TCP的.cc文件代码解释（中文）
#ifndef lint
static const char rcsid[] =
"@(#) $Header: /nfs/jade/vint/CVSROOT/ns-2/tcp/tcp.cc,v 1.163 2005/06/21 01:48:24 sfloyd Exp $ (LBL)";
#endif
#include <stdlib.h>
#include <math.h>
#include <sys/types.h>
#include "ip.h"
#include "tcp.h"
#include "flags.h"
#include "random.h"
#include "basetrace.h"
#include "hdr_qs.h"
int hdr_tcp::offset_;
static class TCPHeaderClass : public PacketHeaderClass {
public:
TCPHeaderClass() : PacketHeaderClass("PacketHeader/TCP",
sizeof(hdr_tcp)) {
bind_offset(&hdr_tcp::offset_);
}
} class_tcphdr;
static class TcpClass : public TclClass {
public:
TcpClass() : TclClass("Agent/TCP") {}
TclObject* create(int , const char*const*) {
return (new TcpAgent());
}
} class_tcp;
TcpAgent::TcpAgent()
: Agent(PT_TCP),
t_seqno_(0), t_rtt_(0), t_srtt_(0), t_rttvar_(0),
t_backoff_(0), ts_peer_(0), ts_echo_(0),
tss(NULL), tss_size_(100),
rtx_timer_(this), delsnd_timer_(this), burstsnd_timer_(this),
dupacks_(0), curseq_(0), highest_ack_(0), cwnd_(0), ssthresh_(0),
maxseq_(0), count_(0), rtt_active_(0), rtt_seq_(-1), rtt_ts_(0.0),
lastreset_(0.0), closed_(0), first_decrease_(1), fcnt_(0),
nrexmit_(0), restart_bugfix_(1), cong_action_(0),
ecn_burst_(0), ecn_backoff_(0), ect_(0),
qs_requested_(0), qs_approved_(0),
qs_window_(0), qs_cwnd_(0), frto_(0)
{
#ifdef TCP_DELAY_BIND_ALL
#else /* ! TCP_DELAY_BIND_ALL */
// not delay-bound because delay-bound tracevars aren't yet supported
bind("t_seqno_", &t_seqno_);
bind("rtt_", &t_rtt_);
bind("srtt_", &t_srtt_);
bind("rttvar_", &t_rttvar_);
bind("backoff_", &t_backoff_);
bind("dupacks_", &dupacks_);
bind("seqno_", &curseq_);
bind("ack_", &highest_ack_);
bind("cwnd_", &cwnd_);
bind("ssthresh_", &ssthresh_);
bind("maxseq_", &maxseq_);
bind("ndatapack_", &ndatapack_);
bind("ndatabytes_", &ndatabytes_);
bind("nackpack_", &nackpack_);
bind("nrexmit_", &nrexmit_);
bind("nrexmitpack_", &nrexmitpack_);
bind("nrexmitbytes_", &nrexmitbytes_);
bind("necnresponses_", &necnresponses_);
bind("ncwndcuts_", &ncwndcuts_);
bind("ncwndcuts1_", &ncwndcuts1_);
#endif /* TCP_DELAY_BIND_ALL */
}
void
TcpAgent::delay_bind_init_all()
{
// Defaults for bound variables should be set in ns-default.tcl.
delay_bind_init_one("window_");
delay_bind_init_one("windowInit_");
delay_bind_init_one("windowInitOption_");
delay_bind_init_one("syn_");
delay_bind_init_one("windowOption_");
delay_bind_init_one("windowConstant_");
delay_bind_init_one("windowThresh_");
delay_bind_init_one("delay_growth_");
delay_bind_init_one("overhead_");
delay_bind_init_one("tcpTick_");
delay_bind_init_one("ecn_");
delay_bind_init_one("SetCWRonRetransmit_");
delay_bind_init_one("old_ecn_");
delay_bind_init_one("eln_");
delay_bind_init_one("eln_rxmit_thresh_");
delay_bind_init_one("packetSize_");
delay_bind_init_one("tcpip_base_hdr_size_");
delay_bind_init_one("ts_option_size_");
delay_bind_init_one("bugFix_");
delay_bind_init_one("bugFix_ack_");
delay_bind_init_one("bugFix_ts_");
delay_bind_init_one("lessCareful_");
delay_bind_init_one("slow_start_restart_");
delay_bind_init_one("restart_bugfix_");
delay_bind_init_one("timestamps_");
delay_bind_init_one("ts_resetRTO_");
delay_bind_init_one("maxburst_");
delay_bind_init_one("aggressive_maxburst_");
delay_bind_init_one("maxcwnd_");
delay_bind_init_one("numdupacks_");
delay_bind_init_one("numdupacksFrac_");
delay_bind_init_one("exitFastRetrans_");
delay_bind_init_one("maxrto_");
delay_bind_init_one("minrto_");
delay_bind_init_one("srtt_init_");
delay_bind_init_one("rttvar_init_");
delay_bind_init_one("rtxcur_init_");
delay_bind_init_one("T_SRTT_BITS");
delay_bind_init_one("T_RTTVAR_BITS");
delay_bind_init_one("rttvar_exp_");
delay_bind_init_one("awnd_");
delay_bind_init_one("decrease_num_");
delay_bind_init_one("increase_num_");
delay_bind_init_one("k_parameter_");
delay_bind_init_one("l_parameter_");
delay_bind_init_one("trace_all_oneline_");
delay_bind_init_one("nam_tracevar_");
delay_bind_init_one("QOption_");
delay_bind_init_one("EnblRTTCtr_");
delay_bind_init_one("control_increase_");
delay_bind_init_one("noFastRetrans_");
delay_bind_init_one("precisionReduce_");
delay_bind_init_one("oldCode_");
delay_bind_init_one("useHeaders_");
delay_bind_init_one("low_window_");
delay_bind_init_one("high_window_");
delay_bind_init_one("high_p_");
delay_bind_init_one("high_decrease_");
delay_bind_init_one("max_ssthresh_");
delay_bind_init_one("cwnd_range_");
delay_bind_init_one("timerfix_");
delay_bind_init_one("rfc2988_");
delay_bind_init_one("singledup_");
delay_bind_init_one("LimTransmitFix_");
delay_bind_init_one("rate_request_");
delay_bind_init_one("qs_enabled_");
delay_bind_init_one("tcp_qs_recovery_");
delay_bind_init_one("qs_request_mode_");
delay_bind_init_one("qs_thresh_");
delay_bind_init_one("qs_rtt_");
delay_bind_init_one("frto_enabled_");
delay_bind_init_one("sfrto_enabled_");
delay_bind_init_one("spurious_response_");
#ifdef TCP_DELAY_BIND_ALL
// out because delay-bound tracevars aren't yet supported
delay_bind_init_one("t_seqno_");
delay_bind_init_one("rtt_");
delay_bind_init_one("srtt_");
delay_bind_init_one("rttvar_");
delay_bind_init_one("backoff_");
delay_bind_init_one("dupacks_");
delay_bind_init_one("seqno_");
delay_bind_init_one("ack_");
delay_bind_init_one("cwnd_");
delay_bind_init_one("ssthresh_");
delay_bind_init_one("maxseq_");
delay_bind_init_one("ndatapack_");
delay_bind_init_one("ndatabytes_");
delay_bind_init_one("nackpack_");
delay_bind_init_one("nrexmit_");
delay_bind_init_one("nrexmitpack_");
delay_bind_init_one("nrexmitbytes_");
delay_bind_init_one("necnresponses_");
delay_bind_init_one("ncwndcuts_");
delay_bind_init_one("ncwndcuts1_");
#endif /* TCP_DELAY_BIND_ALL */
Agent::delay_bind_init_all();
reset();
}
int
TcpAgent::delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer)
{
if (delay_bind(varName, localName, "window_", &wnd_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "windowInit_", &wnd_init_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "windowInitOption_", &wnd_init_option_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "syn_", &syn_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "windowOption_", &wnd_option_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "windowConstant_", &wnd_const_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "windowThresh_", &wnd_th_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "delay_growth_", &delay_growth_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "overhead_", &overhead_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "tcpTick_", &tcp_tick_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "ecn_", &ecn_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "SetCWRonRetransmit_", &SetCWRonRetransmit_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "old_ecn_", &old_ecn_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "eln_", &eln_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "eln_rxmit_thresh_", &eln_rxmit_thresh_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "packetSize_", &size_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "tcpip_base_hdr_size_", &tcpip_base_hdr_size_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ts_option_size_", &ts_option_size_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "bugFix_", &bug_fix_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "bugFix_ack_", &bugfix_ack_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "bugFix_ts_", &bugfix_ts_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "lessCareful_", &less_careful_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "timestamps_", &ts_option_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "ts_resetRTO_", &ts_resetRTO_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "slow_start_restart_", &slow_start_restart_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "restart_bugfix_", &restart_bugfix_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "maxburst_", &maxburst_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "aggressive_maxburst_", &aggressive_maxburst_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "maxcwnd_", &maxcwnd_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "numdupacks_", &numdupacks_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "numdupacksFrac_", &numdupacksFrac_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "exitFastRetrans_", &exitFastRetrans_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "maxrto_", &maxrto_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "minrto_", &minrto_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "srtt_init_", &srtt_init_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rttvar_init_", &rttvar_init_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rtxcur_init_", &rtxcur_init_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "T_SRTT_BITS", &T_SRTT_BITS , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "T_RTTVAR_BITS", &T_RTTVAR_BITS , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rttvar_exp_", &rttvar_exp_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "awnd_", &awnd_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "decrease_num_", &decrease_num_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "increase_num_", &increase_num_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "k_parameter_", &k_parameter_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "l_parameter_", &l_parameter_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "trace_all_oneline_", &trace_all_oneline_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "nam_tracevar_", &nam_tracevar_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "QOption_", &QOption_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "EnblRTTCtr_", &EnblRTTCtr_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "control_increase_", &control_increase_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "noFastRetrans_", &noFastRetrans_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "precisionReduce_", &precision_reduce_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "oldCode_", &oldCode_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "useHeaders_", &useHeaders_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "low_window_", &low_window_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "high_window_", &high_window_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "high_p_", &high_p_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "high_decrease_", &high_decrease_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "max_ssthresh_", &max_ssthresh_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "cwnd_range_", &cwnd_range_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "timerfix_", &timerfix_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "rfc2988_", &rfc2988_, tracer)) return TCL_OK;
