[Namaste-dev] Re: Thoughts on ACP Interoperability

Timothy J. Salo salo at saloits.com
Sun Jul 13 13:12:53 PDT 2008


Frank Brickle wrote:
> ... *What is Required for P25 Compliance? *
> 
> At a minimum, a P25 radio system must provide interoperability with 
> these mandatory P25 Standard components:

No, AMSAT isn't going to build a P25 radio _system_ -- that
is probably a bigger project than building a satellite.
It is conceivable that, under some conditions, AMSAT or
other amateurs _might_ build a _device_ that interfaces
in some fashion to a P25 system (but I doubt it).

>     * /The Common Air Interface (CAI) specifies how information is
>       coded, transmitted and received over the air. /

If anyone wants to communicate over the air with a P25
system (i.e., a P25 repeater) I strongly suggest that
they simply buy a P25 radio, rather than implement the
CAI.  P25 radios aren't all that expensive.

> A set of defined system interfaces allow the P25 system elements to 
> communicate with host computers, data terminals and the public switched 
> telephone network (PSTN).

I understand that there is an interface that enables repeaters
to interconnect over an IP network.  If amateurs really, really
want to interconnect natively with P25 systems, I suggest that
they consider this interface.  But, I also suggest that there
are more useful things for them to spend their time on (like
make sure the ACP works and provides useful functionality).

> However, thanks to the use of IMBE, having an AMSAT system that 
> implements any function where the codec is applied is completely out of 
> bounds until such time as the intellectual property issues surrounding 
> it are resolved.

Not really.  This simply means that amateurs run into
intellectual property issues if they implement the codec
in software.  But, you can simply buy a chip that does
this.  This is what amateurs are doing for D-STAR (which
I understand has the same intellectual property issues):

   <http://www.dvdongle.com/DV_Dongle/Home.html>

> For the sake of completeness, I would point interested readers to other 
> areas of the website where P25 vendors are criticized (by GAO and 
> others) for failing to provide complete implementations of the standard. 
> It would appear that vendors have been lagging grievously in providing 
> precisely the interoperability parts of the standard, while they've 
> shown remarkable alacrity at fielding systems employing the proprietary 
> codec technology.
> 
> In short, the vendors seem largely to have blown off interop, but have 
> demonstrated great motivation at shouldering out competition. My private 
> impression is that AMSAT could implement the full buffet of CAI specs 
> and wind up with systems that have nobody to talk to at the P25 end. A 
> person more cynical than myself might infer that P25 is nothing more 
> than yet another scam to ensure virtual monopolies for large vendors.

Fortunately, most (or probably all) of these issues become
irrelevant to us, if we focus on providing IP connnectivity
that can be used by P25 systems.

-tjs



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