Omni 56K USB Lite
Specifications and Functional Description
3-5
STANDARD
BIT RATE
[BPS]
BAUD RATE
[BAUD]
MODULATION
CARRIER
FREQUENCY [HZ]
V.32bis
4800
2400
1800
V.32
9600
2400
32-TCM
1800
V.32 uncoded
9600
2400
16-QAM
1800
V.32
4800
2400
4-DPSK
1800
V.23
1200/75
1200/75
FSK
V.23
600/75
600/75
FSK
V.22bis
2400
600
16-QAM
1200 Call
2400 Ans
V.22 (BELL 212)
1200
600
4-DPSK
1200 Call
2400 Ans
V.21 (BELL 103)
300
300
FSK
Error Control
Error control keeps the modem data link error-free by detecting and re-transmitting erroneous data. The
Omni 56K USB Lite supports both MNP and V.42 error control protocols. The MNP protocol was an
industry standard developed and licensed by Microcom, Inc. The Omni 56K USB Lite supports level 4 and 3
error control protocols, commonly denoted as MNP4 and MNP3.
V.42 is a standard developed by CCITT (Consultative Committee for International Telephony and
Telegraphy). V.42 supports both LAPM (Link Access Procedure for Modems) and MNP4. A V.42
handshaking tries an LAPM connection first, and if not successful, it tries 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.
The Omni 56K USB Lite supports 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 ruins 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.
