Technical Helpweb

- more articles

RTP and RTN Messages in DM3 Fax

Symptom:
When running R4 on DM3 fax in non-ECM mode, the post-page response messages, RTP and RTN, are neither generated nor responded to. This limitation is not documented in both the Fax Software Reference and the R4 on DM3 Compatibility Guide manuals.

Reason for the Problem:
The RTP and RTN features are currently not implemented in DM3 fax as it is expected that users would use the Error Correction Mode (ECM).

Workaround:
Use the ECM mode as part of the coding scheme.

Technical Discussion: According to the ITU-T T.30 recommendation, RTP and RTN messages apply only the when the Error Correction Mode is not being used. When RTN or RTP messages are generated or expected, it implies the fax session is using either the MH or the MR encoding, both of which do not employ the ECM mode by default. By default, however, DM3 fax uses the Modified-Modified Read (MMR) encoding which, in turn, must use the ECM mode. ECM is an integral part of the MMR encoding scheme and, as such, does not need to be explicitly enabled when MMR is being used. This is why, for DM3 fax, it is recommended to either leave the encoding at the default MMR, or to explicitly enable ECM if MH or MR must be used. The encoding parameters FC_TXCODING and FC_RXCODING should, therefore, include one of the following options:

• DF_MMR
• DF_MR OR’d with DF_ECM
• DF_MF OR’d with DF_ECM

With any of the above three options/combinations both RTP and RTN messages should neither be generated nor expected.

Product Listing:
All DM/F boards
All DM3 combined media boards with fax capability
All supported system releases

Glossary of Acronyms / Terms:
RTP – Retrain Positive
RTN – Retrain Negative
ECM – Error Correction Mode
MMR – Modified-Modified READ
MR – Modified READ
MH – Modified Huffman

Related Documentation: Fax Software Reference: http://www.dialogic.com/~/media/manuals/docs/fax_api_win_v13.pdf