diff --git a/src/BtAnnounce.h b/src/BtAnnounce.h
index 6cdd6804..47523af2 100644
--- a/src/BtAnnounce.h
+++ b/src/BtAnnounce.h
@@ -40,9 +40,12 @@
 #include <string>
 
 #include "a2time.h"
+#include "SharedHandle.h"
 
 namespace aria2 {
 
+class UDPTrackerRequest;
+
 class BtAnnounce {
 public:
   virtual ~BtAnnounce() {}
@@ -65,6 +68,10 @@ public:
    */
   virtual std::string getAnnounceUrl() = 0;
 
+  virtual SharedHandle<UDPTrackerRequest>
+  createUDPTrackerRequest(const std::string& remoteAddr, uint16_t remotePort,
+                          uint16_t localPort) = 0;
+
   /**
    * Tells that the announce process has just started.
    */
@@ -96,6 +103,9 @@ public:
   virtual void processAnnounceResponse(const unsigned char* trackerResponse,
                                        size_t trackerResponseLength) = 0;
 
+  virtual void processUDPTrackerResponse
+  (const SharedHandle<UDPTrackerRequest>& req) = 0;
+
   /**
    * Returns true if no more announce is needed.
    */
diff --git a/src/BtRegistry.cc b/src/BtRegistry.cc
index 1189a652..273f0130 100644
--- a/src/BtRegistry.cc
+++ b/src/BtRegistry.cc
@@ -42,12 +42,14 @@
 #include "BtProgressInfoFile.h"
 #include "bittorrent_helper.h"
 #include "LpdMessageReceiver.h"
+#include "UDPTrackerClient.h"
 #include "NullHandle.h"
 
 namespace aria2 {
 
 BtRegistry::BtRegistry()
-  : tcpPort_(0)
+  : tcpPort_(0),
+    udpPort_(0)
 {}
 
 BtRegistry::~BtRegistry() {}
@@ -107,6 +109,12 @@ void BtRegistry::setLpdMessageReceiver
   lpdMessageReceiver_ = receiver;
 }
 
+void BtRegistry::setUDPTrackerClient
+(const SharedHandle<UDPTrackerClient>& tracker)
+{
+  udpTrackerClient_ = tracker;
+}
+
 BtObject::BtObject
 (const SharedHandle<DownloadContext>& downloadContext,
  const SharedHandle<PieceStorage>& pieceStorage,
diff --git a/src/BtRegistry.h b/src/BtRegistry.h
index a4791210..06c0bfa4 100644
--- a/src/BtRegistry.h
+++ b/src/BtRegistry.h
@@ -51,6 +51,7 @@ class BtRuntime;
 class BtProgressInfoFile;
 class DownloadContext;
 class LpdMessageReceiver;
+class UDPTrackerClient;
 
 struct BtObject {
   SharedHandle<DownloadContext> downloadContext;
@@ -80,7 +81,10 @@ class BtRegistry {
 private:
   std::map<a2_gid_t, SharedHandle<BtObject> > pool_;
   uint16_t tcpPort_;
+  // This is IPv4 port for DHT and UDP tracker. No IPv6 udpPort atm.
+  uint16_t udpPort_;
   SharedHandle<LpdMessageReceiver> lpdMessageReceiver_;
+  SharedHandle<UDPTrackerClient> udpTrackerClient_;
 public:
   BtRegistry();
   ~BtRegistry();
@@ -118,11 +122,26 @@ public:
     return tcpPort_;
   }
 
+  void setUdpPort(uint16_t port)
+  {
+    udpPort_ = port;
+  }
+  uint16_t getUdpPort() const
+  {
+    return udpPort_;
+  }
+
   void setLpdMessageReceiver(const SharedHandle<LpdMessageReceiver>& receiver);
   const SharedHandle<LpdMessageReceiver>& getLpdMessageReceiver() const
   {
     return lpdMessageReceiver_;
   }
+
+  void setUDPTrackerClient(const SharedHandle<UDPTrackerClient>& tracker);
+  const SharedHandle<UDPTrackerClient>& getUDPTrackerClient() const
+  {
+    return udpTrackerClient_;
+  }
 };
 
 } // namespace aria2
diff --git a/src/BtSetup.cc b/src/BtSetup.cc
index 1a8b6403..ce7f3bf8 100644
--- a/src/BtSetup.cc
+++ b/src/BtSetup.cc
@@ -67,6 +67,7 @@
 #include "DHTMessageReceiver.h"
 #include "DHTMessageFactory.h"
 #include "DHTMessageCallback.h"
+#include "UDPTrackerClient.h"
 #include "BtProgressInfoFile.h"
 #include "BtAnnounce.h"
 #include "BtRuntime.h"
diff --git a/src/DHTInteractionCommand.cc b/src/DHTInteractionCommand.cc
index 4fc3f371..096812a8 100644
--- a/src/DHTInteractionCommand.cc
+++ b/src/DHTInteractionCommand.cc
@@ -46,10 +46,16 @@
 #include "LogFactory.h"
 #include "DHTMessageCallback.h"
 #include "DHTNode.h"
+#include "DHTConnection.h"
+#include "UDPTrackerClient.h"
+#include "UDPTrackerRequest.h"
 #include "fmt.h"
+#include "wallclock.h"
 
 namespace aria2 {
 
+// TODO This name of this command is misleading, because now it also
+// handles UDP trackers as well as DHT.
 DHTInteractionCommand::DHTInteractionCommand(cuid_t cuid, DownloadEngine* e)
   : Command(cuid),
     e_(e)
@@ -77,23 +83,60 @@ void DHTInteractionCommand::disableReadCheckSocket(const SharedHandle<SocketCore
 
 bool DHTInteractionCommand::execute()
 {
-  if(e_->getRequestGroupMan()->downloadFinished() || e_->isHaltRequested()) {
+  // We need to keep this command alive while TrackerWatcherCommand
+  // needs this.
+  if(e_->getRequestGroupMan()->downloadFinished() ||
+     (e_->isHaltRequested() && udpTrackerClient_->getNumWatchers() == 0)) {
+    return true;
+  } else if(e_->isForceHaltRequested()) {
+    udpTrackerClient_->failAll();
     return true;
   }
 
   taskQueue_->executeTask();
 
-  while(1) {
-    SharedHandle<DHTMessage> m = receiver_->receiveMessage();
-    if(!m) {
-      break;
+  std::string remoteAddr;
+  uint16_t remotePort;
+  unsigned char data[64*1024];
+  try {
+    while(1) {
+      ssize_t length = connection_->receiveMessage(data, sizeof(data),
+                                                   remoteAddr, remotePort);
+      if(length <= 0) {
+        break;
+      }
+      if(data[0] == 'd') {
+        // udp tracker response does not start with 'd', so assume
+        // this message belongs to DHT. nothrow.
+        receiver_->receiveMessage(remoteAddr, remotePort, data, length);
+      } else {
+        // this may be udp tracker response. nothrow.
+        udpTrackerClient_->receiveReply(data, length, remoteAddr, remotePort,
+                                        global::wallclock());
+      }
     }
+  } catch(RecoverableException& e) {
+    A2_LOG_INFO_EX("Exception thrown while receiving UDP message.", e);
   }
   receiver_->handleTimeout();
-  try {
-    dispatcher_->sendMessages();
-  } catch(RecoverableException& e) {
-    A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, e);
+  udpTrackerClient_->handleTimeout(global::wallclock());
+  dispatcher_->sendMessages();
+  while(!udpTrackerClient_->getPendingRequests().empty()) {
+    // no throw
+    ssize_t length = udpTrackerClient_->createRequest(data, sizeof(data),
+                                                      remoteAddr, remotePort,
+                                                      global::wallclock());
+    if(length == -1) {
+      break;
+    }
+    try {
+      // throw
+      connection_->sendMessage(data, length, remoteAddr, remotePort);
+      udpTrackerClient_->requestSent(global::wallclock());
+    } catch(RecoverableException& e) {
+      A2_LOG_INFO_EX("Exception thrown while sending UDP tracker request.", e);
+      udpTrackerClient_->requestFail(UDPT_ERR_NETWORK);
+    }
   }
   e_->addCommand(this);
   return false;
@@ -114,4 +157,16 @@ void DHTInteractionCommand::setTaskQueue(const SharedHandle<DHTTaskQueue>& taskQ
   taskQueue_ = taskQueue;
 }
 
+void DHTInteractionCommand::setConnection
+(const SharedHandle<DHTConnection>& connection)
+{
+  connection_ = connection;
+}
+
+void DHTInteractionCommand::setUDPTrackerClient
+(const SharedHandle<UDPTrackerClient>& udpTrackerClient)
+{
+  udpTrackerClient_ = udpTrackerClient;
+}
+
 } // namespace aria2
diff --git a/src/DHTInteractionCommand.h b/src/DHTInteractionCommand.h
index f00df78a..e90a1dd6 100644
--- a/src/DHTInteractionCommand.h
+++ b/src/DHTInteractionCommand.h
@@ -45,6 +45,8 @@ class DHTMessageReceiver;
 class DHTTaskQueue;
 class DownloadEngine;
 class SocketCore;
+class DHTConnection;
+class UDPTrackerClient;
 
 class DHTInteractionCommand:public Command {
 private:
@@ -53,6 +55,8 @@ private:
   SharedHandle<DHTMessageReceiver> receiver_;
   SharedHandle<DHTTaskQueue> taskQueue_;
   SharedHandle<SocketCore> readCheckSocket_;
+  SharedHandle<DHTConnection> connection_;
+  SharedHandle<UDPTrackerClient> udpTrackerClient_;
 public:
   DHTInteractionCommand(cuid_t cuid, DownloadEngine* e);
 
@@ -69,6 +73,11 @@ public:
   void setMessageReceiver(const SharedHandle<DHTMessageReceiver>& receiver);
 
   void setTaskQueue(const SharedHandle<DHTTaskQueue>& taskQueue);
+
+  void setConnection(const SharedHandle<DHTConnection>& connection);
+
+  void setUDPTrackerClient
+  (const SharedHandle<UDPTrackerClient>& udpTrackerClient);
 };
 
 } // namespace aria2
diff --git a/src/DHTMessageReceiver.cc b/src/DHTMessageReceiver.cc
index e5558d9d..36e40639 100644
--- a/src/DHTMessageReceiver.cc
+++ b/src/DHTMessageReceiver.cc
@@ -63,18 +63,11 @@ DHTMessageReceiver::DHTMessageReceiver
 
 DHTMessageReceiver::~DHTMessageReceiver() {}
 
-SharedHandle<DHTMessage> DHTMessageReceiver::receiveMessage()
+SharedHandle<DHTMessage> DHTMessageReceiver::receiveMessage
+(const std::string& remoteAddr, uint16_t remotePort, unsigned char *data,
+ size_t length)
 {
-  std::string remoteAddr;
-  uint16_t remotePort;
-  unsigned char data[64*1024];
   try {
-    ssize_t length = connection_->receiveMessage(data, sizeof(data),
-                                                 remoteAddr,
-                                                 remotePort);
-    if(length <= 0) {
-      return SharedHandle<DHTMessage>();
-    }
     bool isReply = false;
     SharedHandle<ValueBase> decoded = bencode2::decode(data, length);
     const Dict* dict = downcast<Dict>(decoded);
@@ -87,13 +80,13 @@ SharedHandle<DHTMessage> DHTMessageReceiver::receiveMessage()
       } else {
         A2_LOG_INFO(fmt("Malformed DHT message. Missing 'y' key. From:%s:%u",
                         remoteAddr.c_str(), remotePort));
-        return handleUnknownMessage(data, sizeof(data), remoteAddr, remotePort);
+        return handleUnknownMessage(data, length, remoteAddr, remotePort);
       }
     } else {
       A2_LOG_INFO(fmt("Malformed DHT message. This is not a bencoded directory."
                       " From:%s:%u",
                       remoteAddr.c_str(), remotePort));
-      return handleUnknownMessage(data, sizeof(data), remoteAddr, remotePort);
+      return handleUnknownMessage(data, length, remoteAddr, remotePort);
     }
     if(isReply) {
       std::pair<SharedHandle<DHTResponseMessage>,
@@ -101,7 +94,7 @@ SharedHandle<DHTMessage> DHTMessageReceiver::receiveMessage()
         tracker_->messageArrived(dict, remoteAddr, remotePort);
       if(!p.first) {
         // timeout or malicious? message
-        return handleUnknownMessage(data, sizeof(data), remoteAddr, remotePort);
+        return handleUnknownMessage(data, length, remoteAddr, remotePort);
       }
       onMessageReceived(p.first);
       if(p.second) {
@@ -114,14 +107,14 @@ SharedHandle<DHTMessage> DHTMessageReceiver::receiveMessage()
       if(*message->getLocalNode() == *message->getRemoteNode()) {
         // drop message from localnode
         A2_LOG_INFO("Received DHT message from localnode.");
-        return handleUnknownMessage(data, sizeof(data), remoteAddr, remotePort);
+        return handleUnknownMessage(data, length, remoteAddr, remotePort);
       }
       onMessageReceived(message);
       return message;
     }
   } catch(RecoverableException& e) {
     A2_LOG_INFO_EX("Exception thrown while receiving DHT message.", e);
-    return handleUnknownMessage(data, sizeof(data), remoteAddr, remotePort);
+    return handleUnknownMessage(data, length, remoteAddr, remotePort);
   }
 }
 
diff --git a/src/DHTMessageReceiver.h b/src/DHTMessageReceiver.h
index 4e2e15fe..f8ed5018 100644
--- a/src/DHTMessageReceiver.h
+++ b/src/DHTMessageReceiver.h
@@ -69,7 +69,9 @@ public:
 
   ~DHTMessageReceiver();
 
