REST/NAMESTORE: rework API
[oweals/gnunet.git] / src / transport / plugin_transport_udp.c
index 4c6a01132a5c078b64a55fea6b25c2c22f827f1a..b05192e063a52324f78585174d2bd7c357bda3f1 100644 (file)
@@ -1,21 +1,21 @@
 /*
  This file is part of GNUnet
- Copyright (C) 2010-2015 Christian Grothoff (and other contributing authors)
+ Copyright (C) 2010-2017 GNUnet e.V.
 
- 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 free software: you can redistribute it and/or modify it
under the terms of the GNU Affero General Public License as published
+ by the Free Software Foundation, either version 3 of the License,
+ 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.
Affero 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.
+ You should have received a copy of the GNU Affero General Public License
+ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+     SPDX-License-Identifier: AGPL3.0-or-later
  */
 
 /**
@@ -30,7 +30,7 @@
 #include "gnunet_hello_lib.h"
 #include "gnunet_util_lib.h"
 #include "gnunet_fragmentation_lib.h"
-#include "gnunet_nat_lib.h"
+#include "gnunet_nat_service.h"
 #include "gnunet_protocols.h"
 #include "gnunet_resolver_service.h"
 #include "gnunet_signatures.h"
@@ -42,6 +42,9 @@
 
 #define LOG(kind,...) GNUNET_log_from (kind, "transport-udp", __VA_ARGS__)
 
+/**
+ * After how much inactivity should a UDP session time out?
+ */
 #define UDP_SESSION_TIME_OUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 60)
 
 /**
 /**
  * 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().
  */
@@ -125,13 +151,18 @@ struct PrettyPrinterContext
 /**
  * Session with another peer.
  */
-struct Session
+struct GNUNET_ATS_Session
 {
   /**
    * Which peer is this session for?
    */
   struct GNUNET_PeerIdentity target;
 
+  /**
+   * Tokenizer for inbound messages.
+   */
+  struct GNUNET_MessageStreamTokenizer *mst;
+
   /**
    * Plugin this session belongs to.
    */
@@ -148,9 +179,11 @@ struct Session
   struct GNUNET_TIME_Relative flow_delay_for_other_peer;
 
   /**
-   * Desired delay for next sending we received from other peer
+   * Desired delay for transmissions we received from other peer.
+   * This is for full messages, the value needs to be adjusted for
+   * fragmented messages.
    */
-  struct GNUNET_TIME_Absolute flow_delay_from_other_peer;
+  struct GNUNET_TIME_Relative flow_delay_from_other_peer;
 
   /**
    * Session timeout task
@@ -162,6 +195,11 @@ struct Session
    */
   struct GNUNET_TIME_Absolute timeout;
 
+  /**
+   * What time did we last transmit?
+   */
+  struct GNUNET_TIME_Absolute last_transmit_time;
+
   /**
    * expected delay for ACKs
    */
@@ -198,7 +236,7 @@ struct Session
   /**
    * Network type of the address.
    */
-  enum GNUNET_ATS_Network_Type scope;
+  enum GNUNET_NetworkType scope;
 
   /**
    * Is this session about to be destroyed (sometimes we cannot
@@ -210,49 +248,6 @@ struct Session
 };
 
 
-/**
- * Closure for #process_inbound_tokenized_messages().
- */
-struct SourceInformation
-{
-  /**
-   * Sender identity.
-   */
-  struct GNUNET_PeerIdentity sender;
-
-  /**
-   * Associated session.
-   */
-  struct Session *session;
-
-};
-
-/**
- * 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;
-
-};
 
 /**
  * Data structure to track defragmentation contexts based
@@ -276,6 +271,12 @@ struct DefragContext
    */
   struct GNUNET_CONTAINER_HeapNode *hnode;
 
+  /**
+   * Source address this receive context is for (allocated at the
+   * end of the struct).
+   */
+  const union UdpAddress *udp_addr;
+
   /**
    * Who's message(s) are we defragmenting here?
    * Only initialized once we succeeded and
@@ -283,12 +284,6 @@ struct DefragContext
    */
   struct GNUNET_PeerIdentity sender;
 
-  /**
-   * Source address this receive context is for (allocated at the
-   * end of the struct).
-   */
-  const union UdpAddress *udp_addr;
-
   /**
    * Length of @e udp_addr.
    */
@@ -297,7 +292,7 @@ struct DefragContext
   /**
    * Network type the address belongs to.
    */
-  enum GNUNET_ATS_Network_Type network_type;
+  enum GNUNET_NetworkType network_type;
 
   /**
    * Has the @e sender field been initialized yet?
@@ -327,14 +322,14 @@ struct UDP_FragmentationContext
   struct Plugin *plugin;
 
   /**
-   * Handle for GNUNET_FRAGMENT context
+   * Handle for fragmentation.
    */
   struct GNUNET_FRAGMENT_Context *frag;
 
   /**
    * The session this fragmentation context belongs to
    */
-  struct Session *session;
+  struct GNUNET_ATS_Session *session;
 
   /**
    * Function to call upon completion of the transmission.
@@ -347,59 +342,56 @@ struct UDP_FragmentationContext
   void *cont_cls;
 
   /**
-   * Message timeout
-   */
-  struct GNUNET_TIME_Absolute timeout;
-
-  /**
-   * Payload size of original unfragmented message
+   * Start time.
    */
-  size_t payload_size;
+  struct GNUNET_TIME_Absolute start_time;
 
   /**
-   * Bytes used to send all fragments on wire including UDP overhead
+   * Transmission time for the next fragment.  Incremented by
+   * the @e flow_delay_from_other_peer for each fragment when
+   * we setup the fragments.
    */
-  size_t on_wire_size;
+  struct GNUNET_TIME_Absolute next_frag_time;
 
   /**
-   * FIXME.
+   * Desired delay for transmissions we received from other peer.
+   * Adjusted to be per fragment (UDP_MTU), even though on the
+   * wire it was for "full messages".
    */
-  unsigned int fragments_used;
-
-};
+  struct GNUNET_TIME_Relative flow_delay_from_other_peer;
 
-
-/**
- * Message types included in a `struct UDP_MessageWrapper`
- */
-enum UDP_MessageType
-{
   /**
-   * Uninitialized (error)
+   * Message timeout
    */
-  UMT_UNDEFINED = 0,
+  struct GNUNET_TIME_Absolute timeout;
 
   /**
-   * Fragment of a message.
+   * Payload size of original unfragmented message
    */
-  UMT_MSG_FRAGMENTED = 1,
+  size_t payload_size;
 
   /**
-   *
+   * Bytes used to send all fragments on wire including UDP overhead
    */
-  UMT_MSG_FRAGMENTED_COMPLETE = 2,
+  size_t on_wire_size;
 
-  /**
-   * Unfragmented message.
-   */
-  UMT_MSG_UNFRAGMENTED = 3,
+};
 
-  /**
-   * Receipt confirmation.
-   */
-  UMT_MSG_ACK = 4
 
-};
+/**
+ * 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);
 
 
 /**
@@ -410,27 +402,38 @@ struct UDP_MessageWrapper
   /**
    * Session this message belongs to
    */
-  struct Session *session;
+  struct GNUNET_ATS_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 with size msg_size including UDP specific overhead
+   * Message with @e msg_size bytes including UDP-specific overhead.
    */
   char *msg_buf;
 
   /**
-   * Function to call upon completion of the transmission.
+   * Function to call once the message wrapper is being removed
+   * from the queue (with success or failure).
+   */
+  QueueContinuation qc;
+
+  /**
+   * Closure for @e qc.
+   */
+  void *qc_cls;
+
+  /**
+   * 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;
 
@@ -440,35 +443,43 @@ struct UDP_MessageWrapper
   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
+   * Message enqueue time.
    */
-  struct GNUNET_TIME_Absolute timeout;
+  struct GNUNET_TIME_Absolute start_time;
 
   /**
-   * Size of UDP message to send including UDP specific overhead
+   * Desired transmission time for this message, based on the
+   * flow limiting information we got from the other peer.
    */
-  size_t msg_size;
+  struct GNUNET_TIME_Absolute transmission_time;
 
   /**
-   * Payload size of original message
+   * Message timeout.
    */
-  size_t payload_size;
+  struct GNUNET_TIME_Absolute timeout;
+
+  /**
+   * Size of UDP message to send, including UDP-specific overhead.
+   */
+  size_t msg_size;
 
   /**
-   * Message type
+   * Payload size of original message.
    */
-  enum UDP_MessageType msg_type;
+  size_t payload_size;
 
 };
 
 
+GNUNET_NETWORK_STRUCT_BEGIN
+
 /**
  * UDP ACK Message-Packet header.
  */
@@ -480,9 +491,11 @@ struct UDP_ACK_Message
   struct GNUNET_MessageHeader header;
 
   /**
-   * Desired delay for flow control
+   * Desired delay for flow control, in us (in NBO).
+   * A value of UINT32_MAX indicates that the other
+   * peer wants us to disconnect.
    */
-  uint32_t delay;
+  uint32_t delay GNUNET_PACKED;
 
   /**
    * What is the identity of the sender
@@ -491,6 +504,11 @@ struct UDP_ACK_Message
 
 };
 
+GNUNET_NETWORK_STRUCT_END
+
+
+/* ************************* Monitoring *********** */
+
 
 /**
  * If a session monitor is attached, notify it about the new
@@ -502,7 +520,7 @@ struct UDP_ACK_Message
  */
 static void
 notify_session_monitor (struct Plugin *plugin,
-                        struct Session *session,
+                        struct GNUNET_ATS_Session *session,
                         enum GNUNET_TRANSPORT_SessionState state)
 {
   struct GNUNET_TRANSPORT_SessionInfo info;
@@ -511,7 +529,9 @@ notify_session_monitor (struct Plugin *plugin,
     return;
   if (GNUNET_YES == session->in_destroy)
     return; /* already destroyed, just RC>0 left-over actions */
-  memset (&info, 0, sizeof (info));
+  memset (&info,
+          0,
+          sizeof (info));
   info.state = state;
   info.is_inbound = GNUNET_SYSERR; /* hard to say */
   info.num_msg_pending = session->msgs_in_queue;
@@ -528,154 +548,409 @@ notify_session_monitor (struct Plugin *plugin,
 
 
 /**
- * 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.
+ * Return information about the given session to the monitor callback.
  *
- * @param cls the plugin handle
- * @param tc the scheduling context (for rescheduling this function again)
+ * @param cls the `struct Plugin` with the monitor callback (`sic`)
+ * @param peer peer we send information about
+ * @param value our `struct GNUNET_ATS_Session` to send information about
+ * @return #GNUNET_OK (continue to iterate)
  */
-static void
-udp_plugin_select (void *cls,
-                   const struct GNUNET_SCHEDULER_TaskContext *tc);
-
+static int
+send_session_info_iter (void *cls,
+                        const struct GNUNET_PeerIdentity *peer,
+                        void *value)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_ATS_Session *session = value;
 
-/**
- * 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
-udp_plugin_select_v6 (void *cls,
-                      const struct GNUNET_SCHEDULER_TaskContext *tc);
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_INIT);
+  notify_session_monitor (plugin,
+                          session,
+                          GNUNET_TRANSPORT_SS_UP);
+  return GNUNET_OK;
+}
 
 
 /**
- * (re)schedule select tasks for this plugin.
+ * 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 plugin plugin to reschedule
+ * @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
-schedule_select (struct Plugin *plugin)
+udp_plugin_setup_monitor (void *cls,
+                          GNUNET_TRANSPORT_SessionInfoCallback sic,
+                          void *sic_cls)
 {
-  struct GNUNET_TIME_Relative min_delay;
-  struct UDP_MessageWrapper *udpw;
-
-  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 != NULL )
-      GNUNET_SCHEDULER_cancel (plugin->select_task);
+  struct Plugin *plugin = cls;
 
-    /* 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_us) ?
-            GNUNET_TIME_UNIT_FOREVER_REL : min_delay, plugin->rs_v4,
-        (0 == min_delay.rel_value_us) ? plugin->ws_v4 : NULL,
-        &udp_plugin_select, plugin);
-  }
-  if ((GNUNET_YES == plugin->enable_ipv6) && (NULL != plugin->sockv6))
+  plugin->sic = sic;
+  plugin->sic_cls = sic_cls;
+  if (NULL != sic)
   {
-    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 (NULL != 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_us) ?
-            GNUNET_TIME_UNIT_FOREVER_REL : min_delay, plugin->rs_v6,
-        (0 == min_delay.rel_value_us) ? plugin->ws_v6 : NULL,
-        &udp_plugin_select_v6, plugin);
+    GNUNET_CONTAINER_multipeermap_iterate (plugin->sessions,
+                                           &send_session_info_iter,
+                                           plugin);
+    /* signal end of first iteration */
+    sic (sic_cls,
+         NULL,
+         NULL);
   }
 }
 
