diff --git a/CHANGES.html b/CHANGES.html
index e3b421b60..97772da87 100644
--- a/CHANGES.html
+++ b/CHANGES.html
@@ -56,6 +56,7 @@ us a note on ns-developers mailing list.</p>
 <ul>
 <li>A new TCP congestion control, <b>TcpLinuxReno</b>, has been added.</li>
 <li>Added, to <b>PIE queue disc</b>, <b>queue delay calculation using timestamp</b> feature (Linux default behavior), <b>cap drop adjustment</b> feature (Section 5.5 of RFC 8033), <b>ECN</b> (Section 5.1 of RFC 8033) and <b>derandomization</b> feature (Section 5.4 of RFC 8033).</li>
+<li>Added <b>L4S Mode</b> to FqCoDel and CoDel queue discs</li>
 </ul>
 <h2>Changes to existing API:</h2>
 <ul>
diff --git a/RELEASE_NOTES b/RELEASE_NOTES
index 5072994d4..ec50c4871 100644
--- a/RELEASE_NOTES
+++ b/RELEASE_NOTES
@@ -21,6 +21,7 @@ New user-visible features
   timestamp feature (Linux default behavior), cap drop adjustment feature
   (Section 5.5 of RFC 8033), ECN (Section 5.1 of RFC 8033) and derandomization
   feature (Section 5.4 of RFC 8033).
+- (traffic-control) Add support for L4S mode to CoDel and FqCoDel queue discs
 
 Bugs fixed
 ----------
diff --git a/src/test/ns3tc/fq-codel-queue-disc-test-suite.cc b/src/test/ns3tc/fq-codel-queue-disc-test-suite.cc
index 9d2c9a367..afe5ff840 100644
--- a/src/test/ns3tc/fq-codel-queue-disc-test-suite.cc
+++ b/src/test/ns3tc/fq-codel-queue-disc-test-suite.cc
@@ -950,6 +950,162 @@ FqCoDelQueueDiscSetLinearProbing::DoRun (void)
   Simulator::Destroy ();
 }
 
+
+/**
+ * This class tests L4S mode
+ * Any future classifier options (e.g. SetAssociativeHash) should be disabled to prevent a hash collision on this test case.
+ */
+class FqCoDelQueueDiscL4sMode : public TestCase
+{
+public:
+  FqCoDelQueueDiscL4sMode ();
+  virtual ~FqCoDelQueueDiscL4sMode ();
+
+private:
+  virtual void DoRun (void);
+  void AddPacket (Ptr<FqCoDelQueueDisc> queue, Ipv4Header hdr, u_int32_t nPkt);
+  void AddPacketWithDelay (Ptr<FqCoDelQueueDisc> queue,Ipv4Header hdr, double delay, uint32_t nPkt);
+  void Dequeue (Ptr<FqCoDelQueueDisc> queue, uint32_t nPkt);
+  void DequeueWithDelay (Ptr<FqCoDelQueueDisc> queue, double delay, uint32_t nPkt);
+};
+
+FqCoDelQueueDiscL4sMode::FqCoDelQueueDiscL4sMode ()
+  : TestCase ("Test L4S mode")
+{
+}
+
+FqCoDelQueueDiscL4sMode::~FqCoDelQueueDiscL4sMode ()
+{
+}
+
+void
+FqCoDelQueueDiscL4sMode::AddPacket (Ptr<FqCoDelQueueDisc> queue, Ipv4Header hdr, uint32_t nPkt)
+{
+  Address dest;
+  Ptr<Packet> p = Create<Packet> (100);
+  for (uint32_t i = 0; i < nPkt; i++)
+    {
+      Ptr<Ipv4QueueDiscItem> item = Create<Ipv4QueueDiscItem> (p, dest, 0, hdr);
+      queue->Enqueue (item);
+    }
+}
+
+void
+FqCoDelQueueDiscL4sMode::AddPacketWithDelay (Ptr<FqCoDelQueueDisc> queue,Ipv4Header hdr, double delay, uint32_t nPkt)
+{
+  for (uint32_t i = 0; i < nPkt; i++)
+    {
+      Simulator::Schedule (Time (Seconds ((i + 1) * delay)), &FqCoDelQueueDiscL4sMode::AddPacket, this, queue, hdr, 1);
+    }
+}
+
+void
+FqCoDelQueueDiscL4sMode::Dequeue (Ptr<FqCoDelQueueDisc> queue, uint32_t nPkt)
+{
+  for (uint32_t i = 0; i < nPkt; i++)
+    {
+      Ptr<QueueDiscItem> item = queue->Dequeue ();
+    }
+}
+
+void
+FqCoDelQueueDiscL4sMode::DequeueWithDelay (Ptr<FqCoDelQueueDisc> queue, double delay, uint32_t nPkt)
+{
+  for (uint32_t i = 0; i < nPkt; i++)
+    {
+      Simulator::Schedule (Time (Seconds ((i + 1) * delay)), &FqCoDelQueueDiscL4sMode::Dequeue, this, queue, 1);
+    }
+}
+
+void
+FqCoDelQueueDiscL4sMode::DoRun (void)
+{
+  // Test is divided into 2 sub test cases:
+  // 1) Without hash collisions
+  // 2) With hash collisions
+
+  // Test case 1, Without hash collisions
+  Ptr<FqCoDelQueueDisc> queueDisc = CreateObjectWithAttributes<FqCoDelQueueDisc> ("MaxSize", StringValue ("10240p"), "UseEcn", BooleanValue (true),
+                                                                                  "Perturbation", UintegerValue (0), "UseL4s", BooleanValue (true),
+                                                                                  "CeThreshold", TimeValue (MilliSeconds (2)));
+
+  queueDisc->SetQuantum (1514);
+  queueDisc->Initialize ();
+  Ipv4Header hdr;
+  hdr.SetPayloadSize (100);
+  hdr.SetSource (Ipv4Address ("10.10.1.1"));
+  hdr.SetDestination (Ipv4Address ("10.10.1.2"));
+  hdr.SetProtocol (7);
+  hdr.SetEcn (Ipv4Header::ECN_ECT1);
+
+  // Add 70 ECT1 (ECN capable) packets from the first flow
+  // Set delay = 0.5ms
+  double delay = 0.0005;
+  Simulator::Schedule (Time (Seconds (0)), &FqCoDelQueueDiscL4sMode::AddPacketWithDelay, this, queueDisc, hdr, delay, 70);
+
+  // Add 70 ECT0 (ECN capable) packets from second flow
+  hdr.SetEcn (Ipv4Header::ECN_ECT0);
+  hdr.SetDestination (Ipv4Address ("10.10.1.10"));
+  Simulator::Schedule (Time (Seconds (0)), &FqCoDelQueueDiscL4sMode::AddPacketWithDelay, this, queueDisc, hdr, delay, 70);
+
+  //Dequeue 140 packets with delay 1ms
+  delay = 0.001;
+  DequeueWithDelay (queueDisc, delay, 140);
+  Simulator::Run ();
+  Simulator::Stop (Seconds (8.0));
+  Ptr<CoDelQueueDisc> q0 = queueDisc->GetQueueDiscClass (0)->GetQueueDisc ()->GetObject <CoDelQueueDisc> ();
+  Ptr<CoDelQueueDisc> q1 = queueDisc->GetQueueDiscClass (1)->GetQueueDisc ()->GetObject <CoDelQueueDisc> ();
+
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNMarkedPackets (CoDelQueueDisc::CE_THRESHOLD_EXCEEDED_MARK), 66, "There should be 66 marked packets"
+                        "4th packet is enqueued at 2ms and dequeued at 4ms hence the delay of 2ms which not greater than CE threshold"
+                        "5th packet is enqueued at 2.5ms and dequeued at 5ms hence the delay of 2.5ms and subsequent packet also do have delay"
+                        "greater than CE threshold so all the packets after 4th packet are marked");
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNDroppedPackets (CoDelQueueDisc::TARGET_EXCEEDED_DROP), 0, "There should not be any dropped packets");
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNMarkedPackets (CoDelQueueDisc::TARGET_EXCEEDED_MARK), 0, "There should not be any marked packets");
+  NS_TEST_EXPECT_MSG_EQ (q1->GetStats ().GetNMarkedPackets (CoDelQueueDisc::TARGET_EXCEEDED_MARK), 1, "There should be 1 marked packets");
+  NS_TEST_EXPECT_MSG_EQ (q1->GetStats ().GetNDroppedPackets (CoDelQueueDisc::TARGET_EXCEEDED_DROP), 0, "There should not be any dropped packets");
+
+  Simulator::Destroy ();
+
+  // Test case 2, With hash collisions
+  queueDisc = CreateObjectWithAttributes<FqCoDelQueueDisc> ("MaxSize", StringValue ("10240p"), "UseEcn", BooleanValue (true),
+                                                                                  "Perturbation", UintegerValue (0), "UseL4s", BooleanValue (true),
+                                                                                  "CeThreshold", TimeValue (MilliSeconds (2)));
+
+  queueDisc->SetQuantum (1514);
+  queueDisc->Initialize ();
+  hdr.SetPayloadSize (100);
+  hdr.SetSource (Ipv4Address ("10.10.1.1"));
+  hdr.SetDestination (Ipv4Address ("10.10.1.2"));
+  hdr.SetProtocol (7);
+  hdr.SetEcn (Ipv4Header::ECN_ECT1);
+
+  // Add 70 ECT1 (ECN capable) packets from the first flow
+  // Set delay = 1ms
+  delay = 0.001;
+  Simulator::Schedule (Time (Seconds (0.0005)), &FqCoDelQueueDiscL4sMode::AddPacket, this, queueDisc, hdr, 1);
+  Simulator::Schedule (Time (Seconds (0.0005)), &FqCoDelQueueDiscL4sMode::AddPacketWithDelay, this, queueDisc, hdr, delay, 69);
+
+  // Add 70 ECT0 (ECN capable) packets from first flow
+  hdr.SetEcn (Ipv4Header::ECN_ECT0);
+  Simulator::Schedule (Time (Seconds (0)), &FqCoDelQueueDiscL4sMode::AddPacketWithDelay, this, queueDisc, hdr, delay, 70);
+
+  //Dequeue 140 packets with delay 1ms
+  DequeueWithDelay (queueDisc, delay, 140);
+  Simulator::Run ();
+  Simulator::Stop (Seconds (8.0));
+  q0 = queueDisc->GetQueueDiscClass (0)->GetQueueDisc ()->GetObject <CoDelQueueDisc> ();
+
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNMarkedPackets (CoDelQueueDisc::CE_THRESHOLD_EXCEEDED_MARK), 68, "There should be 68 marked packets"
+                        "2nd ECT1 packet is enqueued at 1.5ms and dequeued at 3ms hence the delay of 1.5ms which not greater than CE threshold"
+                        "3rd packet is enqueued at 2.5ms and dequeued at 5ms hence the delay of 2.5ms and subsequent packet also do have delay"
+                        "greater than CE threshold so all the packets after 2nd packet are marked");
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNDroppedPackets (CoDelQueueDisc::TARGET_EXCEEDED_DROP), 0, "There should not be any dropped packets");
+  NS_TEST_EXPECT_MSG_EQ (q0->GetStats ().GetNMarkedPackets (CoDelQueueDisc::TARGET_EXCEEDED_MARK), 1, "There should be 1 marked packets");
+
+  Simulator::Destroy ();
+
+}
 class FqCoDelQueueDiscTestSuite : public TestSuite
 {
 public:
@@ -966,6 +1122,7 @@ FqCoDelQueueDiscTestSuite::FqCoDelQueueDiscTestSuite ()
   AddTestCase (new FqCoDelQueueDiscUDPFlowsSeparation, TestCase::QUICK);
   AddTestCase (new FqCoDelQueueDiscECNMarking, TestCase::QUICK);
   AddTestCase (new FqCoDelQueueDiscSetLinearProbing, TestCase::QUICK);
+  AddTestCase (new FqCoDelQueueDiscL4sMode, TestCase::QUICK);
 }
 
