[op25-dev] Re: Full asterisk support?

ikj1234i ikj1234i at yahoo.com
Mon Feb 25 15:22:47 UTC 2013



The build sequence (asterisk vs. gnuradio) is not important.

The folks who produce app_rpt have their own forked version of asterisk, which was the one that I used.

Everything is coupled so loosely that there should not be much problem to mix & match this stuff - although of course ymmv : )

The integration with asterisk is intended to be pretty extensible - currently the examples all use app_rpt in its "dumb" mode.  I'm sure that's a good starting point but that a lot more could be done with some imagination.  The choice of app_rpt was mainly because that already provides almost the perfect set of semantics for what we want, and was pretty mature in terms of capability.  However the link to asterisk should be viewed as a generalized "VOIP" bridge to OP25 not limited to repeaters in the conventional sense... (think "ROIP")

There are some places where the existing asterisk app_rpt metaphor works less than perfectly.  The first is the app_rpt model in which audio that's been received over the RX leg of a FDX link must first be demodulated and re-converted back to analog before feeding through the app_rpt main path.  This is Not Good due to the highly lossy IMBE codec.  A true digital P25 repeater would just regenerate the signal digitally before retransmission.  Unfortunately however this would cut app_rpt out of the picture completely.  A direct digital repeater is being looked at (with very slow progress).

Another problem is that DTMF tones (used heavily within asterisk and app_rpt) are verboten in P25 (P25 has replacements in the form of packets that are defined in the protocol for the purpose of sending dial digits).

At this stage in time I don't view the extra digital/analog/digital reconversion steps as a problem.  That would presuppose that the FDX links were working fully end to end.  Before that can happen we must first debug the individual legs, which is much easier to do separately...

Looking forward to getting feedback from experimenters - it will help to guide the development!

73

Max

--- In op25-dev at yahoogroups.com, "Doug Bade" <kd8b at ...> wrote:
>
> I guess another important question is if I am going to use asterisk, do I
> want to start with an asterisk build first?? Or add it to this Debian box??
> The build information does not really seems to mention where asterisk enters
> in.. ( I have experience with Allstar Link and Asterisk PBX's for phone). 
> 
>  
> 
> Doug
> 
> KD8B
> 
>  
> 
> From: op25-dev at yahoogroups.com [mailto:op25-dev at yahoogroups.com] On Behalf
> Of Doug Bade
> Sent: Monday, February 25, 2013 9:43 AM
> To: op25-dev at yahoogroups.com
> Subject: [op25-dev] Re: Full asterisk support?
> 
>  
> 
>   
> 
> I am going to throw my hat in too as a test site...
> 
> I have been copying the mail on this group for a while but had not really
> caught the fact that the project was repeater capable. I have a station that
> I can direct FM down pretty much to DC... ( Mastr III) ex-edacs station. It
> has modulation ports I have been using for GMSK for D-Star to date using
> sound FOBS. I am going to try to build all this but have a steep learning
> curve as I have not even ever built the GNU radio parts.. So maybe I can
> also be a test bed. I do have a P25 analyzer for setup. ( I maintain P25
> systems (among other things)for a living ) I have some dedicated Atom rack
> mount servers for building on..
> When I built pre-re4quisits last night I had errors on SDCC and
> SDCC-libraries on a fresh Debian build. Is the system particular about
> versions of those? or just go get what I can find?? My Debian box was
> building GNU radio stuff when I went to bed.. so I will get back to it
> tonight..
> 
> I never really introduced myself here just been lurking... I am an LMR
> systems engineer for a living and work on public safety P25 systems.. but am
> an extra ham who likes to tinker.. P25 has always been a goal, as P25 cards
> upgrades for my Mastr III station would run about $8000.00 if I did it the
> Harris way :-)
> 
> Doug
> KD8B 
> 
> -
>


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