if (delay_bind(varName, localName, "singledup_", &singledup_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "LimTransmitFix_", &LimTransmitFix_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rate_request_", &rate_request_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "qs_enabled_", &qs_enabled_ , tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "tcp_qs_recovery_", &tcp_qs_recovery_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "frto_enabled_", &frto_enabled_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "sfrto_enabled_", &sfrto_enabled_, tracer)) return TCL_OK;
if (delay_bind_bool(varName, localName, "spurious_response_", &spurious_response_, tracer)) return TCL_OK;
#ifdef TCP_DELAY_BIND_ALL
// not if (delay-bound delay-bound tracevars aren't yet supported
if (delay_bind(varName, localName, "t_seqno_", &t_seqno_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rtt_", &t_rtt_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "srtt_", &t_srtt_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "rttvar_", &t_rttvar_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "backoff_", &t_backoff_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "dupacks_", &dupacks_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "seqno_", &curseq_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ack_", &highest_ack_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "cwnd_", &cwnd_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ssthresh_", &ssthresh_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "maxseq_", &maxseq_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ndatapack_", &ndatapack_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ndatabytes_", &ndatabytes_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "nackpack_", &nackpack_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "nrexmit_", &nrexmit_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "nrexmitpack_", &nrexmitpack_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "nrexmitbytes_", &nrexmitbytes_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "necnresponses_", &necnresponses_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ncwndcuts_", &ncwndcuts_ , tracer)) return TCL_OK;
if (delay_bind(varName, localName, "ncwndcuts1_", &ncwndcuts1_ , tracer)) return TCL_OK;
#endif
return Agent::delay_bind_dispatch(varName, localName, tracer);
}
#define TCP_WRK_SIZE 512
/* Print out all the traced variables whenever any one is changed */
void
TcpAgent::traceAll() {
if (!channel_)
return;
double curtime;
Scheduler& s = Scheduler::instance();
char wrk[TCP_WRK_SIZE];
curtime = &s ? s.clock() : 0;
snprintf(wrk, TCP_WRK_SIZE,
"time: %-8.5f saddr: %-2d sport: %-2d daddr: %-2d dport:"
" %-2d maxseq: %-4d hiack: %-4d seqno: %-4d cwnd: %-6.3f"
" ssthresh: %-3d dupacks: %-2d rtt: %-6.3f srtt: %-6.3f"
" rttvar: %-6.3f bkoff: %-d/n", curtime, addr(), port(),
daddr(), dport(), int(maxseq_), int(highest_ack_),
int(t_seqno_), double(cwnd_), int(ssthresh_),
int(dupacks_), int(t_rtt_)*tcp_tick_,
(int(t_srtt_) >> T_SRTT_BITS)*tcp_tick_,
int(t_rttvar_)*tcp_tick_/4.0, int(t_backoff_));
(void)Tcl_Write(channel_, wrk, -1);
}
/* Print out just the variable that is modified */
void
TcpAgent::traceVar(TracedVar* v)
{
if (!channel_)
return;
double curtime;
Scheduler& s = Scheduler::instance();
char wrk[TCP_WRK_SIZE];
curtime = &s ? s.clock() : 0;
// XXX comparing addresses is faster than comparing names
if (v == &cwnd_)
snprintf(wrk, TCP_WRK_SIZE,
"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f/n",
curtime, addr(), port(), daddr(), dport(),
v->name(), double(*((TracedDouble*) v)));
else if (v == &t_rtt_)
snprintf(wrk, TCP_WRK_SIZE,
"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f/n",
curtime, addr(), port(), daddr(), dport(),
v->name(), int(*((TracedInt*) v))*tcp_tick_);
else if (v == &t_srtt_)
snprintf(wrk, TCP_WRK_SIZE,
"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f/n",
curtime, addr(), port(), daddr(), dport(),
v->name(),
(int(*((TracedInt*) v)) >> T_SRTT_BITS)*tcp_tick_);
else if (v == &t_rttvar_)
snprintf(wrk, TCP_WRK_SIZE,
"%-8.5f %-2d %-2d %-2d %-2d %s %-6.3f/n",
curtime, addr(), port(), daddr(), dport(),
v->name(),
int(*((TracedInt*) v))*tcp_tick_/4.0);
else
snprintf(wrk, TCP_WRK_SIZE,
"%-8.5f %-2d %-2d %-2d %-2d %s %d/n",
curtime, addr(), port(), daddr(), dport(),
v->name(), int(*((TracedInt*) v)));
(void)Tcl_Write(channel_, wrk, -1);
}
void
TcpAgent::trace(TracedVar* v)
{
if (nam_tracevar_) {
Agent::trace(v);
} else if (trace_all_oneline_)
traceAll();
else
traceVar(v);
}
//
// in 1-way TCP, syn_ indicates we are modeling
// a SYN exchange at the beginning. If this is true
// and we are delaying growth, then use an initial
// window of one. If not, we do whatever initial_window()
// says to do.
//
void
TcpAgent::set_initial_window() //初始化CWND
{
if (syn_ && delay_growth_)
cwnd_ = 1.0; //连接开始，初始窗口为1
else
cwnd_ = initial_window(); //
}
void
TcpAgent::reset_qoption()
{
int now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
T_start = now ;
RTT_count = 0 ;
RTT_prev = 0 ;
RTT_goodcount = 1 ;
F_counting = 0 ;
W_timed = -1 ;
F_full = 0 ;
Backoffs = 0 ;
}
//reset()仅被delay_bind_init_all()调用，用于初始化参数
void
TcpAgent::reset()
{
rtt_init();
rtt_seq_ = -1;
/*XXX lookup variables */
dupacks_ = 0;
curseq_ = 0;
set_initial_window();
t_seqno_ = 0;
maxseq_ = -1;
last_ack_ = -1;
highest_ack_ = -1;
ssthresh_ = int(wnd_); //wnd_默认为20，SSTHRESH初始也为20
if (max_ssthresh_ > 0 && max_ssthresh_ < ssthresh_)
ssthresh_ = max_ssthresh_; //max_ssthresh_默认为0，表示无限
wnd_restart_ = 1.;
awnd_ = wnd_init_ / 2.0;
recover_ = 0;
closed_ = 0;
last_cwnd_action_ = 0;
boot_time_ = Random::uniform(tcp_tick_); //计算RTT时用到，用来模拟系统启动时间（在两个TCP时钟之间）
first_decrease_ = 1; //用于在slowdown()中判断是否第一次减少CWND，＝1，是
/* W.N.: for removing packets from previous incarnations */
lastreset_ = Scheduler::instance().clock();
/* Now these variables will be reset
- Debojyoti Dutta 12th Oct'2000 */
ndatapack_ = 0;
ndatabytes_ = 0;
nackpack_ = 0;
nrexmitbytes_ = 0;
nrexmit_ = 0;
nrexmitpack_ = 0;
necnresponses_ = 0;
ncwndcuts_ = 0;
ncwndcuts1_ = 0;
if (control_increase_) {
prev_highest_ack_ = highest_ack_ ;
}
if (wnd_option_ == 8) {
// HighSpeed TCP
hstcp_.low_p = 1.5/(low_window_*low_window_);
double highLowWin = log(high_window_)-log(low_window_);
double highLowP = log(high_p_) - log(hstcp_.low_p);
hstcp_.dec1 =
0.5 - log(low_window_) * (high_decrease_ - 0.5)/highLowWin;
hstcp_.dec2 = (high_decrease_ - 0.5)/highLowWin;
hstcp_.p1 =
log(hstcp_.low_p) - log(low_window_) * highLowP/highLowWin;
hstcp_.p2 = highLowP/highLowWin;
}
if (QOption_) {
int now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
T_last = now ;
T_prev = now ;
W_used = 0 ;
if (EnblRTTCtr_) {
reset_qoption();
}
}
}
/*仅在reset()作初始化时调用，reset()又被delay_bind_init_all()调用
* Initialize variables for the retransmit timer.
*/
void TcpAgent::rtt_init() //初始化RTT、SRTT、RTTVAR、RTXCUR和回退(补偿)因子
{
t_rtt_ = 0;
t_srtt_ = int(srtt_init_ / tcp_tick_) << T_SRTT_BITS;
t_rttvar_ = int(rttvar_init_ / tcp_tick_) << T_RTTVAR_BITS;
t_rtxcur_ = rtxcur_init_; //初始化重传定时时间
t_backoff_ = 1;
}
//由set_rtx_timer()调用rtt_timeout()设定超时值
double TcpAgent::rtt_timeout() //根据给定的t_rtxcur_（考虑上下限和回退因子）
{
double timeout;
if (rfc2988_) { //按rfc2988的算法，不同处在于2988的minrto要乘回退因子，默认为FALSE
// Correction from Tom Kelly to be RFC2988-compliant, by
// clamping minrto_ before applying t_backoff_.
if (t_rtxcur_ < minrto_) //重传超时值不能小于最小RTO
timeout = minrto_ * t_backoff_; //否则按最小值算
else
timeout = t_rtxcur_ * t_backoff_; //按给定值RTXCUR算，都要乘回退因子
} else {
timeout = t_rtxcur_ * t_backoff_;
if (timeout < minrto_)
timeout = minrto_;
}
if (timeout > maxrto_) //限制最大超时值
timeout = maxrto_;
if (timeout < 2.0 * tcp_tick_) { //超时值为负则退出，小于2个tcp时钟则为2个tcp时钟
if (timeout < 0) {
fprintf(stderr, "TcpAgent: negative RTO! (%f)/n",
timeout);
exit(1);
}
timeout = 2.0 * tcp_tick_;
}
return (timeout);
}
//由newack()调用，再由recv_newack_helper()调用，最终由recv()调用
//算得的t_rtxcur_由rtt_timeout()调用，再由set_rtx_timer()调用rtt_timeout设定超时值，set_rtx_timer()主要由output()等调用
/* This has been modified to use the tahoe code. */
void TcpAgent::rtt_update(double tao) //更新RTT，将双精度的RTT转化成整数的RTT，由此计算t_rtxcur_
{ //tao为newack（）中的now-ts_echo或now-rtt_ts_，相当于未整数化的RTT
double now = Scheduler::instance().clock();
if (ts_option_) //采用回应时间戳的情况，默认不采用
t_rtt_ = int(tao /tcp_tick_ + 0.5); //RTT整数化，＋0.5表示不四舍五入，只要有小数，都入。其中tcp_tick_默认为0.01，即RTT的值精确到0.01秒
else { //不采用时间戳的情况
double sendtime = now - tao; //计算本端发送该序号的时间
sendtime += boot_time_; //发送时间要加上boot时间，boot时间用于系统模拟启动时间？？是个随机数，小于一个tcp嘀哒
double tickoff = fmod(sendtime, tcp_tick_); //取发送时间对tcp_tick_取模的余数，是整数
t_rtt_ = int((tao + tickoff) / tcp_tick_); //计算不采用时间戳的RTT时间
}
if (t_rtt_ < 1) //rtt不能小于一个TCP时钟周期
t_rtt_ = 1;
//
// t_srtt_ has 3 bits to the right of the binary point
// t_rttvar_ has 2
// Thus "t_srtt_ >> T_SRTT_BITS" is the actual srtt,
// and "t_srtt_" is 8*srtt.
// Similarly, "t_rttvar_ >> T_RTTVAR_BITS" is the actual rttvar,
// and "t_rttvar_" is 4*rttvar.
