Re #2 : With probably ~2000 other ns2 postings in "Linux - Newbie", I guess it's OK here.
Re #1, @preethikrishnan : Welcome to LQ.
Tcl scripts with `Mac/802_15_4' tend to do 'Segmentation fault'.
* The examples in ns-2.3x/tcl/ex/wpan are working OK.
A couple more of OK examples : aodv_802_15_4.tcl, beacon_enabled_star.tcl :
Please read :
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Your code is unknown, your tcl script is unknown, etc. etc.