The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...

}hdr_asrm* seh = (hdr_asrm*) p->access(off_asrm_);switch (sh->type()) {case SRM_RQST:sp = get_state(sh->sender());seh->distance() = sp->distance_;break;...}Similarly, the method parseExtendedHeaders() is invoked every time an SRM packet is received. It sets the agentmember variable pdistance_ to the distance advertised by the peer that sent the message. The member variable is boundto an instance variable of the same name, so that the peer distance can be accessed by the appropriate instance procedures.The corresponding parseExtendedHeaders() method for the Adaptive SRM agent is simply:void parseExtendedHeaders(Packet* p) {hdr_asrm* seh = (hdr_asrm*) p->access(off_asrm_);pdistance_ = seh->distance();}Finally, the adaptive SRM agent’s extended headers are defined as struct hdr_asrm. The header declaration is identicalto declaring other packet headers in ns. Unlike most other packet headers, these are not automatically available in the packet.The interpreted constructor for the first adaptive agent will add the header to the packet format. For example, the start of theconstructor for the Agent/SRM/Adaptive agent is:Agent/SRM/Adaptive set done_ 0Agent/SRM/Adaptive instproc init args {if ![$class set done_] {set pm [[Simulator instance] set packetManager_]TclObject set off_asrm_ [$pm allochdr aSRM]$class set done_ 1}}eval $self next $args...36.8 SRM objectsSRM objects are a subclass of agent objects that implement the SRM reliable multicast transport protocol. They inherit all ofthe generic agent functionalities. The methods for this object is described in the next section 36.9. Configuration parametersfor this object are:packetSize_ The data packet size that will be used for repair messages. The default value is 1024.requestFunction_ The algorithm used to produce a retransmission request, e.g., setting request timers. The default value isSRM/request. Other possible request functions are SRM/request/Adaptive, used by the Adaptive SRM code.repairFunction_ The algorithm used to produce a repair, e.g., compute repair timers. The default value is SRM/repair. Otherpossible request functions are SRM/repair/Adaptive, used by the Adaptive SRM code.320