//以下计算srtt和varrtt,算法不必关心
if (t_srtt_ != 0) {
register short delta;
delta = t_rtt_ - (t_srtt_ >> T_SRTT_BITS); // d = (m - a0)
if ((t_srtt_ += delta) <= 0) // srtt的计算：a1 = 7/8 a0 + 1/8 m
t_srtt_ = 1;
if (delta < 0)
delta = -delta;
delta -= (t_rttvar_ >> T_RTTVAR_BITS);
if ((t_rttvar_ += delta) <= 0) // varrtt的计算：var1 = 3/4 var0 + 1/4 |d|
t_rttvar_ = 1;
} else {
t_srtt_ = t_rtt_ << T_SRTT_BITS; // srtt = rtt
t_rttvar_ = t_rtt_ << (T_RTTVAR_BITS-1); // rttvar = rtt / 2
}
//
// Current retransmit value is
// (unscaled) smoothed round trip estimate
// plus 2^rttvar_exp_ times (unscaled) rttvar.
//
//计算重传超时时间RTO= SRTT + max (G, K*RTTVAR)，算法不必关心
t_rtxcur_ = (((t_rttvar_ << (rttvar_exp_ + (T_SRTT_BITS - T_RTTVAR_BITS))) +
t_srtt_) >> T_SRTT_BITS ) * tcp_tick_;
return;
}
//在reset_rtx_timer()中使用,t_backoff用于在重传超时时对RTO进行翻倍
void TcpAgent::rtt_backoff()
{
if (t_backoff_ < 64) /*t_backoff_即RTO补偿因子，初始化为0，启动后为1，
最大为64，即最大重传超时时间为：最初的RTO*64 */
t_backoff_ <<= 1; //每次补偿因子*2
if (t_backoff_ > 8) { //补偿因子>8，说明重发了3次以上，则对rtt平均偏差和平滑值做出修正
/*
* If backed off this far, clobber the srtt
* value, storing it in the mean deviation
* instead.
*/
t_rttvar_ += (t_srtt_ >> T_SRTT_BITS);
t_srtt_ = 0;
}
}
/*
* headersize:
* how big is an IP+TCP header in bytes; include options such as ts
* this function should be virtual so others (e.g. SACK) can override
*/
int TcpAgent::headersize() //IP+TCP头大小＝基本头大小＋时间选项大小
{
int total = tcpip_base_hdr_size_;
if (total < 1) {
fprintf(stderr,
"TcpAgent(%s): warning: tcpip hdr size is only %d bytes/n",
name(), tcpip_base_hdr_size_);
}
if (ts_option_)
total += ts_option_size_;
return (total);
}
//output（）发送单个分组，被send_much、send_one等调用，不直接使用
void TcpAgent::output(int seqno, int reason) //reason表示重发原因，本端不用，传给对端用
{
int force_set_rtx_timer = 0; //后面有highest_ack_ == maxseq_时，该值为0
Packet* p = allocpkt();
hdr_tcp *tcph = hdr_tcp::access(p);
hdr_flags* hf = hdr_flags::access(p);
hdr_ip *iph = hdr_ip::access(p);
int databytes = hdr_cmn::access(p)->size(); //记录本分组的字节数
tcph->seqno() = seqno; //当前将发送的分组号
tcph->ts() = Scheduler::instance().clock(); //记录发送当前分组的时间戳
int is_retransmit = (seqno < maxseq_); //当前分组号<以发最大分组号，表示本次是重传该分组
// Mark packet for diagnosis purposes if we are in Quick-Start Phase
if (qs_approved_) { //不看
hf->qs() = 1;
}
// store timestamps, with bugfix_ts_. From Andrei Gurtov.
// (A real TCP would use scoreboard for this.)
if (bugfix_ts_ && tss==NULL) { //不看
tss = (double*) calloc(tss_size_, sizeof(double));
if (tss==NULL) exit(1);
}
//dynamically grow the timestamp array if it's getting full
if (bugfix_ts_ && window() > tss_size_* 0.9) { //不看
double *ntss;
ntss = (double*) calloc(tss_size_*2, sizeof(double));
printf("resizing timestamp table/n");
if (ntss == NULL) exit(1);
for (int i=0; i<tss_size_; i++)
ntss[(highest_ack_ + i) % (tss_size_ * 2)] =
tss[(highest_ack_ + i) % tss_size_];
free(tss);
tss_size_ *= 2;
tss = ntss;
}
if (tss!=NULL) //不看
tss[seqno % tss_size_] = tcph->ts();
tcph->ts_echo() = ts_peer_; //将对方发送的时间戳返回给对方
tcph->reason() = reason; //重发的原因传给对方
tcph->last_rtt() = int(int(t_rtt_)*tcp_tick_*1000); //将上次的RTT结果传给对方，以毫秒计，只用于统计
if (ecn_) { //不看
hf->ect() = 1; // ECN-capable transport
}
if (cong_action_ && (!is_retransmit || SetCWRonRetransmit_)) { //不看
hf->cong_action() = TRUE;
cong_action_ = FALSE;
}
/* Check if this is the initial SYN packet. */
if (seqno == 0) { //是否支持第一个分组
if (syn_) { //是第一个分组，且支持SYN
databytes = 0; //是SYN分组，则不参加ndatabytes的统计
curseq_ += 1; //应用的最大分组数＋1
hdr_cmn::access(p)->size() = tcpip_base_hdr_size_;
}
if (ecn_) { //不看
hf->ecnecho() = 1;
// hf->cong_action() = 1;
hf->ect() = 0;
}
if (qs_enabled_) { //不看
hdr_qs *qsh = hdr_qs::access(p);
// dataout is kilobytes queued for sending
int dataout = (curseq_ - maxseq_ - 1) * (size_ + headersize()) / 1024;
int qs_rr = rate_request_;
if (qs_request_mode_ == 1) {
// PS: Avoid making unnecessary QS requests
// use a rough estimation of RTT in qs_rtt_
// to calculate the desired rate from dataout.
if (dataout * 1000 / qs_rtt_ < qs_rr) {
qs_rr = dataout * 1000 / qs_rtt_;
}
// qs_thresh_ is minimum number of unsent
// segments needed to activate QS request
if ((curseq_ - maxseq_ - 1) < qs_thresh_) {
qs_rr = 0;
}
}
if (qs_rr > 0) {
// QuickStart code from Srikanth Sundarrajan.
qsh->flag() = QS_REQUEST;
qsh->ttl() = Random::integer(256);
ttl_diff_ = (iph->ttl() - qsh->ttl()) % 256;
qsh->rate() = hdr_qs::Bps_to_rate(qs_rr * 1024);
qs_requested_ = 1;
} else {
qsh->flag() = QS_DISABLE;
}
}
}
else if (useHeaders_ == true) { //不是第一个分组
hdr_cmn::access(p)->size() += headersize(); //计算分组头大小
}
hdr_cmn::access(p)->size();
/* if no outstanding data, be sure to set rtx timer again */
if (highest_ack_ == maxseq_) //最高的已确认ACK号＝最大已发分组号，表示已发送的全都得到了确认，
force_set_rtx_timer = 1; //该数据肯定为新的未收到ACK的数据，肯定要重新设置重传定时器，原因见后面的“注”
/* call helper function to fill in additional fields */
output_helper(p);
++ndatapack_; //统计总的发送分组数
ndatabytes_ += databytes; //统计总发送字节数
send(p, 0); //发送该分组
if (seqno == curseq_ && seqno > maxseq_) //发送序号＝最大允许发送序号，表示已发完
idle(); // 告诉应用程序已经发完数据 Tell application I have sent everything so far
if (seqno > maxseq_) { //发送序号>上次最大发送序号，表示是新发送分组
maxseq_ = seqno; //新发送分组，记录最大发送序号
if (!rtt_active_) { //如果上一个RTT样本刚刚收到，rtt_active=1表示正在等待RTT接收样本ACK返回
rtt_active_ = 1; //表示本分组是新的RTT样本,rtt开始新的计算
if (seqno > rtt_seq_) { //若发送序号>上次RTT样本号
rtt_seq_ = seqno; //则本序号是新的RTT样本
rtt_ts_ = Scheduler::instance().clock(); //且记录该样本的发送时间戳
}
}
} else { //不是新分组了，则是重传
++nrexmitpack_; //统计重传分组数
nrexmitbytes_ += databytes; //统计重传字节数
}
if (!(rtx_timer_.status() == TIMER_PENDING) || force_set_rtx_timer)
/*TIMER_PENDING表示超时重传定时器在等待状态，即对定时器定时的分组号尚未收到ACK，
若该分组的ACK刚刚收到，或在强制重传定时器的情况时，对重传定时器重新设定超时 */
/* No timer pending. Schedule one. */
set_rtx_timer();
}
/*
注：重传定时的原理：只设定一个重传定时器，对每一个发送的分组号，设为A，
设为检查定时器是否已经在用，若没有用，则设定该定时器，此时该定时器对应该分组号；
若在用，则不修改，继续传该分组。
当收到对方对分组A的确认ACK，则将重新设定定时器，到下一个分组号A+1，此时定时器对应A+1分组；
以后，每收到一个新确认，都将定时器对应到该分组号+1。即每次都对第一个未被确认的分组进行监控，
保证此分组一旦得不到确认就超时。
*/
/*
* Must convert bytes into packets for one-way TCPs.
* If nbytes == -1, this corresponds to infinite send. We approximate
* infinite by a very large number (TCP_MAXSEQ).
*/
//该程序由上层应用调用，用来产生TCP流，完成tcp连接、传输、结束全过程，而不用管数据具体怎么传输
void TcpAgent::sendmsg(int nbytes, const char* /*flags*/) //若nbyte=-1,表示发送允许的无限多数据
{
if (nbytes == -1 && curseq_ <= TCP_MAXSEQ) //若无限发送，则确定发送的最大数据量
curseq_ = TCP_MAXSEQ;
else
curseq_ += (nbytes/size_ + (nbytes%size_ ? 1 : 0)); //有限发送，则按字节数计算将发送的总的序列数
send_much(0, 0, maxburst_); //尽量发送多的数据，直到发送完或连接终止，maxburst_是最大允许发送的数值，默认值0，表示不限数量
}
void TcpAgent::advanceby(int delta)
{
curseq_ += delta;
if (delta > 0)
closed_ = 0;
send_much(0, 0, maxburst_);
}
int TcpAgent::command(int argc, const char*const* argv)
{
if (argc == 3) {
if (strcmp(argv[1], "advance") == 0) {
int newseq = atoi(argv[2]);
if (newseq > maxseq_)
advanceby(newseq - curseq_);
else
advanceby(maxseq_ - curseq_);
return (TCL_OK);
}
if (strcmp(argv[1], "advanceby") == 0) {
advanceby(atoi(argv[2]));
return (TCL_OK);
}
if (strcmp(argv[1], "eventtrace") == 0) {
et_ = (EventTrace *)TclObject::lookup(argv[2]);
return (TCL_OK);
}
/*
* Curtis Villamizar's trick to transfer tcp connection
* parameters to emulate http persistent connections.
*
* Another way to do the same thing is to open one tcp
* object and use start/stop/maxpkts_ or advanceby to control
* how much data is sent in each burst.
