ZyXEL Communications 56K - Manual (Page 33)

User's Guide for ZyXEL Omni 56K and Omni 56K Plus Modems
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EIA Class 1/Class 2.0 Command Set
Please refer to Fax Command Set in Chapter 5.
ITU-T T.30 Fax Protocol
The ITU-T T.30 fax protocol is known as the G3 fax handshake signals and procedures. The
modem takes full control of this protocol - initiating and terminating fax calls, managing the
communication session, and transporting the image data. Therefore, the modem relieves the
computer fax software of the T.30 protocol handling.
You modem allows for fax speeds up to 14400 bps when transmitting to a fax machine which
complies with the V.17 fax standard. Speeds will fall back to 12000, 9600, or 7200 bps in poor line
conditions. When connecting to a G3 fax device, your modem allows for fax speeds up to 9600 bps
and will automatically fall back to 7200, 4800, and 2400 bps if the line quality is poor.
Voice Function
Voice capability stands for the modem’s ability to digitize incoming voice messages, which the
computer stores and forwards. It also means that the modem can playback the recorded digitized
voice on line for a message announcement.
Voice IS-101 Command Set
Please refer to the Voice command sets in Chapter 5.
4-bit Voice Data Compression
The main issue in the digitized voice mode is the amount of storage required. A relatively simple
ADPCM algorithm can reduce the speech data rate to half the rate and maintain about the same
voice quality. This algorithm can also be used to reduce the speech data rate to 1/3 or 1/4 of the
original rate, but with voice quality degradation. Only 4-bit ADPCM is used in Omni 56K/Omni
56K Plus.