-static FqCoDelQueueDiscTestSuite fqCoDelQueueDiscTestSuite;
+static FqCoDelQueueDiscTestSuite fqCoDelQueueDiscTestSuite;
\ No newline at end of file
diff --git a/src/traffic-control/doc/fq-codel.rst b/src/traffic-control/doc/fq-codel.rst
index c6d983f84..78e7015f3 100644
--- a/src/traffic-control/doc/fq-codel.rst
+++ b/src/traffic-control/doc/fq-codel.rst
@@ -66,6 +66,15 @@ Neither internal queues nor classes can be configured for an FqCoDel
 queue disc.
 
 
+Possible next steps
+===================
+
+* what to do if ECT(1) and either/both ECT(0) and NotECT are in the same flow queue (hash collisions or tunnels)-- our L4S traffic flows will avoid this situation by supporting AccECN and ECN++ (and if it happens in practice, the CoDel logic will just apply two separate thresholds)
+* adding a ramp marking response instead of step threshold
+* adding a floor value (to suppress marks if the queue length is below a certain number of bytes or packets)
+* adding a heuristic such as in PIE to avoid marking a packet if it arrived to an empty flow queue (check on ingress, remember at egress time)
+
+
 References
 ==========
 
@@ -79,12 +88,15 @@ Attributes
 
 The key attributes that the FqCoDelQueue class holds include the following:
 
+* ``UseEcn:`` True to use ECN (packets are marked instead of being dropped)
 * ``Interval:`` The interval parameter to be used on the CoDel queues. The default value is 100 ms.
 * ``Target:`` The target parameter to be used on the CoDel queues. The default value is 5 ms.
 * ``MaxSize:`` The limit on the maximum number of packets stored by FqCoDel.
 * ``Flows:`` The number of flow queues managed by FqCoDel.
 * ``DropBatchSize:`` The maximum number of packets dropped from the fat flow.
 * ``Perturbation:`` The salt used as an additional input to the hash function used to classify packets.
+* ``CeThreshold`` The FqCoDel CE threshold for marking packets
+* ``UseL4s`` True to use L4S (only ECT1 packets are marked at CE threshold)
 * ``EnableSetAssociativeHash:`` The parameter used to enable set associative hash.
 
 Perturbation is an optional configuration attribute and can be used to generate
@@ -112,6 +124,13 @@ can be configured as follows:
                                                  "Perturbation", UintegerValue (256));
   QueueDiscContainer qdiscs = tch.Install (devices);
 
+The example for FqCoDel's L4S mode is `FqCoDel-L4S-example.cc` located in ``src/traffic-control/examples``.  To run the file (the first invocation below shows the available
+command-line options):
+.. sourcecode:: bash
+   $ ./waf --run "FqCoDel-L4S-example --PrintHelp"
+   $ ./waf --run "FqCoDel-L4S-example --scenarioNum=5" 
+The expected output from the previous command are .dat files.
+
 Validation
 **********
 
@@ -122,7 +141,9 @@ The FqCoDel model is tested using :cpp:class:`FqCoDelQueueDiscTestSuite` class d
 * Test 3: The third test checks the dequeue operation and the deficit round robin-based scheduler.
 * Test 4: The fourth test checks that TCP packets with distinct port numbers are enqueued into different flow queues.
 * Test 5: The fifth test checks that UDP packets with distinct port numbers are enqueued into different flow queues.
-* Test 6: The sixth test checks the working of set associative hashing and its linear probing capabilities by using TCP packets with different hashes enqueued into different sets and queues.
+* Test 6: The sixth test checks that the packets are marked correctly.
+* Test 7: The seventh test checks the working of set associative hashing and its linear probing capabilities by using TCP packets with different hashes enqueued into different sets and queues.
+* Test 8: The eighth test checks the L4S mode of FqCoDel where ECT1 packets are marked at CE threshold (target delay does not matter) while ECT0 packets continue to be marked at target delay (CE threshold does not matter).
 
 The test suite can be run using the following commands::
 
