Public VOIP Trunk/Dialplan to avoid PSTN?

Over the course of setting up some interoffice trunks and setting up a dialplan to avoid hitting our provider, I was curious if there was a way in theory to avoid going through the PSTN and dial other VOIP systems directly. Like a DNS server/DID registration for VOIP Systems. Maybe this is already done at the provider level, but I was just curious more than anything.

i figured this was already thought of. Thanks.

It never really caught on. But if you provide your own peering it can help your routing.

If you’re going to have multiple systems in multiple locations and you want them to be able to dial their DIDs without hitting the PSTN (and thus the actual DID provider) then you need a SIP Proxy/SBC. While DUNDi can work, it is the poorest of choices for this.

You set up the Proxy/SBC so that all the PBX systems are peered with it, they send all their PSTN calls to it. The Proxy can then determine what routes those PSTN calls take, including routing to the PBX where the DID lives. So it’s PBX -> Proxy/SBC -> PBX when needed and PBX -> Proxy/SBC -> PSTN when needed. Then it would be PSTN -> Proxy/SBC -> PBX where DID lives because that routing is there.

Or you can continue to route inbound directly to each PBX but the beauty of the Proxy/SBC doing the inbound as well is if a PBX goes down for some reason and another PBX can take calls for it, the Proxy/SBC can failover and reroute the call to the “backup PBX”.

If this is a small system, just set up Outbound Routes on each PBX that recognize the DIDs of the others and select the appropriate interoffice trunk. Assuming that you can directly dial remote office extensions (via the interoffice trunk) but your users aren’t doing that, perhaps some training is in order.

If this is a very small system (and you don’t have local resources such as POTS, PRI or GSM gateways), it’s simplest to just have one PBX serve all. For such a system, choose a trunking provider that can fail over to staff mobile phones, should the PBX be down or inaccessable.