queueing: mark ECN-capable IPv6 packets in a RED queue instead of dropping them

WHATSNEW

@@ -293,6 +293,22 @@ Notable backward incompatible changes are the following:
    negotiation. The MacQosWithBlockAck example fingerprints are updated; the
    QoS and NonQos showcase fingerprint controls remain unchanged.
 
+17. A Random Early Detection queue with useEcn marks IPv6 packets
+
+   A RedDropper (Random Early Detection, RED) with useEcn = true set
+   Congestion Experienced (CE) on an Explicit Congestion Notification (ECN)
+   capable IPv4 packet above its threshold, but dropped an ECN-capable IPv6
+   packet in the same state. It now marks both. The cause was the
+   EcnMarker::getEcn() and EcnMarker::setEcn() helpers, which read and wrote
+   only the ECN field of an IPv4 header; they now also handle the ECN
+   field of the IPv6 Traffic Class, which RFC 3168 section 5 defines
+   identically. For the same reason, the EcnMarker module now applies an
+   EcnReq tag to IPv6 packets too.
+
+   This changes the results of simulations that send Explicit Congestion
+   Notification (ECN) capable IPv6 traffic through a RedDropper with
+   useEcn = true or through an EcnMarker. IPv4 traffic is unaffected.
+
 Notable backward compatible changes are the following:
 
 1. IEEE 802.11 per-station rate statistics

src/inet/queueing/marker/EcnMarker.cc

@@ -22,6 +22,10 @@
 #include "inet/networklayer/ipv4/Ipv4Header_m.h"
 #endif // ifdef INET_WITH_IPv4
 
+#ifdef INET_WITH_IPv6
+#include "inet/networklayer/ipv6/Ipv6Header.h"
+#endif // ifdef INET_WITH_IPv6
+
 namespace inet {
 namespace queueing {
 
@@ -67,6 +71,19 @@ void EcnMarker::setEcn(Packet *packet, IpEcnCode ecn)
         packet->insertDataAt(ipv4Header, offset);
 #else
         throw cRuntimeError("IPv4 feature is disabled");
+#endif
+    }
+    else if (protocol == &Protocol::ipv6) {
+#ifdef INET_WITH_IPv6
+        packet->removeTagIfPresent<NetworkProtocolInd>();
+        auto ipv6Header = packet->removeDataAt<Ipv6Header>(offset);
+        ipv6Header->setEcn(ecn);
+        auto networkProtocolInd = packet->addTagIfAbsent<NetworkProtocolInd>();
+        networkProtocolInd->setProtocol(protocol);
+        networkProtocolInd->setNetworkProtocolHeader(ipv6Header);
+        packet->insertDataAt(ipv6Header, offset);
+#else
+        throw cRuntimeError("IPv6 feature is disabled");
 #endif
     }
 }
@@ -93,6 +110,12 @@ IpEcnCode EcnMarker::getEcn(const Packet *packet)
 #ifdef INET_WITH_IPv4
         auto ipv4Header = packet->peekDataAt<Ipv4Header>(offset);
         return static_cast<IpEcnCode>(ipv4Header->getEcn());
+#endif
+    }
+    else if (protocol == &Protocol::ipv6) {
+#ifdef INET_WITH_IPv6
+        auto ipv6Header = packet->peekDataAt<Ipv6Header>(offset);
+        return static_cast<IpEcnCode>(ipv6Header->getEcn());
 #endif
     }
     return IP_ECN_NOT_ECT;

src/inet/queueing/marker/EcnMarker.ned

@@ -10,8 +10,8 @@ package inet.queueing.marker;
 import inet.queueing.base.PacketMarkerBase;
 
