Network to Serial » VScom Serial Device Servers

ID #1042

I am using your Netcom 111 for a faxing program. I have an issue with fax operation, what to do?

A typical serial Modem understands two different sets of commands for operating in Fax mode. These sets are named Fax Class 1 and Class 2. Naturally Fax Class 1 has been specified first.

Fax Class 1 provides detailed information on the current status of the transmission, and also detailed commands to control the operation. At the downside the responses to events on the Modem have to be sent in a strict timely manner.
Back in time when the Class 1 command set was defined Windows 3.1 has been a modern operating system. Serial ports did not operate very fast then, and further the required strict timing was not possible in all conditions in Windows.
To provide Fax mode operation even in such systems the Fax command set Class 2 has been defined. Many critical operations are handled by the Modem in autonomous mode, the software just provides more general supervising functions. The requirement for strict timing was removed this way.

Today computers are very fast, and they can control a Fax Modem in the required timely manner. Typical software uses Class 1 commands as default to control the Modem, just to give detailed and realtime feedback to the user interface.
However using NetCom the network adds delays between received data on the serial port, and arrival of these data in the application software. These are some Milliseconds at least, which often is to long for Class 1 commands.

So even when the fax application identifies the Modem as Class 1 capable, such can cause problems when the Modem is connected to the serial port of a NetCom. Simply configure the application software to use the Class 2 command set, and the problems will vanish.

 

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Last update: 2009-03-19 17:20
Author: Support
Revision: 1.0

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