 
+/* ****************** Little Helpers ****************** */
+
+
 /**
- * Function called for a quick conversion of the binary address to
- * a numeric address.  Note that the caller must not free the
- * address and that the next call to this function is allowed
- * to override the address again.
+ * Function to free last resources associated with a session.
  *
- * @param cls closure
- * @param addr binary address (a `union UdpAddress`)
- * @param addrlen length of the @a addr
- * @return string representing the same address
+ * @param s session to free
  */
-const char *
-udp_address_to_string (void *cls,
-                       const void *addr,
-                       size_t addrlen)
+static void
+free_session (struct GNUNET_ATS_Session *s)
 {
-  static char rbuf[INET6_ADDRSTRLEN + 10];
-  char buf[INET6_ADDRSTRLEN];
-  const void *sb;
-  struct in_addr a4;
-  struct in6_addr a6;
-  const struct IPv4UdpAddress *t4;
-  const struct IPv6UdpAddress *t6;
-  int af;
-  uint16_t port;
-  uint32_t options;
-
-  if ((NULL != addr) && (addrlen == sizeof(struct IPv6UdpAddress)))
+  if (NULL != s->address)
   {
-    t6 = addr;
-    af = AF_INET6;
-    options = ntohl (t6->options);
-    port = ntohs (t6->u6_port);
-    memcpy (&a6, &t6->ipv6_addr, sizeof(a6));
-    sb = &a6;
+    GNUNET_HELLO_address_free (s->address);
+    s->address = NULL;
   }
-  else if ((NULL != addr) && (addrlen == sizeof(struct IPv4UdpAddress)))
+  if (NULL != s->frag_ctx)
   {
-    t4 = addr;
-    af = AF_INET;
-    options = ntohl (t4->options);
-    port = ntohs (t4->u4_port);
-    memcpy (&a4, &t4->ipv4_addr, sizeof(a4));
-    sb = &a4;
+    GNUNET_FRAGMENT_context_destroy (s->frag_ctx->frag,
+                                     NULL,
+                                     NULL);
+    GNUNET_free (s->frag_ctx);
+    s->frag_ctx = NULL;
   }
-  else
+  if (NULL != s->mst)
   {
-    return NULL;
+    GNUNET_MST_destroy (s->mst);
+    s->mst = 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);
-  return rbuf;
+  GNUNET_free (s);
 }
 
 
 /**
- * Function called to convert a string address to
- * a binary address.
+ * 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 (`struct Plugin *`)
- * @param addr string address
+ * @param cls closure with the `struct Plugin`
+ * @return keepalive factor
+ */
+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_NetworkType
+udp_plugin_get_network (void *cls,
+                        struct GNUNET_ATS_Session *session)
+{
+  return session->scope;
+}
+
+
+/**
+ * Function obtain the network type for an address.
+ *
+ * @param cls closure (`struct Plugin *`)
+ * @param address the address
+ * @return the network type
+ */
+static enum GNUNET_NetworkType
+udp_plugin_get_network_for_address (void *cls,
+                                    const struct GNUNET_HELLO_Address *address)
+{
+  struct Plugin *plugin = cls;
+  size_t addrlen;
+  struct sockaddr_in a4;
+  struct sockaddr_in6 a6;
+  const struct IPv4UdpAddress *u4;
+  const struct IPv6UdpAddress *u6;
+  const void *sb;
+  size_t sbs;
+
+  addrlen = address->address_length;
+  if (addrlen == sizeof(struct IPv6UdpAddress))
+  {
+    GNUNET_assert (NULL != address->address); /* make static analysis happy */
+    u6 = address->address;
+    memset (&a6, 0, sizeof(a6));
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a6.sin6_len = sizeof (a6);
+#endif
+    a6.sin6_family = AF_INET6;
+    a6.sin6_port = u6->u6_port;
+    GNUNET_memcpy (&a6.sin6_addr, &u6->ipv6_addr, sizeof(struct in6_addr));
+    sb = &a6;
+    sbs = sizeof(a6);
+  }
+  else if (addrlen == sizeof(struct IPv4UdpAddress))
+  {
+    GNUNET_assert (NULL != address->address); /* make static analysis happy */
+    u4 = address->address;
+    memset (&a4, 0, sizeof(a4));
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    a4.sin_len = sizeof (a4);
+#endif
+    a4.sin_family = AF_INET;
+    a4.sin_port = u4->u4_port;
+    a4.sin_addr.s_addr = u4->ipv4_addr;
+    sb = &a4;
+    sbs = sizeof(a4);
+  }
+  else
+  {
+    GNUNET_break (0);
+    return GNUNET_NT_UNSPECIFIED;
+  }
+  return plugin->env->get_address_type (plugin->env->cls,
+                                        sb,
+                                        sbs);
+}
+
+
+/* ******************* Event loop ******************** */
+
+/**
+ * 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
+ */
+static void
+udp_plugin_select_v4 (void *cls);
+
+
+/**
+ * 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
+ */
+static void
+udp_plugin_select_v6 (void *cls);
+
+
+/**
+ * (re)schedule IPv4-select tasks for this plugin.
+ *
+ * @param plugin plugin to reschedule
+ */
+static void
+schedule_select_v4 (struct Plugin *plugin)
+{
+  struct GNUNET_TIME_Relative min_delay;
+  struct GNUNET_TIME_Relative delay;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *min_udpw;
+
+  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;
+    min_udpw = NULL;
+    for (udpw = plugin->ipv4_queue_head; NULL != udpw; udpw = udpw->next)
+    {
+      delay = GNUNET_TIME_absolute_get_remaining (udpw->transmission_time);
+      if (delay.rel_value_us < min_delay.rel_value_us)
+      {
+        min_delay = delay;
+        min_udpw = udpw;
+      }
+    }
+    if (NULL != plugin->select_task_v4)
+      GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+    if (NULL != min_udpw)
+    {
+      if (min_delay.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
+      {
+        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                    "Calculated flow delay for UDPv4 at %s for %s\n",
+                    GNUNET_STRINGS_relative_time_to_string (min_delay,
+                                                            GNUNET_YES),
+                    GNUNET_i2s (&min_udpw->session->target));
+      }
+      else
+      {
+        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                    "Calculated flow delay for UDPv4 at %s for %s\n",
+                    GNUNET_STRINGS_relative_time_to_string (min_delay,
+                                                            GNUNET_YES),
+                    GNUNET_i2s (&min_udpw->session->target));
+      }
+    }
+    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 GNUNET_TIME_Relative delay;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *min_udpw;
+
+  if ( (GNUNET_YES == plugin->enable_ipv6) &&
+       (NULL != plugin->sockv6) )
+  {
+    min_delay = GNUNET_TIME_UNIT_FOREVER_REL;
+    min_udpw = NULL;
+    for (udpw = plugin->ipv6_queue_head; NULL != udpw; udpw = udpw->next)
+    {
+      delay = GNUNET_TIME_absolute_get_remaining (udpw->transmission_time);
+      if (delay.rel_value_us < min_delay.rel_value_us)
+      {
+        min_delay = delay;
+        min_udpw = udpw;
+      }
+    }
+    if (NULL != plugin->select_task_v6)
+      GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
+    if (NULL != min_udpw)
+    {
+      if (min_delay.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
+      {
+        GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                    "Calculated flow delay for UDPv6 at %s for %s\n",
+                    GNUNET_STRINGS_relative_time_to_string (min_delay,
+                                                            GNUNET_YES),
+                    GNUNET_i2s (&min_udpw->session->target));
+      }
+      else
+      {
+        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                    "Calculated flow delay for UDPv6 at %s for %s\n",
+                    GNUNET_STRINGS_relative_time_to_string (min_delay,
+                                                            GNUNET_YES),
+                    GNUNET_i2s (&min_udpw->session->target));
+      }
+    }
+    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
+ * address and that the next call to this function is allowed
+ * to override the address again.
+ *
+ * @param cls closure
+ * @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)
+{
+  static char rbuf[INET6_ADDRSTRLEN + 10];
+  char buf[INET6_ADDRSTRLEN];
+  const void *sb;
+  struct in_addr a4;
+  struct in6_addr a6;
+  const struct IPv4UdpAddress *t4;
+  const struct IPv6UdpAddress *t6;
+  int af;
+  uint16_t port;
+  uint32_t options;
+
+  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);
+    a6 = t6->ipv6_addr;
+    sb = &a6;
+  }
+  else if (addrlen == sizeof(struct IPv4UdpAddress))
+  {
+    t4 = addr;
+    af = AF_INET;
+    options = ntohl (t4->options);
+    port = ntohs (t4->u4_port);
+    a4.s_addr = t4->ipv4_addr;
+    sb = &a4;
+  }
+  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);
+  return rbuf;
+}
+
+
+/**
+ * Function called to convert a string address to a binary address.
+ *
+ * @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.
@@ -700,27 +975,27 @@ udp_string_to_address (void *cls,
   plugin = NULL;
   optionstr = NULL;
 
-  if ((NULL == addr) || (addrlen == 0))
+  if ((NULL == addr) || (0 == addrlen))
   {
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
   if ('\0' != addr[addrlen - 1])
   {
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
   if (strlen (addr) != addrlen - 1)
   {
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
   plugin = GNUNET_strdup (addr);
   optionstr = strchr (plugin, '.');
   if (NULL == optionstr)
   {
-    GNUNET_break(0);
-    GNUNET_free(plugin);
+    GNUNET_break (0);
+    GNUNET_free (plugin);
     return GNUNET_SYSERR;
   }
   optionstr[0] = '\0';
@@ -729,52 +1004,54 @@ udp_string_to_address (void *cls,
   address = strchr (optionstr, '.');
   if (NULL == address)
   {
-    GNUNET_break(0);
-    GNUNET_free(plugin);
+    GNUNET_break (0);
+    GNUNET_free (plugin);
     return GNUNET_SYSERR;
   }
   address[0] = '\0';
   address++;
 
   if (GNUNET_OK !=
-      GNUNET_STRINGS_to_address_ip (address, strlen (address),
+      GNUNET_STRINGS_to_address_ip (address,
+                                    strlen (address),
                                     &socket_address))
   {
-    GNUNET_break(0);
-    GNUNET_free(plugin);
+    GNUNET_break (0);
+    GNUNET_free (plugin);
     return GNUNET_SYSERR;
   }
-
   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_new (struct IPv4UdpAddress);
-    u4->options = htonl (options);
-    u4->ipv4_addr = in4->sin_addr.s_addr;
-    u4->u4_port = in4->sin_port;
-    *buf = u4;
-    *added = sizeof(struct IPv4UdpAddress);
-    return GNUNET_OK;
-  }
+    {
+      struct IPv4UdpAddress *u4;
+      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;
+      *added = sizeof (struct IPv4UdpAddress);
+      return GNUNET_OK;
+    }
   case AF_INET6:
-  {
-    struct IPv6UdpAddress *u6;
-    struct sockaddr_in6 *in6 = (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;
-    *added = sizeof(struct IPv6UdpAddress);
-    return GNUNET_OK;
-  }
+    {
+      struct IPv6UdpAddress *u6;
+      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;
+      *added = sizeof (struct IPv6UdpAddress);
+      return GNUNET_OK;
+    }
   default:
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
 }
@@ -797,13 +1074,13 @@ append_port (void *cls,
   if (NULL == hostname)
   {
     /* Final call, done */
-    ppc->asc (ppc->asc_cls,
-              NULL,
-              GNUNET_OK);
     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;
   }
@@ -829,8 +1106,7 @@ append_port (void *cls,
 
 
 /**
- * Convert the transports address to a nice, human-readable
- * format.
+ * Convert the transports address to a nice, human-readable format.
  *
  * @param cls closure with the `struct Plugin *`
  * @param type name of the transport that generated the address
@@ -855,7 +1131,7 @@ udp_plugin_address_pretty_printer (void *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;
@@ -867,22 +1143,26 @@ udp_plugin_address_pretty_printer (void *cls,
   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;
-    sbs = sizeof(a6);
+    sb = (const struct sockaddr *) &a6;
+    sbs = sizeof (a6);
   }
-  else if (addrlen == sizeof(struct IPv4UdpAddress))
+  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);
@@ -891,15 +1171,19 @@ udp_plugin_address_pretty_printer (void *cls,
     a4.sin_addr.s_addr = u4->ipv4_addr;
     port = ntohs (u4->u4_port);
     options = ntohl (u4->options);
-    sb = &a4;
+    sb = (const struct sockaddr *) &a4;
     sbs = sizeof(a4);
   }
   else
   {
     /* invalid address */
     GNUNET_break_op (0);
-    asc (asc_cls, NULL , GNUNET_SYSERR);
-    asc (asc_cls, NULL, GNUNET_OK);
+    asc (asc_cls,
+         NULL,
+         GNUNET_SYSERR);
+    asc (asc_cls,
+         NULL,
+         GNUNET_OK);
     return;
   }
   ppc = GNUNET_new (struct PrettyPrinterContext);
@@ -908,7 +1192,7 @@ udp_plugin_address_pretty_printer (void *cls,
   ppc->asc_cls = asc_cls;
   ppc->port = port;
   ppc->options = options;
-  if (addrlen == sizeof(struct IPv6UdpAddress))
+  if (addrlen == sizeof (struct IPv6UdpAddress))
     ppc->ipv6 = GNUNET_YES;
   else
     ppc->ipv6 = GNUNET_NO;
@@ -920,236 +1204,26 @@ udp_plugin_address_pretty_printer (void *cls,
                                     sbs,
                                     ! numeric,
                                     timeout,
-                                    &append_port, ppc);
+                                    &append_port,
+                                    ppc);
 }
 
