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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.)
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
Overview of Packet Communication
Packet Modes of Operation
KAM’98 v 8.3
153
User’s Guide
Содержание KAM 98
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Страница 132: ...Getting Started Other Topics User s Guide 114 KAM 98 v 8 3...
Страница 160: ...blank page Non Packet Modes of Communication RTTY Operation User s Guide 142 KAM 98 v 8 3...
Страница 342: ...blank page Command Reference KAM 98 Commands User s Guide 324 KAM 98 v 8 3...
Страница 376: ...ASCII Chart paste in page 1 of 2 ASCII chart Appendix E Additional Information ASCII Chart User s Guide 358 KAM 98 v 8 3...
Страница 378: ...KAM 98 Parts Layout Appendix E Additional Information KAM 98 Parts Layout User s Guide 360 KAM 98 v 8 3...