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I am fairly familiar with VoIP and I have my own VoIP PBX, and my provider is Twilio (for Voice) and CallCentric (for Fax). But How do providers like Twilio work exactly? More specifically:

  • How do VoIP providers get DIDs?
  • When I use my Cell Phone to call my DID on my VoIP SP, how does the cell phone provider know how to route the call to the correct DID?
  • Is there a way to also look up the route that the DID should go to? Is it like a DNS Server?
  • How can I tell who owns a DID?
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DIDs are assigned by the telcos which own them. A VoIP provider buys a block of DIDs from the telcos it uses where its VoIP network interfaces with the POTS network.

Your cell call travels from the cellular network to the POTS network, where it gets routed to the interface with your VoIP provider. POTS call routing is basically the same as it has been for a hundred years, and the subject of POTS routing is far too large to be discussed here, but it basically sets up a single circuit between two points; the cellular network and the VoIP network, in your case.

You would need access to the POTS providers' databases to figure out who owns a DID range.

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