tcp-vegas.cc

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/*
 * Copyright (c) 2016 ResiliNets, ITTC, University of Kansas
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Truc Anh N. Nguyen <annguyen@ittc.ku.edu>
 *
 * James P.G. Sterbenz <jpgs@ittc.ku.edu>, director
 * ResiliNets Research Group  https://resilinets.org/
 * Information and Telecommunication Technology Center (ITTC)
 * and Department of Electrical Engineering and Computer Science
 * The University of Kansas Lawrence, KS USA.
 */
 
#include "tcp-vegas.h"
 
#include "tcp-socket-state.h"
 
#include "ns3/log.h"
 
namespace ns3
{
 
NS_LOG_COMPONENT_DEFINE("TcpVegas");
NS_OBJECT_ENSURE_REGISTERED(TcpVegas);
 
TypeId
TcpVegas::GetTypeId()
{
    static TypeId tid = TypeId("ns3::TcpVegas")
                            .SetParent<TcpNewReno>()
                            .AddConstructor<TcpVegas>()
                            .SetGroupName("Internet")
                            .AddAttribute("Alpha",
                                          "Lower bound of packets in network",
                                          UintegerValue(2),
                                          MakeUintegerAccessor(&TcpVegas::m_alpha),
                                          MakeUintegerChecker<uint32_t>())
                            .AddAttribute("Beta",
                                          "Upper bound of packets in network",
                                          UintegerValue(4),
                                          MakeUintegerAccessor(&TcpVegas::m_beta),
                                          MakeUintegerChecker<uint32_t>())
                            .AddAttribute("Gamma",
                                          "Limit on increase",
                                          UintegerValue(1),
                                          MakeUintegerAccessor(&TcpVegas::m_gamma),
                                          MakeUintegerChecker<uint32_t>());
    return tid;
}
 
TcpVegas::TcpVegas()
    : TcpNewReno(),
      m_alpha(2),
      m_beta(4),
      m_gamma(1),
      m_baseRtt(Time::Max()),
      m_minRtt(Time::Max()),
      m_cntRtt(0),
      m_doingVegasNow(true),
      m_begSndNxt(0)
{
    NS_LOG_FUNCTION(this);
}
 
TcpVegas::TcpVegas(const TcpVegas& sock)
    : TcpNewReno(sock),
      m_alpha(sock.m_alpha),
      m_beta(sock.m_beta),
      m_gamma(sock.m_gamma),
      m_baseRtt(sock.m_baseRtt),
      m_minRtt(sock.m_minRtt),
      m_cntRtt(sock.m_cntRtt),
      m_doingVegasNow(true),
      m_begSndNxt(0)
{
    NS_LOG_FUNCTION(this);
}
 
TcpVegas::~TcpVegas()
{
    NS_LOG_FUNCTION(this);
}
 
Ptr<TcpCongestionOps>
TcpVegas::Fork()
{
    return CopyObject<TcpVegas>(this);
}
 
void
TcpVegas::PktsAcked(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked, const Time& rtt)
{
    NS_LOG_FUNCTION(this << tcb << segmentsAcked << rtt);
 
    if (rtt.IsZero())
    {
        return;
    }
 
    m_minRtt = std::min(m_minRtt, rtt);
    NS_LOG_DEBUG("Updated m_minRtt = " << m_minRtt);
 
    m_baseRtt = std::min(m_baseRtt, rtt);
    NS_LOG_DEBUG("Updated m_baseRtt = " << m_baseRtt);
 
    // Update RTT counter
    m_cntRtt++;
    NS_LOG_DEBUG("Updated m_cntRtt = " << m_cntRtt);
}
 
void
TcpVegas::EnableVegas(Ptr<TcpSocketState> tcb)
{
    NS_LOG_FUNCTION(this << tcb);
 
    m_doingVegasNow = true;
    m_begSndNxt = tcb->m_nextTxSequence;
    m_cntRtt = 0;
    m_minRtt = Time::Max();
}
 
void
TcpVegas::DisableVegas()
{
    NS_LOG_FUNCTION(this);
 
    m_doingVegasNow = false;
}
 
void
TcpVegas::CongestionStateSet(Ptr<TcpSocketState> tcb, const TcpSocketState::TcpCongState_t newState)
{
    NS_LOG_FUNCTION(this << tcb << newState);
    if (newState == TcpSocketState::CA_OPEN)
    {
        EnableVegas(tcb);
    }
    else
    {
        DisableVegas();
    }
}
 
void
TcpVegas::IncreaseWindow(Ptr<TcpSocketState> tcb, uint32_t segmentsAcked)
{
    NS_LOG_FUNCTION(this << tcb << segmentsAcked);
 
    if (!m_doingVegasNow)
    {
        // If Vegas is not on, we follow NewReno algorithm
        NS_LOG_LOGIC("Vegas is not turned on, we follow NewReno algorithm.");
        TcpNewReno::IncreaseWindow(tcb, segmentsAcked);
        return;
    }
 
    if (tcb->m_lastAckedSeq >= m_begSndNxt)
    { // A Vegas cycle has finished, we do Vegas cwnd adjustment every RTT.
 
