ZyXEL p-2802h-i1 Manual Do Utilizador
Chapter 10 Voice
P-2802H(W)(L)-I Series User’s Guide
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Figure 73 SIP Redirect Server
10.2.3.4 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.
mapping. The register server checks your user name and password when you register.
10.2.4 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.
handle voice data transfer. See RFC 1889 for details on RTP.
10.2.5 Pulse Code Modulation
Pulse Code Modulation (PCM) measures analog signal amplitudes at regular time intervals
and converts them into bits.
and converts them into bits.
10.2.6 Voice Coding
A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital
signals back into analog voice signals. The ZyXEL Device supports the following codecs.
signals back into analog voice signals. The ZyXEL Device 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.
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.
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.