ZyXEL Communications P-2304R, User Manual

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Chapter 9 SIP
P-2304R-P1 Series User’s Guide
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9.1.3.2 SIP Service Domain
The SIP service domain of the VoIP service provider (the company that lets you make phone
calls over the Internet) is the domain name in a SIP URI. For example, if the SIP address is
1122334455@VoIP-provider.com , then “VoIP-provider.com” is the SIP service domain.
9.1.4 SIP Call Progression
The following figure displays the basic steps in the setup and tear down of a SIP call. A calls
B.
1
A sends a SIP INVITE request to B. This message is an invitation for B to participate in
a SIP telephone call.
2
B sends a response indicating that the telephone is ringing.
3 B sends an OK response after the call is answered.
4
A then sends an ACK message to acknowledge that B has answered the call.
5 Now A and B exchange voice media (talk).
6
After talking, A hangs up and sends a BYE request.
7 B replies with an OK response confirming receipt of the BYE request and the call is
terminated.
9.1.5 SIP Client Server
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.
9.1.5.1 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