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Community Member

isdn calls are soft


We have received feedbacks that making outgoing ISDN calls via PSTN voice is soft.

Have increase the input gain on the mgcp trunk but it seem like little improvement.

Would like to determine the isolation of this issue ? How to ensure that within the CCM, gateway are all ok and if there is any other way to capture information which can determine is on the service provider end having the issue ?


Hall of Fame Super Gold

isdn calls are soft

All calls produces a low volume? And which side has the low volume? Have you checked "show controllers T1/E1" for errors ?. And more importantly, have you judged the call volume with your own ears ?

VIP Super Bronze

isdn calls are soft

Just to get us started: gain/attenuation changes only take effect following a controller/interface shutdown. A reset is not sufficient.

Following that Paolo is on the right track here: it matters what direction of audio is quiet: PSTN to PBX (inbound) or PBX to PSTN (outbound). You need to find a number to reproduce this with before modifying the gain/attenuation. Some PSTN destinations - or callers for that matter - will be quieter than others; a byproduct of 100-year old infrastructure and electrical distortion over distance. Don't discredit soft-spoken people or a bad headset either; make sure you are chasing a legitimate problem here!

Once you've got an agreed upon and repeatable problem you should use caution modifying the gain/attenuation commands. This is a delicate balancing act and creating an imbalance will cause echo! The echo canceler relies on a delta in electrical signals between the transmit and receive paths to find echo and suppress it. Modifying the gain/attenuation directly influences that delta. Read this document to understand what you're modifying:

(called an ERL)
Hall of Fame Super Gold

isdn calls are soft

I wish I had Jonathan's eloquence sometime ...


Community Member

isdn calls are soft

No errors on show controllers E1

The soft volume from CCM to PSTN, the agents will received soft volume

MGCP a need for shutdown/no shutdown ?

Trunk service providers isolated them from equipments all tested volume ok.

Have raised a TAC case on this issue

Will update the findings and sharings

Thanks for the information

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