-  SharedHandle<DHTMessage> receiveMessage();
+  SharedHandle<DHTMessage> receiveMessage
+  (const std::string& remoteAddr, uint16_t remotePort, unsigned char *data,
+   size_t length);
 
   void handleTimeout();
 
diff --git a/src/DHTSetup.cc b/src/DHTSetup.cc
index 17bd035d..145e0316 100644
--- a/src/DHTSetup.cc
+++ b/src/DHTSetup.cc
@@ -61,6 +61,8 @@
 #include "DHTRegistry.h"
 #include "DHTBucketRefreshTask.h"
 #include "DHTMessageCallback.h"
+#include "UDPTrackerClient.h"
+#include "BtRegistry.h"
 #include "prefs.h"
 #include "Option.h"
 #include "SocketCore.h"
@@ -176,6 +178,8 @@ void DHTSetup::setup
     factory->setTokenTracker(tokenTracker.get());
     factory->setLocalNode(localNode);
 
+    // For now, UDPTrackerClient was enabled along with DHT
+    SharedHandle<UDPTrackerClient> udpTrackerClient(new UDPTrackerClient());
     // assign them into DHTRegistry
     if(family == AF_INET) {
       DHTRegistry::getMutableData().localNode = localNode;
@@ -187,6 +191,8 @@ void DHTSetup::setup
       DHTRegistry::getMutableData().messageDispatcher = dispatcher;
       DHTRegistry::getMutableData().messageReceiver = receiver;
       DHTRegistry::getMutableData().messageFactory = factory;
+      e->getBtRegistry()->setUDPTrackerClient(udpTrackerClient);
+      e->getBtRegistry()->setUdpPort(localNode->getPort());
     } else {
       DHTRegistry::getMutableData6().localNode = localNode;
       DHTRegistry::getMutableData6().routingTable = routingTable;
@@ -244,6 +250,8 @@ void DHTSetup::setup
       command->setMessageReceiver(receiver);
       command->setTaskQueue(taskQueue);
       command->setReadCheckSocket(connection->getSocket());
+      command->setConnection(connection);
+      command->setUDPTrackerClient(udpTrackerClient);
       tempCommands->push_back(command);
     }
     {
@@ -282,12 +290,15 @@ void DHTSetup::setup
     }
     commands.insert(commands.end(), tempCommands->begin(), tempCommands->end());
     tempCommands->clear();
-  } catch(RecoverableException& e) {
+  } catch(RecoverableException& ex) {
     A2_LOG_ERROR_EX(fmt("Exception caught while initializing DHT functionality."
                         " DHT is disabled."),
-                    e);
+                    ex);
     if(family == AF_INET) {
       DHTRegistry::clearData();
+      e->getBtRegistry()->setUDPTrackerClient
+        (SharedHandle<UDPTrackerClient>());
+      e->getBtRegistry()->setUdpPort(0);
     } else {
       DHTRegistry::clearData6();
     }
diff --git a/src/DefaultBtAnnounce.cc b/src/DefaultBtAnnounce.cc
index 6a9cc713..a41f002d 100644
--- a/src/DefaultBtAnnounce.cc
+++ b/src/DefaultBtAnnounce.cc
@@ -52,6 +52,8 @@
 #include "bittorrent_helper.h"
 #include "wallclock.h"
 #include "uri.h"
+#include "UDPTrackerRequest.h"
+#include "SocketCore.h"
 
 namespace aria2 {
 
@@ -115,7 +117,7 @@ bool uriHasQuery(const std::string& uri)
 }
 } // namespace
 
-std::string DefaultBtAnnounce::getAnnounceUrl() {
+bool DefaultBtAnnounce::adjustAnnounceList() {
   if(isStoppedAnnounceReady()) {
     if(!announceList_.currentTierAcceptsStoppedEvent()) {
       announceList_.moveToStoppedAllowedTier();
@@ -135,6 +137,13 @@ std::string DefaultBtAnnounce::getAnnounceUrl() {
       announceList_.setEvent(AnnounceTier::STARTED_AFTER_COMPLETION);
     }
   } else {
+    return false;
+  }
+  return true;
+}
+
+std::string DefaultBtAnnounce::getAnnounceUrl() {
+  if(!adjustAnnounceList()) {
     return A2STR::NIL;
   }
   int numWant = 50;
@@ -193,6 +202,60 @@ std::string DefaultBtAnnounce::getAnnounceUrl() {
   return uri;
 }
 
+SharedHandle<UDPTrackerRequest> DefaultBtAnnounce::createUDPTrackerRequest
+(const std::string& remoteAddr, uint16_t remotePort, uint16_t localPort)
+{
+  if(!adjustAnnounceList()) {
+    return SharedHandle<UDPTrackerRequest>();
+  }
+  NetStat& stat = downloadContext_->getNetStat();
+  int64_t left =
+    pieceStorage_->getTotalLength()-pieceStorage_->getCompletedLength();
+  SharedHandle<UDPTrackerRequest> req(new UDPTrackerRequest());
+  req->remoteAddr = remoteAddr;
+  req->remotePort = remotePort;
+  req->action = UDPT_ACT_ANNOUNCE;
+  req->infohash = bittorrent::getTorrentAttrs(downloadContext_)->infoHash;
+  const unsigned char* peerId = bittorrent::getStaticPeerId();
+  req->peerId.assign(peerId, peerId + PEER_ID_LENGTH);
+  req->downloaded = stat.getSessionDownloadLength();
+  req->left = left;
+  req->uploaded = stat.getSessionUploadLength();
+  switch(announceList_.getEvent()) {
+  case AnnounceTier::STARTED:
+  case AnnounceTier::STARTED_AFTER_COMPLETION:
+    req->event = UDPT_EVT_STARTED;
+    break;
+  case AnnounceTier::STOPPED:
+    req->event = UDPT_EVT_STOPPED;
+    break;
+  case AnnounceTier::COMPLETED:
+    req->event = UDPT_EVT_COMPLETED;
+    break;
+  default:
+    req->event = 0;
+  }
+  if(!option_->blank(PREF_BT_EXTERNAL_IP)) {
+    unsigned char dest[16];
+    if(net::getBinAddr(dest, option_->get(PREF_BT_EXTERNAL_IP)) == 4) {
+      memcpy(&req->ip, dest, 4);
+    } else {
+      req->ip = 0;
+    }
+  } else {
+    req->ip = 0;
+  }
+  req->key = randomizer_->getRandomNumber(INT32_MAX);
+  int numWant = 50;
+  if(!btRuntime_->lessThanMinPeers() || btRuntime_->isHalt()) {
+    numWant = 0;
+  }
+  req->numWant = numWant;
+  req->port = localPort;
+  req->extensions = 0;
+  return req;
+}
+
 void DefaultBtAnnounce::announceStart() {
   ++trackers_;
 }
@@ -287,6 +350,30 @@ DefaultBtAnnounce::processAnnounceResponse(const unsigned char* trackerResponse,
   }
 }
 
+void DefaultBtAnnounce::processUDPTrackerResponse
+(const SharedHandle<UDPTrackerRequest>& req)
+{
+  const SharedHandle<UDPTrackerReply>& reply = req->reply;
+  A2_LOG_DEBUG("Now processing UDP tracker response.");
+  if(reply->interval > 0) {
+    minInterval_ = reply->interval;
+    A2_LOG_DEBUG(fmt("Min interval:%ld", static_cast<long int>(minInterval_)));
+    interval_ = minInterval_;
+  }
+  complete_ = reply->seeders;
+  A2_LOG_DEBUG(fmt("Complete:%d", reply->seeders));
+  incomplete_ = reply->leechers;
+  A2_LOG_DEBUG(fmt("Incomplete:%d", reply->leechers));
+  if(!btRuntime_->isHalt() && btRuntime_->lessThanMinPeers()) {
+    for(std::vector<std::pair<std::string, uint16_t> >::iterator i =
+          reply->peers.begin(), eoi = reply->peers.end(); i != eoi;
+        ++i) {
+      peerStorage_->addPeer(SharedHandle<Peer>(new Peer((*i).first,
+                                                        (*i).second)));
+    }
+  }
+}
+
 bool DefaultBtAnnounce::noMoreAnnounce() {
   return (trackers_ == 0 &&
           btRuntime_->isHalt() &&
diff --git a/src/DefaultBtAnnounce.h b/src/DefaultBtAnnounce.h
index a760a140..5428a42c 100644
--- a/src/DefaultBtAnnounce.h
+++ b/src/DefaultBtAnnounce.h
@@ -66,6 +66,8 @@ private:
   SharedHandle<PieceStorage> pieceStorage_;
   SharedHandle<PeerStorage> peerStorage_;
   uint16_t tcpPort_;
+
+  bool adjustAnnounceList();
 public:
   DefaultBtAnnounce(const SharedHandle<DownloadContext>& downloadContext,
                     const Option* option);
@@ -103,6 +105,10 @@ public:
 
   virtual std::string getAnnounceUrl();
 
+  virtual SharedHandle<UDPTrackerRequest>
+  createUDPTrackerRequest(const std::string& remoteAddr, uint16_t remotePort,
+                          uint16_t localPort);
+
   virtual void announceStart();
 
   virtual void announceSuccess();
@@ -116,6 +122,9 @@ public:
   virtual void processAnnounceResponse(const unsigned char* trackerResponse,
                                        size_t trackerResponseLength);
 
+  virtual void processUDPTrackerResponse
+  (const SharedHandle<UDPTrackerRequest>& req);
+
   virtual bool noMoreAnnounce();
 
   virtual void shuffleAnnounce();
diff --git a/src/DownloadEngine.cc b/src/DownloadEngine.cc
index 9b42bf70..05478fe8 100644
--- a/src/DownloadEngine.cc
+++ b/src/DownloadEngine.cc
@@ -85,7 +85,7 @@ volatile sig_atomic_t globalHaltRequested = 0;
 
 DownloadEngine::DownloadEngine(const SharedHandle<EventPoll>& eventPoll)
   : eventPoll_(eventPoll),
-    haltRequested_(false),
+    haltRequested_(0),
     noWait_(false),
     refreshInterval_(DEFAULT_REFRESH_INTERVAL),
     cookieStorage_(new CookieStorage()),
@@ -239,13 +239,13 @@ void DownloadEngine::afterEachIteration()
 
 void DownloadEngine::requestHalt()
 {
-  haltRequested_ = true;
+  haltRequested_ = std::max(haltRequested_, 1);
   requestGroupMan_->halt();
 }
 
 void DownloadEngine::requestForceHalt()
 {
-  haltRequested_ = true;
+  haltRequested_ = std::max(haltRequested_, 2);
   requestGroupMan_->forceHalt();
 }
 
diff --git a/src/DownloadEngine.h b/src/DownloadEngine.h
index 05a8b03a..d949bff6 100644
--- a/src/DownloadEngine.h
+++ b/src/DownloadEngine.h
@@ -79,7 +79,7 @@ private:
 
   SharedHandle<StatCalc> statCalc_;
 
-  bool haltRequested_;
+  int haltRequested_;
 
   class SocketPoolEntry {
   private:
@@ -230,6 +230,11 @@ public:
     return haltRequested_;
   }
 
+  bool isForceHaltRequested() const
+  {
+    return haltRequested_ >= 2;
+  }
+
   void requestHalt();
 
   void requestForceHalt();
diff --git a/src/Makefile.am b/src/Makefile.am
index bf5805b7..5388ba35 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -522,7 +522,10 @@ SRCS += PeerAbstractCommand.cc PeerAbstractCommand.h\
 	ValueBaseBencodeParser.h\
 	BencodeDiskWriter.h\
 	BencodeDiskWriterFactory.h\
-	MemoryBencodePreDownloadHandler.h
+	MemoryBencodePreDownloadHandler.h\
+	UDPTrackerClient.cc UDPTrackerClient.h\
+	UDPTrackerRequest.cc UDPTrackerRequest.h\
+	NameResolveCommand.cc NameResolveCommand.h
 endif # ENABLE_BITTORRENT
 
