Kantronics KPC-9612 Plus, Руководство пользователя

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the transmission (determined by PACLEN and MAXFRAME) also needs to be
taken into account when deciding how to set FRACK. Longer packets (and more
of them) require more time to be transmitted, more time to be repeated by the
digipeater, and so on down the line. The FRACK timer begins when PTT is re-
leased (the packet has been sent) and is suspended when data carrier from the ra-
dio is present, or when your station is transmitting.
Retries AX.25 Level 2, Version 1 vs. Version 2
The way retries are accomplished depends on AX25L2V2 being OFF or ON. To
explain this we will follow a conversation through its path. First let’s assume sta-
tion “A” is connected to station “B” with Version 1 protocol (AX25L2V2 OFF).
When station A sends a packet to station B, he expects to receive an acknowledg-
ment back indicating that station B has received the information. In order to ver-
ify that the proper packet (or frame) has been acknowledged, each frame has a
number. This number is sent as a part of the frame so the receiving station knows
where this packet belongs in the conversation. The frame numbers range from
0-7 and because of this, we are limited to a MAXFRAME of 7 (we do not want
the same frame number reused in the same transmission). This is also true for
Version 2. If the first acknowledgment is received, there is really no difference
between the two versions, practically speaking. The difference shows up with re-
tries, so let’s assume that the packet did not get through on the first attempt.
Let’s assume that station A sends frame number 3 to station B. Station B does not
receive the frame and therefore no acknowledgment is received by station A.
With version 1, the entire packet is retransmitted (with the same frame number)
to station B and this continues until station A receives an acknowledgment from
station B. This acknowledgment can take two basic forms. The first time station
B receives frame 3 he will send an acknowledgment of the form “ready to receive
frame 4” <rr4>. If this acknowledgment is sent, and station A did not receive it,
station A will again send frame 3. Since station B already received frame 3, he
would acknowledge it with the form “I’ve already got that frame, send me num-
ber 4” <rej4>. This is also known as Reject Frame sent. This process would con-
tinue until the retry count is exceeded when, under version 1, the sending TNC
will initiate a disconnect and discard the packet. (The monitoring of the com-
mands shown in < > depends on the settings of MRESP, MCON and MCOM.)
Modes of Operation Packet Mode of Operation
User’s Guide 116 KPC-9612 Plus v 8.2