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We're running a VOIP system over Comcast. The problems are:

  1. Some calls don't complete (both incoming and outgoing)
  2. Some phone calls get terminated in the middle of the call.

I want to run some kind of throughput test on the Comcast service (which could test the throughput several times per second) to ensure that there is enough bandwidth available for the phonecalls. Which free or trial software or applications would you recommend?

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2 Answers 2

up vote 2 down vote accepted

For the most part, VoIP is not bandwidth-intensive. It is, however, quite sensitive to variable latency. In your testing, you need to test both aspects. I'd recommend you look at setting up an iperf server on one end of your connection. You'll then connect to that from a client on the other end. Iperf will be able to not only report on the bandwidth available, but also on the jitter of the connection, which is quite useful when troubleshooting VoIP issues.

Additionally, you may want to look at doing some real SIP tests using SIPp. You'll be able to send incrementally increasing numbers of calls through and find where things start breaking.

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iperf is a useful bandwidth testing tool. You run it in server mode on a remote server, then run a client to connect to it. This is a Linux/BSD tool, so you may need a LiveCD.

You might be interested to know that we routinely have trouble as well, due to large latency spikes within Comcast's network.

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Thanks for your answers. draeath, how did you solve your problems? Did you switch to a T1 or did you make some changes to Comcast? –  Charles Apr 22 '11 at 23:07
Hi Charles. We're still having the problems, after some workaround to make them sting less. We have our own fiber link scheduled for installation as a permanent solution. One particular note was that we had to tweak the "qualify" sip setting for some of the phones, as they would unregister if they were polled while our ISP was waving 'issues' - we have not found any way to help with the call quality or drops, though. –  draeath Apr 27 '11 at 16:48

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