Timewave PK-900, Operating Manual

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fewer garbled acks and therefore fewer unnecessary retries. An ack
(RR, RNR or REJ frame) in standard AX.25 consists of 19 consecutive
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 between two stations connected directly,
with no digipeating allowed. If digipeaters are introduced 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 so 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.
4.11.1 Enabling Packet Lite
To begin using Packet Lite, first make sure you have made all the
proper HF Packet settings discussed earlier in this chapter. Be
careful to ensure VHF is OFF and a 300 bps Modem has been selected.
Once these settings have been made, to enable the Packet Lite protocol
extensions, turn the command LITE ON for the appropriate Port.
For example to enable Packet Lite on Port 1, type "LITE ON" at the
command prompt. You must not be connected to any other stations on
that Port 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 Packet Lite enabled, a
Packet Lite connection will result and you and the distant station
should enjoy a more reliable QSO than others on the same frequency.
4.11.2 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 that 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}
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