
 
 /**
- * Increment session timeout due to activity
+ * We have been notified that our readset has something to read.  We don't
+ * know which socket needs to be read, so we have to check each one
+ * Then reschedule this function to be called again once more is available.
+ *
+ * @param cls the plugin handle
+ * @param tc the scheduling context (for rescheduling this function again)
  */
 static void
-reschedule_session_timeout (struct Session *s);
+udp_plugin_select_v4 (void *cls,
+                      const struct GNUNET_SCHEDULER_TaskContext *tc);
+
 
 /**
- * Cancel timeout
+ * We have been notified that our readset has something to read.  We don't
+ * know which socket needs to be read, so we have to check each one
+ * Then reschedule this function to be called again once more is available.
+ *
+ * @param cls the plugin handle
+ * @param tc the scheduling context (for rescheduling this function again)
  */
 static void
-stop_session_timeout (struct Session *s);
+udp_plugin_select_v6 (void *cls,
+                      const struct GNUNET_SCHEDULER_TaskContext *tc);
+
 
 /**
- * (re)schedule select tasks for this plugin.
+ * (re)schedule IPv4-select tasks for this plugin.
  *
  * @param plugin plugin to reschedule
  */
 static void
-schedule_select (struct Plugin *plugin)
+schedule_select_v4 (struct Plugin *plugin)
 {
   struct GNUNET_TIME_Relative min_delay;
   struct UDP_MessageWrapper *udpw;
 
-  if ((GNUNET_YES == plugin->enable_ipv4) && (NULL != plugin->sockv4))
+  if ( (GNUNET_YES == plugin->enable_ipv4) &&
+       (NULL != plugin->sockv4) )
   {
     /* Find a message ready to send:
      * Flow delay from other peer is expired or not set (0) */
     min_delay = GNUNET_TIME_UNIT_FOREVER_REL;
     for (udpw = plugin->ipv4_queue_head; NULL != udpw; udpw = udpw->next)
       min_delay = GNUNET_TIME_relative_min (min_delay,
-                                           GNUNET_TIME_absolute_get_remaining (udpw->session->flow_delay_from_other_peer));
-    
-    if (plugin->select_task != GNUNET_SCHEDULER_NO_TASK)
-      GNUNET_SCHEDULER_cancel(plugin->select_task);
-
-    /* Schedule with:
-     * - write active set if message is ready
-     * - timeout minimum delay */
-    plugin->select_task =
-      GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-                                  (0 == min_delay.rel_value) ? GNUNET_TIME_UNIT_FOREVER_REL : min_delay,
-                                  plugin->rs_v4,
-                                  (0 == min_delay.rel_value) ? plugin->ws_v4 : NULL,
-                                  &udp_plugin_select, plugin);  
-  }
-  if ((GNUNET_YES == plugin->enable_ipv6) && (NULL != plugin->sockv6))
+                                            GNUNET_TIME_absolute_get_remaining (udpw->session->flow_delay_from_other_peer));
+    if (NULL != plugin->select_task_v4)
+      GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+    plugin->select_task_v4
+      = GNUNET_SCHEDULER_add_read_net (min_delay,
+                                       plugin->sockv4,
+                                       &udp_plugin_select_v4,
+                                       plugin);
+  }
+}
+
+
+/**
+ * (re)schedule IPv6-select tasks for this plugin.
+ *
+ * @param plugin plugin to reschedule
+ */
+static void
+schedule_select_v6 (struct Plugin *plugin)
+{
+  struct GNUNET_TIME_Relative min_delay;
+  struct UDP_MessageWrapper *udpw;
+
+  if ( (GNUNET_YES == plugin->enable_ipv6) &&
+       (NULL != plugin->sockv6) )
   {
     min_delay = GNUNET_TIME_UNIT_FOREVER_REL;
     for (udpw = plugin->ipv6_queue_head; NULL != udpw; udpw = udpw->next)
       min_delay = GNUNET_TIME_relative_min (min_delay,
-                                           GNUNET_TIME_absolute_get_remaining (udpw->session->flow_delay_from_other_peer));
-    
-    if (GNUNET_SCHEDULER_NO_TASK != plugin->select_task_v6)
-      GNUNET_SCHEDULER_cancel(plugin->select_task_v6);
-    plugin->select_task_v6 =
-      GNUNET_SCHEDULER_add_select (GNUNET_SCHEDULER_PRIORITY_DEFAULT,
-                                  (0 == min_delay.rel_value) ? GNUNET_TIME_UNIT_FOREVER_REL : min_delay,
-                                  plugin->rs_v6,
-                                  (0 == min_delay.rel_value) ? plugin->ws_v6 : NULL,
-                                  &udp_plugin_select_v6, plugin);
+                                            GNUNET_TIME_absolute_get_remaining (udpw->session->flow_delay_from_other_peer));
+    if (NULL != plugin->select_task_v6)
+      GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
+    plugin->select_task_v6
+      = GNUNET_SCHEDULER_add_read_net (min_delay,
+                                       plugin->sockv6,
+                                       &udp_plugin_select_v6,
+                                       plugin);
   }
 }
 
 
+/* ******************* Address to string and back ***************** */
+
+
 /**
  * Function called for a quick conversion of the binary address to
  * a numeric address.  Note that the caller must not free the
@@ -510,12 +719,14 @@ schedule_select (struct Plugin *plugin)
  * to override the address again.
  *
  * @param cls closure
- * @param addr binary address
- * @param addrlen length of the address
+ * @param addr binary address (a `union UdpAddress`)
+ * @param addrlen length of the @a addr
  * @return string representing the same address
  */
 const char *
-udp_address_to_string (void *cls, const void *addr, size_t addrlen)
+udp_address_to_string (void *cls,
+                       const void *addr,
+                       size_t addrlen)
 {
   static char rbuf[INET6_ADDRSTRLEN + 10];
   char buf[INET6_ADDRSTRLEN];
@@ -528,58 +739,69 @@ udp_address_to_string (void *cls, const void *addr, size_t addrlen)
   uint16_t port;
   uint32_t options;
 
-  options = 0;
-  if (addrlen == sizeof (struct IPv6UdpAddress))
+  if (NULL == addr)
+  {
+    GNUNET_break_op (0);
+    return NULL;
+  }
+
+  if (addrlen == sizeof(struct IPv6UdpAddress))
   {
     t6 = addr;
     af = AF_INET6;
     options = ntohl (t6->options);
     port = ntohs (t6->u6_port);
-    memcpy (&a6, &t6->ipv6_addr, sizeof (a6));
+    a6 = t6->ipv6_addr;
     sb = &a6;
   }
-  else if (addrlen == sizeof (struct IPv4UdpAddress))
+  else if (addrlen == sizeof(struct IPv4UdpAddress))
   {
     t4 = addr;
     af = AF_INET;
     options = ntohl (t4->options);
     port = ntohs (t4->u4_port);
-    memcpy (&a4, &t4->ipv4_addr, sizeof (a4));
+    a4.s_addr = t4->ipv4_addr;
     sb = &a4;
   }
-  else if (addrlen == 0)
-       {
-               GNUNET_snprintf (rbuf, sizeof (rbuf), "%s", "<inbound>");
-               return rbuf;
-       }
   else
   {
     GNUNET_break_op (0);
     return NULL;
   }
-  inet_ntop (af, sb, buf, INET6_ADDRSTRLEN);
-
-  GNUNET_snprintf (rbuf, sizeof (rbuf), (af == AF_INET6) ? "%s.%u.[%s]:%u" : "%s.%u.%s:%u",
-                   PLUGIN_NAME, options, buf, port);
+  inet_ntop (af,
+             sb,
+             buf,
+             INET6_ADDRSTRLEN);
+  GNUNET_snprintf (rbuf,
+                   sizeof(rbuf),
+                   (af == AF_INET6)
+                   ? "%s.%u.[%s]:%u"
+                   : "%s.%u.%s:%u",
+                   PLUGIN_NAME,
+                   options,
+                   buf,
+                   port);
   return rbuf;
 }
 
 
 /**
- * Function called to convert a string address to
- * a binary address.
+ * Function called to convert a string address to a binary address.
  *
- * @param cls closure ('struct Plugin*')
+ * @param cls closure (`struct Plugin *`)
  * @param addr string address
  * @param addrlen length of the address
  * @param buf location to store the buffer
  * @param added location to store the number of bytes in the buffer.
- *        If the function returns GNUNET_SYSERR, its contents are undefined.
- * @return GNUNET_OK on success, GNUNET_SYSERR on failure
+ *        If the function returns #GNUNET_SYSERR, its contents are undefined.
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
  */
 static int
-udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
-    void **buf, size_t *added)
+udp_string_to_address (void *cls,
+                       const char *addr,
+                       uint16_t addrlen,
+                       void **buf,
+                       size_t *added)
 {
   struct sockaddr_storage socket_address;
   char *address;
@@ -591,8 +813,8 @@ udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
   address = NULL;
   plugin = NULL;
   optionstr = NULL;
-  options = 0;
-  if ((NULL == addr) || (addrlen == 0))
+
+  if ((NULL == addr) || (0 == addrlen))
   {
     GNUNET_break (0);
     return GNUNET_SYSERR;
@@ -616,7 +838,7 @@ udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
     return GNUNET_SYSERR;
   }
   optionstr[0] = '\0';
-  optionstr ++;
+  optionstr++;
   options = atol (optionstr);
   address = strchr (optionstr, '.');
   if (NULL == address)
@@ -626,27 +848,28 @@ udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
     return GNUNET_SYSERR;
   }
   address[0] = '\0';
-  address ++;
+  address++;
 
   if (GNUNET_OK !=
-      GNUNET_STRINGS_to_address_ip (address, strlen (address),
-                                   &socket_address))
+      GNUNET_STRINGS_to_address_ip (address,
+                                    strlen (address),
+                                    &socket_address))
   {
     GNUNET_break (0);
     GNUNET_free (plugin);
     return GNUNET_SYSERR;
   }
-
-  GNUNET_free (plugin);
+  GNUNET_free(plugin);
 
   switch (socket_address.ss_family)
   {
   case AF_INET:
     {
       struct IPv4UdpAddress *u4;
-      struct sockaddr_in *in4 = (struct sockaddr_in *) &socket_address;
-      u4 = GNUNET_malloc (sizeof (struct IPv4UdpAddress));
-      u4->options =  htonl (options);
+      const struct sockaddr_in *in4 = (const struct sockaddr_in *) &socket_address;
+
+      u4 = GNUNET_new (struct IPv4UdpAddress);
+      u4->options = htonl (options);
       u4->ipv4_addr = in4->sin_addr.s_addr;
       u4->u4_port = in4->sin_port;
       *buf = u4;
@@ -656,9 +879,10 @@ udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
   case AF_INET6:
     {
       struct IPv6UdpAddress *u6;
-      struct sockaddr_in6 *in6 = (struct sockaddr_in6 *) &socket_address;
-      u6 = GNUNET_malloc (sizeof (struct IPv6UdpAddress));
-      u6->options =  htonl (options);
+      const struct sockaddr_in6 *in6 = (const struct sockaddr_in6 *) &socket_address;
+
+      u6 = GNUNET_new (struct IPv6UdpAddress);
+      u6->options = htonl (options);
       u6->ipv6_addr = in6->sin6_addr;
       u6->u6_port = in6->sin6_port;
       *buf = u6;
@@ -675,54 +899,78 @@ udp_string_to_address (void *cls, const char *addr, uint16_t addrlen,
 /**
  * Append our port and forward the result.
  *
- * @param cls a 'struct PrettyPrinterContext'
+ * @param cls a `struct PrettyPrinterContext *`
  * @param hostname result from DNS resolver
  */
 static void
-append_port (void *cls, const char *hostname)
+append_port (void *cls,
+             const char *hostname)
 {
   struct PrettyPrinterContext *ppc = cls;
+  struct Plugin *plugin = ppc->plugin;
   char *ret;
 
-  if (hostname == NULL)
+  if (NULL == hostname)
   {
-    ppc->asc (ppc->asc_cls, NULL);
+    /* Final call, done */
+    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
+                                 plugin->ppc_dll_tail,
+                                 ppc);
+    ppc->resolver_handle = NULL;
+    ppc->asc (ppc->asc_cls,
+              NULL,
+              GNUNET_OK);
     GNUNET_free (ppc);
     return;
   }
   if (GNUNET_YES == ppc->ipv6)
-    GNUNET_asprintf (&ret, "%s.%u.[%s]:%d", PLUGIN_NAME, ppc->options, hostname, ppc->port);
+    GNUNET_asprintf (&ret,
+                     "%s.%u.[%s]:%d",
+                     PLUGIN_NAME,
+                     ppc->options,
+                     hostname,
+                     ppc->port);
   else
-    GNUNET_asprintf (&ret, "%s.%u.%s:%d", PLUGIN_NAME, ppc->options, hostname, ppc->port);
-  ppc->asc (ppc->asc_cls, ret);
+    GNUNET_asprintf (&ret,
+                     "%s.%u.%s:%d",
+                     PLUGIN_NAME,
+                     ppc->options,
+                     hostname,
+                     ppc->port);
+  ppc->asc (ppc->asc_cls,
+            ret,
+            GNUNET_OK);
   GNUNET_free (ret);
 }
 
 
 /**
- * Convert the transports address to a nice, human-readable
- * format.
+ * Convert the transports address to a nice, human-readable format.
  *
- * @param cls closure
+ * @param cls closure with the `struct Plugin *`
  * @param type name of the transport that generated the address
  * @param addr one of the addresses of the host, NULL for the last address
- *        the specific address format depends on the transport
+ *        the specific address format depends on the transport;
+ *        a `union UdpAddress`
  * @param addrlen length of the address
  * @param numeric should (IP) addresses be displayed in numeric form?
  * @param timeout after how long should we give up?
  * @param asc function to call on each string
- * @param asc_cls closure for asc
+ * @param asc_cls closure for @a asc
  */
 static void
-udp_plugin_address_pretty_printer (void *cls, const char *type,
-                                   const void *addr, size_t addrlen,
+udp_plugin_address_pretty_printer (void *cls,
+                                   const char *type,
+                                   const void *addr,
+                                   size_t addrlen,
                                    int numeric,
                                    struct GNUNET_TIME_Relative timeout,
                                    GNUNET_TRANSPORT_AddressStringCallback asc,
                                    void *asc_cls)
 {
+  struct Plugin *plugin = cls;
   struct PrettyPrinterContext *ppc;
-  const void *sb;
+  const struct sockaddr *sb;
   size_t sbs;
   struct sockaddr_in a4;
   struct sockaddr_in6 a6;
@@ -731,26 +979,29 @@ udp_plugin_address_pretty_printer (void *cls, const char *type,
   uint16_t port;
   uint32_t options;
 
-  options = 0;
-  if (addrlen == sizeof (struct IPv6UdpAddress))
+  if (addrlen == sizeof(struct IPv6UdpAddress))
   {
     u6 = addr;
-    memset (&a6, 0, sizeof (a6));
+    memset (&a6,
+            0,
+            sizeof (a6));
     a6.sin6_family = AF_INET6;
 #if HAVE_SOCKADDR_IN_SIN_LEN
     a6.sin6_len = sizeof (a6);
 #endif
     a6.sin6_port = u6->u6_port;
-    memcpy (&a6.sin6_addr, &u6->ipv6_addr, sizeof (struct in6_addr));
+    a6.sin6_addr = u6->ipv6_addr;
     port = ntohs (u6->u6_port);
     options = ntohl (u6->options);
-    sb = &a6;
+    sb = (const struct sockaddr *) &a6;
     sbs = sizeof (a6);
   }
   else if (addrlen == sizeof (struct IPv4UdpAddress))
   {
     u4 = addr;
-    memset (&a4, 0, sizeof (a4));
+    memset (&a4,
+            0,
+            sizeof(a4));
     a4.sin_family = AF_INET;
 #if HAVE_SOCKADDR_IN_SIN_LEN
     a4.sin_len = sizeof (a4);
@@ -759,23 +1010,23 @@ udp_plugin_address_pretty_printer (void *cls, const char *type,
     a4.sin_addr.s_addr = u4->ipv4_addr;
     port = ntohs (u4->u4_port);
     options = ntohl (u4->options);
-    sb = &a4;
-    sbs = sizeof (a4);
-  }
-  else if (0 == addrlen)
-  {
-    asc (asc_cls, "<inbound connection>");
-    asc (asc_cls, NULL);
-    return;
+    sb = (const struct sockaddr *) &a4;
+    sbs = sizeof(a4);
   }
   else
   {
     /* invalid address */
     GNUNET_break_op (0);
-    asc (asc_cls, NULL);
+    asc (asc_cls,
+         NULL,
+         GNUNET_SYSERR);
+    asc (asc_cls,
+         NULL,
+         GNUNET_OK);
     return;
   }
-  ppc = GNUNET_malloc (sizeof (struct PrettyPrinterContext));
+  ppc = GNUNET_new (struct PrettyPrinterContext);
+  ppc->plugin = plugin;
   ppc->asc = asc;
   ppc->asc_cls = asc_cls;
   ppc->port = port;
@@ -784,192 +1035,34 @@ udp_plugin_address_pretty_printer (void *cls, const char *type,
     ppc->ipv6 = GNUNET_YES;
   else
     ppc->ipv6 = GNUNET_NO;
-  GNUNET_RESOLVER_hostname_get (sb, sbs, !numeric, timeout, &append_port, ppc);
-}
-
-
-static void
-call_continuation (struct UDP_MessageWrapper *udpw, int result)
-{
-  size_t overhead;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-      "Calling continuation for %u byte message to `%s' with result %s\n",
-      udpw->payload_size, GNUNET_i2s (&udpw->session->target),
-      (GNUNET_OK == result) ? "OK" : "SYSERR");
-
-  if (udpw->msg_size >= udpw->payload_size)
-    overhead = udpw->msg_size - udpw->payload_size;
-  else
-    overhead = udpw->msg_size;
-
-  switch (result) {
-    case GNUNET_OK:
-      switch (udpw->msg_type) {
-        case MSG_UNFRAGMENTED:
-          if (NULL != udpw->cont)
-          {
-            /* Transport continuation */
-            udpw->cont (udpw->cont_cls, &udpw->session->target, result,
-                      udpw->payload_size, udpw->msg_size);
-          }
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, messages, sent, success",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, bytes payload, sent, success",
-                                    udpw->payload_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, bytes overhead, sent, success",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes overhead, sent",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes payload, sent",
-                                    udpw->payload_size, GNUNET_NO);
-          break;
-        case MSG_FRAGMENTED_COMPLETE:
-          GNUNET_assert (NULL != udpw->frag_ctx);
-          if (udpw->frag_ctx->cont != NULL)
-            udpw->frag_ctx->cont (udpw->frag_ctx->cont_cls, &udpw->session->target, GNUNET_OK,
-                               udpw->frag_ctx->payload_size, udpw->frag_ctx->on_wire_size);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, messages, sent, success",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes payload, sent, success",
-                                    udpw->payload_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes overhead, sent, success",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes overhead, sent",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes payload, sent",
-                                    udpw->payload_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, messages, pending",
-                                    -1, GNUNET_NO);
-          break;
-        case MSG_FRAGMENTED:
-          /* Fragmented message: enqueue next fragment */
-          if (NULL != udpw->cont)
-            udpw->cont (udpw->cont_cls, &udpw->session->target, result,
-                      udpw->payload_size, udpw->msg_size);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, fragments, sent, success",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, fragments bytes, sent, success",
-                                    udpw->msg_size, GNUNET_NO);
-          break;
-        case MSG_ACK:
-          /* No continuation */
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, ACK msgs, messages, sent, success",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, ACK msgs, bytes overhead, sent, success",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes overhead, sent",
-                                    overhead, GNUNET_NO);
-          break;
-        case MSG_BEACON:
-          GNUNET_break (0);
-          break;
-        default:
-          LOG (GNUNET_ERROR_TYPE_ERROR,
-              "ERROR: %u\n", udpw->msg_type);
-          GNUNET_break (0);
-          break;
-      }
-      break;
-    case GNUNET_SYSERR:
-      switch (udpw->msg_type) {
-        case MSG_UNFRAGMENTED:
-          /* Unfragmented message: failed to send */
-          if (NULL != udpw->cont)
-            udpw->cont (udpw->cont_cls, &udpw->session->target, result,
-                      udpw->payload_size, overhead);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                  "# UDP, unfragmented msgs, messages, sent, failure",
-                                  1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, bytes payload, sent, failure",
-                                    udpw->payload_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, bytes overhead, sent, failure",
-                                    overhead, GNUNET_NO);
-          break;
-        case MSG_FRAGMENTED_COMPLETE:
-          GNUNET_assert (NULL != udpw->frag_ctx);
-          if (udpw->frag_ctx->cont != NULL)
-            udpw->frag_ctx->cont (udpw->frag_ctx->cont_cls, &udpw->session->target, GNUNET_SYSERR,
-                               udpw->frag_ctx->payload_size, udpw->frag_ctx->on_wire_size);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, messages, sent, failure",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes payload, sent, failure",
-                                    udpw->payload_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes payload, sent, failure",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes payload, sent, failure",
-                                    overhead, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, messages, pending",
-                                    -1, GNUNET_NO);
-          break;
-        case MSG_FRAGMENTED:
-          GNUNET_assert (NULL != udpw->frag_ctx);
-          /* Fragmented message: failed to send */
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, fragments, sent, failure",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, fragments bytes, sent, failure",
-                                    udpw->msg_size, GNUNET_NO);
-          break;
-        case MSG_ACK:
-          /* ACK message: failed to send */
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, ACK msgs, messages, sent, failure",
-                                    1, GNUNET_NO);
-          break;
-        case MSG_BEACON:
-          /* Beacon message: failed to send */
-          GNUNET_break (0);
-          break;
-        default:
-          GNUNET_break (0);
-          break;
-      }
-      break;
-    default:
-      GNUNET_break (0);
-      break;
-  }
+  GNUNET_CONTAINER_DLL_insert (plugin->ppc_dll_head,
+                               plugin->ppc_dll_tail,
+                               ppc);
+  ppc->resolver_handle
+    = GNUNET_RESOLVER_hostname_get (sb,
+                                    sbs,
+                                    ! numeric,
+                                    timeout,
+                                    &append_port,
+                                    ppc);
 }
 
