Technical Notes for Microsoft Fax

This section describes technical information about Microsoft Fax architecture and Registry entries.

You can send faxes either by using the mail client or the Microsoft Fax printer driver. In each case, the message is sent to the Microsoft Fax service provider by using MAPI. If you sent the message from a mail client, it might contain text, embedded OLE formats, and attachments. If you sent it by using the Microsoft Fax printer driver, the mail message will contain a rendered format of the file as an attachment to the mail message.

MAPI allows messages to be preprocessed based on the transport protocol used to send them. The transport protocol chooses the correct modem connection, uses TAPI to create a dial string, and sends the message to that recipient. The preprocessor determines whether to render the message into a fax form to be printed by a fax machine. The rendered format is attached to the original message as a message property and is deleted either when the message is sent or when the transport protocol tries to send the message but determines it cannot.

If the message does not have to be rendered, the message is converted from its original binary format to a line image (also called a linearized form), and then it is compressed.

After the message is submitted, the transport protocol determines what type of recipient the message is intended for as follows:

• If it is a traditional fax recipient and the user has selected printed form or "best available," Microsoft Fax will render the document into the standard Group 3 image format. This can be used by standard fax machines and software. If the user selects editable form, an error message is returned.
• If the recipient is a Microsoft At Work-enabled recipient and the user has selected printed form, then it will render the document into the Microsoft Fax rendered format. This format provides high-quality images of smaller size than standard Group 3 and it is used between Microsoft At Work devices, including fax machines and printers.
• If the recipient is a Microsoft Fax recipient and the user has selected editable form, no rendering is required.
• If there is a mix of recipients, and the user has selected "best available," then Group 3 and editable versions of the document are packaged in the message.
• If the capabilities of the recipient are unknown, Microsoft Fax creates multiple formats to be sure that the proper format is available upon connect.

Fax-form messages sent to Microsoft At Work devices will be sent by using BFT with the resource-based rendering of the message sent as an attachment.

The Registry keys for a fax modem are found in:

Hkey_Local_Machines\Software\Microsoft\At Work Fax\Local Modems

For each local modem that has been installed by Windows 95, information is stored in the key named TAPInnnnnnnn where nnnnnnnn is an arbitrary number assigned by TAPI. The TAPI key contains subkey values. Values that are important to the system administrator are described in the following tables.

The following table lists the modem command strings used to reset the modem whenever Microsoft Fax acquires it from TAPI:

The following table lists the setup modem command string used to set up the modem before dialing or answering:

For more information about the Registry, see Chapter 33, "Windows 95 Registry."