$def with (squirrel_url, connection_url, ticket)
A PUB
channel will send messages to all of the
SUB
channels wired to the same resource.
A PUSH
channel will send messages to one of
the PULL
channels wired to the same resource.
A REQ
channel will send messages to one of
the REP
channels wired to the same
resource. The response from the REP
channel
is routed back to the original REQ
channel.