diff --git a/src/traffic-control/examples/fqcodel-l4s-example.cc b/src/traffic-control/examples/fqcodel-l4s-example.cc
new file mode 100644
index 000000000..51b74b6f2
--- /dev/null
+++ b/src/traffic-control/examples/fqcodel-l4s-example.cc
@@ -0,0 +1,883 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2020 NITK Surathkal
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Authors: Bhaskar Kataria <bhaskar.k7920@gmail.com>
+ *          Tom Henderson <tomhend@u.washington.edu>
+ *          Mohit P. Tahiliani <tahiliani@nitk.edu.in>
+ *          Vivek Jain <jain.vivek.anand@gmail.com>
+ *          Ankit Deepak <adadeepak8@gmail.com>
+ * This script is written using Tom Henderson's L4S evaluation available at https://gitlab.com/tomhend/modules/l4s-evaluation
+ */
+
+// The 9 configurations below test BIC and DCTCP under various scenarios.
+// The configuration of the scenarios starts from basic TCP BIC without ECN
+// with the base RTT of 80ms and then in the next scenario, ECN is enabled,
+// and gradually, the complexity of the scenario increases and the last scenario
+// consists of 2 flows one with BIC and other with DCTCP and finally tests
+// The performance of the L4S mode of FqCoDel queue disc.
+
+/** Network topology - For Configuration 1, 2
+ *
+ *      1Gbps, 40ms      100Mbps, 1us       1Gbps, 1us
+ *   n0 ---------- n2 ---------------- n3 --------------n4
+ *
+ * Configuration 1: single flow TCP BIC without ECN, base RTT of 80 ms
+ *
+ * Expected Result:
+ * Throughput:        Oscillating around 100ms.
+ * Ping RTT:          Oscillating between 80ms and 80.5ms
+ * Drop frequency:    Should be around 1 drop per 100ms with around 9 spikes in 10 seconds
+ * Length:            below 5ms but with frequent spikes
+ * Mark Frequency:    There should not be any marks
+ * Congestion Window: Oscillating between around 600 segments and 800 segments
+ * TCP RTT:           Oscillating below 5ms frequent spikes up to 90ms
+ * Queue Delay-N0:    Below 5ms with frequent spikes
+ *
+ * Configuration 2: single flow TCP BIC with ECN, base RTT of 80 ms
+ *
+ * Expected Result:
+ * Throughput:        Reaching 100Mbps and oscillating more than the previous configuration.
+ * Ping RTT:          Oscillating between 80ms and 80.5ms
+ * Drop frequency:    There should not be any drops
+ * Length:            Below 5ms with frequent spikes, average around 3ms
+ * Mark Frequency:    Should be around 1 mark per 100ms with around 9 spikes in 10 seconds
+ * Congestion Window: Oscillating between around 400 segments and 800 segments
+ * TCP RTT:           Below 85ms with frequent spikes up to 95ms (more than the previous configuration)
+ * Queue Delay-n0:    Below 5ms with frequent spikes
+ */
+
+/** Network topology - For Configuration 3, 4
+ *
+ *     1Gbps, 1ms      100Mbps, 1us        1Gbps, 1us
+ *   n0 ---------- n2 ---------------- n3 --------------n4
+ *
+ * Configuration 3: single flow DCTCP with ECN ECT(0), CE_threshold = 1ms, base RTT of 1ms
+ *
+ * Expected Result:
+ * Throughput:        Fixed just below 100Mbps.
+ * Ping RTT:          Oscillating below 1.5ms
+ * Drop frequency:    There should not be any drops
+ * Length:            Very frequently oscillating between 0.5ms and 1ms with frequent spikes up to 1.2ms
+ * Mark Frequency:    Around 160 marks per 100ms
+ * Congestion Window: Very frequently oscillating at a low value (below 25)
+ * TCP RTT:           Very frequently oscillating, below 5ms
+ * Queue Delay-n0:    Very frequently oscillating between 0.5ms and 1ms with spikes up to 1.2ms
+ *
+ * Configuration 4: single flow DCTCP with ECN ECT(1), L4S mode enabled on FqCoDel, base RTT of 1ms
+ *
+ * Expected Result:
+ * Throughput:        Fixed just below 100Mbps.
+ * Ping RTT:          Oscillating below 1.5ms
+ * Drop frequency:    There should not be any drops
+ * Length:            Very frequently oscillating between 0.5ms and 1ms with frequent spikes up to 1.2ms
+ * Mark Frequency:    Around 160 marks per 100ms
+ * Congestion Window: Very frequently oscillating at a low value (below 25)
+ * TCP RTT:           Very frequently oscillating, below 5ms
+ * Queue Delay-n0:    Very frequently oscillating between 0.5ms and 1ms with spikes up to 1.2ms
+ */
+
+/** Network topology - For Configuration 5, 6
+ *
+ *    1Gbps, 40ms                            1Gbps, 1us
+ * n0--------------|                    |---------------n4
+ *                 |    100Mbps, 1us    |
+ *                 n2------------------n3
+ *    1Gbps, 40ms  |                    |    1Gbps, 1us
+ * n1--------------|                    |---------------n5
+ *
+ * Configuration 5: Two flows TCP BIC without ECN, base RTT of 80 ms
+ *
+ * Expected Result:
+ * Throughput-n0:        Oscillating around 100 before second flow starts, and after that, oscillating around 50.
+ * Throughput-n1:        Oscillating around 50.
+ * Ping RTT:             Oscillating and reaching around 80.5ms
+ * Drop frequency:       Around 1 drop per 100ms, more spikes than the single flow
+ * Length:               Around 5ms with spikes reaching 10ms
+ * Mark Frequency:       There should not be any marks
+ * Congestion Window-n0: Oscillating between 800 segments and 600 segments before second flow starts,
+ *                       after that oscillating around 300 segments
+ * Congestion Window-n0: Oscillating around 300 segments
+ * TCP RTT-n0:           Below 85ms with spikes reaching 90ms before second flow starts, and after that
+ *                       below 85ms with spikes reaching 90ms
+ * TCP RTT-n0:           Below 85ms with spikes reaching 90ms
+ * Queue Delay-n0:       Below 5ms with spikes reaching 10ms before second flow starts and after that
+ *                       below 5ms with spikes up to 15ms.
+ * Queue Delay-n0:       Below 5ms with spikes up to 15ms.
+ *
+ * Configuration 6: Two flows TCP BIC with ECN, base RTT of 80 ms
+ *
+ * Expected Result:
+ *
+ * Throughput-n0:        Oscillating around 100 before second flow starts, and after that, oscillating around 50.
+ * Throughput-n1:        Oscillating around 50.
+ * Ping RTT:             Oscillating and reaching around 80.5ms
+ * Drop frequency:       There should not be any drops
+ * Mark Frequency:       Around 1 drop per 100ms, more spikes than the single flow
+ * Length:               Around 5ms with spikes reaching 15ms
+ * Congestion Window-n0: Oscillating between 800 segments and 600 segments before second flow starts,
+ *                       after that oscillating around 300 segments
+ * Congestion Window-n0: Oscillating around 300 segments
+ * TCP RTT-n0:           Below 85ms with spikes reaching 95ms before second flow starts, and after that
+ *                       below 85ms with spikes reaching 100ms
+ * TCP RTT-n0:           Below 85ms with spikes reaching 100ms
+ * Queue Delay-n0:       Below 5ms with spikes reaching 15ms before second flow starts and after that
+ *                       below 5ms with spikes up to 20ms.
+ * Queue Delay-n0:       Below 5ms with spikes up to 20ms.
+ */
+
+/**Network topology - For Configuration 7, 8
+ *
+ *    1Gbps, 1ms                            1Gbps, 1us
+ * n0--------------|                    |---------------n4
+ *                 |    100Mbps, 1us    |
+ *                 n2------------------n3
+ *     1Gbps, 1ms  |                    |    1Gbps, 1us
+ * n1--------------|                    |---------------n5
+ *
+ * Configuration 7: Two flows DCTCP with ECN ECT(0), CE_threshold = 1ms, base RTT of 1ms
+ *
+ * Expected Result:
+ * Throughput-n0:        Fixed around 100 before second flow starts, and after that, fixed around 50.
+ * Throughput-n1:        Fixed around 50.
+ * Ping RTT:             Oscillating and reaching around 1.5ms
+ * Drop frequency:       There should not be any drops
+ * Length:               Around 1ms.
+ * Mark Frequency:       Oscillating little above 150 marks per 100ms before second flow start,
+ *                       and after that oscillating little below 250 marks per 100ms
+ * Congestion Window-n0: Oscillating around 20 segments before second flow starts
+ *                       then oscillating around 11 segments
+ * Congestion Window-n1: Oscillating around 11 segments
+ * TCP RTT-n0:           Oscillating between 2ms and 5ms before seconds flow starts and after that
+ *                       oscillating between 3ms and 5ms
+ * TCP RTT-n1:           Oscillating between 3ms and 5ms
+ * Queue Delay-n0:       Oscillating frequently below 1ms before second flow starts and after that just below 1.4ms
+ * Queue Delay-n1:       Oscillating frequently between 0.4ms and 1.4ms
+ *
+ * Configuration 8: Two flows DCTCP with ECN ECT(1), L4S mode enabled on FqCoDel, base RTT of 1ms
+ *
+ * Throughput-n0:        Fixed around 100 before second flow starts, and after that, fixed around 50.
+ * Throughput-n1:        Fixed around 50.
+ * Ping RTT:             Oscillating and reaching around 1.5ms
+ * Drop frequency:       There should not be any drops
+ * Length:               Around 1ms.
+ * Mark Frequency:       Oscillating little above 150 marks per 100ms before second flow start,
+ *                       and after that oscillating little below 250 marks per 100ms
+ * Congestion Window-n0: Oscillating around 20 segments before second flow starts
+ *                       then oscillating around 11 segments
+ * Congestion Window-n1: Oscillating around 11 segments
+ * TCP RTT-n0:           Oscillating between 2ms and 5ms before seconds flow starts and after that
+ *                       oscillating between 3ms and 5ms
+ * TCP RTT-n1:           Oscillating between 3ms and 5ms
+ * Queue Delay-n0:       Oscillating frequently below 1ms before second flow starts and after that just below 1.4ms
+ * Queue Delay-n1:       Oscillating frequently between 0.4ms and 1.4ms
+ */
+
+/**Network topology - For Configuration 9
+ *
+ *    1Gbps, 1ms                            1Gbps, 1us
+ * n0--------------|                    |---------------n4
+ *                 |    100Mbps, 1us    |
+ *                 n2------------------n3
+ *     1Gbps, 80ms |                    |    1Gbps, 1us
+ * n1--------------|                    |---------------n5
+ *
+ * Configuration 9: One TCP BIC (n0) with base RTT of 80 ms, one DCTCP (n1) with ECN ECT(1), L4S mode enabled, base RTT 1ms
+ *
+ * Throughput-n0:        Oscillating below 100Mbps before second flow starts, and after that, oscillating around 50Mbps.
+ * Throughput-n1:        Oscillating around 50Mbps.
+ * Ping RTT:             Oscillating and reaching around 80.5ms
+ * Drop frequency:       There should not be any drops
+ * Length:               Around 5ms with frequent spikes above 10ms before second flow starts and after that spikes below 10ms.
+ * Mark Frequency:       Oscillating 1 marks per 100ms before second flow start,
+ *                       and after that oscillating below 200 marks per 100ms
+ * Congestion Window-n0: Oscillating around 600 segments before second flow starts
+ *                       then oscillating around 300 segments
+ * Congestion Window-n1: Oscillating around 300 segments
+ * TCP RTT-n0:           Around 85ms with spikes reaching around 95ms before second flow starts and after that around 85ms
+ *                       with spikes reaching 100ms
+ * TCP RTT-n1:           Around 85ms with spikes reaching 100ms
+ * Queue Delay-n0:       Around 5ms with spikes above 10ms before second flow starts and nearly the same after that too.
+ * Queue Delay-n1:       Oscillating frequently between 0.4ms and 1.4ms with spikes reaching 3ms.
+ *
+ */
+
+/**
+* clients and servers are configured for ICMP measurements and TCP throughput
+* and latency measurements in the downstream direction
+*
+* Depending on the scenario, the middlebox and endpoints will be
+* configured differently. Scenarios can be configured explicitly by
+* scenario Numbers as well as by combinations of input arguments.
+*
+* All link rates are enforced by a point-to-point (P2P) ns-3 model with full
+* duplex operation.  The link rate and delays are enforced by this model
+* (in contrast to netem and shaping in the testbed).  Dynamic queue limits
+* (BQL) are enabled to allow for queueing to occur at the priority queue layer;
+*
+* By default, the ns-3 FQ-CoDel model is installed on all interfaces.
+*
+* The ns-3 FQ-CoDel model uses ns-3 defaults:
+* - 100ms interval
+* - 5ms target
+* - drop batch size of 64 packets
+* - minbytes of 1500
+*
+* Default simulation time is 70 sec.  For single flow experiments, the flow is
+* started at simulation time 5 sec; if a second flow is used, it starts
+* at 15 sec.
+*
+* ping frequency is set at 100ms
+* Note that pings may miss the peak of queue buildups for short-lived flows;
+* hence, we trace also the queue length expressed in units of time at
+* the bottleneck link rate.
+*
+* A command-line option to enable CE Threshold is provided
+*
+* Results will be available in ns-3-dev/results/FqCoDel-L4S consisting of 14 .dat files
+*
+* Measure:
+*  - ping RTT
+*  - TCP RTT estimate
+*  - TCP throughput
+*  - Queue delay
+*
+* IPv4 addressing
+* ----------------------------
+* pingServer       10.1.1.2 (ping source)
+* n0Server         10.1.2.2 (data sender)
+* n1Server         10.1.3.2 (data sender)
+* pingClient       192.168.1.2