 
 /**
- * FIXME.
- */
-static void
-call_continuation (struct UDP_MessageWrapper *udpw,
-                   int result)
-{
-  struct Session *session = udpw->session;
-  struct Plugin *plugin = session->plugin;
-  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 UMT_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 UMT_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 UMT_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 UMT_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;
-    default:
-      GNUNET_break(0);
-      break;
-    }
-    break;
-  case GNUNET_SYSERR:
-    switch (udpw->msg_type)
-    {
-    case UMT_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 UMT_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 UMT_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 UMT_MSG_ACK:
-      /* ACK message: failed to send */
-      GNUNET_STATISTICS_update (plugin->env->stats,
-                               "# UDP, ACK msgs, messages, sent, failure",
-                               1,
-                               GNUNET_NO);
-      break;
-    default:
-      GNUNET_break(0);
-      break;
-    }
-    break;
-  default:
-    GNUNET_break(0);
-    break;
-  }
-}
-
-
-/**
- * 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.
- *
- * @param plugin global variables
- * @param in_port port number to check
- * @return #GNUNET_OK if port is either open_port or adv_port
+ * 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.
+ *
+ * @param plugin global variables
+ * @param in_port port number to check
+ * @return #GNUNET_OK if port is either our open or advertised port
  */
 static int
-check_port (struct Plugin *plugin,
+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;
 }
@@ -1176,857 +1250,783 @@ udp_plugin_check_address (void *cls,
                           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)) )
+  if (sizeof(struct IPv4UdpAddress) == addrlen)
   {
-    GNUNET_break_op(0);
-    return GNUNET_SYSERR;
-  }
-  if (addrlen == sizeof(struct IPv4UdpAddress))
-  {
-    v4 = (struct IPv4UdpAddress *) addr;
-    if (GNUNET_OK != check_port (plugin, ntohs (v4->u4_port)))
+    struct sockaddr_in s4;
+
+    v4 = (const struct IPv4UdpAddress *) addr;
+    if (GNUNET_OK != check_port (plugin,
+                                 ntohs (v4->u4_port)))
       return GNUNET_SYSERR;
+    memset (&s4, 0, sizeof (s4));
+    s4.sin_family = AF_INET;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    s4.sin_len = sizeof (s4);
+#endif
+    s4.sin_port = v4->u4_port;
+    s4.sin_addr.s_addr = v4->ipv4_addr;
+
     if (GNUNET_OK !=
-        GNUNET_NAT_test_address (plugin->nat,
-                                 &v4->ipv4_addr,
-                                 sizeof (struct in_addr)))
+       GNUNET_NAT_test_address (plugin->nat,
+                                &s4,
+                                sizeof (struct sockaddr_in)))
       return GNUNET_SYSERR;
   }
-  else
+  else if (sizeof(struct IPv6UdpAddress) == addrlen)
   {
-    v6 = (struct IPv6UdpAddress *) addr;
+    struct sockaddr_in6 s6;
+
+    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)))
-      return GNUNET_SYSERR;
+      return GNUNET_OK; /* plausible, if unlikely... */
+    memset (&s6, 0, sizeof (s6));
+    s6.sin6_family = AF_INET6;
+#if HAVE_SOCKADDR_IN_SIN_LEN
+    s6.sin6_len = sizeof (s6);
+#endif
+    s6.sin6_port = v6->u6_port;
+    s6.sin6_addr = v6->ipv6_addr;
+
     if (GNUNET_OK !=
-        GNUNET_NAT_test_address (plugin->nat,
-                                 &v6->ipv6_addr,
-                                 sizeof(struct in6_addr)))
+       GNUNET_NAT_test_address (plugin->nat,
+                                &s6,
+                                sizeof(struct sockaddr_in6)))
       return GNUNET_SYSERR;
   }
-  return GNUNET_OK;
-}
-
-
-/**
- * Function to free last resources associated with a session.
- *
- * @param s session to free
- */
-static void
-free_session (struct Session *s)
-{
-  if (NULL != s->frag_ctx)
+  else
   {
-    GNUNET_FRAGMENT_context_destroy (s->frag_ctx->frag, NULL, NULL );
-    GNUNET_free(s->frag_ctx);
-    s->frag_ctx = NULL;
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
   }
-  GNUNET_free(s);
+  return GNUNET_OK;
 }
 
 
 /**
- * Remove a message from the transmission queue.
+ * Our external IP address/port mapping has changed.
  *
- * @param plugin the UDP plugin
- * @param udpw message wrapper to queue
+ * @param cls closure, the `struct Plugin`
+ * @param app_ctx[in,out] location where the app can store stuff
+ *                  on add and retrieve it on remove
+ * @param add_remove #GNUNET_YES to mean the new public IP address,
+ *                   #GNUNET_NO to mean the previous (now invalid) one
+ * @param ac address class the address belongs to
+ * @param addr either the previous or the new public IP address
+ * @param addrlen actual length of the @a addr
  */
 static void
-dequeue (struct Plugin *plugin,
-         struct UDP_MessageWrapper *udpw)
+udp_nat_port_map_callback (void *cls,
+                          void **app_ctx,
+                           int add_remove,
+                          enum GNUNET_NAT_AddressClass ac,
+                           const struct sockaddr *addr,
+                           socklen_t addrlen)
 {
-  struct Session *session = udpw->session;
+  struct Plugin *plugin = cls;
+  struct GNUNET_HELLO_Address *address;
+  struct IPv4UdpAddress u4;
+  struct IPv6UdpAddress u6;
+  void *arg;
+  size_t args;
 
-  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->address->address_length == sizeof(struct IPv4UdpAddress))
-    GNUNET_CONTAINER_DLL_remove (plugin->ipv4_queue_head,
-                                 plugin->ipv4_queue_tail,
-                                 udpw);
-  else if (udpw->session->address->address_length == sizeof(struct IPv6UdpAddress))
-    GNUNET_CONTAINER_DLL_remove (plugin->ipv6_queue_head,
-                                 plugin->ipv6_queue_tail,
-                                 udpw);
-  else
+  (void) app_ctx;
+  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)
   {
+  case AF_INET:
+    {
+      const struct sockaddr_in *i4;
+
+      GNUNET_assert (sizeof(struct sockaddr_in) == addrlen);
+      i4 = (const struct sockaddr_in *) addr;
+      if (0 == ntohs (i4->sin_port))
+        return; /* Port = 0 means unmapped, ignore these for UDP. */
+      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;
+    }
+  case AF_INET6:
+    {
+      const struct sockaddr_in6 *i6;
+
+      GNUNET_assert (sizeof(struct sockaddr_in6) == addrlen);
+      i6 = (const struct sockaddr_in6 *) addr;
+      if (0 == ntohs (i6->sin6_port))
+        return; /* Port = 0 means unmapped, ignore these for UDP. */
+      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;
   }
-  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;
+  /* modify our published address list */
+  /* TODO: use 'ac' here in the future... */
+  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 ******************* */
+
+
 /**
- * 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 fc fragmentation context to clean up
- * @param result #GNUNET_OK if we succeeded (got ACK),
- *               #GNUNET_SYSERR if the transmission failed
+ * Closure for #session_cmp_it().
  */
-static void
-fragmented_message_done (struct UDP_FragmentationContext *fc,
-                         int result)
+struct GNUNET_ATS_SessionCompareContext
 {
-  struct Plugin *plugin = fc->plugin;
-  struct Session *s = fc->session;
-  struct UDP_MessageWrapper *udpw;
-  struct UDP_MessageWrapper *tmp;
-  struct UDP_MessageWrapper dummy;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "%p : Fragmented message removed with result %s\n",
-       fc,
-       (result == GNUNET_SYSERR) ? "FAIL" : "SUCCESS");
+  /**
+   * Set to session matching the address.
+   */
+  struct GNUNET_ATS_Session *res;
 
-  /* Call continuation for fragmented message */
-  memset (&dummy, 0, sizeof(dummy));
-  dummy.msg_type = UMT_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);
-  /* Remove leftover fragments from queue */
-  if (s->address->address_length == sizeof(struct IPv6UdpAddress))
-  {
-    udpw = plugin->ipv6_queue_head;
-    while (NULL != udpw)
-    {
-      tmp = udpw->next;
-      if ( (udpw->frag_ctx != NULL) &&
-          (udpw->frag_ctx == s->frag_ctx) )
-      {
-       dequeue (plugin, udpw);
-       call_continuation (udpw, GNUNET_SYSERR);
-       GNUNET_free (udpw);
-      }
-      udpw = tmp;
-    }
-  }
-  if (s->address->address_length == sizeof(struct IPv4UdpAddress))
-  {
-    udpw = plugin->ipv4_queue_head;
-    while (udpw != NULL )
-    {
-      tmp = udpw->next;
-      if ((NULL != udpw->frag_ctx) && (udpw->frag_ctx == s->frag_ctx))
-      {
-        dequeue (plugin, udpw);
-        call_continuation (udpw, GNUNET_SYSERR);
-        GNUNET_free(udpw);
-      }
-      udpw = tmp;
-    }
-  }
-  notify_session_monitor (s->plugin,
-                          s,
-                          GNUNET_TRANSPORT_SS_UPDATE);
-  /* 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);
-}
+  /**
+   * Address we are looking for.
+   */
+  const struct GNUNET_HELLO_Address *address;
+};
 
 
 /**
- * Scan the heap for a receive context with the given address.
+ * Find a session with a matching 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.
+ * @param cls the `struct GNUNET_ATS_SessionCompareContext *`
+ * @param key peer identity (unused)
+ * @param value the `struct GNUNET_ATS_Session *`
+ * @return #GNUNET_NO if we found the session, #GNUNET_OK if not
  */
 static int
-find_receive_context (void *cls,
-                      struct GNUNET_CONTAINER_HeapNode *node,
-                      void *element,
-                      GNUNET_CONTAINER_HeapCostType cost)
+session_cmp_it (void *cls,
+                const struct GNUNET_PeerIdentity *key,
+                void *value)
 {
-  struct FindReceiveContext *frc = cls;
-  struct DefragContext *e = element;
+  struct GNUNET_ATS_SessionCompareContext *cctx = cls;
+  struct GNUNET_ATS_Session *s = value;
 
-  if ( (frc->udp_addr_len == e->udp_addr_len) &&
-       (0 == memcmp (frc->udp_addr,
-                     e->udp_addr,
-                     frc->udp_addr_len)) )
+  if (0 == GNUNET_HELLO_address_cmp (s->address,
+                                     cctx->address))
   {
-    frc->rc = e;
+    GNUNET_assert (GNUNET_NO == s->in_destroy);
+    cctx->res = s;
     return GNUNET_NO;
   }
-  return GNUNET_YES;
+  return GNUNET_OK;
 }
 
 
 /**
- * Functions with this signature are called whenever we need
- * to close a session due to a disconnect or failure to
- * establish a connection.
+ * 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 closure with the `struct Plugin`
- * @param s session to close down
- * @return #GNUNET_OK on success
+ * @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 int
-udp_disconnect_session (void *cls,
-                        struct Session *s)
+static struct GNUNET_ATS_Session *
+udp_plugin_lookup_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address)
 {
   struct Plugin *plugin = cls;
-  struct UDP_MessageWrapper *udpw;
-  struct UDP_MessageWrapper *next;
-  struct FindReceiveContext frc;
-
-  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),
-       udp_address_to_string (plugin,
-                              s->address->address,
-                              s->address->address_length));
-  /* stop timeout task */
-  if (NULL != s->timeout_task)
-  {
-    GNUNET_SCHEDULER_cancel (s->timeout_task);
-    s->timeout_task = NULL;
-  }
-  if (NULL != s->frag_ctx)
-  {
-    /* Remove fragmented message due to disconnect */
-    fragmented_message_done (s->frag_ctx,
-                             GNUNET_SYSERR);
-  }
-
-  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;
+  const struct IPv6UdpAddress *udp_a6;
+  const struct IPv4UdpAddress *udp_a4;
+  struct GNUNET_ATS_SessionCompareContext cctx;
 
