[ns] Trace Files

[#LIM XIAOWEI#]

Hi!
 
I'm currently running a video trace through NS simulation, with the aim of 
getting an output trace at the end. 
However, it hasn't been successful.
1) What codes should i add to my tcl script to produce output trace file?
 
2) Should my input trace file be of a certain format? How do i attain that 
trace file?
 
Thanks!
 
Zoe