 
 /**
  * Check if the given port is plausible (must be either our listen
  * port or our advertised port).  If it is neither, we return
- * GNUNET_SYSERR.
+ * #GNUNET_SYSERR.
  *
  * @param plugin global variables
  * @param in_port port number to check
- * @return GNUNET_OK if port is either open_port or adv_port
+ * @return #GNUNET_OK if port is either our open or advertised port
  */
 static int
-check_port (struct Plugin *plugin, uint16_t in_port)
+check_port (const struct Plugin *plugin,
+            uint16_t in_port)
 {
-  if ((in_port == plugin->port) || (in_port == plugin->aport))
+  if ( (plugin->port == in_port) ||
+       (plugin->aport == in_port) )
     return GNUNET_OK;
   return GNUNET_SYSERR;
 }
@@ -985,693 +1078,728 @@ check_port (struct Plugin *plugin, uint16_t in_port)
  * traffic.
  *
  * @param cls closure, should be our handle to the Plugin
- * @param addr pointer to the address
- * @param addrlen length of addr
- * @return GNUNET_OK if this is a plausible address for this peer
- *         and transport, GNUNET_SYSERR if not
- *
+ * @param addr pointer to a `union UdpAddress`
+ * @param addrlen length of @a addr
+ * @return #GNUNET_OK if this is a plausible address for this peer
+ *         and transport, #GNUNET_SYSERR if not
  */
 static int
-udp_plugin_check_address (void *cls, const void *addr, size_t addrlen)
+udp_plugin_check_address (void *cls,
+                          const void *addr,
+                          size_t addrlen)
 {
   struct Plugin *plugin = cls;
-  struct IPv4UdpAddress *v4;
-  struct IPv6UdpAddress *v6;
+  const struct IPv4UdpAddress *v4;
+  const struct IPv6UdpAddress *v6;
 
-  if ((addrlen != sizeof (struct IPv4UdpAddress)) &&
-      (addrlen != sizeof (struct IPv6UdpAddress)))
-  {
-    GNUNET_break_op (0);
-    return GNUNET_SYSERR;
-  }
-  if (addrlen == sizeof (struct IPv4UdpAddress))
+  if (sizeof(struct IPv4UdpAddress) == addrlen)
   {
-    v4 = (struct IPv4UdpAddress *) addr;
-    if (GNUNET_OK != check_port (plugin, ntohs (v4->u4_port)))
+    v4 = (const struct IPv4UdpAddress *) addr;
+    if (GNUNET_OK != check_port (plugin,
+                                 ntohs (v4->u4_port)))
       return GNUNET_SYSERR;
     if (GNUNET_OK !=
-        GNUNET_NAT_test_address (plugin->nat, &v4->ipv4_addr,
+        GNUNET_NAT_test_address (plugin->nat,
+                                 &v4->ipv4_addr,
                                  sizeof (struct in_addr)))
       return GNUNET_SYSERR;
   }
-  else
+  else if (sizeof(struct IPv6UdpAddress) == addrlen)
   {
-    v6 = (struct IPv6UdpAddress *) addr;
+    v6 = (const struct IPv6UdpAddress *) addr;
     if (IN6_IS_ADDR_LINKLOCAL (&v6->ipv6_addr))
     {
       GNUNET_break_op (0);
       return GNUNET_SYSERR;
     }
-    if (GNUNET_OK != check_port (plugin, ntohs (v6->u6_port)))
+    if (GNUNET_OK != check_port (plugin,
+                                 ntohs (v6->u6_port)))
       return GNUNET_SYSERR;
     if (GNUNET_OK !=
-        GNUNET_NAT_test_address (plugin->nat, &v6->ipv6_addr,
+        GNUNET_NAT_test_address (plugin->nat,
+                                 &v6->ipv6_addr,
                                  sizeof (struct in6_addr)))
       return GNUNET_SYSERR;
   }
+  else
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
   return GNUNET_OK;
 }
 
 
 /**
- * Task to free resources associated with a session.
+ * Our external IP address/port mapping has changed.
  *
- * @param s session to free
+ * @param cls closure, the `struct Plugin`
+ * @param add_remove #GNUNET_YES to mean the new public IP address,
+ *                   #GNUNET_NO to mean the previous (now invalid) one
+ * @param addr either the previous or the new public IP address
+ * @param addrlen actual length of the @a addr
  */
 static void
-free_session (struct Session *s)
-{
-  if (NULL != s->frag_ctx)
-  {
-    GNUNET_FRAGMENT_context_destroy(s->frag_ctx->frag, NULL, NULL);
-    GNUNET_free (s->frag_ctx);
-    s->frag_ctx = NULL;
-  }
-  GNUNET_free (s);
-}
-
-
-static void
-dequeue (struct Plugin *plugin, struct UDP_MessageWrapper * udpw)
-{
-  if (plugin->bytes_in_buffer < udpw->msg_size)
-      GNUNET_break (0);
-  else
-  {
-    GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, total, bytes in buffers",
-                              - (long long) udpw->msg_size, GNUNET_NO);
-    plugin->bytes_in_buffer -= udpw->msg_size;
-  }
-  GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, msgs in buffers",
-                            -1, GNUNET_NO);
-  if (udpw->session->addrlen == sizeof (struct sockaddr_in))
-    GNUNET_CONTAINER_DLL_remove (plugin->ipv4_queue_head,
-                                 plugin->ipv4_queue_tail, udpw);
-  if (udpw->session->addrlen == sizeof (struct sockaddr_in6))
-    GNUNET_CONTAINER_DLL_remove (plugin->ipv6_queue_head,
-                                 plugin->ipv6_queue_tail, udpw);
-}
-
-static void
-fragmented_message_done (struct UDP_FragmentationContext *fc, int result)
+udp_nat_port_map_callback (void *cls,
+                           int add_remove,
+                           const struct sockaddr *addr,
+                           socklen_t addrlen)
 {
-  struct UDP_MessageWrapper *udpw;
-  struct UDP_MessageWrapper *tmp;
-  struct UDP_MessageWrapper dummy;
-  struct Session *s = fc->session;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "%p : Fragmented message removed with result %s\n", fc, (result == GNUNET_SYSERR) ? "FAIL" : "SUCCESS");
-  
-  /* Call continuation for fragmented message */
-  memset (&dummy, 0, sizeof (dummy));
-  dummy.msg_type = MSG_FRAGMENTED_COMPLETE;
-  dummy.msg_size = s->frag_ctx->on_wire_size;
-  dummy.payload_size = s->frag_ctx->payload_size;
-  dummy.frag_ctx = s->frag_ctx;
-  dummy.cont = NULL;
-  dummy.cont_cls = NULL;
-  dummy.session = s;
-
-  call_continuation (&dummy, result);
+  struct Plugin *plugin = cls;
+  struct GNUNET_HELLO_Address *address;
+  struct IPv4UdpAddress u4;
+  struct IPv6UdpAddress u6;
+  void *arg;
+  size_t args;
 
-  /* Remove leftover fragments from queue */
-  if (s->addrlen == sizeof (struct sockaddr_in6))
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       (GNUNET_YES == add_remove)
+       ? "NAT notification to add address `%s'\n"
+       : "NAT notification to remove address `%s'\n",
+       GNUNET_a2s (addr,
+                   addrlen));
+  /* convert 'address' to our internal format */
+  switch (addr->sa_family)
   {
-    udpw = plugin->ipv6_queue_head;
-    while (NULL != udpw)
+  case AF_INET:
     {
-      tmp = udpw->next;
-      if ((udpw->frag_ctx != NULL) && (udpw->frag_ctx == s->frag_ctx))
+      const struct sockaddr_in *i4;
+
+      GNUNET_assert (sizeof(struct sockaddr_in) == addrlen);
+      i4 = (const struct sockaddr_in *) addr;
+      if (0 == ntohs (i4->sin_port))
       {
-        dequeue (plugin, udpw);
-        call_continuation (udpw, GNUNET_SYSERR);
-        GNUNET_free (udpw);
+        GNUNET_break (0);
+        return;
       }
-      udpw = tmp;
+      memset (&u4,
+              0,
+              sizeof(u4));
+      u4.options = htonl (plugin->myoptions);
+      u4.ipv4_addr = i4->sin_addr.s_addr;
+      u4.u4_port = i4->sin_port;
+      arg = &u4;
+      args = sizeof (struct IPv4UdpAddress);
+      break;
     }
-  }
-  if (s->addrlen == sizeof (struct sockaddr_in))
-  {
-    udpw = plugin->ipv4_queue_head;
-    while (udpw!= NULL)
+  case AF_INET6:
     {
-      tmp = udpw->next;
-      if ((NULL != udpw->frag_ctx) && (udpw->frag_ctx == s->frag_ctx))
+      const struct sockaddr_in6 *i6;
+
+      GNUNET_assert (sizeof(struct sockaddr_in6) == addrlen);
+      i6 = (const struct sockaddr_in6 *) addr;
+      if (0 == ntohs (i6->sin6_port))
       {
-        dequeue (plugin, udpw);
-        call_continuation (udpw, GNUNET_SYSERR);
-        GNUNET_free (udpw);
+        GNUNET_break (0);
+        return;
       }
-      udpw = tmp;
+      memset (&u6,
+              0,
+              sizeof(u6));
+      u6.options = htonl (plugin->myoptions);
+      u6.ipv6_addr = i6->sin6_addr;
+      u6.u6_port = i6->sin6_port;
+      arg = &u6;
+      args = sizeof (struct IPv6UdpAddress);
+      break;
     }
+  default:
+    GNUNET_break (0);
+    return;
   }
-
-  /* Destroy fragmentation context */
-  GNUNET_FRAGMENT_context_destroy (fc->frag,
-                                     &s->last_expected_msg_delay,
-                                     &s->last_expected_ack_delay);
-  s->frag_ctx = NULL;
-  GNUNET_free (fc );
+  /* modify our published address list */
+  address = GNUNET_HELLO_address_allocate (plugin->env->my_identity,
+                                           PLUGIN_NAME,
+                                           arg,
+                                           args,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  plugin->env->notify_address (plugin->env->cls,
+                               add_remove,
+                               address);
+  GNUNET_HELLO_address_free (address);
 }
 
+
+/* ********************* Finding sessions ******************* */
+
+
 /**
- * Functions with this signature are called whenever we need
- * to close a session due to a disconnect or failure to
- * establish a connection.
- *
- * @param s session to close down
+ * Closure for #session_cmp_it().
  */
-static void
-disconnect_session (struct Session *s)
+struct SessionCompareContext
 {
-  struct UDP_MessageWrapper *udpw;
-  struct UDP_MessageWrapper *next;
+  /**
+   * Set to session matching the address.
+   */
+  struct Session *res;
 
-  GNUNET_assert (GNUNET_YES != s->in_destroy);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Session %p to peer `%s' address ended \n",
-         s,
-         GNUNET_i2s (&s->target),
-         GNUNET_a2s (s->sock_addr, s->addrlen));
-  stop_session_timeout (s);
+  /**
+   * Address we are looking for.
+   */
+  const struct GNUNET_HELLO_Address *address;
+};
 
-  if (NULL != s->frag_ctx)
+
+/**
+ * Find a session with a matching address.
+ *
+ * @param cls the `struct SessionCompareContext *`
+ * @param key peer identity (unused)
+ * @param value the `struct Session *`
+ * @return #GNUNET_NO if we found the session, #GNUNET_OK if not
+ */
+static int
+session_cmp_it (void *cls,
+                const struct GNUNET_PeerIdentity *key,
+                void *value)
+{
+  struct SessionCompareContext *cctx = cls;
+  struct Session *s = value;
+
+  if (0 == GNUNET_HELLO_address_cmp (s->address,
+                                     cctx->address))
   {
-    /* Remove fragmented message due to disconnect */
-    fragmented_message_done (s->frag_ctx, GNUNET_SYSERR);
+    GNUNET_assert (GNUNET_NO == s->in_destroy);
+    cctx->res = s;
+    return GNUNET_NO;
   }
+  return GNUNET_OK;
+}
 
-  next = plugin->ipv4_queue_head;
-  while (NULL != (udpw = next))
+
+/**
+ * Locate an existing session the transport service is using to
+ * send data to another peer.  Performs some basic sanity checks
+ * on the address and then tries to locate a matching session.
+ *
+ * @param cls the plugin
+ * @param address the address we should locate the session by
+ * @return the session if it exists, or NULL if it is not found
+ */
+static struct Session *
+udp_plugin_lookup_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  const struct IPv6UdpAddress *udp_a6;
+  const struct IPv4UdpAddress *udp_a4;
+  struct SessionCompareContext cctx;
+
+  if (NULL == address->address)
   {
-    next = udpw->next;
-    if (udpw->session == s)
-    {
-      dequeue (plugin, udpw);
-      call_continuation(udpw, GNUNET_SYSERR);
-      GNUNET_free (udpw);
-    }
+    GNUNET_break (0);
+    return NULL;
   }
-  next = plugin->ipv6_queue_head;
-  while (NULL != (udpw = next))
+  if (sizeof(struct IPv4UdpAddress) == address->address_length)
   {
-    next = udpw->next;
-    if (udpw->session == s)
+    if (NULL == plugin->sockv4)
+      return NULL;
+    udp_a4 = (const struct IPv4UdpAddress *) address->address;
+    if (0 == udp_a4->u4_port)
     {
-      dequeue (plugin, udpw);
-      call_continuation(udpw, GNUNET_SYSERR);
-      GNUNET_free (udpw);
+      GNUNET_break (0);
+      return NULL;
     }
-    udpw = next;
   }
-  plugin->env->session_end (plugin->env->cls, &s->target, s);
-
-  if (NULL != s->frag_ctx)
+  else if (sizeof(struct IPv6UdpAddress) == address->address_length)
   {
-    if (NULL != s->frag_ctx->cont)
+    if (NULL == plugin->sockv6)
+      return NULL;
+    udp_a6 = (const struct IPv6UdpAddress *) address->address;
+    if (0 == udp_a6->u6_port)
     {
-      s->frag_ctx->cont (s->frag_ctx->cont_cls, &s->target, GNUNET_SYSERR,
-                         s->frag_ctx->payload_size, s->frag_ctx->on_wire_size);
-      LOG (GNUNET_ERROR_TYPE_DEBUG,
-          "Calling continuation for fragemented message to `%s' with result SYSERR\n",
-          GNUNET_i2s (&s->target));
+      GNUNET_break (0);
+      return NULL;
     }
   }
-
-  GNUNET_assert (GNUNET_YES ==
-                 GNUNET_CONTAINER_multihashmap_remove (plugin->sessions,
-                                                       &s->target.hashPubKey,
-                                                       s));
-  GNUNET_STATISTICS_set(plugin->env->stats,
-                        "# UDP, sessions active",
-                        GNUNET_CONTAINER_multihashmap_size(plugin->sessions),
-                        GNUNET_NO);
-  if (s->rc > 0)
-    s->in_destroy = GNUNET_YES;
   else
-    free_session (s);
-}
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
 
-/**
- * Destroy a session, plugin is being unloaded.
- *
- * @param cls unused
- * @param key hash of public key of target peer
- * @param value a 'struct PeerSession*' to clean up
- * @return GNUNET_OK (continue to iterate)
- */
-static int
-disconnect_and_free_it (void *cls, const struct GNUNET_HashCode * key, void *value)
-{
-  disconnect_session(value);
-  return GNUNET_OK;
+  /* check if session already exists */
+  cctx.address = address;
+  cctx.res = NULL;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Looking for existing session for peer `%s' with address `%s'\n",
+       GNUNET_i2s (&address->peer),
+       udp_address_to_string (plugin,
+                              address->address,
+                              address->address_length));
+  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
+                                              &address->peer,
+                                              &session_cmp_it,
+                                              &cctx);
+  if (NULL == cctx.res)
+    return NULL;
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Found existing session %p\n",
+       cctx.res);
+  return cctx.res;
 }
 
 
+/* ********************** Timeout ****************** */
+
+
 /**
- * Disconnect from a remote node.  Clean up session if we have one for this peer
+ * Increment session timeout due to activity.
  *
- * @param cls closure for this call (should be handle to Plugin)
- * @param target the peeridentity of the peer to disconnect
- * @return GNUNET_OK on success, GNUNET_SYSERR if the operation failed
+ * @param s session to reschedule timeout activity for
  */
 static void
-udp_disconnect (void *cls, const struct GNUNET_PeerIdentity *target)
+reschedule_session_timeout (struct Session *s)
 {
-  struct Plugin *plugin = cls;
-  GNUNET_assert (plugin != NULL);
-
-  GNUNET_assert (target != NULL);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Disconnecting from peer `%s'\n", GNUNET_i2s (target));
-  /* Clean up sessions */
-  GNUNET_CONTAINER_multihashmap_get_multiple (plugin->sessions, &target->hashPubKey, &disconnect_and_free_it, plugin);
+  if (GNUNET_YES == s->in_destroy)
+    return;
+  GNUNET_assert (NULL != s->timeout_task);
+  s->timeout = GNUNET_TIME_relative_to_absolute (UDP_SESSION_TIME_OUT);
 }
 
 
+
 /**
- * Session was idle, so disconnect it
+ * Function that will be called whenever the transport service wants to
+ * notify the plugin that a session is still active and in use and
+ * therefore the session timeout for this session has to be updated
+ *
+ * @param cls closure with the `struct Plugin`
+ * @param peer which peer was the session for
+ * @param session which session is being updated
  */
 static void
-session_timeout (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
+udp_plugin_update_session_timeout (void *cls,
+                                   const struct GNUNET_PeerIdentity *peer,
+                                   struct Session *session)
 {
-  GNUNET_assert (NULL != cls);
-  struct Session *s = cls;
+  struct Plugin *plugin = cls;
 
-  s->timeout_task = GNUNET_SCHEDULER_NO_TASK;
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Session %p was idle for %llu ms, disconnecting\n",
-              s, (unsigned long long) GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT.rel_value);
-  /* call session destroy function */
-  disconnect_session (s);
+  if (GNUNET_YES !=
+      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
+                                                    peer,
+                                                    session))
+  {
+    GNUNET_break (0);
+    return;
+  }
+  /* Reschedule session timeout */
+  reschedule_session_timeout (session);
 }
 
 
-/**
- * Start session timeout
- */
-static void
-start_session_timeout (struct Session *s)
-{
-  GNUNET_assert (NULL != s);
-  GNUNET_assert (GNUNET_SCHEDULER_NO_TASK == s->timeout_task);
-  s->timeout_task =  GNUNET_SCHEDULER_add_delayed (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
-                                                   &session_timeout,
-                                                   s);
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Timeout for session %p set to %llu ms\n",
-              s,  (unsigned long long) GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT.rel_value);
-}
+/* ************************* Sending ************************ */
 
 
 /**
- * Increment session timeout due to activity
+ * Remove the given message from the transmission queue and
+ * update all applicable statistics.
+ *
+ * @param plugin the UDP plugin
+ * @param udpw message wrapper to dequeue
  */
 static void
-reschedule_session_timeout (struct Session *s)
+dequeue (struct Plugin *plugin,
+         struct UDP_MessageWrapper *udpw)
 {
-  GNUNET_assert (NULL != s);
-  GNUNET_assert (GNUNET_SCHEDULER_NO_TASK != s->timeout_task);
-
-  GNUNET_SCHEDULER_cancel (s->timeout_task);
-  s->timeout_task =  GNUNET_SCHEDULER_add_delayed (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT,
-                                                   &session_timeout,
-                                                   s);
-  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-              "Timeout rescheduled for session %p set to %llu ms\n",
-              s, (unsigned long long) GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT.rel_value);
+  struct Session *session = udpw->session;
+
+  if (plugin->bytes_in_buffer < udpw->msg_size)
+  {
+    GNUNET_break (0);
+  }
+  else
+  {
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total bytes in send buffers",
+                              - (long long) udpw->msg_size,
+                              GNUNET_NO);
+    plugin->bytes_in_buffer -= udpw->msg_size;
+  }
+  GNUNET_STATISTICS_update (plugin->env->stats,
+                            "# UDP, total messages in send buffers",
+                            -1,
+                            GNUNET_NO);
+  if (sizeof(struct IPv4UdpAddress) == udpw->session->address->address_length)
+  {
+    GNUNET_CONTAINER_DLL_remove (plugin->ipv4_queue_head,
+                                 plugin->ipv4_queue_tail,
+                                 udpw);
+  }
+  else if (sizeof(struct IPv6UdpAddress) == udpw->session->address->address_length)
+  {
+    GNUNET_CONTAINER_DLL_remove (plugin->ipv6_queue_head,
+                                 plugin->ipv6_queue_tail,
+                                 udpw);
+  }
+  else
+  {
+    GNUNET_break (0);
+    return;
+  }
+  GNUNET_assert (session->msgs_in_queue > 0);
+  session->msgs_in_queue--;
+  GNUNET_assert (session->bytes_in_queue >= udpw->msg_size);
+  session->bytes_in_queue -= udpw->msg_size;
 }
 
