3.6. Data Encoding Schemes

Several data encoding methods exist that compress fax data and reduce the size of the file to be transmitted, thereby increasing the speed of a fax transmission.

The following data encoding schemes are supported for transmitting fax data and storing incoming fax data. Support for data encoding schemes varies by product; for details, see Section 2.4. Key Product Features on page 8.

• Modified Huffman (MH) ITU-T T.4 Recommendation for Group 3 fax.
• Modified Read (MR) ITU-T T.4 Recommendation for Group 3 fax (transmit only). If negotiated during Phase B of the T.30 protocol, MH and MMR stored fax data is converted to MR line encoded data.
• Modified Modified Read (MMR) ITU-T T.6 Recommendation for Group 4 fax.

MH is a one-dimensional encoding scheme that compresses each horizontal scan line of the image.

Modified Read (MR) and Modified Modified Read (MMR) are two-dimensional encoding schemes that make use of the high degree of vertical correlation between each scan line in the fax image to achieve a higher compression than MH.

The highest data compression is achieved using the MMR encoding scheme.

Although not all fax machines can receive MR or MMR encoded data, some Dialogic fax products are capable of converting MH or MMR stored fax data to MH, MR or MMR line encoding schemes during fax transmission, and converting incoming fax data to MH or MMR for data storage during fax reception.

NOTE:

An error is returned to your application if unsupported encoding schemes are used.

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