-      GNUNET_CONTAINER_heap_remove_node (d_ctx->hnode);
-      GNUNET_DEFRAGMENT_context_destroy (d_ctx->defrag);
-      GNUNET_free (d_ctx);
-    }
-  }
-  next = plugin->ipv4_queue_head;
-  while (NULL != (udpw = next))
+  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;
     }
   }
-  notify_session_monitor (s->plugin,
-                          s,
-                          GNUNET_TRANSPORT_SS_DONE);
-  plugin->env->session_end (plugin->env->cls,
-                            s->address,
-                            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_multipeermap_remove (plugin->sessions,
-                                                       &s->target,
-                                                       s));
-  GNUNET_STATISTICS_set (plugin->env->stats,
-                         "# UDP sessions active",
-                         GNUNET_CONTAINER_multipeermap_size (plugin->sessions),
-                         GNUNET_NO);
-  if (s->rc > 0)
-  {
-    s->in_destroy = GNUNET_YES;
-  }
   else
   {
-    GNUNET_HELLO_address_free (s->address);
-    free_session (s);
+    GNUNET_break (0);
+    return NULL;
   }
-  return GNUNET_OK;
-}
 
-
-/**
- * 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 unsigned int
-udp_query_keepalive_factor (void *cls)
-{
-  return 15;
+  /* 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;
 }
 
 
-/**
- * Destroy a session, plugin is being unloaded.
- *
- * @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
-disconnect_and_free_it (void *cls,
-                        const struct GNUNET_PeerIdentity *key,
-                        void *value)
-{
-  struct Plugin *plugin = cls;
-
-  udp_disconnect_session (plugin, value);
-  return GNUNET_OK;
-}
+/* ********************** 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 GNUNET_ATS_Session *s)
 {
-  struct Plugin *plugin = cls;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Disconnecting from peer `%s'\n",
-       GNUNET_i2s (target));
-  /* Clean up sessions */
-  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
-                                              target,
-                                              &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 the `struct Session` to time out
- * @param tc scheduler context
+ * @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 GNUNET_ATS_Session *session)
 {
-  struct Session *s = cls;
-  struct Plugin *plugin = s->plugin;
-  struct GNUNET_TIME_Relative left;
+  struct Plugin *plugin = cls;
 
-  s->timeout_task = NULL;
-  left = GNUNET_TIME_absolute_get_remaining (s->timeout);
-  if (left.rel_value_us > 0)
+  if (GNUNET_YES !=
+      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
+                                                    peer,
+                                                    session))
   {
-    /* 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);
+    GNUNET_break (0);
     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);
+  /* Reschedule session timeout */
+  reschedule_session_timeout (session);
 }
 
 
+/* ************************* Sending ************************ */
+
+
 /**
- * Increment session timeout due to activity
+ * Remove the given message from the transmission queue and
+ * update all applicable statistics.
  *
- * @param s session to reschedule timeout activity for
+ * @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)
 {
-  if (GNUNET_YES == s->in_destroy)
+  struct GNUNET_ATS_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(NULL != s->timeout_task);
-  s->timeout = GNUNET_TIME_relative_to_absolute (UDP_SESSION_TIME_OUT);
+  }
+  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;
 }
 
 
 /**
- * Function obtain the network type for a session
+ * Enqueue a message for transmission and update statistics.
  *
- * @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;
-}
-
-
-/**
- * Closure for #session_cmp_it().
+ * @param plugin the UDP plugin
+ * @param udpw message wrapper to queue
  */
-struct SessionCompareContext
+static void
+enqueue (struct Plugin *plugin,
+         struct UDP_MessageWrapper *udpw)
 {
-  /**
-   * Set to session matching the address.
-   */
-  struct Session *res;
-
-  /**
-   * Address we are looking for.
-   */
-  const struct GNUNET_HELLO_Address *address;
-};
-
+  struct GNUNET_ATS_Session *session = udpw->session;
 
-/**
- * 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;
-  const struct GNUNET_HELLO_Address *address = cctx->address;
-  struct Session *s = value;
-
-  if (0 == GNUNET_HELLO_address_cmp (s->address,
-                                     cctx->address))
+  if (GNUNET_YES == session->in_destroy)
   {
-    cctx->res = s;
-    return GNUNET_NO;
+    GNUNET_break (0);
+    GNUNET_free (udpw);
+    return;
   }
-  return GNUNET_YES;
+  if (plugin->bytes_in_buffer > INT64_MAX - udpw->msg_size)
+  {
+    GNUNET_break (0);
+  }
+  else
+  {
+    GNUNET_STATISTICS_update (plugin->env->stats,
+                              "# UDP, total bytes in send buffers",
+                              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_insert(plugin->ipv4_queue_head,
+                                plugin->ipv4_queue_tail,
+                                udpw);
+  }
+  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;
 }
 
 
 /**
- * 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.
+ * 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 we should locate the session by
- * @return the session if it exists, or NULL if it is not found
+ * @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;
-  const struct IPv6UdpAddress *udp_a6;
-  const struct IPv4UdpAddress *udp_a4;
-  struct SessionCompareContext cctx;
+  struct Plugin *plugin = frag_ctx->plugin;
+  struct GNUNET_ATS_Session *s = frag_ctx->session;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *tmp;
+  size_t overhead;
+  struct GNUNET_TIME_Relative delay;
 
-  if ( (NULL == address->address) ||
-       ((address->address_length != sizeof (struct IPv4UdpAddress)) &&
-        (address->address_length != sizeof (struct IPv6UdpAddress))))
+  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;
+  delay = GNUNET_TIME_absolute_get_duration (frag_ctx->start_time);
+  if (delay.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
   {
     LOG (GNUNET_ERROR_TYPE_WARNING,
-         "Trying to locate session for address of unexpected length %u (should be %u or %u)\n",
-         address->address_length,
-         sizeof (struct IPv4UdpAddress),
-         sizeof (struct IPv6UdpAddress));
-    return NULL;
+         "Fragmented message acknowledged after %s (expected at %s)\n",
+         GNUNET_STRINGS_relative_time_to_string (delay,
+                                                 GNUNET_YES),
+         GNUNET_STRINGS_absolute_time_to_string (frag_ctx->next_frag_time));
   }
-
-  if (address->address_length == sizeof(struct IPv4UdpAddress))
+  else
   {
-    if (NULL == plugin->sockv4)
-      return NULL;
-    udp_a4 = (const struct IPv4UdpAddress *) address->address;
-    if (0 == udp_a4->u4_port)
-      return NULL;
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "Fragmented message acknowledged after %s (expected at %s)\n",
+         GNUNET_STRINGS_relative_time_to_string (delay,
+                                                 GNUNET_YES),
+         GNUNET_STRINGS_absolute_time_to_string (frag_ctx->next_frag_time));
   }
 
-  if (address->address_length == sizeof(struct IPv6UdpAddress))
+  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 (GNUNET_OK == result)
   {
-    if (NULL == plugin->sockv6)
-      return NULL;
-    udp_a6 = (const struct IPv6UdpAddress *) address->address;
-    if (0 == udp_a6->u6_port)
-      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);
+  }
+  else
+  {
+    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);
   }
 
-  /* check if session already exists */
-  cctx.address = 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 (plugin,
-                              address->address,
-                              address->address_length));
-  GNUNET_CONTAINER_multipeermap_get_multiple (plugin->sessions,
-                                              &address->peer,
-                                              &session_cmp_it,
-                                              &cctx);
-  if (NULL != cctx.res)
+  /* Remove remaining fragments from queue, no need to transmit those
+     any longer. */
+  if (s->address->address_length == sizeof(struct IPv6UdpAddress))
   {
-    LOG (GNUNET_ERROR_TYPE_DEBUG,
-         "Found existing session %p\n",
-         cctx.res);
-    return cctx.res;
+    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;
+    }
   }
-  return NULL;
+  if (s->address->address_length == sizeof(struct IPv4UdpAddress))
+  {
+    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;
+    }
+  }
+  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);
 }
 
 
 /**
- * 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).
+ * We are finished with a fragment in the message queue.
+ * Notify the continuation and update statistics.
  *
- * @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
+ * @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_create_session (void *cls,
-                           const struct GNUNET_HELLO_Address *address,
-                           enum GNUNET_ATS_Network_Type network_type)
+static void
+qc_fragment_sent (void *cls,
+                  struct UDP_MessageWrapper *udpw,
+                  int result)
 {
   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);
-  return s;
+  GNUNET_assert (NULL != udpw->frag_ctx);
+  if (GNUNET_OK == result)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Fragment of message with %u bytes transmitted to %s\n",
+                (unsigned int) udpw->payload_size,
+                GNUNET_i2s (&udpw->session->target));
+    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);
+  }
+  else
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+                "Failed to transmit fragment of message with %u bytes to %s\n",
+                (unsigned int) udpw->payload_size,
+                GNUNET_i2s (&udpw->session->target));
+    fragmented_message_done (udpw->frag_ctx,
+                             GNUNET_SYSERR);
+    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);
+  }
 }
 
 
 /**
- * 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
+ * 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().
  *
- * @param cls closure with the `struct Plugin`
- * @param peer which peer was the session for
- * @param session which session is being updated
+ * @param cls closure, the `struct UDP_FragmentationContext`
+ * @param msg the message that was created
  */
 static void
-udp_plugin_update_session_timeout (void *cls,
-                                   const struct GNUNET_PeerIdentity *peer,
-                                   struct Session *session)
+enqueue_fragment (void *cls,
+                  const struct GNUNET_MessageHeader *msg)
 {
-  struct Plugin *plugin = cls;
+  struct UDP_FragmentationContext *frag_ctx = cls;
+  struct Plugin *plugin = frag_ctx->plugin;
+  struct UDP_MessageWrapper *udpw;
+  struct GNUNET_ATS_Session *session = frag_ctx->session;
+  size_t msg_len = ntohs (msg->size);
 
-  if (GNUNET_YES !=
-      GNUNET_CONTAINER_multipeermap_contains_value (plugin->sessions,
-                                                    peer,
-                                                    session))
-  {
-    GNUNET_break(0);
-    return;
-  }
-  /* Reschedule session timeout */
-  reschedule_session_timeout (session);
+  LOG (GNUNET_ERROR_TYPE_DEBUG,
+       "Enqueuing fragment with %u bytes\n",
+       msg_len);
+  udpw = GNUNET_malloc (sizeof (struct UDP_MessageWrapper) + msg_len);
+  udpw->session = session;
+  udpw->msg_buf = (char *) &udpw[1];
+  udpw->msg_size = msg_len;
+  udpw->payload_size = msg_len; /* FIXME: minus fragment overhead */
+  udpw->timeout = frag_ctx->timeout;
+  udpw->start_time = frag_ctx->start_time;
+  udpw->transmission_time = frag_ctx->next_frag_time;
+  frag_ctx->next_frag_time
+    = GNUNET_TIME_absolute_add (frag_ctx->next_frag_time,
+                                frag_ctx->flow_delay_from_other_peer);
+  udpw->frag_ctx = frag_ctx;
+  udpw->qc = &qc_fragment_sent;
+  udpw->qc_cls = plugin;
+  GNUNET_memcpy (udpw->msg_buf,
+                msg,
+                msg_len);
+  enqueue (plugin,
+           udpw);
+  if (session->address->address_length == sizeof (struct IPv4UdpAddress))
+    schedule_select_v4 (plugin);
+  else
+    schedule_select_v6 (plugin);
 }
 
 
 /**
- * Creates a new outbound session the transport service will use to
- * send data to the peer.
+ * We are finished with a message from the message queue.
+ * Notify the continuation and update statistics.
  *
  * @param cls the `struct Plugin *`
- * @param address the address
- * @return the session or NULL of max connections exceeded
+ * @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_message_sent (void *cls,
+                 struct UDP_MessageWrapper *udpw,
+                 int result)
 {
   struct Plugin *plugin = cls;
-  struct Session *s;
-  enum GNUNET_ATS_Network_Type network_type;
-  struct IPv4UdpAddress *udp_v4;
-  struct IPv6UdpAddress *udp_v6;
-
-  if (NULL == address)
-  {
-    GNUNET_break (0);
-    return NULL;
-  }
-  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 = (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 = (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));
-  }
-  return udp_plugin_create_session (cls,
-                                   address,
-                                   network_type);
-}
-
+  size_t overhead;
+  struct GNUNET_TIME_Relative delay;
 
-/**
- * Enqueue a message for transmission.
- *
- * @param plugin the UDP plugin
- * @param udpw message wrapper to queue
- */
-static void
-enqueue (struct Plugin *plugin,
-         struct UDP_MessageWrapper *udpw)
-{
-  struct Session *session = udpw->session;
+  if (udpw->msg_size >= udpw->payload_size)
+    overhead = udpw->msg_size - udpw->payload_size;
+  else
+    overhead = udpw->msg_size;
 
