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User's Guide for ZyXEL Omni 56K and Omni 56K Plus Modems
3-6
Error Control
Error control keeps the modem data link error-free by detecting and re-transmitting erroneous data.
Omni 56K/Omni 56K Plus modems support both MNP and V.42 error control protocols. The MNP
protocol was an industry standard developed and licensed by Microcom, Inc. Omni 56K/Omni 56K
Plus modems support level 4 and 3 error control protocols, commonly denoted as MNP4 and
MNP3.
V42 is a developed standard by CCITT. V.42 supports both LAPM and MNP4. A V.42
handshaking will try an LAPM connection first, and if not successful, it will try MNP4.
Data Compression
In the modem, the data compression is activated in an attempt to reduce the number of bits actually
sent. The receiving modem applies these techniques in reverse to recover the actual data from the
compressed data stream.
Omni 56K/Omni 56K Plus modems support both V.42bis and MNP5 data compression protocols.
Data compression needs an error-free data link to work correctly, otherwise the corrupted
compressed data stream will ruin the decompression process. MNP5 is used with MNP4 error
control and V.42bis is used with V.42 error control. The compression efficiency of V.42bis is
generally higher than that of MNP5. In some cases, V.42bis can be 50 % to 100% higher and in
other cases it is just slightly higher. In general, it is about 50 % more efficient.
Repeat Dial
The modem will dial the default number stored in non-volatile RAM , EEPROM , repeatedly if not
connected.(s38.0=1,*Dn)
Cyclic Dial
Dial the number stored in EEPROM at location n(0-3) if cyclic dial s44.3=1 is set.
If the first dial is not successful, the modem will cycle dial through the four numbers stored in
memory.