ns tips

1. Traces
To trace additional variables, use TraceVar, as explained in the manual,
Section 3.4.3. See also the following snippet:

set cf [open "cwnd.out" w]
$tcp_fwd trace cwnd_
$tcp_fwd attach $cf


2. Advertised window
The size of the advertised window cannot be set by simply changing the 
value of the window_ parameter. In reality, the advertised window depends
on several parameters that can be set as follows (in this case, the 
target window is 128):

# Set default TCP parameters
Agent/TCP set window_ 128
Agent/TCP set maxcwnd_ 128
Agent/TCP set windowInitOption_ 1
Agent/TCP set windowInit_ 2
Agent/TCP set slow_start_restart_ false

The exact meaning of these parameters can be obtained from an analysis of
the tcp.cc source file.