[ns] bugs and fixes in FullTcp & Eifel

[Andrei Gurtov <gurtov@cs.Helsinki.FI>]

Hi,

 Here are several fixes for tcp-full.cc. These are quick hacks and
are not claimed to be complete (or even fully correct :) but they seem to
work.

1) Ignoring DUPACKs after RTO.

This is a nasty thing. If RTO happens during fast recovery and DUPACKs
arrive after that, they inflate cwnd and clock-out segment
retransmissions.

                                //AG fix to prevent fast recovery after RTO
                                     if (cwnd_==1)
                                        goto drop;

                                        if (++dupacks_ == tcprexmtthresh_) {


2) CWR bug

The CWR bit ('A' flag) sometimes appears in FIN-ACK segment. This causes
the other side to ingore it and it is retransmitted forever.

/* ECT, ECN, and congestion action */

        hdr_flags *fh = hdr_flags::access(p);
        fh->ect() = ect_;       // on after mutual agreement on ECT
        if (ecn_ && !ect_)      // initializing; ect = 0, ecnecho = 1
                fh->ecnecho() = 1;
        else {
                fh->ecnecho() = recent_ce_;
        }

        if (ecn_) //AG
                fh->cong_action() =  cong_action_;

3) SYN drop bug

A sanity check in the code causes sometimes drop of a SYN segment with a
message 'Got packet lacking ACK'

// K: added TH_SYN, but it is already known here!
        if ((tiflags & TH_ACK) == 0) {
                fprintf(stderr, "%f: FullTcpAgent::recv(%s) got packet lacking ACK (seq %d)\n",
                        now(), name(), tcph->seqno());
                // goto drop; AG: this kills SYNS!!
        }


4) Reset of variables after closing of connection.

This has been already said on the list. Variables are not re-initialized
properly and the next TCP connection has problems.

if (ourfinisacked) {
                                newstate(TCPS_CLOSED);
#ifdef notdef
cancel_timers();        // DOES THIS BELONG HERE?, probably (see tcp_cose
#endif
                                finish();
                                reset(); //AG
                                goto drop;

5) Compile fix for Eifel algorithm.

This is a small fix for Morten Schl�ger tcp-eifel.cc in order to make it
compile properly in current NS release.

void EifelFullTcpAgent::pack_action(Packet *p){
// hdr_tcp *tcph = (hdr_tcp*)p->access(off_tcp_);
    //AG: -> off_tcp_ -> p
    hdr_tcp *tcph = hdr_tcp::access(p);

Andrei