Microsoft KB Archive/97497

= Adjustments to Achieve 9600 bps/14.4K Modem Transfer =

Article ID: 97497

Article Last Modified on 2/19/2002



This article was previously published under Q97497



SUMMARY
Systems using LAN Manager with RAS and modems require some adjustments to connect at 9600 bits per second (bps) and support a 14.4K transfer rate. Here is a sample configuration for which this connection has proven troublesome:

Server
LAN Man 2.2 with RAS

Digiboard

US Robotics v.32bis external modem

Client
Windows

RAS 1.1

US Robotics v.32bis internal modem

Below are procedures for achieving the 14.4K rate, and other suggestions for boosting performance.

PERFORMANCE ADJUSTMENTS

 * Make sure that MAXBAUD=19200 on both sides: this sets DTE rate (port to modem speed) to 19200, enabling a connection rate of 14400.
 * Change &B0 to &B1 in the init string on both sides: this keeps the DTE rate at 19200 while the connection rate is 14400.
 * Set client workstation WRKHEURISTICS digit 14 to 0 (enabling raw I/O). This ensures a smoother data flow when moving big chunks.

Note: Using these three suggestions and sticking with the defaults in MODEMS.INF (add &M0 to disable error control) is a good solution. Below are some other performance improvement ideas, although they may hurt reliability because RAS 1.1 doesn't support flow control.

A test with US Robotics dual standard modems (externals) and RAS 1.1 (server with Digiboard) yielded a top throughput of 18,359 bps (file copy of 1,294,336 bytes in 705 seconds). The init string for both modems was:   COMMAND = AT&F&C1&D2  V1 S0=0 S2=128 S7=55 &B1 &R2 &K1 &M4 *cr Where:

&M4 - Enables error control (default)

&M0 - Disables error control

&K1 - Enables data compression if &B1 (default)

&K0 - Disables data compression

&R2 - Enables hardware flow control of received data (may not be needed with RAS)

&R1 - Disables hardware flow control

&B1 - DTE rate is fixed (to the value set by MAXBAUD)

&B0 - allows variable rates (DTE syncs with connect rate)

Additional query words: 2.00 2.0 2.10 2.1 2.10a 2.1a 2.20 2.2 usr

Keywords: kbnetwork KB97497

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