Why is it that I can send fax but cannot receive fax or vice versa when using the fax modem PCMCIA card?

Why is it that I can send fax but cannot receive fax or vice versa when using the fax modem PCMCIA card?
or
What is the difference between Class 1 and Class 2 fax modem?

Whenever error messages relating to the inability to send or receive fax are received, it is normally due to the improper setting in the fax/modem softwares. The following procedures can help to isolate the software setting error.

A) Check the fax/modem card is configured properly by Windows.
1) Go to [Start]->[Control Panel]->[Modems] and select the current modem in use.
2) Click the [Diagnostics] tab and highlight the COM port that associated to the modem current in use.
3) Click the [More Info] box, and it should show the Port Information after communicating with modem.
4) Otherwise, check the fax/modem card and reinstall the driver again.

B) Most of the fax modem software should allow you to select either Class 1 or Class 2 operation. This setting can usually be checked from the modem properties or advanced properties of the software. It is recommended that whenever using the fax.modem PCMCIA card to fax or receive fax, change the modem properties to Class 1 or Class 2 either way, when error messages of inability to send or receive fax are received.

e.g In Winfax Pro software, certain fax/modem requires Class 2 operation in order to send faxes and Class 1 operation to receive fax. The Class 1 or 2 setting can be manually changed in the Modem and Fax Device Properties.

**** INFORMATION ****

Class 1 refers to a fax modem standard designed as an extension of the Hayes AT command set that permits computers to send and receive faxes using fax modems. This standard requires that most of the fax protocol work and image generation be handled by the software, and the basic communication handled by the modem. This standard is very sensitive to network traffic and maintaining the fax connection.

Class 2 refers to a more recent fax modem standard designed to an extension of the Hayes AT command set that permits computers to send and receive faxes using fax modems. This higher-level standard lets the modem handle much of the fax protocol work and basic communication, freeing the software to manage the session and image generation. Class 2 fax modems are recommended for network environments and offer greater reliability for transmission delivery.