-  if (plugin->bytes_in_buffer + udpw->msg_size > INT64_MAX)
+  if (NULL != udpw->cont)
   {
-    GNUNET_break (0);
+    delay = GNUNET_TIME_absolute_get_duration (udpw->start_time);
+    if (delay.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
+    {
+      LOG (GNUNET_ERROR_TYPE_WARNING,
+           "Message sent via UDP with delay of %s\n",
+           GNUNET_STRINGS_relative_time_to_string (delay,
+                                                   GNUNET_YES));
+    }
+    else
+    {
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Message sent via UDP with delay of %s\n",
+           GNUNET_STRINGS_relative_time_to_string (delay,
+                                                   GNUNET_YES));
+    }
+    udpw->cont (udpw->cont_cls,
+                &udpw->session->target,
+                result,
+                udpw->payload_size,
+                overhead);
   }
-  else
+  if (GNUNET_OK == result)
   {
     GNUNET_STATISTICS_update (plugin->env->stats,
-        "# UDP, total, bytes in buffers", udpw->msg_size, GNUNET_NO);
-    plugin->bytes_in_buffer += udpw->msg_size;
+                              "# 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);
   }
-  GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, msgs in buffers",
-                            1, GNUNET_NO);
-  if (udpw->session->address->address_length == sizeof (struct IPv4UdpAddress))
-    GNUNET_CONTAINER_DLL_insert(plugin->ipv4_queue_head,
-                                plugin->ipv4_queue_tail,
-                                udpw);
-  else if (udpw->session->address->address_length == sizeof (struct IPv6UdpAddress))
-    GNUNET_CONTAINER_DLL_insert (plugin->ipv6_queue_head,
-                                 plugin->ipv6_queue_tail,
-                                 udpw);
   else
   {
-    GNUNET_break (0);
-    return;
+    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);
   }
-  session->msgs_in_queue++;
-  session->bytes_in_queue += udpw->msg_size;
-}
-
-
-/**
- * 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().
- *
- * @param cls closure, the 'struct FragmentationContext'
- * @param msg the message that was created
- */
-static void
-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;
-  size_t msg_len = ntohs (msg->size);
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Enqueuing fragment with %u bytes\n",
-       msg_len);
-  frag_ctx->fragments_used++;
-  udpw = GNUNET_malloc (sizeof (struct UDP_MessageWrapper) + msg_len);
-  udpw->session = frag_ctx->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->timeout = frag_ctx->timeout;
-  udpw->frag_ctx = frag_ctx;
-  udpw->msg_type = UMT_MSG_FRAGMENTED;
-  memcpy (udpw->msg_buf, msg, msg_len);
-  enqueue (plugin, udpw);
-  schedule_select (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.
+ * 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
@@ -2037,14 +2037,14 @@ enqueue_fragment (void *cls,
  *        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,
+                 struct GNUNET_ATS_Session *s,
                  const char *msgbuf,
                  size_t msgbuf_size,
                  unsigned int priority,
@@ -2054,20 +2054,21 @@ udp_plugin_send (void *cls,
 {
   struct Plugin *plugin = cls;
   size_t udpmlen = msgbuf_size + sizeof(struct UDPMessage);
-  struct UDP_FragmentationContext * frag_ctx;
-  struct UDP_MessageWrapper * udpw;
+  struct UDP_FragmentationContext *frag_ctx;
+  struct UDP_MessageWrapper *udpw;
   struct UDPMessage *udp;
-  char mbuf[udpmlen];
+  char mbuf[udpmlen] GNUNET_ALIGN;
+  struct GNUNET_TIME_Relative latency;
 
-  if ( (s->address->address_length == sizeof(struct IPv6UdpAddress)) &&
-       (plugin->sockv6 == NULL) )
+  if ( (sizeof(struct IPv6UdpAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv6) )
     return GNUNET_SYSERR;
-  if ( (s->address->address_length == sizeof(struct IPv4UdpAddress)) &&
-       (plugin->sockv4 == NULL) )
+  if ( (sizeof(struct IPv4UdpAddress) == s->address->address_length) &&
+       (NULL == plugin->sockv4) )
     return GNUNET_SYSERR;
-  if (udpmlen >= GNUNET_SERVER_MAX_MESSAGE_SIZE)
+  if (udpmlen >= GNUNET_MAX_MESSAGE_SIZE)
   {
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
   if (GNUNET_YES !=
@@ -2075,7 +2076,7 @@ udp_plugin_send (void *cls,
                                                     &s->target,
                                                     s))
   {
-    GNUNET_break(0);
+    GNUNET_break (0);
     return GNUNET_SYSERR;
   }
   LOG (GNUNET_ERROR_TYPE_DEBUG,
@@ -2086,19 +2087,19 @@ udp_plugin_send (void *cls,
                               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;
 
-  /* We do not update the session time out here!
-   * Otherwise this session will not timeout since we send keep alive before
-   * session can timeout
+  /* 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 response!
+   * 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)
   {
@@ -2108,35 +2109,58 @@ 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->start_time = GNUNET_TIME_absolute_get ();
+    udpw->timeout = GNUNET_TIME_relative_to_absolute (to);
+    udpw->transmission_time = s->last_transmit_time;
+    s->last_transmit_time
+      = GNUNET_TIME_absolute_add (s->last_transmit_time,
+                                  s->flow_delay_from_other_peer);
     udpw->cont = cont;
     udpw->cont_cls = cont_cls;
     udpw->frag_ctx = NULL;
-    udpw->msg_type = UMT_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;
+    GNUNET_memcpy (udpw->msg_buf,
+            udp,
+            sizeof (struct UDPMessage));
+    GNUNET_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,
+                              "# UDP, unfragmented bytes payload queued total",
+                              msgbuf_size,
                               GNUNET_NO);
+    if (s->address->address_length == sizeof (struct IPv4UdpAddress))
+      schedule_select_v4 (plugin);
+    else
+      schedule_select_v6 (plugin);
   }
   else
   {
     /* fragmented message */
-    if (s->frag_ctx != NULL)
+    if (NULL != s->frag_ctx)
       return GNUNET_SYSERR;
-    memcpy (&udp[1], msgbuf, msgbuf_size);
+    GNUNET_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->start_time = GNUNET_TIME_absolute_get ();
+    frag_ctx->next_frag_time = s->last_transmit_time;
+    frag_ctx->flow_delay_from_other_peer
+      = GNUNET_TIME_relative_divide (s->flow_delay_from_other_peer,
+                                     1 + (msgbuf_size /
+                                          UDP_MTU));
+    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,
@@ -2148,123 +2172,583 @@ udp_plugin_send (void *cls,
                                                      &enqueue_fragment,
                                                      frag_ctx);
     s->frag_ctx = frag_ctx;
+    s->last_transmit_time = frag_ctx->next_frag_time;
+    latency = GNUNET_TIME_absolute_get_remaining (s->last_transmit_time);
+    if (latency.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
+      LOG (GNUNET_ERROR_TYPE_WARNING,
+           "Enqueued fragments will take %s for transmission to %s (queue size: %u)\n",
+           GNUNET_STRINGS_relative_time_to_string (latency,
+                                                   GNUNET_YES),
+           GNUNET_i2s (&s->target),
+           (unsigned int) s->msgs_in_queue);
+    else
+      LOG (GNUNET_ERROR_TYPE_DEBUG,
+           "Enqueued fragments will take %s for transmission to %s (queue size: %u)\n",
+           GNUNET_STRINGS_relative_time_to_string (latency,
+                                                   GNUNET_YES),
+           GNUNET_i2s (&s->target),
+           (unsigned int) s->msgs_in_queue);
+
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, messages, pending",
+                              "# UDP, fragmented messages active",
                               1,
                               GNUNET_NO);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, messages, attempt",
+                              "# UDP, fragmented messages, total",
                               1,
                               GNUNET_NO);
     GNUNET_STATISTICS_update (plugin->env->stats,
-                              "# UDP, fragmented msgs, bytes payload, attempt",
+                              "# UDP, fragmented bytes (payload)",
                               frag_ctx->payload_size,
                               GNUNET_NO);
   }
   notify_session_monitor (s->plugin,
                           s,
-                          GNUNET_TRANSPORT_SS_UPDATE);
-  schedule_select (plugin);
-  return udpmlen;
+                          GNUNET_TRANSPORT_SS_UPDATE);
+  return udpmlen;
+}
+
+
+/* ********************** Receiving ********************** */
+
+
+/**
+ * Closure for #find_receive_context().
+ */
+struct FindReceiveContext
+{
+  /**
+   * Where to store the result.
+   */
+  struct DefragContext *rc;
+
+  /**
+   * Session associated with this context.
+   */
+  struct GNUNET_ATS_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;
+}
+
+
+/**
+ * Functions with this signature are called whenever we need to close
+ * a session due to a disconnect or failure to establish a connection.
+ *
+ * @param cls closure with the `struct Plugin`
+ * @param s session to close down
+ * @return #GNUNET_OK on success
+ */
+static int
+udp_disconnect_session (void *cls,
+                        struct GNUNET_ATS_Session *s)
+{
+  struct Plugin *plugin = cls;
+  struct UDP_MessageWrapper *udpw;
+  struct UDP_MessageWrapper *next;
+  struct FindReceiveContext frc;
+
+  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_SCHEDULER_cancel (s->timeout_task);
+    s->timeout_task = NULL;
+  }
+  if (NULL != s->frag_ctx)
+  {
+    /* 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;
+
+      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))
+  {
+    next = udpw->next;
+    if (udpw->session == s)
+    {
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_free (udpw);
+    }
+  }
+  next = plugin->ipv6_queue_head;
+  while (NULL != (udpw = next))
+  {
+    next = udpw->next;
+    if (udpw->session == s)
+    {
+      dequeue (plugin,
+               udpw);
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_SYSERR);
+      GNUNET_free (udpw);
+    }
+  }
+  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;
+}
+
+
+/**
+ * Handle a #GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_ACK message.
+ *
+ * @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
+read_process_ack (struct Plugin *plugin,
+                  const struct GNUNET_MessageHeader *msg,
+                  const union UdpAddress *udp_addr,
+                  socklen_t udp_addr_len)
+{
+  const struct GNUNET_MessageHeader *ack;
+  const struct UDP_ACK_Message *udp_ack;
+  struct GNUNET_HELLO_Address *address;
+  struct GNUNET_ATS_Session *s;
+  struct GNUNET_TIME_Relative flow_delay;
+
+  /* check message format */
+  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;
+  }
+
+  /* Locate session */
+  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);
+
+  /* evaluate flow delay: how long should we wait between messages? */
+  if (UINT32_MAX == ntohl (udp_ack->delay))
+  {
+    /* Other peer asked for us to terminate the session */
+    LOG (GNUNET_ERROR_TYPE_INFO,
+         "Asked to disconnect UDP session of %s\n",
+         GNUNET_i2s (&udp_ack->sender));
+    udp_disconnect_session (plugin,
+                            s);
+    return;
+  }
+  flow_delay.rel_value_us = (uint64_t) ntohl (udp_ack->delay);
+  if (flow_delay.rel_value_us > GNUNET_CONSTANTS_LATENCY_WARN.rel_value_us)
+    LOG (GNUNET_ERROR_TYPE_WARNING,
+         "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));
+  else
+    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));
+  /* Flow delay is for the reassembled packet, however, our delay
+     is per packet, so we need to adjust: */
+  s->flow_delay_from_other_peer = flow_delay;
+
+  /* Handle ACK */
+  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),
+         udp_address_to_string (plugin,
+                                udp_addr,
+                                udp_addr_len));
+    /* Expect more ACKs to arrive */
+    return;
+  }
+
+  /* Remove fragmented message after successful sending */
+  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));
+  fragmented_message_done (s->frag_ctx,
+                           GNUNET_OK);
+}
+
+
+/**
+ * Message tokenizer has broken up an incomming message. Pass it on
+ * to the service.
+ *
+ * @param cls the `struct GNUNET_ATS_Session *`
+ * @param hdr the actual message
+ * @return #GNUNET_OK (always)
+ */
+static int
+process_inbound_tokenized_messages (void *cls,
+                                    const struct GNUNET_MessageHeader *hdr)
+{
+  struct GNUNET_ATS_Session *session = cls;
+  struct Plugin *plugin = session->plugin;
+
+  if (GNUNET_YES == session->in_destroy)
+    return GNUNET_OK;
+  reschedule_session_timeout (session);
+  session->flow_delay_for_other_peer
+    = plugin->env->receive (plugin->env->cls,
+                            session->address,
+                            session,
+                            hdr);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Destroy a session, plugin is being unloaded.
+ *
+ * @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
+disconnect_and_free_it (void *cls,
+                        const struct GNUNET_PeerIdentity *key,
+                        void *value)
+{
+  struct Plugin *plugin = cls;
+
+  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 GNUNET_ATS_Session` to time out
+ */
+static void
+session_timeout (void *cls)
+{
+  struct GNUNET_ATS_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 GNUNET_ATS_Session *
+udp_plugin_create_session (void *cls,
+                           const struct GNUNET_HELLO_Address *address,
+                           enum GNUNET_NetworkType network_type)
+{
+  struct Plugin *plugin = cls;
+  struct GNUNET_ATS_Session *s;
+
+  s = GNUNET_new (struct GNUNET_ATS_Session);
+  s->mst = GNUNET_MST_create (&process_inbound_tokenized_messages,
+                              s);
+  s->plugin = plugin;
+  s->address = GNUNET_HELLO_address_copy (address);
+  s->target = address->peer;
+  s->last_transmit_time = GNUNET_TIME_absolute_get ();
+  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;
+  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;
 }
 