+* n4Client         192.168.2.2
+* n5Client         192.168.3.2
+*
+* Program options
+* ---------------
+*    --n0TcpType:           First TCP type (bic, dctcp, or reno) [bic]
+*    --n1TcpType:           Second TCP type (cubic, dctcp, or reno) []
+*    --bottleneckQueueType: M3 queue type (fq or codel) [fq]
+*    --baseRtt:             base RTT [80ms]
+*    --useCeThreshold:      use CE threshold [false]
+*    --ceThreshold:         CE threshold [1ms]
+*    --bottleneckRate       data rate of bottleneck [100Mbps]
+*    --linkrate:            data rate of edge link to bottleneck link [1Gbps]
+*    --stopTime:            simulation stop time [70s]
+*    --enablePcap:          enable Pcap [false]
+*    (additional arguments to control trace names)
+**/
+
+#include "ns3/core-module.h"
+#include "ns3/network-module.h"
+#include "ns3/internet-module.h"
+#include "ns3/flow-monitor-helper.h"
+#include "ns3/point-to-point-module.h"
+#include "ns3/applications-module.h"
+#include "ns3/internet-apps-module.h"
+#include "ns3/traffic-control-module.h"
+
+using namespace ns3;
+
+NS_LOG_COMPONENT_DEFINE ("FqCoDelL4SExample");
+
+uint32_t checkTimes;
+double avgQueueDiscSize;
+
+uint32_t g_n0BytesReceived = 0;
+uint32_t g_n1BytesReceived = 0;
+uint32_t g_marksObserved = 0;
+uint32_t g_dropsObserved = 0;
+
+void
+TraceN0Cwnd (std::ofstream* ofStream, uint32_t oldCwnd, uint32_t newCwnd)
+{
+  // TCP segment size is configured below to be 1448 bytes
+  // so that we can report cwnd in units of segments
+  *ofStream << Simulator::Now ().GetSeconds () << " " << static_cast<double> (newCwnd) / 1448 << std::endl;
+}
+
+void
+TraceN1Cwnd (std::ofstream* ofStream, uint32_t oldCwnd, uint32_t newCwnd)
+{
+  // TCP segment size is configured below to be 1448 bytes
+  // so that we can report cwnd in units of segments
+  *ofStream << Simulator::Now ().GetSeconds () << " " << static_cast<double> (newCwnd) / 1448 << std::endl;
+}
+
+void
+TraceN0Rtt (std::ofstream* ofStream, Time oldRtt, Time newRtt)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << newRtt.GetSeconds () * 1000 << std::endl;
+}
+
+void
+TraceN1Rtt (std::ofstream* ofStream, Time oldRtt, Time newRtt)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << newRtt.GetSeconds () * 1000 << std::endl;
+}
+
+void
+TracePingRtt (std::ofstream* ofStream, Time rtt)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << rtt.GetSeconds () * 1000 << std::endl;
+}
+
+void
+TraceN0Rx (Ptr<const Packet> packet, const Address &address)
+{
+  g_n0BytesReceived += packet->GetSize ();
+}
+
+void
+TraceN1Rx (Ptr<const Packet> packet, const Address &address)
+{
+  g_n1BytesReceived += packet->GetSize ();
+}
+
+void
+TraceDrop (std::ofstream* ofStream, Ptr<const QueueDiscItem> item)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << std::hex << item->Hash () << std::endl;
+  g_dropsObserved++;
+}
+
+void
+TraceMark (std::ofstream* ofStream, Ptr<const QueueDiscItem> item, const char* reason)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << std::hex << item->Hash () << std::endl;
+  g_marksObserved++;
+}
+
+void
+TraceQueueLength  (std::ofstream* ofStream, DataRate linkRate, uint32_t oldVal, uint32_t newVal)
+{
+  // output in units of ms
+  *ofStream << Simulator::Now ().GetSeconds () << " " << std::fixed << static_cast<double> (newVal * 8) / (linkRate.GetBitRate () / 1000) << std::endl;
+}
+
+void
+TraceDropsFrequency (std::ofstream* ofStream, Time dropsSamplingInterval)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << g_dropsObserved << std::endl;
+  g_dropsObserved = 0;
+  Simulator::Schedule (dropsSamplingInterval, &TraceDropsFrequency, ofStream, dropsSamplingInterval);
+}
+
+void
+TraceMarksFrequency (std::ofstream* ofStream, Time marksSamplingInterval)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << g_marksObserved << std::endl;
+  g_marksObserved = 0;
+  Simulator::Schedule (marksSamplingInterval, &TraceMarksFrequency, ofStream, marksSamplingInterval);
+}
+
+void
+TraceN0Throughput (std::ofstream* ofStream, Time throughputInterval)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << g_n0BytesReceived * 8 / throughputInterval.GetSeconds () / 1e6 << std::endl;
+  g_n0BytesReceived = 0;
+  Simulator::Schedule (throughputInterval, &TraceN0Throughput, ofStream, throughputInterval);
+}
+
+void
+TraceN1Throughput (std::ofstream* ofStream, Time throughputInterval)
+{
+  *ofStream << Simulator::Now ().GetSeconds () << " " << g_n1BytesReceived * 8 / throughputInterval.GetSeconds () / 1e6 << std::endl;
+  g_n1BytesReceived = 0;
+  Simulator::Schedule (throughputInterval, &TraceN1Throughput, ofStream, throughputInterval);
+}
+
+void
+ScheduleN0TcpCwndTraceConnection (std::ofstream* ofStream)
+{
+  Config::ConnectWithoutContext ("/NodeList/1/$ns3::TcpL4Protocol/SocketList/0/CongestionWindow", MakeBoundCallback (&TraceN0Cwnd, ofStream));
+}
+
+void
+ScheduleN0TcpRttTraceConnection (std::ofstream* ofStream)
+{
+  Config::ConnectWithoutContext ("/NodeList/1/$ns3::TcpL4Protocol/SocketList/0/RTT", MakeBoundCallback (&TraceN0Rtt, ofStream));
+}
+
+void
+ScheduleN0PacketSinkConnection (void)
+{
+  Config::ConnectWithoutContext ("/NodeList/6/ApplicationList/*/$ns3::PacketSink/Rx", MakeCallback (&TraceN0Rx));
+}
+
+void
+ScheduleN1TcpCwndTraceConnection (std::ofstream* ofStream)
+{
+  Config::ConnectWithoutContext ("/NodeList/2/$ns3::TcpL4Protocol/SocketList/0/CongestionWindow", MakeBoundCallback (&TraceN1Cwnd, ofStream));
+}
+
+void
+ScheduleN1TcpRttTraceConnection (std::ofstream* ofStream)
+{
+  Config::ConnectWithoutContext ("/NodeList/2/$ns3::TcpL4Protocol/SocketList/0/RTT", MakeBoundCallback (&TraceN1Rtt, ofStream));
+}
+
+void
+ScheduleN1PacketSinkConnection (void)
+{
+  Config::ConnectWithoutContext ("/NodeList/7/ApplicationList/*/$ns3::PacketSink/Rx", MakeCallback (&TraceN1Rx));
+}
+
+static void
+PacketDequeue (std::ofstream* n0OfStream, std::ofstream* n1OfStream, Ptr<QueueDiscItem const> item)
+{
+  Ptr<Packet> p = item->GetPacket ();
+  Ptr<const Ipv4QueueDiscItem> iqdi = Ptr<const Ipv4QueueDiscItem> (dynamic_cast<const Ipv4QueueDiscItem *> (PeekPointer (item)));
+  Ipv4Address address = iqdi->GetHeader ().GetDestination ();
+  Time qDelay = Simulator::Now () - item->GetTimeStamp ();
+  if (address == "192.168.2.2")
+    {
+      *n0OfStream << Simulator::Now ().GetSeconds () << " " << qDelay.GetMicroSeconds () / 1000.0 << std::endl;
+    }
+  else if (address == "192.168.3.2")
+    {
+      *n1OfStream << Simulator::Now ().GetSeconds () << " " << qDelay.GetMicroSeconds () / 1000.0 << std::endl;
+    }
+}
+
+int
+main (int argc, char *argv[])
+{
+  ////////////////////////////////////////////////////////////
+  // variables not configured at command line               //
+  ////////////////////////////////////////////////////////////
+  Time stopTime = Seconds (70);
+  Time baseRtt = MilliSeconds (80);
+  uint32_t pingSize = 100; // bytes
+  Time pingInterval = MilliSeconds (100);
+  Time marksSamplingInterval = MilliSeconds (100);
+  Time throughputSamplingInterval = MilliSeconds (200);
+  DataRate bottleneckRate ("100Mbps");
+
+  std::string dir = "results/FqCoDel-L4S/";
+  std::string dirToSave = "mkdir -p " + dir;
+  if (system (dirToSave.c_str ()) == -1)
+    {
+      exit (1);
+    }
+
+  std::string pingTraceFile = dir + "ping.dat";
+  std::string n0TcpRttTraceFile = dir + "n0-tcp-rtt.dat";
+  std::string n0TcpCwndTraceFile = dir + "n0-tcp-cwnd.dat";
+  std::string n0TcpThroughputTraceFile = dir + "n0-tcp-throughput.dat";
+  std::string n1TcpRttTraceFile = dir + "n1-tcp-rtt.dat";
+  std::string n1TcpCwndTraceFile = dir + "n1-tcp-cwnd.dat";
+  std::string n1TcpThroughputTraceFile = dir + "n1-tcp-throughput.dat";
+  std::string dropTraceFile = dir + "drops.dat";
+  std::string dropsFrequencyTraceFile = dir + "drops-frequency.dat";
+  std::string lengthTraceFile = dir + "length.dat";
+  std::string markTraceFile = dir + "mark.dat";
+  std::string marksFrequencyTraceFile = dir + "marks-frequency.dat";
+  std::string queueDelayN0TraceFile = dir + "queue-delay-n0.dat";
+  std::string queueDelayN1TraceFile = dir + "queue-delay-n1.dat";
+
+  ////////////////////////////////////////////////////////////
+  // variables configured at command line                   //
+  ////////////////////////////////////////////////////////////
+  bool enablePcap = false;
+  bool useCeThreshold = false;
+  Time ceThreshold = MilliSeconds (1);
+  std::string n0TcpType = "bic";
+  std::string n1TcpType = "";
+  bool enableN1Tcp = false;
+  bool useEcn = true;
+  std::string queueType = "fq";
+  std::string linkDataRate = "1Gbps";
+  uint32_t scenarioNum = 0;
+
+  ////////////////////////////////////////////////////////////
+  // Override ns-3 defaults                                 //
+  ////////////////////////////////////////////////////////////
+  Config::SetDefault ("ns3::TcpSocket::SegmentSize", UintegerValue (1448));
+  // Increase default buffer sizes to improve throughput over long delay paths
+  Config::SetDefault ("ns3::TcpSocket::SndBufSize",UintegerValue (8192000));
+  Config::SetDefault ("ns3::TcpSocket::RcvBufSize",UintegerValue (8192000));
+  Config::SetDefault ("ns3::TcpSocket::InitialCwnd", UintegerValue (10));
+  Config::SetDefault ("ns3::TcpL4Protocol::RecoveryType", TypeIdValue (TcpPrrRecovery::GetTypeId ()));
+
+  ////////////////////////////////////////////////////////////
+  // command-line argument parsing                          //
+  ////////////////////////////////////////////////////////////
+  CommandLine cmd;
+  cmd.AddValue ("n0TcpType", "n0 TCP type (bic, dctcp, or reno)", n0TcpType);
+  cmd.AddValue ("n1TcpType", "n1 TCP type (bic, dctcp, or reno)", n1TcpType);
+  cmd.AddValue ("scenarioNum", "Scenario number from the scenarios avalaible in the file (1-9)", scenarioNum);
+  cmd.AddValue ("bottleneckQueueType", "n2 queue type (fq or codel)", queueType);
+  cmd.AddValue ("baseRtt", "base RTT", baseRtt);
+  cmd.AddValue ("useCeThreshold", "use CE Threshold", useCeThreshold);
+  cmd.AddValue ("useEcn", "use ECN", useEcn);
+  cmd.AddValue ("ceThreshold", "CoDel CE threshold", ceThreshold);
+  cmd.AddValue ("bottleneckRate", "data rate of bottleneck", bottleneckRate);
+  cmd.AddValue ("linkRate", "data rate of edge link", linkDataRate);
+  cmd.AddValue ("stopTime", "simulation stop time", stopTime);
+  cmd.AddValue ("enablePcap", "enable Pcap", enablePcap);
+  cmd.AddValue ("pingTraceFile", "filename for ping tracing", pingTraceFile);
+  cmd.AddValue ("n0TcpRttTraceFile", "filename for n0 rtt tracing", n0TcpRttTraceFile);
+  cmd.AddValue ("n0TcpCwndTraceFile", "filename for n0 cwnd tracing", n0TcpCwndTraceFile);
+  cmd.AddValue ("n0TcpThroughputTraceFile", "filename for n0 throughput tracing", n0TcpThroughputTraceFile);
+  cmd.AddValue ("n1TcpRttTraceFile", "filename for n1 rtt tracing", n1TcpRttTraceFile);
+  cmd.AddValue ("n1TcpCwndTraceFile", "filename for n1 cwnd tracing", n1TcpCwndTraceFile);
+  cmd.AddValue ("n1TcpThroughputTraceFile", "filename for n1 throughput tracing", n1TcpThroughputTraceFile);
+  cmd.AddValue ("dropTraceFile", "filename for n2 drops tracing", dropTraceFile);
+  cmd.AddValue ("dropsFrequencyTraceFile", "filename for n2 drop frequency tracing", dropsFrequencyTraceFile);
+  cmd.AddValue ("lengthTraceFile", "filename for n2 queue length tracing", lengthTraceFile);
+  cmd.AddValue ("markTraceFile", "filename for n2 mark tracing", markTraceFile);
+  cmd.AddValue ("marksFrequencyTraceFile", "filename for n2 mark frequency tracing", marksFrequencyTraceFile);
+  cmd.AddValue ("queueDelayN0TraceFile", "filename for n0 queue delay tracing", queueDelayN0TraceFile);
+  cmd.AddValue ("queueDelayN1TraceFile", "filename for n1 queue delay tracing", queueDelayN1TraceFile);
+  cmd.Parse (argc, argv);
+  Time oneWayDelay = baseRtt / 2;
+  TypeId n0TcpTypeId;
+  TypeId n1TcpTypeId;
+  TypeId queueTypeId;
+  if (!scenarioNum)
+    {
+      if (useEcn)
+        {
+          Config::SetDefault ("ns3::TcpSocketBase::UseEcn", StringValue ("On"));
+        }
+
+      if (n0TcpType == "reno")
+        {
+          n0TcpTypeId = TcpNewReno::GetTypeId ();
+        }
+      else if (n0TcpType == "bic")
+        {
+          n0TcpTypeId = TcpBic::GetTypeId ();
+        }
+      else if (n0TcpType == "dctcp")
+        {
+          n0TcpTypeId = TcpDctcp::GetTypeId ();
+        }
+      else
+        {
+          NS_FATAL_ERROR ("Fatal error:  tcp unsupported");
+        }
+
+      if (n1TcpType == "reno")
+        {
+          enableN1Tcp = true;
+          n1TcpTypeId = TcpNewReno::GetTypeId ();
+        }
+      else if (n1TcpType == "bic")
+        {
+          enableN1Tcp = true;
+          n1TcpTypeId = TcpBic::GetTypeId ();
+        }
+      else if (n1TcpType == "dctcp")
+        {
+          enableN1Tcp = true;
+          n1TcpTypeId = TypeId::LookupByName ("ns3::TcpDctcp");
+        }
+      else if (n1TcpType == "")
+        {
+          NS_LOG_DEBUG ("No N1 TCP selected");
+        }
+      else
+        {
+          NS_FATAL_ERROR ("Fatal error:  tcp unsupported");
+        }
+
+      if (queueType == "fq")
+        {
+          queueTypeId = FqCoDelQueueDisc::GetTypeId ();
+        }
+      else if (queueType == "codel")
+        {
+          queueTypeId = CoDelQueueDisc::GetTypeId ();
