11.2 Agent methods

The Agent../ns-2/agent.h supports packet generation and reception. The following member functions are implemented by the C++ Agent class, and are generally not over-ridden by derived classes:

[]Packet* allocpkt	allocate new packet and assign its fields
[int]Packet* allocpkt	allocate new packet with a data payload of n bytes and assign its fields

The following member functions are also defined by the class Agent, but are intended to be over-ridden by classes deriving from Agent:

[timeout number]void timeout	subclass-specific time out method
[Packet*, Handler*]void recv	receiving agent main receive path

The []allocpkt method is used by derived classes to create packets to send. The function fills in the following fields in the common packet headerSectionchap:pformat: uid, ptype, size, and the following fields in the IP header: src, dst, flowid, prio, ttl. It also zero-fills in the following fields of the Flags header: ecn, pri, usr1, usr2. Any packet header information not included in these lists must be must be handled in the classes derived from Agent.

The []recv method is the main entry point for an Agent which receives packets, and is invoked by upstream nodes when sending a packet. In most cases, Agents make no use of the second argument (the handler defined by upstream nodes).