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New Member

Clipped voice when calling mobile phones

We have a CM 3.0 installed with an IOS H323 gateway having an NM-HDV-1E1 card for ISDN PRI connection to the PSTN. We had some impedance mismatches with this card which were fixed (hopefully) by inserting an adaptor between the 75ohm BNC output of the CSU/DSU PRI unit and the E1 RJ-48 port (which is balanced 120ohm). When calls are made to any PSTN phone everything sounds great, except when we call mobile phones. The voice stream is clipped and is not continueous all the time.

Does anyone encountered the above problem before?

Thank you in advance.

New Member

Re: Clipped voice when calling mobile phones

Have you looked into "no vad" on the dial peer statements? This may solve some of the clipping since the gateway may be interpreting the cell phone delay as the end of an audio segment (finish of a sentence from the conversation) and therefore could be not transmitting voice at that time, giving a clipped result. This is the way VAD (Voice Activity Detection) is designed to work.

Also keep in mind that cell phones in general are not the best mechanism to be testing voip quality to.


New Member

Re: Clipped voice when calling mobile phones

dear abertram thanks for the reply. Actually the problem was duplex-mismatch on the router gateway ethernet interface which was causing a lot of CRC errors and collisions.

However, I still get problems with this configuration. On my Call Manager application event report I get A LOT of "tcpenvprocess connection error" with the IOS gateway. Also the Attendant complains all the time that she loses calls when she tries to transfer them etc...anyway, I'll look into it. Thanks

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