Message Session Relay Protocol (MSRP) is a protocol for exchanging a series of related instant messages across an IP network in the context of a session. The protocol can also be used to transfer large files or images or sharing remote desktops or whiteboards.
A session starts with a Session Initiation Protocol (SIP) INVITE transaction, which carries a Session Description Protocol (SDP) offer/answer exchange to establish the session. An MSRP session is terminated with a SIP BYE request.
The MSRP protocol is defined in RFC 4975. An example of a client that uses MSRP is Blink, a real-time communications client that runs on Windows, Linux and OS X. MSRP is also implemented in popular libraries, including Java's MSRP Peer library and Python MSRPlib.
Dig Deeper on Unified Communications Architecture and Service Models