[aprssig] Fw: APRS-B? Protocol translation - please no.

Heikki Hannikainen hessu at hes.iki.fi
Wed Jun 26 00:36:31 CDT 2013


On Tue, Jun 25, 2013 at 4:30 PM, Andrew P. <andrewemt at hotmail.com> wrote:
> Would there be interest in a protocol-translating OpenTRAC-to-APRS digipeater (working both ways)?

Such digipeaters have been problematic before, and I would recommend
to be very, very cautious about it. In the past there were some
digipeaters which converted mic-e packets to plain APRS packets so
that clients not understanding mic-e could receive mic-e packets.
Sounds like a great idea, right?

The obvious problem is that then we had two different variants of the
same packet on the network, which would both proceed through duplicate
packet checking (different data contents: unique packets). Immediate
double traffic on the channel.

The next problem is that when the protocol capabilities differ, you'll
have degrade the packet contents, leave some fields out. And then you
can't restore them when converting back to the original format.

You'll also soon have more than one variation of the translation,
either due to you improving your converter, or another programming
implementing a slightly different algorithm, or somebody using
slightly floating point or integer data types and getting slightly
different rounding for coordinates or speed, or something like that.
Again, packet contents are going to be different, and duplicates will
be hard or impossible to avoid.

Some systems (like my aprs.fi) are going to receive both the degraded
translated versions and original packets, causing additional work to
figure out how to discard the translated ones.

I would very strongly support improving network level elements
(digipeaters, igates and such) to the direction where they keep the
transported packet content as intact as possible, and leave content
encoding/decoding to the endpoint applications. That would be a real
improvement and better allow further protocol improvements. Currently
a bigger problem is that digipeaters and igates corrupt packet
contents, remove whitespace or modify unprintable characters.

The Internet works great, and new applications have been easily
developed on top of it over the years, largely due to the fact that IP
routers do not care what is inside the packet. We should follow the
same approach.

- Hessu, OH7LZB


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