+        }
+      else
+        {
+          NS_FATAL_ERROR ("Fatal error:  queueType unsupported");
+        }
+      if (useCeThreshold)
+        {
+          Config::SetDefault ("ns3::FqCoDelQueueDisc::CeThreshold", TimeValue (ceThreshold));
+        }
+    }
+  else if (scenarioNum == 1 || scenarioNum == 2 || scenarioNum == 5 || scenarioNum == 6)
+    {
+      if (scenarioNum == 2 || scenarioNum == 6)
+        {
+          Config::SetDefault ("ns3::TcpSocketBase::UseEcn", StringValue ("On"));
+        }
+      n0TcpTypeId = TcpBic::GetTypeId ();
+      if (scenarioNum == 5 || scenarioNum == 6)
+        {
+          enableN1Tcp = true;
+          n1TcpTypeId = TcpBic::GetTypeId ();
+        }
+      queueTypeId = FqCoDelQueueDisc::GetTypeId ();
+    }
+  else if (scenarioNum == 3 || scenarioNum == 4 || scenarioNum == 7 || scenarioNum == 8 || scenarioNum == 9)
+    {
+      Config::SetDefault ("ns3::TcpSocketBase::UseEcn", StringValue ("On"));
+      n0TcpTypeId = TcpDctcp::GetTypeId ();
+      queueTypeId = FqCoDelQueueDisc::GetTypeId ();
+      oneWayDelay = MicroSeconds (500);
+      Config::SetDefault ("ns3::FqCoDelQueueDisc::CeThreshold", TimeValue (MilliSeconds (1)));
+      if (scenarioNum == 9)
+        {
+          n0TcpTypeId = TcpBic::GetTypeId ();
+          // For TCP Bic base RTT is 80 and base RTT for dctcp is set to 1 while setting delay for p2p devices
+          oneWayDelay = MilliSeconds (40);
+        }
+      if (scenarioNum == 4 || scenarioNum == 8 || scenarioNum == 9)
+        {
+          Config::SetDefault ("ns3::FqCoDelQueueDisc::UseL4s", BooleanValue (true));
+          Config::SetDefault ("ns3::TcpDctcp::UseEct0", BooleanValue (false));
+        }
+      if (scenarioNum == 7 || scenarioNum == 8 || scenarioNum == 9)
+        {
+          enableN1Tcp = true;
+          n1TcpTypeId = TcpDctcp::GetTypeId ();
+        }
+    }
+  else
+    {
+      NS_FATAL_ERROR ("Fatal error:  scenario unavailble");
+    }
+
+  std::ofstream pingOfStream;
+  pingOfStream.open (pingTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n0TcpRttOfStream;
+  n0TcpRttOfStream.open (n0TcpRttTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n0TcpCwndOfStream;
+  n0TcpCwndOfStream.open (n0TcpCwndTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n0TcpThroughputOfStream;
+  n0TcpThroughputOfStream.open (n0TcpThroughputTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n1TcpRttOfStream;
+  n1TcpRttOfStream.open (n1TcpRttTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n1TcpCwndOfStream;
+  n1TcpCwndOfStream.open (n1TcpCwndTraceFile.c_str (), std::ofstream::out);
+  std::ofstream n1TcpThroughputOfStream;
+  n1TcpThroughputOfStream.open (n1TcpThroughputTraceFile.c_str (), std::ofstream::out);
+
+  // Queue disc files
+  std::ofstream dropOfStream;
+  dropOfStream.open (dropTraceFile.c_str (), std::ofstream::out);
+  std::ofstream markOfStream;
+  markOfStream.open (markTraceFile.c_str (), std::ofstream::out);
+  std::ofstream dropsFrequencyOfStream;
+  dropsFrequencyOfStream.open (dropsFrequencyTraceFile.c_str (), std::ofstream::out);
+  std::ofstream marksFrequencyOfStream;
+  marksFrequencyOfStream.open (marksFrequencyTraceFile.c_str (), std::ofstream::out);
+  std::ofstream lengthOfStream;
+  lengthOfStream.open (lengthTraceFile.c_str (), std::ofstream::out);
+  std::ofstream queueDelayN0OfStream;
+  queueDelayN0OfStream.open (queueDelayN0TraceFile.c_str (), std::ofstream::out);
+  std::ofstream queueDelayN1OfStream;
+  queueDelayN1OfStream.open (queueDelayN1TraceFile.c_str (), std::ofstream::out);
+
+  ////////////////////////////////////////////////////////////
+  // scenario setup                                         //
+  ////////////////////////////////////////////////////////////
+  Ptr<Node> pingServer = CreateObject<Node> ();
+  Ptr<Node> n0Server = CreateObject<Node> ();
+  Ptr<Node> n1Server = CreateObject<Node> ();
+  Ptr<Node> n2 = CreateObject<Node> ();
+  Ptr<Node> n3 = CreateObject<Node> ();
+  Ptr<Node> pingClient = CreateObject<Node> ();
+  Ptr<Node> n4Client = CreateObject<Node> ();
+  Ptr<Node> n5Client = CreateObject<Node> ();
+
+  // Device containers
+  NetDeviceContainer pingServerDevices;
+  NetDeviceContainer n0ServerDevices;
+  NetDeviceContainer n1ServerDevices;
+  NetDeviceContainer n2n3Devices;
+  NetDeviceContainer pingClientDevices;
+  NetDeviceContainer n4ClientDevices;
+  NetDeviceContainer n5ClientDevices;
+
+  PointToPointHelper p2p;
+  p2p.SetQueue ("ns3::DropTailQueue", "MaxSize", QueueSizeValue (QueueSize ("3p")));
+  p2p.SetDeviceAttribute ("DataRate", DataRateValue (DataRate (linkDataRate)));
+  // Add delay only on the server links
+  p2p.SetChannelAttribute ("Delay", TimeValue (oneWayDelay));
+  pingServerDevices = p2p.Install (n2, pingServer);
+  n0ServerDevices = p2p.Install (n2, n0Server);
+
+  // In scenario 9, base RTT of n1server (dctcp) is 1ms
+  if (scenarioNum == 9)
+    {
+      p2p.SetChannelAttribute ("Delay", TimeValue (MicroSeconds (500)));
+    }
+  n1ServerDevices = p2p.Install (n2, n1Server);
+  p2p.SetChannelAttribute ("Delay", TimeValue (MicroSeconds (1)));
+  n2n3Devices = p2p.Install (n2, n3);
+  pingClientDevices = p2p.Install (n3, pingClient);
+  n4ClientDevices = p2p.Install (n3, n4Client);
+  n5ClientDevices = p2p.Install (n3, n5Client);
+  Ptr<PointToPointNetDevice> p = n2n3Devices.Get (0)->GetObject<PointToPointNetDevice> ();
+  p->SetAttribute ("DataRate", DataRateValue (bottleneckRate));
+
+  InternetStackHelper stackHelper;
+  stackHelper.InstallAll ();
+
+  // Set the per-node TCP type here
+  Ptr<TcpL4Protocol> proto;
+  proto = n4Client->GetObject<TcpL4Protocol> ();
+  proto->SetAttribute ("SocketType", TypeIdValue (n0TcpTypeId));
+  proto = n0Server->GetObject<TcpL4Protocol> ();
+  proto->SetAttribute ("SocketType", TypeIdValue (n0TcpTypeId));
+  if (enableN1Tcp)
+    {
+      proto = n5Client->GetObject<TcpL4Protocol> ();
+      proto->SetAttribute ("SocketType", TypeIdValue (n1TcpTypeId));
+      proto = n1Server->GetObject<TcpL4Protocol> ();
+      proto->SetAttribute ("SocketType", TypeIdValue (n1TcpTypeId));
+    }
+
+  // InternetStackHelper will install a base TrafficControLayer on the node,
+  // but the Ipv4AddressHelper below will install the default FqCoDelQueueDisc
+  // on all single device nodes.  The below code overrides the configuration
+  // that is normally done by the Ipv4AddressHelper::Install() method by
+  // instead explicitly configuring the queue discs we want on each device.
+  TrafficControlHelper tchFq;
+  tchFq.SetRootQueueDisc ("ns3::FqCoDelQueueDisc");
+  tchFq.SetQueueLimits ("ns3::DynamicQueueLimits", "HoldTime", StringValue ("1ms"));
+  tchFq.Install (pingServerDevices);
+  tchFq.Install (n0ServerDevices);
+  tchFq.Install (n1ServerDevices);
+  tchFq.Install (n2n3Devices.Get (1));  // n2 queue for bottleneck link
+  tchFq.Install (pingClientDevices);
+  tchFq.Install (n4ClientDevices);
+  tchFq.Install (n5ClientDevices);
+  TrafficControlHelper tchN2;
+  tchN2.SetRootQueueDisc (queueTypeId.GetName ());
+  tchN2.SetQueueLimits ("ns3::DynamicQueueLimits", "HoldTime", StringValue ("1000ms"));
+  tchN2.Install (n2n3Devices.Get (0));
+
+  Ipv4AddressHelper ipv4;
+  ipv4.SetBase ("10.1.1.0", "255.255.255.0");
+  Ipv4InterfaceContainer pingServerIfaces = ipv4.Assign (pingServerDevices);
+  ipv4.SetBase ("10.1.2.0", "255.255.255.0");
+  Ipv4InterfaceContainer n0ServerIfaces = ipv4.Assign (n0ServerDevices);
+  ipv4.SetBase ("10.1.3.0", "255.255.255.0");
+  Ipv4InterfaceContainer secondServerIfaces = ipv4.Assign (n1ServerDevices);
+  ipv4.SetBase ("172.16.1.0", "255.255.255.0");
+  Ipv4InterfaceContainer n2n3Ifaces = ipv4.Assign (n2n3Devices);
+  ipv4.SetBase ("192.168.1.0", "255.255.255.0");
+  Ipv4InterfaceContainer pingClientIfaces = ipv4.Assign (pingClientDevices);
+  ipv4.SetBase ("192.168.2.0", "255.255.255.0");
+  Ipv4InterfaceContainer n4ClientIfaces = ipv4.Assign (n4ClientDevices);
+  ipv4.SetBase ("192.168.3.0", "255.255.255.0");
+  Ipv4InterfaceContainer n5ClientIfaces = ipv4.Assign (n5ClientDevices);
+
+  Ipv4GlobalRoutingHelper::PopulateRoutingTables ();
+
+  ////////////////////////////////////////////////////////////
+  // application setup                                      //
+  ////////////////////////////////////////////////////////////
+
+  V4PingHelper pingHelper ("192.168.1.2");
+  pingHelper.SetAttribute ("Interval", TimeValue (pingInterval));
+  pingHelper.SetAttribute ("Size", UintegerValue (pingSize));
+  ApplicationContainer pingContainer = pingHelper.Install (pingServer);
+  Ptr<V4Ping> v4Ping = pingContainer.Get (0)->GetObject<V4Ping> ();
+  v4Ping->TraceConnectWithoutContext ("Rtt", MakeBoundCallback (&TracePingRtt, &pingOfStream));
+  pingContainer.Start (Seconds (1));
+  pingContainer.Stop (stopTime - Seconds (1));
+
+  BulkSendHelper tcp ("ns3::TcpSocketFactory", Address ());
+  // set to large value:  e.g. 1000 Mb/s for 60 seconds = 7500000000 bytes
+  tcp.SetAttribute ("MaxBytes", UintegerValue (7500000000));
+  // Configure n4/n0 TCP client/server pair
+  uint16_t n4Port = 5000;
+  ApplicationContainer n0App;
+  InetSocketAddress n0DestAddress (n4ClientIfaces.GetAddress (1), n4Port);
+  tcp.SetAttribute ("Remote", AddressValue (n0DestAddress));
+  n0App = tcp.Install (n0Server);
+  n0App.Start (Seconds (5));
+  n0App.Stop (stopTime - Seconds (1));
+
+  Address n4SinkAddress (InetSocketAddress (Ipv4Address::GetAny (), n4Port));
+  PacketSinkHelper n4SinkHelper ("ns3::TcpSocketFactory", n4SinkAddress);
+  ApplicationContainer n4SinkApp;
+  n4SinkApp = n4SinkHelper.Install (n4Client);
+  n4SinkApp.Start (Seconds (5));
+  n4SinkApp.Stop (stopTime - MilliSeconds (500));
+
+  // Configure second TCP client/server pair
+  if (enableN1Tcp)
+    {
+      uint16_t n5Port = 5000;
+      ApplicationContainer secondApp;
+      InetSocketAddress n1DestAddress (n5ClientIfaces.GetAddress (1), n5Port);
+      tcp.SetAttribute ("Remote", AddressValue (n1DestAddress));
+      secondApp = tcp.Install (n1Server);
+      secondApp.Start (Seconds (15));
+      secondApp.Stop (stopTime - Seconds (1));
+
+      Address n5SinkAddress (InetSocketAddress (Ipv4Address::GetAny (), n5Port));
+      PacketSinkHelper n5SinkHelper ("ns3::TcpSocketFactory", n5SinkAddress);
+      ApplicationContainer n5SinkApp;
+      n5SinkApp = n5SinkHelper.Install (n5Client);
+      n5SinkApp.Start (Seconds (15));
+      n5SinkApp.Stop (stopTime - MilliSeconds (500));
+    }
+
+  // Setup traces that can be hooked now
+  Ptr<TrafficControlLayer> tc;
+  Ptr<QueueDisc> qd;
+  tc = n2n3Devices.Get (0)->GetNode ()->GetObject<TrafficControlLayer> ();
+  qd = tc->GetRootQueueDiscOnDevice (n2n3Devices.Get (0));
+  qd->TraceConnectWithoutContext ("Drop", MakeBoundCallback (&TraceDrop, &dropOfStream));
+  qd->TraceConnectWithoutContext ("Mark", MakeBoundCallback (&TraceMark, &markOfStream));
+  qd->TraceConnectWithoutContext ("BytesInQueue", MakeBoundCallback (&TraceQueueLength, &lengthOfStream, bottleneckRate));
+  qd->TraceConnectWithoutContext ("Dequeue", MakeBoundCallback (&PacketDequeue, &queueDelayN0OfStream, &queueDelayN1OfStream));
+
+  // Setup scheduled traces; TCP traces must be hooked after socket creation
+  Simulator::Schedule (Seconds (5) + MilliSeconds (100), &ScheduleN0TcpRttTraceConnection, &n0TcpRttOfStream);
+  Simulator::Schedule (Seconds (5) + MilliSeconds (100), &ScheduleN0TcpCwndTraceConnection, &n0TcpCwndOfStream);
+  Simulator::Schedule (Seconds (5) + MilliSeconds (100), &ScheduleN0PacketSinkConnection);
+  Simulator::Schedule (throughputSamplingInterval, &TraceN0Throughput, &n0TcpThroughputOfStream, throughputSamplingInterval);
+  // Setup scheduled traces; TCP traces must be hooked after socket creation
+  Simulator::Schedule (Seconds (15) + MilliSeconds (100), &ScheduleN1TcpRttTraceConnection, &n1TcpRttOfStream);
+  Simulator::Schedule (Seconds (15) + MilliSeconds (100), &ScheduleN1TcpCwndTraceConnection, &n1TcpCwndOfStream);
+  Simulator::Schedule (Seconds (15) + MilliSeconds (100), &ScheduleN1PacketSinkConnection);
+  Simulator::Schedule (throughputSamplingInterval, &TraceN1Throughput, &n1TcpThroughputOfStream, throughputSamplingInterval);
+  Simulator::Schedule (marksSamplingInterval, &TraceMarksFrequency, &marksFrequencyOfStream, marksSamplingInterval);
+  Simulator::Schedule (marksSamplingInterval, &TraceDropsFrequency, &dropsFrequencyOfStream, marksSamplingInterval);
+
+  if (enablePcap)
+    {
+      p2p.EnablePcapAll ("FqCoDel-L4S-example", false);
+    }
+
+  Simulator::Stop (stopTime);
+  Simulator::Run ();
+
+  pingOfStream.close ();
+  n0TcpCwndOfStream.close ();
+  n0TcpRttOfStream.close ();
+  n0TcpThroughputOfStream.close ();
+  n1TcpCwndOfStream.close ();
+  n1TcpRttOfStream.close ();
+  n1TcpThroughputOfStream.close ();
+  dropOfStream.close ();
+  markOfStream.close ();
+  dropsFrequencyOfStream.close ();
+  marksFrequencyOfStream.close ();
+  lengthOfStream.close ();
+  queueDelayN0OfStream.close ();
+  queueDelayN1OfStream.close ();
+}
\ No newline at end of file
diff --git a/src/traffic-control/examples/wscript b/src/traffic-control/examples/wscript
index 57b99db5c..0b9d677c9 100644
--- a/src/traffic-control/examples/wscript
+++ b/src/traffic-control/examples/wscript
@@ -23,3 +23,6 @@ def build(bld):
 
