[Namaste-dev] Re: Thoughts on ACP Interoperability

Timothy J. Salo salo at saloits.com
Mon Jul 28 14:45:26 PDT 2008


I think I never replied to this...

Rick Hambly (W2GPS) wrote:
> Thank you for your input. I strongly agree that any external interface with
> the ground station should be IP based. That opens up a number of Ham-centric
> and emergency communications application interfaces that can easily be built
> on top of IP. 

Perhaps most importantly, using IP as the standard
interface for the ACP systems provides a satellite-based
communications service that will enable others to innovate
in the future.  If the ACP gracefully transports IP packets
between ground stations, then other people and projects can
develop and experiment with all sorts of not-yet-dreamed-up
projects. And, all this can happen without the involvement
of, or maybe even the knowledge of, AMSAT and the ACP project
team.

> The average satellite user of this ground station will be an individual in
> his or her home. Even then, the IP interface will allow that user to connect
> the ground station to their computer and exchange IP voice, pictures, video,
> files, etc. with the users on the communications channel.
> 
> Could we put applications like a P25/IP interface in our PC or laptop,
> thereby separating this applications issue from the immediate need to get an
> affordable ACP ground station built soon? I don't really know enough about
> P25 or its implications (technical, legal) to know.

My general answer is that _all_ of the application-layer
functionality should probably be removed from the ACP ground
station. The ACP ground station should, I claim, provide an
IP interface, and _maybe_ nothing more.  (_Maybe_ it should
include a microphone/speaker connection, but I doubt it.)

<Insert here my general whine about the apparent lack of an
ACP system-level architecture...>

With regards to P25, it's not apparent to me that anyone
has a clear picture of what the technical requirements are.

Some appear to want to develop a P25 transceiver that
is somehow associated with the ACP ground station.  This
appears to me to be completely infeasible (never mind that
you can simply buy a P25 transceiver).  In my view,
and I have never actually seen the P25 specifications,
this would be a very complicated project.  It would be
complicated technically (there are a lot of P25
specifications, and they provide lots of functionality).
And, while amateurs can transmit with pretty much anything
they can cobble together on amateur bands, I don't believe
that they can do so in any other part of the RF spectrum.
So, an AMSAT P25 transceiver would have to be FCC certified,
and maybe APCO certified.  I could continue, but I don't
want to beat this horse if it is already dead.

I think AMSAT should focus on making the ACP real, and
not get sidetracked into unrelated topics like P25.

Based on looking at this once before, if AMSAT really,
really wanted to interoperate with a P25 system, I
suggest that the ACP ground station look like a P25
repeater connected to an IP link.  I think there is a
P25 standard for linking P25 repeaters over an IP
network (or at least I think that one was under
development when I last looked at this).  But,
again, I recommend that AMSAT _not_ consider this.  It
is technically hard, and has a high risk of failure.

But, the fundamental question that hasn't been answered
is: What [technical] P25 problem is being solved?

o Let an amateur with an ACP ground station talk, though
   the ACP payload with someone far away who is using P25?

o Connect two P25 systems (with no amateur voice) through
   the ACP payload?

o ...

-tjs



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