tcp-reno.zip_cognitive_reno_tcp reno_tcp reno wireless_拥挤算法reno

/* -*- Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */ /* * Copyright (c) 1990, 1997 Regents of the University of California. * All rights reserved. * * Redistribution and use in source and binary forms are permitted * provided that the above copyright notice and this paragraph are * duplicated in all such forms and that any documentation, * advertising materials, and other materials related to such * distribution and use acknowledge that the software was developed * by the University of California, Lawrence Berkeley Laboratory, * Berkeley, CA. The name of the University may not be used to * endorse or promote products derived from this software without * specific prior written permission. * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. */ #ifndef lint static const char rcsid[] = "@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/tcp-reno.cc,v 1.42 2005/07/13 03:51:32 tomh Exp $ (LBL)"; #endif #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include "ip.h" #include "tcp.h" #include "flags.h" static class RenoTcpClass : public TclClass { public: RenoTcpClass() : TclClass("Agent/TCP/Reno") {} TclObject* create(int, const char*const*) { return (new RenoTcpAgent()); } } class_reno; int RenoTcpAgent::window() { // // reno: inflate the window by dupwnd_ // dupwnd_ will be non-zero during fast recovery, // at which time it contains the number of dup acks // int win = int(cwnd_) + dupwnd_; //在快速恢复时，增加发送窗口，dupwnd_=0(初始)或者＝numdupacks_，在dupack_>numdupacks_时，dupwnd_每次还要+1 if (frto_ == 2) { // First ack after RTO has arrived. // Open window to allow two new segments out with F-RTO. win = force_wnd(2); } if (win > int(wnd_)) win = int(wnd_); return (win); } double RenoTcpAgent::windowd() { // // reno: inflate the window by dupwnd_ // dupwnd_ will be non-zero during fast recovery, // at which time it contains the number of dup acks // double win = cwnd_ + dupwnd_; if (win > wnd_) win = wnd_; return (win); } RenoTcpAgent::RenoTcpAgent() : TcpAgent(), dupwnd_(0) { } void RenoTcpAgent::recv(Packet *pkt, Handler*) { hdr_tcp *tcph = hdr_tcp::access(pkt); int valid_ack = 0; if (qs_approved_ == 1 && tcph->seqno() > last_ack_) endQuickStart(); if (qs_requested_ == 1) processQuickStart(pkt); #ifdef notdef if (pkt->type_ != PT_ACK) { fprintf(stderr, "ns: confiuration error: tcp received non-ack\n"); exit(1); } #endif /* W.N.: check if this is from a previous incarnation */ if (tcph->ts() < lastreset_) { // Remove packet and do nothing Packet::free(pkt); return; } ++nackpack_; ts_peer_ = tcph->ts(); if (hdr_flags::access(pkt)->ecnecho() && ecn_) ecn(tcph->seqno()); recv_helper(pkt); recv_frto_helper(pkt); if (tcph->seqno() > last_ack_) { //本ACK序号>上次记录的ACK序号，表示是新的ACK if (last_cwnd_action_ == CWND_ACTION_DUPACK) //*本次新ACK，则退出快速重传 last_cwnd_action_ = CWND_ACTION_EXITED; //* dupwnd_ = 0; //*设置dupwnd_=0,用于下次计算发送窗口win recv_newack_helper(pkt); if (last_ack_ == 0 && delay_growth_) { //是连接以来的第一个ACK cwnd_ = initial_window(); //初始化CWND } } else if (tcph->seqno() == last_ack_) { // 本次不是新ACK,是上次的重复ACK if (hdr_flags::access(pkt)->eln_ && eln_) { tcp_eln(pkt); return; } //以下是重复数ACK=1-2、3和3以上的三种情况的处理 if (++dupacks_ == numdupacks_) { //*默认numdupacks_＝3，有3个重传就执行快速恢复和快速重传 dupack_action(); //改变SSTHRESH、CWND，并重设定时器超时 if (!exitFastRetrans_) //*exitFastRetrans_默认为1，reno专用 dupwnd_ = numdupacks_; } else if (dupacks_ > numdupacks_ && (!exitFastRetrans_ //*超过numdupacks_次重传ACK，且上次也是重传ACK || last_cwnd_action_ == CWND_ACTION_DUPACK )) { ++dupwnd_; //* 执行快速恢复：在超过numdupacks_次重传ACK后，每次再收到一个重复ACK,使发送窗口+1,加快发送，fast recovery } else if (dupacks_ < numdupacks_ && singledup_ ) { //如果是1次到2次重复ACK，发送一个新分组 ，这是限制传输机制 send_one(); } } if (tcph->seqno() >= last_ack_) //本ACK序号>=上次ACK，表示是新ACK或重复ACK,是合法的 // Check if ACK is valid. Suggestion by Mark Allman. valid_ack = 1; Packet::free(pkt); //合法，回收该分组内存 #ifdef notyet if (trace_) plot(); #endif /* * Try to send more data */ if (valid_ack || aggressive_maxburst_) //aggressive_maxburst_默认值为1 if (dupacks_ == 0 || dupacks_ > numdupacks_ - 1) //*如果是新的ACK或者重复ACK数>=3,尽量发送更多的数据 send_much(0, 0, maxburst_); //即如果重复ACK＝1或者2，则不这样传，而按照上面只发送一个分组 } /*注： 限制传输机制（Limited Transmit mechanism） 我们知道，当前的TCP应用主要有两种重传机制－快速重传和超时重传。当TCP源端收到3个ACK副本时， 就会触发快速重传机制，此时源端重传丢失的数据包并且将拥塞窗口大小减半。这种情况下，TCP流往往能 够很快从丢包中恢复过来，重新回到原先的发送速率。但如果TCP源端没有收到3个ACK副本，例如拥塞窗口 大小小于4，那么TCP源端则需要等待相当长时间，以便超时重发。这样，小窗口的TCP流就很容易陷入不必 要的超时重发，使其吞吐量大大下降。 为了避免这种不必要的超时重传，一种改进办法就是只要TCP源端收到一个或者两个ACK副本，并且如果 通告窗口允许，便继续发送新的数据包。这是因为只要收到ACK副本，就表明有数据包已经离开网络被接受 端接收了，而此时源端还无法判断数据包是否被丢弃，根据“数据包守恒”原则，只要遵守拥塞窗口的规范， 也即同时在网络中传送的数据包数量不能超过拥塞窗口的大小（以数据包为单位），源端就可以继续发送新 的数据包。这种机制称为限制传输机制（Limited Transmit mechanism），这种机制对排序的数据包尤其有效。 限制传输机制可以使小窗口的TCP流很快从丢包中恢复过来。例如，对于拥塞窗口大小为4地TCP流，如果 其第二个数据包丢失，那么按传统地做法需要等待超时重传。而在限制传输机制下，当源端收到对第三个数据 包确认的ACK副本时（ACK中要求源端发送第二个数据包），继续发送新的数据包，最终源端可以收到三个ACK 副本从而触发快速重传，从而减少了不必要的超时重传。 */ //last_cwnd_action_即上次对CWND的动作为DUPACK，则本次允许快速重传 //本次 int RenoTcpAgent::allow_fast_retransmit(int last_cwnd_action_) { return (last_cwnd_action_ == CWND_ACTION_DUPACK); } /* * Dupack-action: what to do on a DUP ACK. After the initial check * of 'recover' below, this function implements the following truth * table: * * bugfix ecn last-cwnd == ecn action * * 0 0 0 reno_action * 0 0 1 reno_action [impossible] * 0 1 0 reno_action * 0 1 1 retransmit, return * 1 0 0 nothing * 1 0 1 nothing [impossible] * 1 1 0 nothing * 1 1 1 retransmit, return */ //重复ACK满3个，执行下面程序 void RenoTcpAgent::dupack_action() { int recovered = (highest_ack_ > recover_); int allowFastRetransmit = allow_fast_retransmit(last_cwnd_action_); //*上次是DUPACK状态，本次仍是重复ACK，允许本次快速重传 if (recovered || (!bug_fix_ && !ecn_) || allowFastRetransmit) { //*若允许快速重传，跳转 goto reno_action; } if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) { last_cwnd_action_ = CWND_ACTION_DUPACK; /* * What if there is a DUPACK action followed closely by ECN * followed closely by a DUPACK action? * The optimal thing to do would be to remember all * congestion actions from the most recent window * of data. Otherwise "bugfi