NS3学习——tcpVegas算法代码详解（1）

目录

一、源码

二、详解

1.定义日志和命名空间

2.注册Typeld类:TcpVegas和GetTypeId方法的实现

3.构造函数和析构函数

4.TcpVegas类中成员函数

(1) Fork函数

(2) PktsAcked函数

(3) EnableVegas函数

(4) DisableVegas函数

一、源码

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
 * Copyright (c) 2016 ResiliNets, ITTC, University of Kansas
 *
 * 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
 *
 * Author: Truc Anh N. Nguyen <annguyen@ittc.ku.edu>
 *
 * James P.G. Sterbenz <jpgs@ittc.ku.edu>, director
 * ResiliNets Research Group  http://wiki.ittc.ku.edu/resilinets
 * 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 (void)
{
  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 (void)
  : 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 (void)
{
  NS_LOG_FUNCTION (this);
}

Ptr<TcpCongestionOps>
TcpVegas::Fork (void)
{
  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

二、详解

1.定义日志和命名空间

#include "tcp-vegas.h" //包含TCP Vegas算法的头文件。
#include "tcp-socket-state.h"  //包含TCP套接字状态的头文件
 
#include "ns3/log.h"  //包含NS-3日志功能的头文件

namespace ns3 {

NS_LOG_COMPONENT_DEFINE ("TcpVegas"); //定义了一个日志组件，用于记录日志信息。
NS_OBJECT_ENSURE_REGISTERED (TcpVegas);

2.注册Typeld类:TcpVegas和GetTypeId方法的实现

TypeId
TcpVegas::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::TcpVegas") //设置类的名称为TcpVegas 位于ns3命名空间下
    .SetParent<TcpNewReno> () //设置TcpVegas的父类为TcpNewReno
    .AddConstructor<TcpVegas> () //添加TcpVegas类的构造函数 创建相关对象
    .SetGroupName ("Internet") //将TcpVegas分类到"Internet"组下
     .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; //返回TcpVegas的TypeId对象
}

AddAttribute方法用于添加类的属性，这些属性可以在NS-3的配置系统中设置和获取。

•  "Alpha"、"Beta"和"Gamma"是TcpVegas算法的三个参数，它们分别控制算法的行为：
  • "Alpha"：网络中数据包的下界，初始值为2。
  • "Beta"：网络中数据包的上界，初始值为4。
  • "Gamma"：增加的极限，初始值为1。
• UintegerValue：设置属性的初始值。
• MakeUintegerAccessor：创建一个访问器，用于访问和修改属性值。
• MakeUintegerChecker<uint32_t>()：创建一个检查器，确保属性值是有效的无符号整数。

该段代码在NS-3中注册TcpVegas类，并设置其属性和行为，使得TcpVegas可以在NS-3的模拟中被创建和配置。

3.构造函数和析构函数

TcpVegas::TcpVegas (void) //默认构造函数
  : TcpNewReno (), //TcpVegas通过调用其父类TcpNewReno的默认构造函数来进行初始化
    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); //日志记录构造函数的调用，this指向当前对象的指针
}

TcpVegas::TcpVegas (const TcpVegas& sock) //复制构造函数
  : 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 (void) //析构函数
{
  NS_LOG_FUNCTION (this);
}

默认构造函数：

• m_alpha (2), m_beta (4), m_gamma (1)：这些行初始化TcpVegas算法的参数alpha、beta和gamma，分别设置为2、4和1。
• m_baseRtt (Time::Max ()), m_minRtt (Time::Max ())：将基础往返时间（baseRtt）和最小往返时间（minRtt）初始化为最大时间值，表示它们尚未被设置。
• m_cntRtt (0)：初始化往返时间计数器（cntRtt）为0。即用于计数自连接建立以来观测到的RTT样本数量。
• m_doingVegasNow (true)：初始化标志doingVegasNow为true，表示Vegas算法默认是启用的。
• m_begSndNxt (0)：初始化发送下一个序列号（begSndNxt）为0。
• 日志系统记录构造函数的调用，this指向当前对象的指针。