* With a single connection, slow_start_restart_
* should be configured as desired.
*
* This implementation (persist) may not correctly
* emulate pure-BSD-based systems which close cwnd
* after the connection goes idle (slow-start
* restart). See appendix C in
* Jacobson and Karels ``Congestion
* Avoidance and Control'' at
* <ftp://ftp.ee.lbl.gov/papers/congavoid.ps.Z>
* (*not* the original
* '88 paper) for why BSD does this. See
* ``Performance Interactions Between P-HTTP and TCP
* Implementations'' in CCR 27(2) for descriptions of
* what other systems do the same.
*
*/
if (strcmp(argv[1], "persist") == 0) {
TcpAgent *other
= (TcpAgent*)TclObject::lookup(argv[2]);
cwnd_ = other->cwnd_;
awnd_ = other->awnd_;
ssthresh_ = other->ssthresh_;
t_rtt_ = other->t_rtt_;
t_srtt_ = other->t_srtt_;
t_rttvar_ = other->t_rttvar_;
t_backoff_ = other->t_backoff_;
return (TCL_OK);
}
}
return (Agent::command(argc, argv));
}
/*
* Returns the window size adjusted to allow <num> segments past recovery
* point to be transmitted on next ack.
*/
int TcpAgent::force_wnd(int num)
{
return recover_ + num - (int)highest_ack_;
}
//整数型的发送窗口，发送窗口＝min(wnd_,cwnd_)
int TcpAgent::window()
{
/*
* If F-RTO is enabled and first ack has come in, temporarily open
* window for sending two segments.
* The F-RTO code is from Pasi Sarolahti. F-RTO is an algorithm
* for detecting spurious retransmission timeouts.
*/
if (frto_ == 2) {
return (force_wnd(2) < wnd_ ?
force_wnd(2) : (int)wnd_);
} else {
return (cwnd_ < wnd_ ? (int)cwnd_ : (int)wnd_);
}
}
//双精度的发送窗口，发送窗口＝min(wnd_,cwnd_)
double TcpAgent::windowd()
{
return (cwnd_ < wnd_ ? (double)cwnd_ : (double)wnd_);
}
/*被recv(),timeout(),timeout_nonrtx(),sendmsg()等调用
* Try to send as much data as the window will allow. The link layer will
* do the buffering; we ask the application layer for the size of the packets.
*/
void TcpAgent::send_much(int force, int reason, int maxburst)
//在窗口范围内把尽量多的数据发出去，完成连接、传输、结束全过程
{
send_idle_helper();
int win = window(); //整型的发送窗口
int npackets = 0; // 本次发送分组数
if (!force && delsnd_timer_.status() == TIMER_PENDING) //通常force＝0，在处理非重传的超时时为1
/*非重传超时，即延迟随机时间发送数据，用于模拟网络的延迟，由timeout_nonrtx()调用，再被DelSndTimer::expire()调用
这里表示如果不是非重传超时，但延迟定时器还在工作，就不发送，直接退出 */
return;
/* Save time when first packet was sent, for newreno --Allman */
if (t_seqno_ == 0)
firstsent_ = Scheduler::instance().clock(); //记录第一个分组发送时间，newreno用
if (burstsnd_timer_.status() == TIMER_PENDING) //？
return;
while (t_seqno_ <= highest_ack_ + win && t_seqno_ < curseq_) {
//分组号在发送窗口内，且小于最大分组号，即满足条件就尽量发送，不满足条件才退出
if (overhead_ == 0 || force || qs_approved_) {
//overhead是固定值，默认0;force＝1，即非重传超时；qs，即快启动
//只要是正常情况，或非重传超时，或快启动，就按下面运行
output(t_seqno_, reason); //发送该分组，原因发到对端
npackets++; //已发送分组数记录
if (QOption_)
process_qoption_after_send () ;
t_seqno_ ++ ; //将要发送分组号＋1
if (qs_approved_ == 1) {
// delay = effective RTT / window
double delay = (double) t_rtt_ * tcp_tick_ / win;
if (overhead_) {
delsnd_timer_.resched(delay + Random::uniform(overhead_));
} else {
delsnd_timer_.resched(delay);
}
return;
}
} else if (!(delsnd_timer_.status() == TIMER_PENDING)) {
//不是上面的三种情况，但延迟定时器没有等待了，就重新设置随机延迟时间，并返回
/*
* Set a delayed send timeout.
*/
delsnd_timer_.resched(Random::uniform(overhead_));
return;
}
win = window(); //发送了一个分组，发送窗口重新计算
if (maxburst && npackets == maxburst) //maxburst是一次最多发送的分组数，默认为0，表示不限制数量
break;
}
/* call helper function */
send_helper(maxburst);
}
/*主要在timeout()、dupack_action()中使用
* We got a timeout or too many duplicate acks. Clear the retransmit timer.
* Resume the sequence one past the last packet acked.
* "mild" is 0 for timeouts and Tahoe dup acks, 1 for Reno dup acks.
* "backoff" is 1 if the timer should be backed off, 0 otherwise.
*/
void TcpAgent::reset_rtx_timer(int mild, int backoff)
{
if (backoff) //重传时，backoff=1,见timeout(),表示要对RTO做出调整，RTO=RTO*2
rtt_backoff();
set_rtx_timer(); //根据调整
if (!mild) //程序只用到了mild=0的情况，RENO用到mild=1的情况
t_seqno_ = highest_ack_ + 1;
rtt_active_ = 0;
}
/*
* Set retransmit timer using current rtt estimate. By calling resched(),
* it does not matter whether the timer was already running.
*/
void TcpAgent::set_rtx_timer()
{
rtx_timer_.resched(rtt_timeout());
}
/*只被newack()调用，用来设置重传定时器，pkt是接收到的ACK分组
* Set new retransmission timer if not all outstanding
* or available data acked, or if we are unable to send because
* cwnd is less than one (as when the ECN bit is set when cwnd was 1).
* Otherwise, if a timer is still outstanding, cancel it.
*/
void TcpAgent::newtimer(Packet* pkt)
{
hdr_tcp *tcph = hdr_tcp::access(pkt);
/*
* t_seqno_, the next packet to send, is reset (decreased)
* to highest_ack_ + 1 after a timeout,
* so we also have to check maxseq_, the highest seqno sent.
* In addition, if the packet sent after the timeout has
* the ECN bit set, then the returning ACK caused cwnd_ to
* be decreased to less than one, and we can't send another
* packet until the retransmit timer again expires.
* So we have to check for "cwnd_ < 1" as well.
*/
//当前将发送序号>本次接收ack号
if (t_seqno_ > tcph->seqno() || tcph->seqno() < maxseq_ || cwnd_ < 1)
set_rtx_timer();
else
cancel_rtx_timer(); //程序中没有该子程序
}
/*
* for experimental, high-speed TCP
*/
double TcpAgent::linear(double x, double x_1, double y_1, double x_2, double y_2)
{
// The y coordinate factor ranges from y_1 to y_2
// as the x coordinate ranges from x_1 to x_2.
double y = y_1 + ((y_2 - y_1) * ((x - x_1)/(x_2-x_1)));
return y;
}
/*
* Limited Slow-Start for large congestion windows.
* This is only used when max_ssthresh_ is non-zero.
*/
double TcpAgent::limited_slow_start(double cwnd, double max_ssthresh, double increment)
{
int round = int(cwnd / (double(max_ssthresh)/2.0));
double increment1 = 1.0/(double(round));
if (increment < increment1)
increment = increment1;
return increment;
}
/*
* For retrieving numdupacks_.
*/
int TcpAgent::numdupacks(double cwnd)
{
int cwndfraction = (int) cwnd/numdupacksFrac_;
if (numdupacks_ > cwndfraction) {
return numdupacks_;
} else {
return cwndfraction;
}
}
/*
* Calculating the decrease parameter for highspeed TCP.
*/
double TcpAgent::decrease_param()
{
double decrease;
// OLD:
// decrease = linear(log(cwnd_), log(low_window_), 0.5, log(high_window_), high_decrease_);
// NEW (but equivalent):
decrease = hstcp_.dec1 + log(cwnd_) * hstcp_.dec2;
return decrease;
}
/*
* Calculating the increase parameter for highspeed TCP.
*/
double TcpAgent::increase_param()
{
double increase, decrease, p, answer;
/* extending the slow-start for high-speed TCP */
/* for highspeed TCP -- from Sylvia Ratnasamy, */
/* modifications by Sally Floyd and Evandro de Souza */
// p ranges from 1.5/W^2 at congestion window low_window_, to
// high_p_ at congestion window high_window_, on a log-log scale.
// The decrease factor ranges from 0.5 to high_decrease
// as the window ranges from low_window to high_window,
// as the log of the window.
// For an efficient implementation, this would just be looked up
// in a table, with the increase and decrease being a function of the
// congestion window.
if (cwnd_ <= low_window_) {
answer = 1 / cwnd_;
return answer;
} else if (cwnd_ >= hstcp_.cwnd_last_ &&
cwnd_ < hstcp_.cwnd_last_ + cwnd_range_) {
// cwnd_range_ can be set to 0 to be disabled,
// or can be set from 1 to 100
answer = hstcp_.increase_last_ / cwnd_;
return answer;
} else {
// OLD:
// p = exp(linear(log(cwnd_), log(low_window_), log(hstcp_.low_p), log(high_window_), log(high_p_)));
// NEW, but equivalent:
p = exp(hstcp_.p1 + log(cwnd_) * hstcp_.p2);
decrease = decrease_param();
// OLD:
// increase = cwnd_*cwnd_*p *(2.0*decrease)/(2.0 - decrease);
// NEW, but equivalent:
increase = cwnd_ * cwnd_ * p /(1/decrease - 0.5);
// if (increase > max_increase) {
// increase = max_increase;
// }
answer = increase / cwnd_;
hstcp_.cwnd_last_ = cwnd_;
hstcp_.increase_last_ = increase;
return answer;
}
}
/*仅被recv_newack_helper()调用，再被recv调用，在收到新ACK后，用于慢启动和拥塞避免，调整CWND，不调整SSTHRESH
* open up the congestion window
*/
void TcpAgent::opencwnd()
{
double increment;
if (cwnd_ < ssthresh_) { //慢启动情况，CWND=CWND+1,数据指数增加
/* slow-start (exponential) */
cwnd_ += 1;
} else { //cwnd_>=ssthresh_情况，CWND=CWND+1/CWND,数据线性增加
/* linear */
double f;
switch (wnd_option_) { //wnd_option_是窗口策略，系统固定设置，默认为1
case 0:
if (++count_ >= cwnd_) {
count_ = 0;
++cwnd_;
}
break;
case 1: //默认情况，其他的情况不用看
/* This is the standard algorithm. */
increment = increase_num_ / cwnd_; //increase_num_：加法增策略因子，默认1.0
//算出增加量1/CWND
if ((last_cwnd_action_ == 0 || //last_cwnd_action_初始化为0
last_cwnd_action_ == CWND_ACTION_TIMEOUT)
&& max_ssthresh_ > 0) {
increment = limited_slow_start(cwnd_,
max_ssthresh_, increment);
}
cwnd_ += increment;
break;
case 2:
/* These are window increase algorithms
* for experimental purposes only. */
/* This is the Constant-Rate increase algorithm
* from the 1991 paper by S. Floyd on "Connections
* with Multiple Congested Gateways".
