Problem running FTP over TCP

[Subhasree Mandal <subha@cse.ucsc.edu>]

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.  The commend used to run this FTP was

$ns at 1.41 "$ftp12 start" 

the following were the last few lines of the sequence number trace

18.91257 4607
18.91310 4608
18.94483 4609
18.94483 4610
18.97710 4611
18.97737 4612
19.00937 4613
19.30937 4611
19.30937 4612
19.34137 4613

What may go wrong with it?

If I change the start time to 1.45 say, the problem vanishes.  I had ecn
gateways, in this case.  If I use RED (with drop) instead, I do not face
the same problem.

subha