 
 /**
- * Our external IP address/port mapping has changed.
+ * Creates a new outbound session the transport service will use to
+ * send data to the peer.
  *
- * @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 cls the `struct Plugin *`
+ * @param address the address
+ * @return the session or NULL of max connections exceeded
  */
-static void
-udp_nat_port_map_callback (void *cls,
-                           int add_remove,
-                           const struct sockaddr *addr,
-                           socklen_t addrlen)
+static struct GNUNET_ATS_Session *
+udp_plugin_get_session (void *cls,
+                        const struct GNUNET_HELLO_Address *address)
 {
   struct Plugin *plugin = cls;
-  struct GNUNET_HELLO_Address *address;
-  struct IPv4UdpAddress u4;
-  struct IPv6UdpAddress u6;
-  void *arg;
-  size_t args;
+  struct GNUNET_ATS_Session *s;
+  enum GNUNET_NetworkType network_type = GNUNET_NT_UNSPECIFIED;
+  const struct IPv4UdpAddress *udp_v4;
+  const struct IPv6UdpAddress *udp_v6;
 
-  LOG (GNUNET_ERROR_TYPE_INFO,
-       "NAT notification to %s address `%s'\n",
-       (GNUNET_YES == add_remove) ? "add" : "remove",
-       GNUNET_a2s (addr, addrlen));
-
-  /* convert 'address' to our internal format */
-  switch (addr->sa_family)
+  if (NULL == address)
   {
-  case AF_INET:
-    GNUNET_assert(addrlen == sizeof(struct sockaddr_in));
-    memset (&u4, 0, sizeof(u4));
-    u4.options = htonl (plugin->myoptions);
-    u4.ipv4_addr = ((struct sockaddr_in *) addr)->sin_addr.s_addr;
-    u4.u4_port = ((struct sockaddr_in *) addr)->sin_port;
-    if (0 == ((struct sockaddr_in *) addr)->sin_port)
-      return;
-    arg = &u4;
-    args = sizeof(struct IPv4UdpAddress);
-    break;
-  case AF_INET6:
-    GNUNET_assert(addrlen == sizeof(struct sockaddr_in6));
-    memset (&u6, 0, sizeof(u6));
-    u6.options = htonl (plugin->myoptions);
-    if (0 == ((struct sockaddr_in6 *) addr)->sin6_port)
-      return;
-    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);
-    return;
+    GNUNET_break (0);
+    return NULL;
   }
-  /* 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);
-}
+  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;
 
-/**
- * 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 hdr the actual message
- * @return #GNUNET_OK (always)
- */
-static int
-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;
+    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;
 
-  GNUNET_assert (NULL != si->session);
-  if (GNUNET_YES == si->session->in_destroy)
-    return GNUNET_OK;
-  /* setup ATS */
-  reschedule_session_timeout (si->session);
-  delay = plugin->env->receive (plugin->env->cls,
-                                si->session->address,
-                                si->session,
-                                hdr);
-  si->session->flow_delay_for_other_peer = delay;
-  return GNUNET_OK;
+    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_NT_UNSPECIFIED != network_type);
+  return udp_plugin_create_session (cls,
+                                   address,
+                                   network_type);
 }
 
 
@@ -2282,13 +2766,12 @@ 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)
+                     enum GNUNET_NetworkType network_type)
 {
-  struct SourceInformation si;
-  struct Session *s;
+  struct GNUNET_ATS_Session *s;
   struct GNUNET_HELLO_Address *address;
 
-  GNUNET_break (GNUNET_ATS_NET_UNSPECIFIED != network_type);
+  GNUNET_break (GNUNET_NT_UNSPECIFIED != network_type);
   if (0 != ntohl (msg->reserved))
   {
     GNUNET_break_op(0);
@@ -2307,7 +2790,8 @@ process_udp_message (struct Plugin *plugin,
                                            udp_addr_len,
                                            GNUNET_HELLO_ADDRESS_INFO_NONE);
   if (NULL ==
-      (s = udp_plugin_lookup_session (plugin, address)))
+      (s = udp_plugin_lookup_session (plugin,
+                                      address)))
   {
     s = udp_plugin_create_session (plugin,
                                    address,
@@ -2316,27 +2800,21 @@ process_udp_message (struct Plugin *plugin,
                                 address,
                                 s,
                                 s->scope);
-    notify_session_monitor (s->plugin,
-                            s,
-                            GNUNET_TRANSPORT_SS_INIT);
-    notify_session_monitor (s->plugin,
+    notify_session_monitor (plugin,
                             s,
                             GNUNET_TRANSPORT_SS_UP);
   }
   GNUNET_free (address);
 
-  /* iterate over all embedded messages */
-  si.session = s;
-  si.sender = msg->sender;
   s->rc++;
-  GNUNET_SERVER_mst_receive (plugin->mst,
-                             &si,
-                             (const char *) &msg[1],
-                             ntohs (msg->header.size) - sizeof(struct UDPMessage),
-                             GNUNET_YES,
-                             GNUNET_NO);
+  GNUNET_MST_from_buffer (s->mst,
+                          (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 ( (0 == s->rc) &&
+       (GNUNET_YES == s->in_destroy) )
     free_session (s);
 }
 
@@ -2351,27 +2829,60 @@ static void
 fragment_msg_proc (void *cls,
                    const struct GNUNET_MessageHeader *msg)
 {
-  struct DefragContext *rc = cls;
+  struct DefragContext *dc = cls;
   const struct UDPMessage *um;
 
   if (ntohs (msg->type) != GNUNET_MESSAGE_TYPE_TRANSPORT_UDP_MESSAGE)
   {
-    GNUNET_break(0);
+    GNUNET_break_op (0);
     return;
   }
   if (ntohs (msg->size) < sizeof(struct UDPMessage))
   {
-    GNUNET_break(0);
+    GNUNET_break_op (0);
     return;
   }
   um = (const struct UDPMessage *) msg;
-  rc->sender = um->sender;
-  rc->have_sender = GNUNET_YES;
-  process_udp_message (rc->plugin,
+  dc->sender = um->sender;
+  dc->have_sender = GNUNET_YES;
+  process_udp_message (dc->plugin,
                        um,
-                       rc->udp_addr,
-                       rc->udp_addr_len,
-                       rc->network_type);
+                       dc->udp_addr,
+                       dc->udp_addr_len,
+                       dc->network_type);
+}
+
+
+/**
+ * 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 Plugin *plugin = cls;
+
+  if (GNUNET_OK == result)
+  {
+    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);
+  }
 }
 
 
@@ -2388,17 +2899,22 @@ ack_proc (void *cls,
           const struct GNUNET_MessageHeader *msg)
 {
   struct DefragContext *rc = cls;
+  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 GNUNET_ATS_Session *s;
   struct GNUNET_HELLO_Address *address;
 
   if (GNUNET_NO == rc->have_sender)
   {
     /* tried to defragment but never succeeded, hence will not ACK */
-    GNUNET_break_op (0);
+    /* 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,
@@ -2406,148 +2922,65 @@ ack_proc (void *cls,
                                            rc->udp_addr,
                                            rc->udp_addr_len,
                                            GNUNET_HELLO_ADDRESS_INFO_NONE);
-  s = udp_plugin_lookup_session (rc->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 (rc->plugin,
-                                rc->udp_addr,
-                                rc->udp_addr_len));
-    GNUNET_CONTAINER_heap_remove_node (rc->hnode);
-    GNUNET_DEFRAGMENT_context_destroy (rc->defrag);
-    GNUNET_free (rc);
-    return;
-  }
-  if (s->flow_delay_for_other_peer.rel_value_us <= UINT32_MAX)
-    delay = s->flow_delay_for_other_peer.rel_value_us;
-
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Sending ACK to `%s' including delay of %s\n",
-       udp_address_to_string (rc->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 = UMT_MSG_ACK;
-  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);
-  notify_session_monitor (s->plugin,
-                          s,
-                          GNUNET_TRANSPORT_SS_UPDATE);
-  schedule_select (rc->plugin);
-}
-
-
-/**
- * Handle an ACK message.
- *
- * @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
-read_process_ack (struct Plugin *plugin,
-                  const struct GNUNET_MessageHeader *msg,
-                  const union UdpAddress *udp_addr,
-                  socklen_t udp_addr_len)
-{
-  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;
-
-  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;
-  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_WARNING,
-         "Fragmentation context of address %s for ACK not found\n",
-         udp_address_to_string (plugin,
-                                address->address,
-                                address->address_length));
-    GNUNET_HELLO_address_free (address);
-    return;
-  }
-  GNUNET_HELLO_address_free (address);
-
-  flow_delay.rel_value_us = (uint64_t) ntohl (udp_ack->delay);
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "We received a sending delay of %s\n",
-       GNUNET_STRINGS_relative_time_to_string (flow_delay,
-                                               GNUNET_YES));
-  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 (GNUNET_OK !=
-      GNUNET_FRAGMENT_process_ack (s->frag_ctx->frag,
-                                   ack))
+                                 address);
+  GNUNET_HELLO_address_free (address);
+  if (NULL == s)
   {
-    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 */
+    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 (GNUNET_TIME_UNIT_FOREVER_REL.rel_value_us ==
+      s->flow_delay_for_other_peer.rel_value_us)
+    delay = UINT32_MAX;
+  else 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 - 1; /* largest value we can communicate */
   LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Message full ACK'ed\n",
-       (unsigned int ) ntohs (msg->size),
-       GNUNET_i2s (&udp_ack->sender),
+       "Sending ACK to `%s' including delay of %s\n",
        udp_address_to_string (plugin,
-                              udp_addr,
-                              udp_addr_len));
-
-  /* Remove fragmented message after successful sending */
-  fragmented_message_done (s->frag_ctx,
-                           GNUNET_OK);
+                              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->start_time = GNUNET_TIME_absolute_get ();
+  udpw->timeout = GNUNET_TIME_UNIT_FOREVER_ABS;
+  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 = *plugin->env->my_identity;
+  GNUNET_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);
 }
 
 
@@ -2565,7 +2998,7 @@ read_process_fragment (struct Plugin *plugin,
                        const struct GNUNET_MessageHeader *msg,
                        const union UdpAddress *udp_addr,
                        size_t udp_addr_len,
-                       enum GNUNET_ATS_Network_Type network_type)
+                       enum GNUNET_NetworkType network_type)
 {
   struct DefragContext *d_ctx;
   struct GNUNET_TIME_Absolute now;
@@ -2586,7 +3019,7 @@ read_process_fragment (struct Plugin *plugin,
   {
     /* Create a new defragmentation context */
     d_ctx = GNUNET_malloc (sizeof (struct DefragContext) + udp_addr_len);
-    memcpy (&d_ctx[1],
+    GNUNET_memcpy (&d_ctx[1],
             udp_addr,
             udp_addr_len);
     d_ctx->udp_addr = (const union UdpAddress *) &d_ctx[1];
@@ -2601,10 +3034,10 @@ read_process_fragment (struct Plugin *plugin,
                                                       &ack_proc);
     d_ctx->hnode = GNUNET_CONTAINER_heap_insert (plugin->defrag_ctxs,
                                                  d_ctx,
-        (GNUNET_CONTAINER_HeapCostType) now.abs_value_us);
+                                                 (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),
+         (unsigned int) ntohs (msg->size),
          udp_address_to_string (plugin,
                                 udp_addr,
                                 udp_addr_len));
@@ -2613,19 +3046,19 @@ read_process_fragment (struct Plugin *plugin,
   {
     LOG (GNUNET_ERROR_TYPE_DEBUG,
          "Found existing defragmentation context for %u-byte fragment from `%s'\n",
-         (unsigned int ) ntohs (msg->size),
+         (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))
+      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_us);
+    GNUNET_CONTAINER_heap_update_cost (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)
@@ -2635,6 +3068,10 @@ 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);
   }
 }
 