 
 /**
- * Cancel timeout
+ * Enqueue a message for transmission and update statistics.
+ *
+ * @param plugin the UDP plugin
+ * @param udpw message wrapper to queue
  */
 static void
-stop_session_timeout (struct Session *s)
+enqueue (struct Plugin *plugin,
+         struct UDP_MessageWrapper *udpw)
 {
-  GNUNET_assert (NULL != s);
+  struct Session *session = udpw->session;
 
-  if (GNUNET_SCHEDULER_NO_TASK != s->timeout_task)
+  if (GNUNET_YES == session->in_destroy)
   {
-    GNUNET_SCHEDULER_cancel (s->timeout_task);
-    s->timeout_task = GNUNET_SCHEDULER_NO_TASK;
-    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
-                "Timeout stopped for session %p canceled\n",
-                s, (unsigned long long) GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT.rel_value);
+    GNUNET_break (0);
+    return;
   }
-}
-
-
-static struct Session *
-create_session (struct Plugin *plugin, const struct GNUNET_PeerIdentity *target,
-                const void *addr, size_t addrlen,
-                GNUNET_TRANSPORT_TransmitContinuation cont, void *cont_cls)
-{
-  struct Session *s;
-  const struct IPv4UdpAddress *t4;
-  const struct IPv6UdpAddress *t6;
-  struct sockaddr_in *v4;
-  struct sockaddr_in6 *v6;
-  size_t len;
-
-  switch (addrlen)
+  if (plugin->bytes_in_buffer + udpw->msg_size > INT64_MAX)
   {
-  case sizeof (struct IPv4UdpAddress):
-    if (NULL == plugin->sockv4)
-    {
-      return NULL;
-    }
-    t4 = addr;
-    s = GNUNET_malloc (sizeof (struct Session) + sizeof (struct sockaddr_in));
-    len = sizeof (struct sockaddr_in);
-    v4 = (struct sockaddr_in *) &s[1];
-    v4->sin_family = AF_INET;
-#if HAVE_SOCKADDR_IN_SIN_LEN
-    v4->sin_len = sizeof (struct sockaddr_in);
-#endif
-    v4->sin_port = t4->u4_port;
-    v4->sin_addr.s_addr = t4->ipv4_addr;
-    s->ats = plugin->env->get_address_type (plugin->env->cls, (const struct sockaddr *) v4, sizeof (struct sockaddr_in));
-    break;
-  case sizeof (struct IPv6UdpAddress):
-    if (NULL == plugin->sockv6)
-    {
-      return NULL;
-    }
-    t6 = addr;
-    s =
-        GNUNET_malloc (sizeof (struct Session) + sizeof (struct sockaddr_in6));
-    len = sizeof (struct sockaddr_in6);
-    v6 = (struct sockaddr_in6 *) &s[1];
-    v6->sin6_family = AF_INET6;
-#if HAVE_SOCKADDR_IN_SIN_LEN
-    v6->sin6_len = sizeof (struct sockaddr_in6);
-#endif
-    v6->sin6_port = t6->u6_port;
-    v6->sin6_addr = t6->ipv6_addr;
-    s->ats = plugin->env->get_address_type (plugin->env->cls, (const struct sockaddr *) v6, sizeof (struct sockaddr_in6));
-    break;
-  default:
-    /* Must have a valid address to send to */
-    GNUNET_break_op (0);
-    return NULL;
+    GNUNET_break (0);
   }
-  s->addrlen = len;
-  s->target = *target;
-  s->sock_addr = (const struct sockaddr *) &s[1];
-  s->last_expected_ack_delay = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MILLISECONDS, 250);
-  s->last_expected_msg_delay = GNUNET_TIME_UNIT_MILLISECONDS;
-  s->flow_delay_from_other_peer = GNUNET_TIME_UNIT_ZERO_ABS;
-  s->flow_delay_for_other_peer = GNUNET_TIME_UNIT_ZERO;
-  s->inbound = GNUNET_NO;
-  start_session_timeout (s);
-  return s;
-}
-
-
-static int
-session_cmp_it (void *cls,
-               const struct GNUNET_HashCode * key,
-               void *value)
-{
-  struct SessionCompareContext * cctx = cls;
-  const struct GNUNET_HELLO_Address *address = cctx->addr;
-  struct Session *s = value;
-
-  socklen_t s_addrlen = s->addrlen;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "Comparing  address %s <-> %s\n",
-      udp_address_to_string (NULL, (void *) address->address, address->address_length),
-      GNUNET_a2s (s->sock_addr, s->addrlen));
-  if ((address->address_length == sizeof (struct IPv4UdpAddress)) &&
-      (s_addrlen == sizeof (struct sockaddr_in)))
+  else
   {
-    struct IPv4UdpAddress * u4 = NULL;
-    u4 = (struct IPv4UdpAddress *) address->address;
-    const struct sockaddr_in *s4 = (const struct sockaddr_in *) s->sock_addr;
-    if ((0 == memcmp ((const void *) &u4->ipv4_addr,(const void *) &s4->sin_addr, sizeof (struct in_addr))) &&
-        (u4->u4_port == s4->sin_port))
-    {
-      cctx->res = s;
-      return GNUNET_NO;
-    }
-
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total bytes in send buffers",
+                              udpw->msg_size,
+                              GNUNET_NO);
+    plugin->bytes_in_buffer += udpw->msg_size;
   }
-  if ((address->address_length == sizeof (struct IPv6UdpAddress)) &&
-      (s_addrlen == sizeof (struct sockaddr_in6)))
+  GNUNET_STATISTICS_update (plugin->env->stats,
+                            "# UDP, total messages in send buffers",
+                            1,
+                            GNUNET_NO);
+  if (sizeof (struct IPv4UdpAddress) == udpw->session->address->address_length)
   {
-    struct IPv6UdpAddress * u6 = NULL;
-    u6 = (struct IPv6UdpAddress *) address->address;
-    const struct sockaddr_in6 *s6 = (const struct sockaddr_in6 *) s->sock_addr;
-    if ((0 == memcmp (&u6->ipv6_addr, &s6->sin6_addr, sizeof (struct in6_addr))) &&
-        (u6->u6_port == s6->sin6_port))
-    {
-      cctx->res = s;
-      return GNUNET_NO;
-    }
+    GNUNET_CONTAINER_DLL_insert(plugin->ipv4_queue_head,
+                                plugin->ipv4_queue_tail,
+                                udpw);
   }
-  return GNUNET_YES;
+  else if (sizeof (struct IPv6UdpAddress) == udpw->session->address->address_length)
+  {
+    GNUNET_CONTAINER_DLL_insert (plugin->ipv6_queue_head,
+                                 plugin->ipv6_queue_tail,
+                                 udpw);
+  }
+  else
+  {
+    GNUNET_break (0);
+    udpw->cont (udpw->cont_cls,
+                &session->target,
+                GNUNET_SYSERR,
+                udpw->msg_size,
+                0);
+    GNUNET_free (udpw);
+    return;
+  }
+  session->msgs_in_queue++;
+  session->bytes_in_queue += udpw->msg_size;
 }
 
-/**
- * Function obtain the network type for a session
- *
- * @param cls closure ('struct Plugin*')
- * @param session the session
- * @return the network type in HBO or GNUNET_SYSERR
- */
-static enum GNUNET_ATS_Network_Type
-udp_get_network (void *cls, void *session)
-{
-       struct Session *s = (struct Session *) session;
-
-       return ntohl(s->ats.value);
-}
 
 /**
- * Creates a new outbound session the transport service will use to send data to the
- * peer
+ * We have completed our (attempt) to transmit a message that had to
+ * be fragmented -- either because we got an ACK saying that all
+ * fragments were received, or because of timeout / disconnect.  Clean
+ * up our state.
  *
- * @param cls the plugin
- * @param address the address
- * @return the session or NULL of max connections exceeded
+ * @param frag_ctx fragmentation context to clean up
+ * @param result #GNUNET_OK if we succeeded (got ACK),
+ *               #GNUNET_SYSERR if the transmission failed
  */
-static struct Session *
-udp_plugin_lookup_session (void *cls,
-                 const struct GNUNET_HELLO_Address *address)
+static void
+fragmented_message_done (struct UDP_FragmentationContext *frag_ctx,
+                         int result)
 {
-  struct Plugin * plugin = cls;
-  struct IPv6UdpAddress * udp_a6;
-  struct IPv4UdpAddress * udp_a4;
-
-  GNUNET_assert (plugin != NULL);
-  GNUNET_assert (address != NULL);
+  struct Plugin *plugin = frag_ctx->plugin;
+  struct Session *s = frag_ctx->session;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *tmp;
+  size_t overhead;
 
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "%p: Fragmented message removed with result %s\n",
+       frag_ctx,
+       (result == GNUNET_SYSERR) ? "FAIL" : "SUCCESS");
+  /* Call continuation for fragmented message */
+  if (frag_ctx->on_wire_size >= frag_ctx->payload_size)
+    overhead = frag_ctx->on_wire_size - frag_ctx->payload_size;
+  else
+    overhead = frag_ctx->on_wire_size;
+  if (NULL != frag_ctx->cont)
+    frag_ctx->cont (frag_ctx->cont_cls,
+                    &s->target,
+                    result,
+                    s->frag_ctx->payload_size,
+                    frag_ctx->on_wire_size);
+  GNUNET_STATISTICS_update (plugin->env->stats,
+                            "# UDP, fragmented messages active",
+                            -1,
+                            GNUNET_NO);
 
-  if ((address->address == NULL) ||
-      ((address->address_length != sizeof (struct IPv4UdpAddress)) &&
-      (address->address_length != sizeof (struct IPv6UdpAddress))))
+  if (GNUNET_OK == result)
   {
-    LOG (GNUNET_ERROR_TYPE_WARNING,
-       _("Trying to create session for address of unexpected length %u (should be %u or %u)\n"),
-       address->address_length,
-       sizeof (struct IPv4UdpAddress),
-       sizeof (struct IPv6UdpAddress));
-    return NULL;
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, messages, sent, success",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, bytes payload, sent, success",
+                              s->frag_ctx->payload_size,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, bytes overhead, sent, success",
+                              overhead,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total, bytes overhead, sent",
+                              overhead,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total, bytes payload, sent",
+                              s->frag_ctx->payload_size,
+                              GNUNET_NO);
   }
-
-  if (address->address_length == sizeof (struct IPv4UdpAddress))
+  else
   {
-    if (plugin->sockv4 == NULL)
-      return NULL;
-    udp_a4 = (struct IPv4UdpAddress *) address->address;
-    if (udp_a4->u4_port == 0)
-      return NULL;
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, messages, sent, failure",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, bytes payload, sent, failure",
+                              s->frag_ctx->payload_size,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, bytes payload, sent, failure",
+                              overhead,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, bytes payload, sent, failure",
+                              overhead,
+                              GNUNET_NO);
   }
 
-  if (address->address_length == sizeof (struct IPv6UdpAddress))
+  /* Remove remaining fragments from queue, no need to transmit those
+     any longer. */
+  if (s->address->address_length == sizeof(struct IPv6UdpAddress))
   {
-    if (plugin->sockv6 == NULL)
-      return NULL;
-    udp_a6 = (struct IPv6UdpAddress *) address->address;
-    if (udp_a6->u6_port == 0)
-      return NULL;
+    udpw = plugin->ipv6_queue_head;
+    while (NULL != udpw)
+    {
+      tmp = udpw->next;
+      if ( (udpw->frag_ctx != NULL) &&
+          (udpw->frag_ctx == frag_ctx) )
+      {
+       dequeue (plugin,
+                 udpw);
+       GNUNET_free (udpw);
+      }
+      udpw = tmp;
+    }
   }
-
-  /* check if session already exists */
-  struct SessionCompareContext cctx;
-  cctx.addr = address;
-  cctx.res = NULL;
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Looking for existing session for peer `%s' `%s' \n", 
-       GNUNET_i2s (&address->peer), 
-       udp_address_to_string(NULL, address->address, address->address_length));
-  GNUNET_CONTAINER_multihashmap_get_multiple(plugin->sessions, &address->peer.hashPubKey, session_cmp_it, &cctx);
-  if (cctx.res != NULL)
+  if (s->address->address_length == sizeof(struct IPv4UdpAddress))
   {
-    LOG (GNUNET_ERROR_TYPE_DEBUG, "Found existing session %p\n", cctx.res);
-    return cctx.res;
+    udpw = plugin->ipv4_queue_head;
+    while (NULL != udpw)
+    {
+      tmp = udpw->next;
+      if ( (NULL != udpw->frag_ctx) &&
+           (udpw->frag_ctx == frag_ctx) )
+      {
+        dequeue (plugin,
+                 udpw);
+        GNUNET_free (udpw);
+      }
+      udpw = tmp;
+    }
   }
-  return NULL;
-}
-
-static struct Session *
-udp_plugin_create_session (void *cls,
-                  const struct GNUNET_HELLO_Address *address)
-{
-  struct Session * s = NULL;
-
-  /* otherwise create new */
-  s = create_session (plugin,
-      &address->peer,
-      address->address,
-      address->address_length,
-      NULL, NULL);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Creating new session %p for peer `%s' address `%s'\n",
-       s,
-       GNUNET_i2s(&address->peer),
-       udp_address_to_string(NULL,address->address,address->address_length));
-  GNUNET_assert (GNUNET_OK ==
-                 GNUNET_CONTAINER_multihashmap_put (plugin->sessions,
-                                                    &s->target.hashPubKey,
-                                                    s,
-                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
-  GNUNET_STATISTICS_set(plugin->env->stats,
-                        "# UDP, sessions active",
-                        GNUNET_CONTAINER_multihashmap_size(plugin->sessions),
-                        GNUNET_NO);
-  return s;
+  notify_session_monitor (s->plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_UPDATE);
+  GNUNET_FRAGMENT_context_destroy (frag_ctx->frag,
+                                   &s->last_expected_msg_delay,
+                                   &s->last_expected_ack_delay);
+  s->frag_ctx = NULL;
+  GNUNET_free (frag_ctx);
 }
 
 
-
 /**
- * Creates a new outbound session the transport service will use to send data to the
- * peer
+ * We are finished with a fragment in the message queue.
+ * Notify the continuation and update statistics.
  *
- * @param cls the plugin
- * @param address the address
- * @return the session or NULL of max connections exceeded
+ * @param cls the `struct Plugin *`
+ * @param udpw the queue entry
+ * @param result #GNUNET_OK on success, #GNUNET_SYSERR on failure
  */
-static struct Session *
-udp_plugin_get_session (void *cls,
-                  const struct GNUNET_HELLO_Address *address)
+static void
+qc_fragment_sent (void *cls,
+                  struct UDP_MessageWrapper *udpw,
+                  int result)
 {
-  struct Session * s = NULL;
+  struct Plugin *plugin = cls;
 
-  if (NULL == address)
+  GNUNET_assert (NULL != udpw->frag_ctx);
+  if (GNUNET_OK == result)
   {
-       GNUNET_break (0);
-       return NULL;
+    GNUNET_FRAGMENT_context_transmission_done (udpw->frag_ctx->frag);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, fragments, sent, success",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, fragments bytes, sent, success",
+                              udpw->msg_size,
+                              GNUNET_NO);
   }
-  if ((address->address_length != sizeof (struct IPv4UdpAddress)) &&
-               (address->address_length != sizeof (struct IPv6UdpAddress)))
-               return NULL;
-
-  /* otherwise create new */
-  if (NULL != (s = udp_plugin_lookup_session(cls, address)))
-       return s;
-  else
-       return udp_plugin_create_session (cls, address);
-}
-
-
-static void 
-enqueue (struct Plugin *plugin, struct UDP_MessageWrapper * udpw)
-{
-  if (plugin->bytes_in_buffer + udpw->msg_size > INT64_MAX)
-      GNUNET_break (0);
   else
   {
+    fragmented_message_done (udpw->frag_ctx,
+                             GNUNET_SYSERR);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, total, bytes in buffers",
-                              udpw->msg_size, GNUNET_NO);
-    plugin->bytes_in_buffer += udpw->msg_size;
+                              "# UDP, fragmented msgs, fragments, sent, failure",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragmented msgs, fragments bytes, sent, failure",
+                              udpw->msg_size,
+                              GNUNET_NO);
   }
-  GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, msgs in buffers",
-                            1, GNUNET_NO);
-  if (udpw->session->addrlen == sizeof (struct sockaddr_in))
-    GNUNET_CONTAINER_DLL_insert (plugin->ipv4_queue_head,
-                                 plugin->ipv4_queue_tail, udpw);
-  if (udpw->session->addrlen == sizeof (struct sockaddr_in6))
-    GNUNET_CONTAINER_DLL_insert (plugin->ipv6_queue_head,
-                                 plugin->ipv6_queue_tail, udpw);
-}
-
-
-
-/**
- * Fragment message was transmitted via UDP, let fragmentation know
- * to send the next fragment now.
- *
- * @param cls the 'struct UDPMessageWrapper' of the fragment
- * @param target destination peer (ignored)
- * @param result GNUNET_OK on success (ignored)
- * @param payload bytes payload sent
- * @param physical bytes physical sent
- */
-static void
-send_next_fragment (void *cls,
-                   const struct GNUNET_PeerIdentity *target,
-                   int result, size_t payload, size_t physical)
-{
-  struct UDP_MessageWrapper *udpw = cls;
-  GNUNET_FRAGMENT_context_transmission_done (udpw->frag_ctx->frag);  
 }
 
 
 /**
  * Function that is called with messages created by the fragmentation
- * module.  In the case of the 'proc' callback of the
- * GNUNET_FRAGMENT_context_create function, this function must
- * eventually call 'GNUNET_FRAGMENT_context_transmission_done'.
+ * module.  In the case of the `proc` callback of the
+ * #GNUNET_FRAGMENT_context_create() function, this function must
+ * eventually call #GNUNET_FRAGMENT_context_transmission_done().
  *
- * @param cls closure, the 'struct FragmentationContext'
+ * @param cls closure, the `struct UDP_FragmentationContext`
  * @param msg the message that was created
  */
 static void
-enqueue_fragment (void *cls, const struct GNUNET_MessageHeader *msg)
+enqueue_fragment (void *cls,
+                  const struct GNUNET_MessageHeader *msg)
 {
   struct UDP_FragmentationContext *frag_ctx = cls;
   struct Plugin *plugin = frag_ctx->plugin;
-  struct UDP_MessageWrapper * udpw;
+  struct UDP_MessageWrapper *udpw;
+  struct Session *session = frag_ctx->session;
   size_t msg_len = ntohs (msg->size);
-  LOG (GNUNET_ERROR_TYPE_DEBUG, 
-       "Enqueuing fragment with %u bytes\n", msg_len);
-  frag_ctx->fragments_used ++;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Enqueuing fragment with %u bytes\n",
+       msg_len);
   udpw = GNUNET_malloc (sizeof (struct UDP_MessageWrapper) + msg_len);
-  udpw->session = frag_ctx->session;
+  udpw->session = session;
   udpw->msg_buf = (char *) &udpw[1];
   udpw->msg_size = msg_len;
-  udpw->payload_size = msg_len; /*FIXME: minus fragment overhead */
-  udpw->cont = &send_next_fragment;
-  udpw->cont_cls = udpw;
+  udpw->payload_size = msg_len; /* FIXME: minus fragment overhead */
   udpw->timeout = frag_ctx->timeout;
   udpw->frag_ctx = frag_ctx;
-  udpw->msg_type = MSG_FRAGMENTED;
-  memcpy (udpw->msg_buf, msg, msg_len);
-  enqueue (plugin, udpw);
-  schedule_select (plugin);
+  udpw->qc = &qc_fragment_sent;
+  udpw->qc_cls = plugin;
+  memcpy (udpw->msg_buf,
+          msg,
+          msg_len);
+  enqueue (plugin,
+           udpw);
+  if (sizeof (struct IPv4UdpAddress) == session->address->address_length)
+    schedule_select_v4 (plugin);
+  else
+    schedule_select_v6 (plugin);
 }
 
