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Rick RudolphFlag for United States of America

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Routing 25 ATA's over 5 VOIP lines

We are installing a number ATA's either Cisco SPA's or Grandstream ATA's at a number of different locations. Each location is on a private network, however we do have static WAN IP's for the Firewalls. Each ATA has ethernet Available, but not Copper 2 pair.  Our goal is to pay a VOIP provider for about 5 VOIP Lines, that would be shared by 25 ATA's. Most of the traffic will be outbound dialing, and we would want the ATA's to rollover to the first available outbound line. We do ideally, want to be able to inbound dial to the ATA's using extensions.

Where would we get started in finding a VOIP provider that can help us with this, or would this be best done with on some sort of On Premise Gateway, which we would host at our NOC?

All comments and suggestions are appreciated.
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ArneLovius
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Each ATA will need its own VoIP "line", this is equivalent to 25 phones each needing their own line.

To be able to use 5 "lines" across 25 ATAs you would need to run a VoIP PBX.
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So the VOIP PBX would need to be on the same Local Area Network as the ATA's correct?
That's unlikely to work as you describe it.

You can use SIP FORKING however you probably need to run your own PBX to achieve this. I suspect a voip supplier would not support that confguration.

We would use 3CX, locally or cloud hosted, and set each ATA up as an extension, and a sip trunk from a suitable supplier. I'm unclear if you want a single number to ring multiple ATAs or each to have its own, but with a proper PBX set up to control the system you are able to do whatever you want.
PS - can't speak for all PBXs but with 3CX no, each phone can be "remote". If you only have one phone per location, you just need the phone. If you have lots of phones in one particular location, running an SBC on that location would be recommended. The SBC s/w is free, you would just need a suitable box to run it on.
The dialing back is a feature that is very much a wish list item, not really a necessity. The key feature is the dialing out and the possibility of sharing rollover outbound lines for many ATA's. The reason for dialing in is simply to test the health of the system. I can also do that by monitoring the activity of the ATA's on the IP side.

The ATA's will be connected to a door access control systems where a visitor will be using a telephone key pad to request entrance from a resident. So I need dial tone at the device. The phone call goes over the PSTN, is either answered or not by the resident. The resident then presses a key if they want the door to open. The DTMF tone is monitored by the system and a solenoid is activated if the correct key was pressed.

So we have very low volume of calls going out of any one device, and all of the calls are of a very short duration.
What type of PBX do you have now? And I assume each location has multiple doors. All you'd really need are voice gateways at each location with enough FXS ports at each location. You should be able to have extensions assigned to each FXS port and interface with the VoIP system in place.

You'd be best off hosting your own PBX (and might as well leverage it for the business operations in the building as well). ccomley described how it could be done with 3CX. It's very true that you don't HAVE to have a PBX on the same LAN, especially if you get SBCs in place at each location. Another option would be to take advantage of a VPN tunnel if one is already in place between all of the locations.

Here's a link where you can read on devices that work with 3CX: https://www.3cx.com/voip-gateways/

If you tell us more about your existing telco layout, we might be able to leverage what you already have
OR of there are multiple doors at any given site, instead of individual ATAs, use an FXS gateway with sufficient ports, e.g. Patton Smartnode. These are quite smart and can probably be configured to work without a PBX in the system BUT, they're fiddly and I'd personally still use 3CX as teh main call switching hub, and have it configure the Patton units as individual extensions pure and simple.
FXS gateways, FXO gateways, and voice gateways are fundamentally the same thing. I used the term voice gateways to try to stay brand agnostic, but it really is more of a Cisco term. VoIP gateway would actually be the most appropriate term. The response from ccomley is correct, but is very 3CX specific (I'm a certified engineer with a dusty certificate). Also correct is the fact that Patton equipment is a PITA to configure. Even 3CX support would sooner set the devices up for you themselves than walk you through making sure it's set up correctly.

But it would still come back to the very same thing: Do you have phone systems in place at any of the locations now, and if so, which one? 3CX is a good one assuming that you don't have one in place.
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