     obj = bld.create_ns3_program('pie-example', ['point-to-point', 'internet', 'applications', 'flow-monitor', 'traffic-control'])
     obj.source = 'pie-example.cc'
+    
+    obj = bld.create_ns3_program('fqcodel-l4s-example', ['point-to-point', 'internet', 'applications', 'flow-monitor','internet-apps', 'traffic-control'])
+    obj.source = 'fqcodel-l4s-example.cc'
diff --git a/src/traffic-control/model/codel-queue-disc.cc b/src/traffic-control/model/codel-queue-disc.cc
index 4c52bd8cb..c9835b9b5 100644
--- a/src/traffic-control/model/codel-queue-disc.cc
+++ b/src/traffic-control/model/codel-queue-disc.cc
@@ -78,6 +78,11 @@ TypeId CoDelQueueDisc::GetTypeId (void)
                    BooleanValue (false),
                    MakeBooleanAccessor (&CoDelQueueDisc::m_useEcn),
                    MakeBooleanChecker ())
+    .AddAttribute ("UseL4s",
+                   "True to use L4S (only ECT1 packets are marked at CE threshold)",
+                   BooleanValue (false),
+                   MakeBooleanAccessor (&CoDelQueueDisc::m_useL4s),
+                   MakeBooleanChecker ())
     .AddAttribute ("MaxSize",
                    "The maximum number of packets/bytes accepted by this queue disc.",
                    QueueSizeValue (QueueSize (QueueSizeUnit::BYTES, 1500 * DEFAULT_CODEL_LIMIT)),
@@ -239,6 +244,21 @@ CoDelQueueDisc::DoDequeue (void)
       NS_LOG_LOGIC ("Queue empty");
       return 0;
     }
+  uint32_t ldelay = Time2CoDel (Simulator::Now () - item->GetTimeStamp ());
+  if (item && m_useL4s)
+    {
+      uint8_t tosByte = 0;
+      if (item->GetUint8Value (QueueItem::IP_DSFIELD, tosByte) && ((tosByte & 0x3) == 1))
+        {
+          NS_LOG_DEBUG ("ECT1 packet " << static_cast<uint16_t> (tosByte & 0x3));
+          if (CoDelTimeAfter (ldelay, Time2CoDel (m_ceThreshold)) && Mark (item, CE_THRESHOLD_EXCEEDED_MARK))
+            {
+              NS_LOG_LOGIC ("Marking due to CeThreshold " << m_ceThreshold.GetSeconds ());
+            }
+          return item;
+        }
+    }
+
   uint32_t now = CoDelGetTime ();
 