 
 /**
- * Function that can be used by the transport service to transmit
- * a message using the plugin.   Note that in the case of a
- * peer disconnecting, the continuation MUST be called
- * prior to the disconnect notification itself.  This function
- * will be called with this peer's HELLO message to initiate
- * a fresh connection to another peer.
+ * We are finished with a message from the message queue.
+ * Notify the continuation and update statistics.
+ *
+ * @param cls the `struct Plugin *`
+ * @param udpw the queue entry
+ * @param result #GNUNET_OK on success, #GNUNET_SYSERR on failure
+ */
+static void
+qc_message_sent (void *cls,
+                 struct UDP_MessageWrapper *udpw,
+                 int result)
+{
+  struct Plugin *plugin = cls;
+  size_t overhead;
+
+  if (udpw->msg_size >= udpw->payload_size)
+    overhead = udpw->msg_size - udpw->payload_size;
+  else
+    overhead = udpw->msg_size;
+
+  if (NULL != udpw->cont)
+    udpw->cont (udpw->cont_cls,
+                &udpw->session->target,
+                result,
+                udpw->payload_size,
+                overhead);
+  if (GNUNET_OK == result)
+  {
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, messages, sent, success",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, bytes payload, sent, success",
+                              udpw->payload_size,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, bytes overhead, sent, success",
+                              overhead,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total, bytes overhead, sent",
+                              overhead,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total, bytes payload, sent",
+                              udpw->payload_size,
+                              GNUNET_NO);
+  }
+  else
+  {
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, messages, sent, failure",
+                              1,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, bytes payload, sent, failure",
+                              udpw->payload_size,
+                              GNUNET_NO);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, unfragmented msgs, bytes overhead, sent, failure",
+                              overhead,
+                              GNUNET_NO);
+  }
+}
+
+
+/**
+ * Function that can be used by the transport service to transmit a
+ * message using the plugin.  Note that in the case of a peer
+ * disconnecting, the continuation MUST be called prior to the
+ * disconnect notification itself.  This function will be called with
+ * this peer's HELLO message to initiate a fresh connection to another
+ * peer.
  *
  * @param cls closure
  * @param s which session must be used
  * @param msgbuf the message to transmit
- * @param msgbuf_size number of bytes in 'msgbuf'
+ * @param msgbuf_size number of bytes in @a msgbuf
  * @param priority how important is the message (most plugins will
  *                 ignore message priority and just FIFO)
  * @param to how long to wait at most for the transmission (does not
@@ -1682,38 +1810,43 @@ enqueue_fragment (void *cls, const struct GNUNET_MessageHeader *msg)
  *        been transmitted (or if the transport is ready
  *        for the next transmission call; or if the
  *        peer disconnected...); can be NULL
- * @param cont_cls closure for cont
+ * @param cont_cls closure for @a cont
  * @return number of bytes used (on the physical network, with overheads);
  *         -1 on hard errors (i.e. address invalid); 0 is a legal value
  *         and does NOT mean that the message was not transmitted (DV)
  */
 static ssize_t
 udp_plugin_send (void *cls,
-                  struct Session *s,
-                  const char *msgbuf, size_t msgbuf_size,
-                  unsigned int priority,
-                  struct GNUNET_TIME_Relative to,
-                  GNUNET_TRANSPORT_TransmitContinuation cont, void *cont_cls)
+                 struct Session *s,
+                 const char *msgbuf,
+                 size_t msgbuf_size,
+                 unsigned int priority,
+                 struct GNUNET_TIME_Relative to,
+                 GNUNET_TRANSPORT_TransmitContinuation cont,
+                 void *cont_cls)
 {
   struct Plugin *plugin = cls;
-  size_t udpmlen = msgbuf_size + sizeof (struct UDPMessage);
-  struct UDP_FragmentationContext * frag_ctx;
-  struct UDP_MessageWrapper * udpw;
+  size_t udpmlen = msgbuf_size + sizeof(struct UDPMessage);
+  struct UDP_FragmentationContext *frag_ctx;
+  struct UDP_MessageWrapper *udpw;
   struct UDPMessage *udp;
-  char mbuf[udpmlen];
-  GNUNET_assert (plugin != NULL);
-  GNUNET_assert (s != NULL);
+  char mbuf[udpmlen] GNUNET_ALIGN;
 
-  if ((s->addrlen == sizeof (struct sockaddr_in6)) && (plugin->sockv6 == NULL))
+  if ( (sizeof(struct IPv6UdpAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv6) )
     return GNUNET_SYSERR;
-  if ((s->addrlen == sizeof (struct sockaddr_in)) && (plugin->sockv4 == NULL))
+  if ( (sizeof(struct IPv4UdpAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv4) )
     return GNUNET_SYSERR;
   if (udpmlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
   {
     GNUNET_break (0);
     return GNUNET_SYSERR;
   }
-  if (GNUNET_YES != GNUNET_CONTAINER_multihashmap_contains_value(plugin->sessions, &s->target.hashPubKey, s))
+  if (GNUNET_YES !=
+      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
+                                                    &s->target,
+                                                    s))
   {
     GNUNET_break (0);
     return GNUNET_SYSERR;
@@ -1722,17 +1855,24 @@ udp_plugin_send (void *cls,
        "UDP transmits %u-byte message to `%s' using address `%s'\n",
        udpmlen,
        GNUNET_i2s (&s->target),
-       GNUNET_a2s(s->sock_addr, s->addrlen));
+       udp_address_to_string (plugin,
+                              s->address->address,
+                              s->address->address_length));
 
-
-  /* Message */
   udp = (struct UDPMessage *) mbuf;
   udp->header.size = htons (udpmlen);
   udp->header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_MESSAGE);
   udp->reserved = htonl (0);
   udp->sender = *plugin->env->my_identity;
 
-  reschedule_session_timeout(s);
+  /* We do not update the session time out here!  Otherwise this
+   * session will not timeout since we send keep alive before session
+   * can timeout.
+   *
+   * For UDP we update session timeout only on receive, this will
+   * cover keep alives, since remote peer will reply with keep alive
+   * responses!
+   */
   if (udpmlen <= UDP_MTU)
   {
     /* unfragmented message */
@@ -1741,483 +1881,853 @@ udp_plugin_send (void *cls,
     udpw->msg_buf = (char *) &udpw[1];
     udpw->msg_size = udpmlen; /* message size with UDP overhead */
     udpw->payload_size = msgbuf_size; /* message size without UDP overhead */
-    udpw->timeout = GNUNET_TIME_absolute_add(GNUNET_TIME_absolute_get(), to);
+    udpw->timeout = GNUNET_TIME_relative_to_absolute (to);
     udpw->cont = cont;
     udpw->cont_cls = cont_cls;
     udpw->frag_ctx = NULL;
-    udpw->msg_type = MSG_UNFRAGMENTED;
-    memcpy (udpw->msg_buf, udp, sizeof (struct UDPMessage));
-    memcpy (&udpw->msg_buf[sizeof (struct UDPMessage)], msgbuf, msgbuf_size);
-    enqueue (plugin, udpw);
-
+    udpw->qc = &qc_message_sent;
+    udpw->qc_cls = plugin;
+    memcpy (udpw->msg_buf,
+            udp,
+            sizeof (struct UDPMessage));
+    memcpy (&udpw->msg_buf[sizeof(struct UDPMessage)],
+            msgbuf,
+            msgbuf_size);
+    enqueue (plugin,
+             udpw);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, unfragmented msgs, messages, attempt",
-                              1, GNUNET_NO);
+                              "# UDP, unfragmented messages queued total",
+                              1,
+                              GNUNET_NO);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, unfragmented msgs, bytes payload, attempt",
-                              udpw->payload_size, GNUNET_NO);
+                              "# UDP, unfragmented bytes payload queued total",
+                              msgbuf_size,
+                              GNUNET_NO);
   }
   else
   {
     /* fragmented message */
-    if  (s->frag_ctx != NULL)
+    if (NULL != s->frag_ctx)
       return GNUNET_SYSERR;
-    memcpy (&udp[1], msgbuf, msgbuf_size);
-    frag_ctx = GNUNET_malloc (sizeof (struct UDP_FragmentationContext));
+    memcpy (&udp[1],
+            msgbuf,
+            msgbuf_size);
+    frag_ctx = GNUNET_new (struct UDP_FragmentationContext);
     frag_ctx->plugin = plugin;
     frag_ctx->session = s;
     frag_ctx->cont = cont;
     frag_ctx->cont_cls = cont_cls;
-    frag_ctx->timeout = GNUNET_TIME_absolute_add(GNUNET_TIME_absolute_get(), to);
+    frag_ctx->timeout = GNUNET_TIME_relative_to_absolute (to);
     frag_ctx->payload_size = msgbuf_size; /* unfragmented message size without UDP overhead */
     frag_ctx->on_wire_size = 0; /* bytes with UDP and fragmentation overhead */
     frag_ctx->frag = GNUNET_FRAGMENT_context_create (plugin->env->stats,
-                                                    UDP_MTU,
-                                                    &plugin->tracker,
-                                                    s->last_expected_msg_delay, 
-                                                    s->last_expected_ack_delay, 
-                                                    &udp->header,
-                                                    &enqueue_fragment,
-                                                    frag_ctx);    
+                                                     UDP_MTU,
+                                                     &plugin->tracker,
+                                                     s->last_expected_msg_delay,
+                                                     s->last_expected_ack_delay,
+                                                     &udp->header,
+                                                     &enqueue_fragment,
+                                                     frag_ctx);
     s->frag_ctx = frag_ctx;
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, messages, pending",
-                              1, GNUNET_NO);
+                              "# UDP, fragmented messages active",
+                              1,
+                              GNUNET_NO);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, messages, attempt",
-                              1, GNUNET_NO);
+                              "# UDP, fragmented messages, total",
+                              1,
+                              GNUNET_NO);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, bytes payload, attempt",
-                              frag_ctx->payload_size, GNUNET_NO);
-  }
-  schedule_select (plugin);
+                              "# UDP, fragmented bytes (payload)",
+                              frag_ctx->payload_size,
+                              GNUNET_NO);
+  }
+  notify_session_monitor (s->plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_UPDATE);
+  if (s->address->address_length == sizeof (struct IPv4UdpAddress))
+    schedule_select_v4 (plugin);
+  else
+    schedule_select_v6 (plugin);
   return udpmlen;
 }
 
 
 /**
- * Our external IP address/port mapping has changed.
+ * Handle an ACK message.
  *
- * @param cls closure, the 'struct LocalAddrList'
- * @param add_remove GNUNET_YES to mean the new public IP address, GNUNET_NO to mean
- *     the previous (now invalid) one
- * @param addr either the previous or the new public IP address
- * @param addrlen actual lenght of the address
+ * @param plugin the UDP plugin
+ * @param msg the (presumed) UDP ACK message
+ * @param udp_addr sender address
+ * @param udp_addr_len number of bytes in @a udp_addr
  */
 static void
-udp_nat_port_map_callback (void *cls, int add_remove,
-                           const struct sockaddr *addr, socklen_t addrlen)
+read_process_ack (struct Plugin *plugin,
+                  const struct GNUNET_MessageHeader *msg,
+                  const union UdpAddress *udp_addr,
+                  socklen_t udp_addr_len)
 {
-  struct Plugin *plugin = cls;
-  struct IPv4UdpAddress u4;
-  struct IPv6UdpAddress u6;
-  void *arg;
-  size_t args;
+  const struct GNUNET_MessageHeader *ack;
+  const struct UDP_ACK_Message *udp_ack;
+  struct GNUNET_HELLO_Address *address;
+  struct Session *s;
+  struct GNUNET_TIME_Relative flow_delay;
 
-  LOG (GNUNET_ERROR_TYPE_INFO,
-       "NAT notification to %s address `%s'\n",
-       (GNUNET_YES == add_remove) ? "add" : "remove",
-       GNUNET_a2s (addr, addrlen));
+  if (ntohs (msg->size)
+      < sizeof(struct UDP_ACK_Message) + sizeof(struct GNUNET_MessageHeader))
+  {
+    GNUNET_break_op (0);
+    return;
+  }
+  udp_ack = (const struct UDP_ACK_Message *) msg;
+  ack = (const struct GNUNET_MessageHeader *) &udp_ack[1];
+  if (ntohs (ack->size) != ntohs (msg->size) - sizeof(struct UDP_ACK_Message))
+  {
+    GNUNET_break_op(0);
+    return;
+  }
+  address = GNUNET_HELLO_address_allocate (&udp_ack->sender,
+                                           PLUGIN_NAME,
+                                           udp_addr,
+                                           udp_addr_len,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  s = udp_plugin_lookup_session (plugin,
+                                 address);
+  if (NULL == s)
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "UDP session of address %s for ACK not found\n",
+         udp_address_to_string (plugin,
+                                address->address,
+                                address->address_length));
+    GNUNET_HELLO_address_free (address);
+    return;
+  }
+  if (NULL == s->frag_ctx)
+  {
+    LOG (GNUNET_ERROR_TYPE_DEBUG | GNUNET_ERROR_TYPE_BULK,
+         "Fragmentation context of address %s for ACK (%s) not found\n",
+         udp_address_to_string (plugin,
+                                address->address,
+                                address->address_length),
+         GNUNET_FRAGMENT_print_ack (ack));
+    GNUNET_HELLO_address_free (address);
+    return;
+  }
+  GNUNET_HELLO_address_free (address);
 
-  /* convert 'addr' to our internal format */
-  switch (addr->sa_family)
+  flow_delay.rel_value_us = (uint64_t) ntohl (udp_ack->delay);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "We received a sending delay of %s for %s\n",
+       GNUNET_STRINGS_relative_time_to_string (flow_delay,
+                                               GNUNET_YES),
+       GNUNET_i2s (&udp_ack->sender));
+  s->flow_delay_from_other_peer = GNUNET_TIME_relative_to_absolute (flow_delay);
+
+
+  if (GNUNET_OK !=
+      GNUNET_FRAGMENT_process_ack (s->frag_ctx->frag,
+                                   ack))
   {
-  case AF_INET:
-    GNUNET_assert (addrlen == sizeof (struct sockaddr_in));
-    memset (&u4, 0, sizeof (u4));
-    u4.options = htonl(myoptions);
-    u4.ipv4_addr = ((struct sockaddr_in *) addr)->sin_addr.s_addr;
-    u4.u4_port = ((struct sockaddr_in *) addr)->sin_port;
-    arg = &u4;
-    args = sizeof (struct IPv4UdpAddress);
-    break;
-  case AF_INET6:
-    GNUNET_assert (addrlen == sizeof (struct sockaddr_in6));
-    memset (&u4, 0, sizeof (u4));
-    u6.options = htonl(myoptions);
-    memcpy (&u6.ipv6_addr, &((struct sockaddr_in6 *) addr)->sin6_addr,
-            sizeof (struct in6_addr));
-    u6.u6_port = ((struct sockaddr_in6 *) addr)->sin6_port;
-    arg = &u6;
-    args = sizeof (struct IPv6UdpAddress);
-    break;
-  default:
-    GNUNET_break (0);
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "UDP processes %u-byte acknowledgement from `%s' at `%s'\n",
+         (unsigned int) ntohs (msg->size),
+         GNUNET_i2s (&udp_ack->sender),
+         udp_address_to_string (plugin,
+                                udp_addr,
+                                udp_addr_len));
+    /* Expect more ACKs to arrive */
     return;
   }
-  /* modify our published address list */
-  plugin->env->notify_address (plugin->env->cls, add_remove, arg, args, "udp");
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Message from %s at %s full ACK'ed\n",
+       GNUNET_i2s (&udp_ack->sender),
+       udp_address_to_string (plugin,
+                              udp_addr,
+                              udp_addr_len));
+
+  /* Remove fragmented message after successful sending */
+  fragmented_message_done (s->frag_ctx,
+                           GNUNET_OK);
 }
 
 
+/* ********************** Receiving ********************** */
+
+
+/**
+ * Closure for #find_receive_context().
+ */
+struct FindReceiveContext
+{
+  /**
+   * Where to store the result.
+   */
+  struct DefragContext *rc;
+
+  /**
+   * Session associated with this context.
+   */
+  struct Session *session;
+
+  /**
+   * Address to find.
+   */
+  const union UdpAddress *udp_addr;
+
+  /**
+   * Number of bytes in @e udp_addr.
+   */
+  size_t udp_addr_len;
+
+};
+
+
+/**
+ * Scan the heap for a receive context with the given address.
+ *
+ * @param cls the `struct FindReceiveContext`
+ * @param node internal node of the heap
+ * @param element value stored at the node (a `struct ReceiveContext`)
+ * @param cost cost associated with the node
+ * @return #GNUNET_YES if we should continue to iterate,
+ *         #GNUNET_NO if not.
+ */
+static int
+find_receive_context (void *cls,
+                      struct GNUNET_CONTAINER_HeapNode *node,
+                      void *element,
+                      GNUNET_CONTAINER_HeapCostType cost)
+{
+  struct FindReceiveContext *frc = cls;
+  struct DefragContext *e = element;
+
+  if ( (frc->udp_addr_len == e->udp_addr_len) &&
+       (0 == memcmp (frc->udp_addr,
+                     e->udp_addr,
+                     frc->udp_addr_len)) )
+  {
+    frc->rc = e;
+    return GNUNET_NO;
+  }
+  return GNUNET_YES;
+}
+
 
 /**
  * Message tokenizer has broken up an incomming message. Pass it on
  * to the service.
  *
- * @param cls the 'struct Plugin'
- * @param client the 'struct SourceInformation'
+ * @param cls the `struct Plugin *`
+ * @param client the `struct Session *`
  * @param hdr the actual message
+ * @return #GNUNET_OK (always)
  */
 static int
-process_inbound_tokenized_messages (void *cls, void *client,
+process_inbound_tokenized_messages (void *cls,
+                                    void *client,
                                     const struct GNUNET_MessageHeader *hdr)
 {
   struct Plugin *plugin = cls;
-  struct SourceInformation *si = client;
-  struct GNUNET_TIME_Relative delay;
+  struct Session *session = client;
 
-  GNUNET_assert (si->session != NULL);
-  if (GNUNET_YES == si->session->in_destroy)
+  if (GNUNET_YES == session->in_destroy)
     return GNUNET_OK;
-  /* setup ATS */
-  GNUNET_break (ntohl(si->session->ats.value) != GNUNET_ATS_NET_UNSPECIFIED);
-  delay = plugin->env->receive (plugin->env->cls,
-                               &si->sender,
-                               hdr,
-                               si->session,
-                (GNUNET_YES == si->session->inbound) ? NULL : si->arg,
-                (GNUNET_YES == si->session->inbound) ? 0 : si->args);
-
-  plugin->env->update_address_metrics (plugin->env->cls,
-                                      &si->sender,
-                                        (GNUNET_YES == si->session->inbound) ? NULL : si->arg,
-                                        (GNUNET_YES == si->session->inbound) ? 0 : si->args,
-                                      si->session,
-                                      &si->session->ats, 1);
-
-  si->session->flow_delay_for_other_peer = delay;
-  reschedule_session_timeout(si->session);
+  reschedule_session_timeout (session);
+  session->flow_delay_for_other_peer
+    = plugin->env->receive (plugin->env->cls,
+                            session->address,
+                            session,
+                            hdr);
   return GNUNET_OK;
 }
 
 
 /**
- * We've received a UDP Message.  Process it (pass contents to main service).
+ * Functions with this signature are called whenever we need to close
+ * a session due to a disconnect or failure to establish a connection.
  *
- * @param plugin plugin context
- * @param msg the message
- * @param sender_addr sender address
- * @param sender_addr_len number of bytes in sender_addr
+ * @param cls closure with the `struct Plugin`
+ * @param s session to close down
+ * @return #GNUNET_OK on success
  */
-static void
-process_udp_message (struct Plugin *plugin, const struct UDPMessage *msg,
-                     const struct sockaddr *sender_addr,
-                     socklen_t sender_addr_len)
+static int
+udp_disconnect_session (void *cls,
+                        struct Session *s)
 {
-  struct SourceInformation si;
-  struct Session * s;
-  struct IPv4UdpAddress u4;
-  struct IPv6UdpAddress u6;
-  const void *arg;
-  size_t args;
+  struct Plugin *plugin = cls;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *next;
+  struct FindReceiveContext frc;
 
-  if (0 != ntohl (msg->reserved))
+  GNUNET_assert (GNUNET_YES != s->in_destroy);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Session %p to peer `%s' at address %s ended\n",
+       s,
+       GNUNET_i2s (&s->target),
+       udp_address_to_string (plugin,
+                              s->address->address,
+                              s->address->address_length));
+  if (NULL != s->timeout_task)
   {
-    GNUNET_break_op (0);
-    return;
+    GNUNET_SCHEDULER_cancel (s->timeout_task);
+    s->timeout_task = NULL;
   }
-  if (ntohs (msg->header.size) <
-      sizeof (struct GNUNET_MessageHeader) + sizeof (struct UDPMessage))
+  if (NULL != s->frag_ctx)
   {
-    GNUNET_break_op (0);
-    return;
+    /* Remove fragmented message due to disconnect */
+    fragmented_message_done (s->frag_ctx,
+                             GNUNET_SYSERR);
   }
+  GNUNET_assert (GNUNET_YES ==
+                 GNUNET_CONTAINER_multipeermap_remove (plugin->sessions,
+                                                       &s->target,
+                                                       s));
+  frc.rc = NULL;
+  frc.udp_addr = s->address->address;
+  frc.udp_addr_len = s->address->address_length;
+  /* Lookup existing receive context for this address */
+  if (NULL != plugin->defrag_ctxs)
+  {
+    GNUNET_CONTAINER_heap_iterate (plugin->defrag_ctxs,
+                                   &find_receive_context,
+                                   &frc);
+    if (NULL != frc.rc)
+    {
+      struct DefragContext *d_ctx = frc.rc;
 
