tcp: (fixes #1001) Add TCP-friendliness heuristic to TCP Cubic

examples/tcp/tcp-validation.cc

@@ -663,6 +663,9 @@ main(int argc, char* argv[])
     Config::SetDefault("ns3::TcpSocket::InitialCwnd", UintegerValue(10));
     Config::SetDefault("ns3::TcpL4Protocol::RecoveryType",
                        TypeIdValue(TcpPrrRecovery::GetTypeId()));
+    // Validation criteria were written for TCP Cubic without Reno-friendly behavior, so disable it
+    // for these tests
+    Config::SetDefault("ns3::TcpCubic::TcpFriendliness", BooleanValue(false));
 
     ////////////////////////////////////////////////////////////
     // command-line argument parsing                          //

src/internet/model/tcp-cubic.cc

@@ -45,6 +45,11 @@ TcpCubic::GetTypeId()
                           BooleanValue(true),
                           MakeBooleanAccessor(&TcpCubic::m_fastConvergence),
                           MakeBooleanChecker())
+            .AddAttribute("TcpFriendliness",
+                          "Enable (true) or disable (false) TCP friendliness",
+                          BooleanValue(true),
+                          MakeBooleanAccessor(&TcpCubic::m_tcpFriendliness),
+                          MakeBooleanChecker())
             .AddAttribute("Beta",
                           "Beta for multiplicative decrease",
                           DoubleValue(0.7),
@@ -209,7 +214,7 @@ TcpCubic::IncreaseWindow(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
     if (tcb->m_cWnd >= tcb->m_ssThresh && segmentsAcked > 0)
     {
         m_cWndCnt += segmentsAcked;
-        uint32_t cnt = Update(tcb);
+        uint32_t cnt = Update(tcb, segmentsAcked);
 
         /* According to RFC 6356 even once the new cwnd is
          * calculated you must compare this to the number of ACKs received since
@@ -232,19 +237,24 @@ TcpCubic::IncreaseWindow(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
 }
 
 uint32_t
-TcpCubic::Update(Ptr<TcpSocketState> tcb)
+TcpCubic::Update(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
 {
     NS_LOG_FUNCTION(this);
     Time t;
     uint32_t delta;
     uint32_t bicTarget;
     uint32_t cnt = 0;
+    uint32_t maxCnt;
     double offs;
     uint32_t segCwnd = tcb->GetCwndInSegments();
 
+    m_ackCnt += segmentsAcked;
+
     if (m_epochStart == Time::Min())
     {
         m_epochStart = Simulator::Now(); // record the beginning of an epoch
+        m_ackCnt = segmentsAcked;
+        m_tcpCwnd = segCwnd;
 
         if (m_lastMaxCwnd <= segCwnd)
         {
@@ -311,6 +321,26 @@ TcpCubic::Update(Ptr<TcpSocketState> tcb)
         cnt = m_cntClamp;
     }
 
+    if (m_tcpFriendliness)
+    {
+        auto scale = static_cast<uint32_t>(8 * (1024 + m_beta * 1024) / 3 / (1024 - m_beta * 1024));
+        delta = (segCwnd * scale) >> 3;
+        while (m_ackCnt > delta)
+        {
+            m_ackCnt -= delta;
+            m_tcpCwnd++;
+        }
+        if (m_tcpCwnd > segCwnd)
+        {
+            delta = m_tcpCwnd - segCwnd;
+            maxCnt = segCwnd / delta;
+            if (cnt > maxCnt)
+            {
+                cnt = maxCnt;
+            }
+        }
+    }
+
     // The maximum rate of cwnd increase CUBIC allows is 1 packet per
     // 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
     return std::max(cnt, 2U);
@@ -463,6 +493,8 @@ TcpCubic::CubicReset(Ptr<const TcpSocketState> tcb)
     m_lastMaxCwnd = 0;
     m_bicOriginPoint = 0;
     m_bicK = 0;
+    m_ackCnt = 0;
+    m_tcpCwnd = 0;
     m_delayMin = Time::Min();
     m_found = false;
 }

src/internet/model/tcp-cubic.h

@@ -104,6 +104,7 @@ class TcpCubic : public TcpCongestionOps
 
   private:
     bool m_fastConvergence; //!< Enable or disable fast convergence algorithm
+    bool m_tcpFriendliness; //!< Enable or disable TCP-friendliness heuristic
     double m_beta;          //!< Beta for cubic multiplicative increase
 
     bool m_hystart;                        //!< Enable or disable HyStart algorithm
@@ -134,6 +135,8 @@ class TcpCubic : public TcpCongestionOps
     Time m_cubicDelta;         //!<  Time to wait after recovery before update
     Time m_currRtt;            //!<  Current Rtt
     uint32_t m_sampleCnt;      //!<  Count of samples for HyStart
+    uint32_t m_ackCnt;         //!<  Count the number of ACKed packets
+    uint32_t m_tcpCwnd;        //!<  Estimated tcp cwnd (for Reno-friendliness)
 
   private:
     /**
@@ -151,9 +154,10 @@ class TcpCubic : public TcpCongestionOps
     /**
      * \brief Cubic window update after a new ack received
      * \param tcb Transmission Control Block of the connection
+     * \param segmentsAcked Segments acked
      * \returns the congestion window update counter
      */
-    uint32_t Update(Ptr<TcpSocketState> tcb);
+    uint32_t Update(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked);
 
     /**
      * \brief Update HyStart parameters