ZyXEL Communications P-2602HWLNI, User Manual, Page: 175 / 496

Chapter 11 Voice
P-2602HWLNI User’s Guide
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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.
11.2.7 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.
• 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.
• G.729 is an Analysis-by-Synthesis (AbS) hybrid waveform codec that uses a filter based
on information about how the human vocal tract produces sounds. G.729 provides good
sound quality and reduces the required bandwidth to 8 kbps.
11.2.8 PSTN Call Setup Signaling
Dual-Tone MultiFrequency (DTMF) signaling uses pairs of frequencies (one lower frequency
and one higher frequency) to set up calls. It is also known as Touch Tone®. Each of the keys
on a DTMF telephone corresponds to a different pair of frequencies.
Pulse dialing sends a series of clicks to the local phone office in order to dial numbers.
4
11.2.9 MWI (Message Waiting Indication)
Enable Message Waiting Indication (MWI) enables your phone to give you a message–waiting
(beeping) dial tone when you have a voice message(s). Your VoIP service provider must have
a messaging system that sends message waiting status SIP packets as defined in RFC 3842.
4. The ZyXEL Device does not support pulse dialing at the time of writing.