Canon fax basic 2000 サービスマニュアル

G3 FACSIMILE COMMUNICATIONS

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of 256 frames that are in an HDLC structure, and partitions image data

coded by the MH, MR, MMR or JBIG schemes into 256 bytes. Accord-

ingly, a single data block is 64 kbytes. The content of the coded image is

the same as in general G3 communications.

When the receiving side receives the image data of a single block, it checks

for errors by each individual frame. Error detection is performed by verify-

ing the continuity of the frame and the CRC check. The receiving side then

performs a re-transmit request for error frames by PPR. After the transmit-

ting side receives the re-transmit request, it transmits only the error frame

as the re-transmit block. When the receiving side receives the re-transmit

block, it checks for errors again by each individual frame, and returns the

result by PPR. When block has finished being transmitted normally by this

re-transmit processing, the receiving side returns the signal indicating that

the block was received normally. Fig. 5-85 shows an example of a commu-

nications procedure using ECM.