   NS_LOG_LOGIC ("Popped " << item);
@@ -358,12 +378,12 @@ CoDelQueueDisc::DoDequeue (void)
         }
     }
   end:
-  uint32_t ldelay = Time2CoDel (Simulator::Now () - item->GetTimeStamp ());
+  ldelay = Time2CoDel (Simulator::Now () - item->GetTimeStamp ());
   // In Linux, this branch of code is executed even if the packet has been marked
   // according to the target delay above. If the ns-3 code were to do the same here,
   // it would result in two counts of mark in the queue statistics. Therefore, we
   // use the isMarked flag to suppress a second attempt at marking.
-  if (!isMarked && item && m_useEcn && CoDelTimeAfter (ldelay, Time2CoDel (m_ceThreshold)) && Mark (item, CE_THRESHOLD_EXCEEDED_MARK))
+  if (!isMarked && item && !m_useL4s && m_useEcn && CoDelTimeAfter (ldelay, Time2CoDel (m_ceThreshold)) && Mark (item, CE_THRESHOLD_EXCEEDED_MARK))
     {
       NS_LOG_LOGIC ("Marking due to CeThreshold " << m_ceThreshold.GetSeconds ());
     }
diff --git a/src/traffic-control/model/codel-queue-disc.h b/src/traffic-control/model/codel-queue-disc.h
index 6adfdd11b..24790c201 100644
--- a/src/traffic-control/model/codel-queue-disc.h
+++ b/src/traffic-control/model/codel-queue-disc.h
@@ -202,6 +202,7 @@ private:
   virtual void InitializeParams (void);
 
