What is MSRP Message session relay protocol

Technical details of the Message Session Relay Protocol (MSRP).

1. Overview:
   • MSRP is a session-oriented instant message transport protocol.
   • It is designed for transmitting a series of related instant messages within the context of a communication session.
   • These message sessions are treated like any other media stream when set up via a rendezvous or session creation protocol, such as the Session Initiation Protocol (SIP).
   • MSRP can be used not only for instant messaging but also for image sharing or file transfer.
2. Key Concepts:
   • MSRP Framing and Message Chunking:
     • MSRP messages are divided into chunks for efficient transmission.
     • Each chunk is framed with a header that includes information about the message, such as its length and content type.
     • Chunks can be reassembled at the receiver to reconstruct the complete message.
   • MSRP Addressing:
     • MSRP uses Uniform Resource Identifiers (URIs) for addressing.
     • URIs specify the location of the MSRP endpoint (e.g., msrp:user@example.com:12345/abcde).
   • MSRP Transaction and Report Model:
     • MSRP follows a transaction model similar to HTTP.
     • Requests (e.g., SEND) and responses (e.g., 200 OK) are part of transactions.
     • Reports (e.g., success or failure reports) provide feedback on message delivery.
   • MSRP Connection Model:
     • MSRP connections can be established over TCP or TLS.
     • Connections are set up between MSRP endpoints (e.g., user agents or servers).
3. Using MSRP with SIP and SDP:
   • SDP Connection and Media-Lines:
     • MSRP sessions are negotiated using SDP (Session Description Protocol).
     • SDP describes the media streams (including MSRP) in a session.
     • MSRP sessions are associated with specific media lines in SDP.
   • URI Negotiations:
     • MSRP URIs are exchanged during session setup.
     • Negotiation involves determining the MSRP endpoints and their capabilities.