-  /* convert address */
-  switch (sender_addr->sa_family)
+      GNUNET_CONTAINER_heap_remove_node (d_ctx->hnode);
+      GNUNET_DEFRAGMENT_context_destroy (d_ctx->defrag);
+      GNUNET_free (d_ctx);
+    }
+  }
+  s->in_destroy = GNUNET_YES;
+  next = plugin->ipv4_queue_head;
+  while (NULL != (udpw = next))
   {
-  case AF_INET:
-    GNUNET_assert (sender_addr_len == sizeof (struct sockaddr_in));
-    memset (&u4, 0, sizeof (u4));
-    u6.options = htonl (0);
-    u4.ipv4_addr = ((struct sockaddr_in *) sender_addr)->sin_addr.s_addr;
-    u4.u4_port = ((struct sockaddr_in *) sender_addr)->sin_port;
-    arg = &u4;
-    args = sizeof (u4);
-    break;
-  case AF_INET6:
-    GNUNET_assert (sender_addr_len == sizeof (struct sockaddr_in6));
-    memset (&u6, 0, sizeof (u6));
-    u6.options = htonl (0);
-    u6.ipv6_addr = ((struct sockaddr_in6 *) sender_addr)->sin6_addr;
-    u6.u6_port = ((struct sockaddr_in6 *) sender_addr)->sin6_port;
-    arg = &u6;
-    args = sizeof (u6);
-    break;
-  default:
-    GNUNET_break (0);
-    return;
+    next = udpw->next;
+    if (udpw->session == s)
+    {
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_free (udpw);
+    }
   }
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Received message with %u bytes from peer `%s' at `%s'\n",
-       (unsigned int) ntohs (msg->header.size), GNUNET_i2s (&msg->sender),
-       GNUNET_a2s (sender_addr, sender_addr_len));
-
-  struct GNUNET_HELLO_Address * address = GNUNET_HELLO_address_allocate(&msg->sender, "udp", arg, args);
-  if (NULL == (s = udp_plugin_lookup_session (plugin, address)))
+  next = plugin->ipv6_queue_head;
+  while (NULL != (udpw = next))
   {
-               s = udp_plugin_create_session(plugin, address);
-               s->inbound = GNUNET_YES;
-         plugin->env->session_start (NULL, &address->peer, PLUGIN_NAME,
-                       (GNUNET_YES == s->inbound) ? NULL : address->address,
-                       (GNUNET_YES == s->inbound) ? 0 : address->address_length,
-                 s, NULL, 0);
+    next = udpw->next;
+    if (udpw->session == s)
+    {
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_free (udpw);
+    }
   }
-  GNUNET_free (address);
-
-  /* iterate over all embedded messages */
-  si.session = s;
-  si.sender = msg->sender;
-  si.arg = arg;
-  si.args = args;
-  s->rc++;
-  GNUNET_SERVER_mst_receive (plugin->mst, &si, (const char *) &msg[1],
-                             ntohs (msg->header.size) -
-                             sizeof (struct UDPMessage), GNUNET_YES, GNUNET_NO);
-  s->rc--;
-  if ( (0 == s->rc) && (GNUNET_YES == s->in_destroy))
+  if ( (NULL != s->frag_ctx) &&
+       (NULL != s->frag_ctx->cont) )
+  {
+    /* The 'frag_ctx' itself will be freed in #free_session() a bit
+       later, as it might be in use right now */
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Calling continuation for fragemented message to `%s' with result SYSERR\n",
+         GNUNET_i2s (&s->target));
+    s->frag_ctx->cont (s->frag_ctx->cont_cls,
+                       &s->target,
+                       GNUNET_SYSERR,
+                       s->frag_ctx->payload_size,
+                       s->frag_ctx->on_wire_size);
+  }
+  notify_session_monitor (s->plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_DONE);
+  plugin->env->session_end (plugin->env->cls,
+                            s->address,
+                            s);
+  GNUNET_STATISTICS_set (plugin->env->stats,
+                         "# UDP sessions active",
+                         GNUNET_CONTAINER_multipeermap_size (plugin->sessions),
+                         GNUNET_NO);
+  if (0 == s->rc)
     free_session (s);
+  return GNUNET_OK;
 }
 
 
 /**
- * Scan the heap for a receive context with the given address.
+ * Destroy a session, plugin is being unloaded.
  *
- * @param cls the 'struct FindReceiveContext'
- * @param node internal node of the heap
- * @param element value stored at the node (a 'struct ReceiveContext')
- * @param cost cost associated with the node
- * @return GNUNET_YES if we should continue to iterate,
- *         GNUNET_NO if not.
+ * @param cls the `struct Plugin`
+ * @param key hash of public key of target peer
+ * @param value a `struct PeerSession *` to clean up
+ * @return #GNUNET_OK (continue to iterate)
  */
 static int
-find_receive_context (void *cls, struct GNUNET_CONTAINER_HeapNode *node,
-                      void *element, GNUNET_CONTAINER_HeapCostType cost)
+disconnect_and_free_it (void *cls,
+                        const struct GNUNET_PeerIdentity *key,
+                        void *value)
 {
-  struct FindReceiveContext *frc = cls;
-  struct DefragContext *e = element;
+  struct Plugin *plugin = cls;
 
-  if ((frc->addr_len == e->addr_len) &&
-      (0 == memcmp (frc->addr, e->src_addr, frc->addr_len)))
+  udp_disconnect_session (plugin,
+                          value);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Disconnect from a remote node.  Clean up session if we have one for
+ * this peer.
+ *
+ * @param cls closure for this call (should be handle to Plugin)
+ * @param target the peeridentity of the peer to disconnect
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR if the operation failed
+ */
+static void
+udp_disconnect (void *cls,
+                const struct GNUNET_PeerIdentity *target)
+{
+  struct Plugin *plugin = cls;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Disconnecting from peer `%s'\n",
+       GNUNET_i2s (target));
+  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
+                                              target,
+                                              &disconnect_and_free_it,
+                                              plugin);
+}
+
+
+/**
+ * Session was idle, so disconnect it.
+ *
+ * @param cls the `struct Session` to time out
+ * @param tc scheduler context
+ */
+static void
+session_timeout (void *cls,
+                 const struct GNUNET_SCHEDULER_TaskContext *tc)
+{
+  struct Session *s = cls;
+  struct Plugin *plugin = s->plugin;
+  struct GNUNET_TIME_Relative left;
+
+  s->timeout_task = NULL;
+  left = GNUNET_TIME_absolute_get_remaining (s->timeout);
+  if (left.rel_value_us > 0)
+  {
+    /* not actually our turn yet, but let's at least update
+       the monitor, it may think we're about to die ... */
+    notify_session_monitor (s->plugin,
+                            s,
+                            GNUNET_TRANSPORT_SS_UPDATE);
+    s->timeout_task = GNUNET_SCHEDULER_add_delayed (left,
+                                                    &session_timeout,
+                                                    s);
+    return;
+  }
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Session %p was idle for %s, disconnecting\n",
+       s,
+       GNUNET_STRINGS_relative_time_to_string (UDP_SESSION_TIME_OUT,
+                                               GNUNET_YES));
+  /* call session destroy function */
+  udp_disconnect_session (plugin,
+                          s);
+}
+
+
+/**
+ * Allocate a new session for the given endpoint address.
+ * Note that this function does not inform the service
+ * of the new session, this is the responsibility of the
+ * caller (if needed).
+ *
+ * @param cls the `struct Plugin`
+ * @param address address of the other peer to use
+ * @param network_type network type the address belongs to
+ * @return NULL on error, otherwise session handle
+ */
+static struct Session *
+udp_plugin_create_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address,
+                           enum GNUNET_ATS_Network_Type network_type)
+{
+  struct Plugin *plugin = cls;
+  struct Session *s;
+
+  s = GNUNET_new (struct Session);
+  s->plugin = plugin;
+  s->address = GNUNET_HELLO_address_copy (address);
+  s->target = address->peer;
+  s->last_expected_ack_delay = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MILLISECONDS,
+                                                              250);
+  s->last_expected_msg_delay = GNUNET_TIME_UNIT_MILLISECONDS;
+  s->flow_delay_from_other_peer = GNUNET_TIME_UNIT_ZERO_ABS;
+  s->flow_delay_for_other_peer = GNUNET_TIME_UNIT_ZERO;
+  s->timeout = GNUNET_TIME_relative_to_absolute (UDP_SESSION_TIME_OUT);
+  s->timeout_task = GNUNET_SCHEDULER_add_delayed (UDP_SESSION_TIME_OUT,
+                                                  &session_timeout,
+                                                  s);
+  s->scope = network_type;
+
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Creating new session %p for peer `%s' address `%s'\n",
+       s,
+       GNUNET_i2s (&address->peer),
+       udp_address_to_string (plugin,
+                              address->address,
+                              address->address_length));
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CONTAINER_multipeermap_put (plugin->sessions,
+                                                    &s->target,
+                                                    s,
+                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE));
+  GNUNET_STATISTICS_set (plugin->env->stats,
+                         "# UDP sessions active",
+                         GNUNET_CONTAINER_multipeermap_size (plugin->sessions),
+                         GNUNET_NO);
+  notify_session_monitor (plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_INIT);
+  return s;
+}
+
+
+/**
+ * Creates a new outbound session the transport service will use to
+ * send data to the peer.
+ *
+ * @param cls the `struct Plugin *`
+ * @param address the address
+ * @return the session or NULL of max connections exceeded
+ */
+static struct Session *
+udp_plugin_get_session (void *cls,
+                        const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  struct Session *s;
+  enum GNUNET_ATS_Network_Type network_type = GNUNET_ATS_NET_UNSPECIFIED;
+  const struct IPv4UdpAddress *udp_v4;
+  const struct IPv6UdpAddress *udp_v6;
+
+  if (NULL == address)
   {
-    frc->rc = e;
-    return GNUNET_NO;
+    GNUNET_break (0);
+    return NULL;
   }
-  return GNUNET_YES;
+  if ( (address->address_length != sizeof(struct IPv4UdpAddress)) &&
+       (address->address_length != sizeof(struct IPv6UdpAddress)) )
+  {
+    GNUNET_break_op (0);
+    return NULL;
+  }
+  if (NULL != (s = udp_plugin_lookup_session (cls,
+                                              address)))
+    return s;
+
+  /* need to create new session */
+  if (sizeof (struct IPv4UdpAddress) == address->address_length)
+  {
+    struct sockaddr_in v4;
+
+    udp_v4 = (const struct IPv4UdpAddress *) address->address;
+    memset (&v4, '\0', sizeof (v4));
+    v4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v4.sin_len = sizeof (struct sockaddr_in);
+#endif
+    v4.sin_port = udp_v4->u4_port;
+    v4.sin_addr.s_addr = udp_v4->ipv4_addr;
+    network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                  (const struct sockaddr *) &v4,
+                                                  sizeof (v4));
+  }
+  if (sizeof (struct IPv6UdpAddress) == address->address_length)
+  {
+    struct sockaddr_in6 v6;
+
+    udp_v6 = (const struct IPv6UdpAddress *) address->address;
+    memset (&v6, '\0', sizeof (v6));
+    v6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    v6.sin6_len = sizeof (struct sockaddr_in6);
+#endif
+    v6.sin6_port = udp_v6->u6_port;
+    v6.sin6_addr = udp_v6->ipv6_addr;
+    network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                  (const struct sockaddr *) &v6,
+                                                  sizeof (v6));
+  }
+  GNUNET_break (GNUNET_ATS_NET_UNSPECIFIED != network_type);
+  return udp_plugin_create_session (cls,
+                                   address,
+                                   network_type);
 }
 
 
 /**
- * Process a defragmented message.
+ * We've received a UDP Message.  Process it (pass contents to main service).
  *
- * @param cls the 'struct ReceiveContext'
+ * @param plugin plugin context
  * @param msg the message
+ * @param udp_addr sender address
+ * @param udp_addr_len number of bytes in @a udp_addr
+ * @param network_type network type the address belongs to
  */
 static void
-fragment_msg_proc (void *cls, const struct GNUNET_MessageHeader *msg)
+process_udp_message (struct Plugin *plugin,
+                     const struct UDPMessage *msg,
+                     const union UdpAddress *udp_addr,
+                     size_t udp_addr_len,
+                     enum GNUNET_ATS_Network_Type network_type)
 {
-  struct DefragContext *rc = cls;
+  struct Session *s;
+  struct GNUNET_HELLO_Address *address;
 
-  if (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_MESSAGE)
+  GNUNET_break (GNUNET_ATS_NET_UNSPECIFIED != network_type);
+  if (0 != ntohl (msg->reserved))
   {
-    GNUNET_break (0);
+    GNUNET_break_op(0);
     return;
   }
-  if (ntohs (msg->size) < sizeof (struct UDPMessage))
+  if (ntohs (msg->header.size)
+      < sizeof(struct GNUNET_MessageHeader) + sizeof(struct UDPMessage))
   {
-    GNUNET_break (0);
+    GNUNET_break_op(0);
     return;
   }
-  process_udp_message (rc->plugin, (const struct UDPMessage *) msg,
-                       rc->src_addr, rc->addr_len);
+
+  address = GNUNET_HELLO_address_allocate (&msg->sender,
+                                           PLUGIN_NAME,
+                                           udp_addr,
+                                           udp_addr_len,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  if (NULL ==
+      (s = udp_plugin_lookup_session (plugin,
+                                      address)))
+  {
+    s = udp_plugin_create_session (plugin,
+                                   address,
+                                   network_type);
+    plugin->env->session_start (plugin->env->cls,
+                                address,
+                                s,
+                                s->scope);
+    notify_session_monitor (plugin,
+                            s,
+                            GNUNET_TRANSPORT_SS_UP);
+  }
+  GNUNET_free (address);
+
+  s->rc++;
+  GNUNET_SERVER_mst_receive (plugin->mst,
+                             s,
+                             (const char *) &msg[1],
+                             ntohs (msg->header.size) - sizeof(struct UDPMessage),
+                             GNUNET_YES,
+                             GNUNET_NO);
+  s->rc--;
+  if ( (0 == s->rc) &&
+       (GNUNET_YES == s->in_destroy) )
+    free_session (s);
 }
 
 
-struct LookupContext
+/**
+ * Process a defragmented message.
+ *
+ * @param cls the `struct DefragContext *`
+ * @param msg the message
+ */
+static void
+fragment_msg_proc (void *cls,
+                   const struct GNUNET_MessageHeader *msg)
 {
-  const struct sockaddr * addr;
-
-  struct Session *res;
+  struct DefragContext *dc = cls;
+  const struct UDPMessage *um;
 
-  size_t addrlen;
-};
+  if (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_MESSAGE)
+  {
+    GNUNET_break_op (0);
+    return;
+  }
+  if (ntohs (msg->size) < sizeof(struct UDPMessage))
+  {
+    GNUNET_break_op (0);
+    return;
+  }
+  um = (const struct UDPMessage *) msg;
+  dc->sender = um->sender;
+  dc->have_sender = GNUNET_YES;
+  process_udp_message (dc->plugin,
+                       um,
+                       dc->udp_addr,
+                       dc->udp_addr_len,
+                       dc->network_type);
+}
 
 
-static int
-lookup_session_by_addr_it (void *cls, const struct GNUNET_HashCode * key, void *value)
+/**
+ * We finished sending an acknowledgement.  Update
+ * statistics.
+ *
+ * @param cls the `struct Plugin`
+ * @param udpw message queue entry of the ACK
+ * @param result #GNUNET_OK if the transmission worked,
+ *               #GNUNET_SYSERR if we failed to send the ACK
+ */
+static void
+ack_message_sent (void *cls,
+                  struct UDP_MessageWrapper *udpw,
+                  int result)
 {
-  struct LookupContext *l_ctx = cls;
-  struct Session * s = value;
+  struct Plugin *plugin = cls;
 
-  if ((s->addrlen == l_ctx->addrlen) &&
-      (0 == memcmp (s->sock_addr, l_ctx->addr, s->addrlen)))
+  if (GNUNET_OK == result)
   {
-    l_ctx->res = s;
-    return GNUNET_NO;
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, ACK messages sent",
+                              1,
+                              GNUNET_NO);
+  }
+  else
+  {
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, ACK transmissions failed",
+                              1,
+                              GNUNET_NO);
   }
-  return GNUNET_YES;
 }
 
 
 /**
  * Transmit an acknowledgement.
  *
- * @param cls the 'struct ReceiveContext'
+ * @param cls the `struct DefragContext *`
  * @param id message ID (unused)
  * @param msg ack to transmit
  */
 static void
-ack_proc (void *cls, uint32_t id, const struct GNUNET_MessageHeader *msg)
+ack_proc (void *cls,
+          uint32_t id,
+          const struct GNUNET_MessageHeader *msg)
 {
   struct DefragContext *rc = cls;
-  size_t msize = sizeof (struct UDP_ACK_Message) + ntohs (msg->size);
+  struct Plugin *plugin = rc->plugin;
+  size_t msize = sizeof(struct UDP_ACK_Message) + ntohs (msg->size);
   struct UDP_ACK_Message *udp_ack;
-  uint32_t delay = 0;
+  uint32_t delay;
   struct UDP_MessageWrapper *udpw;
   struct Session *s;
-  struct LookupContext l_ctx;
-
-  l_ctx.addr = rc->src_addr;
-  l_ctx.addrlen = rc->addr_len;
-  l_ctx.res = NULL;
-  GNUNET_CONTAINER_multihashmap_iterate (rc->plugin->sessions,
-      &lookup_session_by_addr_it,
-      &l_ctx);
-  s = l_ctx.res;
+  struct GNUNET_HELLO_Address *address;
 
+  if (GNUNET_NO == rc->have_sender)
+  {
+    /* tried to defragment but never succeeded, hence will not ACK */
+    /* This can happen if we just lost msgs */
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, fragments discarded without ACK",
+                              1,
+                              GNUNET_NO);
+    return;
+  }
+  address = GNUNET_HELLO_address_allocate (&rc->sender,
+                                           PLUGIN_NAME,
+                                           rc->udp_addr,
+                                           rc->udp_addr_len,
+                                           GNUNET_HELLO_ADDRESS_INFO_NONE);
+  s = udp_plugin_lookup_session (plugin,
+                                 address);
+  GNUNET_HELLO_address_free (address);
   if (NULL == s)
+  {
+    LOG (GNUNET_ERROR_TYPE_ERROR,
+         "Trying to transmit ACK to peer `%s' but no session found!\n",
+         udp_address_to_string (plugin,
+                                rc->udp_addr,
+                                rc->udp_addr_len));
+    GNUNET_CONTAINER_heap_remove_node (rc->hnode);
+    GNUNET_DEFRAGMENT_context_destroy (rc->defrag);
+    GNUNET_free (rc);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, ACK transmissions failed",
+                              1,
+                              GNUNET_NO);
     return;
-
-  if (s->flow_delay_for_other_peer.rel_value <= UINT32_MAX)
-    delay = s->flow_delay_for_other_peer.rel_value;
-
+  }
+  if (s->flow_delay_for_other_peer.rel_value_us <= UINT32_MAX)
+    delay = s->flow_delay_for_other_peer.rel_value_us;
+  else
+    delay = UINT32_MAX;
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Sending ACK to `%s' including delay of %u ms\n",
-       GNUNET_a2s (rc->src_addr,
-                   (rc->src_addr->sa_family ==
-                    AF_INET) ? sizeof (struct sockaddr_in) : sizeof (struct
-                                                                     sockaddr_in6)),
-       delay);
+       "Sending ACK to `%s' including delay of %s\n",
+       udp_address_to_string (plugin,
+                              rc->udp_addr,
+                              rc->udp_addr_len),
+       GNUNET_STRINGS_relative_time_to_string (s->flow_delay_for_other_peer,
+                                               GNUNET_YES));
   udpw = GNUNET_malloc (sizeof (struct UDP_MessageWrapper) + msize);
   udpw->msg_size = msize;
   udpw->payload_size = 0;
   udpw->session = s;
   udpw->timeout = GNUNET_TIME_UNIT_FOREVER_ABS;
-  udpw->msg_buf = (char *)&udpw[1];
-  udpw->msg_type = MSG_ACK;
+  udpw->msg_buf = (char *) &udpw[1];
+  udpw->qc = &ack_message_sent;
+  udpw->qc_cls = plugin;
   udp_ack = (struct UDP_ACK_Message *) udpw->msg_buf;
   udp_ack->header.size = htons ((uint16_t) msize);
   udp_ack->header.type = htons (GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_ACK);
   udp_ack->delay = htonl (delay);
-  udp_ack->sender = *rc->plugin->env->my_identity;
-  memcpy (&udp_ack[1], msg, ntohs (msg->size));
-  enqueue (rc->plugin, udpw);
-}
-
-
-static void 
-read_process_msg (struct Plugin *plugin,
-                 const struct GNUNET_MessageHeader *msg,
-                 const char *addr,
-                 socklen_t fromlen)
-{
-  if (ntohs (msg->size) < sizeof (struct UDPMessage))
-  {
-    GNUNET_break_op (0);
-    return;
-  }
-  process_udp_message (plugin, (const struct UDPMessage *) msg,
-                       (const struct sockaddr *) addr, fromlen);
-}
-
-
-static void 
-read_process_ack (struct Plugin *plugin,
-                 const struct GNUNET_MessageHeader *msg,
-                 char *addr,
-                 socklen_t fromlen)
-{
-  const struct GNUNET_MessageHeader *ack;
-  const struct UDP_ACK_Message *udp_ack;
-  struct LookupContext l_ctx;
-  struct Session *s;
-  struct GNUNET_TIME_Relative flow_delay;
-
-  if (ntohs (msg->size) <
-      sizeof (struct UDP_ACK_Message) + sizeof (struct GNUNET_MessageHeader))
-  {
-    GNUNET_break_op (0);
-    return;
-  }
-  udp_ack = (const struct UDP_ACK_Message *) msg;
-  l_ctx.addr = (const struct sockaddr *) addr;
-  l_ctx.addrlen = fromlen;
-  l_ctx.res = NULL;
-  GNUNET_CONTAINER_multihashmap_iterate (plugin->sessions,
-                                        &lookup_session_by_addr_it,
-                                        &l_ctx);
-  s = l_ctx.res;
-
-  if ((NULL == s) || (NULL == s->frag_ctx))
-  {
-    return;
-  }
-
-  flow_delay.rel_value = (uint64_t) ntohl (udp_ack->delay);
-  LOG (GNUNET_ERROR_TYPE_DEBUG, 
-       "We received a sending delay of %llu\n",
-       flow_delay.rel_value);
-  s->flow_delay_from_other_peer =
-      GNUNET_TIME_relative_to_absolute (flow_delay);
-
-  ack = (const struct GNUNET_MessageHeader *) &udp_ack[1];
-  if (ntohs (ack->size) !=
-      ntohs (msg->size) - sizeof (struct UDP_ACK_Message))
-  {
-    GNUNET_break_op (0);
-    return;
-  }
-
-  if (0 != memcmp (&l_ctx.res->target, &udp_ack->sender, sizeof (struct GNUNET_PeerIdentity)))
-    GNUNET_break (0);
-  if (GNUNET_OK != GNUNET_FRAGMENT_process_ack (s->frag_ctx->frag, ack))
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "UDP processes %u-byte acknowledgement from `%s' at `%s'\n",
-        (unsigned int) ntohs (msg->size), GNUNET_i2s (&udp_ack->sender),
-        GNUNET_a2s ((const struct sockaddr *) addr, fromlen));
-    /* Expect more ACKs to arrive */
-    return;
-  }
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Message full ACK'ed\n",
-       (unsigned int) ntohs (msg->size), GNUNET_i2s (&udp_ack->sender),
-       GNUNET_a2s ((const struct sockaddr *) addr, fromlen));
-
-  /* Remove fragmented message after successful sending */
-  fragmented_message_done (s->frag_ctx, GNUNET_OK);
+  udp_ack->sender = *plugin->env->my_identity;
+  memcpy (&udp_ack[1],
+          msg,
+          ntohs (msg->size));
+  enqueue (plugin,
+           udpw);
+  notify_session_monitor (plugin,
+                          s,
+                          GNUNET_TRANSPORT_SS_UPDATE);
+  if (s->address->address_length == sizeof (struct IPv4UdpAddress))
+    schedule_select_v4 (plugin);
+  else
+    schedule_select_v6 (plugin);
 }
 
