One Way audio problem from SCCP to SIP phone

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Jul 7th, 2009
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I am having a one way audio issue with a set up that was working for a long time. We have a SIP 'door phone' (third party) which can make calls to our internal phones and from the SIP phone you can hear everything, voice and dtmf from the phone that its calling, but the one receiving the call cannot hear anything we are using SCCP 7975g and 7940 phones. Its interesting that it just stopped working. Is there anything i can do to find out where the traffic is stopping?

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Steven Smith Tue, 07/07/2009 - 09:52
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Is the phone on the voice subnet or the data subnet?  You might want to try to sniff the traffic from the SIP device to see if it is transmitting, and from the phone to see if it is receiving the traffic.  After that, you should look to see if you have any ACL's that might be interfering with the RTP traffic.

Also, on the phones, you can press the ? button twice (quickly) to see if they are receiving packets.  If you are, you might not have any audio in the actual packets.  If you can capture the audio using wireshark, I can check to see if there is audio in the packets.

ismaelcolon Tue, 07/07/2009 - 10:01
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ok, i am pretty sure there are no acl's blocking traffic as it was working properly. the sip phone is on its own vlan and we do have ip routes in the uc500. also i did the call statistic by pressing ? teice and it shows that its sending and receiving packets. i am not sure how to use wireshark to capture the audio apckets. i will look around to see how.

Steven Smith Tue, 07/07/2009 - 10:11
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You should be able to plug in behind a phone and turn on the sniffer.  It has been awhile since I have done this, so I am not sure if there are any settings that need to be changed.  If you can't see the packets from behind the phone, let me know.


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