VoIP calls dropping out

Hi Experts,

I have a problem with my VoIP phone - conversations only last for a few minutes before they go dead.
This has happened with 2 different called numbers, so I don't think the problem is at the other end.

I have been using the same hardware and software settings for many months - without any problems until today.

My VoIP Router is a Fritz!Box 7490.
My phone is a Cisco SPA504G.
My VoIP provider is Maxo Telecommunications Pty Ltd.
I have a normal ADSL line - that is not used for any other purpose.

What could be causing this problem?
Are there any logs that would help identify the problem?

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Salah Eddine ELMRABETTechnical Lead Manager (Owner)Commented:

Which type of number your dialing?? maybe this can be caused by routes used by you Voip provider to reach the destination!! if the route use a slow connection or bad quality gateway the dead can occurs.

Best Regards.

José MéndezCommented:
What do you mean by "go dead"? Dead air?

Does it always occur at the same time mark? 5minutes? 6 minutes? Random?

Did you change the firewall settings?
LeighWardleAuthor Commented:
What I mean by "go dead" is:  I am talking, then there is silence at the other end, I ask if my callee is still there, there is no reply - clearly the connection has been terminated.

This happened with 3 calls yesterday - 2 calls were to a number that's with my VoIP provider.  The other one - I don't know if it was VoIP or POTS?

I have no record the call durations - but will use a stopwatch in future.

I have not changed firewall settings.
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José MéndezCommented:
It does not sound like your connection is terminated. One thing is to loose the audio suddenly, and another to experience a call drop. What you are describing seems like a call drop.

A sniffer capture would be very helpful to understand what happens to the both the SIP Signaling and to the RTP traffic carrying the audio.
LeighWardleAuthor Commented:
willlywilburwonka:  Thanks for your comments.
How do I organize a sniffer capture?
José MéndezCommented:
1- connect a computer to the back of the IP Phone and start a Wireshark capture. Initiate a SIP call. If you can see the SIP packets from the phone then you will be able to monitor its traffic when the issue reccurs. i don't know for sure if these models actually span the voice traffic over to the PC port just as the 7940-7960s do.

2- If you connect that phone to a Cisco switch, try configuring a monitor session like this:
(config)#monitor session 1 source fas0/9
(config)#monitor session 1 dest fas0/10

Connect a computer on port fas 0/10 and start a wireshark capture. Reproduce the issue, this setup will copy all the incoming and outgoing packets from port 0/9 over to 0/10.

3- Connect the phone to an old hub (not a switch) and connect a computer to the same hub. ALl traffic will be available to devices connected to the hub. Start a wireshark on the computer and reproduce the problem.

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