 if ENABLE_METALINK
diff --git a/src/NameResolveCommand.cc b/src/NameResolveCommand.cc
new file mode 100644
index 00000000..cf09ebb6
--- /dev/null
+++ b/src/NameResolveCommand.cc
@@ -0,0 +1,193 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#include "NameResolveCommand.h"
+#include "DownloadEngine.h"
+#include "NameResolver.h"
+#include "prefs.h"
+#include "message.h"
+#include "util.h"
+#include "Option.h"
+#include "RequestGroupMan.h"
+#include "Logger.h"
+#include "LogFactory.h"
+#include "fmt.h"
+#include "UDPTrackerRequest.h"
+#include "UDPTrackerClient.h"
+#include "BtRegistry.h"
+#ifdef ENABLE_ASYNC_DNS
+#include "AsyncNameResolver.h"
+#endif // ENABLE_ASYNC_DNS
+
+namespace aria2 {
+
+NameResolveCommand::NameResolveCommand
+(cuid_t cuid, DownloadEngine* e,
+ const SharedHandle<UDPTrackerRequest>& req)
+  : Command(cuid),
+    e_(e),
+    req_(req)
+{
+  setStatus(Command::STATUS_ONESHOT_REALTIME);
+}
+
+NameResolveCommand::~NameResolveCommand()
+{
+#ifdef ENABLE_ASYNC_DNS
+  disableNameResolverCheck(resolver_);
+#endif // ENABLE_ASYNC_DNS
+}
+
+bool NameResolveCommand::execute()
+{
+  // This is UDP tracker specific, but we need to keep this command
+  // alive until force shutdown is
+  // commencing. RequestGroupMan::downloadFinished() is useless here
+  // at the moment.
+  if(e_->isForceHaltRequested()) {
+    onShutdown();
+    return true;
+  }
+#ifdef ENABLE_ASYNC_DNS
+  if(!resolver_) {
+    int family = AF_INET;
+    resolver_.reset(new AsyncNameResolver(family
+#ifdef HAVE_ARES_ADDR_NODE
+                                          , e_->getAsyncDNSServers()
+#endif // HAVE_ARES_ADDR_NODE
+                                          ));
+  }
+#endif // ENABLE_ASYNC_DNS
+  std::string hostname = req_->remoteAddr;
+  std::vector<std::string> res;
+  if(util::isNumericHost(hostname)) {
+    res.push_back(hostname);
+  } else {
+#ifdef ENABLE_ASYNC_DNS
+    if(e_->getOption()->getAsBool(PREF_ASYNC_DNS)) {
+      try {
+        if(resolveHostname(hostname, resolver_)) {
+          res = resolver_->getResolvedAddresses();
+        } else {
+          e_->addCommand(this);
+          return false;
+        }
+      } catch(RecoverableException& e) {
+        A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, e);
+      }
+    } else
+#endif // ENABLE_ASYNC_DNS
+      {
+        NameResolver resolver;
+        resolver.setSocktype(SOCK_DGRAM);
+        try {
+          resolver.resolve(res, hostname);
+        } catch(RecoverableException& e) {
+          A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, e);
+        }
+      }
+  }
+  if(res.empty()) {
+    onFailure();
+  } else {
+    onSuccess(res, e_);
+  }
+  return true;
+}
+
+void NameResolveCommand::onShutdown()
+{
+  req_->state = UDPT_STA_COMPLETE;
+  req_->error = UDPT_ERR_SHUTDOWN;
+}
+
+void NameResolveCommand::onFailure()
+{
+  req_->state = UDPT_STA_COMPLETE;
+  req_->error = UDPT_ERR_NETWORK;
+}
+
+void NameResolveCommand::onSuccess
+(const std::vector<std::string>& addrs, DownloadEngine* e)
+{
+  req_->remoteAddr = addrs[0];
+  e->getBtRegistry()->getUDPTrackerClient()->addRequest(req_);
+}
+
+#ifdef ENABLE_ASYNC_DNS
+
+bool NameResolveCommand::resolveHostname
+(const std::string& hostname,
+ const SharedHandle<AsyncNameResolver>& resolver)
+{
+  switch(resolver->getStatus()) {
+  case AsyncNameResolver::STATUS_READY:
+      A2_LOG_INFO(fmt(MSG_RESOLVING_HOSTNAME,
+                      getCuid(),
+                      hostname.c_str()));
+    resolver->resolve(hostname);
+    setNameResolverCheck(resolver);
+    return false;
+  case AsyncNameResolver::STATUS_SUCCESS:
+    A2_LOG_INFO(fmt(MSG_NAME_RESOLUTION_COMPLETE,
+                    getCuid(),
+                    resolver->getHostname().c_str(),
+                    resolver->getResolvedAddresses().front().c_str()));
+    return true;
+    break;
+  case AsyncNameResolver::STATUS_ERROR:
+    throw DL_ABORT_EX
+      (fmt(MSG_NAME_RESOLUTION_FAILED,
+           getCuid(),
+           hostname.c_str(),
+           resolver->getError().c_str()));
+  default:
+    return false;
+  }
+}
+
+void NameResolveCommand::setNameResolverCheck
+(const SharedHandle<AsyncNameResolver>& resolver)
+{
+  e_->addNameResolverCheck(resolver, this);
+}
+
+void NameResolveCommand::disableNameResolverCheck
+(const SharedHandle<AsyncNameResolver>& resolver)
+{
+  e_->deleteNameResolverCheck(resolver, this);
+}
+#endif // ENABLE_ASYNC_DNS
+
+} // namespace aria2
diff --git a/src/NameResolveCommand.h b/src/NameResolveCommand.h
new file mode 100644
index 00000000..0d3aa8a8
--- /dev/null
+++ b/src/NameResolveCommand.h
@@ -0,0 +1,87 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#ifndef D_NAME_RESOLVE_COMMAND_H
+#define D_NAME_RESOLVE_COMMAND_H
+
+#include "Command.h"
+
+#include <string>
+#include <vector>
+
+#include "SharedHandle.h"
+
+// TODO Make this class generic.
+namespace aria2 {
+
+class DownloadEngine;
+#ifdef ENABLE_ASYNC_DNS
+class AsyncNameResolver;
+#endif // ENABLE_ASYNC_DNS
+class UDPTrackerRequest;
+
+class NameResolveCommand:public Command {
+private:
+  DownloadEngine* e_;
+
+#ifdef ENABLE_ASYNC_DNS
+  SharedHandle<AsyncNameResolver> resolver_;
+#endif // ENABLE_ASYNC_DNS
+
+#ifdef ENABLE_ASYNC_DNS
+  bool resolveHostname(const std::string& hostname,
+                       const SharedHandle<AsyncNameResolver>& resolver);
+
+  void setNameResolverCheck(const SharedHandle<AsyncNameResolver>& resolver);
+
+  void disableNameResolverCheck(const SharedHandle<AsyncNameResolver>& resolver);
+#endif // ENABLE_ASYNC_DNS
+
+  SharedHandle<UDPTrackerRequest> req_;
+  void onShutdown();
+  void onFailure();
+  void onSuccess
+  (const std::vector<std::string>& addrs, DownloadEngine* e);
+public:
+  NameResolveCommand(cuid_t cuid, DownloadEngine* e,
+                     const SharedHandle<UDPTrackerRequest>& req);
+
+  virtual ~NameResolveCommand();
+
+  virtual bool execute();
+};
+
+} // namespace aria2
+
+#endif // D_NAME_RESOVE_COMMAND_H
diff --git a/src/TrackerWatcherCommand.cc b/src/TrackerWatcherCommand.cc
index 0eba057f..06d7fc3e 100644
--- a/src/TrackerWatcherCommand.cc
+++ b/src/TrackerWatcherCommand.cc
@@ -63,32 +63,156 @@
 #include "a2functional.h"
 #include "util.h"
 #include "fmt.h"
+#include "UDPTrackerRequest.h"
+#include "UDPTrackerClient.h"
+#include "BtRegistry.h"
+#include "NameResolveCommand.h"
 
 namespace aria2 {
 
+HTTPAnnRequest::HTTPAnnRequest(const SharedHandle<RequestGroup>& rg)
+  : rg_(rg)
+{}
+
+HTTPAnnRequest::~HTTPAnnRequest()
+{}
+
+bool HTTPAnnRequest::stopped() const
+{
+  return rg_->getNumCommand() == 0;
+}
+
+bool HTTPAnnRequest::success() const
+{
+  return rg_->downloadFinished();
+}
+
+void HTTPAnnRequest::stop(DownloadEngine* e)
+{
+  rg_->setForceHaltRequested(true);
+}
+
+bool HTTPAnnRequest::issue(DownloadEngine* e)
+{
+  try {
+    std::vector<Command*>* commands = new std::vector<Command*>();
+    auto_delete_container<std::vector<Command*> > commandsDel(commands);
+    rg_->createInitialCommand(*commands, e);
+    e->addCommand(*commands);
+    e->setNoWait(true);
+    commands->clear();
+    A2_LOG_DEBUG("added tracker request command");
+    return true;
+  } catch(RecoverableException& ex) {
+    A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, ex);
+    return false;
+  }
+}
+
+bool HTTPAnnRequest::processResponse
+(const SharedHandle<BtAnnounce>& btAnnounce)
+{
+  try {
+    std::stringstream strm;
+    unsigned char data[2048];
+    rg_->getPieceStorage()->getDiskAdaptor()->openFile();
+    while(1) {
+      ssize_t dataLength = rg_->getPieceStorage()->
+        getDiskAdaptor()->readData(data, sizeof(data), strm.tellp());
+      if(dataLength == 0) {
+        break;
+      }
+      strm.write(reinterpret_cast<const char*>(data), dataLength);
+    }
+    std::string res = strm.str();
+    btAnnounce->processAnnounceResponse
+      (reinterpret_cast<const unsigned char*>(res.c_str()), res.size());
+    return true;
+  } catch(RecoverableException& e) {
+    A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, e);
+    return false;
+  }
+}
+
+UDPAnnRequest::UDPAnnRequest(const SharedHandle<UDPTrackerRequest>& req)
+  : req_(req)
+{}
+
+UDPAnnRequest::~UDPAnnRequest()
+{}
+
+bool UDPAnnRequest::stopped() const
+{
+  return !req_ || req_->state == UDPT_STA_COMPLETE;
+}
+
+bool UDPAnnRequest::success() const
+{
+  return req_ && req_->state == UDPT_STA_COMPLETE &&
+    req_->error == UDPT_ERR_SUCCESS;
+}
+
+void UDPAnnRequest::stop(DownloadEngine* e)
+{
+  if(req_) {
+    req_.reset();
+  }
+}
+
+bool UDPAnnRequest::issue(DownloadEngine* e)
+{
+  if(req_) {
+    NameResolveCommand* command = new NameResolveCommand
+      (e->newCUID(), e, req_);
+    e->addCommand(command);
+    e->setNoWait(true);
+    return true;
+  } else {
+    return false;
+  }
+}
+
+bool UDPAnnRequest::processResponse
+(const SharedHandle<BtAnnounce>& btAnnounce)
+{
+  if(req_) {
+    btAnnounce->processUDPTrackerResponse(req_);
+    return true;
+  } else {
+    return false;
+  }
+}
+
 TrackerWatcherCommand::TrackerWatcherCommand
 (cuid_t cuid, RequestGroup* requestGroup, DownloadEngine* e)
   : Command(cuid),
     requestGroup_(requestGroup),
-    e_(e)
+    e_(e),
+    udpTrackerClient_(e_->getBtRegistry()->getUDPTrackerClient())
 {
   requestGroup_->increaseNumCommand();
+  if(udpTrackerClient_) {
+    udpTrackerClient_->increaseWatchers();
+  }
 }
 
 TrackerWatcherCommand::~TrackerWatcherCommand()
 {
   requestGroup_->decreaseNumCommand();
+  if(udpTrackerClient_) {
+    udpTrackerClient_->decreaseWatchers();
+  }
 }
 
 bool TrackerWatcherCommand::execute() {
   if(requestGroup_->isForceHaltRequested()) {
-    if(!trackerRequestGroup_) {
+    if(!trackerRequest_) {
       return true;
-    } else if(trackerRequestGroup_->getNumCommand() == 0 ||
-              trackerRequestGroup_->downloadFinished()) {
+    } else if(trackerRequest_->stopped() ||
+              trackerRequest_->success()) {
       return true;
     } else {
-      trackerRequestGroup_->setForceHaltRequested(true);
+      trackerRequest_->stop(e_);
       e_->setRefreshInterval(0);
       e_->addCommand(this);
       return false;
@@ -98,44 +222,32 @@ bool TrackerWatcherCommand::execute() {
     A2_LOG_DEBUG("no more announce");
     return true;
   }
-  if(!trackerRequestGroup_) {
-    trackerRequestGroup_ = createAnnounce();
-    if(trackerRequestGroup_) {
-      try {
-        std::vector<Command*>* commands = new std::vector<Command*>();
-        auto_delete_container<std::vector<Command*> > commandsDel(commands);
-        trackerRequestGroup_->createInitialCommand(*commands, e_);
-        e_->addCommand(*commands);
-        commands->clear();
-        A2_LOG_DEBUG("added tracker request command");
-      } catch(RecoverableException& ex) {
-        A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, ex);
-      }
+  if(!trackerRequest_) {
+    trackerRequest_ = createAnnounce(e_);
+    if(trackerRequest_) {
+      trackerRequest_->issue(e_);
     }
-  } else if(trackerRequestGroup_->getNumCommand() == 0) {
+  } else if(trackerRequest_->stopped()) {
     // We really want to make sure that tracker request has finished
     // by checking getNumCommand() == 0. Because we reset
     // trackerRequestGroup_, if it is still used in other Command, we
     // will get Segmentation fault.
-    if(trackerRequestGroup_->downloadFinished()) {
-      try {
-        std::string trackerResponse = getTrackerResponse(trackerRequestGroup_);
-
-        processTrackerResponse(trackerResponse);
+    if(trackerRequest_->success()) {
+      if(trackerRequest_->processResponse(btAnnounce_)) {
         btAnnounce_->announceSuccess();
         btAnnounce_->resetAnnounce();
-      } catch(RecoverableException& ex) {
-        A2_LOG_ERROR_EX(EX_EXCEPTION_CAUGHT, ex);
+        addConnection();
+      } else {
         btAnnounce_->announceFailure();
         if(btAnnounce_->isAllAnnounceFailed()) {
           btAnnounce_->resetAnnounce();
         }
       }
-      trackerRequestGroup_.reset();
+      trackerRequest_.reset();
     } else {
       // handle errors here
       btAnnounce_->announceFailure(); // inside it, trackers = 0.
-      trackerRequestGroup_.reset();
+      trackerRequest_.reset();
       if(btAnnounce_->isAllAnnounceFailed()) {
         btAnnounce_->resetAnnounce();
       }
@@ -145,30 +257,8 @@ bool TrackerWatcherCommand::execute() {
   return false;
 }
 
