Message Session Relay Protocol
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. MSRP is used in the RCS context, especially for the instant messaging, file transfer and photo sharing features. Protocol design MSRP syntax is similar to other IETF text based protocols such as SIP, HTTP and RTSP. MSRP requires a reliable transport layer, like TCP. Each message is either a request or a response and uses URIs; a message contains headers and a body that can carry any type of data, including binary information. The first 2 headers must be To-Path and From-Path and the last must be Content-Type; this significantly reduces the complexity of parsers. Messages must also end with 7 dash ('-') characters, followed by a transaction identifier which appears in the first line; these are followed by a continuation flag, which is a single