User's Manual

Chapter 15 VoIP
B222s User’s Guide
139
3 Client device A t hen sends t he call invitat ion to client device C.
Figure 78 SI P Redirect Server
SIP Register Server
A SI P register server m aint ains a dat abase of SI P identit y- to- I P addr ess ( or dom ain nam e)
m apping. The register server checks your user nam e and password when you regist er.
RTP
When you m ake a VoI P call using SI P, t he RTP ( Real t im e Transpor t Prot ocol) is used t o handle voice
dat a t ransfer. See RFC 3550 for det ails on RTP.
Pulse Code Modulation
Pulse Code Modulation ( PCM) m easures analog signal am plit udes at regular t im e int ervals and
converts t hem int o bit s.
SIP Call Progression
The following figure displays t he basic steps in t he set up and tear down of a SI P call. A calls B.
Table 56 SI P Call Progression
A B
1. I NVI TE
2. Ringing
3. OK
4. ACK
5.Dialogue ( voice t raffic)
6. BYE
7. OK
1
2
3
A
B
C