PK-232 MBX – OPERATING MANUAL PACKET-RADIO
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Packet Lite reduces the length of an I-frame slightly, but its real strength is the shortening
of the acknowledgment frames, resulting in fewer garbled acks and therefore fewer un-
necessary retries. An ack (RR, RNR or REJ frame) in standard AX.25 consists of 19 consecu-
tive bytes that must be copied with no hits; Packet Lite reduces the length to 9 bytes, or
47 % of the standard ack length.
A couple of restrictions are necessary to accomplish this. First, Packet Lite works only be-
tween two stations connected directly, with no digipeating allowed. If digipeaters are intro-
duced to the address field, the advantage of the reduced overhead disappears.
Second, all Packet Lite connections emulate AX.25 version 2.0 (RR polling instead of retrying
I-frames). This is necessary for the 10 minute identification described below. Also, the main
reason version 1 continues to be used on HF is that on a retry a (RR,P) polling frame is BO
long that one might as well just send the I-frame again. Packet Lite's polling and ack frames
are so short that the AX.25 version 2.0 polling method is now worth doing.
4.10.1 Enabling Packet Life
To begin using Packet Lite, first make sure you have made all the proper HF Packet set-
tings discussed earlier in this chapter. Be especially careful to ensure VHF is OFF and
HBAUD is set to 300.
Once these settings have been made, to enable the Packet Lite protocol extensions, turn
the PK-232 command LITE ON. You must not be connected to any other stations or you
will not be allowed to change the LITE command.
Initiating a Packet Lite Connection
Once all the above settings have been made, simply issue the standard CONNECT request
as described earlier in the chapter.
If the station you are connecting to also has the command LITE ON, a Packet Lite connec-
tion will result and you and the distant station should enjoy a more reliable QSO than
others on the same frequency.
4.10.2 Compatibility With Standard AX.25 Stations
If the station you connect to does not have the Packet LITE protocol extensions, there are
three known possibilities of what will occur.
1. WA1ABC>WB2XYZ [C,P] 01 3E 38 58 32 {Packet Lite attempt}
WB2XYZ>WA1ABC (UA, F) {standard ack}
In this case, the non-Lite station sees the [C,P] control byte but ignores the non-standard
bytes following it. It replies with a standard UA frame, and the connection proceeds as
standard AX.25.
2. WA1ABC>WB2XYZ [C, P] 01 3E 38 58 32 {packet Lite attempt}
WB2XYZ>WA1ABC (FR): 3F 00 03 {Frame Reject}
WA1ABC>WB2XYZ (C, P) {Standard attempt}
WB2XYZ>WA1ABC (UA, F) {Standard ack}
In this case, the non-Lite station notices the non-standard bytes following the control byte
and issues a FP-MR (Frame Reject) to signify that a protocol violation has taken place.
The PK-232 receives the FRMR and automatically reverts to standard AX.25, sending the
connect retries without the Lite PID and address bytes.
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