GDK Version 5.0 Programming Reference Manual Phases of a Fax Session

Phases of a Fax Session

Fax Programming Models

A facsimile session between two fax devices consists of five distinct phases (see Table 25). The ITU T.30 recommendation describes the interaction between two fax devices in more detail.

Table 25. Facsimile Session Phases

ITU T.30 Phase

Description

Fax Modem

Phase A - Call Setup

This phase establishes a call connection between the two devices, which includes dialing, call progress, answer and supervision (start the billing).

Calling fax device transmits CNG 1100 Hz tone, .5 second ON, 3 seconds OFF
Answering fax device transmits CED 2100 Hz tone, 3 second duration

Phase B -
Pre-Message Procedure

This phase consists of the mutual recognition of the fax devices (known as a handshake). It is a negotiation procedure that identifies their respective capabilities, identities and any non-standard facilities. This phase selects the session parameters for the message transmission including speed, compression and error correction.

V.21 mode, HDLC
300 bps

Phase C - Message Transmission

This phase is where the data is transmitted. The fax devices send/receive page files of the document, at the selected speeds performing T.4, T.6 and/or ECM as negotiated in Phase B.

v.17, v.29, v.27, v.33
14400, 12000, 9600, 7200,4800, 2400 bps
optional HDLC (ECM mode)

Phase D -
Post-Message
Procedure

After sending/receiving a page file of the document, a message exchange occurs between the fax devices indicating the success or failure to receive the page file, continue to next page file under same conditions, retrain to new conditions or to confirm the document transmission is complete.

V.21 mode, HDLC

Phase E -
Call Release

In this phase the fax transaction is complete, good or failed, and the call is released (OFF-HOOK) terminating the billing and the connection.

(inactive)

Fax Programming Models

Dialogic CP Fax Series products define and support two programming models for facsimile communications - batch mode and run-time interactive models. The GFQ functions are used with the batch programming model, and the GRT functions are used with the run-time interactive programming model.

Click here to contact Dialogic Customer Engineering

ITU T.30 Phase	Description	Fax Modem
Phase A - Call Setup	This phase establishes a call connection between the two devices, which includes dialing, call progress, answer and supervision (start the billing).	Calling fax device transmits CNG 1100 Hz tone, .5 second ON, 3 seconds OFF Answering fax device transmits CED 2100 Hz tone, 3 second duration
Phase B - Pre-Message Procedure	This phase consists of the mutual recognition of the fax devices (known as a handshake). It is a negotiation procedure that identifies their respective capabilities, identities and any non-standard facilities. This phase selects the session parameters for the message transmission including speed, compression and error correction.	V.21 mode, HDLC 300 bps
Phase C - Message Transmission	This phase is where the data is transmitted. The fax devices send/receive page files of the document, at the selected speeds performing T.4, T.6 and/or ECM as negotiated in Phase B.	v.17, v.29, v.27, v.33 14400, 12000, 9600, 7200,4800, 2400 bps optional HDLC (ECM mode)
Phase D - Post-Message Procedure	After sending/receiving a page file of the document, a message exchange occurs between the fax devices indicating the success or failure to receive the page file, continue to next page file under same conditions, retrain to new conditions or to confirm the document transmission is complete.	V.21 mode, HDLC
Phase E - Call Release	In this phase the fax transaction is complete, good or failed, and the call is released (OFF-HOOK) terminating the billing and the connection.	(inactive)