Fax Protocols; G3 Ecm (G3 Error Correction Mode - NEC NEFAX 671 Service Manual

7.

Fax Protocols

7-1.

G3 ECM (G3 Error Correction Mode)

• G3 ECM is the error correction system newly recommended by Consultative Committee
of International Telephone & Telegraph of 1988.
• By G3 ECM, documents are divided into blocks (called partial page) for transmission. If
any error takes place in any frame (one partial page consists of 256 frames) on a partial
page, the receiving party generates the retransmit request with erroneous frame num-
bers.
Here is an example where frame 1 and frame 3 are subjected to error:
Transmis-
Partial page
(High-speed Modem
Signal)
300 dps Modem Signal
Re-transmission for
error (High-speed
modem Signal)
300 dps Modem Signal
Receiving
Error
Note: If one page end
and consists of plural
number of partial pages,
PPS.
NULL signal is transmit-
ted from the transmis-
sion side.
Partial page end and
End procedure
Re-transmit request
(MCF is repeated if
there is no error)
Re-transmission
Partial page end
Message check
(Received without error)
S-157
4507M501AA