H3C XE 200 IP, Operation Manual

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Operation Manual – Process Server Configuration
H3C XE 200/2000 IP PBX
Chapter 4 SIP Overview
4-1
Chapter 4 SIP Overview
4.1 Introduction to SIP
Session initiation protocol (SIP) is an application layer control protocol that establishes,
modifies, and terminates multimedia sessions such as IP phone calls, multimedia
distribution, and multimedia conferences. It is the core component in the multimedia
data and control architecture of IETF and the RFC for it is RFC3261.
SIP involves issues such as signaling control in IP networks and communication with
soft switch platforms, intending to build a next generation value-added service platform
to deliver better value-added services to telecom carriers, banks, and financial
organizations.
SIP is used for initiating sessions. It sets up and terminates a multimedia session
involving a group of participants and dynamically adjusts and modifies session
characteristics such as media type (voice, video, or data), media encoding/decoding
format, and multicast/unicast. SIP is based on text encoding and constructed taking
HTTP, a quite mature protocol, as a model. Easy to extend and implement, it is suitable
for implementing Internet-based multimedia conference systems.
SIP adopts the Client/Server model and sets up user calls through communication
between user agents and proxy servers.
A SIP endpoint can directly send an INVITE carrying its description to another endpoint
to set up a session. Upon receipt of the message, the destination endpoint accepts or
rejects it considering its own capabilities and the information in the message. The
sender can also send the INVITE to the destination endpoint through one or more
entities called proxy servers. A proxy server works on behalf of a requestor, locating its
destination endpoint, routing, authenticating and authorizing as required, and even
providing a call routing policy.
SIP records description information of each endpoint on registrars, such as address,
route, and number. SIP endpoints can register or update their descriptions by sending
REGISTER messages to their registrars.
As an application layer protocol, SIP uses either TCP or UDP for transport and can
work with both IPv4 and IPv6.
4.1.1 Terms
I. Multimedia session
According to RFC2327, "A multimedia session is a set of multimedia senders and
receivers and the data streams flowing from senders to receivers. A multimedia
conference is an example of a multimedia session." A session is identified by a set of