ZyXEL Communications omni series user manual Error Correction and Data Compression with

to dial the (n+1)th phone number for the first connection and the (m+1)th phone number for the second connection.

For example, ATDIS0+S1<Enter> will dial the number stored in location ‘0’, and the number stored in location ‘1’ for the bundle connection.

Error Correction and Data Compression with V.120

With V.120, the default setting is for LAPD error correction only. No data compression will be negotiated. The following AT commands are used to switch the V.42bis data compression on or off for ISDN data calls when using V.120 protocol.

∙AT&K44 - enables V.42bis on ISDN calls.

∙AT&K00 - disables V.42bis on ISDN calls.

With the &K44 setting, the TA will try to connect using V.42bis data compression. If the remote device doesn’t support V.42, then LAPD error correction will be used.

When a connection is made using V.42bis compression, the following connect message will be displayed.

CONNECT 115200/V120 56000/LAPD/V42b.

It takes extra time for the calling ISDN TA to negotiate V.42bis. If you know in advance that the called site has no V.42bis capability, it would be better to issue the AT&K00 command beforehand in order to get a quick connection.

Since the V.42bis algorithm needs an error-free transmission channel between the compression and decompression processes, it can only work with a protocol with error control competence. X.75 and V.120 are such protocols that can be used together with V.42bis data compression. V.110, on the other hand, is just an R-interface layer 1 adaptation protocol without error-control and is thus inadequate for V.42bis.

62 V.120 ISDN Communications