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Polycom ISDN Gateway, audio quality issues

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Polycom ISDN Gateway, audio quality issues

Dear appreciated community members, we have recently deployed a Polycom ISDN Gateway (software version 1.0.0-77) which is registered on a GNU Gatekeeper (registered in GDS). On the same GK, we've registered a Cisco MCU 4520 (sw version 4.5(1.85)). The Polycom ISDN GW is connected to LAN and to a BRI line. We have frequent use cases of participants calling in to videoconferences by using mobile/landline phones (if for whatever reason one has no VC device nearby...).


We can successfully establish an audio-only call from any mobile/landline phone to a MCU channel via the ISDN GW, but the audio announcement received from the MCU is not audible/understandable because what one can hear is practically only random noise.

The next thing we tried is to establish a phone call via ISDN GW to a Cisco MX300, and audio tests gave the same result, a very bad audio quality (just noise), not usable for a normal call.

We have already tested the ISDN BRI line which seems ok. Other calls to the same devices which do not involve the ISDN GW (to MCU, MX300) provide good audio quality.

I can confirm that we are using the standard cables which were delivered with the device.

I already tried to register a support ticket with Polycom technical support but the ticket was immediately closed as we have only basic warranty from Polycom and there's no possibility currently to file a support ticket.

Studying the product documentation, I found a setting in "BRI network interface settings", which is called "ISDN Voice Algorithm" and which does not appear in our software version. It would allow to change aLaw/uLaw used for ISDN voice calls - any experience with that? Does it appear in other Polycom ISDN GW software versions? Could that possibly cause the audio quality issue?

Another doubt is : the ISDN GW receives electricity via PoE - could possible interferences here cause bad audio quality? And if yes - how to solve that?

We are now waiting to be contacted by the vendor company to see if we can get a replacement unit, but I'd like to know whether anyone else has experienced a similar issue with the ISDN gateway and how to solve it - just in case it is not the ISDN Gateway itself which is causing the audio issue.

Many thanks in advance for any hints.


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