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
4-4
4.1.3 SIP Fundamentals
I. Registration
In a complete SIP system, all SIP endpoints working as UAs should register with SIP
registrars through proxy servers, providing information such as location, session
capabilities, and call policy.
Normally, a SIP UA sends its registrar a REGISTER request at startup or in response to
an administratively registration operation, carrying all the information that must be
recorded. Upon receipt of the request, the registrar sends back a response notifying
receipt of the request and if the registration is accepted an OK (SUCCESS) message
as well. See the following figure.
Internet
SIP Server
VG
(User Agent)
REGISTER
200 OK
Figure 4-1 Message exchange for a UA to register with a Registrar via a proxy server
II. Call setup
SIP operates in Client/Server model and sets up calls through UA-proxy server
communication.
Internet
Phone1
Phone 2
PC 1
PC 2
XE
SIP Server
VG 1
(UA)
VG 2
(UA) PBX
Figure 4-2 Connect UAs through proxy servers
In the above figure, Phone1 wants to call Phone 2; and two voice gateways, VG 1 and
VG 2, work as SIP endpoints (UAs).
The following are the procedures for connecting a call from Phone 1 to Phone 2: