AudioCodes Mediant 1000 MSBG – Audio Quality Issue

So it’s been a long time since I last posted an article on the site, Microsoft Lync Server 2010 has been keeping me busy to say the least. During a recent deployment I experienced an issue with audio quality for both inbound and outbound calls when utilising an AudioCodes Mediant 1000 MSBG gateway running firmware version 6.2. The best way I can describe the problem was that when the call was answered it sounded like the person on the other end was stood next to a jet engine, there was a lost of noise and loss on the connection. When running  a syslog on the mediant, in debug level five, and reproducing the issue I could see the following events:

SRTP Error – failed decrypting RTCP packet: authentication failure (2) [Code:3700e] [CID:30]
SRTP Error – failed decrypting RTCP packet: wrong SSRC (11)
SRTP_PCK_DROP_AUTH:1  [Code:5004] [CID:30]
ErrMgs=9 Invalid RTP version (= 0)

When initially looking at these errors I was thinking either a coders or certificate issue could be causing the problem. This was actually incorrect, after some investigation it turned out that my TDM Bus Settings were not configured with the correct LAW attributes. To resolve the issue I performed the following:

1. Log in to the AudioCodes Mediant 1000 MSBG device.

2. On the left hand side of the screen select the “Full” radio button.

3. Ensure you have select the configuration tab and expand the “VoIP” container.

4. Expand the “TDM” container and then select “TDM Bus Settings”.

5. In the TDM Bus Settings page, if you are located in Europe set the “PCM LAW Select” value to “ALaw”. If you are based in the United States this should be set to “ULaw”.

6. Set the TDM Bus Clock Source value to “Network” and click submit in the bottom right hand corner of the screen.

7. At the top of the screen click the “Burn” button to save the configuration to flash and then reset the gateway.

That’s it, your poor quality audio issue should now be resolved.

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