Canon FACSIMILE BASIC 2000 Service Manual page 270

G3 FACSIMILE COMMUNICATIONS
• CTC and CTR
When there is an error frame however many times the same block is trans-
mitted, delaying the image transmission speed will reduce the rate (error
rate) at which errors occur. For this reason, the transmitter outputs CTC
when PPR is received four times in the same block to notify the receiver
that it will transmit (fallback) at a delayed image transmission speed. After
the receiver receives CTC, it outputs the CTR. The transmitter then re-
transmit the same block at a lower transmission speed.
the rate (error rate) by which
5–128
Calling Side (transmitter)
1st transmit of
1st block
1st re-transmit
of 1st block
2nd re-transmit
of 1st block
3rd re-transmit
of 1st block
Next is transmitted
at 7200 bps.
4th re-transmit
of 1st block
(7200 bps)
Transmission of
2nd block
Fig. 5-87 CTC and CTR
Frame 0
Frame 1
9600bps
Frame 255
PPS-NULL
PPR
Frame
Frame
9600bps
Frame
PPS-NULL
PPR
Frame
Frame
9600bps
Frame
PPS-NULL
PPR
Frame
Frame
9600bps
Frame
PPS-NULL
PPR
CTC
"I understand."
CTR
Frame
7200bps
Frame
PPS-NULL
MCF
Frame 0
Frame 1
7200bps
Frame 255
Called Side (receiver)
Error present
Error present
Error present
Error present
No error