ZyXEL Elite 2864 User Guide - Page 126

Bidirectional Compression Processing data compression consumes a lot of the modem controller CPU's computation power. Though data compression protocols of V.42bis and MNP5 are bidirectional, most modems slow down when doing bidirectional file transfers because of limited processing power. ZyXEL 2864 series modems use a powerful 16-bit processor that does not slow down during bidirectional file transfers. Negotiation Fail Fall-Back There are two options you can choose from if the error control negotiation fails at the initial modem connection handshaking: STAYS ON-LINE DISCONNECT AT*E0 AT*E1 Maintains the non-error control connection, if error control negotiation fails. (Default) Disconnects the line if not error control linked. DTE to DCE Connection No matter what control level is enabled, DTE speed can always be set separately from the modem's speed, except in the case where you set FOLLOW LINK RATE. For maximum throughput, it is better to set AT&B1 (default) FIXED AT DTE RATE. The DTE speed will be independent of the speed the modem is linked to. The DTE speed options range from 300 bps to 460800 bps. What DTE speed is optimized for your application depends on how fast your computer and communication software can process the serial port data. 2864 series modems use certain controls and commands to enable the modem to optimize its performance. Averaging Throughput At high DTE speeds, slow computers tend to lose characters. Even though most transfer programs offer protocols with error correction capabilities, it will still take time to recover from errors. ZyXEL modems average the throughput before sending characters to the DTE. This will decrease the probability of the computer losing characters due to "burst" high-speed character strings. Since new computers are much faster and there is an increasing use of serial port chips with internal buffers like the 16550A UART, the computer's speed has become less of a problem. The default setting for throughput averaging is disabled. This will reduce data delay and increase throughput in Unix applications. You can enable throughput averaging by setting S42b1 to 1. 10-4