This document describes how to solve the problem when Cisco Unity does not accept DTMF tones from a PIMG (PBX IP Media Gateway).
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The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
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The Cisco Unity PBX IP Media Gateway products are integration devices designed to offer a high-quality connection between Cisco Unity or Cisco Unity Connection servers and your existing traditional private branch exchange (PBX). The Cisco Unity PBX IP Media Gateway (PIMG) is an 8-port, stackable integration device that emulates a digital or analog phone (station) on the PBX side and uses the Session Initiation Protocol (SIP) in order to connect to the Cisco Unity server over a LAN or WAN.
Unity does not accept digits (DTMF signals) entered from phones connected to PBX, but you can hear the Unity greeting and other messages.
PIMG uses SIP in order to connect PBX and Cisco Unity server over a LAN or WAN. Cisco recommends that you use RFC 2833 dtmf-relay mode when the SIP protocol is used between PIMG and Cisco Unity.
In the PIMG configurarion, change the RTP DTMF-relay mode value in the Gateway Advanced tab settings to RFC2833.
This configuration change allows the PIMG to pass DTMF SIP signaling from the PBX to Cisco Unity.