* The window is increased by roughly
* wnd_const_*RTT^2 packets per round-trip time. */
f = (t_srtt_ >> T_SRTT_BITS) * tcp_tick_;
f *= f;
f *= wnd_const_;
/* f = wnd_const_ * RTT^2 */
f += fcnt_;
if (f > cwnd_) {
fcnt_ = 0;
++cwnd_;
} else
fcnt_ = f;
break;
case 3:
/* The window is increased by roughly
* awnd_^2 * wnd_const_ packets per RTT,
* for awnd_ the average congestion window. */
f = awnd_;
f *= f;
f *= wnd_const_;
f += fcnt_;
if (f > cwnd_) {
fcnt_ = 0;
++cwnd_;
} else
fcnt_ = f;
break;
case 4:
/* The window is increased by roughly
* awnd_ * wnd_const_ packets per RTT,
* for awnd_ the average congestion window. */
f = awnd_;
f *= wnd_const_;
f += fcnt_;
if (f > cwnd_) {
fcnt_ = 0;
++cwnd_;
} else
fcnt_ = f;
break;
case 5:
/* The window is increased by roughly wnd_const_*RTT
* packets per round-trip time, as discussed in
* the 1992 paper by S. Floyd on "On Traffic
* Phase Effects in Packet-Switched Gateways". */
f = (t_srtt_ >> T_SRTT_BITS) * tcp_tick_;
f *= wnd_const_;
f += fcnt_;
if (f > cwnd_) {
fcnt_ = 0;
++cwnd_;
} else
fcnt_ = f;
break;
case 6:
/* binomial controls */
cwnd_ += increase_num_ / (cwnd_*pow(cwnd_,k_parameter_));
break;
case 8:
/* high-speed TCP, RFC 3649 */
increment = increase_param();
if ((last_cwnd_action_ == 0 ||
last_cwnd_action_ == CWND_ACTION_TIMEOUT)
&& max_ssthresh_ > 0) {
increment = limited_slow_start(cwnd_,
max_ssthresh_, increment);
}
cwnd_ += increment;
break;
default:
#ifdef notdef
/*XXX*/
error("illegal window option %d", wnd_option_);
#endif
abort();
}
}
// if maxcwnd_ is set (nonzero), make it the cwnd limit
if (maxcwnd_ && (int(cwnd_) > maxcwnd_)) //限制CWND,不能超过最大值，最大值默认为0，表示不限制
cwnd_ = maxcwnd_;
return;
}
//被timeout、dupack_action等调用，用来降低拥塞窗口CWND和门限SSTHRESH
void
TcpAgent::slowdown(int how)
{
double decrease; /* added for highspeed - sylvia */
double win, halfwin, decreasewin;
int slowstart = 0; //慢启动参数，＝1表示是慢启动
++ncwndcuts_; //统计CWND被减少的次数，不管任何原因
if (!(how & TCP_IDLE) && !(how & NO_OUTSTANDING_DATA)){
++ncwndcuts1_; //统计因拥塞CWND被减少的次数
}
// we are in slowstart for sure if cwnd < ssthresh
if (cwnd_ < ssthresh_) //判断是否在慢启动状态
slowstart = 1;
//下面一段分别按双精度和整型计算出发送窗口WND
if (precision_reduce_) { //是否按双精度计算发送窗口win，而不是整数减，默认为FALSE
halfwin = windowd() / 2;
if (wnd_option_ == 6) { //wnd_option_值见opencwnd()，默认＝1， ＝6或8不用看
/* binomial controls */
decreasewin = windowd() - (1.0-decrease_num_)*pow(windowd(),l_parameter_);
} else if (wnd_option_ == 8 && (cwnd_ > low_window_)) {
/* experimental highspeed TCP */
decrease = decrease_param();
//if (decrease < 0.1)
// decrease = 0.1;
decrease_num_ = decrease;
decreasewin = windowd() - (decrease * windowd());
} else { //wnd_option_＝1到5的情况，＝1是默认情况，见opencwnd()
decreasewin = decrease_num_ * windowd(); //decreasewin为窗口减少量
}
win = windowd(); //双精度发送窗口
} else { //默认情况，按整数计算发送窗口win，算法同上面一样
int temp;
temp = (int)(window() / 2);
halfwin = (double) temp;
if (wnd_option_ == 6) {
/* binomial controls */
temp = (int)(window() - (1.0-decrease_num_)*pow(window(),l_parameter_));
} else if ((wnd_option_ == 8) && (cwnd_ > low_window_)) {
/* experimental highspeed TCP */
decrease = decrease_param();
//if (decrease < 0.1)
// decrease = 0.1;
decrease_num_ = decrease;
temp = (int)(windowd() - (decrease * windowd()));
} else {
temp = (int)(decrease_num_ * window());
}
decreasewin = (double) temp;
win = (double) window(); //整型发送窗口
}
//以下按照HOW的值，针对各种情况，减少CWND和SSTHRESH
if (how & CLOSE_SSTHRESH_HALF)
// For the first decrease, decrease by half
// even for non-standard values of decrease_num_.
if (first_decrease_ == 1 || slowstart || //在第一次减少，慢启动状态或超时重传时（为何第一次减少时一定要SSTHRESH减半？）
last_cwnd_action_ == CWND_ACTION_TIMEOUT) { //SSTHRESH降低到一半，wnd_option_＝默认1时，下面两种算法应该一样
//正常应该CWND=decreasewin
// Do we really want halfwin instead of decreasewin
// after a timeout?
ssthresh_ = (int) halfwin;
} else {
ssthresh_ = (int) decreasewin; //即:SSTHRESH=CWND
}
else if (how & THREE_QUARTER_SSTHRESH) //SSTHRESH减少到3/4窗口
if (ssthresh_ < 3*cwnd_/4)
ssthresh_ = (int)(3*cwnd_/4);
if (how & CLOSE_CWND_HALF) //CWND减少一半
// For the first decrease, decrease by half
// even for non-standard values of decrease_num_.
if (first_decrease_ == 1 || slowstart || decrease_num_ == 0.5) {
cwnd_ = halfwin;
} else cwnd_ = decreasewin; //如果设decreasewin为其他值，则是用于测试
else if (how & CWND_HALF_WITH_MIN) { //QOPTION,不看
// We have not thought about how non-standard TCPs, with
// non-standard values of decrease_num_, should respond
// after quiescent periods.
cwnd_ = decreasewin;
if (cwnd_ < 1)
cwnd_ = 1;
}
else if (how & CLOSE_CWND_RESTART) //超时时使SSTHRESH减半，CWND＝1
cwnd_ = int(wnd_restart_); //wnd_restart_初始化为1
else if (how & CLOSE_CWND_INIT) //快速启动丢失时使用，不看
cwnd_ = int(wnd_init_);
else if (how & CLOSE_CWND_ONE) //无显著数据，重复ACK，及F-RTO时使 CWND=1
cwnd_ = 1;
else if (how & CLOSE_CWND_HALF_WAY) { //QOPTION时使用，不看
// cwnd_ = win - (win - W_used)/2 ;
cwnd_ = W_used + decrease_num_ * (win - W_used);
if (cwnd_ < 1)
cwnd_ = 1;
}
if (ssthresh_ < 2) //SSTHRESH不能小于2
ssthresh_ = 2;
if (how & (CLOSE_CWND_HALF|CLOSE_CWND_RESTART|CLOSE_CWND_INIT|CLOSE_CWND_ONE))
cong_action_ = TRUE; //根据HOW判断当前是否拥塞
fcnt_ = count_ = 0; //用于wnd_option_＝2，3，4，5的情况，不看
if (first_decrease_ == 1) //本次是第一次减少,下次就不是了：每次连接只有一次减少
first_decrease_ = 0;
// for event tracing slow start
if (cwnd_ == 1 || slowstart) //跟踪慢启动
// Not sure if this is best way to capture slow_start
// This is probably tracing a superset of slowdowns of
// which all may not be slow_start's --Padma, 07/'01.
trace_event("SLOW_START");
}
/*被recv_newack_helper()调用，recv_newack_helper再被recv()调用，pkt为接收ACK分组
* Process a packet that acks previously unacknowleged data.
*/
void TcpAgent::newack(Packet* pkt)
{
double now = Scheduler::instance().clock();
hdr_tcp *tcph = hdr_tcp::access(pkt);
/*
* Wouldn't it be better to set the timer *after*
* updating the RTT, instead of *before*?
*/
if (!timerfix_) newtimer(pkt); //采用在更新RTT以前更新RTO定时器的策略
dupacks_ = 0; //新ACK，将重复ACK的统计恢复为0
last_ack_ = tcph->seqno(); // 记录本次新ACK号到last_ack_
prev_highest_ack_ = highest_ack_ ;
highest_ack_ = last_ack_; //记录本次新ACK号到last_ack_
if (t_seqno_ < last_ack_ + 1) // 更新下一次要发送的包的记录
t_seqno_ = last_ack_ + 1;
/*
* Update RTT only if it's OK to do so from info in the flags header.
* This is needed for protocols in which intermediate agents
* in the network intersperse acks (e.g., ack-reconstructors) for
* various reasons (without violating e2e semantics).
*/
hdr_flags *fh = hdr_flags::access(pkt);
//以下是有时间戳的RTT处理情况
if (!fh->no_ts_) { //该ACK有时间戳
if (ts_option_) { //本连接可以采用时间戳
ts_echo_=tcph->ts_echo(); //记录该新ACK的回应时间，相当于rtt_ts_
rtt_update(now - tcph->ts_echo()); //更新RTT值，now-回应时间即为rtt时间
if (ts_resetRTO_ && (!ect_ || !ecn_backoff_ ||
!hdr_flags::access(pkt)->ecnecho())) {
// From Andrei Gurtov
/*
* Don't end backoff if still in ECN-Echo with
* a congestion window of 1 packet.
*/
t_backoff_ = 1;
ecn_backoff_ = 0;
}
}
if (rtt_active_ && tcph->seqno() >= rtt_seq_) {
if (!ect_ || !ecn_backoff_ ||
!hdr_flags::access(pkt)->ecnecho()) {
/*
* Don't end backoff if still in ECN-Echo with
* a congestion window of 1 packet.
*/
t_backoff_ = 1;
ecn_backoff_ = 0;
}
rtt_active_ = 0;
if (!ts_option_) //本连接不能采用时间戳
rtt_update(now - rtt_ts_);
}
}
if (timerfix_) newtimer(pkt); //采用在更新RTT以前更新RTO定时器的策略，更科学
/* update average window */ //更新平均窗口awnd_=(1 - wnd_th_)*awnd+wnd_th_*cwnd
awnd_ *= 1.0 - wnd_th_;
awnd_ += wnd_th_ * cwnd_;
}
/*
* Respond either to a source quench or to a congestion indication bit.
