Wednesday, July 29, 2009

Improving call quality with Dialogic gateways

I've implemented my fair share of Microsoft OCS Enterprise Voice projects and each one has it's own nuances around voice quality. I've gathered a list of the common issues encountered with Dialogic gateways and their fixes which have worked well for me.


Tanjay phone doesn’t produce “comfort noise”

Description: When a user from a “Tanjay” phone calls a PSTN user across a voice gateway such as a Dialogic, the PSTN user doesn’t hear the white noise (comfort noise) typically present on traditional phone conversations. The PSTN user assumes the line has been disconnected and often will say “hello, are you still there?”.

Resolution (Dialogic): Typically you don’t want to enable VAD (Voice Activity Detection) on the gateway however this feature fixes this issue. From the voice gateway click on VOIP then Media and set the VAD to “on”.


Audio levels rise and fall through conversation

Description: When an OCS user calls a PSTN user through a voice gateway, the audio levels rise and fall as though something is adjusting volume. Also at the beginning of a phone call the audio is lower than normal.

Resolution (Dialogic): Set the Automatic Gain Control (AGC) for both IP to TDM and TDM to IP calls to “off”. The reason for this change is that in R2 they included AGC as part of the base application. Levels are automatically adjusted at the client device (and server).


The ringback tone continues to play after the caller picks up

This issue is caused by the gateway not accepting “early media”. With the release of OCS R2, “early media” is a feature which permits OCS devices to complete the call setup quicker. The Dialogic gateway must be set to “Always” for this to function properly.


I hope this helps some of you out there.



  1. It is not a good idea to set early media to "Always on".
    Some GSM cards connected to the PBX for cheaper GSM calls play an informational voice prompt before the call is actually connected. If you dont enable early media, this prompt cannot be heard, and you only hear the ringback until the called person picks up his GSM phone. If you enable early media, you will hear the prompt, and also the counter for the call starts, even before the person picks up the GSM phone.

    So a trial and error is always required for early media setting.

  2. Thank you for your post. We are deploying a new Lync system, and these changes fixed our quality issues!