tcp-full.cc

Ns2 TCP 协议改进 版本 提高goodput

			} else {
				flags_ |= TF_ACKNOW;	// ACK peer's SYN
			}

                        /*
                         * Received <SYN,ACK> in SYN_SENT[*] state.
                         * Transitions:
                         *      SYN_SENT  --> ESTABLISHED
                         *      SYN_SENT* --> FIN_WAIT_1
                         */

			if (flags_ & TF_NEEDFIN) {
				newstate(TCPS_FIN_WAIT_1);
				flags_ &= ~TF_NEEDFIN;
				tiflags &= ~TH_SYN;
			} else {
				newstate(TCPS_ESTABLISHED);
			}

			// special to ns:
			//  generate pure ACK here.
			//  this simulates the ordinary connection establishment
			//  where the ACK of the peer's SYN+ACK contains
			//  no data.  This is typically caused by the way
			//  the connect() socket call works in which the
			//  entire 3-way handshake occurs prior to the app
			//  being able to issue a write() [which actually
			//  causes the segment to be sent].
			sendpacket(t_seqno_, rcv_nxt_, TH_ACK, 0, 0);
		} else {
			// Check ECN-SYN packet
                        if (ecn_ && fh->ecnecho() && fh->cong_action())
                                ect_ = TRUE;

			// SYN (no ACK) (simultaneous active opens)
			flags_ |= TF_ACKNOW;
			cancel_rtx_timer();
			newstate(TCPS_SYN_RECEIVED);
			/*
			 * decrement t_seqno_: we are sending a
			 * 2nd SYN (this time in the form of a
			 * SYN+ACK, so t_seqno_ will have been
			 * advanced to 2... reduce this
			 */
			t_seqno_--;	// CHECKME
		}

trimthenstep6:
		/*
		 * advance the seq# to correspond to first data byte
		 */
		tcph->seqno()++;

		if (tiflags & TH_ACK)
			goto process_ACK;

		goto step6;

	case TCPS_LAST_ACK:
		/* 
		 * The only way we're in LAST_ACK is if we've already
		 * received a FIN, so ignore all retranmitted FINS.
		 * -M. Weigle 7/23/02
		 */
		if (tiflags & TH_FIN) {
			goto drop;
		}
		break;
	case TCPS_CLOSING:
		break;
	} /* end switch(state_) */

        /*
         * States other than LISTEN or SYN_SENT.
         * First check timestamp, if present.
         * Then check that at least some bytes of segment are within
         * receive window.  If segment begins before rcv_nxt,
         * drop leading data (and SYN); if nothing left, just ack.
         *
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than ts_recent, drop it.
         */

	if (ts_option_ && !fh->no_ts_ && recent_ && tcph->ts() < recent_) {
		if ((now() - recent_age_) > TCP_PAWS_IDLE) {
			/*
			 * this is basically impossible in the simulator,
			 * but here it is...
			 */
                        /*
                         * Invalidate ts_recent.  If this segment updates
                         * ts_recent, the age will be reset later and ts_recent
                         * will get a valid value.  If it does not, setting
                         * ts_recent to zero will at least satisfy the
                         * requirement that zero be placed in the timestamp
                         * echo reply when ts_recent isn't valid.  The
                         * age isn't reset until we get a valid ts_recent
                         * because we don't want out-of-order segments to be
                         * dropped when ts_recent is old.
                         */
			recent_ = 0.0;
		} else {
			fprintf(stderr, "%f: FullTcpAgent(%s): dropped pkt due to bad ts\n",
				now(), name());
			goto dropafterack;
		}
	}

	// check for redundant data at head/tail of segment
	//	note that the 4.4bsd [Net/3] code has
	//	a bug here which can cause us to ignore the
	//	perfectly good ACKs on duplicate segments.  The
	//	fix is described in (Stevens, Vol2, p. 959-960).
	//	This code is based on that correction.
	//
	// In addition, it has a modification so that duplicate segments
	// with dup acks don't trigger a fast retransmit when dupseg_fix_
	// is enabled.
	//
	// Yet one more modification: make sure that if the received
	//	segment had datalen=0 and wasn't a SYN or FIN that
	//	we don't turn on the ACKNOW status bit.  If we were to
	//	allow ACKNOW to be turned on, normal pure ACKs that happen
	//	to have seq #s below rcv_nxt can trigger an ACK war by
	//	forcing us to ACK the pure ACKs
	//
	// Update: if we have a dataless FIN, don't really want to
	// do anything with it.  In particular, would like to
	// avoid ACKing an incoming FIN+ACK while in CLOSING
	//
	todrop = rcv_nxt_ - tcph->seqno();  // how much overlap?

	if (todrop > 0 && ((tiflags & (TH_SYN)) || datalen > 0)) {
//printf("%f(%s): trim 1..todrop:%d, dlen:%d\n",now(), name(), todrop, datalen);
		if (tiflags & TH_SYN) {
			tiflags &= ~TH_SYN;
			tcph->seqno()++;
			th->size()--;	// XXX Must decrease packet size too!!
					// Q: Why?.. this is only a SYN
			todrop--;
		}
		//
		// see Stevens, vol 2, p. 960 for this check;
		// this check is to see if we are dropping
		// more than this segment (i.e. the whole pkt + a FIN),
		// or just the whole packet (no FIN)
		//
		if ((todrop > datalen) ||
		    (todrop == datalen && ((tiflags & TH_FIN) == 0))) {
//printf("%f(%s): trim 2..todrop:%d, dlen:%d\n",now(), name(), todrop, datalen);
                        /*
                         * Any valid FIN must be to the left of the window.
                         * At this point the FIN must be a duplicate or out
                         * of sequence; drop it.
                         */

			tiflags &= ~TH_FIN;

			/*
			 * Send an ACK to resynchronize and drop any data.
			 * But keep on processing for RST or ACK.
			 */

			flags_ |= TF_ACKNOW;
			todrop = datalen;
			dupseg = TRUE;	// *completely* duplicate

		}

		/*
		 * Trim duplicate data from the front of the packet
		 */

		tcph->seqno() += todrop;
		th->size() -= todrop;	// XXX Must decrease size too!!
					// why? [kf]..prob when put in RQ
		datalen -= todrop;

	} /* data trim */

	/*
	 * If we are doing timstamps and this packet has one, and
	 * If last ACK falls within this segment's sequence numbers,
	 * record the timestamp.
	 * See RFC1323 (now RFC1323 bis)
	 */
	if (ts_option_ && !fh->no_ts_ && tcph->seqno() <= last_ack_sent_) {
		/*
		 * this is the case where the ts value is newer than
		 * the last one we've seen, and the seq # is the one we expect
		 * [seqno == last_ack_sent_] or older
		 */
		recent_age_ = now();
		recent_ = tcph->ts();
	}

	if (tiflags & TH_SYN) {
		fprintf(stderr,
		    "%f: FullTcpAgent::recv(%s) received unexpected SYN (state:%d): ",
		        now(), name(), state_);
		prpkt(pkt);
		goto dropwithreset;
	}

	if ((tiflags & TH_ACK) == 0) {
		/*
		 * Added check for state != SYN_RECEIVED.  We will receive a 
		 * duplicate SYN in SYN_RECEIVED when our SYN/ACK was dropped.
		 * We should just ignore the duplicate SYN (our timeout for 
		 * resending the SYN/ACK is about the same as the client's 
		 * timeout for resending the SYN), but give no error message. 
		 * -M. Weigle 07/24/01
		 */
		if (state_ != TCPS_SYN_RECEIVED) {
			fprintf(stderr, "%f: FullTcpAgent::recv(%s) got packet lacking ACK (state:%d): ",
				now(), name(), state_);
			prpkt(pkt);
			goto drop;
		}
	}

	/*
	 * Ack processing.
	 */

	switch (state_) {
	case TCPS_SYN_RECEIVED:	/* want ACK for our SYN+ACK */
		if (ackno < highest_ack_ || ackno > maxseq_) {
			// not in useful range
		    	fprintf(stderr,
		    		"%f: FullTcpAgent(%s): ack(%d) not in range while in SYN_RECEIVED: ",
			 	now(), name(), ackno);
			prpkt(pkt);
			goto dropwithreset;
		}
                /*
                 * Make transitions:
                 *      SYN-RECEIVED  -> ESTABLISHED
                 *      SYN-RECEIVED* -> FIN-WAIT-1
                 */
                if (flags_ & TF_NEEDFIN) {
			newstate(TCPS_FIN_WAIT_1);
                        flags_ &= ~TF_NEEDFIN;
                } else {
                        newstate(TCPS_ESTABLISHED);
                }
		cwnd_ = initial_window();
		/* fall into ... */

        /*
         * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
         * ACKs.  If the ack is in the range
         *      tp->snd_una < ti->ti_ack <= tp->snd_max
         * then advance tp->snd_una to ti->ti_ack and drop
         * data from the retransmission queue.
	 *
	 * note that state TIME_WAIT isn't used
	 * in the simulator
         */

        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
	case TCPS_CLOSE_WAIT:
        case TCPS_CLOSING:
        case TCPS_LAST_ACK:

		//
		// look for ECNs in ACKs, react as necessary
		//

		if (fh->ecnecho() && (!ecn_ || !ect_)) {
			fprintf(stderr,
			    "%f: FullTcp(%s): warning, recvd ecnecho but I am not ECN capable!\n",
				now(), name());
		}