* This is done at most once a roundtrip time; after a source quench,
* another one will not be done until the last packet transmitted before
* the previous source quench has been ACKed.
*
* Note that this procedure is called before "highest_ack_" is
* updated to reflect the current ACK packet.
*/
void TcpAgent::ecn(int seqno)
{
if (seqno > recover_ ||
last_cwnd_action_ == CWND_ACTION_TIMEOUT) {
recover_ = maxseq_;
last_cwnd_action_ = CWND_ACTION_ECN;
if (cwnd_ <= 1.0) {
if (ecn_backoff_)
rtt_backoff();
else ecn_backoff_ = 1;
} else ecn_backoff_ = 0;
slowdown(CLOSE_CWND_HALF|CLOSE_SSTHRESH_HALF);
++necnresponses_ ;
// added by sylvia to count number of ecn responses
}
}
/*
* Is the connection limited by the network (instead of by a lack
* of data from the application?
*/
int TcpAgent::network_limited() {
int win = window () ;
if (t_seqno_ > (prev_highest_ack_ + win))
return 1;
else
return 0;
}
//由recv()调用，收到新ACK的情况，用于新ack处理（newack(pkt)），及cwnd设置，关闭连接等处理
void TcpAgent::recv_newack_helper(Packet *pkt) {
//hdr_tcp *tcph = hdr_tcp::access(pkt);
newack(pkt); //新ACK处理
if (qs_window_ && highest_ack_ >= qs_window_) { //QS处理，不用看
// All segments in the QS window have been acknowledged.
// We can exit the Quick-Start phase.
qs_window_ = 0;
}
if (!ect_ || !hdr_flags::access(pkt)->ecnecho() || //不是ECN分组，或"old ecn"。正常的新分组
(old_ecn_ && ecn_burst_)) {
/* If "old_ecn", this is not the first ACK carrying ECN-Echo
* after a period of ACKs without ECN-Echo.
* Therefore, open the congestion window. */
/* if control option is set, and the sender is not
window limited, then do not increase the window size
control_increase_设为1，则发方窗口不受限，不用增加窗口大小？
*/
if (!control_increase_ || //control_increase_系统固定值，默认为0
(control_increase_ && (network_limited() == 1)))
opencwnd(); //正常情况，收到新ACK，就打开CWND设置
}
if (ect_) { //是ECN分组
if (!hdr_flags::access(pkt)->ecnecho())
ecn_backoff_ = 0;
if (!ecn_burst_ && hdr_flags::access(pkt)->ecnecho())
ecn_burst_ = TRUE;
else if (ecn_burst_ && ! hdr_flags::access(pkt)->ecnecho())
ecn_burst_ = FALSE;
}
if (!ect_ && hdr_flags::access(pkt)->ecnecho() &&
!hdr_flags::access(pkt)->cong_action())
ect_ = 1;
/* if the connection is done, call finish() */
if ((highest_ack_ >= curseq_-1) && !closed_) { //最大ACK>=应用程序最大值-1，表示连接结束
closed_ = 1; //关闭连接，运行finish();
finish();
}
if (QOption_ && curseq_ == highest_ack_ +1) { //不看
cancel_rtx_timer();
}
if (frto_ == 1) {
/*
* New ack after RTO. If F-RTO is enabled, try to transmit new
* previously unsent segments.
* If there are no new data or receiver window limits the
* transmission, revert to traditional recovery.
*/
if (recover_ + 1 >= highest_ack_ + wnd_ ||
recover_ + 1 >= curseq_) {
frto_ = 0;
} else if (highest_ack_ == recover_) {
/*
* F-RTO step 2a) RTO retransmission fixes whole
* window => cancel F-RTO
*/
frto_ = 0;
} else {
t_seqno_ = recover_ + 1;
frto_ = 2;
}
} else if (frto_ == 2) {
/*
* Second new ack after RTO. If F-RTO is enabled, RTO can be
* declared spurious
*/
spurious_timeout();
}
}
/*
* Set the initial window.
*/
double
TcpAgent::initial_window()
{
// If Quick-Start Request was approved, use that as a basis for
// initial window
if (qs_cwnd_) {
return (qs_cwnd_);
}
//
// init_option = 1: static iw of wnd_init_
//
if (wnd_init_option_ == 1) { //使用默认初始启动窗口
return (wnd_init_);
}
else if (wnd_init_option_ == 2) { //使用大的初始启动窗口
// do iw according to Internet draft
if (size_ <= 1095) { //根据分组数据大小分段
return (4.0);
} else if (size_ < 2190) {
return (3.0);
} else {
return (2.0);
}
}
// XXX what should we return here???
fprintf(stderr, "Wrong number of wnd_init_option_ %d/n",
wnd_init_option_);
abort();
return (2.0); // XXX make msvc happy.
}
/*
* 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 tahoe_action
* 0 0 1 tahoe_action [impossible]
* 0 1 0 tahoe_action
* 0 1 1 slow-start, return
* 1 0 0 nothing
* 1 0 1 nothing [impossible]
* 1 1 0 nothing
* 1 1 1 slow-start, return
*/
/*
* A first or second duplicate acknowledgement has arrived, and
* singledup_ is enabled.
* If the receiver's advertised window permits, and we are exceeding our
* congestion window by less than numdupacks_, then send a new packet.
*/
//发送单个分组，可以是重传分组
void
TcpAgent::send_one()
{
if (t_seqno_ <= highest_ack_ + wnd_ && t_seqno_ < curseq_ &&
t_seqno_ <= highest_ack_ + cwnd_ + dupacks_ ) {
output(t_seqno_, 0); //
if (QOption_)
process_qoption_after_send () ;
t_seqno_ ++ ;
// send_helper(); ??
}
return;
}
//在recv()中，满足了快速重传的条件后调用，用于减少CWND和SSTHRESH,并重启重传定时器
void
TcpAgent::dupack_action()
{
int recovered = (highest_ack_ > recover_);
//recover_用于记录超时和快速重传前已发送分组的最大序号,用于F-RTO
if (recovered || (!bug_fix_ && !ecn_)) {
goto tahoe_action; //跳到tahoe_action
}
if (ecn_ && last_cwnd_action_ == CWND_ACTION_ECN) { //不看
last_cwnd_action_ = CWND_ACTION_DUPACK;
slowdown(CLOSE_CWND_ONE);
reset_rtx_timer(0,0);
return;
}
if (bug_fix_) {
/*
* The line below, for "bug_fix_" true, avoids
* problems with multiple fast retransmits in one
* window of data.
*/
return;
}
tahoe_action: //tcp tahoe
recover_ = maxseq_; //记录超时和快速重传前已发送分组的最大序号
if (!lossQuickStart()) { //
// we are now going to fast-retransmit and willtrace that event
trace_event("FAST_RETX"); //跟踪快速重传
last_cwnd_action_ = CWND_ACTION_DUPACK; //记录本次快速重传
slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_ONE); //SSTHRESH减半，CWND＝1
}
reset_rtx_timer(0,0); //重设重传定时器
return;
}
/*
* When exiting QuickStart, reduce the congestion window to the
* size that was actually used.
*/
void TcpAgent::endQuickStart()
{
qs_approved_ = 0;
qs_cwnd_ = 0;
qs_window_ = maxseq_;
int new_cwnd = maxseq_ - last_ack_;
if (new_cwnd > 1 && new_cwnd < cwnd_) {
cwnd_ = new_cwnd;
if (cwnd_ < initial_window())
cwnd_ = initial_window();
}
}
void TcpAgent::processQuickStart(Packet *pkt)
{
// QuickStart code from Srikanth Sundarrajan.
hdr_tcp *tcph = hdr_tcp::access(pkt);
hdr_qs *qsh = hdr_qs::access(pkt);
double now = Scheduler::instance().clock();
int app_rate;
// printf("flag: %d ttl: %d ttl_diff: %d rate: %d/n", qsh->flag(),
// qsh->ttl(), ttl_diff_, qsh->rate());
qs_requested_ = 0;
qs_approved_ = 0;
if (qsh->flag() == QS_RESPONSE && qsh->ttl() == ttl_diff_ &&
qsh->rate() > 0) {
app_rate = (int) (hdr_qs::rate_to_Bps(qsh->rate()) *
(now - tcph->ts_echo()) / (size_ + headersize()));
#ifdef QS_DEBUG
printf("Quick Start approved, rate %d, window %d/n",
qsh->rate(), app_rate);
#endif
if (app_rate > initial_window()) {
qs_cwnd_ = app_rate;
qs_approved_ = 1;
}
} else { // Quick Start rejected
#ifdef QS_DEBUG
printf("Quick Start rejected/n");
#endif
}
}
/*
* ACK has been received, hook from recv()
*/
void TcpAgent::recv_frto_helper(Packet *pkt)
{
hdr_tcp *tcph = hdr_tcp::access(pkt);
if (tcph->seqno() == last_ack_ && frto_ != 0) {
/*
* Duplicate ACK while in F-RTO indicates that the
* timeout was valid. Go to slow start retransmissions.
*/
t_seqno_ = highest_ack_ + 1;
cwnd_ = frto_;
frto_ = 0;
// Must zero dupacks (in order to trigger send_much at recv)
// dupacks is increased in recv after exiting this function
dupacks_ = -1;
}
}
/*
* A spurious timeout has been detected. Do appropriate actions.
*/
void TcpAgent::spurious_timeout()
{
frto_ = 0;
switch (spurious_response_) {
case 1:
default:
/*
* Full revert of congestion window
* (FlightSize before last acknowledgment)
*/
cwnd_ = t_seqno_ - prev_highest_ack_;
break;
case 2:
/*
* cwnd = reduced ssthresh (approx. half of the earlier pipe)
*/
cwnd_ = ssthresh_; break;
case 3:
/*
* slow start, but without retransmissions
*/
cwnd_ = 1; break;
}
/*
* Revert ssthresh to size before retransmission timeout
*/
ssthresh_ = pipe_prev_;
/* If timeout was spurious, bugfix is not needed */
recover_ = highest_ack_ - 1;
}
/*
* Loss occurred in Quick-Start window.
* If Quick-Start is enabled, packet loss in the QS phase should
* trigger slow start instead of the regular fast retransmit,
* see [draft-amit-quick-start-03.txt] (to appear).
* We use variable tcp_qs_recovery_ to toggle this behaviour on and off.
* If tcp_qs_recovery_ is true, initiate slow start to probe for
* a correct window size.
