Overview
This article describes the difference between various Fax classes.
Information
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Class 1: A class 1 fax modem is little more than a data modem that has a very basic fax command set for handling group 3 fax transmissions. Because of this, the application software has to control all the data flow between the fax modem and the remote fax device.
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Class 1.0: is exactly the same as for Class 1 (above). The ITU (International Telecommunication Union) recommended changing the name of the Class 1 fax command set to Class 1.0 for a common naming convention.
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Class 2: Class 2 is a higher level specification than class 1. More of the fax protocol work is done within the fax modem firmware. This fax service class specification was never formally approved by the ITU. Every modem manufacturer is left to implement any command set of Class 2. This makes it difficult for application software to support all types of Class 2 fax modems.
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Class 2.0: Class 2.0 is similar to the Class 2 specification that has been formally approved by the ITU. Every modem manufacturer has a basic Class 2.0 command set that has to be implemented in the firmware. The advantage of class 2/2.0 support over class 1/1.0 is that driving the modem does not hold up the PC with fax timing issues. This is particularly important in a multitasking environment and for network fax servers (as opposed to single user fax systems - where the user is often happy to wait for a fax to be transmitted).
Difference between Class 1/1.0 and Class 2/2.0
| Class 1/1.0 | Class 2/2.0 |
| Controlled by software | Depend upon the quality of the fax firmware in the modem |
Difference between Class 2 and Class 2.0
| Class 2 | Class 2.0 |
| Not approved by ITU | formally documented and approved by the ITU |
| No uniformity | All devices behave in the same way |
To know the class of the Fax Modem:
Type the following AT command in Windows (Hyper)Terminal or Putty:
AT+FCLASS=?
The modem reply will be of the form:
0,1,1.0,2,2.0 where
0 is for data.
1 is for class 1 fax.
1.0 is for class 1.0 fax.
2 is class 2 fax and
2.0 is class 2.0 fax.