 
-static void 
+/**
+ * We received a fragment, process it.
+ *
+ * @param plugin our plugin
+ * @param msg a message of type #GNUNET_MESSAGE_TYPE_FRAGMENT
+ * @param udp_addr sender address
+ * @param udp_addr_len number of bytes in @a udp_addr
+ * @param network_type network type the address belongs to
+ */
+static void
 read_process_fragment (struct Plugin *plugin,
-                      const struct GNUNET_MessageHeader *msg,
-                      char *addr,
-                      socklen_t fromlen)
+                       const struct GNUNET_MessageHeader *msg,
+                       const union UdpAddress *udp_addr,
+                       size_t udp_addr_len,
+                       enum GNUNET_ATS_Network_Type network_type)
 {
   struct DefragContext *d_ctx;
   struct GNUNET_TIME_Absolute now;
   struct FindReceiveContext frc;
 
   frc.rc = NULL;
-  frc.addr = (const struct sockaddr *) addr;
-  frc.addr_len = fromlen;
+  frc.udp_addr = udp_addr;
+  frc.udp_addr_len = udp_addr_len;
 
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "UDP processes %u-byte fragment from `%s'\n",
-       (unsigned int) ntohs (msg->size),
-       GNUNET_a2s ((const struct sockaddr *) addr, fromlen));
   /* Lookup existing receive context for this address */
   GNUNET_CONTAINER_heap_iterate (plugin->defrag_ctxs,
                                  &find_receive_context,
@@ -2225,41 +2735,51 @@ read_process_fragment (struct Plugin *plugin,
   now = GNUNET_TIME_absolute_get ();
   d_ctx = frc.rc;
 
-  if (d_ctx == NULL)
+  if (NULL == d_ctx)
   {
     /* Create a new defragmentation context */
-    d_ctx = GNUNET_malloc (sizeof (struct DefragContext) + fromlen);
-    memcpy (&d_ctx[1], addr, fromlen);
-    d_ctx->src_addr = (const struct sockaddr *) &d_ctx[1];
-    d_ctx->addr_len = fromlen;
+    d_ctx = GNUNET_malloc (sizeof (struct DefragContext) + udp_addr_len);
+    memcpy (&d_ctx[1],
+            udp_addr,
+            udp_addr_len);
+    d_ctx->udp_addr = (const union UdpAddress *) &d_ctx[1];
+    d_ctx->udp_addr_len = udp_addr_len;
+    d_ctx->network_type = network_type;
     d_ctx->plugin = plugin;
-    d_ctx->defrag =
-        GNUNET_DEFRAGMENT_context_create (plugin->env->stats, UDP_MTU,
-                                          UDP_MAX_MESSAGES_IN_DEFRAG, d_ctx,
-                                          &fragment_msg_proc, &ack_proc);
-    d_ctx->hnode =
-        GNUNET_CONTAINER_heap_insert (plugin->defrag_ctxs, d_ctx,
-                                      (GNUNET_CONTAINER_HeapCostType)
-                                      now.abs_value);
-    LOG (GNUNET_ERROR_TYPE_DEBUG, 
-        "Created new defragmentation context for %u-byte fragment from `%s'\n",
-        (unsigned int) ntohs (msg->size),
-        GNUNET_a2s ((const struct sockaddr *) addr, fromlen));
+    d_ctx->defrag = GNUNET_DEFRAGMENT_context_create (plugin->env->stats,
+                                                      UDP_MTU,
+                                                      UDP_MAX_MESSAGES_IN_DEFRAG,
+                                                      d_ctx,
+                                                      &fragment_msg_proc,
+                                                      &ack_proc);
+    d_ctx->hnode = GNUNET_CONTAINER_heap_insert (plugin->defrag_ctxs,
+                                                 d_ctx,
+                                                 (GNUNET_CONTAINER_HeapCostType) now.abs_value_us);
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Created new defragmentation context for %u-byte fragment from `%s'\n",
+         (unsigned int) ntohs (msg->size),
+         udp_address_to_string (plugin,
+                                udp_addr,
+                                udp_addr_len));
   }
   else
   {
     LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "Found existing defragmentation context for %u-byte fragment from `%s'\n",
-        (unsigned int) ntohs (msg->size),
-        GNUNET_a2s ((const struct sockaddr *) addr, fromlen));
+         "Found existing defragmentation context for %u-byte fragment from `%s'\n",
+         (unsigned int) ntohs (msg->size),
+         udp_address_to_string (plugin,
+                                udp_addr,
+                                udp_addr_len));
   }
 
-  if (GNUNET_OK == GNUNET_DEFRAGMENT_process_fragment (d_ctx->defrag, msg))
+  if (GNUNET_OK ==
+      GNUNET_DEFRAGMENT_process_fragment (d_ctx->defrag,
+                                          msg))
   {
     /* keep this 'rc' from expiring */
-    GNUNET_CONTAINER_heap_update_cost (plugin->defrag_ctxs, d_ctx->hnode,
-                                       (GNUNET_CONTAINER_HeapCostType)
-                                       now.abs_value);
+    GNUNET_CONTAINER_heap_update_cost (plugin->defrag_ctxs,
+                                       d_ctx->hnode,
+                                       (GNUNET_CONTAINER_HeapCostType) now.abs_value_us);
   }
   if (GNUNET_CONTAINER_heap_get_size (plugin->defrag_ctxs) >
       UDP_MAX_SENDER_ADDRESSES_WITH_DEFRAG)
@@ -2269,6 +2789,10 @@ read_process_fragment (struct Plugin *plugin,
     GNUNET_assert (NULL != d_ctx);
     GNUNET_DEFRAGMENT_context_destroy (d_ctx->defrag);
     GNUNET_free (d_ctx);
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, Defragmentations aborted",
+                              1,
+                              GNUNET_NO);
   }
 }
 
@@ -2280,18 +2804,33 @@ read_process_fragment (struct Plugin *plugin,
  * @param rsock socket to read from
  */
 static void
-udp_select_read (struct Plugin *plugin, struct GNUNET_NETWORK_Handle *rsock)
+udp_select_read (struct Plugin *plugin,
+                 struct GNUNET_NETWORK_Handle *rsock)
 {
   socklen_t fromlen;
-  char addr[32];
+  struct sockaddr_storage addr;
   char buf[65536] GNUNET_ALIGN;
   ssize_t size;
   const struct GNUNET_MessageHeader *msg;
+  struct IPv4UdpAddress v4;
+  struct IPv6UdpAddress v6;
+  const struct sockaddr *sa;
+  const struct sockaddr_in *sa4;
+  const struct sockaddr_in6 *sa6;
+  const union UdpAddress *int_addr;
+  size_t int_addr_len;
+  enum GNUNET_ATS_Network_Type network_type;
 
   fromlen = sizeof (addr);
-  memset (&addr, 0, sizeof (addr));
-  size = GNUNET_NETWORK_socket_recvfrom (rsock, buf, sizeof (buf),
-                                      (struct sockaddr *) &addr, &fromlen);
+  memset (&addr,
+          0,
+          sizeof(addr));
+  size = GNUNET_NETWORK_socket_recvfrom (rsock,
+                                         buf,
+                                         sizeof(buf),
+                                         (struct sockaddr *) &addr,
+                                         &fromlen);
+  sa = (const struct sockaddr *) &addr;
 #if MINGW
   /* On SOCK_DGRAM UDP sockets recvfrom might fail with a
    * WSAECONNRESET error to indicate that previous sendto() (yes, sendto!)
@@ -2303,314 +2842,429 @@ udp_select_read (struct Plugin *plugin, struct GNUNET_NETWORK_Handle *rsock)
    *   error indicates a previous send operation resulted in an ICMP Port
    *   Unreachable message.
    */
-  if ( (-1 == size) && (ECONNRESET == errno) )
+  if ( (-1 == size) &&
+       (ECONNRESET == errno) )
     return;
 #endif
   if (-1 == size)
   {
     LOG (GNUNET_ERROR_TYPE_DEBUG,
-        "UDP failed to receive data: %s\n", STRERROR (errno));
+         "UDP failed to receive data: %s\n",
+         STRERROR (errno));
     /* Connection failure or something. Not a protocol violation. */
     return;
   }
-  if (size < sizeof (struct GNUNET_MessageHeader))
+  if (size < sizeof(struct GNUNET_MessageHeader))
   {
     LOG (GNUNET_ERROR_TYPE_WARNING,
-        "UDP got %u bytes, which is not enough for a GNUnet message header\n",
-        (unsigned int) size);
+         "UDP got %u bytes from %s, which is not enough for a GNUnet message header\n",
+         (unsigned int ) size,
+         GNUNET_a2s (sa,
+                     fromlen));
     /* _MAY_ be a connection failure (got partial message) */
     /* But it _MAY_ also be that the other side uses non-GNUnet protocol. */
     GNUNET_break_op (0);
     return;
   }
   msg = (const struct GNUNET_MessageHeader *) buf;
-
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "UDP received %u-byte message from `%s' type %i\n", (unsigned int) size,
-       GNUNET_a2s ((const struct sockaddr *) addr, fromlen), ntohs (msg->type));
-
+       "UDP received %u-byte message from `%s' type %u\n",
+       (unsigned int) size,
+       GNUNET_a2s (sa,
+                   fromlen),
+       ntohs (msg->type));
   if (size != ntohs (msg->size))
   {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "UDP malformed message header from %s\n",
+         (unsigned int) size,
+         GNUNET_a2s (sa,
+                     fromlen));
     GNUNET_break_op (0);
     return;
   }
-
   GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, bytes, received",
-                            size, GNUNET_NO);
+                            "# UDP, total bytes received",
+                            size,
+                            GNUNET_NO);
+  network_type = plugin->env->get_address_type (plugin->env->cls,
+                                                sa,
+                                                fromlen);
+  switch (sa->sa_family)
+  {
+  case AF_INET:
+    sa4 = (const struct sockaddr_in *) &addr;
+    v4.options = 0;
+    v4.ipv4_addr = sa4->sin_addr.s_addr;
+    v4.u4_port = sa4->sin_port;
+    int_addr = (union UdpAddress *) &v4;
+    int_addr_len = sizeof (v4);
+    break;
+  case AF_INET6:
+    sa6 = (const struct sockaddr_in6 *) &addr;
+    v6.options = 0;
+    v6.ipv6_addr = sa6->sin6_addr;
+    v6.u6_port = sa6->sin6_port;
+    int_addr = (union UdpAddress *) &v6;
+    int_addr_len = sizeof (v6);
+    break;
+  default:
+    GNUNET_break (0);
+    return;
+  }
 
   switch (ntohs (msg->type))
   {
   case GNUNET_MESSAGE_TYPE_TRANSPORT_BROADCAST_BEACON:
-    udp_broadcast_receive (plugin, &buf, size, addr, fromlen);
+    if (GNUNET_YES == plugin->enable_broadcasting_receiving)
+      udp_broadcast_receive (plugin,
+                             buf,
+                             size,
+                             int_addr,
+                             int_addr_len,
+                             network_type);
     return;
-
   case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_MESSAGE:
-    read_process_msg (plugin, msg, addr, fromlen);
+    if (ntohs (msg->size) < sizeof(struct UDPMessage))
+    {
+      GNUNET_break_op(0);
+      return;
+    }
+    process_udp_message (plugin,
+                         (const struct UDPMessage *) msg,
+                         int_addr,
+                         int_addr_len,
+                         network_type);
     return;
-
   case GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_ACK:
-    read_process_ack (plugin, msg, addr, fromlen);
+    read_process_ack (plugin,
+                      msg,
+                      int_addr,
+                      int_addr_len);
     return;
-
   case GNUNET_MESSAGE_TYPE_FRAGMENT:
-    read_process_fragment (plugin, msg, addr, fromlen);
+    read_process_fragment (plugin,
+                           msg,
+                           int_addr,
+                           int_addr_len,
+                           network_type);
     return;
-
   default:
-    GNUNET_break_op (0);
+    GNUNET_break_op(0);
     return;
   }
 }
 
+
+/**
+ * Removes messages from the transmission queue that have
+ * timed out, and then selects a message that should be
+ * transmitted next.
+ *
+ * @param plugin the UDP plugin
+ * @param sock which socket should we process the queue for (v4 or v6)
+ * @return message selected for transmission, or NULL for none
+ */
 static struct UDP_MessageWrapper *
-remove_timeout_messages_and_select (struct UDP_MessageWrapper *head,
+remove_timeout_messages_and_select (struct Plugin *plugin,
                                     struct GNUNET_NETWORK_Handle *sock)
 {
-  struct UDP_MessageWrapper *udpw = NULL;
+  struct UDP_MessageWrapper *udpw;
   struct GNUNET_TIME_Relative remaining;
+  struct Session *session;
+  int removed;
 
-  udpw = head;
-  while (udpw != NULL)
+  removed = GNUNET_NO;
+  udpw = (sock == plugin->sockv4)
+    ? plugin->ipv4_queue_head
+    : plugin->ipv6_queue_head;
+  while (NULL != udpw)
   {
+    session = udpw->session;
     /* Find messages with timeout */
     remaining = GNUNET_TIME_absolute_get_remaining (udpw->timeout);
-    if (GNUNET_TIME_UNIT_ZERO.rel_value == remaining.rel_value)
+    if (GNUNET_TIME_UNIT_ZERO.rel_value_us == remaining.rel_value_us)
     {
       /* Message timed out */
-      switch (udpw->msg_type) {
-        case MSG_UNFRAGMENTED:
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes, sent, timeout",
-                                    udpw->msg_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, messages, sent, timeout",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, messages, sent, timeout",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, unfragmented msgs, bytes, sent, timeout",
-                                    udpw->payload_size, GNUNET_NO);
-          /* Not fragmented message */
-          LOG (GNUNET_ERROR_TYPE_DEBUG,
-               "Message for peer `%s' with size %u timed out\n",
-               GNUNET_i2s(&udpw->session->target), udpw->payload_size);
-          call_continuation (udpw, GNUNET_SYSERR);
-          /* Remove message */
-          dequeue (plugin, udpw);
-          GNUNET_free (udpw);
-          break;
-        case MSG_FRAGMENTED:
-          /* Fragmented message */
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes, sent, timeout",
-                                    udpw->frag_ctx->on_wire_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, messages, sent, timeout",
-                                    1, GNUNET_NO);
-          call_continuation (udpw, GNUNET_SYSERR);
-          LOG (GNUNET_ERROR_TYPE_DEBUG,
-               "Fragment for message for peer `%s' with size %u timed out\n",
-               GNUNET_i2s(&udpw->session->target), udpw->frag_ctx->payload_size);
-
-
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, messages, sent, timeout",
-                                    1, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, fragmented msgs, bytes, sent, timeout",
-                                    udpw->frag_ctx->payload_size, GNUNET_NO);
-          /* Remove fragmented message due to timeout */
-          fragmented_message_done (udpw->frag_ctx, GNUNET_SYSERR);
-          break;
-        case MSG_ACK:
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, bytes, sent, timeout",
-                                    udpw->msg_size, GNUNET_NO);
-          GNUNET_STATISTICS_update (plugin->env->stats,
-                                    "# UDP, total, messages, sent, timeout",
-                                    1, GNUNET_NO);
-          LOG (GNUNET_ERROR_TYPE_DEBUG,
-               "ACK Message for peer `%s' with size %u timed out\n",
-               GNUNET_i2s(&udpw->session->target), udpw->payload_size);
-          call_continuation (udpw, GNUNET_SYSERR);
-          dequeue (plugin, udpw);
-          GNUNET_free (udpw);
-          break;
-        default:
-          break;
-      }
+      removed = GNUNET_YES;
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_free (udpw);
+
       if (sock == plugin->sockv4)
+      {
         udpw = plugin->ipv4_queue_head;
+      }
       else if (sock == plugin->sockv6)
+      {
         udpw = plugin->ipv6_queue_head;
+      }
       else
       {
         GNUNET_break (0); /* should never happen */
         udpw = NULL;
       }
       GNUNET_STATISTICS_update (plugin->env->stats,
-                                "# messages dismissed due to timeout",
-                                1, GNUNET_NO);
+                                "# messages discarded due to timeout",
+                                1,
+                                GNUNET_NO);
     }
     else
     {
       /* Message did not time out, check flow delay */
       remaining = GNUNET_TIME_absolute_get_remaining (udpw->session->flow_delay_from_other_peer);
-      if (GNUNET_TIME_UNIT_ZERO.rel_value == remaining.rel_value)
+      if (0 == remaining.rel_value_us)
       {
         /* this message is not delayed */
-        LOG (GNUNET_ERROR_TYPE_DEBUG, 
+        LOG (GNUNET_ERROR_TYPE_DEBUG,
              "Message for peer `%s' (%u bytes) is not delayed \n",
-             GNUNET_i2s(&udpw->session->target), udpw->payload_size);
+             GNUNET_i2s (&udpw->session->target),
+             udpw->payload_size);
         break; /* Found message to send, break */
       }
       else
       {
         /* Message is delayed, try next */
         LOG (GNUNET_ERROR_TYPE_DEBUG,
-             "Message for peer `%s' (%u bytes) is delayed for %llu \n",
-             GNUNET_i2s(&udpw->session->target), udpw->payload_size, remaining.rel_value);
+             "Message for peer `%s' (%u bytes) is delayed for %s\n",
+             GNUNET_i2s (&udpw->session->target),
+            udpw->payload_size,
+             GNUNET_STRINGS_relative_time_to_string (remaining,
+                                                    GNUNET_YES));
         udpw = udpw->next;
       }
     }
   }
+  if (GNUNET_YES == removed)
+    notify_session_monitor (session->plugin,
+                            session,
+                            GNUNET_TRANSPORT_SS_UPDATE);
   return udpw;
 }
 
 
+/**
+ * We failed to transmit a message via UDP. Generate
+ * a descriptive error message.
+ *
+ * @param plugin our plugin
+ * @param sa target address we were trying to reach
+ * @param slen number of bytes in @a sa
+ * @param error the errno value returned from the sendto() call
+ */
 static void
 analyze_send_error (struct Plugin *plugin,
-                    const struct sockaddr * sa,
+                    const struct sockaddr *sa,
                     socklen_t slen,
                     int error)
 {
-  static int network_down_error;
-  struct GNUNET_ATS_Information type;
-
- type = plugin->env->get_address_type (plugin->env->cls,sa, slen);
- if (((GNUNET_ATS_NET_LAN == ntohl(type.value)) || (GNUNET_ATS_NET_WAN == ntohl(type.value))) &&
-     ((ENETUNREACH == errno) || (ENETDOWN == errno)))
- {
-   if ((network_down_error == GNUNET_NO) && (slen == sizeof (struct sockaddr_in)))
-   {
-     /* IPv4: "Network unreachable" or "Network down"
-      *
-      * This indicates we do not have connectivity
-      */
-     LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
-         _("UDP could not transmit message to `%s': "
-           "Network seems down, please check your network configuration\n"),
-         GNUNET_a2s (sa, slen));
-   }
-   if ((network_down_error == GNUNET_NO) && (slen == sizeof (struct sockaddr_in6)))
-   {
-     /* IPv6: "Network unreachable" or "Network down"
-      *
-      * This indicates that this system is IPv6 enabled, but does not
-      * have a valid global IPv6 address assigned or we do not have
-      * connectivity
-      */
-
-    LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
-        _("UDP could not transmit message to `%s': "
-          "Please check your network configuration and disable IPv6 if your "
-          "connection does not have a global IPv6 address\n"),
-        GNUNET_a2s (sa, slen));
-   }
- }
- else
- {
-   LOG (GNUNET_ERROR_TYPE_WARNING,
-      "UDP could not transmit message to `%s': `%s'\n",
-      GNUNET_a2s (sa, slen), STRERROR (error));
- }
+  enum GNUNET_ATS_Network_Type type;
+
+  type = plugin->env->get_address_type (plugin->env->cls,
+                                        sa,
+                                        slen);
+  if ( ( (GNUNET_ATS_NET_LAN == type) ||
+         (GNUNET_ATS_NET_WAN == type) ) &&
+       ( (ENETUNREACH == errno) ||
+         (ENETDOWN == errno) ) )
+  {
+    if (slen == sizeof (struct sockaddr_in))
+    {
+      /* IPv4: "Network unreachable" or "Network down"
+       *
+       * This indicates we do not have connectivity
+       */
+      LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
+           _("UDP could not transmit message to `%s': "
+             "Network seems down, please check your network configuration\n"),
+           GNUNET_a2s (sa,
+                       slen));
+    }
+    if (slen == sizeof (struct sockaddr_in6))
+    {
+      /* IPv6: "Network unreachable" or "Network down"
+       *
+       * This indicates that this system is IPv6 enabled, but does not
+       * have a valid global IPv6 address assigned or we do not have
+       * connectivity
+       */
+      LOG (GNUNET_ERROR_TYPE_WARNING | GNUNET_ERROR_TYPE_BULK,
+           _("UDP could not transmit IPv6 message! "
+             "Please check your network configuration and disable IPv6 if your "
+             "connection does not have a global IPv6 address\n"));
+    }
+  }
+  else
+  {
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "UDP could not transmit message to `%s': `%s'\n",
+         GNUNET_a2s (sa,
+                     slen),
+         STRERROR (error));
+  }
 }
 