@@ -2661,12 +3098,17 @@ udp_select_read (struct Plugin *plugin,
   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);
+  enum GNUNET_NetworkType network_type;
+
+  fromlen = sizeof (addr);
+  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
@@ -2679,8 +3121,9 @@ udp_select_read (struct Plugin *plugin,
    *   error indicates a previous send operation resulted in an ICMP Port
    *   Unreachable message.
    */
-  if ( (-1 == size) && (ECONNRESET == errno) )
-  return;
+  if ( (-1 == size) &&
+       (ECONNRESET == errno) )
+    return;
 #endif
   if (-1 == size)
   {
@@ -2690,17 +3133,29 @@ udp_select_read (struct Plugin *plugin,
     /* Connection failure or something. Not a protocol violation. */
     return;
   }
+
+  /* Check if this is a STUN packet */
+  if (GNUNET_NO !=
+      GNUNET_NAT_stun_handle_packet (plugin->nat,
+                                    (const struct sockaddr *) &addr,
+                                    fromlen,
+                                    buf,
+                                    size))
+    return; /* was STUN, do not process further */
+
   if (size < sizeof(struct GNUNET_MessageHeader))
   {
     LOG (GNUNET_ERROR_TYPE_WARNING,
          "UDP got %u bytes from %s, which is not enough for a GNUnet message header\n",
          (unsigned int ) size,
-         GNUNET_a2s (sa, fromlen));
+         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);
+    GNUNET_break_op (0);
     return;
   }
+
   msg = (const struct GNUNET_MessageHeader *) buf;
   LOG (GNUNET_ERROR_TYPE_DEBUG,
        "UDP received %u-byte message from `%s' type %u\n",
@@ -2711,7 +3166,7 @@ udp_select_read (struct Plugin *plugin,
   if (size != ntohs (msg->size))
   {
     LOG (GNUNET_ERROR_TYPE_WARNING,
-         "UDP malformed message header from %s\n",
+         "UDP malformed message (size %u) header from %s\n",
          (unsigned int) size,
          GNUNET_a2s (sa,
                      fromlen));
@@ -2719,7 +3174,7 @@ udp_select_read (struct Plugin *plugin,
     return;
   }
   GNUNET_STATISTICS_update (plugin->env->stats,
-                            "# UDP, total, bytes, received",
+                            "# UDP, total bytes received",
                             size,
                             GNUNET_NO);
   network_type = plugin->env->get_address_type (plugin->env->cls,
@@ -2804,9 +3259,9 @@ static struct UDP_MessageWrapper *
 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;
+  struct GNUNET_ATS_Session *session;
   int removed;
 
   removed = GNUNET_NO;
@@ -2821,95 +3276,25 @@ remove_timeout_messages_and_select (struct Plugin *plugin,
     if (GNUNET_TIME_UNIT_ZERO.rel_value_us == remaining.rel_value_us)
     {
       /* Message timed out */
-      switch (udpw->msg_type)
-      {
-      case UMT_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 */
-        removed = GNUNET_YES;
-        dequeue (plugin, udpw);
-        GNUNET_free(udpw);
-        break;
-      case UMT_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 UMT_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);
-        removed = GNUNET_YES;
-        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 */
+        GNUNET_break (0); /* should never happen */
         udpw = NULL;
       }
       GNUNET_STATISTICS_update (plugin->env->stats,
@@ -2919,9 +3304,9 @@ remove_timeout_messages_and_select (struct Plugin *plugin,
     }
     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_us == remaining.rel_value_us)
+      /* Message did not time out, check transmission time */
+      remaining = GNUNET_TIME_absolute_get_remaining (udpw->transmission_time);
+      if (0 == remaining.rel_value_us)
       {
         /* this message is not delayed */
         LOG (GNUNET_ERROR_TYPE_DEBUG,
@@ -2952,19 +3337,29 @@ remove_timeout_messages_and_select (struct Plugin *plugin,
 
 
 /**
- * FIXME.
+ * 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,
-                    socklen_t slen, int error)
+                    socklen_t slen,
+                    int 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)))
+  enum GNUNET_NetworkType type;
+
+  type = plugin->env->get_address_type (plugin->env->cls,
+                                        sa,
+                                        slen);
+  if ( ( (GNUNET_NT_LAN == type) ||
+         (GNUNET_NT_WAN == type) ) &&
+       ( (ENETUNREACH == errno) ||
+         (ENETDOWN == errno) ) )
   {
     if (slen == sizeof (struct sockaddr_in))
     {
@@ -2975,7 +3370,8 @@ analyze_send_error (struct Plugin *plugin,
       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));
+           GNUNET_a2s (sa,
+                       slen));
     }
     if (slen == sizeof (struct sockaddr_in6))
     {
@@ -2995,7 +3391,9 @@ analyze_send_error (struct Plugin *plugin,
   {
     LOG (GNUNET_ERROR_TYPE_WARNING,
          "UDP could not transmit message to `%s': `%s'\n",
-         GNUNET_a2s (sa, slen), STRERROR (error));
+         GNUNET_a2s (sa,
+                     slen),
+         STRERROR (error));
   }
 }
 
@@ -3006,147 +3404,158 @@ analyze_send_error (struct Plugin *plugin,
  *
  * @param plugin the plugin
  * @param sock which socket (v4/v6) to send on
- * @return number of bytes transmitted, #GNUNET_SYSERR on failure
  */
-static size_t
+static void
 udp_select_send (struct Plugin *plugin,
                  struct GNUNET_NETWORK_Handle *sock)
 {
   ssize_t sent;
   socklen_t slen;
-  struct sockaddr *a;
+  const struct sockaddr *a;
   const struct IPv4UdpAddress *u4;
   struct sockaddr_in a4;
   const struct IPv6UdpAddress *u6;
   struct sockaddr_in6 a6;
   struct UDP_MessageWrapper *udpw;
 
-  /* Find message to send */
-  udpw = remove_timeout_messages_and_select (plugin,
-                                             sock);
-  if (NULL == udpw)
-    return 0; /* No message to send */
-
-  if (sizeof (struct IPv4UdpAddress) == udpw->session->address->address_length)
+  /* Find message(s) to send */
+  while (NULL != (udpw = remove_timeout_messages_and_select (plugin,
+                                                             sock)))
   {
-    u4 = udpw->session->address->address;
-    memset (&a4, 0, sizeof(a4));
-    a4.sin_family = AF_INET;
+    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);
+      a4.sin_len = sizeof (a4);
 #endif
-    a4.sin_port = u4->u4_port;
-    memcpy (&a4.sin_addr,
-           &u4->ipv4_addr,
-           sizeof(struct in_addr));
-    a = (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;
+      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);
+      a6.sin6_len = sizeof (a6);
 #endif
-    a6.sin6_port = u6->u6_port;
-    memcpy (&a6.sin6_addr, &u6->ipv6_addr, sizeof(struct in6_addr));
-    a = (struct sockaddr *) &a6;
-    slen = sizeof (a6);
-  }
-  else
-  {
-    call_continuation (udpw,
-                      GNUNET_OK);
+      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);
+    udpw->session->last_transmit_time
+      = GNUNET_TIME_absolute_max (GNUNET_TIME_absolute_get (),
+                                  udpw->session->last_transmit_time);
     dequeue (plugin,
-            udpw);
+             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;
+      udpw->qc (udpw->qc_cls,
+                udpw,
+                GNUNET_OK);
+    }
     notify_session_monitor (plugin,
                             udpw->session,
                             GNUNET_TRANSPORT_SS_UPDATE);
     GNUNET_free (udpw);
-    return GNUNET_SYSERR;
-  }
-  sent = GNUNET_NETWORK_socket_sendto (sock,
-                                       udpw->msg_buf,
-                                       udpw->msg_size,
-                                       a,
-                                       slen);
-  if (GNUNET_SYSERR == sent)
-  {
-    /* Failure */
-    analyze_send_error (plugin,
-                       a,
-                       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
-  {
-    /* 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);
   }
-  dequeue (plugin, udpw);
-  notify_session_monitor (plugin,
-                          udpw->session,
-                          GNUNET_TRANSPORT_SS_UPDATE);
-  GNUNET_free (udpw);
-  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)
  */
 static void
-udp_plugin_select (void *cls,
-                   const struct GNUNET_SCHEDULER_TaskContext *tc)
+udp_plugin_select_v4 (void *cls)
 {
   struct Plugin *plugin = cls;
+  const struct GNUNET_SCHEDULER_TaskContext *tc;
 
-  plugin->select_task = NULL;
-  if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
+  plugin->select_task_v4 = NULL;
+  if (NULL == plugin->sockv4)
     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);
+  tc = GNUNET_SCHEDULER_get_task_context ();
+  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);
 }
 
 
@@ -3156,28 +3565,32 @@ udp_plugin_select (void *cls,
  * 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
-udp_plugin_select_v6 (void *cls,
-                      const struct GNUNET_SCHEDULER_TaskContext *tc)
+udp_plugin_select_v6 (void *cls)
 {
   struct Plugin *plugin = cls;
+  const struct GNUNET_SCHEDULER_TaskContext *tc;
 
   plugin->select_task_v6 = NULL;
-  if (0 != (tc->reason & GNUNET_SCHEDULER_REASON_SHUTDOWN))
+  if (NULL == plugin->sockv6)
     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);
+  tc = GNUNET_SCHEDULER_get_task_context ();
+  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.
  *
@@ -3186,17 +3599,17 @@ udp_plugin_select_v6 (void *cls,
  * @param bind_v4 IPv4 address to bind to (can be NULL, for 'any')
  * @return number of sockets that were successfully bound
  */
-static int
+static unsigned int
 setup_sockets (struct Plugin *plugin,
                const struct sockaddr_in6 *bind_v6,
                const struct sockaddr_in *bind_v4)
 {
   int tries;
-  int sockets_created = 0;
+  unsigned int sockets_created = 0;
   struct sockaddr_in6 server_addrv6;
   struct sockaddr_in server_addrv4;
-  struct sockaddr *server_addr;
-  struct sockaddr *addrs[2];
+  const struct sockaddr *server_addr;
+  const struct sockaddr *addrs[2];
   socklen_t addrlens[2];
   socklen_t addrlen;
   int eno;
@@ -3205,16 +3618,20 @@ setup_sockets (struct Plugin *plugin,
   eno = EINVAL;
   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)
     {
-      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 (&server_addrv6, '\0', sizeof(struct sockaddr_in6));
+      memset (&server_addrv6,
+              0,
+              sizeof(struct sockaddr_in6));
 #if HAVE_SOCKADDR_IN_SIN_LEN
       server_addrv6.sin6_len = sizeof (struct sockaddr_in6);
 #endif
@@ -3226,19 +3643,21 @@ setup_sockets (struct Plugin *plugin,
 
       if (0 == plugin->port) /* autodetect */
         server_addrv6.sin6_port
-          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537)
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
                    + 32000);
       else
         server_addrv6.sin6_port = htons (plugin->port);
-      addrlen = sizeof(struct sockaddr_in6);
-      server_addr = (struct sockaddr *) &server_addrv6;
+      addrlen = sizeof (struct sockaddr_in6);
+      server_addr = (const struct sockaddr *) &server_addrv6;
 
       tries = 0;
       while (tries < 10)
       {
         LOG(GNUNET_ERROR_TYPE_DEBUG,
             "Binding to IPv6 `%s'\n",
-            GNUNET_a2s (server_addr, addrlen));
+            GNUNET_a2s (server_addr,
+                        addrlen));
         /* binding */
         if (GNUNET_OK ==
             GNUNET_NETWORK_socket_bind (plugin->sockv6,
@@ -3253,7 +3672,8 @@ setup_sockets (struct Plugin *plugin,
         }
         /* autodetect */
         server_addrv6.sin6_port
-          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537)
+          = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                             33537)
                    + 32000);
         tries++;
       }
@@ -3270,17 +3690,19 @@ setup_sockets (struct Plugin *plugin,
       if (NULL != plugin->sockv6)
       {
         LOG (GNUNET_ERROR_TYPE_DEBUG,
-             "IPv6 socket created on port %s\n",
-             GNUNET_a2s (server_addr, addrlen));
-        addrs[sockets_created] = (struct sockaddr *) &server_addrv6;
-        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 (server_addr, addrlen),
+        LOG (GNUNET_ERROR_TYPE_WARNING,
+             _("Failed to bind UDP socket to %s: %s\n"),
+             GNUNET_a2s (server_addr,
+                         addrlen),
              STRERROR (eno));
       }
     }
@@ -3288,18 +3710,22 @@ setup_sockets (struct Plugin *plugin,
 