 //
-// Sets Explicit Congestion Notification (ECN) bits in the IPv4 header based on the
-// attached `EcnReq` tag on the packets.
+// Sets Explicit Congestion Notification (ECN) bits in the IPv4 header or in the
+// Traffic Class of the IPv6 header based on the attached `EcnReq` tag on the packets.
 //
 simple EcnMarker extends PacketMarkerBase
 {

tests/module/IPv6_red_ecn_marking.test

@@ -0,0 +1,87 @@
+%description:
+A Random Early Detection (RED) queue with useEcn marks an IPv6 packet that is
+Explicit Congestion Notification (ECN) capable with Congestion Experienced (CE)
+instead of dropping it (RFC 3168 section 5; the ECN field is the low two bits
+of the IPv6 Traffic Class).
+
+Topology: client --100Mbps-- router --10Mbps-- server. The RedDropperQueue on
+the router's bottleneck interface has minth = 0, maxth = 1 and wq = 1, so a
+packet that finds another packet waiting in the queue is above maxth. At 10 s,
+after IPv6 address autoconfiguration, the client sends 5 User Datagram Protocol
+(UDP) packets with the ECN codepoint ECT(0) (ECN-Capable Transport, traffic
+class 2), faster than the bottleneck forwards them. Expected:
+- UdpBasicAppData-2, -3 and -4, which arrive above maxth, reach the server
+  with traffic class 3 (CE);
+- all 5 packets reach the server: RED drops none of them.
+
+%#--------------------------------------------------------------------------------------------------------------
+%file: test.ned
+
+import inet.networklayer.configurator.ipv6.Ipv6FlatNetworkConfigurator;
+import inet.node.ipv6.Router6;
+import inet.node.ipv6.StandardHost6;
+import ned.DatarateChannel;
+
+network Ipv6RedEcnTestNetwork
+{
+    submodules:
+        configurator: Ipv6FlatNetworkConfigurator;
+        client: StandardHost6;
+        router: Router6;
+        server: StandardHost6;
+    connections:
+        client.ethg++ <--> DatarateChannel { datarate = 100Mbps; delay = 0.1us; } <--> router.ethg++;
+        router.ethg++ <--> DatarateChannel { datarate = 10Mbps; delay = 0.1us; } <--> server.ethg++;
+}
+
+%#--------------------------------------------------------------------------------------------------------------
+%inifile: omnetpp.ini
+
+[General]
+record-vector-results = false
+network = Ipv6RedEcnTestNetwork
+ned-path = .;../../../../src
+sim-time-limit = 11s
+cmdenv-express-mode = false
+cmdenv-log-prefix = "%C: "
+
+**.router.eth[1].queue.typename = "RedDropperQueue"
+**.router.eth[1].queue.red.useEcn = true
+**.router.eth[1].queue.red.minth = 0
+**.router.eth[1].queue.red.maxth = 1
+**.router.eth[1].queue.red.wq = 1
+**.router.eth[1].queue.red.packetCapacity = 100
+
+**.client.numApps = 1
+**.client.app[0].typename = "UdpBasicApp"
+**.client.app[0].destAddresses = "server"
+**.client.app[0].destPort = 1000
+**.client.app[0].messageLength = 1000B
+**.client.app[0].sendInterval = 0.1ms
+**.client.app[0].startTime = 10s
+**.client.app[0].stopTime = 10.00049s
+**.client.app[0].tos = 2
+
+**.server.numApps = 1
+**.server.app[0].typename = "UdpSink"
+**.server.app[0].localPort = 1000
+
+%#--------------------------------------------------------------------------------------------------------------
+%subst: /omnetpp:://
+%#--------------------------------------------------------------------------------------------------------------
+%contains-regex: stdout
+Ipv6RedEcnTestNetwork\.server\.app\[0\]: Received packet: \(inet::Packet\)UdpBasicAppData-2 .* TOS=3 DSCP
+%#--------------------------------------------------------------------------------------------------------------
+%contains-regex: stdout
+Ipv6RedEcnTestNetwork\.server\.app\[0\]: Received packet: \(inet::Packet\)UdpBasicAppData-3 .* TOS=3 DSCP
+%#--------------------------------------------------------------------------------------------------------------
+%contains-regex: stdout
+Ipv6RedEcnTestNetwork\.server\.app\[0\]: Received packet: \(inet::Packet\)UdpBasicAppData-4 .* TOS=3 DSCP
+%#--------------------------------------------------------------------------------------------------------------
+%contains: stdout
+Ipv6RedEcnTestNetwork.server.app[0]: received 5 packets
+%#--------------------------------------------------------------------------------------------------------------
+%postrun-command: grep "undisposed object:" test.out > test_undisposed.out || true
+%not-contains: test_undisposed.out
+undisposed object: (
+%#--------------------------------------------------------------------------------------------------------------