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Chapter 18 Voice over 3G
LTE5366 Series User’s Guide
131
1
User Agent 1
sends a SIP INVITE request to
Proxy 1
. This message is an invitation to
User Agent 2
to
participate in a SIP telephone call.
Proxy 1
sends a response indicating that it is trying to complete the
request.
2
Proxy 1
sends a SIP INVITE request to
Proxy 2
.
Proxy 2
sends a response indicating that it is trying to
complete the request.
3
Proxy 2
sends a SIP INVITE request to
User Agent 2
.
4
User Agent 2
sends a response back to
Proxy 2
indicating that the phone is ringing. The response is
relayed back to
User Agent 1
via
Proxy 1
.
5
User Agent 2
sends an OK response to
Proxy 2
after the call is answered. This is also relayed back to
User
Agent 1
via
Proxy 1
.
6
User Agent 1
and
User Agent 2
exchange RTP packets containing voice data directly, without involving
the proxies.
7
When
User Agent 2
hangs up, he sends a BYE request.
8
User Agent 1
replies with an OK response confirming receipt of the BYE request, and the call is
terminated.
Voice Coding
A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital
signals back into analog voice signals. The LTE5366 supports the following codecs.
• G.711 is a Pulse Code Modulation (PCM) waveform codec. PCM measures analog signal amplitudes
at regular time intervals and converts them into digital samples. G.711 provides very good sound
quality but requires 64 kbps of bandwidth.
• G.726 is an Adaptive Differential PCM (ADPCM) waveform codec that uses a lower bitrate than
standard PCM conversion. ADPCM converts analog audio into digital signals based on the difference
between each audio sample and a prediction based on previous samples. The more similar the
audio sample is to the prediction, the less space needed to describe it. G.726 operates at 16, 24, 32 or
40 kbps.
180 Ringing
180 Ringing
180 Ringing
200 OK
200 OK
200 OK
ACK
RTP
RTP
BYE
200 OK
Table 58 SIP Call Progression
UA 1
PROXY 1
PROXY 2
UA 2
Содержание LTE5366 Series
Страница 12: ...12 PART I User s Guide...
Страница 44: ...Chapter 4 Tutorials LTE5366 Series User s Guide 44...
Страница 45: ...45 PART II Technical Reference...
Страница 53: ...Chapter 5 Monitor LTE5366 Series User s Guide 53...
Страница 59: ...Chapter 6 WAN LTE5366 Series User s Guide 59 Figure 33 Configuration Network WAN Management WAN Edit...