Canadian Hydro Electric Utility Establishes Phone to Radio Interoperability

The challenge was to provide a simple device that would accept a call from an IP PBX phone and make a connection to a radio. Furthermore, the device would need to ring a phone from a mobile radio. The Omnitronics IPR110+ RoIP Gateway offered a unique solution.

An IPR110+ Radio over IP Gateway was installed to accept SIP (Session Initiated Protocol) calls to and from an extension using Radio produced DTMF signals. The DTMF audio from the radio is decoded and translated to 1 of 12 SIP addresses. Depending on the DTMF number, up to 12 SIP extensions can be called or for more contacts, the switchboard can be added to the list.

In some cases, the PBX does not support the digital status messages of connectivity. Omnitronics was able to modify the device firmware to add a “Go Ahead Tone” indicating to the phone user that the call connection has been made. Normal procedural protocol would then require the phone user to listen to the radio to make sure they didn’t interrupt a current conversation.

VAD (Voice Activity Detection) is used by the IPR110+ RoIP Gateway to generate a PTT on the radio. Unlike VOX (Voice Operated Switch), all syllables of speech are sent to mobile users. Whilst the PTT is being set on the radio, voice data is stored in the IPR device and only released after the RF path is stable.