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Published on August 21st, 2007 | by Kieran


The Five Phases of a Fax

Extracted from the ITU Recommendation T.30 (09/05), Here the are five phases that make up a fax transmission

Phase A – Call establishment
Call establishment can be realized manually and/or automatically.

Phase B – Pre-message procedure
The pre-message procedure consists of the identification of capabilities and the commanding of the chosen conditions as well as the confirmation of acceptable conditions. When connection is established between a terminal operating in accordance with this Recommendation and a terminal operating in a non-ITU-T manner, the terminals should disconnect before the in-message procedure unless both terminals include optional, compatible procedures.

Identification section

  • capabilities identification
  • confirmation for reception
  • terminal identification (option)
  • non-standard facilities identification (option).

Command section

  • capabilities command
  • training
  • synchronization

as well as the following optional commands:

  • non-standard facilities command
  • terminal identification command
  • polling (send) command
  • echo suppressor disabling.

Phase C1 – In-message procedure
The in-message procedure takes place at the same time as message transmission and controls the complete signalling for in-message procedure, e.g., in-message synchronization, error detection and correction and line supervision.

Phase C2 – Message transmission
The message transmission procedure is covered by ITU-T Rec. T.4.

Phase D – Post-message procedure
The post-message procedure includes information regarding:

  • end-of-message signalling
  • confirmation signalling
  • multipage signalling
  • end-of-facsimile procedure signalling.

Phase E – Call release
Call release shall be realized manually and/or automatically.

About the Author

has worked with computers and technology for over 20 years. Based in the United Kingdom, he works as a Solution Engineer for Salesforce, specialising in all things Commerce, Digital and the Internet. Predominantly blogging on he can also be found on Twitter @KieranLane, Instagram and Flickr.

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