ZyXEL Omni 56K USB Lite User Guide - Page 37

Omni 56K USB Lite STANDARD V.32bis V.32 V.32 uncoded V.32 V.23 V.23 V.22bis 2400 Ans V.22 (BELL 212) 2400 Ans V.21 (BELL 103) BIT RATE [BPS] 4800 9600 9600 4800 1200/75 600/75 2400 1200 300 BAUD RATE [BAUD] 2400 2400 2400 2400 1200/75 600/75 600 MODULATION 32-TCM 16-QAM 4-DPSK FSK FSK 16-QAM CARRIER FREQUENCY [HZ] 1800 1800 1800 1800 1200 Call 600 4-DPSK 1200 Call 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. Specifications and Functional Description 3-5