复制构造函数：用于创建一个与另一个TcpVegas对象sock相同的新对象。

• : TcpNewReno (sock)：表明TcpVegas复制构造函数首先调用其父类TcpNewReno的复制构造函数来复制父类成员。
• 接下来，复制sock对象中的alpha、beta、gamma、baseRtt、minRtt和cntRtt成员变量的值到新对象。
• m_doingVegasNow (true)和m_begSndNxt (0)：与默认构造函数类似，初始化doingVegasNow为true和begSndNxt为0。
• const TcpVegas& sock：参数sock是TcpVegas类型的对象引用，它指向一个已经存在的对象

4.TcpVegas类中成员函数

(1) Fork函数

Ptr<TcpCongestionOps>
TcpVegas::Fork (void)
{
  return CopyObject<TcpVegas> (this);
}

• Fork函数用于创建当前TcpVegas对象的一个副本，并返回这个副本的智能指针；
• Ptr<TcpCongestionOps>是一个智能指针，指向TcpCongestionOps类型的对象。Ptr是NS-3中用于管理对象生命周期的智能指针模板类，而TcpCongestionOps是一个抽象基类，代表TCP拥塞控制操作。
• CopyObject<TcpVegas> (this)：这是NS-3中用于复制对象的模板函数，它创建了当前对象的一个副本，并返回一个指向新对象的智能指针。这里的this指针指向当前的TcpVegas对象。

(2) PktsAcked函数

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);
}

• PktsAcked函数在收到ACK时被调用，用于更新最小 RTT（m_minRtt）和基础 RTT（m_baseRtt），并统计 RTT 样本的数量 (m_cntRtt)。
• 如果 rtt 为零，则直接返回，不进行任何操作。这通常是为了避免处理无效的数据（例如无效的 ACK 或零延迟的情况）。
• std::min 是 C++ 标准库中的一个函数模板，它返回两个参数中的较小值。
• m_minRtt 表示当前连接或当前窗口内的最小 RTT。在每次收到 ACK 包时，如果新的 RTT 比当前记录的 m_minRtt 小，就会更新 m_minRtt。
  std::min(m_minRtt, rtt) 会选择 m_minRtt 和当前 RTT 中较小的一个，并将其赋值给 m_minRtt。确保 m_minRtt 始终保持为最小的 RTT 值。
• m_baseRtt 用于记录连接过程中观察到的最小 RTT（通常是在连接的初期或网络的稳定阶段）。这代表了网络的基准延迟（即理想的延迟）。
• 与 m_minRtt 类似，m_baseRtt 会更新为当前 RTT 和已有的 m_baseRtt 中的最小值。这可以确保 m_baseRtt 始终为连接期间的最小延迟。
• m_cntRtt 是 RTT 样本的计数器。每次收到 ACK 包时，都会增加 m_cntRtt 的值，表示新的 RTT 样本被记录。

baseRtt 和 minRtt的区别见：

TCP Vegas拥塞控制算法——baseRtt 和 minRtt的区别-CSDN博客

(3) EnableVegas函数

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;
}

• EnableVegas函数用于启用Vegas算法。
• m_doingVegasNow标志被设置为true，表示Vegas算法现在被激活。
• m_begSndNxt被设置为下一个传输序列号，用于跟踪Vegas周期的开始。
• 将m_cntRtt成员变量重置为0，在每个新的Vegas周期开始时重置这个计数器。
• 将m_minRtt重置为Time::Max()，即最大可能的时间值；用于在新的Vegas周期中重新寻找最小的RTT值。

(4) DisableVegas函数

void TcpVegas::DisableVegas ()
{
  NS_LOG_FUNCTION (this);

  m_doingVegasNow = false;
}

• DisableVegas函数用于禁用Vegas算法。
• m_doingVegasNow标志被设置为false，表示Vegas算法现在被禁用。