4.6. Setting Parameters for Send Fax

• 4.6.1. Selecting a Transmission Baud Rate
• 4.6.2. Specifying a Preferred Encoding Scheme for Transmission
• 4.6.3. Defining a Fax Page Header
• 4.6.4. Retransmitting a Fax

The fax parameters described in this section are set using fx_setparm( ). For more information on fx_setparm( ), see Chapter 9. Fax Library Function Reference.

4.6.1. Selecting a Transmission Baud Rate

Using the FC_TXBAUDRATE parameter in fx_setparm( ), you can specify an initial transmission baud rate lower than the default which is the highest supported baud rate for a product. Issue fx_setparm( ) prior to issuing fx_sendfax( ).

Support for transmission baud rate varies by product. For a listing of key features by product, see Section 2.4. Key Product Features on page 8.

4.6.2. Specifying a Preferred Encoding Scheme for Transmission

Using the FC_TXCODING parameter in fx_setparm( ), you can specify the preferred line encoding scheme in which to transmit fax data.

The available values for FC_TXCODING are:

• DF_MH - Modified Huffman
• DF_MR - Modified Read
• DF_MMR - Modified Modified Read
• DF_ECM - Error Correction Mode switch (logically "OR" this bit flag with an encoding scheme)

The transmitting channel uses the FC_TXCODING value during Phase B negotiation with the remote receiver. The fax image data provided via the DF_IOTT structures is automatically converted to the negotiated line encoding scheme at the time of transmission. The final negotiated line encoding scheme for transmission depends on the receiver's capability.

To determine the negotiated line encoding scheme, call ATFX_CODING( ) after the negotiation of Phase B is completed.

ECM can be explicitly specified for Phase B negotiation in fax transmission. Use of ECM is determined by the receiver's capability.

The following guidelines are provided on the use of FC_TXCODING and the ECM switch:

• When you send fax data using MH line encoding, scan line correction can occur after each scan line.
• When you send fax data using MR line encoding, scan line correction can occur after every other scan line (coarse resolution) or every fourth scan line (fine resolution).
• For applications that require transmitted MH or MR encoded fax data to be received error-free, set ECM as an option. Fax machines and applications with ECM and MH or MR capability will receive the fax data exactly as it was sent.
• Sending fax data using MMR line encoding always requires ECM.

Using ECM adds time to the fax transfer based on the size of the fax and the quality of the transmission line.

The following chart shows the highest compression line encoding scheme for a fax transmission determined by the FC_TXCODING value in the transmitter application and the capabilities of the fax receiver.

	Fax Receiver Capabilities
FC_TXCODING Parameter Setting	MH	MH w/ECM	MR	MR w/ECM	MMR w/ECM
DF_MH	MH	MH	MH	MH	MH
DF_MH | DF_ECM	MH	MH w/ECM	MH	MH w/ECM	MH w/ECM
DF_MR	MH	MH	MR	MR	MR
DF_MR | DF_ECM	MH	MH w/ECM	MR	MR w/ECM	MR w/ECM
DF_MMR	MH	MH	MR	MR	MMR w/ECM
DF_MMR | DF_ECM	MH	MH w/ECM	MR	MR w/ECM	MMR w/ECM

Setting the FC_TXCODING parameter to DF_MMR|DF_ECM specifies that ECM is used whenever the receiver is capable of ECM for receiving a fax at MMR, MR or MH line encoding.

Setting the FC_TXCODING parameter to DF_MMR specifies that ECM is not used even if the receiver is capable of ECM for receiving a fax at MR or MH line encoding. Note that MMR line encoding always requires ECM.

4.6.3. Defining a Fax Page Header

Fax page header parameters can be set to print a special line of text in a compressed font at the top of every transmitted fax page. There are two possible formats for the fax page header. For more information, see FC_HDRATTRIB and other FC_HDRname parameters in the fx_setparm( ) function reference.

The Telephone Consumer Protection Act requires that a fax transmission include specific information identifying the sender. For more information on the requirements, see Section 2.10. Complying with the Telephone Consumer Protection Act on page 23.

4.6.4. Retransmitting a Fax

When a fax page is not successfully received, the fax receiver sends a Phase D status value of DFS_RTN (Retrain Negative) or DFS_PIN (Procedure Interrupt Negative) to the transmitter. The fax transmitter can automatically retransmit a fax page that is not successfully received.

If operator intervention (also called voice request) is disabled, only RTN (Retrain Negative) is sent to indicate unsuccessful reception of a fax page.

The number of attempts to retransmit pages from a file is set by the FC_RETRYCNT parameter in fx_setparm( ); the default is zero retries. The unsuccessfully received page can be retransmitted once (DF_RETRY1), twice (DF_RETRY2) or three (DF_RETRY3) times.

After the specified number of retry attempts, you can set the transmitter to disconnect the fax call. To do so, logically "OR" the DF_RETRYn value with the DF_RETRYDCN value.

Retry counter parameter values are set with fx_setparm( ) and read with fx_getparm( ).

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