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The telos H.323-ISDN Gateway has retired

At telos we still receive numerous support requests and other feedback about our ISDN to H.323 Linux gateway. However, meanwhile there are other and probably more flexible solutions for interfacing ISDN (BRI or PRI lines) to H.323, SIP and other voice over IP systems.

The most advanced of them being the Asterisk open source PBX.

More information on Asterisk can be found at

When interfacing ISDN lines to h.323 signalling, there are several major things you can achieve with Asterisk that are not possible with our gateway:

  • You can in addition interface to the more modern SIP protocol. H.323 is getting less and less popular.
  • You can use CAPI, MISDN or ISDN4Linux based hardware.
  • You can use a virtually unlimited number of channels in either direction.
  • You have a full-featured PBX controlled by a flexible dial plan.
  • Using HFC chip-based ISDN cards you can operate in NT mode. This means that you can connect an ISDN telephone directly to your computer. Please see for a description.
  • Asterisk is widely used and fairly well tested.

One thing you'll note when looking at Asterisk is the complexity of the configuration files. Since it is an open and flexible system there are many parameters to set. One of the smallest possible useful applications is to obtain a voice-over-IP account and have asterisk rout all incoming internet calls to a predefined number within the companies PBX. A computer with an ordinary ISDN card and a network connection is all you'll need for that.

However, it is also possible to use Asterisk as the PBX for a large company including interactive voice services (IVR). It is understood that this requires a lot of complex configuration.

If you are looking for professional support and/or consulting regarding Linux-based PBX set-up, please don't hesitate to contact us.