Canon fax basic 2000 서비스 매뉴얼
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G3 FACSIMILE COMMUNICATIONS
6.10 ECM Communications
ECM stands for Error Correction Mode. ECM enables transmission and
reception of images without any omitted lines. It achieves this by re-trans-
mitting image data containing omissions caused by noise, for example, on
the telephone line. ECM partitions image data in block units, and divides
these data blocks into several frames to be transmitted to the other party.
The receiving side performs error judgment as each single frame is
received, and this judgment is repeated until reception of a single block is
completed. If there is an error frame at the moment that reception of a sin-
gle block ends, the transmitting side is requested to re-transmit the error
frame. After the transmitting side has received this re-transmit request,
only the frame on which the error occurred is re-transmitted, and transmis-
sion of the next data block is restarted at the moment that it has been veri-
fied that the image data has been transmitted and received successfully.
On facsimiles that do not support ECM communications, an error occurs
on each single line when an error occurs during communications of the
image signal, and the line is omitted. Though error control has been per-
formed to correct this shortcoming, ECM was appended as a G3 standard
optional function in 1987 as an additional recommendation to
T.30
and T.4.
6.10.1 Error re-transmission mechanism
A half-duplex system by which the data communications direction is
switched alternately is currently adopted for ECM communications on a
G3 facsimile. First of all, it is verified that both the transmitter and the
receiver have an ECM function by the pre-procedure. The transmitter reads
the image to memory to configure a block of data. A data block is a group
CIG
Calling side
→
Called side
Binary signal
Signal for communicating the telephone number of the calling side to
the called side. (option)
DTC
Calling side
→
Called side
Binary signal
Command for instructing transmission after receiving the DIS from the
called side and verifying that there is a document loaded at the other
party.
As the calling side from then on becomes the receiver, the same infor-
mation as DIS is contained in the signal.