ZyXEL GS-105I User Guide - Page 242

Authorization Requirements, SIP Servers, SIP User Agent, SIP Proxy Server

Page 242 highlights

Chapter 21 VoIP A SIP registration has a limited lifespan. The User Agent Client must renew its registration within this lifespan. If it does not do so, the registration data will be deleted from the SIP registrar's database and the connection broken. The Zyxel Device attempts to register all enabled subscriber ports when it is switched on. When you enable a subscriber port that was previously disabled, the Zyxel Device attempts to register the port immediately. Authorization Requirements SIP registrations (and subsequent SIP requests) require a username and password for authorization. These credentials are validated via a challenge / response system using the HTTP digest mechanism (as detailed in RFC 3261, "SIP: Session Initiation Protocol"). SIP Servers SIP is a client-server protocol. A SIP client is an application program or device that sends SIP requests. A SIP server responds to the SIP requests. When you use SIP to make a VoIP call, it originates at a client and terminates at a server. A SIP client could be a computer or a SIP phone. One device can act as both a SIP client and a SIP server. SIP User Agent A SIP user agent can make and receive VoIP telephone calls. This means that SIP can be used for peerto-peer communications even though it is a client-server protocol. In the following figure, either A or B can act as a SIP user agent client to initiate a call. A and B can also both act as a SIP SIP user agent to receive the call. Figure 148 SIP User Agent SIP Proxy Server A SIP proxy server receives requests from clients and forwards them to another server. In the following example, you want to use client device A to call someone who is using client device C. 1 The client device (A in the figure) sends a call invitation to the SIP proxy server (B). 2 The SIP proxy server forwards the call invitation to C. PX7511-B0 User's Guide 242

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Chapter 21 VoIP
PX7511-B0 User’s Guide
242
A SIP registration has a limited lifespan. The User Agent Client must renew its registration within this
lifespan. If it does not do so, the registration data will be deleted from the SIP registrar's database and
the connection broken.
The Zyxel Device attempts to register all enabled subscriber ports when it is switched on. When you
enable a subscriber port that was previously disabled, the Zyxel Device attempts to register the port
immediately.
Authorization Requirements
SIP registrations (and subsequent SIP requests) require a username and password for authorization. These
credentials are validated via a challenge / response system using the HTTP digest mechanism (as
detailed in RFC 3261, "SIP: Session Initiation Protocol").
SIP Servers
SIP is a client-server protocol. A SIP client is an application program or device that sends SIP requests. A
SIP server responds to the SIP requests.
When you use SIP to make a VoIP call, it originates at a client and terminates at a server. A SIP client
could be a computer or a SIP phone. One device can act as both a SIP client and a SIP server.
SIP User Agent
A SIP user agent can make and receive VoIP telephone calls. This means that SIP can be used for peer-
to-peer communications even though it is a client-server protocol. In the following figure, either
A
or
B
can act as a SIP user agent client to initiate a call.
A
and
B
can also both act as a SIP SIP user agent to
receive the call.
Figure 148
SIP User Agent
SIP Proxy Server
A SIP proxy server receives requests from clients and forwards them to another server.
In the following example, you want to use client device
A
to call someone who is using client device C.
1
The client device (
A
in the figure) sends a call invitation to the SIP proxy server (
B
).
2
The SIP proxy server forwards the call invitation to
C
.