*
* Return value: non-zero if Quick-Start specific loss recovery took place
*/
int TcpAgent::lossQuickStart()
{
if (qs_window_ && tcp_qs_recovery_) {
//recover_ = maxseq_;
//reset_rtx_timer(1,0);
slowdown(CLOSE_CWND_INIT);
// reset ssthresh to half of W-D/2?
qs_window_ = 0;
output(last_ack_ + 1, TCP_REASON_DUPACK);
return 1;
}
return 0;
}
/*
* main reception path - should only see acks, otherwise the
* network connections are misconfigured
*/
void TcpAgent::recv(Packet *pkt, Handler*)
{
hdr_tcp *tcph = hdr_tcp::access(pkt); //接受分组TCP头
int valid_ack = 0;
if (qs_approved_ == 1 && tcph->seqno() > last_ack_) //快启动处理，不看
endQuickStart();
if (qs_requested_ == 1)
processQuickStart(pkt);
#ifdef notdef
if (pkt->type_ != PT_ACK) { //ACK包类型判断
Tcl::instance().evalf("%s error /"received non-ack/"",
name());
Packet::free(pkt);
return; //不是ACK包，退出
}
#endif
/* W.N.: check if this is from a previous incarnation */
if (tcph->ts() < lastreset_) { //判断是否上次连接的尸体包
// Remove packet and do nothing
Packet::free(pkt); //是尸体分组，释放该分组内存，并退出
return;
}
++nackpack_; //ACK包数＋1
ts_peer_ = tcph->ts(); //记录对端发此ACK包时的时间
int ecnecho = hdr_flags::access(pkt)->ecnecho(); //ECN处理，不看
if (ecnecho && ecn_)
ecn(tcph->seqno());
recv_helper(pkt); //helper处理，不必看
recv_frto_helper(pkt);
/* grow cwnd and check if the connection is done */
if (tcph->seqno() > last_ack_) { //本ACK序号>上次记录的ACK序号，表示是新的ACK
recv_newack_helper(pkt); //新ACK的helper
if (last_ack_ == 0 && delay_growth_) { //是连接以来的第一个ACK
cwnd_ = initial_window(); //初始化CWND
} //下面一段处理重复ACK
} else if (tcph->seqno() == last_ack_) { // 不是新ACK,是上次的重复ACK
if (hdr_flags::access(pkt)->eln_ && eln_) { //ELN处理，不必看
tcp_eln(pkt);
return;
}
if (++dupacks_ == numdupacks_ && !noFastRetrans_) { //重复ACK数＝numdupacks并且允许快速重传时，表示满足了快速快速重传条件，但tahoe中不支持快速重传
dupack_action(); //快速重传动作，用于减少CWND和SSTHRESH,并重启重传定时器
} else if (dupacks_ < numdupacks_ && singledup_ ) { //这里singledup_是系统的固定值，这里使TCP不采用快速重传策略，
send_one(); //而是收到一个或两个重复ACK，就重传的策略
}
}
if (QOption_ && EnblRTTCtr_) //QOPTION，不必看
process_qoption_after_ack (tcph->seqno());
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
/*
* Try to send more data.
*/
if (valid_ack || aggressive_maxburst_) //aggressive_maxburst_默认为1，接收处理完了，继续发送尽可能多的分组
send_much(0, 0, maxburst_);
}
/*处理非重传的超时，即用于将发送数据进行随机延迟，模拟网络的延迟情况
* Process timeout events other than rtx timeout. Having this as a separate
* function allows derived classes to make alterations/enhancements (e.g.,
* response to new types of timeout events).
*/
void TcpAgent::timeout_nonrtx(int tno)
{
if (tno == TCP_TIMER_DELSND) {
/*
* delayed-send timer, with random overhead
* to avoid phase effects
*/
send_much(1, TCP_REASON_TIMEOUT, maxburst_);
}
}
//直接被几个定时器的expire()调用，即在超时后，各定时器通过超时类型，选择执行下面代码
void TcpAgent::timeout(int tno)
{
/* retransmit timer */
if (tno == TCP_TIMER_RTX) { //超时重传的情况
// There has been a timeout - will trace this event
trace_event("TIMEOUT"); //跟踪超时
frto_ = 0; //F-RTO
// Set pipe_prev as per Eifel Response
pipe_prev_ = (window() > ssthresh_) ?
window() : (int)ssthresh_;
if (cwnd_ < 1) cwnd_ = 1; //CWND至少为1
if (qs_approved_ == 1) qs_approved_ = 0;
//此段对SSTHRESH和CWND做出调整
if (highest_ack_ == maxseq_ && !slow_start_restart_) {
/* 无显著数据：即发送的数据都已收到了应答
这是无显著数据并且不是慢启动重启的情况，什么都不做，正常不会出现
* TCP option:
* If no outstanding data, then don't do anything.
*/
// Should this return be here?
// What if CWND_ACTION_ECN and cwnd < 1?
// return;
} else { //
recover_ = maxseq_;
if (highest_ack_ == -1 && wnd_init_option_ == 2)
/* 上次ack号为－1，表示未收到ACK,第一个分组丢失了
* First packet dropped, so don't use larger
* initial windows.
*/
wnd_init_option_ = 1;
if (highest_ack_ == maxseq_ && restart_bugfix_)
/* 无显著数据的情况
* if there is no outstanding data, don't cut
* down ssthresh_.
*/
slowdown(CLOSE_CWND_ONE|NO_OUTSTANDING_DATA);
else if (highest_ack_ < recover_ &&
last_cwnd_action_ == CWND_ACTION_ECN) {
/*
* if we are in recovery from a recent ECN,
* don't cut down ssthresh_.
*/
slowdown(CLOSE_CWND_ONE);
if (frto_enabled_ || sfrto_enabled_) {
frto_ = 1;
}
}
else { //
++nrexmit_; //重传超时计数＋1
last_cwnd_action_ = CWND_ACTION_TIMEOUT; //记录本次超时
slowdown(CLOSE_SSTHRESH_HALF|CLOSE_CWND_RESTART); //超时，ssthresh减半，cwnd重启动
if (frto_enabled_ || sfrto_enabled_) {
frto_ = 1;
}
}
}
/* if there is no outstanding data, don't back off rtx timer */
if (highest_ack_ == maxseq_ && restart_bugfix_) { //无显著数据，重新设置重传定时器
reset_rtx_timer(0,0);
}
else {
reset_rtx_timer(0,1); //这是发送的数据有未收到ACK的情况,这时是重传，backoff＝1，使RTO翻倍
}
last_cwnd_action_ = CWND_ACTION_TIMEOUT; //记录本次超时
send_much(0, TCP_REASON_TIMEOUT, maxburst_); //重传尽可能多的数据
}
else {
timeout_nonrtx(tno); //不是超时重传的情况，如：tno == TCP_TIMER_DELSND
}
}
/*
* Check if the packet (ack) has the ELN bit set, and if it does, and if the
* last ELN-rxmitted packet is smaller than this one, then retransmit the
* packet. Do not adjust the cwnd when this happens.
*/
void TcpAgent::tcp_eln(Packet *pkt)
{
//int eln_rxmit;
hdr_tcp *tcph = hdr_tcp::access(pkt);
int ack = tcph->seqno();
if (++dupacks_ == eln_rxmit_thresh_ && ack > eln_last_rxmit_) {
/* Retransmit this packet */
output(last_ack_ + 1, TCP_REASON_DUPACK);
eln_last_rxmit_ = last_ack_+1;
} else
send_much(0, 0, maxburst_);
Packet::free(pkt);
return;
}
/*
* This function is invoked when the connection is done. It in turn
* invokes the Tcl finish procedure that was registered with TCP.
*/
void TcpAgent::finish()
{
Tcl::instance().evalf("%s done", this->name());
}
void RtxTimer::expire(Event*)
{
a_->timeout(TCP_TIMER_RTX);
}
void DelSndTimer::expire(Event*)
{
a_->timeout(TCP_TIMER_DELSND);
}
void BurstSndTimer::expire(Event*)
{
a_->timeout(TCP_TIMER_BURSTSND);
}
/*
* THE FOLLOWING FUNCTIONS ARE OBSOLETE, but REMAIN HERE
* DUE TO OTHER PEOPLE's TCPs THAT MIGHT USE THEM
*
* These functions are now replaced by ecn() and slowdown(),
* respectively.
*/
/*
* Respond either to a source quench or to a congestion indication bit.
* This is done at most once a roundtrip time; after a source quench,
* another one will not be done until the last packet transmitted before
* the previous source quench has been ACKed.
*/
//不被调用？是否其他非tahoe的TCP协议使用？
void TcpAgent::quench(int how)
{
if (highest_ack_ >= recover_) {
recover_ = maxseq_;
last_cwnd_action_ = CWND_ACTION_ECN;
closecwnd(how);
}
}
/*
* close down the congestion window
*/
//仅仅被quench所调用
void TcpAgent::closecwnd(int how)
{
static int first_time = 1;
if (first_time == 1) {
fprintf(stderr, "the TcpAgent::closecwnd() function is now deprecated, please use the function slowdown() instead/n");
}
switch (how) {
case 0:
/* timeouts */
ssthresh_ = int( window() / 2 );
if (ssthresh_ < 2)
ssthresh_ = 2;
cwnd_ = int(wnd_restart_);
break;
case 1:
/* Reno dup acks, or after a recent congestion indication. */
// cwnd_ = window()/2;
cwnd_ = decrease_num_ * window();
ssthresh_ = int(cwnd_);
if (ssthresh_ < 2)
ssthresh_ = 2;
break;
case 2:
/* Tahoe dup acks
* after a recent congestion indication */
cwnd_ = wnd_init_;
break;
case 3:
/* Retransmit timeout, but no outstanding data. */
cwnd_ = int(wnd_init_);
break;
case 4:
/* Tahoe dup acks */
ssthresh_ = int( window() / 2 );
if (ssthresh_ < 2)
ssthresh_ = 2;
cwnd_ = 1;
break;
default:
abort();
}
fcnt_ = 0.;
count_ = 0;
}
/*
* Check if the sender has been idle or application-limited for more
* than an RTO, and if so, reduce the congestion window.
*/
void TcpAgent::process_qoption_after_send ()
{
int tcp_now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
int rto = (int)(t_rtxcur_/tcp_tick_) ;
/*double ct = Scheduler::instance().clock();*/
if (!EnblRTTCtr_) {
if (tcp_now - T_last >= rto) {
// The sender has been idle.
slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
for (int i = 0 ; i < (tcp_now - T_last)/rto; i ++) {
slowdown(CWND_HALF_WITH_MIN|TCP_IDLE);
}
T_prev = tcp_now ;
W_used = 0 ;
}
T_last = tcp_now ;
if (t_seqno_ == highest_ack_+ window()) {
T_prev = tcp_now ;
W_used = 0 ;
}
else if (t_seqno_ == curseq_-1) {
// The sender has no more data to send.
int tmp = t_seqno_ - highest_ack_ ;
if (tmp > W_used)
W_used = tmp ;
if (tcp_now - T_prev >= rto) {
// The sender has been application-limited.
slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE);
slowdown(CLOSE_CWND_HALF_WAY|TCP_IDLE);
T_prev = tcp_now ;
W_used = 0 ;
}
}
} else {
rtt_counting();
}
}
/*
* Check if the sender has been idle or application-limited for more
* than an RTO, and if so, reduce the congestion window, for a TCP sender
* that "counts RTTs" by estimating the number of RTTs that fit into
* a single clock tick.
*/
//仅被process_qoption_after_send ()所调用，不看
void
TcpAgent::rtt_counting()
{
int tcp_now = (int)(Scheduler::instance().clock()/tcp_tick_ + 0.5);
int rtt = (int(t_srtt_) >> T_SRTT_BITS) ;
if (rtt < 1)
rtt = 1 ;
if (tcp_now - T_last >= 2*rtt) {
// The sender has been idle.
int RTTs ;
RTTs = (tcp_now -T_last)*RTT_goodcount/(rtt*2) ;
RTTs = RTTs - Backoffs ;
Backoffs = 0 ;
if (RTTs > 0) {
slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
for (int i = 0 ; i < RTTs ; i ++) {
slowdown(CWND_HALF_WITH_MIN|TCP_IDLE);
RTT_prev = RTT_count ;
W_used = 0 ;
}
}
}
T_last = tcp_now ;
if (tcp_now - T_start >= 2*rtt) {
if ((RTT_count > RTT_goodcount) || (F_full == 1)) {
RTT_goodcount = RTT_count ;
if (RTT_goodcount < 1) RTT_goodcount = 1 ;
}
RTT_prev = RTT_prev - RTT_count ;
RTT_count = 0 ;
T_start = tcp_now ;
F_full = 0;
}
if (t_seqno_ == highest_ack_ + window()) {
W_used = 0 ;
F_full = 1 ;
RTT_prev = RTT_count ;
}
else if (t_seqno_ == curseq_-1) {
// The sender has no more data to send.
int tmp = t_seqno_ - highest_ack_ ;
if (tmp > W_used)
W_used = tmp ;
if (RTT_count - RTT_prev >= 2) {
// The sender has been application-limited.
slowdown(THREE_QUARTER_SSTHRESH|TCP_IDLE) ;
slowdown(CLOSE_CWND_HALF_WAY|TCP_IDLE);
RTT_prev = RTT_count ;
Backoffs ++ ;
W_used = 0;
}
}
if (F_counting == 0) {
W_timed = t_seqno_ ;
F_counting = 1 ;
}
}
void TcpAgent::process_qoption_after_ack (int seqno)
{
if (F_counting == 1) {
if (seqno >= W_timed) {
RTT_count ++ ;
F_counting = 0 ;
}
else {
if (dupacks_ == numdupacks_)
RTT_count ++ ;
}
}
}
void TcpAgent::trace_event(char *eventtype)
{
if (et_ == NULL) return;
int seqno = t_seqno_;
char *wrk = et_->buffer();
char *nwrk = et_->nbuffer();
if (wrk != 0)
sprintf(wrk,
"E "TIME_FORMAT" %d %d TCP %s %d %d %d",
et_->round(Scheduler::instance().clock()), // time
addr(), // owner (src) node id
daddr(), // dst node id
eventtype, // event type
fid_, // flow-id
seqno, // current seqno
int(cwnd_) //cong. window
);
if (nwrk != 0)
sprintf(nwrk,
"E -t "TIME_FORMAT" -o TCP -e %s -s %d.%d -d %d.%d",
et_->round(Scheduler::instance().clock()), // time
eventtype, // event type
addr(), // owner (src) node id
port(), // owner (src) port id
daddr(), // dst node id
dport() // dst port id
);
et_->trace();
}
/*
结论1：接收RECV和发送OUTPUT时都没有去/自对方的窗口大小通告，
拥塞仅凭借自己的推算来进行发送端的拥塞控制，对端的通告窗口设为一个常量wnd_，
本端发送窗口为min(cwnd_,wnd_)，范围为: highest_ack----highest_ack+win
发送窗口：从未确认的最小序号开始，如下
1 2 3 4
----------|----------|----------|----------
SND.UNA SND.NXT SND.UNA
+SND.WND
结论2：有三个超时定时器
rtxtimer 用于重传超时
delsndtimer 用于随机产生延迟，模拟网络的延迟？发送端延迟？
burstsndtimer ？ 用途不明，sendmuch中有一句，但程序中没有用处，
它超时调用timeout，但timeout和timeout_nonrtx没有对TCP_TIMER_BURSTSND的处理
可能是非tahoe的TCP协议使用
*/
/*
F-RTO算法：
有人指出，重传定时器可能虚假超时，引起未丢失段不必要的重传[LK00, GL02,
LM03]。在虚假的重传超时发生后，源发送段迟到的确认到达了发送方，通常会在RTO
恢复期间触发一个不必要的整个窗口的重传。而且，在虚假重传超时后，通常TCP发送
方处于慢启动阶段，在此期间每次收到迟到的确认时，就使拥塞窗口增加1。这使在一
个往返时间内，大量的数据段涌入网络，从而违背了“数据包守恒”的原则[Jac88]。
当RTO到期后，F-RTO发送方像通常一样，重传第一个未确认段[APS99]。不同于
通常操作的是，对于第一个超时后的到达的确认（假设该确认在窗口之前），它开始
发送新的、当前未发送过的数据。如果在超时后到达的第二个确认在窗口之前（比如
说：未被重传的确认数据），F-RTO发送方宣布超时是虚假的，并且退出RTO恢复。
然而，如果两个确认的任意一个是重复ACK，就没有明显的证据表明超时是虚假超时。
因此，此时F-RTO发送方采用传统的慢启动策略，重传未确认段。采用SACK增强版本
的F-RTO算法，在RTO重传后收到重复ACK时，仍然可以检测出虚假超时。
算法(rfc4138)
1)当RTO到期时，重传第一个未确认段，并设SpuriousRecovery为FALSE。同时，
将最高的已发送序号存入变量“recover”中。
2)当RTO重传后的第一个确认到达发送方，发送方按照是否该ACK在窗口之前，
或是否该ACK为重复确认，选择下面的其中一步。
a)如果该确认是重复ACK，或是等于“recover”序号值的段，或是没有确
认第1步重传的所有数据，则转回到常规的RTO恢复过程，开始慢启动过程，并
重传未确认数据。切勿进入本算法的第3步。“SpuriousRecovery”参数保持为
FALSE。
b)否则，如果该确认在窗口之前并且它小于“recover”值，发送两个新段
(前面未发送过的段)，并转入本算法的第3步。如果TCP发送方没有足够的未发送
数据，则只发送一个段。另外，TCP发送方可能略过Nagle算法[Nag84]，需要的
时候直接发送一个段。注意发送两个段符合TCP拥塞控制的要求[APS99]：F-RTO
的TCP发送方只需要选择不同的段发送出去。
如果TCP发送方并没有任何新的数据发送，或通告窗口不允许发送新数据，
推荐操作是跳过本算法的第3步，按照常规RTO恢复算法，继续慢启动重传。然而，
一些处理窗口受限的替换方法可以取得更好的性能，这将在附件C中讨论。
3)当RTO重传后的第二个确认到达发送方时，TCP发送方可以选择宣布超时是虚假的，
或者也可以开始重传未确认的段。
a)如果该确认是重复确认，将拥塞窗口设置为不超过3×MSS，并且继续慢
启动策略，重传未确认的段。拥塞窗口可以设为3×MSS，因为在RTO超时后，已经
过了两个往返时间，同时常规的TCP发送方已经增加cwnd到了3。保持参数
SpuriousRecovery为FALSE。
b)如果该确认在窗口之前（比如，它确认了超时后没有重传的数据），则
则宣布超时是虚假的，设置SpuriousRecovery为SPUR_TO，并将“recover”变量值
设为SNA.UNA（最后一个未确认的序号）。
讨论
当重传超时后收到重复确认时，F-RTO发送方采取了谨慎的措施。因为重复确认
表示有可能段已经丢失，由于缺乏其他信息，可靠地检测一个虚假超时是很困难的。
因此，在这种情况下，算法谨慎地遵循了常规的TCP恢复方法。
在算法(2a)中，如果RTO重传后的第一个确认涵盖了“recover”点，则没有证据
表明超时后有非重传段到达接收方。一种常见情况是，快速重传丢失，RTO超时后，
该段又被重传,同时，在重传超时后，其他的未确认段成功地送到TCP接收端。因此，
此时该超时不能宣布为假超时。
如果RTO重传后的第一个确认没有确认第1步中重传的所有数据，TCP发送方转到
常规的RTO恢复程序。否则，不怀好意的接收方只确认部分数据，会导致发送方会在
数据丢失时宣布虚假超时。
在算法分支(2b)中，TCP发送方允许发送两个新段，因为在常规TCP中，RTO重传
后，当收到新的ACK，发送方将发送两个段。如果在算法分支(2b)中不能发送新段，
或是接收窗口限制了传输，TCP发送方必须要发送数据以防止TCP停转。如果没有数据
发送了，发送方和接收方在管道允许的范围内可能都已经发完了段，不会再有下一个
确认到达。因此，在窗口受限的情况下，推荐转回常规的RTO慢启动重传恢复阶段。
附件C讨论了一些可选的窗口受限情况。
如果重传超时被宣布为虚假，TCP发送方将“recover”变量设置为SNA.UNA，
以允许快速重传[FHG04]。“recover”变量用于在NewReno TCP快速恢复期间,当RTO
超时时，避免不必要的、成倍的快速重传。因为发送方只重传哪些触发了超时的段，
不必要的成倍快速重传的问题不可能发生。因此，如果超时后有3个重复ACK到达了
发送方，就表示可能丢失了包，使用快速重传以加快恢复效率。如果包丢失后没有
足够的重复ACK到达接收方，重传定时器又会出现超时，发送方即转入算法的第1步。
当超时被宣布为虚假时，TCP发送方不能检测到是否存在不必要的RTO重传丢失。
原则上，RTO的重传丢失应该被视为一个拥塞信号。因此，如果在检测到虚假超时后，
F-RTO发送方选择完全还原到拥塞控制参数，则违反拥塞控制原则的可能性较小。
Eifel检测算法有相似的性质，其DSACK选项可以用于检测是否重传段成功地发送到
了接收方。
F-RTO算法在TCP往返时间测算中有副作用。TCP发送方在检测到虚假超时后，
能避免大多数不必要的重传，这使发送方能够在延迟的段上取得往返时间的采样。
如果在不使用TCP时间戳时采用常规的RTO恢复策略，因为重传的模糊性，不会出现
这种情况。结果是，同常规TCP比较，由于采用了F-RTO，在因为段的延迟而触发了
虚假超时，使RTO趋向于更精确，数值更大。我们相信在那些延迟尖峰较多的网络
中，这是一个优势。
在虚假超时后，存在F-RTO算法不能避免产生不必要重传的情况。如果包重排
序或重复包出现在触发虚假超时的段中，由于收到的重复ACK,F-RTO算法可能不能
检测虚假超时。另外，如果虚假超时发生在快速重传中，由于一些段在快速恢复触
发重复ACK前发送，F-RTO算法通常不能检测虚假重传。然而，我们认为这些情况
很少出现，注意在F-RTO没能检测到虚假超时的情况下，它采用慢启动策略，重传
未确认段，同常规的RTO恢复方法相似。
拥塞算法的具体响应措施见 rfc4015