-std::string TrackerWatcherCommand::getTrackerResponse
-(const SharedHandle<RequestGroup>& requestGroup)
+void TrackerWatcherCommand::addConnection()
 {
-  std::stringstream strm;
-  unsigned char data[2048];
-  requestGroup->getPieceStorage()->getDiskAdaptor()->openFile();
-  while(1) {
-    ssize_t dataLength = requestGroup->getPieceStorage()->
-      getDiskAdaptor()->readData(data, sizeof(data), strm.tellp());
-    if(dataLength == 0) {
-      break;
-    }
-    strm.write(reinterpret_cast<const char*>(data), dataLength);
-  }
-  return strm.str();
-}
-
-// TODO we have to deal with the exception thrown By BtAnnounce
-void TrackerWatcherCommand::processTrackerResponse
-(const std::string& trackerResponse)
-{
-  btAnnounce_->processAnnounceResponse
-    (reinterpret_cast<const unsigned char*>(trackerResponse.c_str()),
-     trackerResponse.size());
   while(!btRuntime_->isHalt() && btRuntime_->lessThanMinPeers()) {
     if(!peerStorage_->isPeerAvailable()) {
       break;
@@ -180,8 +270,8 @@ void TrackerWatcherCommand::processTrackerResponse
       break;
     }
     PeerInitiateConnectionCommand* command;
-    command = new PeerInitiateConnectionCommand(ncuid, requestGroup_, peer, e_,
-                                                btRuntime_);
+    command = new PeerInitiateConnectionCommand(ncuid, requestGroup_, peer,
+                                                e_, btRuntime_);
     command->setPeerStorage(peerStorage_);
     command->setPieceStorage(pieceStorage_);
     e_->addCommand(command);
@@ -190,13 +280,48 @@ void TrackerWatcherCommand::processTrackerResponse
   }
 }
 
-SharedHandle<RequestGroup> TrackerWatcherCommand::createAnnounce() {
-  SharedHandle<RequestGroup> rg;
-  if(btAnnounce_->isAnnounceReady()) {
-    rg = createRequestGroup(btAnnounce_->getAnnounceUrl());
-    btAnnounce_->announceStart(); // inside it, trackers++.
+SharedHandle<AnnRequest>
+TrackerWatcherCommand::createAnnounce(DownloadEngine* e)
+{
+  SharedHandle<AnnRequest> treq;
+  while(!btAnnounce_->isAllAnnounceFailed() &&
+        btAnnounce_->isAnnounceReady()) {
+    std::string uri = btAnnounce_->getAnnounceUrl();
+    uri_split_result res;
+    memset(&res, 0, sizeof(res));
+    if(uri_split(&res, uri.c_str()) == 0) {
+      // Without UDP tracker support, send it to normal tracker flow
+      // and make it fail.
+      if(udpTrackerClient_ &&
+         uri::getFieldString(res, USR_SCHEME, uri.c_str()) == "udp") {
+        uint16_t localPort;
+        localPort = e->getBtRegistry()->getUdpPort();
+        treq = createUDPAnnRequest
+          (uri::getFieldString(res, USR_HOST, uri.c_str()), res.port,
+           localPort);
+      } else {
+        treq = createHTTPAnnRequest(btAnnounce_->getAnnounceUrl());
+      }
+      btAnnounce_->announceStart(); // inside it, trackers++.
+      break;
+    } else {
+      btAnnounce_->announceFailure();
+    }
   }
-  return rg;
+  if(btAnnounce_->isAllAnnounceFailed()) {
+    btAnnounce_->resetAnnounce();
+  }
+  return treq;
+}
+
+SharedHandle<AnnRequest>
+TrackerWatcherCommand::createUDPAnnRequest(const std::string& host,
+                                           uint16_t port,
+                                           uint16_t localPort)
+{
+  SharedHandle<UDPTrackerRequest> req =
+    btAnnounce_->createUDPTrackerRequest(host, port, localPort);
+  return SharedHandle<AnnRequest>(new UDPAnnRequest(req));
 }
 
 namespace {
@@ -219,8 +344,8 @@ bool backupTrackerIsAvailable
 }
 } // namespace
 
-SharedHandle<RequestGroup>
-TrackerWatcherCommand::createRequestGroup(const std::string& uri)
+SharedHandle<AnnRequest>
+TrackerWatcherCommand::createHTTPAnnRequest(const std::string& uri)
 {
   std::vector<std::string> uris;
   uris.push_back(uri);
@@ -261,7 +386,7 @@ TrackerWatcherCommand::createRequestGroup(const std::string& uri)
   dctx->setAcceptMetalink(false);
   A2_LOG_INFO(fmt("Creating tracker request group GID#%s",
                   GroupId::toHex(rg->getGID()).c_str()));
-  return rg;
+  return SharedHandle<AnnRequest>(new HTTPAnnRequest(rg));
 }
 
 void TrackerWatcherCommand::setBtRuntime
diff --git a/src/TrackerWatcherCommand.h b/src/TrackerWatcherCommand.h
index 73887f8a..99ff91b4 100644
--- a/src/TrackerWatcherCommand.h
+++ b/src/TrackerWatcherCommand.h
@@ -50,6 +50,50 @@ class PieceStorage;
 class BtRuntime;
 class BtAnnounce;
 class Option;
+class UDPTrackerRequest;
+class UDPTrackerClient;
+
+class AnnRequest {
+public:
+  virtual ~AnnRequest() {}
+  // Returns true if tracker request is finished, regardless of the
+  // outcome.
+  virtual bool stopped() const = 0;
+  // Returns true if tracker request is successful.
+  virtual bool success() const = 0;
+  // Returns true if issuing request is successful.
+  virtual bool issue(DownloadEngine* e) = 0;
+  // Stop this request.
+  virtual void stop(DownloadEngine* e) = 0;
+  // Returns true if processing tracker response is successful.
+  virtual bool processResponse(const SharedHandle<BtAnnounce>& btAnnounce) = 0;
+};
+
+class HTTPAnnRequest:public AnnRequest {
+public:
+  HTTPAnnRequest(const SharedHandle<RequestGroup>& rg);
+  virtual ~HTTPAnnRequest();
+  virtual bool stopped() const;
+  virtual bool success() const;
+  virtual bool issue(DownloadEngine* e);
+  virtual void stop(DownloadEngine* e);
+  virtual bool processResponse(const SharedHandle<BtAnnounce>& btAnnounce);
+private:
+  SharedHandle<RequestGroup> rg_;
+};
+
+class UDPAnnRequest:public AnnRequest {
+public:
+  UDPAnnRequest(const SharedHandle<UDPTrackerRequest>& req);
+  virtual ~UDPAnnRequest();
+  virtual bool stopped() const;
+  virtual bool success() const;
+  virtual bool issue(DownloadEngine* e);
+  virtual void stop(DownloadEngine* e);
+  virtual bool processResponse(const SharedHandle<BtAnnounce>& btAnnounce);
+private:
+  SharedHandle<UDPTrackerRequest> req_;
+};
 
 class TrackerWatcherCommand : public Command
 {
@@ -58,6 +102,8 @@ private:
 
   DownloadEngine* e_;
 
+  SharedHandle<UDPTrackerClient> udpTrackerClient_;
+
   SharedHandle<PeerStorage> peerStorage_;
 
   SharedHandle<PieceStorage> pieceStorage_;
@@ -66,16 +112,20 @@ private:
 
   SharedHandle<BtAnnounce> btAnnounce_;
 
-  SharedHandle<RequestGroup> trackerRequestGroup_;
+  SharedHandle<AnnRequest> trackerRequest_;
+
   /**
    * Returns a command for announce request. Returns 0 if no announce request
    * is needed.
    */
-  SharedHandle<RequestGroup> createRequestGroup(const std::string& url);
+  SharedHandle<AnnRequest>
+  createHTTPAnnRequest(const std::string& uri);
 
-  std::string getTrackerResponse(const SharedHandle<RequestGroup>& requestGroup);
+  SharedHandle<AnnRequest>
+  createUDPAnnRequest(const std::string& host, uint16_t port,
+                      uint16_t localPort);
 
-  void processTrackerResponse(const std::string& response);
+  void addConnection();
 
   const SharedHandle<Option>& getOption() const;
 public:
@@ -85,7 +135,7 @@ public:
 
   virtual ~TrackerWatcherCommand();
 
-  SharedHandle<RequestGroup> createAnnounce();
+  SharedHandle<AnnRequest> createAnnounce(DownloadEngine* e);
 
   virtual bool execute();
 
