ZyXEL Communications P-2802H(W)(L)-I Series - Manual (Page 130)

Chapter 10 Voice
P-2802H(W)(L)-I Series User’s Guide
130
10.2.1.2 SIP Service Domain
The SIP service domain of the VoIP service provider is the domain name in a SIP URI. For
example, if the SIP address is
[email protected] , then “VoIP-provider.com” is
the SIP service domain.
10.2.2 SIP Call Progression
The following figure displays the basic steps in the setup and tear down of a SIP call. A calls
B.
A sends a SIP INVITE request to B. This message is an invitation for B to participate in a SIP
telephone call.
6 B sends a response indicating that the telephone is ringing.
7 B sends an OK response after the call is answered.
8 A then sends an ACK message to acknowledge that B has answered the call.
9 Now A and B exchange voice media (talk).
10 After talking, A hangs up and sends a BYE request.
11 B replies with an OK response confirming receipt of the BYE request and the call is
terminated.
10.2.3 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.
10.2.3.1 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.
Table 46 SIP Call Progression
A B
1. INVITE
2. Ringing
3. OK
4. ACK
5.Dialogue (voice traffic)
6. BYE
7. OK