The SIP MESSAGE method is used to send instant messages, where each message is independent of any other message. This is often called pager-mode messaging, due to the fact that this model is similar to that of most two-way pager devices. Another model is called session-mode. In session-mode, the instant messages are part of a media session that provides ordering, a security context, and other functions. This media session is established using a SIP INVITE, just as an audio or video session would be established. This document describes a The Message Session Relay Protocol (MSRP), a mechanism for transmitting session-mode messages with minimal relay support. Additionally, this document describes using the SDP offer/ answer model to initiate such sessions.