[ns] using SRM

[Haobo Yu]

> thank you for your reply, I have another thing not very clear. To me it is
> a little strange to use SRM in tcl level, usually in multicast
> application, the sender has:
> 
> $srm(0) set dst_addr_ $group
> $srm(0) set dst_port_ 0
> 
> to my best understanding, the receiver should call:
> 
> $ns join-group $rcvagent(0) $group

This is done by start{} in tcl/mcast/srm.tcl
 
> I wonder how can the receiveing srm agents get data???

Pakcet processing is in c++, see recv() in srm.cc.