Data Compression; Table 9-1 Error Control And Data Compression - ZyXEL Communications U-90E User Manual

U-90E Data/Fax Modem
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.
AT
You can issue commands to the modem to enable its error control and data
compression option as shown in the following table.
Control Level
NONE
MNP3/MNP4
MNP4, MNP5
V.42, MNP3/MNP4
V.42bis, MNP4/MNP5
9-2

Table 9-1 Error Control and Data Compression

AT Command
AT&K0
AT&K1
AT&K2
AT&K3
AT&K4 (default)
Error Control Data Compression
None None
MNP3/MNP4 None
MNP4 MNP5
Auto detection none
Auto detection Auto detection
Error Control and Data Compression