Kantronics KPC-9612 Plus, Руководство пользователя

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Now let’s look at the same conditions under version 2 (AX25L2V2 ON).
Station B does not receive frame number 3 from A and therefore sends no ac-
knowledgment to station A. This time, station A sends a POLL or question to sta-
tion B saying, in effect, I’m expecting frame number 0 from you; what frame are
you expecting from me?" <<RR0>>.Since station B did not receive the frame,
station B would respond with <<rr3>>, saying “I’m ready to receive frame 3.”
At this point, station A, upon receiving the rr3 would immediately resend the en-
tire frame. If station B had already received frame 3 once but the acknowledg-
ment never got to station A the question from station A for the retry would be the
same. Station B’s response however, would be different. He would respond with
“ready to receive frame 4” <<rr4>>. If station A does not receive station B’s re-
ply, this “POLL/REPLY” sequence would continue for the number of retries set
in the sending TNC; if no response was received, and the RELINK
parameter is ON, the TNC at station A would then begin to issue connect re-
quests to station B since there is still an outstanding packet of information. This
is the major difference between version 1 and version 2. The connect attempts
would then continue for the number of retries set in the TNC, and if no response
was received from station B after all of the above, station A would disconnect
and discard the packet. The parameter RELINK is defaulted OFF to avoid the re-
connect attempt.
Flow Control
The flow control commands insure that the TNC gets everything that is sent to it
by the computer and that the computer gets everything the TNC sends it. When
the computer sends the TNC data, the TNC stores this data in a buffer until it can
packetize it, send it, and get acknowledgments. Similarly, when the TNC sends
the computer data, the computer stores the data in a buffer until it can be pro-
cessed, stored to disk, sent to printer, or whatever.
This buffer area is of limited size; if more data is sent than will fit in the buffer
the extra data will be lost. To make sure each device gets all the data it should
from the other device, the two devices can tell each other to start and stop send-
ing data. This is called Flow Control and it can be accomplished in either of two
ways, via software or via hardware.
Packet Mode of Operation Modes of Operation
KPC-9612 Plus v 8.2 117 User’s Guide