Success! P25 international linked repeater system

[VK2LK]

Hi all,

As many of you know, there are several P25 machines round Sydney, as per the post here. We now have the P25 repeater at GPT linked into a global network the currently has repeaters in VK, ZL and Hawaii. Previously as a proof of concept, John, ZL4JY and myself set up a temporary link between two P25 repeaters (specifically the Motorola Quantar) one on the bench in my shack, other on Johns bench in his shack and we communicated between VK and ZL

The linking is established by a second hand CIsco router, with a V.24 synchronous serial interface on it. The router encapsulates the V.24 traffic, then into an IPsec VPN tunnel to our hub site, located in Hawaii. In the future, we will be adding more stations, so stay tuned.

For anyone that is interested in how we did it, John, ZL4JY has documented the whole project on this site here:- V.24 Link project at p25.ca

To anyone with P25 gear, please feel free to hop and have a chat. The repeaters are there for everyone to use.

Enjoy!
73
VK2LK

[VK2PR]

Congratulations Matt, John and Justin! Love your work.

[VK2LK]

Cheers Peter,

It's awesome to work "DX" with the awesome clarity of a P25 signal, no noise, just crystal clear voice

Cheers,
Matt

[VK2AAH]

Hi Matt,

Brilliant work...

I assume that this would work for a mixed network of Quantars and Tait TB9100s?

What service provider are you using for the VPN and how tolerant to latency is this network?

Cheers


Richard
VK2AAH

[VK4DU]

Well done to all involved.

Catch you next time I'm in Sydney.

Rgds
Glenn

[VK2AAH]

I just tested it out locally from my office in town- I haven't heard anything yet from ZL or KH6... very interested in testing this.

The potential for this type of strategy to be used for a inter-VK network without needing to clog the band with links is something I think the WIA and clubs should be looking very closely at... even think about putting some money into funding the IP links.

Cheers


Richard
VK2AAH

[VK2JDH]

IThe potential for this type of strategy to be used for a inter-VK network without needing to clog the band with links is something I think the WIA and clubs should be looking very closely at... even think about putting some money into funding the IP links.

Cheers


Richard
VK2AAH

Good work. As aside the IRLP network has been doing this for 15 years, althought the RF tail at each end is generally not digital.

The only issue I can see is the hub and spoke topology adding voice delays for say a VK to VK call if it's got to go to a hub OS. Plus the reliability / redundancy of a single point of failure

A mesh is better, but harder to implement I guess.

Appologies in advance if any of my assumptions above are incorrect.

Dave

[VK2AAH]

Dave,

If the linking between sites is IP based the only single point of failure would be up to each site. You don't need a mesh system to achieve very good reliability as long as you can set up a VPN using 3rd party infrastructure (such as a Telstra cloud). We configure my employers emergency services network that way, though the IP service is very expensive... hence why I"m curious how they are doing this! If an affordable solution that supports P25 were available it has potential for an inter-VK linked network to be achieved.

Cheers

Richard
VK2AAH

[VK2JDH]

Dave,

If the linking between sites is IP based the only single point of failure would be up to each site. Richard
VK2AAH

True , I was basing my comments off the statement the they are linking to a hub OS, to which other P25s connect to.

If the VPN tunnel could be made to 'on demand' connect to the appropiate P25 repeater directly or a hub in VK if would reduce the delays.

In any case ,as with the IRLP reflectors, if you know there is a delay you allow for it in the QSO.

[VK2LK]

Thanks Richard,

At this stage, only V.24 Synchronous equipment will work on this network. This is a limitation of the vote comparator we are using, which only has V.24 inputs/outputs. I believe the more modern gear is native IP, and Motorola make it backwards compatible in order to make migration easier. I can't speak for the Tait gear, but I'm pretty sure it doesn't support Synchronous V.24 (as it's really a legacy Motorola thing)

The VPN is provided by us - the Cisco routers contain IPsec VPN endpoints, and they all go back to a central site. Latency isn't too bad, about 130ms pings on average. Latency doesn't seem to bother it at all, it just adds delays, and sometimes you can de-key and hear the last word or two of your own over, which sounds strange at first until you realise whats going on. The best bit? Those Cisco routers cost well under $100 each, and some even have the WIC-1T serial card in them that does the V.24 work.

Oh - one final thing, if the V.24 circuit drops out, or the VPN drops, or for whatever reason, the Quantar can't connect to the master site, it will go into "fall back in-cabinet repeat" mode, which means it just reverts to being a repeater, with no network connectivity.

There are plans to do some more with this network, as theres a VK3 that wants to be linked in as well.

Hi Matt,

Brilliant work...

I assume that this would work for a mixed network of Quantars and Tait TB9100s?

What service provider are you using for the VPN and how tolerant to latency is this network?

Cheers


Richard
VK2AAH

[VK2AAH]

Hi Matt,

It is a brilliant system and you & Justin deserve a lot of credit for pursuing this. I'm disappointed that it is very Motocentric (by necessity) as that limits the ability to source gear, though that it is not a problem now because of the sheer volume of surplus Moto bases. In the future surely ethernet based linking would be the way to go?

And sub-$100 Ciscos... you really don't want to know what we pay for them...

Cheers


Richard
VK2AAH

[VK2LK]

Yes,

That's pretty much it in a nutshell - full P25 IP based voters are still very new in the grand scheme of things, and as I'm sure you know, they charge like wounded bulls - I would expect a new GCM8000 to be in the region of $30-50k - easily. Maybe more.

John, ZL4JY and myself have done analysis of the traffic going over the V.24 serial interface at this thread here, and also have investigated the current P25 IP connectivity and the two seem to be very similar once you ignore the PHY layer. I believe with time and effort it would be possible to build a bi-directional V.24 to IP bridge with something simple like an Atmel AVR, though there are licensing concerns as it deals directly with the P25 DVSI/IMBE codec. Even if the licensing was not a problem, the effort involved in programming would take a fair bit of time.

The P25 standards specify how fixed infrastructure talks over TCP/IP, and I'm pretty sure that the Tait gear would use this to interface to the networks infrastructure.

Thanks for the kind words! as the system grows activity will grow as well..

Cheers,
Matt

[VK4DU]

As Richard says, it really is a great job.

P25 works so much better mobile than D-Star (specifically designed for it, bandwidth considerations, etc), but P25 development was held back (to a certain extent) by a lack of linking.

[VK2AAH]

Matt,

Just had my first contact with Bob, NH6XO and I had my boss keenly listening to the audio quality. I couldn't detect any latency, just a very slight slurring of the odd word but still a massive improvement over an analogue repeater. I'm already looking at this strategy using IP for overseas taskforces... it has enormous potential.

Cheers

Richard

[VK2LK]

Hi Richard,

Thanks again for the compliments and feedback. The next steps from here are already happening, expect some more progress soon!

Cheers,
Matt

[VK4DU]

Hello Matt

Is the link still up?

Rgds
Glenn

[VK2LK]

Hi All,

The linking has changed since this last post. Currently GPT P25 repeater is running in standalone mode due to a hardware failure on the linking router. GPT will be linked back to Horsely Park and the international linked system as time permits..

Since then, Horsely Park has been added into a new global linked system that has repeaters in Hawaii, USA, Germany, New Zealand and Australia. Please hop on and put a call out! The more people that use this system the better!

Cheers,
Matt

[VK2PR]

Awesome Matt, great work! Congratulations to you and everyone involved.

[VK2AVR]

Great effort Matt, well done

[VK4DU]

Thanks very much for your efforts.

Will give it a shot in December when I am in Sydney.