Dialogic Blog

What is MSRP?

by Jolene Pierangeli

Mar 25, 2015 10:18:00 AM

MSRP Diagram for media server

What is MSRP?  What are the advantages?

Message Session Relay Protocol (MSRP) is a protocol for text or multimedia instant messaging (SMS), which exchanges a series of related instant messages across an IP Network in the context of a session. There are many ways to do messaging, but MSRP offers some unique advantages


  • Transmission of text messages of any length
  • Add video or pictures in the same message
  • Can be included in the same session as real-time audio/video call
  • End-to-end message reliability
  • Authentication and message integrity
  • Low message delay


How do you establish a session and flow in MSRP?

Now that you know the advantages of the MSRP protocol, we can look at establishing a session and what the flow looks like.  We establish a session connection on the PowerMedia XMS (media server) by:

  1. SIP Invite that includes SDP media type (m=message)
  2. TCP port negotiated through exchange (similar to RTP)
  3. XMS Negotiates TCP port with MSRP Server
  4. MSRP message session is established

So, what is happening within the message session?  Within the session, the media exchange is handled as well as the file (message) by chunking. Each chunk is then acknowledged by the endpoint and handles retransmission as well.  Reports are then run to verify that the complete message has been successful.  Connection termination does not happen until the SIP session has ended. The media session will remain active until it explicitly ended.  A SIP BYE will terminate the message session.  See Diagram below.

MSRP message session

Which PowerMedia XMS APIs support MSRP?

The PowerMedia XMS RESTful API and MSML API both support the MSRP protocol, each one with its own distinctive capabilities for each specific application environment.   For RESTful API, there is support for file, text and binary messaging.  This includes MSRP peer-to-peer, text messaging, photo sharing and chat services.  The MSML API supports file transfer as defined in the MSRP protocol, but with support for sending in only one direction, similar to store and forward architecture. 

The more you know about MSRP, the better you’ll begin to understand how it works with PowerMedia XMS for video and voicemail applications.  We’re happy to provide you with the latest information as this technology continues to evolve. You can stay ahead of the curve by checking our blogs periodically to find out the latest developments in this space. You can also find tutorial videos, A Journey to Media Server Enlightenment, on our YouTube channel.

Follow us on Twitter @Dialogic for the latest videos and updates.

Topics: WebRTC