AASTRA BluStar 8000i BAS-Mode Administrator Guides EN - Manual (Page 164)

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Chapter 13
SIP Services
Overview
SIP, the Session Initiation Protocol, is a standard developed by the Internet Engineering Task Force (IETF) as a signalling
layer on top of IP for controlling various types of sessions (such as Voice over IP). The standard, originally put forth as
RFC2543, can be found on the IETF website at:
http://www.ietf.org/rfc/rfc3261.txt.
The reader of this section is expected to have reasonable background knowledge of the SIP protocol, but a short expla-
nation of the key concepts and selected excerpts from the draft standard are provided.
Abstract (from RFC3261):
The Session Initiation Protocol (SIP) is an application-layer control (signalling) protocol for creating, modifying, and ter-
minating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribu-
tion, and multimedia conferences.
SIP invitations used to create sessions carry session descriptions that allow participants to agree on a set of compatible
media types. SIP makes use of elements called proxy servers to help route requests to the user's current location, authen-
ticate and authorize users for services, implement provider call-routing policies, and provide features to users. SIP also
provides a registration function that allows users to upload their current locations for use by proxy servers. SIP runs on
top of several different transport protocols.
Excerpt from the introduction and overview:
There are many applications of the Internet that require the creation and management of a session, where a session is
considered an exchange of data between an association of participants. The implementation of these applications is
complicated by the practices of participants: users may move between endpoints, they may be addressable by multiple
names, and they may communicate in several different media - sometimes simultaneously. Numerous protocols have
been authored that carry various forms of real-time multimedia session data such as voice, video, or text messages.
The Session Initiation Protocol (SIP) works in concert with these protocols by enabling Internet endpoints (called user
agents) to discover one another and to agree on a characterization of a session they would like to share. For locating pro-
spective session participants, and for other functions, SIP enables the creation of an infrastructure of network hosts
(called proxy servers) to which user agents can send registrations, invitations to sessions, and other requests. SIP is an
agile, general-purpose tool for creating, modifying, and terminating sessions that works independently of underlying
transport protocols and without dependency on the type of session that is being established.