ZyXEL Communications NVG2053, Руководство пользователя

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Chapter 17 Voice
NVG2053 User’s Guide
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the UA, and knows the IP address to which the SIP requests and responses should
be sent.
Registration is initiated by the User Agent Client (UAC) running in the VoIP
gateway (the NVG2053). The gateway must be configured with information letting
it know where to send the REGISTER message, as well as the relevant user and
authorization data.
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 NVG2053 attempts to register all enabled subscriber ports when it is switched
on. When you enable a subscriber port that was previously disabled, the NVG2053
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 RFC3261, "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 user agent to receive the call.
Figure 80 SIP User Agent