                //
                // generate a stream of ecnecho bits until we see a true
                // cong_action bit
                // 
                if (ecn_) {
                        if (fh->ce() && fh->ect())
                                recent_ce_ = TRUE;
                        else if (fh->cwr())
                                recent_ce_ = FALSE;
                }

		//
		// If ESTABLISHED or starting to close, process SACKS
		//

		if (state_ >= TCPS_ESTABLISHED && tcph->sa_length() > 0) {
			process_sack(tcph);
		}

		//
		// ACK indicates packet left the network
		//	try not to be fooled by data
		//

		if (fastrecov_ && (datalen == 0 || ackno > highest_ack_))
			pipe_ -= maxseg_;

		// look for dup ACKs (dup ack numbers, no data)
		//
		// do fast retransmit/recovery if at/past thresh
		if (ackno <= highest_ack_) {
			// a pure ACK which doesn't advance highest_ack_
			if (datalen == 0 && (!dupseg_fix_ || !dupseg)) {

                                /*
                                 * If we have outstanding data
                                 * this is a completely
                                 * duplicate ack,
                                 * the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshhold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 *
                                 * We know we're losing at the current
                                 * window size so do congestion avoidance.
                                 *
                                 * Dup acks mean that packets have left the
                                 * network (they're now cached at the receiver)
                                 * so bump cwnd by the amount in the receiver
                                 * to keep a constant cwnd packets in the
                                 * network.
                                 */

				if ((rtx_timer_.status() != TIMER_PENDING) ||
				    ackno < highest_ack_) {
					// Q: significance of timer not pending?
					// ACK below highest_ack_
					oldack();
				} else if (++dupacks_ == tcprexmtthresh_) {
					// ACK at highest_ack_ AND meets threshold
					//trace_event("FAST_RECOVERY");

					dupack_action(); // maybe fast rexmt
					goto drop;

				} else if (dupacks_ > tcprexmtthresh_) {
					// ACK at highest_ack_ AND above threshole
					//trace_event("FAST_RECOVERY");
					extra_ack();

					// send whatever window allows
					send_much(0, REASON_DUPACK, maxburst_);
					goto drop;
				}
			} else {
				// non zero-length [dataful] segment
				// with a dup ack (normal for dataful segs)
				// (or window changed in real TCP).
				if (dupack_reset_) {
					dupacks_ = 0;
					fastrecov_ = FALSE;
				}
			}
			break;	/* take us to "step6" */
		} /* end of dup/old acks */

		/*
		 * we've finished the fast retransmit/recovery period
		 * (i.e. received an ACK which advances highest_ack_)
		 * The ACK may be "good" or "partial"
		 */

process_ACK:

		if (ackno > maxseq_) {
			// ack more than we sent(!?)
			fprintf(stderr,
			    "%f: FullTcpAgent::recv(%s) too-big ACK (maxseq:%d): ",
				now(), name(), int(maxseq_));
			prpkt(pkt);
			goto dropafterack;
		}

                /*
                 * If we have a timestamp reply, update smoothed
                 * round trip time.  If no timestamp is present but
                 * transmit timer is running and timed sequence
                 * number was acked, update smoothed round trip time.
                 * Since we now have an rtt measurement, cancel the
                 * timer backoff (cf., Phil Karn's retransmit alg.).
                 * Recompute the initial retransmit timer.
		 *
                 * If all outstanding data is acked, stop retransmit
                 * If there is more data to be acked, restart retransmit
                 * timer, using current (possibly backed-off) value.
                 */
		newack(pkt);	// handle timers, update highest_ack_

		/*
		 * if this is a partial ACK, invoke whatever we should
		 * note that newack() must be called before the action
		 * functions, as some of them depend on side-effects
		 * of newack()
		 */

		int partial = pack(pkt);

		if (partial)
			pack_action(pkt);
		else
			ack_action(pkt);

		/*
		 * if this is an ACK with an ECN indication, handle this
		 * but not if it is a syn packet
		 */

		if (fh->ecnecho() && !(tiflags&TH_SYN) )
		if (fh->ecnecho()) {
			// Note from Sally: In one-way TCP,
			// ecn() is called before newack()...
			ecn(highest_ack_);  // updated by newack(), above
			// "set_rtx_timer();" from T. Kelly.
			if (cwnd_ < 1)
			 	set_rtx_timer();
		}
		// CHECKME: handling of rtx timer
		if (ackno == maxseq_) {
			needoutput = TRUE;
		}

		/*
		 * If no data (only SYN) was ACK'd,
		 *    skip rest of ACK processing.
		 */
		if (ackno == (highest_ack_ + 1))
			goto step6;

		// if we are delaying initial cwnd growth (probably due to
		// large initial windows), then only open cwnd if data has
		// been received
		// Q: check whe