   bool m_useEcn;                          //!< True if ECN is used (packets are marked instead of being dropped)
+  bool m_useL4s;                          //!< True if L4S is used (ECT1 packets are marked at CE threshold)
   uint32_t m_minBytes;                    //!< Minimum bytes in queue to allow a packet drop
   Time m_interval;                        //!< 100 ms sliding minimum time window width
   Time m_target;                          //!< 5 ms target queue delay
diff --git a/src/traffic-control/model/fq-codel-queue-disc.cc b/src/traffic-control/model/fq-codel-queue-disc.cc
index 4d8053136..3a4c59a47 100644
--- a/src/traffic-control/model/fq-codel-queue-disc.cc
+++ b/src/traffic-control/model/fq-codel-queue-disc.cc
@@ -163,6 +163,11 @@ TypeId FqCoDelQueueDisc::GetTypeId (void)
                    UintegerValue (8),
                    MakeUintegerAccessor (&FqCoDelQueueDisc::m_setWays),
                    MakeUintegerChecker<uint32_t> ())
+    .AddAttribute ("UseL4s",
+                   "True to use L4S (only ECT1 packets are marked at CE threshold)",
+                   BooleanValue (false),
+                   MakeBooleanAccessor (&FqCoDelQueueDisc::m_useL4s),
+                   MakeBooleanChecker ())
   ;
   return tid;
 }
@@ -269,6 +274,7 @@ FqCoDelQueueDisc::DoEnqueue (Ptr<QueueDiscItem> item)
         {
           codel->SetAttribute ("UseEcn", BooleanValue (m_useEcn));
           codel->SetAttribute ("CeThreshold", TimeValue (m_ceThreshold));
+          codel->SetAttribute ("UseL4s", BooleanValue (m_useL4s));
         }
       qd->Initialize ();
       flow->SetQueueDisc (qd);
@@ -429,6 +435,14 @@ FqCoDelQueueDisc::CheckConfig (void)
       return false;
     }
 
+  if (m_useL4s)
+    {
+      NS_ABORT_MSG_IF (m_ceThreshold == Time::Max(), "CE threshold not set");
+      if (m_useEcn == false)
+        {
+          NS_LOG_WARN ("Enabling ECN as L4S mode is enabled");
+        }
+    }
   return true;
 }
 
diff --git a/src/traffic-control/model/fq-codel-queue-disc.h b/src/traffic-control/model/fq-codel-queue-disc.h
index c2820ac89..e60c484a3 100644
--- a/src/traffic-control/model/fq-codel-queue-disc.h
+++ b/src/traffic-control/model/fq-codel-queue-disc.h
@@ -172,6 +172,7 @@ private:
   uint32_t m_perturbation;   //!< hash perturbation value
   Time m_ceThreshold;        //!< Threshold above which to CE mark
   bool m_enableSetAssociativeHash; //!< whether to enable set associative hash
+  bool m_useL4s;             //!< True if L4S is used (ECT1 packets are marked at CE threshold)
 
   std::list<Ptr<FqCoDelFlow> > m_newFlows;    //!< The list of new flows
   std::list<Ptr<FqCoDelFlow> > m_oldFlows;    //!< The list of old flows