diff --git a/src/UDPTrackerClient.cc b/src/UDPTrackerClient.cc
new file mode 100644
index 00000000..81d6e8e2
--- /dev/null
+++ b/src/UDPTrackerClient.cc
@@ -0,0 +1,616 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#include "UDPTrackerClient.h"
+
+#include "UDPTrackerRequest.h"
+#include "bittorrent_helper.h"
+#include "util.h"
+#include "LogFactory.h"
+#include "SimpleRandomizer.h"
+#include "fmt.h"
+
+namespace aria2 {
+
+UDPTrackerClient::UDPTrackerClient()
+{}
+
+namespace {
+template<typename InputIterator>
+void failRequest(InputIterator first, InputIterator last, int error)
+{
+  for(; first != last; ++first) {
+    (*first)->state = UDPT_STA_COMPLETE;
+    (*first)->error = error;
+  }
+}
+} // namespace
+
+namespace {
+int32_t generateTransactionId()
+{
+  return SimpleRandomizer::getInstance()->getRandomNumber(INT32_MAX);
+}
+} // namespace
+
+namespace {
+void logInvalidLength(const std::string& remoteAddr, uint16_t remotePort,
+                      int action, unsigned long expected, unsigned long actual)
+{
+  A2_LOG_INFO(fmt("UDPT received %s reply from %s:%u invalid length "
+                  "expected:%lu, actual:%lu",
+                  getUDPTrackerActionStr(action),
+                  remoteAddr.c_str(), remotePort, expected, actual));
+}
+} // namespace
+
+namespace {
+void logInvalidTransaction(const std::string& remoteAddr, uint16_t remotePort,
+                           int action, int32_t transactionId)
+{
+  A2_LOG_INFO(fmt("UDPT received %s reply from %s:%u invalid transaction_id=%d",
+                  getUDPTrackerActionStr(action),
+                  remoteAddr.c_str(), remotePort, transactionId));
+}
+} // namespace
+
+namespace {
+void logTooShortLength(const std::string& remoteAddr, uint16_t remotePort,
+                       int action,
+                       unsigned long minLength, unsigned long actual)
+{
+  A2_LOG_INFO(fmt("UDPT received %s reply from %s:%u length too short "
+                  "min:%lu, actual:%lu",
+                  getUDPTrackerActionStr(action),
+                  remoteAddr.c_str(), remotePort, minLength, actual));
+}
+} // namespace
+
+UDPTrackerClient::~UDPTrackerClient()
+{
+  // Make all contained requests fail
+  int error = UDPT_ERR_SHUTDOWN;
+  failRequest(inflightRequests_.begin(), inflightRequests_.end(), error);
+  failRequest(pendingRequests_.begin(), pendingRequests_.end(), error);
+  failRequest(connectRequests_.begin(), connectRequests_.end(), error);
+}
+
+namespace {
+struct CollectAddrPortMatch {
+  bool operator()(const SharedHandle<UDPTrackerRequest>& req) const
+  {
+    if(req->remoteAddr == remoteAddr && req->remotePort == remotePort) {
+      dest.push_back(req);
+      return true;
+    } else {
+      return false;
+    }
+  }
+  std::vector<SharedHandle<UDPTrackerRequest> >& dest;
+  std::string remoteAddr;
+  uint16_t remotePort;
+  CollectAddrPortMatch(std::vector<SharedHandle<UDPTrackerRequest> >& dest,
+                       const std::string& remoteAddr, uint16_t remotePort)
+    : dest(dest), remoteAddr(remoteAddr), remotePort(remotePort)
+  {}
+};
+} // namespace
+
+int UDPTrackerClient::receiveReply
+(const unsigned char* data, size_t length, const std::string& remoteAddr,
+ uint16_t remotePort, const Timer& now)
+{
+  int32_t action = bittorrent::getIntParam(data, 0);
+  switch(action) {
+  case UDPT_ACT_CONNECT: {
+    if(length != 16) {
+      logInvalidLength(remoteAddr, remotePort, action, 16, length);
+      return -1;
+    }
+    int32_t transactionId = bittorrent::getIntParam(data, 4);
+    SharedHandle<UDPTrackerRequest> req =
+      findInflightRequest(remoteAddr, remotePort, transactionId, true);
+    if(!req) {
+      logInvalidTransaction(remoteAddr, remotePort, action, transactionId);
+      return -1;
+    }
+    req->state = UDPT_STA_COMPLETE;
+
+    int64_t connectionId = bittorrent::getLLIntParam(data, 8);
+    A2_LOG_INFO(fmt("UDPT received CONNECT reply from %s:%u transaction_id=%u,"
+                    "connection_id=%"PRId64, remoteAddr.c_str(), remotePort,
+                    transactionId, connectionId));
+    UDPTrackerConnection c(UDPT_CST_CONNECTED, connectionId, now);
+    connectionIdCache_[std::make_pair(remoteAddr, remotePort)] = c;
+    // Now we have connecion ID, push requests which are waiting for
+    // it.
+    std::vector<SharedHandle<UDPTrackerRequest> > reqs;
+    connectRequests_.erase(std::remove_if
+                           (connectRequests_.begin(), connectRequests_.end(),
+                            CollectAddrPortMatch(reqs, remoteAddr, remotePort)),
+                           connectRequests_.end());
+    pendingRequests_.insert(pendingRequests_.begin(),
+                            reqs.begin(), reqs.end());
+    break;
+  }
+  case UDPT_ACT_ANNOUNCE: {
+    if(length < 20) {
+      logTooShortLength(remoteAddr, remotePort, action, 20, length);
+      return - 1;
+    }
+    int32_t transactionId = bittorrent::getIntParam(data, 4);
+    SharedHandle<UDPTrackerRequest> req =
+      findInflightRequest(remoteAddr, remotePort, transactionId, true);
+    if(!req) {
+      logInvalidTransaction(remoteAddr, remotePort, action, transactionId);
+      return -1;
+    }
+    req->state = UDPT_STA_COMPLETE;
+
+    req->reply.reset(new UDPTrackerReply());
+    req->reply->action = action;
+    req->reply->transactionId = transactionId;
+    req->reply->interval = bittorrent::getIntParam(data, 8);
+    req->reply->leechers = bittorrent::getIntParam(data, 12);
+    req->reply->seeders = bittorrent::getIntParam(data, 16);
+
+    int numPeers = 0;
+    for(size_t i = 20; i < length; i += 6) {
+      std::pair<std::string, uint16_t> hostport =
+        bittorrent::unpackcompact(data+i, AF_INET);
+      if(!hostport.first.empty()) {
+        req->reply->peers.push_back(hostport);
+        ++numPeers;
+      }
+    }
+
+    A2_LOG_INFO(fmt("UDPT received ANNOUNCE reply from %s:%u transaction_id=%u,"
+                    "connection_id=%"PRId64", event=%s, infohash=%s, "
+                    "interval=%d, leechers=%d, "
+                    "seeders=%d, num_peers=%d", remoteAddr.c_str(), remotePort,
+                    transactionId, req->connectionId,
+                    getUDPTrackerEventStr(req->event),
+                    util::toHex(req->infohash).c_str(),
+                    req->reply->interval, req->reply->leechers,
+                    req->reply->seeders, numPeers));
+    break;
+  }
+  case UDPT_ACT_ERROR: {
+    if(length < 8) {
+      logTooShortLength(remoteAddr, remotePort, action, 8, length);
+      return -1;
+    }
+    int32_t transactionId = bittorrent::getIntParam(data, 4);
+    SharedHandle<UDPTrackerRequest> req =
+      findInflightRequest(remoteAddr, remotePort, transactionId, true);
+    if(!req) {
+      logInvalidTransaction(remoteAddr, remotePort, action, transactionId);
+      return -1;
+    }
+    std::string errorString(data+8, data+length);
+    errorString = util::encodeNonUtf8(errorString);
+
+    req->state = UDPT_STA_COMPLETE;
+    req->error = UDPT_ERR_TRACKER;
+
+    A2_LOG_INFO(fmt("UDPT received ERROR reply from %s:%u transaction_id=%u,"
+                    "connection_id=%"PRId64", action=%d, error_string=%s",
+                    remoteAddr.c_str(),
+                    remotePort, transactionId, req->connectionId, action,
+                    errorString.c_str()));
+    if(req->action == UDPT_ACT_CONNECT) {
+      failConnect(req->remoteAddr, req->remotePort, UDPT_ERR_TRACKER);
+    }
+    break;
+  }
+  case UDPT_ACT_SCRAPE:
+    A2_LOG_INFO("unexpected scrape action reply");
+    return -1;
+  default:
+    A2_LOG_INFO("unknown action reply");
+    return -1;
+  }
+  return 0;
+}
+
+ssize_t UDPTrackerClient::createRequest
+(unsigned char* data, size_t length, std::string& remoteAddr,
+ uint16_t& remotePort, const Timer& now)
+{
+  if(pendingRequests_.empty()) {
+    return -1;
+  }
+  while(!pendingRequests_.empty()) {
+    const SharedHandle<UDPTrackerRequest>& req = pendingRequests_.front();
+    if(req->action == UDPT_ACT_CONNECT) {
+      ssize_t rv;
+      rv = createUDPTrackerConnect(data, length, remoteAddr, remotePort, req);
+      return rv;
+    }
+    UDPTrackerConnection* c = getConnectionId(req->remoteAddr,
+                                              req->remotePort,
+                                              now);
+    if(!c) {
+      SharedHandle<UDPTrackerRequest> creq(new UDPTrackerRequest());
+      creq->action = UDPT_ACT_CONNECT;
+      creq->remoteAddr = req->remoteAddr;
+      creq->remotePort = req->remotePort;
+      creq->transactionId = generateTransactionId();
+      pendingRequests_.push_front(creq);
+      ssize_t rv;
+      rv = createUDPTrackerConnect(data, length, remoteAddr, remotePort, creq);
+      return rv;
+    }
+    if(c->state == UDPT_CST_CONNECTING) {
+      connectRequests_.push_back(req);
+      pendingRequests_.pop_front();
+      continue;
+    }
+    req->connectionId = c->connectionId;
+    req->transactionId = generateTransactionId();
+    ssize_t rv;
+    rv = createUDPTrackerAnnounce(data, length, remoteAddr, remotePort, req);
+    return rv;
+  }
+  return -1;
+}
+
+void UDPTrackerClient::requestSent(const Timer& now)
+{
+  if(pendingRequests_.empty()) {
+    A2_LOG_WARN("pendingRequests_ is empty");
+    return;
+  }
+  const SharedHandle<UDPTrackerRequest>& req = pendingRequests_.front();
+  switch(req->action) {
+  case UDPT_ACT_CONNECT:
+    A2_LOG_INFO(fmt("UDPT sent CONNECT to %s:%u transaction_id=%u",
+                    req->remoteAddr.c_str(), req->remotePort,
+                    req->transactionId));
+    break;
+  case UDPT_ACT_ANNOUNCE:
+    A2_LOG_INFO(fmt("UDPT sent ANNOUNCE to %s:%u transaction_id=%u, "
+                    "connection_id=%"PRId64", event=%s, infohash=%s",
+                    req->remoteAddr.c_str(), req->remotePort,
+                    req->transactionId, req->connectionId,
+                    getUDPTrackerEventStr(req->event),
+                    util::toHex(req->infohash).c_str()));
+    break;
+  default:
+    // unreachable
+    assert(0);
+  }
+  req->dispatched = now;
+  switch(req->action) {
+  case UDPT_ACT_CONNECT: {
+    connectionIdCache_[std::make_pair(req->remoteAddr, req->remotePort)]
+      = UDPTrackerConnection();
+    break;
+  }
+  }
+  inflightRequests_.push_back(req);
+  pendingRequests_.pop_front();
+}
+
+void UDPTrackerClient::requestFail(int error)
+{
+  if(pendingRequests_.empty()) {
+    A2_LOG_WARN("pendingRequests_ is empty");
+    return;
+  }
+  const SharedHandle<UDPTrackerRequest>& req = pendingRequests_.front();
+  switch(req->action) {
+  case UDPT_ACT_CONNECT:
+    A2_LOG_INFO(fmt("UDPT fail CONNECT to %s:%u transaction_id=%u",
+                    req->remoteAddr.c_str(), req->remotePort,
+                    req->transactionId));
+    failConnect(req->remoteAddr, req->remotePort, error);
+    break;
+  case UDPT_ACT_ANNOUNCE:
+    A2_LOG_INFO(fmt("UDPT fail ANNOUNCE to %s:%u transaction_id=%u, "
+                    "connection_id=%"PRId64", event=%s, infohash=%s",
+                    req->remoteAddr.c_str(), req->remotePort,
+                    req->transactionId, req->connectionId,
+                    getUDPTrackerEventStr(req->event),
+                    util::toHex(req->infohash).c_str()));
+    break;
+  default:
+    // unreachable
+    assert(0);
+  }
+  req->state = UDPT_STA_COMPLETE;
+  req->error = error;
+  pendingRequests_.pop_front();
+}
+
+void UDPTrackerClient::addRequest(const SharedHandle<UDPTrackerRequest>& req)
+{
+  req->state = UDPT_STA_PENDING;
+  req->error = UDPT_ERR_SUCCESS;
+  pendingRequests_.push_back(req);
+}
+
+namespace {
+struct TimeoutCheck {
+  bool operator()(const SharedHandle<UDPTrackerRequest>& req) const
+  {
+    int t = req->dispatched.difference(now);
+    if(req->failCount == 0) {
+      if(t >= 15) {
+        switch(req->action) {
+        case UDPT_ACT_CONNECT:
+          A2_LOG_INFO(fmt("UDPT resend CONNECT to %s:%u transaction_id=%u",
+                          req->remoteAddr.c_str(), req->remotePort,
+                          req->transactionId));
+          break;
+        case  UDPT_ACT_ANNOUNCE:
+          A2_LOG_INFO(fmt("UDPT resend ANNOUNCE to %s:%u transaction_id=%u, "
+                          "connection_id=%"PRId64", event=%s, infohash=%s",
+                          req->remoteAddr.c_str(), req->remotePort,
+                          req->transactionId, req->connectionId,
+                          getUDPTrackerEventStr(req->event),
+                          util::toHex(req->infohash).c_str()));
+          break;
+        default:
+          // unreachable
+          assert(0);
+        }
+        ++req->failCount;
+        dest.push_back(req);
+        return true;
+      } else {
+        return false;
+      }
+    } else {
+      if(t >= 60) {
+        switch(req->action) {
+        case UDPT_ACT_CONNECT:
+          A2_LOG_INFO(fmt("UDPT timeout CONNECT to %s:%u transaction_id=%u",
+                          req->remoteAddr.c_str(), req->remotePort,
+                          req->transactionId));
+          client->failConnect(req->remoteAddr, req->remotePort,
+                              UDPT_ERR_TIMEOUT);
+          break;
+        case UDPT_ACT_ANNOUNCE:
+          A2_LOG_INFO(fmt("UDPT timeout ANNOUNCE to %s:%u transaction_id=%u, "
+                          "connection_id=%"PRId64", event=%s, infohash=%s",
+                          req->remoteAddr.c_str(), req->remotePort,
+                          req->transactionId, req->connectionId,
+                          getUDPTrackerEventStr(req->event),
+                          util::toHex(req->infohash).c_str()));
+          break;
+        default:
+          // unreachable
+          assert(0);
+        }
+        ++req->failCount;
+        req->state = UDPT_STA_COMPLETE;
+        req->error = UDPT_ERR_TIMEOUT;
+        return true;
+      } else {
+        return false;
+      }
+    }
+  }
+  std::vector<SharedHandle<UDPTrackerRequest> >& dest;
+  UDPTrackerClient* client;
+  const Timer& now;
+  TimeoutCheck(std::vector<SharedHandle<UDPTrackerRequest> >& dest,
+               UDPTrackerClient* client,
+               const Timer& now)
+    : dest(dest), client(client), now(now)
+  {}
+};
+} // namespace
+
+void UDPTrackerClient::handleTimeout(const Timer& now)
+{
+  std::vector<SharedHandle<UDPTrackerRequest> > dest;
+  inflightRequests_.erase(std::remove_if(inflightRequests_.begin(),
+                                         inflightRequests_.end(),
+                                         TimeoutCheck(dest, this, now)),
+                          inflightRequests_.end());
+  pendingRequests_.insert(pendingRequests_.begin(), dest.begin(), dest.end());
+}
+
+SharedHandle<UDPTrackerRequest> UDPTrackerClient::findInflightRequest
+(const std::string& remoteAddr, uint16_t remotePort, int32_t transactionId,
+ bool remove)
+{
+  SharedHandle<UDPTrackerRequest> res;
+  for(std::deque<SharedHandle<UDPTrackerRequest> >::iterator i =
+        inflightRequests_.begin(), eoi = inflightRequests_.end(); i != eoi;
+      ++i) {
+    if((*i)->remoteAddr == remoteAddr && (*i)->remotePort == remotePort &&
+       (*i)->transactionId == transactionId) {
+      res = *i;
+      if(remove) {
+        inflightRequests_.erase(i);
+      }
+      break;
+    }
+  }
+  return res;
+}
+
+UDPTrackerConnection* UDPTrackerClient::getConnectionId
+(const std::string& remoteAddr, uint16_t remotePort, const Timer& now)
+{
+  std::map<std::pair<std::string, uint16_t>,
+           UDPTrackerConnection>::iterator i =
+    connectionIdCache_.find(std::make_pair(remoteAddr, remotePort));
+  if(i == connectionIdCache_.end()) {
+    return 0;
+  }
+  if((*i).second.state == UDPT_CST_CONNECTED &&
+     (*i).second.lastUpdated.difference(now) > 60) {
+    connectionIdCache_.erase(i);
+    return 0;
+  } else {
+    return &(*i).second;
+  }
+}
+
+namespace {
+struct FailConnectDelete {
+  bool operator()(const SharedHandle<UDPTrackerRequest>& req) const
+  {
+    if(req->action == UDPT_ACT_ANNOUNCE &&
+       req->remoteAddr == remoteAddr && req->remotePort == remotePort) {
+      A2_LOG_INFO(fmt("Force fail infohash=%s",
+                      util::toHex(req->infohash).c_str()));
+      req->state = UDPT_STA_COMPLETE;
+      req->error = error;
+      return true;
+    } else {
+      return false;
+    }
+  }
+  std::string remoteAddr;
+  uint16_t remotePort;
+  int error;
+  FailConnectDelete(const std::string& remoteAddr, uint16_t remotePort,
+                    int error)
+    : remoteAddr(remoteAddr), remotePort(remotePort), error(error)
+  {}
+};
+} // namespace
+
+void UDPTrackerClient::failConnect(const std::string& remoteAddr,
+                                   uint16_t remotePort, int error)
+{
+  connectionIdCache_.erase(std::make_pair(remoteAddr, remotePort));
+  // Fail all requests which are waiting for connecion ID of the host.
+  connectRequests_.erase(std::remove_if(connectRequests_.begin(),
+                                        connectRequests_.end(),
+                                        FailConnectDelete
+                                        (remoteAddr, remotePort, error)),
+                         connectRequests_.end());
+  pendingRequests_.erase(std::remove_if(pendingRequests_.begin(),
+                                        pendingRequests_.end(),
+                                        FailConnectDelete
+                                        (remoteAddr, remotePort, error)),
+                         pendingRequests_.end());
+}
+
+void UDPTrackerClient::failAll()
+{
+  int error = UDPT_ERR_SHUTDOWN;
+  failRequest(inflightRequests_.begin(), inflightRequests_.end(), error);
+  failRequest(pendingRequests_.begin(), pendingRequests_.end(), error);
+  failRequest(connectRequests_.begin(), connectRequests_.end(), error);
+}
+
+void UDPTrackerClient::increaseWatchers()
+{
+  ++numWatchers_;
+}
+
+void UDPTrackerClient::decreaseWatchers()
+{
+  --numWatchers_;
+}
+
+ssize_t createUDPTrackerConnect
+(unsigned char* data, size_t length,
+ std::string& remoteAddr, uint16_t& remotePort,
+ const SharedHandle<UDPTrackerRequest>& req)
+{
+  assert(length >= 16);
+  remoteAddr = req->remoteAddr;
+  remotePort = req->remotePort;
+  bittorrent::setLLIntParam(data, UDPT_INITIAL_CONNECTION_ID);
+  bittorrent::setIntParam(data+8, req->action);
+  bittorrent::setIntParam(data+12, req->transactionId);
+  return 16;
+}
+
+ssize_t createUDPTrackerAnnounce
+(unsigned char* data, size_t length,
+ std::string& remoteAddr, uint16_t& remotePort,
+ const SharedHandle<UDPTrackerRequest>& req)
+{
+  assert(length >= 100);
+  remoteAddr = req->remoteAddr;
+  remotePort = req->remotePort;
+  bittorrent::setLLIntParam(data, req->connectionId);
+  bittorrent::setIntParam(data+8, req->action);
+  bittorrent::setIntParam(data+12, req->transactionId);
+  memcpy(data+16, req->infohash.c_str(), req->infohash.size());
+  memcpy(data+36, req->peerId.c_str(), req->peerId.size());
+  bittorrent::setLLIntParam(data+56, req->downloaded);
+  bittorrent::setLLIntParam(data+64, req->left);
+  bittorrent::setLLIntParam(data+72, req->uploaded);
+  bittorrent::setIntParam(data+80, req->event);
+  // ip is already network-byte order
+  memcpy(data+84, &req->ip, sizeof(req->ip));
+  bittorrent::setIntParam(data+88, req->key);
+  bittorrent::setIntParam(data+92, req->numWant);
+  bittorrent::setShortIntParam(data+96, req->port);
+  // extensions is always 0
+  bittorrent::setShortIntParam(data+98, 0);
+  return 100;
+}
+
+const char* getUDPTrackerActionStr(int action)
+{
+  switch(action) {
+  case UDPT_ACT_CONNECT:
+    return "CONNECT";
+  case UDPT_ACT_ANNOUNCE:
+    return "ANNOUNCE";
+  case UDPT_ACT_ERROR:
+    return "ERROR";
+  default:
+    return "(unknown)";
+  }
+}
+
+const char* getUDPTrackerEventStr(int event)
+{
+  switch(event) {
+  case UDPT_EVT_NONE:
+    return "NONE";
+  case UDPT_EVT_COMPLETED:
+    return "COMPLETED";
+  case UDPT_EVT_STARTED:
+    return "STARTED";
+  case UDPT_EVT_STOPPED:
+    return "STOPPED";
+  default:
+    return "(unknown)";
+  }
+}
+
+} // namespace aria2
diff --git a/src/UDPTrackerClient.h b/src/UDPTrackerClient.h
new file mode 100644
index 00000000..a1e9fc9a
--- /dev/null
+++ b/src/UDPTrackerClient.h
@@ -0,0 +1,171 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#ifndef D_UDP_TRACKER_CLIENT_H
+#define D_UDP_TRACKER_CLIENT_H
+
+#include "common.h"
+
+#include <string>
+#include <deque>
+#include <map>
+
+#include "SharedHandle.h"
+#include "TimerA2.h"
+
+namespace aria2 {
+
+#define UDPT_INITIAL_CONNECTION_ID 0x41727101980LL
+
+class UDPTrackerRequest;
+
+enum UDPTrackerConnectionState {
+  UDPT_CST_CONNECTING,
+  UDPT_CST_CONNECTED
+};
+
+struct UDPTrackerConnection {
+  int state;
+  int64_t connectionId;
+  Timer lastUpdated;
+  UDPTrackerConnection()
+    : state(UDPT_CST_CONNECTING),
+      connectionId(UDPT_INITIAL_CONNECTION_ID),
+      lastUpdated(0)
+  {}
+  UDPTrackerConnection(int state, int64_t connectionId,
+                       const Timer& lastUpdated)
+    : state(state),
+      connectionId(connectionId),
+      lastUpdated(lastUpdated)
+  {}
+};
+
+class UDPTrackerClient {
+public:
+  UDPTrackerClient();
+  ~UDPTrackerClient();
+
+  int receiveReply
+  (const unsigned char* data, size_t length, const std::string& remoteAddr,
+   uint16_t remotePort, const Timer& now);
+
+  // Creates data frame for the next pending request. This function
+  // always processes first entry of pendingRequests_.  If the data is
+  // sent successfully, call requestSent(). Otherwise call
+  // requestFail().
+  ssize_t createRequest
+  (unsigned char* data, size_t length, std::string& remoteAddr,
+   uint16_t& remotePort, const Timer& now);
+
+  // Tells this object that first entry of pendingRequests_ is
+  // successfully sent.
+  void requestSent(const Timer& now);
+  // Tells this object that first entry of pendingRequests_ is not
+  // successfully sent. The |error| should indicate error situation.
+  void requestFail(int error);
+
+  void addRequest(const SharedHandle<UDPTrackerRequest>& req);
+
+  // Handles timeout for inflight requests.
+  void handleTimeout(const Timer& now);
+
+  const std::deque<SharedHandle<UDPTrackerRequest> >&
+  getPendingRequests() const
+  {
+    return pendingRequests_;
+  }
+  const std::deque<SharedHandle<UDPTrackerRequest> >&
+  getConnectRequests() const
+  {
+    return connectRequests_;
+  }
+  const std::deque<SharedHandle<UDPTrackerRequest> >&
+  getInflightRequests() const
+  {
+    return inflightRequests_;
+  }
+
+  bool noRequest() const
+  {
+    return pendingRequests_.empty() && connectRequests_.empty() &&
+      getInflightRequests().empty();
+  }
+
+  // Makes all contained requests fail.
+  void failAll();
+
+  int getNumWatchers() const
+  {
+    return numWatchers_;
+  }
+
+  void increaseWatchers();
+  void decreaseWatchers();
+
+  // Actually private function, but made public, to be used by unnamed
+  // function.
+  void failConnect(const std::string& remoteAddr, uint16_t remotePort,
+                   int error);
+private:
+  SharedHandle<UDPTrackerRequest> findInflightRequest
+  (const std::string& remoteAddr, uint16_t remotePort, int32_t transactionId,
+   bool remove);
+
+  UDPTrackerConnection* getConnectionId
+  (const std::string& remoteAddr, uint16_t remotePort, const Timer& now);
+
+  std::map<std::pair<std::string, uint16_t>,
+           UDPTrackerConnection> connectionIdCache_;
+  std::deque<SharedHandle<UDPTrackerRequest> > inflightRequests_;
+  std::deque<SharedHandle<UDPTrackerRequest> > pendingRequests_;
+  std::deque<SharedHandle<UDPTrackerRequest> > connectRequests_;
+  int numWatchers_;
+};
+
+ssize_t createUDPTrackerConnect
+(unsigned char* data, size_t length, std::string& remoteAddr,
+ uint16_t& remotePort, const SharedHandle<UDPTrackerRequest>& req);
+
+ssize_t createUDPTrackerAnnounce
+(unsigned char* data, size_t length, std::string& remoteAddr,
+ uint16_t& remotePort, const SharedHandle<UDPTrackerRequest>& req);
+
+const char* getUDPTrackerActionStr(int action);
+
+const char* getUDPTrackerEventStr(int event);
+
+} // namespace aria2
+
+#endif // D_UDP_TRACKER_CLIENT_H
diff --git a/src/UDPTrackerRequest.cc b/src/UDPTrackerRequest.cc
new file mode 100644
index 00000000..94ae0f47
--- /dev/null
+++ b/src/UDPTrackerRequest.cc
@@ -0,0 +1,51 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#include "UDPTrackerRequest.h"
+
+namespace aria2 {
+
+UDPTrackerReply::UDPTrackerReply()
+  : action(0), transactionId(0), interval(0), leechers(0), seeders(0)
+{}
+
+UDPTrackerRequest::UDPTrackerRequest()
+  : remotePort(0), action(UDPT_ACT_CONNECT), transactionId(0), downloaded(0),
+    left(0), uploaded(0), event(UDPT_EVT_NONE), ip(0), key(0), numWant(0),
+    port(0), extensions(0), state(UDPT_STA_PENDING), error(UDPT_ERR_SUCCESS),
+    dispatched(0),
+    failCount(0)
+{}
+
+} // namespace aria2
diff --git a/src/UDPTrackerRequest.h b/src/UDPTrackerRequest.h
new file mode 100644
index 00000000..8012b182
--- /dev/null
+++ b/src/UDPTrackerRequest.h
@@ -0,0 +1,112 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Tatsuhiro Tsujikawa
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#ifndef D_UDP_TRACKER_REQUEST_H
+#define D_UDP_TRACKER_REQUEST_H
+
+#include "common.h"
+
+#include <string>
+#include <vector>
+
+#include "SharedHandle.h"
+#include "TimerA2.h"
+
+namespace aria2 {
+
+enum UDPTrackerAction {
+  UDPT_ACT_CONNECT = 0,
+  UDPT_ACT_ANNOUNCE = 1,
+  UDPT_ACT_SCRAPE = 2,
+  UDPT_ACT_ERROR = 3
+};
+
+enum UDPTrackerError {
+  UDPT_ERR_SUCCESS,
+  UDPT_ERR_TRACKER,
+  UDPT_ERR_TIMEOUT,
+  UDPT_ERR_NETWORK,
+  UDPT_ERR_SHUTDOWN
+};
+
+enum UDPTrackerState {
+  UDPT_STA_PENDING,
+  UDPT_STA_COMPLETE
+};
+
+enum UDPTrackerEvent {
+  UDPT_EVT_NONE = 0,
+  UDPT_EVT_COMPLETED = 1,
+  UDPT_EVT_STARTED = 2,
+  UDPT_EVT_STOPPED = 3
+};
+
+struct UDPTrackerReply {
+  int32_t action;
+  int32_t transactionId;
+  int32_t interval;
+  int32_t leechers;
+  int32_t seeders;
+  std::vector<std::pair<std::string, uint16_t> > peers;
+  UDPTrackerReply();
+};
+
+struct UDPTrackerRequest {
+  std::string remoteAddr;
+  uint16_t remotePort;
+  int64_t connectionId;
+  int32_t action;
+  int32_t transactionId;
+  std::string infohash;
+  std::string peerId;
+  int64_t downloaded;
+  int64_t left;
+  int64_t uploaded;
+  int32_t event;
+  uint32_t ip;
+  uint32_t key;
+  int32_t numWant;
+  uint16_t port;
+  uint16_t extensions;
+  int state;
+  int error;
+  Timer dispatched;
+  int failCount;
+  SharedHandle<UDPTrackerReply> reply;
+  UDPTrackerRequest();
+};
+
+} // namespace aria2
+
+#endif // D_UDP_TRACKER_REQUEST_H
diff --git a/src/bittorrent_helper.cc b/src/bittorrent_helper.cc
index f24f4ae7..7924b2db 100644
--- a/src/bittorrent_helper.cc
+++ b/src/bittorrent_helper.cc
@@ -731,6 +731,13 @@ uint8_t getId(const unsigned char* msg)
   return msg[0];
 }
 
