telos Gateway

Legacy, telos discontinued work on this free software

For companies of a certain size, optimally sized PBX (20-30 branches) are hard to find. Most currently available PBX either offer too few branches or far more than needed (for an unacceptable high price).

Looking for other concepts, one finds that an existing local area data network might as well be used for transfer of telephony audio and signalling information, interfaced to the wide area telephone network be means of some gateway.

Locally, a network of IP phones and PCs with sound cards, running software like Netmeeting or ohphone, could be used as a replacement for the traditional PBX system. The mentioned gateway then provides the interface to the traditional phone network.

There are several standards available describing the transmission of real-time audio data over local area networks, which do not provide a guaranteed Quality of Service (QoS). One of these standards is the ITU standard H.323.

isdn2h323 is a Linux based H.323 - ISDN gateway.

• ISDN and H.323 users can initiate a connection.
• The number of simultaneous incoming and outgoing calls is limited by the number of available ISDN channels only.
• H.323 users can specify the ISDN number of the other party.
• The gateway's administrator can assign an ISDN MSN to a H.323 user. This makes it possible for an ISDN user to call a H.323 user directly. The gateway will choose the H.323 user id depending on the called ISDN MSN.
• The gateway discovers an available H.323 gatekeeper and registers with the gatekeeper. It's possible to specify one or more phone prefixes the gateway is responsible for.
• ISDN's touch-tones (DTMF) are translated to H.323's user input messages and vice versa.
• Automatic gain control (AGC)
• Automatic echo compensation (AEC)
• To avoid security problems the gateway offers an option to restrict the IPs allowed to use the gateway for an outgoing ISDN call.
• The status of the lines and the configuration of the gateway are written to a HTML file.
• Errors and some other informations are logged using Linux's syslog() feature.
• Three H.323 codecs are supported: ALaw, muLaw, and GSM.
• Least Cost Router

This gateway has got two major problems at the moment, that makes the program a development and not a production version:

• You can get a bad audio quality with some H.323 clients.
• The bugs seems to be caused by the used third-party openh323 library. If you know a solution for one of these bugs, send us an e-mail.

You can download the latest isdn2h323 version as source code or as RPM package. Because the gateway depends on the libraries openh323 (version 1.6.0) and pwlib, you have to install them, too. You can get the libraries as source or as RPM packages. Proceed to the download page.

There is a newsletter on the gateway.

If you find a bug, be sure to report it to us.

• We do not support the RedHat distribution.
• We only support isdn2h323 by the mailing list, not by phone.