Phaser 6128MFP Service Manual 2-61
Theory of Operation
Protocol Monitor
Overview of Communication Protocol
A protocol refers to an agreed-upon set of special rules to be adhered to by
endpoints attempting to establish a telecommunication connection.
The communication protocol for the G3 fax specifications is stipulated by an
international specification known as ITU-T Recommendation T.30 (page 2-65).
All G3 fax machines conform to this protocol when exchanging signal to establish
communication.
The G3 fax session consists of five phases from “Phase A” to “Phase E.”
• Phase A – Call Establishment
• Phase B – Capability Negotiations
•Phase C – Image Data Transfer
• Phase D – Post-transfer Procedure
• Phase E – Call Release
The following flow chart provides a typical G3 fax session of a one-page
document.
• Phase A – Call Establishment
In order for a fax to be established, both ends of the line must recognize that
the other end is a non-voice (Fax) terminal. Since G3 fax communication is
intended for a transmission over the conventional voice network, a fax
communication must be initiated via audible tones.
Sending Fax Station Receiving Fax Station
s6128-061
CNG
CED
NSF/CSI/DIS
(NSS)/TSI/DCS
TCF
CFR
EOP
MCF
DCN
Training Signal
PIX (Image Data)
Phase A
Phase B
Phase C
Phase D
Phase E
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