Pdcp: do not tweak srcId/destId in FlowControlInfo when sending DL packet over the X2 link

For DualConnectivity / Split Bearer, all DL packets arrive at the Master,
and those that go via the Secondary Node must be tunnelled over to it
via X2. Existing code tweaked the FlowControlInfo srcId/destId field to make it
look like the packet goes Enb-to-Enb, but that is not necessary.
This patch gets rid of that tweaking.

Note: the useNR flag selects whether the packet should go via the Master
or Secondary Enb.

Author: avarga

src/simu5g/stack/pdcp/NrPdcpEnb.cc

@@ -86,6 +86,14 @@ void NrPdcpEnb::analyzePacket(inet::Packet *pkt)
     ConnectionKey key{srcAddr, destAddr, lteInfo->getTypeOfService(), lteInfo->getDirection()};
     LogicalCid lcid = lookupOrAssignLcid(key);
 
+    // Dual Connectivity: adjust source and dest IDs for downlink packets in DC scenarios.
+    // If this is a master eNB in DC and there's a secondary for this UE which will get this packet via X2 and transmit it via its RAN
+    MacNodeId secondaryNodeId = binder_->getSecondaryNode(nodeId_);
+    if (dualConnectivityEnabled_ && secondaryNodeId != NODEID_NONE && lteInfo->getUseNR()) {
+        lteInfo->setSourceId(secondaryNodeId);
+        lteInfo->setDestId(binder_->getNrMacNodeId(destAddr)); // use NR nodeId of the UE
+    }
+
     // assign LCID
     lteInfo->setLcid(lcid);
 }
@@ -142,21 +150,13 @@ void NrPdcpEnb::receiveDataFromSourceNode(Packet *pkt, MacNodeId sourceNode)
     Enter_Method("receiveDataFromSourceNode");
     take(pkt);
 
-    auto ctrlInfo = pkt->getTagForUpdate<FlowControlInfo>();
+    auto ctrlInfo = pkt->getTag<FlowControlInfo>();
     if (ctrlInfo->getDirection() == DL) {
-        // if DL, forward the PDCP PDU to the RLC layer
-
-        // recover the original destId of the UE, using the destAddress and write it into the ControlInfo
-        MacNodeId destId = binder_->getNrMacNodeId(Ipv4Address(ctrlInfo->getDstAddr()));
-        ctrlInfo->setSourceId(nodeId_);
-        ctrlInfo->setDestId(destId);
-
+        MacNodeId destId = ctrlInfo->getDestId();
         EV << NOW << " NrPdcpEnb::receiveDataFromSourceNode - Received PDCP PDU from master node with id " << sourceNode << " - destination node[" << destId << "]" << endl;
-
         sendToLowerLayer(pkt);
     }
     else { // UL
-        // if UL, call the handler for reception from RLC layer (of the secondary node)
         EV << NOW << " NrPdcpEnb::receiveDataFromSourceNode - Received PDCP PDU from secondary node with id " << sourceNode << endl;
         fromLowerLayer(pkt);
     }

src/simu5g/stack/pdcp/NrTxPdcpEntity.cc

@@ -29,30 +29,26 @@ void NrTxPdcpEntity::deliverPdcpPdu(Packet *pkt)
         LteTxPdcpEntity::deliverPdcpPdu(pkt);
     }
     else { // ENODEB
-        if (!pdcp_->isDualConnectivityEnabled()) {
-            MacNodeId destId = lteInfo->getDestId();
-            if (getNodeTypeById(destId) != UE)
-                throw cRuntimeError("NrTxPdcpEntity::deliverPdcpPdu - the destination is not a UE, but Dual Connectivity is not enabled.");
+        MacNodeId destId = lteInfo->getDestId();
+        if (getNodeTypeById(destId) != UE)
+            throw cRuntimeError("NrTxPdcpEntity::deliverPdcpPdu - destination must be a UE");
 
+        if (!pdcp_->isDualConnectivityEnabled()) {
             EV << NOW << " NrTxPdcpEntity::deliverPdcpPdu - LCID[" << lteInfo->getLcid() << "] - the destination is a UE. Sending packet to lower layer" << endl;
             LteTxPdcpEntity::deliverPdcpPdu(pkt);
         }
         else {
-            MacNodeId destId = lteInfo->getDestId();
             bool useNR = lteInfo->getUseNR();
             if (!useNR) {
-                if (getNodeTypeById(destId) != UE)
-                    throw cRuntimeError("NrTxPdcpEntity::deliverPdcpPdu - the destination is a UE under the control of a secondary node, but the packet has not been marked as NR packet.");
-
                 EV << NOW << " NrTxPdcpEntity::deliverPdcpPdu - LCID[" << lteInfo->getLcid() << "] useNR[" << useNR << "] - the destination is a UE. Sending packet to lower layer." << endl;
                 LteTxPdcpEntity::deliverPdcpPdu(pkt);
             }
             else { // useNR
-                if (getNodeTypeById(destId) == UE)
-                    throw cRuntimeError("NrTxPdcpEntity::deliverPdcpPdu - the packet has been marked as NR packet, but the destination is not the secondary node");
-
                 EV << NOW << " NrTxPdcpEntity::deliverPdcpPdu - LCID[" << lteInfo->getLcid() << "] - the destination is under the control of a secondary node" << endl;
-                pdcp_->forwardDataToTargetNode(pkt, destId);
+                MacNodeId secondaryNodeId = pdcp_->binder_->getSecondaryNode(pdcp_->nodeId_);
+                ASSERT(secondaryNodeId != NODEID_NONE);
+                ASSERT(secondaryNodeId != pdcp_->nodeId_);
+                pdcp_->forwardDataToTargetNode(pkt, secondaryNodeId);
             }
         }
     }