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Horrible static when unmuting.


Tom Waterman
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Ok so here I have a snom 820 running firmware ver snom820-SIP 8.4.22 55096 with PBXnSIP version 2011-4.2.0.3981 (Linux). When someone places a person on mute everything works fine. They can stay on mute forever. However, sometimes when the unmute themselves the phones plays very loud static to everyone. It happens randomly but often. Any thoughts would be greatly appreciated. The owner of the company has one and is now asking if I should find him a different phone. Please help.I have also posted this in the snom phone forum. I am not sure it is a PBX problem but I have had it with different versions of Snom phones.

 

Regards,

Tom

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This is definitevely a problem with the SRTP MAC decoding which seems to be wrong. The phone actually should never play out anything if the MAC (like a cheksum of the SRTP packet) is not okay. The problem is obviously that the rollover counter increments (happens every 22 minutes @ 20 ms packets), and the phone gets out of sync. I believe in e.g. snom 821 or m9 it should be fine, but the 820 has a relatively old SRTP implementation that obviously need some extra TLV. If you have a 821 around, this is definitevely worth a try.

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This is definitevely a problem with the SRTP MAC decoding which seems to be wrong. The phone actually should never play out anything if the MAC (like a cheksum of the SRTP packet) is not okay. The problem is obviously that the rollover counter increments (happens every 22 minutes @ 20 ms packets), and the phone gets out of sync. I believe in e.g. snom 821 or m9 it should be fine, but the 820 has a relatively old SRTP implementation that obviously need some extra TLV. If you have a 821 around, this is definitely worth a try.

 

I am not sure I can tell the president of the company sorry you need a new phone. Is there anyway to upgrade this via firmware? I have an 870 on my desk does that suffer from the same issues? thank you for all the help.

 

Tom

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There should also be a way to use a new firmware. 8.4.22 is not the latest AFAIK, http://wiki.snom.com/Firmware/V8/Release_Notes/Change_Log_V8 lists the things that have been fixed in the meantime. If 8.4.31 still has the same problem (sorry I dont have a 820 here for checking), you need to open a trouble ticket for the phone and ask them to provide a fix.

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