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Chapter 18 VoIP
EMG5324-D10A User’s Guide
236
1 Client device A sends a call invitation for C to the SIP redirect server B.
2 The SIP redirect server sends the invitation back to A with C’s IP address (or domain name).
3 Client device A then sends the call invitation to client device C.
Figure 126 SIP Redirect Server
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 3550 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 86 SIP Call Progression
A B
1. INVITE
2. Ringing
3. OK
4. ACK
1
2
3
A
B
C