lte: (fixes #885) Don't send RAR when UE context is not created

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

@@ -526,6 +526,14 @@ LteEnbMac::DoSubframeIndication(uint32_t frameNo, uint32_t subframeNo)
                 else
                 {
                     rnti = m_cmacSapUser->AllocateTemporaryCellRnti();
+
+                    if (rnti == 0)
+                    {
+                        // If rnti = 0, UE context was not created (not enough SRS)
+                        // Therefore don't send RAR for this preamble
+                        NS_LOG_INFO("UE Context not created, no RAR is send");
+                        continue;
+                    }
                     NS_LOG_INFO("preambleId " << (uint32_t)it->first << ": allocated T-C-RNTI "
                                               << (uint32_t)rnti << ", sending RAR");
                 }

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

@@ -3123,6 +3123,7 @@ LteEnbRrc::DoAllocateTemporaryCellRnti(uint8_t componentCarrierId)
     // if no SRS index is available, then do not create a new UE context.
     if (IsMaxSrsReached())
     {
+        NS_LOG_WARN("Not enough SRS configuration index, UE context not created");
         return 0; // return 0 since new RNTI was not assigned for the received preamble
     }
     return AddUe(UeManager::INITIAL_RANDOM_ACCESS, componentCarrierId);