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MNP and V.42

Data compression

Modem port flow control

Modem port flow control refers to flow control between the modems of the local station and remote station.

If data transmission from the modem under serial port flow control is interrupted because the computer cannot catch up with it, modem port flow control is applied to the remote modem so that transmitted data will not exceed buffer capacity. This flow control functions in normal mode only.

Data compression

Protocols MNP class 5 and V.42bis are included in the modem to compress data received from the computer. The receiving modem decompresses the received data and sends it to its own computer. This data compression function increases actual transmission speed up to twofold in communications using MNP5 or up to three or fourfold in communications using V.42bis. The compression ratio varies depending on the data. Actual speed will not always be raised close to the maximum compression ratio.

The V.44 compression standard provides more efficient data compression than V.42bis, significantly increasing the received throughput and reducing the download time for Web pages.

Commands (%Cn)

Select whether or not to compress data in communications by MNP class 5 or V.42bis as follows:

%C1 Enables data compression

For details, refer to “AT Commands” on page 51.