lte: Implement packet buffering in handover procedure

src/lte/model/lte-enb-rrc.cc

@@ -555,6 +555,7 @@ UeManager::ReleaseDataRadioBearer (uint8_t drbid)
 void
 LteEnbRrc::DoSendReleaseDataRadioBearer (uint64_t imsi, uint16_t rnti, uint8_t bearerId)
 {
+  NS_LOG_FUNCTION (this << imsi << rnti << (uint16_t) bearerId);
   Ptr<UeManager> ueManager = GetUeManager (rnti);
   // Bearer de-activation towards UE
   ueManager->ReleaseDataRadioBearer (bearerId);
@@ -724,6 +725,28 @@ UeManager::GetRrcConnectionReconfigurationForHandover ()
   return BuildRrcConnectionReconfiguration ();
 }
 
+void
+UeManager::SendPacket (uint8_t bid, Ptr<Packet> p)
+{
+  NS_LOG_FUNCTION (this << p << (uint16_t) bid);
+  LtePdcpSapProvider::TransmitPdcpSduParameters params;
+  params.pdcpSdu = p;
+  params.rnti = m_rnti;
+  params.lcid = Bid2Lcid (bid);
+  uint8_t drbid = Bid2Drbid (bid);
+  // Transmit PDCP sdu only if DRB ID found in drbMap
+  std::map<uint8_t, Ptr<LteDataRadioBearerInfo> >::iterator it = m_drbMap.find (drbid);
+  if (it != m_drbMap.end ())
+    {
+      Ptr<LteDataRadioBearerInfo> bearerInfo = GetDataRadioBearerInfo (drbid);
+      if (bearerInfo != NULL)
+        {
+          LtePdcpSapProvider* pdcpSapProvider = bearerInfo->m_pdcp->GetLtePdcpSapProvider ();
+          pdcpSapProvider->TransmitPdcpSdu (params);
+        }
+    }
+}
+
 void
 UeManager::SendData (uint8_t bid, Ptr<Packet> p)
 {
@@ -740,26 +763,18 @@ UeManager::SendData (uint8_t bid, Ptr<Packet> p)
     case CONNECTION_RECONFIGURATION:
     case CONNECTION_REESTABLISHMENT:
     case HANDOVER_PREPARATION:
-    case HANDOVER_JOINING:
     case HANDOVER_PATH_SWITCH:
       {
         NS_LOG_LOGIC ("queueing data on PDCP for transmission over the air");
-        LtePdcpSapProvider::TransmitPdcpSduParameters params;
-        params.pdcpSdu = p;
-        params.rnti = m_rnti;
-        params.lcid = Bid2Lcid (bid);
-        uint8_t drbid = Bid2Drbid (bid);
-        //Transmit PDCP sdu only if DRB ID found in drbMap
-        std::map<uint8_t, Ptr<LteDataRadioBearerInfo> >::iterator it = m_drbMap.find (drbid);
-        if (it != m_drbMap.end ())
-          {
-            Ptr<LteDataRadioBearerInfo> bearerInfo = GetDataRadioBearerInfo (drbid);
-            if (bearerInfo != NULL)
-              {
-                LtePdcpSapProvider* pdcpSapProvider = bearerInfo->m_pdcp->GetLtePdcpSapProvider ();
-                pdcpSapProvider->TransmitPdcpSdu (params);
-              }
-          }
+        SendPacket (bid, p);
+      }
+      break;
+
+    case HANDOVER_JOINING:
+      {
+        // Buffer data until RRC Connection Reconfiguration Complete message is received
+        NS_LOG_LOGIC ("buffering data");
+        m_packetBuffer.push_back (std::make_pair (bid, p));
       }
       break;
 
@@ -1005,6 +1020,20 @@ UeManager::RecvRrcConnectionReconfigurationCompleted (LteRrcSap::RrcConnectionRe
     case HANDOVER_JOINING:
       {
         m_handoverJoiningTimeout.Cancel ();
+
+        while (!m_packetBuffer.empty ())
+          {
+            NS_LOG_LOGIC ("dequeueing data from buffer");
+            std::pair <uint8_t, Ptr<Packet> > bidPacket = m_packetBuffer.front ();
+            uint8_t bid = bidPacket.first;
+            Ptr<Packet> p = bidPacket.second;
+
+            NS_LOG_LOGIC ("queueing data on PDCP for transmission over the air");
+            SendPacket (bid, p);
+
+            m_packetBuffer.pop_front ();
+          }
+
         NS_LOG_INFO ("Send PATH SWITCH REQUEST to the MME");
         EpcEnbS1SapProvider::PathSwitchRequestParameters params;
         params.rnti = m_rnti;

src/lte/model/lte-enb-rrc.h

@@ -218,9 +218,14 @@ public:
    */
   LteRrcSap::RrcConnectionReconfiguration GetRrcConnectionReconfigurationForHandover ();
 
-  /** 
-   * Send a data packet over the appropriate Data Radio Bearer
-   * 
+  /**
+   * Send a data packet over the appropriate Data Radio Bearer.
+   * If state is HANDOVER_JOINING (i.e. target eNB has received the
+   * Handover Request), the packet is buffered.
+   * If state is HANDOVER_LEAVING (i.e. source eNB has received the
+   * RRC Connection Reconfiguration, the packet is sent through the
+   * X2 interface.
+   *
    * \param bid the corresponding EPS Bearer ID
    * \param p the packet
    */
@@ -469,6 +474,17 @@ private:
    */
   uint8_t Bid2Drbid (uint8_t bid);
 
+  /**
+   * Send a data packet over the appropriate Data Radio Bearer.
+   * It is called by SendData if the UE is in a connected state
+   * or when the RRC Connection Reconfiguration Complete message
+   * is received and the packets are debuffered.
+   *
+   * \param bid the corresponding EPS Bearer ID
+   * \param p the packet
+   */
+  void SendPacket (uint8_t bid, Ptr<Packet> p);
+
   /** 
    * Switch the UeManager to the given state
    * 
@@ -572,6 +588,18 @@ private:
   /// Pending start data radio bearers
   bool m_pendingStartDataRadioBearers;
 
+
+  /**
+   * Packet buffer for when UE is doing the handover.
+   * The packets are stored with the bid (bearer ID).
+   *
+   * Source eNB starts forwarding data to target eNB through the X2 interface
+   * when it sends RRC Connection Reconfiguration to the UE.
+   * Target eNB buffers data until it receives RRC Connection Reconfiguration
+   * Complete from the UE.
+   */
+  std::list<std::pair<uint8_t, Ptr<Packet> > > m_packetBuffer;
+
 }; // end of `class UeManager`