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40 Dialogic
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Global Call IP Technology Guide — November 2007
Dialogic Corporation
IP Overview
Redirect Server
Accepts a request from a client and maps the address to zero or more new addresses and
returns the new addresses to the client. The server does not accept calls or generate SIP
requests on behalf of clients.
Registrar Server
Accepts REGISTER requests from clients. Often, the registrar server is located on the same
physical server as the proxy server or redirect server.
1.3.3 Basic SIP Operation
Callers and callees are identified by SIP addresses. When making a SIP call, a caller first locates
the appropriate server and then sends a SIP request. The most common SIP operation is the
invitation request. Instead of directly reaching the intended callee, a SIP request may be redirected
or may trigger a chain of new SIP requests by proxies. Users can register their location(s) with SIP
servers.
1.3.4 Basic SIP Call Scenario
Figure 4 shows the basic SIP call establishment and teardown scenario.
Figure 4. Basic SIP Call Scenario
1.3.5 SIP Messages
In SIP, there are two types of messages:
• SIP Request Messages
• SIP Response Messages
SIP Phone
User A
SIP Phone
User B
INVITE
User picks up
phone and dials
Phone
Rings
180, Ringing
User answers
200, OK
ACK
Voice Exchange (RTP)
User hangs up
BYE
200, OK