This document outlines a set of such guidelines for authors of SIP extensions. These sessions include Internet multimedia conferences, Internet telephone calls and multimedia distribution. Members in a session can communicate via multicast or via a mesh of unicast relations, or a combination of these. SIP invitations used to create sessions carry session descriptions which allow participants to agree on a set of compatible media types. SIP supports user mobility by proxying and redirecting requests to the user's current location.
Users can register their current location.
SIP is not tied to any particular conference control protocol. SIP is designed to be independent of the lower-layer transport protocol and can be extended with additional capabilities. This document describes how a SIP client locates a SIP server based on the Request-URI or a preconfigured outbound proxy server. This document updates the process described in RFC 2543. The state information can be returned to the proxy when the user agent requests a change in the characteristics of the active call.