In computer networking, the Message Session Relay Protocol (MSRP) is a protocol for transmitting a series of related instant messages in the context of a communications session. An application instantiates the session with the Session Description Protocol (SDP) over Session Initiation Protocol (SIP) or other rendezvous methods. The MSRP protocol is defined in RFC 4975. MSRP messages can also be transmitted by using intermediaries peers, by using the relay extensions defined in RFC 4976.