U-90E Data/Fax Modem
Error Control and Data Compression
9-2
9.2 Data
Compression
In the modems, data compression is activated between asynchronous to synchronous
conversion 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 U-90E 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. Hence 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 it can be 50 % to 100% higher and in other cases it is just slightly higher. In
general, it is about 50 % more efficient.
You can issue
AT
commands to the modem to enable its error control and data
compression option as shown in the following table.
Table 9-1 Error Control and Data Compression
Control Level
AT Command
Error Control
Data Compression
NONE AT&K0
None
None
MNP3/MNP4 AT&K1 MNP3/MNP4
None
MNP4, MNP5
AT&K2
MNP4
MNP5
V.42, MNP3/MNP4
AT&K3
Auto detection
none
V.42bis, MNP4/MNP5
AT&K4 (default)
Auto detection
Auto detection
Содержание U-90E
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