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15. Use Your ISDN Codec as a POTS Phone Patch.   7/12/12 by Dave Immer

New ISDN codecs and some legacy models can make and receive calls to and from standard POTS (Plain Old Telephone Service) telephones, and any phone available via the PSTN (Public Switched Telephone Network). Your ISDN line must be configured for Alternate Circuit Switched Data and Voice, which is what you typically get anyway.

It sounds as good if not better than standard POTS hybrid units such as Telos One or Gentner. And you will have the advantage of better metering and, in some units, digital i/o.

I have tested a handful of ISDN codecs that deliver a relatively clean POTS signal:
1. APT Tokyo & Equinox
2. Musicam Suprima & RoadWarrior
3. Telos Zephyr Xstream  & Classic

Other brands like TieLine and Mayah have the capability also.

Older models such as the CDQ Prima, PrimaLT, RoadRunner, APT Milano, 3D2 and DolbyFax do not have this capability, even if you do have a CSD/CSV enabled ISDN circuit.

But if your codec is able to initiate a call to a POTS phone, place the encoder in the G.711 mode and choose mu-law (ยต-law) as the protocol (North America.) Some of the newer models auto-sense incoming Voice mode calls and adjust accordingly.

Let me know if you have questions or comments about a phone patch. Thanks,

-Dave