+uint64_t getLLIntParam(const unsigned char* msg, size_t pos)
+{
+  uint64_t nParam;
+  memcpy(&nParam, msg+pos, sizeof(nParam));
+  return ntoh64(nParam);
+}
+
 uint32_t getIntParam(const unsigned char* msg, size_t pos)
 {
   uint32_t nParam;
@@ -798,6 +805,12 @@ void checkBitfield
   }
 }
 
+void setLLIntParam(unsigned char* dest, uint64_t param)
+{
+  uint64_t nParam = hton64(param);
+  memcpy(dest, &nParam, sizeof(nParam));
+}
+
 void setIntParam(unsigned char* dest, uint32_t param)
 {
   uint32_t nParam = htonl(param);
diff --git a/src/bittorrent_helper.h b/src/bittorrent_helper.h
index a8cef945..95d0d6a6 100644
--- a/src/bittorrent_helper.h
+++ b/src/bittorrent_helper.h
@@ -160,6 +160,11 @@ getInfoHash(const SharedHandle<DownloadContext>& downloadContext);
 std::string
 getInfoHashString(const SharedHandle<DownloadContext>& downloadContext);
 
+// Returns 8bytes unsigned integer located at offset pos.  The integer
+// in msg is network byte order. This function converts it into host
+// byte order and returns it.
+uint64_t getLLIntParam(const unsigned char* msg, size_t pos);
+
 // Returns 4bytes unsigned integer located at offset pos.  The integer
 // in msg is network byte order. This function converts it into host
 // byte order and returns it.
@@ -170,6 +175,10 @@ uint32_t getIntParam(const unsigned char* msg, size_t pos);
 // byte order and returns it.
 uint16_t getShortIntParam(const unsigned char* msg, size_t pos);
 
