lte: Handle handover joining timeout

Upon HO joining timeout, the target eNB sends the HO preparation failure message to the source eNB and deletes the UE context. On the other hand, the source eNB after receiving this msg releases the resources towards a UE by sending the RRC connection release msg in an ideal way irrespective of the RRC protocol used; and also requests the core network to delete that UE.

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

@@ -996,6 +996,12 @@ UeManager::RecvHandoverPreparationFailure (uint16_t cellId)
       NS_LOG_INFO ("target eNB sent HO preparation failure, aborting HO");
       SwitchToState (CONNECTED_NORMALLY);
       break;
+    case HANDOVER_LEAVING: //case added to tackle HO joining timer expiration
+      NS_ASSERT (cellId == m_targetCellId);
+      NS_LOG_INFO ("target eNB sent HO preparation failure, aborting HO");
+      m_handoverLeavingTimeout.Cancel ();
+      SendRrcConnectionRelease ();
+      break;
 
     default:
       NS_FATAL_ERROR ("method unexpected in state " << ToString (m_state));
@@ -1030,6 +1036,24 @@ UeManager::RecvUeContextRelease (EpcX2SapUser::UeContextReleaseParams params)
   m_handoverLeavingTimeout.Cancel ();
 }
 
+void
+UeManager::SendRrcConnectionRelease ()
+{
+  // TODO implement in the 3gpp way, see Section 5.3.8 of 3GPP TS 36.331.
+  NS_LOG_FUNCTION (this << (uint32_t) m_rnti);
+  // De-activation towards UE, it will deactivate all bearers
+  LteRrcSap::RrcConnectionRelease msg;
+  msg.rrcTransactionIdentifier = this->GetNewRrcTransactionIdentifier ();
+  m_rrc->m_rrcSapUser->SendRrcConnectionRelease (m_rnti, msg);
+
+  /**
+   * Bearer de-activation indication towards epc-enb application
+   * and removal of UE context at the eNodeB
+   *
+   */
+  m_rrc->DoRecvIdealUeContextRemoveRequest (m_rnti);
+}
+
 
 // methods forwarded from RRC SAP
 
@@ -2505,6 +2529,17 @@ LteEnbRrc::HandoverJoiningTimeout (uint16_t rnti)
                  "HandoverJoiningTimeout in unexpected state " << ToString (GetUeManager (rnti)->GetState ()));
   m_rrcTimeoutTrace (GetUeManager (rnti)->GetImsi (), rnti,
                      ComponentCarrierToCellId (GetUeManager (rnti)->GetComponentCarrierId ()), "HandoverJoiningTimeout");
+
+  /**
+   * When the handover joining timer expires at the target cell,
+   * then notify the source cell to release the RRC connection and
+   * delete the UE context at eNodeB and SGW/PGW. The
+   * HandoverPreparationFailure message is reused to notify the source cell
+   * through the X2 interface instead of creating a new message.
+   */
+  Ptr<UeManager> ueManger = GetUeManager (rnti);
+  EpcX2Sap::HandoverPreparationFailureParams msg = ueManger->BuildHoPrepFailMsg ();
+  m_x2SapProvider->SendHandoverPreparationFailure (msg);
   RemoveUe (rnti);
 }
 

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

@@ -380,6 +380,13 @@ public:
    */
   void CancelPendingEvents ();
 
+  /**
+   *  \brief This function acts as an interface to trigger the connection
+   *  release towards eNB, EPC and UE.
+   *
+   */
+  void SendRrcConnectionRelease ();
+
   /**
    * \brief build handover preparation failure message
    */
@@ -1048,6 +1055,14 @@ public:
    */
   void DoSendReleaseDataRadioBearer (uint64_t imsi, uint16_t rnti, uint8_t bearerId);
 
+  /**
+   *  \brief Send RRC connection release function
+   *
+   *  This function acts as an interface to trigger the connection
+   *  release towards eNB, EPC and UE.
+   */
+  void SendRrcConnectionRelease ();
+
   /**
    * Identifies how EPS Bearer parameters are mapped to different RLC types
    *

src/lte/model/lte-rrc-protocol-real.cc

@@ -657,6 +657,8 @@ LteEnbRrcProtocolReal::DoSendRrcConnectionReestablishmentReject (uint16_t rnti,
 void
 LteEnbRrcProtocolReal::DoSendRrcConnectionRelease (uint16_t rnti, LteRrcSap::RrcConnectionRelease msg)
 {
+  //The code below is commented so RRC connection release can be sent in an ideal way
+  /*
   Ptr<Packet> packet = Create<Packet> ();
 
   RrcConnectionReleaseHeader rrcConnectionReleaseHeader;
@@ -670,6 +672,18 @@ LteEnbRrcProtocolReal::DoSendRrcConnectionRelease (uint16_t rnti, LteRrcSap::Rrc
   transmitPdcpSduParameters.lcid = 1;
 
   m_setupUeParametersMap[rnti].srb1SapProvider->TransmitPdcpSdu (transmitPdcpSduParameters);
+  */
+  /**
+   * Send RRC connection release in an idle way to ensure UE goes
+   * to idle mode during handover failure and connection setup timeout.
+   * Implemented to avoid unnecessary triggering of assert msgs due to reception of
+   * msgs (SRS CQI reports) from UE after UE context is deleted at eNodeB.
+   * TODO: Detection of handover failure and connection setup timeout at UE,
+   * so that the RRC connection release can be sent through the physical channel again.
+   */
+  NS_LOG_FUNCTION(this<<rnti);
+  Simulator::Schedule (RRC_REAL_MSG_DELAY, &LteUeRrcSapProvider::RecvRrcConnectionRelease,
+                       GetUeRrcSapProvider (rnti), msg);
 }
 
 void

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

@@ -1196,6 +1196,16 @@ LteUeRrc::DoRecvRrcConnectionRelease (LteRrcSap::RrcConnectionRelease msg)
 {
   NS_LOG_FUNCTION (this << " RNTI " << m_rnti);
   /// \todo Currently not implemented, see Section 5.3.8 of 3GPP TS 36.331.
+
+  m_lastRrcTransactionIdentifier = msg.rrcTransactionIdentifier;
+  //release resources at UE
+  if (!m_rlfDetected)
+    {
+      m_rlfDetected = true;
+      SwitchToState (CONNECTED_PHY_PROBLEM);
+      m_rrcSapUser->SendIdealUeContextRemoveRequest (m_rnti);
+      m_asSapUser->NotifyConnectionReleased ();
+    }
 }
 
 void