-static size_t
-udp_select_send (struct Plugin *plugin, struct GNUNET_NETWORK_Handle *sock)
+
+/**
+ * It is time to try to transmit a UDP message.  Select one
+ * and send.
+ *
+ * @param plugin the plugin
+ * @param sock which socket (v4/v6) to send on
+ */
+static void
+udp_select_send (struct Plugin *plugin,
+                 struct GNUNET_NETWORK_Handle *sock)
 {
-  const struct sockaddr * sa;
   ssize_t sent;
   socklen_t slen;
+  const struct sockaddr *a;
+  const struct IPv4UdpAddress *u4;
+  struct sockaddr_in a4;
+  const struct IPv6UdpAddress *u6;
+  struct sockaddr_in6 a6;
+  struct UDP_MessageWrapper *udpw;
 
-  struct UDP_MessageWrapper *udpw = NULL;
-
-  /* Find message to send */
-  udpw = remove_timeout_messages_and_select ((sock == plugin->sockv4) ? plugin->ipv4_queue_head : plugin->ipv6_queue_head,
-                                             sock);
-  if (NULL == udpw)
-    return 0; /* No message to send */
-
-  sa = udpw->session->sock_addr;
-  slen = udpw->session->addrlen;
-
-  sent = GNUNET_NETWORK_socket_sendto (sock, udpw->msg_buf, udpw->msg_size, sa, slen);
-
-  if (GNUNET_SYSERR == sent)
-  {
-    /* Failure */
-    analyze_send_error (plugin, sa, slen, errno);
-    call_continuation(udpw, GNUNET_SYSERR);
-    GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, bytes, sent, failure",
-                            sent, GNUNET_NO);
-    GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, total, messages, sent, failure",
-                              1, GNUNET_NO);
-  }
-  else
+  /* Find message(s) to send */
+  while (NULL != (udpw = remove_timeout_messages_and_select (plugin,
+                                                             sock)))
   {
-    /* Success */
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "UDP transmitted %u-byte message to  `%s' `%s' (%d: %s)\n",
-         (unsigned int) (udpw->msg_size), GNUNET_i2s(&udpw->session->target) ,GNUNET_a2s (sa, slen), (int) sent,
-         (sent < 0) ? STRERROR (errno) : "ok");
-    GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, total, bytes, sent, success",
-                              sent, GNUNET_NO);
-    GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, total, messages, sent, success",
-                              1, GNUNET_NO);
-    if (NULL != udpw->frag_ctx)
+    if (sizeof (struct IPv4UdpAddress) == udpw->session->address->address_length)
+    {
+      u4 = udpw->session->address->address;
+      memset (&a4,
+              0,
+              sizeof(a4));
+      a4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+      a4.sin_len = sizeof (a4);
+#endif
+      a4.sin_port = u4->u4_port;
+      a4.sin_addr.s_addr = u4->ipv4_addr;
+      a = (const struct sockaddr *) &a4;
+      slen = sizeof (a4);
+    }
+    else if (sizeof (struct IPv6UdpAddress) == udpw->session->address->address_length)
+    {
+      u6 = udpw->session->address->address;
+      memset (&a6,
+              0,
+              sizeof(a6));
+      a6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+      a6.sin6_len = sizeof (a6);
+#endif
+      a6.sin6_port = u6->u6_port;
+      a6.sin6_addr = u6->ipv6_addr;
+      a = (const struct sockaddr *) &a6;
+      slen = sizeof (a6);
+    }
+    else
+    {
+      GNUNET_break (0);
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      notify_session_monitor (plugin,
+                              udpw->session,
+                              GNUNET_TRANSPORT_SS_UPDATE);
+      GNUNET_free (udpw);
+      continue;
+    }
+    sent = GNUNET_NETWORK_socket_sendto (sock,
+                                         udpw->msg_buf,
+                                         udpw->msg_size,
+                                         a,
+                                         slen);
+    dequeue (plugin,
+             udpw);
+    if (GNUNET_SYSERR == sent)
+    {
+      /* Failure */
+      analyze_send_error (plugin,
+                          a,
+                          slen,
+                          errno);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_STATISTICS_update (plugin->env->stats,
+                                "# UDP, total, bytes, sent, failure",
+                                sent,
+                                GNUNET_NO);
+      GNUNET_STATISTICS_update (plugin->env->stats,
+                                "# UDP, total, messages, sent, failure",
+                                1,
+                                GNUNET_NO);
+    }
+    else
+    {
+      /* Success */
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "UDP transmitted %u-byte message to  `%s' `%s' (%d: %s)\n",
+           (unsigned int) (udpw->msg_size),
+           GNUNET_i2s (&udpw->session->target),
+           GNUNET_a2s (a,
+                       slen),
+           (int ) sent,
+           (sent < 0) ? STRERROR (errno) : "ok");
+      GNUNET_STATISTICS_update (plugin->env->stats,
+                                "# UDP, total, bytes, sent, success",
+                                sent,
+                                GNUNET_NO);
+      GNUNET_STATISTICS_update (plugin->env->stats,
+                                "# UDP, total, messages, sent, success",
+                                1,
+                                GNUNET_NO);
+      if (NULL != udpw->frag_ctx)
         udpw->frag_ctx->on_wire_size += udpw->msg_size;
-    call_continuation (udpw, GNUNET_OK);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_OK);
+    }
+    notify_session_monitor (plugin,
+                            udpw->session,
+                            GNUNET_TRANSPORT_SS_UPDATE);
+    GNUNET_free (udpw);
   }
-  dequeue (plugin, udpw);
-  GNUNET_free (udpw);
-  udpw = NULL;
-
-  return sent;
 }
 
 
+/* ***************** Event loop (part 2) *************** */
+
+
 /**
  * We have been notified that our readset has something to read.  We don't
  * know which socket needs to be read, so we have to check each one
  * Then reschedule this function to be called again once more is available.
  *
  * @param cls the plugin handle
- * @param tc the scheduling context (for rescheduling this function again)
+ * @param tc the scheduling context
  */
 static void
-udp_plugin_select (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
+udp_plugin_select_v4 (void *cls,
+                      const struct GNUNET_SCHEDULER_TaskContext *tc)
 {
   struct Plugin *plugin = cls;
 
-  plugin->select_task = GNUNET_SCHEDULER_NO_TASK;
+  plugin->select_task_v4 = NULL;
   if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
     return;
-  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
-       (NULL != plugin->sockv4) &&
-       (GNUNET_NETWORK_fdset_isset (tc->read_ready, plugin->sockv4)) )
-    udp_select_read (plugin, plugin->sockv4);
-  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) &&
-       (NULL != plugin->sockv4) && 
-       (NULL != plugin->ipv4_queue_head) &&
-       (GNUNET_NETWORK_fdset_isset (tc->write_ready, plugin->sockv4)) )
-    udp_select_send (plugin, plugin->sockv4);   
-  schedule_select (plugin);
+  if (NULL == plugin->sockv4)
+    return;
+  if ((0 != (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
+      (GNUNET_NETWORK_fdset_isset (tc->read_ready,
+                                   plugin->sockv4)))
+    udp_select_read (plugin,
+                     plugin->sockv4);
+  udp_select_send (plugin,
+                   plugin->sockv4);
+  schedule_select_v4 (plugin);
 }
 
 
@@ -2620,95 +3274,119 @@ udp_plugin_select (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
  * Then reschedule this function to be called again once more is available.
  *
  * @param cls the plugin handle
- * @param tc the scheduling context (for rescheduling this function again)
+ * @param tc the scheduling context
  */
 static void
-udp_plugin_select_v6 (void *cls, const struct GNUNET_SCHEDULER_TaskContext *tc)
+udp_plugin_select_v6 (void *cls,
+                      const struct GNUNET_SCHEDULER_TaskContext *tc)
 {
   struct Plugin *plugin = cls;
 
-  plugin->select_task_v6 = GNUNET_SCHEDULER_NO_TASK;
+  plugin->select_task_v6 = NULL;
   if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
     return;
-  if ( ((tc->reason & GNUNET_SCHEDULER_REASON_READ_READY) != 0) &&
-       (NULL != plugin->sockv6) &&
-       (GNUNET_NETWORK_fdset_isset (tc->read_ready, plugin->sockv6)) )
-    udp_select_read (plugin, plugin->sockv6);
-  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_WRITE_READY)) &&
-       (NULL != plugin->sockv6) && (plugin->ipv6_queue_head != NULL) &&
-       (GNUNET_NETWORK_fdset_isset (tc->write_ready, plugin->sockv6)) )    
-    udp_select_send (plugin, plugin->sockv6);
-  schedule_select (plugin);
+  if (NULL == plugin->sockv6)
+    return;
+  if ( (0 != (tc->reason & GNUNET_SCHEDULER_REASON_READ_READY)) &&
+       (GNUNET_NETWORK_fdset_isset (tc->read_ready,
+                                    plugin->sockv6)) )
+    udp_select_read (plugin,
+                     plugin->sockv6);
+
+  udp_select_send (plugin,
+                   plugin->sockv6);
+  schedule_select_v6 (plugin);
 }
 
 
+/* ******************* Initialization *************** */
+
+
 /**
+ * Setup the UDP sockets (for IPv4 and IPv6) for the plugin.
  *
+ * @param plugin the plugin to initialize
+ * @param bind_v6 IPv6 address to bind to (can be NULL, for 'any')
+ * @param bind_v4 IPv4 address to bind to (can be NULL, for 'any')
  * @return number of sockets that were successfully bound
  */
 static int
-setup_sockets (struct Plugin *plugin, 
-              const struct sockaddr_in6 *bind_v6,
-              const struct sockaddr_in *bind_v4)
+setup_sockets (struct Plugin *plugin,
+               const struct sockaddr_in6 *bind_v6,
+               const struct sockaddr_in *bind_v4)
 {
   int tries;
   int sockets_created = 0;
-  struct sockaddr_in6 serverAddrv6;
-  struct sockaddr_in serverAddrv4;
-  struct sockaddr *serverAddr;
-  struct sockaddr *addrs[2];
+  struct sockaddr_in6 server_addrv6;
+  struct sockaddr_in server_addrv4;
+  const struct sockaddr *server_addr;
+  const struct sockaddr *addrs[2];
   socklen_t addrlens[2];
   socklen_t addrlen;
   int eno;
 
   /* Create IPv6 socket */
   eno = EINVAL;
-  if (plugin->enable_ipv6 == GNUNET_YES)
+  if (GNUNET_YES == plugin->enable_ipv6)
   {
-    plugin->sockv6 = GNUNET_NETWORK_socket_create (PF_INET6, SOCK_DGRAM, 0);
+    plugin->sockv6 = GNUNET_NETWORK_socket_create (PF_INET6,
+                                                   SOCK_DGRAM,
+                                                   0);
     if (NULL == plugin->sockv6)
     {
-       GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "socket");
-      LOG (GNUNET_ERROR_TYPE_WARNING, "Disabling IPv6 since it is not supported on this system!\n");
+      LOG (GNUNET_ERROR_TYPE_INFO,
+           _("Disabling IPv6 since it is not supported on this system!\n"));
       plugin->enable_ipv6 = GNUNET_NO;
     }
     else
     {
-       memset (&serverAddrv6, '\0', sizeof (struct sockaddr_in6));
+      memset (&server_addrv6,
+              0,
+              sizeof(struct sockaddr_in6));
 #if HAVE_SOCKADDR_IN_SIN_LEN
-      serverAddrv6.sin6_len = sizeof (struct sockaddr_in6);
+      server_addrv6.sin6_len = sizeof (struct sockaddr_in6);
 #endif
-      serverAddrv6.sin6_family = AF_INET6;
+      server_addrv6.sin6_family = AF_INET6;
       if (NULL != bind_v6)
-       serverAddrv6.sin6_addr = bind_v6->sin6_addr;
+        server_addrv6.sin6_addr = bind_v6->sin6_addr;
       else
-       serverAddrv6.sin6_addr = in6addr_any;
+        server_addrv6.sin6_addr = in6addr_any;
 
       if (0 == plugin->port) /* autodetect */
-               serverAddrv6.sin6_port = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000);
+        server_addrv6.sin6_port
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
+                   + 32000);
       else
-               serverAddrv6.sin6_port = htons (plugin->port);
+        server_addrv6.sin6_port = htons (plugin->port);
       addrlen = sizeof (struct sockaddr_in6);
-      serverAddr = (struct sockaddr *) &serverAddrv6;
+      server_addr = (const struct sockaddr *) &server_addrv6;
 
       tries = 0;
       while (tries < 10)
       {
-               LOG (GNUNET_ERROR_TYPE_DEBUG, "Binding to IPv6 `%s'\n",
-                                GNUNET_a2s (serverAddr, addrlen));
-               /* binding */
-               if (GNUNET_OK == GNUNET_NETWORK_socket_bind (plugin->sockv6,
-                                                            serverAddr, addrlen, 0))
-                       break;
-               eno = errno;
-               if (0 != plugin->port)
-               {
-                               tries = 10; /* fail */
-                               break; /* bind failed on specific port */
-               }
-               /* autodetect */
-               serverAddrv6.sin6_port = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000);
-               tries ++;
+        LOG(GNUNET_ERROR_TYPE_DEBUG,
+            "Binding to IPv6 `%s'\n",
+            GNUNET_a2s (server_addr,
+                        addrlen));
+        /* binding */
+        if (GNUNET_OK ==
+            GNUNET_NETWORK_socket_bind (plugin->sockv6,
+                                        server_addr,
+                                        addrlen))
+          break;
+        eno = errno;
+        if (0 != plugin->port)
+        {
+          tries = 10; /* fail immediately */
+          break; /* bind failed on specific port */
+        }
+        /* autodetect */
+        server_addrv6.sin6_port
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
+                   + 32000);
+        tries++;
       }
       if (tries >= 10)
       {
@@ -2716,142 +3394,146 @@ setup_sockets (struct Plugin *plugin,
         plugin->enable_ipv6 = GNUNET_NO;
         plugin->sockv6 = NULL;
       }
-
-      if (plugin->sockv6 != NULL)
+      else
+      {
+        plugin->port = ntohs (server_addrv6.sin6_port);
+      }
+      if (NULL != plugin->sockv6)
       {
         LOG (GNUNET_ERROR_TYPE_DEBUG,
-             "IPv6 socket created on port %s\n",
-             GNUNET_a2s (serverAddr, addrlen));
-        addrs[sockets_created] = (struct sockaddr *) &serverAddrv6;
-        addrlens[sockets_created] = sizeof (struct sockaddr_in6);
+             "IPv6 UDP socket created listinging at %s\n",
+             GNUNET_a2s (server_addr,
+                         addrlen));
+        addrs[sockets_created] = server_addr;
+        addrlens[sockets_created] = addrlen;
         sockets_created++;
       }
       else
       {
-          LOG (GNUNET_ERROR_TYPE_ERROR,
-               "Failed to bind UDP socket to %s: %s\n",
-               GNUNET_a2s (serverAddr, addrlen),
-              STRERROR (eno));
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             _("Failed to bind UDP socket to %s: %s\n"),
+             GNUNET_a2s (server_addr,
+                         addrlen),
+             STRERROR (eno));
       }
     }
   }
 
   /* Create IPv4 socket */
   eno = EINVAL;
-  plugin->sockv4 = GNUNET_NETWORK_socket_create (PF_INET, SOCK_DGRAM, 0);
+  plugin->sockv4 = GNUNET_NETWORK_socket_create (PF_INET,
+                                                 SOCK_DGRAM,
+                                                 0);
   if (NULL == plugin->sockv4)
   {
-    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "socket");
-    LOG (GNUNET_ERROR_TYPE_WARNING, "Disabling IPv4 since it is not supported on this system!\n");
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                         "socket");
+    LOG (GNUNET_ERROR_TYPE_INFO,
+         _("Disabling IPv4 since it is not supported on this system!\n"));
     plugin->enable_ipv4 = GNUNET_NO;
   }
   else
   {
-    memset (&serverAddrv4, '\0', sizeof (struct sockaddr_in));
+    memset (&server_addrv4,
+            0,
+            sizeof(struct sockaddr_in));
 #if HAVE_SOCKADDR_IN_SIN_LEN
-    serverAddrv4.sin_len = sizeof (struct sockaddr_in);
+    server_addrv4.sin_len = sizeof (struct sockaddr_in);
 #endif
-    serverAddrv4.sin_family = AF_INET;
+    server_addrv4.sin_family = AF_INET;
     if (NULL != bind_v4)
-      serverAddrv4.sin_addr = bind_v4->sin_addr;
+      server_addrv4.sin_addr = bind_v4->sin_addr;
     else
-      serverAddrv4.sin_addr.s_addr = INADDR_ANY;
-    
+      server_addrv4.sin_addr.s_addr = INADDR_ANY;
+
     if (0 == plugin->port)
       /* autodetect */
-      serverAddrv4.sin_port = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000);
+      server_addrv4.sin_port
+        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                           33537)
+                 + 32000);
     else
-      serverAddrv4.sin_port = htons (plugin->port);
-    
-    
+      server_addrv4.sin_port = htons (plugin->port);
+
     addrlen = sizeof (struct sockaddr_in);
-    serverAddr = (struct sockaddr *) &serverAddrv4;
-    
+    server_addr = (const struct sockaddr *) &server_addrv4;
+
     tries = 0;
     while (tries < 10)
     {
-      LOG (GNUNET_ERROR_TYPE_DEBUG, "Binding to IPv4 `%s'\n",
-                       GNUNET_a2s (serverAddr, addrlen));
-      
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Binding to IPv4 `%s'\n",
+           GNUNET_a2s (server_addr,
+                       addrlen));
+
       /* binding */
-      if (GNUNET_OK == GNUNET_NETWORK_socket_bind (plugin->sockv4,
-                                                   serverAddr, addrlen, 0))
-               break;
+      if (GNUNET_OK ==
+          GNUNET_NETWORK_socket_bind (plugin->sockv4,
+                                      server_addr,
+                                      addrlen))
+        break;
       eno = errno;
       if (0 != plugin->port)
       {
-               tries = 10; /* fail */
-               break; /* bind failed on specific port */
+        tries = 10; /* fail */
+        break; /* bind failed on specific port */
       }
-      
+
       /* autodetect */
-      serverAddrv4.sin_port = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537) + 32000);
-      tries ++;
+      server_addrv4.sin_port
+        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                           33537)
+                 + 32000);
+      tries++;
     }
-    
     if (tries >= 10)
     {
       GNUNET_NETWORK_socket_close (plugin->sockv4);
       plugin->enable_ipv4 = GNUNET_NO;
       plugin->sockv4 = NULL;
     }
-    
-    if (plugin->sockv4 != NULL)
+    else
+    {
+      plugin->port = ntohs (server_addrv4.sin_port);
+    }
+
+    if (NULL != plugin->sockv4)
     {
       LOG (GNUNET_ERROR_TYPE_DEBUG,
-               "IPv4 socket created on port %s\n", GNUNET_a2s (serverAddr, addrlen));
-      addrs[sockets_created] = (struct sockaddr *) &serverAddrv4;
-      addrlens[sockets_created] = sizeof (struct sockaddr_in);
+           "IPv4 socket created on port %s\n",
+           GNUNET_a2s (server_addr,
+                       addrlen));
+      addrs[sockets_created] = server_addr;
+      addrlens[sockets_created] = addrlen;
       sockets_created++;
     }
     else
-    {            
+    {
       LOG (GNUNET_ERROR_TYPE_ERROR,
-               "Failed to bind UDP socket to %s: %s\n",
-               GNUNET_a2s (serverAddr, addrlen), STRERROR (eno));
+           _("Failed to bind UDP socket to %s: %s\n"),
+           GNUNET_a2s (server_addr,
+                       addrlen),
+           STRERROR (eno));
     }
   }
-  
-  if (0 == sockets_created)
-  {
-               LOG (GNUNET_ERROR_TYPE_WARNING, _("Failed to open UDP sockets\n"));
-               return 0; /* No sockets created, return */
-  }
-
-  /* Create file descriptors */
-  if (plugin->enable_ipv4 == GNUNET_YES)
-  {
-                       plugin->rs_v4 = GNUNET_NETWORK_fdset_create ();
-                       plugin->ws_v4 = GNUNET_NETWORK_fdset_create ();
-                       GNUNET_NETWORK_fdset_zero (plugin->rs_v4);
-                       GNUNET_NETWORK_fdset_zero (plugin->ws_v4);
-                       if (NULL != plugin->sockv4)
-                       {
-                               GNUNET_NETWORK_fdset_set (plugin->rs_v4, plugin->sockv4);
-                               GNUNET_NETWORK_fdset_set (plugin->ws_v4, plugin->sockv4);
-                       }
-  }
 