   /* 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");
+    LOG (GNUNET_ERROR_TYPE_INFO,
+         _("Disabling IPv4 since it is not supported on this system!\n"));
     plugin->enable_ipv4 = GNUNET_NO;
   }
   else
   {
-    memset (&server_addrv4, '\0', sizeof(struct sockaddr_in));
+    memset (&server_addrv4,
+            0,
+            sizeof(struct sockaddr_in));
 #if HAVE_SOCKADDR_IN_SIN_LEN
     server_addrv4.sin_len = sizeof (struct sockaddr_in);
 #endif
@@ -3318,15 +3744,16 @@ setup_sockets (struct Plugin *plugin,
     else
       server_addrv4.sin_port = htons (plugin->port);
 
-    addrlen = sizeof(struct sockaddr_in);
-    server_addr = (struct sockaddr *) &server_addrv4;
+    addrlen = sizeof (struct sockaddr_in);
+    server_addr = (const struct sockaddr *) &server_addrv4;
 
     tries = 0;
     while (tries < 10)
     {
       LOG (GNUNET_ERROR_TYPE_DEBUG,
            "Binding to IPv4 `%s'\n",
-           GNUNET_a2s (server_addr, addrlen));
+           GNUNET_a2s (server_addr,
+                       addrlen));
 
       /* binding */
       if (GNUNET_OK ==
@@ -3343,7 +3770,8 @@ setup_sockets (struct Plugin *plugin,
 
       /* autodetect */
       server_addrv4.sin_port
-        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG, 33537)
+        = htons (GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_STRONG,
+                                           33537)
                  + 32000);
       tries++;
     }
@@ -3362,16 +3790,18 @@ setup_sockets (struct Plugin *plugin,
     {
       LOG (GNUNET_ERROR_TYPE_DEBUG,
            "IPv4 socket created on port %s\n",
-           GNUNET_a2s (server_addr, addrlen));
-      addrs[sockets_created] = (struct sockaddr *) &server_addrv4;
-      addrlens[sockets_created] = sizeof(struct sockaddr_in);
+           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 (server_addr, addrlen),
+           GNUNET_a2s (server_addr,
+                       addrlen),
            STRERROR (eno));
     }
   }
@@ -3382,108 +3812,21 @@ setup_sockets (struct Plugin *plugin,
          _("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)
-  {
-    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);
-    }
-  }
-
-  schedule_select (plugin);
+  schedule_select_v4 (plugin);
+  schedule_select_v6 (plugin);
   plugin->nat = GNUNET_NAT_register (plugin->env->cfg,
-                                     GNUNET_NO,
-                                     plugin->port,
+                                    "transport-udp",
+                                    IPPROTO_UDP,
                                      sockets_created,
-                                     (const struct sockaddr **) addrs,
+                                     addrs,
                                      addrlens,
                                      &udp_nat_port_map_callback,
                                      NULL,
                                      plugin);
-
   return sockets_created;
 }
 
 
-/**
- * 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)
- */
-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;
-}
-
-
-/**
- * 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 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_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);
-  }
-}
-
-
 /**
  * The exported method. Makes the core api available via a global and
  * returns the udp transport API.
@@ -3500,16 +3843,15 @@ libgnunet_plugin_transport_udp_init (void *cls)
   unsigned long long port;
   unsigned long long aport;
   unsigned long long udp_max_bps;
-  unsigned long long enable_v6;
-  unsigned long long enable_broadcasting;
-  unsigned long long enable_broadcasting_recv;
+  int enable_v6;
+  int enable_broadcasting;
+  int enable_broadcasting_recv;
   char *bind4_address;
   char *bind6_address;
-  char *fancy_interval;
   struct GNUNET_TIME_Relative interval;
   struct sockaddr_in server_addrv4;
   struct sockaddr_in6 server_addrv6;
-  int res;
+  unsigned int res;
   int have_bind4;
   int have_bind6;
 
@@ -3530,54 +3872,76 @@ libgnunet_plugin_transport_udp_init (void *cls)
   if (GNUNET_OK !=
       GNUNET_CONFIGURATION_get_value_number (env->cfg,
                                              "transport-udp",
-                                             "PORT", &port))
+                                             "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))
+                                             "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"))
+      GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
+                                            "nat",
+                                            "DISABLEV6"))
     enable_v6 = GNUNET_NO;
   else
     enable_v6 = GNUNET_YES;
 
-  /* Addresses */
   have_bind4 = GNUNET_NO;
-  memset (&server_addrv4, 0, sizeof(server_addrv4));
+  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,
                         &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;
     }
     have_bind4 = GNUNET_YES;
   }
-  GNUNET_free_non_null(bind4_address);
+  GNUNET_free_non_null (bind4_address);
   have_bind6 = GNUNET_NO;
-  memset (&server_addrv6, 0, sizeof(server_addrv6));
+  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",
@@ -3586,9 +3950,10 @@ libgnunet_plugin_transport_udp_init (void *cls)
                         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;
     }
@@ -3596,40 +3961,35 @@ libgnunet_plugin_transport_udp_init (void *cls)
   }
   GNUNET_free_non_null (bind6_address);
 
-  /* Enable neighbour discovery */
   enable_broadcasting = GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
-      "transport-udp", "BROADCAST");
+                                                              "transport-udp",
+                                                              "BROADCAST");
   if (enable_broadcasting == GNUNET_SYSERR)
     enable_broadcasting = GNUNET_NO;
 
   enable_broadcasting_recv = GNUNET_CONFIGURATION_get_value_yesno (env->cfg,
-      "transport-udp", "BROADCAST_RECEIVE");
+                                                                   "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))
+      GNUNET_CONFIGURATION_get_value_time (env->cfg,
+                                           "transport-udp",
+                                           "BROADCAST_INTERVAL",
+                                           &interval))
   {
-    interval = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS, 10);
+    interval = GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_SECONDS,
+                                              10);
   }
-  else
-  {
-    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);
-  }
-
-  /* Maximum datarate */
   if (GNUNET_OK !=
-      GNUNET_CONFIGURATION_get_value_number (env->cfg, "transport-udp",
-                                             "MAX_BPS", &udp_max_bps))
+      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_new (struct Plugin);
@@ -3641,38 +4001,38 @@ libgnunet_plugin_transport_udp_init (void *cls)
   p->enable_broadcasting = enable_broadcasting;
   p->enable_broadcasting_receiving = enable_broadcasting_recv;
   p->env = env;
-  p->sessions = GNUNET_CONTAINER_multipeermap_create (10, 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->sessions = GNUNET_CONTAINER_multipeermap_create (16,
+                                                      GNUNET_NO);
+  p->defrag_ctxs = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
   GNUNET_BANDWIDTH_tracker_init (&p->tracker,
                                  NULL,
                                  NULL,
                                  GNUNET_BANDWIDTH_value_init ((uint32_t) udp_max_bps),
                                  30);
-  LOG(GNUNET_ERROR_TYPE_DEBUG,
-      "Setting up sockets\n");
   res = setup_sockets (p,
                        (GNUNET_YES == have_bind6) ? &server_addrv6 : NULL,
                        (GNUNET_YES == have_bind4) ? &server_addrv4 : NULL);
-  if ((res == 0) || ((p->sockv4 == NULL )&& (p->sockv6 == NULL)))
+  if ( (0 == res) ||
+       ( (NULL == p->sockv4) &&
+         (NULL == p->sockv6) ) )
   {
     LOG (GNUNET_ERROR_TYPE_ERROR,
-        _("Failed to create network sockets, plugin failed\n"));
+        _("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);
+    if (NULL != p->nat)
+      GNUNET_NAT_unregister (p->nat);
     GNUNET_free (p);
     return NULL;
   }
 
   /* Setup broadcasting and receiving beacons */
-  setup_broadcast (p, &server_addrv6, &server_addrv4);
+  setup_broadcast (p,
+                   &server_addrv6,
+                   &server_addrv4);
 
   api = GNUNET_new (struct GNUNET_TRANSPORT_PluginFunctions);
   api->cls = p;
-  api->send = NULL;
   api->disconnect_session = &udp_disconnect_session;
   api->query_keepalive_factor = &udp_query_keepalive_factor;
   api->disconnect_peer = &udp_disconnect;
@@ -3682,7 +4042,8 @@ libgnunet_plugin_transport_udp_init (void *cls)
   api->check_address = &udp_plugin_check_address;
   api->get_session = &udp_plugin_get_session;
   api->send = &udp_plugin_send;
-  api->get_network = &udp_get_network;
+  api->get_network = &udp_plugin_get_network;
+  api->get_network_for_address = &udp_plugin_get_network_for_address;
   api->update_session_timeout = &udp_plugin_update_session_timeout;
   api->setup_monitor = &udp_plugin_setup_monitor;
   return api;
@@ -3727,49 +4088,35 @@ libgnunet_plugin_transport_udp_done (void *cls)
   struct GNUNET_TRANSPORT_PluginFunctions *api = cls;
   struct Plugin *plugin = api->cls;
   struct PrettyPrinterContext *cur;
-  struct PrettyPrinterContext *next;
   struct UDP_MessageWrapper *udpw;
 
   if (NULL == plugin)
   {
-    GNUNET_free(api);
+    GNUNET_free (api);
     return NULL;
   }
   stop_broadcast (plugin);
-  if (plugin->select_task != NULL)
+  if (NULL != plugin->select_task_v4)
   {
-    GNUNET_SCHEDULER_cancel (plugin->select_task);
-    plugin->select_task = NULL;
+    GNUNET_SCHEDULER_cancel (plugin->select_task_v4);
+    plugin->select_task_v4 = NULL;
   }
-  if (plugin->select_task_v6 != NULL)
+  if (NULL != plugin->select_task_v6)
   {
     GNUNET_SCHEDULER_cancel (plugin->select_task_v6);
     plugin->select_task_v6 = NULL;
   }
-
-  /* Closing sockets */
-  if (GNUNET_YES == plugin->enable_ipv4)
+  if (NULL != plugin->sockv4)
   {
-    if (NULL != plugin->sockv4)
-    {
-      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 (NULL != plugin->sockv6)
-    {
-      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)
   {
@@ -3779,52 +4126,46 @@ libgnunet_plugin_transport_udp_done (void *cls)
   if (NULL != plugin->defrag_ctxs)
   {
     GNUNET_CONTAINER_heap_iterate (plugin->defrag_ctxs,
-                                   &heap_cleanup_iterator, NULL);
+                                   &heap_cleanup_iterator,
+                                   NULL);
     GNUNET_CONTAINER_heap_destroy (plugin->defrag_ctxs);
     plugin->defrag_ctxs = NULL;
   }
-  if (NULL != plugin->mst)
-  {
-    GNUNET_SERVER_mst_destroy (plugin->mst);
-    plugin->mst = NULL;
-  }
-
-  /* Clean up leftover messages */
-  udpw = plugin->ipv4_queue_head;
-  while (NULL != udpw)
+  while (NULL != (udpw = plugin->ipv4_queue_head))
   {
-    struct UDP_MessageWrapper *tmp = udpw->next;
-    dequeue (plugin, udpw);
-    call_continuation (udpw, GNUNET_SYSERR);
-    GNUNET_free(udpw);
-    udpw = tmp;
+    dequeue (plugin,
+             udpw);
+    udpw->qc (udpw->qc_cls,
+              udpw,
+              GNUNET_SYSERR);
+    GNUNET_free (udpw);
   }
-  udpw = plugin->ipv6_queue_head;
-  while (NULL != udpw)
+  while (NULL != (udpw = plugin->ipv6_queue_head))
   {
-    struct UDP_MessageWrapper *tmp = udpw->next;
-    dequeue (plugin, udpw);
-    call_continuation (udpw, GNUNET_SYSERR);
-    GNUNET_free(udpw);
-    udpw = tmp;
+    dequeue (plugin,
+             udpw);
+    udpw->qc (udpw->qc_cls,
+              udpw,
+              GNUNET_SYSERR);
+    GNUNET_free (udpw);
   }
-
-  /* Clean up sessions */
-  LOG (GNUNET_ERROR_TYPE_DEBUG,
-       "Cleaning up sessions\n");
   GNUNET_CONTAINER_multipeermap_iterate (plugin->sessions,
-                                         &disconnect_and_free_it, plugin);
+                                         &disconnect_and_free_it,
+                                         plugin);
   GNUNET_CONTAINER_multipeermap_destroy (plugin->sessions);
 
-  next = plugin->ppc_dll_head;
-  for (cur = next; NULL != cur; cur = next)
+  while (NULL != (cur = plugin->ppc_dll_head))
   {
-    GNUNET_break(0);
-    next = cur->next;
+    GNUNET_break (0);
     GNUNET_CONTAINER_DLL_remove (plugin->ppc_dll_head,
                                  plugin->ppc_dll_tail,
                                  cur);
     GNUNET_RESOLVER_request_cancel (cur->resolver_handle);
+    if (NULL != cur->timeout_task)
+    {
+      GNUNET_SCHEDULER_cancel (cur->timeout_task);
+      cur->timeout_task = NULL;
+    }
     GNUNET_free (cur);
   }
   GNUNET_free (plugin);