AMQP (Advanced Message Queueing Protocol) is an open standard that applications can use to communicate routing and queuing information over IANA-assigned port 5672 (TCP, UDP, SCTP). It includes two-way authentication and message receipts with network-level event notification. Wireshark has an pre-alpha AMQP dissector written.
It covers both very high performance pub-sub (with speeds of up to 150k messages/second through a single broker) and high-reliability messaging (with guaranteed delivery no matter what). There are several open source AMQP implementations including iMatix’s OpenAMQ.
The connection life-cycle and message flow can be found in the Specification v. 09, which calls AMQP a “General-Purpose Middleware Standard”.