Re: Problem running FTP over TCP

[Sally Floyd <floyd@aciri.org>]

>> > I was running a configuration with a bunch of FTP connections on TCP.  In
>> > one particular case one particular connections sends its last packet at
>> > time 19.34137 sec and does not send any more data after that, though the
>> > simulation runs till til 40 sec.  

In NS, when the TCP congestion window is one and the ECN/CE bit is set,
the TCP sender reduces the congestion window and waits for the
retransmit timer to expire before sending another packet.
In the validation tests for the one-way TCP, this works fine,
and does not cause TCP to permanently stall.  If you would send
me the script that you are using, I would look to see if you have
uncovered a bug in the code.

(ECN functionality has not yet been fully verified for the two-way
TCP implementation.  We are in the process of doing that now.  The
ECN validation test suites in the current distribution only apply
to one-way Tahoe, Reno, NewReno, and SACK TCP.  They are discussed in
the note ECN Implementations in the NS Simulator available from
"http://www.aciri.org/floyd/ecn.html", and in the file "test-suite-ecn.txt"
in the ns directory tcl/test.

- Sally
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http://www.aciri.org/floyd/
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