        NS_LOG_LOGIC("A Vegas cycle has finished, we adjust cwnd once per RTT.");
 
        // Save the current right edge for next Vegas cycle
        m_begSndNxt = tcb->m_nextTxSequence;
 
        /*
         * We perform Vegas calculations only if we got enough RTT samples to
         * insure that at least 1 of those samples wasn't from a delayed ACK.
         */
        if (m_cntRtt <= 2)
        { // We do not have enough RTT samples, so we should behave like Reno
            NS_LOG_LOGIC(
                "We do not have enough RTT samples to do Vegas, so we behave like NewReno.");
            TcpNewReno::IncreaseWindow(tcb, segmentsAcked);
        }
        else
        {
            NS_LOG_LOGIC("We have enough RTT samples to perform Vegas calculations");
            /*
             * We have enough RTT samples to perform Vegas algorithm.
             * Now we need to determine if cwnd should be increased or decreased
             * based on the calculated difference between the expected rate and actual sending
             * rate and the predefined thresholds (alpha, beta, and gamma).
             */
            uint32_t diff;
            uint32_t targetCwnd;
            uint32_t segCwnd = tcb->GetCwndInSegments();
 
            /*
             * Calculate the cwnd we should have. baseRtt is the minimum RTT
             * per-connection, minRtt is the minimum RTT in this window
             *
             * little trick:
             * desidered throughput is currentCwnd * baseRtt
             * target cwnd is throughput / minRtt
             */
            double tmp = m_baseRtt.GetSeconds() / m_minRtt.GetSeconds();
            targetCwnd = static_cast<uint32_t>(segCwnd * tmp);
            NS_LOG_DEBUG("Calculated targetCwnd = " << targetCwnd);
            NS_ASSERT(segCwnd >= targetCwnd); // implies baseRtt <= minRtt
 
            /*
             * Calculate the difference between the expected cWnd and
             * the actual cWnd
             */
            diff = segCwnd - targetCwnd;
            NS_LOG_DEBUG("Calculated diff = " << diff);
 
            if (diff > m_gamma && (tcb->m_cWnd < tcb->m_ssThresh))
            {
                /*
                 * We are going too fast. We need to slow down and change from
                 * slow-start to linear increase/decrease mode by setting cwnd
                 * to target cwnd. We add 1 because of the integer truncation.
                 */
                NS_LOG_LOGIC("We are going too fast. We need to slow down and "
                             "change to linear increase/decrease mode.");
                segCwnd = std::min(segCwnd, targetCwnd + 1);
                tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
                tcb->m_ssThresh = GetSsThresh(tcb, 0);
                NS_LOG_DEBUG("Updated cwnd = " << tcb->m_cWnd << " ssthresh=" << tcb->m_ssThresh);
            }
            else if (tcb->m_cWnd < tcb->m_ssThresh)
            { // Slow start mode
                NS_LOG_LOGIC("We are in slow start and diff < m_gamma, so we "
                             "follow NewReno slow start");
                TcpNewReno::SlowStart(tcb, segmentsAcked);
            }
            else
            { // Linear increase/decrease mode
                NS_LOG_LOGIC("We are in linear increase/decrease mode");
                if (diff > m_beta)
                {
                    // We are going too fast, so we slow down
                    NS_LOG_LOGIC("We are going too fast, so we slow down by decrementing cwnd");
                    segCwnd--;
                    tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
                    tcb->m_ssThresh = GetSsThresh(tcb, 0);
                    NS_LOG_DEBUG("Updated cwnd = " << tcb->m_cWnd
                                                   << " ssthresh=" << tcb->m_ssThresh);
                }
                else if (diff < m_alpha)
                {
                    // We are going too slow (having too little data in the network),
                    // so we speed up.
                    NS_LOG_LOGIC("We are going too slow, so we speed up by incrementing cwnd");
                    segCwnd++;
                    tcb->m_cWnd = segCwnd * tcb->m_segmentSize;
                    NS_LOG_DEBUG("Updated cwnd = " << tcb->m_cWnd
                                                   << " ssthresh=" << tcb->m_ssThresh);
                }
                else
                {
                    // We are going at the right speed
                    NS_LOG_LOGIC("We are sending at the right speed");
                }
            }
            tcb->m_ssThresh = std::max(tcb->m_ssThresh, 3 * tcb->m_cWnd / 4);
            NS_LOG_DEBUG("Updated ssThresh = " << tcb->m_ssThresh);
        }
 
        // Reset cntRtt & minRtt every RTT
        m_cntRtt = 0;
        m_minRtt = Time::Max();
    }
    else if (tcb->m_cWnd < tcb->m_ssThresh)
    {
        TcpNewReno::SlowStart(tcb, segmentsAcked);
    }
}
 
std::string
TcpVegas::GetName() const
{
    return "TcpVegas";
}
 
uint32_t
TcpVegas::GetSsThresh(Ptr<const TcpSocketState> tcb, uint32_t bytesInFlight)
{
    NS_LOG_FUNCTION(this << tcb << bytesInFlight);
    return std::max(std::min(tcb->m_ssThresh.Get(), tcb->m_cWnd.Get() - tcb->m_segmentSize),
                    2 * tcb->m_segmentSize);
}
 
} // namespace ns3