Ticket #39012

XMODEM ACK/NACK used out of sequence

Open Date: 2019-03-05 20:30 Last Update: 2019-03-05 20:30

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(Anonymous)
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Status:
Open
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Priority:
5 - Medium
Severity:
5 - Medium
Resolution:
None
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Details

I use teraterm xmodem to send a file to my application X. Please note teh timing are NOT the remmended timing for xmodem, but they are no real specification, just suggestion for the author. When X receive a full block (lets say block 1), send back an ACK and wait ~15ms to see new data; but seems xmodem is taking up to 30ms. That is not a big problem, my program send a NACK after 15ms, then wait again; I expect to receive again block 1 if the fisrt ACK was lost, or block 2 if ACK was received. teraterm send block 2. Not a problem, i receive it and send an ACK. BUT now teraterm does NOT use the last receive byte (ACK) but instead uses the "old" NACK; it will resend block 2! that does not look as a big problem until you realize that ACK i sent will be seen as ACK for block 3, something we didn't even initialize.

A possible solution would be to use last received byte

Ticket History (1/1 Histories)

2019-03-05 20:30 Updated by: None
  • New Ticket "XMODEM ACK/NACK used out of sequence" created

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