[aprssig] Precedence Bit and IP Encapsulation

[Robert Bruninga]

I'd love to hear if any system in APRS actually implemented the Precedence
bit?
http://aprs.org/aprs12/precedence-bit.txt

Basically it is making the Table-Overlay character a lower case character.
Back in 2013, the limit on implementing it was UIVIEW that wouild not let
a user enter a lower case overlay character.
But UIVIEW should no longer be a holdback...  Though probably radios
cannot enter a lower case either...

Bob, WB4APR


-----Original Message-----
From: aprssig <aprssig-bounces at lists.tapr.org> On Behalf Of Iain R.
Learmonth
Sent: Tuesday, May 19, 2020 11:38 AM
To: aprssig <aprssig at lists.tapr.org>
Subject: [aprssig] Precedence Bit and IP Encapsulation

Hi,

I am planning to begin work on an AX.25 over IP interface for the HamBSD
system. This will be based on RFC1226 [0] however I am interested in
updating this document to additionally cover quality of service and
security considerations. I have a draft published and would be very happy
to receive reviews and/or comments [1].

A question that I do not have an answer to is what to do about the
precedence bit when carrying APRS over IP networks. I'm talking here about
putting APRS frames directly into IP datagrams, not using APRS-IS.

It is possible to specify the quality of service that a packet will
receive by setting the differentiated services codepoint field in the IP
header. By default, IP traffic is "best effort". In my draft, I currently
set APRS traffic to be prioritized above other traffic, except for that
which has set the precedence bit. APRS traffic setting the precedence bit
will receive best effort treatment on the IP network, and will be dropped
in preference to dropping other APRS traffic.

An alternative is to treat APRS traffic with the default best effort
treatment, and APRS traffic with the precedence bit sit as "lower effort"
[2].

The decision here will rest on what this bit is actually used for in
practice. If it's for traffic that is of little value then perhaps it is
better to drop this traffic before dropping other traffic sharing an IP
link. What is the value of APRS traffic with the precedence bit set
compared to other "routine" IP traffic?

Thanks,
Iain MM0ROR.

P.S. If you know of someone that would be interested in commenting on this
draft, please feel free to forward this message on to them. I'm happy to
take reviews/comments directly about general AX.25 usage if they are not
relevant for this mailing list.

[0]: https://www.rfc-editor.org/info/rfc1226
[1]: https://tools.ietf.org/html/draft-learmonth-rfc1226-bis-03
[2]: https://tools.ietf.org/html/rfc8622

--
https://hambsd.org/

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