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Client device A then sends the call invitation to client device C.
3
Figure 58 SIP Redirect Server
A
SIP Register Server
A SIP register server maintains a database of SIP identity-to-IP address (or
domain name) mapping. The register server checks your user name and password
when you register.
RTP
When you make a VoIP call using SIP, the RTP (Real time Transport Protocol) is
used to handle voice data transfer. See RFC 1889 for details on RTP.
Pulse Code Modulation
Pulse Code Modulation (PCM) measures analog signal amplitudes at regular time
intervals and converts them into bits.
SIP Call Progression
The following figure displays the basic steps in the setup and tear down of a SIP
call. A calls B.
Table 44 SIP Call Progression
A
1. INVITE
4. ACK
FSG2200HNU User's Guide
1
3
2
B
C
B
2. Ringing
3. OK
Chapter 9 Voice
151
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