[ns] updating the default initial window for TCP

[Sally Floyd <floyd@aciri.org>]

I have just updated another default in NS, the default
initial window, which I have changed from 1 to 2 (packets).
This means that in the last two weeks I have changed
the following defaults for TCP:

# Agent/TCP set windowInit_ 1
Agent/TCP set windowInit_ 2 ;           # default changed on 2001/5/26.
# Agent/TCP set syn_ false
Agent/TCP set syn_ true ;               # default changed on 2001/5/17.
# Agent/TCP set delay_growth_ false
Agent/TCP set delay_growth_ true ;              # default changed on 2001/5/17.
#Agent/TCP set minrto_ 0 ;              # Variable added on 2001/05/10
Agent/TCP set minrto_ 1 ;               # Default set to 1 on 2001/05/14.

All of the changes to the default values are clearly marked
in tcl/lib/ns-default.tcl.

The new defaults mean that for one-way TCP, the first TCP packet
sent is a 40-byte packet, modeling a SYN packet.  After that packet
is ACKed, the initial window of two data packets is sent.  Results
from TBIT ("http://www.aciri.org/tbit/") show that most current TCP
implementations use an initial window of two packets.

In addition, the minimum RTO has now been set to one second.

Most of the validation tests still use the old values of the defaults,
but test-suite-simple.tcl has been modified to use the new values
for the defaults.

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