+// Put param at location pointed by dest. param is converted into
+// network byte order.
+void setLLIntParam(unsigned char* dest, uint64_t param);
+
 // Put param at location pointed by dest. param is converted into
 // network byte order.
 void setIntParam(unsigned char* dest, uint32_t param);
diff --git a/test/BtRegistryTest.cc b/test/BtRegistryTest.cc
index 71b408ac..b66557bf 100644
--- a/test/BtRegistryTest.cc
+++ b/test/BtRegistryTest.cc
@@ -11,6 +11,7 @@
 #include "BtRuntime.h"
 #include "FileEntry.h"
 #include "bittorrent_helper.h"
+#include "UDPTrackerRequest.h"
 
 namespace aria2 {
 
diff --git a/test/DefaultBtAnnounceTest.cc b/test/DefaultBtAnnounceTest.cc
index edc4c52c..952853ac 100644
--- a/test/DefaultBtAnnounceTest.cc
+++ b/test/DefaultBtAnnounceTest.cc
@@ -18,6 +18,8 @@
 #include "DownloadContext.h"
 #include "bittorrent_helper.h"
 #include "array_fun.h"
+#include "UDPTrackerRequest.h"
+#include "SocketCore.h"
 
 namespace aria2 {
 
@@ -34,6 +36,7 @@ class DefaultBtAnnounceTest:public CppUnit::TestFixture {
   CPPUNIT_TEST(testProcessAnnounceResponse_malformed);
   CPPUNIT_TEST(testProcessAnnounceResponse_failureReason);
   CPPUNIT_TEST(testProcessAnnounceResponse);
+  CPPUNIT_TEST(testProcessUDPTrackerResponse);
   CPPUNIT_TEST_SUITE_END();
 private:
   SharedHandle<DownloadContext> dctx_;
@@ -87,6 +90,7 @@ public:
   void testProcessAnnounceResponse_malformed();
   void testProcessAnnounceResponse_failureReason();
   void testProcessAnnounceResponse();
+  void testProcessUDPTrackerResponse();
 };
 
 
@@ -197,24 +201,49 @@ void DefaultBtAnnounceTest::testGetAnnounceUrl()
   btAnnounce.setBtRuntime(btRuntime_);
   btAnnounce.setRandomizer(SharedHandle<Randomizer>(new FixedNumberRandomizer()));
   btAnnounce.setTcpPort(6989);
+  SharedHandle<UDPTrackerRequest> req;
 
   CPPUNIT_ASSERT_EQUAL(std::string("http://localhost/announce?info_hash=%01%23Eg%89%AB%CD%EF%01%23Eg%89%AB%CD%EF%01%23Eg&peer_id=%2Daria2%2Dultrafastdltl&uploaded=1572864&downloaded=1310720&left=1572864&compact=1&key=fastdltl&numwant=50&no_peer_id=1&port=6989&event=started&supportcrypto=1"), btAnnounce.getAnnounceUrl());
+  req = btAnnounce.createUDPTrackerRequest("localhost", 80, 6989);
+  CPPUNIT_ASSERT_EQUAL(std::string("localhost"), req->remoteAddr);
+  CPPUNIT_ASSERT_EQUAL((uint16_t)80, req->remotePort);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE, req->action);
+  CPPUNIT_ASSERT_EQUAL(bittorrent::getInfoHashString(dctx_),
+                       util::toHex(req->infohash));
+  CPPUNIT_ASSERT_EQUAL(std::string("-aria2-ultrafastdltl"), req->peerId);
+  CPPUNIT_ASSERT_EQUAL((int64_t)1310720, req->downloaded);
+  CPPUNIT_ASSERT_EQUAL((int64_t)1572864, req->left);
+  CPPUNIT_ASSERT_EQUAL((int64_t)1572864, req->uploaded);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_EVT_STARTED, req->event);
+  CPPUNIT_ASSERT_EQUAL((uint32_t)0, req->ip);
+  CPPUNIT_ASSERT_EQUAL((int32_t)50, req->numWant);
+  CPPUNIT_ASSERT_EQUAL((uint16_t)6989, req->port);
+  CPPUNIT_ASSERT_EQUAL((uint16_t)0, req->extensions);
 
   btAnnounce.announceSuccess();
 
   CPPUNIT_ASSERT_EQUAL(std::string("http://localhost/announce?info_hash=%01%23Eg%89%AB%CD%EF%01%23Eg%89%AB%CD%EF%01%23Eg&peer_id=%2Daria2%2Dultrafastdltl&uploaded=1572864&downloaded=1310720&left=1572864&compact=1&key=fastdltl&numwant=50&no_peer_id=1&port=6989&supportcrypto=1"), btAnnounce.getAnnounceUrl());
+  req = btAnnounce.createUDPTrackerRequest("localhost", 80, 6989);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE, req->action);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_EVT_NONE, req->event);
 
   btAnnounce.announceSuccess();
 
   pieceStorage_->setAllDownloadFinished(true);
 
   CPPUNIT_ASSERT_EQUAL(std::string("http://localhost/announce?info_hash=%01%23Eg%89%AB%CD%EF%01%23Eg%89%AB%CD%EF%01%23Eg&peer_id=%2Daria2%2Dultrafastdltl&uploaded=1572864&downloaded=1310720&left=1572864&compact=1&key=fastdltl&numwant=50&no_peer_id=1&port=6989&event=completed&supportcrypto=1"), btAnnounce.getAnnounceUrl());
+  req = btAnnounce.createUDPTrackerRequest("localhost", 80, 6989);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE, req->action);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_EVT_COMPLETED, req->event);
 
   btAnnounce.announceSuccess();
 
   btRuntime_->setHalt(true);
 
   CPPUNIT_ASSERT_EQUAL(std::string("http://localhost/announce?info_hash=%01%23Eg%89%AB%CD%EF%01%23Eg%89%AB%CD%EF%01%23Eg&peer_id=%2Daria2%2Dultrafastdltl&uploaded=1572864&downloaded=1310720&left=1572864&compact=1&key=fastdltl&numwant=0&no_peer_id=1&port=6989&event=stopped&supportcrypto=1"), btAnnounce.getAnnounceUrl());
+  req = btAnnounce.createUDPTrackerRequest("localhost", 80, 6989);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE, req->action);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_EVT_STOPPED, req->event);
 }
 
 void DefaultBtAnnounceTest::testGetAnnounceUrl_withQuery()
@@ -262,6 +291,13 @@ void DefaultBtAnnounceTest::testGetAnnounceUrl_externalIP()
                  "key=fastdltl&numwant=50&no_peer_id=1&port=6989&event=started&"
                  "supportcrypto=1&ip=192.168.1.1"),
      btAnnounce.getAnnounceUrl());
+
+  SharedHandle<UDPTrackerRequest> req;
+  req = btAnnounce.createUDPTrackerRequest("localhost", 80, 6989);
+  char host[NI_MAXHOST];
+  int rv = inetNtop(AF_INET, &req->ip, host, sizeof(host));
+  CPPUNIT_ASSERT_EQUAL(0, rv);
+  CPPUNIT_ASSERT_EQUAL(std::string("192.168.1.1"), std::string(host));
 }
 
 void DefaultBtAnnounceTest::testIsAllAnnounceFailed()
@@ -411,4 +447,34 @@ void DefaultBtAnnounceTest::testProcessAnnounceResponse()
                        peer->getIPAddress());
 }
 
+void DefaultBtAnnounceTest::testProcessUDPTrackerResponse()
+{
+  SharedHandle<UDPTrackerRequest> req(new UDPTrackerRequest());
+  req->action = UDPT_ACT_ANNOUNCE;
+  SharedHandle<UDPTrackerReply> reply(new UDPTrackerReply());
+  reply->interval = 1800;
+  reply->leechers = 200;
+  reply->seeders = 100;
+  for(int i = 0; i < 2; ++i) {
+    reply->peers.push_back(std::make_pair("192.168.0."+util::uitos(i+1),
+                                          6890+i));
+  }
+  req->reply = reply;
+  DefaultBtAnnounce an(dctx_, option_);
+  an.setPeerStorage(peerStorage_);
+  an.setBtRuntime(btRuntime_);
+  an.processUDPTrackerResponse(req);
+  CPPUNIT_ASSERT_EQUAL((time_t)1800, an.getInterval());
+  CPPUNIT_ASSERT_EQUAL((time_t)1800, an.getMinInterval());
+  CPPUNIT_ASSERT_EQUAL(100, an.getComplete());
+  CPPUNIT_ASSERT_EQUAL(200, an.getIncomplete());
+  CPPUNIT_ASSERT_EQUAL((size_t)2, peerStorage_->getUnusedPeers().size());
+  for(int i = 0; i < 2; ++i) {
+    SharedHandle<Peer> peer;
+    peer = peerStorage_->getUnusedPeers()[i];
+    CPPUNIT_ASSERT_EQUAL("192.168.0."+util::uitos(i+1), peer->getIPAddress());
+    CPPUNIT_ASSERT_EQUAL((uint16_t)(6890+i), peer->getPort());
+  }
+}
+
 } // namespace aria2
diff --git a/test/Makefile.am b/test/Makefile.am
index d9f4457b..3b7a7790 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -214,7 +214,8 @@ aria2c_SOURCES += BtAllowedFastMessageTest.cc\
 	Bencode2Test.cc\
 	PeerConnectionTest.cc\
 	ValueBaseBencodeParserTest.cc\
-	ExtensionMessageRegistryTest.cc
+	ExtensionMessageRegistryTest.cc\
+	UDPTrackerClientTest.cc
 endif # ENABLE_BITTORRENT
 
 if ENABLE_METALINK
diff --git a/test/MockBtAnnounce.h b/test/MockBtAnnounce.h
index b1493e32..1236c8c2 100644
--- a/test/MockBtAnnounce.h
+++ b/test/MockBtAnnounce.h
@@ -26,6 +26,12 @@ public:
     return announceUrl;
   }
 
+  virtual SharedHandle<UDPTrackerRequest>
+  createUDPTrackerRequest(const std::string& remoteAddr, uint16_t remotePort,
+                          uint16_t localPort) {
+    return SharedHandle<UDPTrackerRequest>();
+  }
+
   void setAnnounceUrl(const std::string& url) {
     this->announceUrl = url;
   }
@@ -45,6 +51,9 @@ public:
   virtual void processAnnounceResponse(const unsigned char* trackerResponse,
                                        size_t trackerResponseLength) {}
 
