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G3 FACSIMILE COMMUNICATIONS
6.6
Method for Detecting Image Signal Transmission
Errors
Although image signals are sent after equalizing the MODEM and train-
ing, a transmission error may occur when sudden noise or an instantaneous
power interruption is generated during image signal transmission. To
detect whether a transmission error has occurred in the image signal on the
receiving side, the number of bits in each line after decoding is compared
with the specified number of bits according to the document size (1728
bits for A4). If the number of bits match, then it is judged that there is no
transmission error. If they do not match, it is judged that something has
caused a transmission error.
6.6.1 When there are no errors in the received image
The receiver returns the MCF that shows that the image was received suc-
cessfully.
6.6.2 When errors are detected in the received image
When an transmission error has occurred on the receiving side, all of the
data to be recorded for that line is lost. However, with a regular image, the
omission of several lines will not greatly affect the image. For this reason,
a reference is provided and occurrence of an error of a fixed amount is
counted as the record of the error. If the error occurs at this reference or
less, it is judged that the image was received successfully. In this case, the
lines for which the error occurred are not printed, and the next line is
printed. Note, however, that some facsimiles have a function for selecting
re-printing of the previous line.
6.6.3 RTN and RTP
When an error has occurred in excess of the fixed amount in the received
image, the receiving side returns the RTN instead of the MCF. This means
that that page could not be received successfully. When RTN is received,
an error occurs on the transmitting side, and communications is ended if
there are no more documents. If the next document is present, DCS is
returned to and a fallback is caused to enable transmission of the next doc-
ument. On facsimiles transmtting by memory transmission, a fallback to
the document that was in error can also be made to transmit the document.
If the number of occurrences is at the reference or less, if an error has
occurred, the RTP is returned instead of RTN. In this case, that page is
regarded as a successfully received page. However, to transmit documents
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