[ns] tcp tunnel

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

hi all,
  i need to implement a topology in which a tcp tunnel exists between the
source and the sink.
the source can be a tcp or a udp source which passes through  the tunnel to
be received by the sink.
can the existing methods of ns be used to achieve this.i think tcp agents
can be used 
only at the end node in ns.Hence in this case ,can you suggest anyway by
which i can implement the above 
mentioned topology??
  please send in your valuable suggestions.
     regards.
     Renjish.