+  virtual void processUDPTrackerResponse
+  (const SharedHandle<UDPTrackerRequest>& req) {}
+
   virtual bool noMoreAnnounce() {
     return false;
   }
diff --git a/test/UDPTrackerClientTest.cc b/test/UDPTrackerClientTest.cc
new file mode 100644
index 00000000..993dc750
--- /dev/null
+++ b/test/UDPTrackerClientTest.cc
@@ -0,0 +1,453 @@
+#include "UDPTrackerClient.h"
+
+#include <cstring>
+
+#include <cppunit/extensions/HelperMacros.h>
+
+#include "TestUtil.h"
+#include "UDPTrackerRequest.h"
+#include "bittorrent_helper.h"
+#include "wallclock.h"
+
+namespace aria2 {
+
+class UDPTrackerClientTest:public CppUnit::TestFixture {
+
+  CPPUNIT_TEST_SUITE(UDPTrackerClientTest);
+  CPPUNIT_TEST(testCreateUDPTrackerConnect);
+  CPPUNIT_TEST(testCreateUDPTrackerAnnounce);
+  CPPUNIT_TEST(testConnectFollowedByAnnounce);
+  CPPUNIT_TEST(testRequestFailure);
+  CPPUNIT_TEST(testTimeout);
+  CPPUNIT_TEST_SUITE_END();
+public:
+  void setUp()
+  {
+  }
+
+  void testCreateUDPTrackerConnect();
+  void testCreateUDPTrackerAnnounce();
+  void testConnectFollowedByAnnounce();
+  void testRequestFailure();
+  void testTimeout();
+};
+
+CPPUNIT_TEST_SUITE_REGISTRATION( UDPTrackerClientTest );
+
+namespace {
+SharedHandle<UDPTrackerRequest> createAnnounce(const std::string& remoteAddr,
+                                               uint16_t remotePort,
+                                               int32_t transactionId)
+{
+  SharedHandle<UDPTrackerRequest> req(new UDPTrackerRequest());
+  req->connectionId = INT64_MAX;
+  req->action = UDPT_ACT_ANNOUNCE;
+  req->remoteAddr = remoteAddr;
+  req->remotePort = remotePort;
+  req->transactionId = transactionId;
+  req->infohash = "bittorrent-infohash-";
+  req->peerId =   "bittorrent-peer-id--";
+  req->downloaded = INT64_MAX - 1;
+  req->left = INT64_MAX - 2;
+  req->uploaded = INT64_MAX - 3;
+  req->event = UDPT_EVT_STARTED;
+  req->ip = 0;
+  req->key = 1000000007;
+  req->numWant = 50;
+  req->port = 6889;
+  req->extensions = 0;
+  return req;
+}
+} // namespace
+
+namespace {
+ssize_t createErrorReply(unsigned char* data, size_t len,
+                         int32_t transactionId, const std::string& errorString)
+{
+  bittorrent::setIntParam(data, UDPT_ACT_ERROR);
+  bittorrent::setIntParam(data+4, transactionId);
+  memcpy(data+8, errorString.c_str(), errorString.size());
+  return 8+errorString.size();
+}
+} // namespace
+
+namespace {
+ssize_t createConnectReply(unsigned char* data, size_t len,
+                           uint64_t connectionId, int32_t transactionId)
+{
+  bittorrent::setIntParam(data, UDPT_ACT_CONNECT);
+  bittorrent::setIntParam(data+4, transactionId);
+  bittorrent::setLLIntParam(data+8, connectionId);
+  return 16;
+}
+} // namespace
+
+namespace {
+ssize_t createAnnounceReply(unsigned char*data, size_t len,
+                            int32_t transactionId, int numPeers = 0)
+{
+  bittorrent::setIntParam(data, UDPT_ACT_ANNOUNCE);
+  bittorrent::setIntParam(data+4, transactionId);
+  bittorrent::setIntParam(data+8, 1800);
+  bittorrent::setIntParam(data+12, 100);
+  bittorrent::setIntParam(data+16, 256);
+  for(int i = 0; i < numPeers; ++i) {
+    bittorrent::packcompact(data+20+6*i, "192.168.0."+util::uitos(i+1),
+                            6990+i);
+  }
+  return 20 + 6 * numPeers;
+}
+} // namespace
+
+void UDPTrackerClientTest::testCreateUDPTrackerConnect()
+{
+  unsigned char data[16];
+  std::string remoteAddr;
+  uint16_t remotePort = 0;
+  SharedHandle<UDPTrackerRequest> req(new UDPTrackerRequest());
+  req->action = UDPT_ACT_CONNECT;
+  req->remoteAddr = "192.168.0.1";
+  req->remotePort = 6991;
+  req->transactionId = 1000000009;
+  ssize_t rv = createUDPTrackerConnect(data, sizeof(data), remoteAddr,
+                                       remotePort, req);
+  CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+  CPPUNIT_ASSERT_EQUAL(req->remoteAddr, remoteAddr);
+  CPPUNIT_ASSERT_EQUAL(req->remotePort, remotePort);
+  CPPUNIT_ASSERT_EQUAL((int64_t)UDPT_INITIAL_CONNECTION_ID,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+  CPPUNIT_ASSERT_EQUAL((int)req->action, (int)bittorrent::getIntParam(data, 8));
+  CPPUNIT_ASSERT_EQUAL(req->transactionId,
+                       (int32_t)bittorrent::getIntParam(data, 12));
+}
+
+void UDPTrackerClientTest::testCreateUDPTrackerAnnounce()
+{
+  unsigned char data[100];
+  std::string remoteAddr;
+  uint16_t remotePort = 0;
+  SharedHandle<UDPTrackerRequest> req(createAnnounce("192.168.0.1", 6991,
+                                                     1000000009));
+  ssize_t rv = createUDPTrackerAnnounce(data, sizeof(data), remoteAddr,
+                                        remotePort, req);
+  CPPUNIT_ASSERT_EQUAL((ssize_t)100, rv);
+  CPPUNIT_ASSERT_EQUAL(req->connectionId,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+  CPPUNIT_ASSERT_EQUAL((int)req->action, (int)bittorrent::getIntParam(data, 8));
+  CPPUNIT_ASSERT_EQUAL(req->transactionId,
+                       (int32_t)bittorrent::getIntParam(data, 12));
+  CPPUNIT_ASSERT_EQUAL(req->infohash, std::string(&data[16], &data[36]));
+  CPPUNIT_ASSERT_EQUAL(req->peerId, std::string(&data[36], &data[56]));
+  CPPUNIT_ASSERT_EQUAL(req->downloaded,
+                       (int64_t)bittorrent::getLLIntParam(data, 56));
+  CPPUNIT_ASSERT_EQUAL(req->left,
+                       (int64_t)bittorrent::getLLIntParam(data, 64));
+  CPPUNIT_ASSERT_EQUAL(req->uploaded,
+                       (int64_t)bittorrent::getLLIntParam(data, 72));
+  CPPUNIT_ASSERT_EQUAL(req->event, (int32_t)bittorrent::getIntParam(data, 80));
+  CPPUNIT_ASSERT_EQUAL(req->ip, bittorrent::getIntParam(data, 84));
+  CPPUNIT_ASSERT_EQUAL(req->key, bittorrent::getIntParam(data, 88));
+  CPPUNIT_ASSERT_EQUAL(req->numWant,
+                       (int32_t)bittorrent::getIntParam(data, 92));
+  CPPUNIT_ASSERT_EQUAL(req->port, bittorrent::getShortIntParam(data, 96));
+  CPPUNIT_ASSERT_EQUAL(req->extensions, bittorrent::getShortIntParam(data, 98));
+}
+
+void UDPTrackerClientTest::testConnectFollowedByAnnounce()
+{
+  ssize_t rv;
+  UDPTrackerClient tr;
+  unsigned char data[100];
+  std::string remoteAddr;
+  uint16_t remotePort;
+  Timer now;
+
+  SharedHandle<UDPTrackerRequest> req1(createAnnounce("192.168.0.1", 6991, 0));
+  SharedHandle<UDPTrackerRequest> req2(createAnnounce("192.168.0.1", 6991, 0));
+  req2->infohash = "bittorrent-infohash2";
+
+  tr.addRequest(req1);
+  tr.addRequest(req2);
+  CPPUNIT_ASSERT_EQUAL((size_t)2, tr.getPendingRequests().size());
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  // CONNECT request was inserted
+  CPPUNIT_ASSERT_EQUAL((size_t)3, tr.getPendingRequests().size());
+  CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+  CPPUNIT_ASSERT_EQUAL(req1->remoteAddr, remoteAddr);
+  CPPUNIT_ASSERT_EQUAL(req1->remotePort, remotePort);
+  CPPUNIT_ASSERT_EQUAL((int64_t)UDPT_INITIAL_CONNECTION_ID,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+  int32_t transactionId = bittorrent::getIntParam(data, 12);
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  // Duplicate CONNECT request was not inserted
+  CPPUNIT_ASSERT_EQUAL((size_t)3, tr.getPendingRequests().size());
+  CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+
+  tr.requestSent(now);
+  // CONNECT request was moved to inflight
+  CPPUNIT_ASSERT_EQUAL((size_t)2, tr.getPendingRequests().size());
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  // Now all pending requests were moved to connect
+  CPPUNIT_ASSERT_EQUAL((ssize_t)-1, rv);
+  CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+
+  int64_t connectionId = 12345;
+  rv = createConnectReply(data, sizeof(data), connectionId, transactionId);
+  rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+  CPPUNIT_ASSERT_EQUAL(0, (int)rv);
+  // Now 2 requests get back to pending
+  CPPUNIT_ASSERT_EQUAL((size_t)2, tr.getPendingRequests().size());
+
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  // Creates announce for req1
+  CPPUNIT_ASSERT_EQUAL((ssize_t)100, rv);
+  CPPUNIT_ASSERT_EQUAL((size_t)2, tr.getPendingRequests().size());
+  CPPUNIT_ASSERT_EQUAL(connectionId,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE,
+                       (int)bittorrent::getIntParam(data, 8));
+  CPPUNIT_ASSERT_EQUAL(req1->infohash,
+                       std::string(&data[16], &data[36]));
+
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  // Don't duplicate same request data
+  CPPUNIT_ASSERT_EQUAL((ssize_t)100, rv);
+  CPPUNIT_ASSERT_EQUAL((size_t)2, tr.getPendingRequests().size());
+  int32_t transactionId1 = bittorrent::getIntParam(data, 12);
+
+  tr.requestSent(now);
+  CPPUNIT_ASSERT_EQUAL((size_t)1, tr.getPendingRequests().size());
+
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  int32_t transactionId2 = bittorrent::getIntParam(data, 12);
+  // Creates announce for req2
+  CPPUNIT_ASSERT_EQUAL((ssize_t)100, rv);
+  CPPUNIT_ASSERT_EQUAL((size_t)1, tr.getPendingRequests().size());
+  CPPUNIT_ASSERT_EQUAL(connectionId,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE,
+                       (int)bittorrent::getIntParam(data, 8));
+  CPPUNIT_ASSERT_EQUAL(req2->infohash,
+                       std::string(&data[16], &data[36]));
+
+  tr.requestSent(now);
+  // Now all requests are inflight
+  CPPUNIT_ASSERT_EQUAL((size_t)0, tr.getPendingRequests().size());
+
+  // Reply for req2
+  rv = createAnnounceReply(data, sizeof(data), transactionId2);
+  rv = tr.receiveReply(data, rv, req2->remoteAddr, req2->remotePort, now);
+  CPPUNIT_ASSERT_EQUAL(0, (int)rv);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req2->state);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_SUCCESS, req2->error);
+
+  // Reply for req1
+  rv = createAnnounceReply(data, sizeof(data), transactionId1, 2);
+  rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+  CPPUNIT_ASSERT_EQUAL(0, (int)rv);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+  CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_SUCCESS, req1->error);
+  CPPUNIT_ASSERT_EQUAL((size_t)2, req1->reply->peers.size());
+  for(int i = 0; i < 2; ++i) {
+    CPPUNIT_ASSERT_EQUAL("192.168.0."+util::uitos(i+1),
+                         req1->reply->peers[i].first);
+    CPPUNIT_ASSERT_EQUAL((uint16_t)(6990+i), req1->reply->peers[i].second);
+  }
+
+  // Since we have connection ID, next announce request can be sent
+  // immediately
+  SharedHandle<UDPTrackerRequest> req3(createAnnounce("192.168.0.1", 6991, 0));
+  req3->infohash = "bittorrent-infohash3";
+  tr.addRequest(req3);
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+  CPPUNIT_ASSERT_EQUAL((ssize_t)100, rv);
+  CPPUNIT_ASSERT_EQUAL(req3->infohash,
+                       std::string(&data[16], &data[36]));
+
+  tr.requestSent(now);
+
+  SharedHandle<UDPTrackerRequest> req4(createAnnounce("192.168.0.1", 6991, 0));
+  req4->infohash = "bittorrent-infohash4";
+  tr.addRequest(req4);
+  Timer future = now;
+  future.advance(3600);
+  rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort,
+                        future);
+  // connection ID is stale because of the timeout
+  CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+  CPPUNIT_ASSERT_EQUAL((int64_t)UDPT_INITIAL_CONNECTION_ID,
+                       (int64_t)bittorrent::getLLIntParam(data, 0));
+}
+
+void UDPTrackerClientTest::testRequestFailure()
+{
+  ssize_t rv;
+  UDPTrackerClient tr;
+  unsigned char data[100];
+  std::string remoteAddr;
+  uint16_t remotePort;
+  Timer now;
+  {
+    SharedHandle<UDPTrackerRequest> req1
+      (createAnnounce("192.168.0.1", 6991, 0));
+    SharedHandle<UDPTrackerRequest> req2
+      (createAnnounce("192.168.0.1", 6991, 0));
+
+    tr.addRequest(req1);
+    tr.addRequest(req2);
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    tr.requestFail(UDPT_ERR_NETWORK);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_NETWORK, req1->error);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req2->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_NETWORK, req2->error);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+  }
+  {
+    SharedHandle<UDPTrackerRequest> req1
+      (createAnnounce("192.168.0.1", 6991, 0));
+    SharedHandle<UDPTrackerRequest> req2
+      (createAnnounce("192.168.0.1", 6991, 0));
+
+    tr.addRequest(req1);
+    tr.addRequest(req2);
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    int32_t transactionId = bittorrent::getIntParam(data, 12);
+    tr.requestSent(now);
+
+    rv = createErrorReply(data, sizeof(data), transactionId, "error");
+    rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TRACKER, req1->error);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req2->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TRACKER, req2->error);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+  }
+  {
+    SharedHandle<UDPTrackerRequest> req1
+      (createAnnounce("192.168.0.1", 6991, 0));
+
+    tr.addRequest(req1);
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    int32_t transactionId = bittorrent::getIntParam(data, 12);
+    tr.requestSent(now);
+
+    int64_t connectionId = 12345;
+    rv = createConnectReply(data, sizeof(data), connectionId, transactionId);
+    rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+    CPPUNIT_ASSERT_EQUAL(0, (int)rv);
+
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE,
+                         (int)bittorrent::getIntParam(data, 8));
+    transactionId = bittorrent::getIntParam(data, 12);
+    tr.requestSent(now);
+
+    rv = createErrorReply(data, sizeof(data), transactionId, "announce error");
+    rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TRACKER, req1->error);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+  }
+}
+
+void UDPTrackerClientTest::testTimeout()
+{
+  ssize_t rv;
+  unsigned char data[100];
+  std::string remoteAddr;
+  uint16_t remotePort;
+  Timer now;
+  UDPTrackerClient tr;
+  {
+    SharedHandle<UDPTrackerRequest> req1
+      (createAnnounce("192.168.0.1", 6991, 0));
+    SharedHandle<UDPTrackerRequest> req2
+      (createAnnounce("192.168.0.1", 6991, 0));
+
+    tr.addRequest(req1);
+    tr.addRequest(req2);
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    tr.requestSent(now);
+    now.advance(20);
+    // 15 seconds 1st stage timeout passed
+    tr.handleTimeout(now);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT_EQUAL((size_t)3, tr.getPendingRequests().size());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    // CONNECT request was inserted
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    tr.requestSent(now);
+    now.advance(65);
+    // 60 seconds 2nd stage timeout passed
+    tr.handleTimeout(now);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TIMEOUT, req1->error);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req2->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TIMEOUT, req2->error);
+  }
+  {
+    SharedHandle<UDPTrackerRequest> req1
+      (createAnnounce("192.168.0.1", 6991, 0));
+
+    tr.addRequest(req1);
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((ssize_t)16, rv);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_CONNECT,
+                         (int)bittorrent::getIntParam(data, 8));
+    int32_t transactionId = bittorrent::getIntParam(data, 12);
+    tr.requestSent(now);
+
+    int64_t connectionId = 12345;
+    rv = createConnectReply(data, sizeof(data), connectionId, transactionId);
+    rv = tr.receiveReply(data, rv, req1->remoteAddr, req1->remotePort, now);
+    CPPUNIT_ASSERT_EQUAL(0, (int)rv);
+
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE,
+                         (int)bittorrent::getIntParam(data, 8));
+    tr.requestSent(now);
+    now.advance(20);
+    // 15 seconds 1st stage timeout passed
+    tr.handleTimeout(now);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT_EQUAL((size_t)1, tr.getPendingRequests().size());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+
+    rv = tr.createRequest(data, sizeof(data), remoteAddr, remotePort, now);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ACT_ANNOUNCE,
+                         (int)bittorrent::getIntParam(data, 8));
+    tr.requestSent(now);
+    now.advance(65);
+    // 60 seconds 2nd stage timeout passed
+    tr.handleTimeout(now);
+    CPPUNIT_ASSERT(tr.getConnectRequests().empty());
+    CPPUNIT_ASSERT(tr.getPendingRequests().empty());
+    CPPUNIT_ASSERT(tr.getInflightRequests().empty());
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_STA_COMPLETE, req1->state);
+    CPPUNIT_ASSERT_EQUAL((int)UDPT_ERR_TIMEOUT, req1->error);
+  }
+}
+
+} // namespace aria2