ZyXEL Communications Comet 3356, User Manual

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Advanced Data Communications 21
Standard BPS rate
(+/-0,01%) Baud rate
(+/-0,01%) Modulation Carrier Freq
[Hz]
K56flex 56,000 - 32,000 multiple PCM multiple
V.34bis 33,600/31,200 2,400 TCM 1,800
V.32bis 14,400 2,400 128-TCM 1,800
V.32bis 12,000 2,400 64-TCM 1,800
V.32bis 7,200 2,400 16-TCM 1,800
V.32 9,600 2,400 32-TCM 1,800
V.32 uncoded 9,600 2,400 16-QAM 1,800
V.32 4,800 2,400 4-DPSK 1,800
V.29* 9,600 2,400 16-QAM 1,700
V.29* 7,200 2,400 8-QAM 1,700
V.29* 4,800 2,400 4-DPSK 1,700
V.27bis* 4,800 1,600 8-PSK 1,800
V.27bis* 2,400 1,200 4-DPSK 1,800
V.26bis* 2,400 1,200 4-DPSK 1,800
V.23 1,200 / 75 1,200 / 75 FSK
V.23 600 / 75 600 / 75 FSK
V.22bis† 2,400 600 16-QAM 1,200 Orig.
2,400 Ans.
V.22† 1,200 600 4-DPSK 1,200 Orig.
2,400 Ans.
V.21 300 300 FSK
BELL 103 300 300 FSK
G3 FAX Implemented according to T.30, V.17,V.29 and V.27ter.
Error Control
Error control keeps the modem data link error-free by detecting and re-transmitting
erroneous data. ZyXEL modems support both MNP and V.42 error control protocols.
The MNP protocol was an industry de facto standard developed and licensed by
Microcom, Inc. ZyXEL modems support level 4 and 3 error control protocols,
commonly denoted as MNP4 and MNP3. V.42 is a standard developed by ITU-T. V.42
supports both LAPM (Link Access Procedure for Modem) and MNP4. A V.42
handshake will try an LAPM connection first, and if not successful, it will try MNP4.
The error control (MNP4, LAPM) methods in modem to modem connections are based
on techniques utilized by both modems. They are explained below.
CRC (Cyclical Redundancy Check) Error Detection
At the end of every data block, a 16-bit number CRC, which is calculated through a
polynomial function, is sent. The receiving modem receives the block, calculates its
own CRC through the same polynomial function, then compares the numbers. If it
matches the received CRC, everything is all right. If not, an error(s) has occurred
somewhere in the block. The modem checks every block received for error(s).