Given an agent, the procedure attach will
add the agent to its list of agents_,
assign a port number the agent and set its source address,
set the target of the agent to be its (, the node's) entry,
and add a pointer to the port demultiplexer at the node (dmux_)
to the agent at the corresponding slot in the dmux_ classifier.
Conversely, detachwill remove the agent from agents_,
and point the agent's target, and the entry in the node dmux_