-  if (plugin->enable_ipv6 == GNUNET_YES)
+  if (0 == sockets_created)
   {
-    plugin->rs_v6 = GNUNET_NETWORK_fdset_create ();
-    plugin->ws_v6 = GNUNET_NETWORK_fdset_create ();
-    GNUNET_NETWORK_fdset_zero (plugin->rs_v6);
-    GNUNET_NETWORK_fdset_zero (plugin->ws_v6);
-    if (NULL != plugin->sockv6)
-    {
-      GNUNET_NETWORK_fdset_set (plugin->rs_v6, plugin->sockv6);
-      GNUNET_NETWORK_fdset_set (plugin->ws_v6, plugin->sockv6);
-    }
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         _("Failed to open UDP sockets\n"));
+    return 0; /* No sockets created, return */
   }
-
-  schedule_select (plugin);
+  schedule_select_v4 (plugin);
+  schedule_select_v6 (plugin);
   plugin->nat = GNUNET_NAT_register (plugin->env->cfg,
-                           GNUNET_NO, plugin->port,
-                           sockets_created,
-                           (const struct sockaddr **) addrs, addrlens,
-                           &udp_nat_port_map_callback, NULL, plugin);
-
+                                     GNUNET_NO,
+                                     plugin->port,
+                                     sockets_created,
+                                     addrs,
+                                     addrlens,
+                                     &udp_nat_port_map_callback,
+                                     NULL,
+                                     plugin);
   return sockets_created;
 }
 
@@ -2860,8 +3542,8 @@ setup_sockets (struct Plugin *plugin,
  * The exported method. Makes the core api available via a global and
  * returns the udp transport API.
  *
- * @param cls our 'struct GNUNET_TRANSPORT_PluginEnvironment'
- * @return our 'struct GNUNET_TRANSPORT_PluginFunctions'
+ * @param cls our `struct GNUNET_TRANSPORT_PluginEnvironment`
+ * @return our `struct GNUNET_TRANSPORT_PluginFunctions`
  */
 void *
 libgnunet_plugin_transport_udp_init (void *cls)
@@ -2871,15 +3553,15 @@ libgnunet_plugin_transport_udp_init (void *cls)
   struct Plugin *p;
   unsigned long long port;
   unsigned long long aport;
-  unsigned long long broadcast;
   unsigned long long udp_max_bps;
   unsigned long long enable_v6;
-  char * bind4_address;
-  char * bind6_address;
-  char * fancy_interval;
+  unsigned long long enable_broadcasting;
+  unsigned long long enable_broadcasting_recv;
+  char *bind4_address;
+  char *bind6_address;
   struct GNUNET_TIME_Relative interval;
-  struct sockaddr_in serverAddrv4;
-  struct sockaddr_in6 serverAddrv6;
+  struct sockaddr_in server_addrv4;
+  struct sockaddr_in6 server_addrv6;
   int res;
   int have_bind4;
   int have_bind6;
@@ -2887,8 +3569,8 @@ libgnunet_plugin_transport_udp_init (void *cls)
   if (NULL == env->receive)
   {
     /* run in 'stub' mode (i.e. as part of gnunet-peerinfo), don't fully
-       initialze the plugin or the API */
-    api = GNUNET_malloc (sizeof (struct GNUNET_TRANSPORT_PluginFunctions));
+     initialze the plugin or the API */
+    api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
     api->cls = NULL;
     api->address_pretty_printer = &udp_plugin_address_pretty_printer;
     api->address_to_string = &udp_address_to_string;
@@ -2896,47 +3578,66 @@ libgnunet_plugin_transport_udp_init (void *cls)
     return api;
   }
 
-  GNUNET_assert (NULL != env->stats);
-
   /* Get port number: port == 0 : autodetect a port,
-   *                                                                                           > 0 : use this port,
-   *                                                             not given : 2086 default */
+   * > 0 : use this port, not given : 2086 default */
   if (GNUNET_OK !=
-      GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-udp", "PORT",
+      GNUNET_CONFIGURATION_get_value_number (env->cfg,
+                                             "transport-udp",
+                                             "PORT",
                                              &port))
     port = 2086;
+  if (port > 65535)
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "transport-udp",
+                               "PORT",
+                               _("must be in [0,65535]"));
+    return NULL;
+  }
   if (GNUNET_OK !=
-      GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-udp",
-                                             "ADVERTISED_PORT", &aport))
+      GNUNET_CONFIGURATION_get_value_number (env->cfg,
+                                             "transport-udp",
+                                             "ADVERTISED_PORT",
+                                             &aport))
     aport = port;
-  if (port > 65535)
+  if (aport > 65535)
   {
-    LOG (GNUNET_ERROR_TYPE_WARNING,
-         _("Given `%s' option is out of range: %llu > %u\n"), "PORT", port,
-         65535);
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "transport-udp",
+                               "ADVERTISED_PORT",
+                               _("must be in [0,65535]"));
     return NULL;
   }
 
-  /* Protocols */
-  if ((GNUNET_YES ==
-       GNUNET_CONFIGURATION_get_value_yesno (env->cfg, "nat",
-                                             "DISABLEV6")))
+  if (GNUNET_YES ==
+      GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
+                                            "nat",
+                                            "DISABLEV6"))
     enable_v6 = GNUNET_NO;
   else
     enable_v6 = GNUNET_YES;
 
-  /* Addresses */
   have_bind4 = GNUNET_NO;
-  memset (&serverAddrv4, 0, sizeof (serverAddrv4));
+  memset (&server_addrv4,
+          0,
+          sizeof (server_addrv4));
   if (GNUNET_YES ==
-      GNUNET_CONFIGURATION_get_value_string (env->cfg, "transport-udp",
-                                             "BINDTO", &bind4_address))
+      GNUNET_CONFIGURATION_get_value_string (env->cfg,
+                                             "transport-udp",
+                                             "BINDTO",
+                                             &bind4_address))
   {
     LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Binding udp plugin to specific address: `%s'\n",
+         "Binding UDP plugin to specific address: `%s'\n",
          bind4_address);
-    if (1 != inet_pton (AF_INET, bind4_address, &serverAddrv4.sin_addr))
+    if (1 != inet_pton (AF_INET,
+                        bind4_address,
+                        &server_addrv4.sin_addr))
     {
+      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                                 "transport-udp",
+                                 "BINDTO",
+                                 _("must be valid IPv4 address"));
       GNUNET_free (bind4_address);
       return NULL;
     }
@@ -2944,19 +3645,26 @@ libgnunet_plugin_transport_udp_init (void *cls)
   }
   GNUNET_free_non_null (bind4_address);
   have_bind6 = GNUNET_NO;
-  memset (&serverAddrv6, 0, sizeof (serverAddrv6));
+  memset (&server_addrv6,
+          0,
+          sizeof (server_addrv6));
   if (GNUNET_YES ==
-      GNUNET_CONFIGURATION_get_value_string (env->cfg, "transport-udp",
-                                             "BINDTO6", &bind6_address))
+      GNUNET_CONFIGURATION_get_value_string (env->cfg,
+                                             "transport-udp",
+                                             "BINDTO6",
+                                             &bind6_address))
   {
     LOG (GNUNET_ERROR_TYPE_DEBUG,
          "Binding udp plugin to specific address: `%s'\n",
          bind6_address);
-    if (1 !=
-        inet_pton (AF_INET6, bind6_address, &serverAddrv6.sin6_addr))
+    if (1 != inet_pton (AF_INET6,
+                        bind6_address,
+                        &server_addrv6.sin6_addr))
     {
-      LOG (GNUNET_ERROR_TYPE_ERROR, _("Invalid IPv6 address: `%s'\n"),
-           bind6_address);
+      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                                 "transport-udp",
+                                 "BINDTO6",
+                                 _("must be valid IPv6 address"));
       GNUNET_free (bind6_address);
       return NULL;
     }
@@ -2964,73 +3672,82 @@ libgnunet_plugin_transport_udp_init (void *cls)
   }
   GNUNET_free_non_null (bind6_address);
 
-  /* Initialize my flags */
-  myoptions = 0;
+  enable_broadcasting = GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
+                                                              "transport-udp",
+                                                              "BROADCAST");
+  if (enable_broadcasting == GNUNET_SYSERR)
+    enable_broadcasting = GNUNET_NO;
 
-  /* Enable neighbour discovery */
-  broadcast = GNUNET_CONFIGURATION_get_value_yesno (env->cfg, "transport-udp",
-                                            "BROADCAST");
-  if (broadcast == GNUNET_SYSERR)
-    broadcast = GNUNET_NO;
+  enable_broadcasting_recv = GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
+                                                                   "transport-udp",
+                                                                   "BROADCAST_RECEIVE");
+  if (enable_broadcasting_recv == GNUNET_SYSERR)
+    enable_broadcasting_recv = GNUNET_YES;
 
-  if (GNUNET_SYSERR == GNUNET_CONFIGURATION_get_value_string (env->cfg, "transport-udp",
-                                           "BROADCAST_INTERVAL", &fancy_interval))
-  {
-    interval = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 10);
-  }
-  else
+  if (GNUNET_SYSERR ==
+      GNUNET_CONFIGURATION_get_value_time (env->cfg,
+                                           "transport-udp",
+                                           "BROADCAST_INTERVAL",
+                                           &interval))
   {
-     if (GNUNET_SYSERR == GNUNET_STRINGS_fancy_time_to_relative(fancy_interval, &interval))
-     {
-       interval = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 30);
-     }
-     GNUNET_free (fancy_interval);
+    interval = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
+                                              10);
   }
-
-  /* Maximum datarate */
-  if (GNUNET_OK != GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-udp",
-                                             "MAX_BPS", &udp_max_bps))
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (env->cfg,
+                                             "transport-udp",
+                                             "MAX_BPS",
+                                             &udp_max_bps))
   {
-    udp_max_bps = 1024 * 1024 * 50;     /* 50 MB/s == infinity for practical purposes */
+    /* 50 MB/s == infinity for practical purposes */
+    udp_max_bps = 1024 * 1024 * 50;
   }
 
-  p = GNUNET_malloc (sizeof (struct Plugin));
+  p = GNUNET_new (struct Plugin);
   p->port = port;
   p->aport = aport;
   p->broadcast_interval = interval;
   p->enable_ipv6 = enable_v6;
   p->enable_ipv4 = GNUNET_YES; /* default */
+  p->enable_broadcasting = enable_broadcasting;
+  p->enable_broadcasting_receiving = enable_broadcasting_recv;
   p->env = env;
-  p->sessions = GNUNET_CONTAINER_multihashmap_create (10, GNUNET_NO);
+  p->sessions = GNUNET_CONTAINER_multipeermap_create (16,
+                                                      GNUNET_NO);
   p->defrag_ctxs = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
-  p->mst = GNUNET_SERVER_mst_create (&process_inbound_tokenized_messages, p);
+  p->mst = GNUNET_SERVER_mst_create (&process_inbound_tokenized_messages,
+                                     p);
   GNUNET_BANDWIDTH_tracker_init (&p->tracker,
-                                 GNUNET_BANDWIDTH_value_init ((uint32_t)udp_max_bps), 30);
-  plugin = p;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG, "Setting up sockets\n");
-  res = setup_sockets (p, (GNUNET_YES == have_bind6) ? &serverAddrv6 : NULL,
-                                                                               (GNUNET_YES == have_bind4) ? &serverAddrv4 : NULL);
-  if ((res == 0) || ((p->sockv4 == NULL) && (p->sockv6 == NULL)))
+                                 NULL,
+                                 NULL,
+                                 GNUNET_BANDWIDTH_value_init ((uint32_t) udp_max_bps),
+                                 30);
+  res = setup_sockets (p,
+                       (GNUNET_YES == have_bind6) ? &server_addrv6 : NULL,
+                       (GNUNET_YES == have_bind4) ? &server_addrv4 : NULL);
+  if ( (0 == res) ||
+       ( (NULL == p->sockv4) &&
+         (NULL == p->sockv6) ) )
   {
     LOG (GNUNET_ERROR_TYPE_ERROR,
-        _("Failed to create network sockets, plugin failed\n"));
-    GNUNET_CONTAINER_multihashmap_destroy (p->sessions);
+        _("Failed to create UDP network sockets\n"));
+    GNUNET_CONTAINER_multipeermap_destroy (p->sessions);
     GNUNET_CONTAINER_heap_destroy (p->defrag_ctxs);
     GNUNET_SERVER_mst_destroy (p->mst);
     GNUNET_free (p);
     return NULL;
   }
-  else if (broadcast == GNUNET_YES)
-  {
-    LOG (GNUNET_ERROR_TYPE_DEBUG, "Starting broadcasting\n");
-    setup_broadcast (p, &serverAddrv6, &serverAddrv4);
-  }
 
-  api = GNUNET_malloc (sizeof (struct GNUNET_TRANSPORT_PluginFunctions));
+  /* Setup broadcasting and receiving beacons */
+  setup_broadcast (p,
+                   &server_addrv6,
+                   &server_addrv4);
+
+  api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
   api->cls = p;
-  api->send = NULL;
-  api->disconnect = &udp_disconnect;
+  api->disconnect_session = &udp_disconnect_session;
+  api->query_keepalive_factor = &udp_query_keepalive_factor;
+  api->disconnect_peer = &udp_disconnect;
   api->address_pretty_printer = &udp_plugin_address_pretty_printer;
   api->address_to_string = &udp_address_to_string;
   api->string_to_address = &udp_string_to_address;
@@ -3038,24 +3755,33 @@ libgnunet_plugin_transport_udp_init (void *cls)
   api->get_session = &udp_plugin_get_session;
   api->send = &udp_plugin_send;
   api->get_network = &udp_get_network;
-
+  api->update_session_timeout = &udp_plugin_update_session_timeout;
+  api->setup_monitor = &udp_plugin_setup_monitor;
   return api;
 }
 
 
+/**
+ * Function called on each entry in the defragmentation heap to
+ * clean it up.
+ *
+ * @param cls NULL
+ * @param node node in the heap (to be removed)
+ * @param element a `struct DefragContext` to be cleaned up
+ * @param cost unused
+ * @return #GNUNET_YES
+ */
 static int
 heap_cleanup_iterator (void *cls,
-                      struct GNUNET_CONTAINER_HeapNode *
-                      node, void *element,
-                      GNUNET_CONTAINER_HeapCostType
-                      cost)
+                       struct GNUNET_CONTAINER_HeapNode *node,
+                       void *element,
+                       GNUNET_CONTAINER_HeapCostType cost)
 {
-  struct DefragContext * d_ctx = element;
+  struct DefragContext *d_ctx = element;
 
   GNUNET_CONTAINER_heap_remove_node (node);
-  GNUNET_DEFRAGMENT_context_destroy(d_ctx->defrag);
+  GNUNET_DEFRAGMENT_context_destroy (d_ctx->defrag);
   GNUNET_free (d_ctx);
-
   return GNUNET_YES;
 }
 
@@ -3064,7 +3790,7 @@ heap_cleanup_iterator (void *cls,
  * The exported method. Makes the core api available via a global and
  * returns the udp transport API.
  *
- * @param cls our 'struct GNUNET_TRANSPORT_PluginEnvironment'
+ * @param cls our `struct GNUNET_TRANSPORT_PluginEnvironment`
  * @return NULL
  */
 void *
@@ -3072,113 +3798,90 @@ libgnunet_plugin_transport_udp_done (void *cls)
 {
   struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
   struct Plugin *plugin = api->cls;
+  struct PrettyPrinterContext *cur;
+  struct UDP_MessageWrapper *udpw;
 
   if (NULL == plugin)
   {
     GNUNET_free (api);
     return NULL;
   }
-
   stop_broadcast (plugin);
-  if (plugin->select_task != GNUNET_SCHEDULER_NO_TASK)
+  if (NULL != plugin->select_task_v4)
   {
-    GNUNET_SCHEDULER_cancel (plugin->select_task);
-    plugin->select_task = GNUNET_SCHEDULER_NO_TASK;
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+    plugin->select_task_v4 = NULL;
   }
-  if (plugin->select_task_v6 != GNUNET_SCHEDULER_NO_TASK)
+  if (NULL != plugin->select_task_v6)
   {
     GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
-    plugin->select_task_v6 = GNUNET_SCHEDULER_NO_TASK;
+    plugin->select_task_v6 = NULL;
   }
-
-  /* Closing sockets */
-  if (GNUNET_YES ==plugin->enable_ipv4)
+  if (NULL != plugin->sockv4)
   {
-               if (plugin->sockv4 != NULL)
-               {
-                       GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (plugin->sockv4));
-                       plugin->sockv4 = NULL;
-               }
-               GNUNET_NETWORK_fdset_destroy (plugin->rs_v4);
-               GNUNET_NETWORK_fdset_destroy (plugin->ws_v4);
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (plugin->sockv4));
+    plugin->sockv4 = NULL;
   }
-  if (GNUNET_YES ==plugin->enable_ipv6)
+  if (NULL != plugin->sockv6)
   {
-               if (plugin->sockv6 != NULL)
-               {
-                       GNUNET_break (GNUNET_OK == GNUNET_NETWORK_socket_close (plugin->sockv6));
-                       plugin->sockv6 = NULL;
-
-                       GNUNET_NETWORK_fdset_destroy (plugin->rs_v6);
-                       GNUNET_NETWORK_fdset_destroy (plugin->ws_v6);
-               }
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (plugin->sockv6));
+    plugin->sockv6 = NULL;
   }
   if (NULL != plugin->nat)
-       GNUNET_NAT_unregister (plugin->nat);
-
-  if (plugin->defrag_ctxs != NULL)
   {
-    GNUNET_CONTAINER_heap_iterate(plugin->defrag_ctxs,
-        heap_cleanup_iterator, NULL);
-    GNUNET_CONTAINER_heap_destroy(plugin->defrag_ctxs);
+    GNUNET_NAT_unregister (plugin->nat);
+    plugin->nat = NULL;
+  }
+  if (NULL != plugin->defrag_ctxs)
+  {
+    GNUNET_CONTAINER_heap_iterate (plugin->defrag_ctxs,
+                                   &heap_cleanup_iterator,
+                                   NULL);
+    GNUNET_CONTAINER_heap_destroy (plugin->defrag_ctxs);
     plugin->defrag_ctxs = NULL;
   }
-  if (plugin->mst != NULL)
+  if (NULL != plugin->mst)
   {
-    GNUNET_SERVER_mst_destroy(plugin->mst);
+    GNUNET_SERVER_mst_destroy (plugin->mst);
     plugin->mst = NULL;
   }
-
-  /* Clean up leftover messages */
-  struct UDP_MessageWrapper * udpw;
-  udpw = plugin->ipv4_queue_head;
-  while (udpw != NULL)
+  while (NULL != (udpw = plugin->ipv4_queue_head))
   {
-    struct UDP_MessageWrapper *tmp = udpw->next;
-    dequeue (plugin, udpw);
-    call_continuation(udpw, GNUNET_SYSERR);
+    dequeue (plugin,
+             udpw);
+    udpw->qc (udpw->qc_cls,
+              udpw,
+              GNUNET_SYSERR);
     GNUNET_free (udpw);
-
-    udpw = tmp;
   }
-  udpw = plugin->ipv6_queue_head;
-  while (udpw != NULL)
+  while (NULL != (udpw = plugin->ipv6_queue_head))
   {
-    struct UDP_MessageWrapper *tmp = udpw->next;
-    dequeue (plugin, udpw);
-    call_continuation(udpw, GNUNET_SYSERR);
+    dequeue (plugin,
+             udpw);
+    udpw->qc (udpw->qc_cls,
+              udpw,
+              GNUNET_SYSERR);
     GNUNET_free (udpw);
-
-    udpw = tmp;
   }
+  GNUNET_CONTAINER_multipeermap_iterate (plugin->sessions,
+                                         &disconnect_and_free_it,
+                                         plugin);
+  GNUNET_CONTAINER_multipeermap_destroy (plugin->sessions);
 
-  /* Clean up sessions */
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Cleaning up sessions\n");
-  GNUNET_CONTAINER_multihashmap_iterate (plugin->sessions, &disconnect_and_free_it, plugin);
-  GNUNET_CONTAINER_multihashmap_destroy (plugin->sessions);
-
-  plugin->nat = NULL;
-  GNUNET_free (plugin);
-  GNUNET_free (api);
-#if DEBUG_MALLOC
-  struct Allocation *allocation;
-  while (NULL != ahead)
-  {
-      allocation = ahead;
-      GNUNET_CONTAINER_DLL_remove (ahead, atail, allocation);
-      GNUNET_free (allocation);
-  }
-  struct Allocator *allocator;
-  while (NULL != aehead)
+  while (NULL != (cur = plugin->ppc_dll_head))
   {
-      allocator = aehead;
-      GNUNET_CONTAINER_DLL_remove (aehead, aetail, allocator);
-      GNUNET_free (allocator);
+    GNUNET_break (0);
+    GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
+                                 plugin->ppc_dll_tail,
+                                 cur);
+    GNUNET_RESOLVER_request_cancel (cur->resolver_handle);
+    GNUNET_free (cur);
   }
-#endif
+  GNUNET_free (plugin);
+  GNUNET_free (api);
   return NULL;
 }
 
-
 /* end of plugin_transport_udp.c */