[ns] Encapsulation

[Kaleelazhicathu R R Kumar <iscp9133@nus.edu.sg>]

hi all,
   is there any document which describes Encapsulators and Decapsulators?? i
want to encapsulate a packet with a TCP and Ip header . I think this can be
done with the above mentioned agents..but i am not able to figure out where
should i mention about the type of headers(in this case tcp and ip headers)
to be encapsulated...i could see the variable off_encap_ in the agent code
which i guess is the offset where the newly encapsulated header starts.how
can i then access each of the new headers which are added..say new TCP and
IP headers?? i am trying to create a TCP tunnel.any help will be
appreciated.any pointers??
   thanks.
    Renjish.