Message 27995 in JNOS2.WW
From: VE4KLM
Date: Sat, 15 Aug 26 13:39:00 Z
Newsgroups: JNOS2.WW
Subject: Re: update on ax.25 v2.2 support
Message-ID: <C29S6_VE4KLM>
Path: K7EK|N2NOV|K5DAT|VE2PKT|VA3BAL|VE3LNZ|VA3PJB|VE4KLM
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R:260815/1405Z 49361@K5DAT.#NEWI.WI.USA.NOAM LinBPQ6.0.25
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I forgot the all important SREJ frame, so here is more info on that
I should add, that ax25 v2.2 features the SREJ frame [ vs the REJ frame ]
(again parroting what is easiliy found online)
The SREJ (Selective Reject) is an AX.25 v2.2 protocol feature that
significantly improves channel efficiency by retransmitting ONLY the
specific data frames that were corrupted or lost.
Compared to the standard, legacy REJ (Reject / Go-Back-N) mechanism used
in AX.25 v2.0, SREJ offers several distinct operational advantages:
Drastically Saves Bandwidth: Under a standard REJ frame command, if for
example, Frame 3 of 7 fails, the system throws away everything and forces
a retransmission of frames 3, 4, 5, 6, and 7.
SREJ explicitly requests only Frame 3, leaving the rest untouched.
Maximizes Throughput on Noisy RF Channels: High-frequency (HF) and Very
High Frequency (VHF) channels are heavily prone to random bursts of
interference, noise, and collisions.
SREJ prevents the entire transmission window from collapsing due to
a single dropped packet.
Reduces Transmit Times and Duty Cycles: Because fewer redundant frames
are put over the air, radios spend less time transmitting.
Optimizes Larger Window Sizes: AX.25 v2.2 introduced extended sequence
numbers (allowing up to 128 outstanding frames instead of just 8). SREJ
is crucial here; without it, using a large window over radio would be
unusable because a single error would require re-sending dozens of
valid frames.
Maiko / VE4KLM
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