SIP SIMPLE Client SDK » Python-msrplib

A series of related instant messages between two or more parties can be
viewed as part of a "message session", that is, a conversational exchange of
messages with a definite beginning and end. This is in contrast to
individual messages each sent independently. Messaging schemes that track
only individual messages can be described as "page-mode" messaging, whereas
messaging that is part of a "session" with a definite start and end is
called "session-mode" messaging.

Page-mode messaging is enabled in SIP via the SIP MESSAGE method, as defined
in RFC 3428. Session-mode messaging has a number of benefits over page-mode
messaging, however, such as explicit rendezvous, tighter integration with
other media-types, direct client-to-client operation, and brokered privacy
and security.

Message Session Relay Protocol (MSRP) is a protocol for transmitting a
series of related instant messages in the context of a session. 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 sessions are defined in RFC 4975. The relay extension that can be used
for NAT traversal purposes is defined in RFC 4976.