Adding option to remove UE contexts if SCTP error occors.

This was done as after an SCTP error, the MME would try to page the UE,
but the UE was already RRC Connected.

srsenb/src/stack/s1ap/s1ap.cc

@@ -553,17 +553,29 @@ bool s1ap::handle_mme_rx_msg(srsran::unique_byte_buffer_t pdu,
     // Received notification
     union sctp_notification* notification = (union sctp_notification*)pdu->msg;
     logger.info("SCTP Notification %04x", notification->sn_header.sn_type);
+    bool restart_s1 = false;
     if (notification->sn_header.sn_type == SCTP_SHUTDOWN_EVENT) {
       logger.info("SCTP Association Shutdown. Association: %d", sri.sinfo_assoc_id);
       srsran::console("SCTP Association Shutdown. Association: %d\n", sri.sinfo_assoc_id);
-      rx_socket_handler->remove_socket(mme_socket.get_socket());
+      restart_s1 = true;
-      mme_socket.close();
     } else if (notification->sn_header.sn_type == SCTP_PEER_ADDR_CHANGE &&
                notification->sn_paddr_change.spc_state == SCTP_ADDR_UNREACHABLE) {
       logger.info("SCTP peer addres unreachable. Association: %d", sri.sinfo_assoc_id);
       srsran::console("SCTP peer address unreachable. Association: %d\n", sri.sinfo_assoc_id);
+      restart_s1 = true;
+    }
+    if (restart_s1) {
+      logger.info("Restarting S1 connection");
+      srsran::console("Restarting S1 connection\n");
       rx_socket_handler->remove_socket(mme_socket.get_socket());
       mme_socket.close();
+      while (users.size() != 0) {
+        std::unordered_map<uint32_t, std::unique_ptr<ue> >::iterator it   = users.begin();
+        uint16_t                                                     rnti = it->second->ctxt.rnti;
+        rrc->release_erabs(rnti);
+        rrc->release_ue(rnti);
+        users.erase(it->second.get());
+      }
     }
   } else if (pdu->N_bytes == 0) {
     logger.error("SCTP return 0 bytes. Closing socket");