How do you determine the amount of bandwidth required for VoIP?


Is there an easy way to determine the amount of bandwidth required for a given number of voice paths through an IP network? I want to be certain that there is sufficient bandwidth to avoid quality issues with voice transmissions before going down the VoIP road.

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Here's an article that covers bandwidth consumption. You might find it helpful, TheCount. See the links on that page as well, for more information.

"VOIP Bandwidth consumption naturally depends on the codec used.

When calculating bandwidth, one can't assume that every channel is used all the time. Normal conversation includes a lot of silence, which often means no packets are sent at all. So even if one voice call sets up two 64 Kbit RTP streams over UDP over IP over Ethernet (which adds overhead), the full bandwidth is not used at all times.

A codec that sends a 64kb stream results in a much larger IP network stream. The main cause of the extra bandwidth usage is IP and UDP headers. VoIP sends small packets and so, many times, the headers are actually much larger than the data part of the packet."

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There is a simple calculator that will help you determine this:

You need to know something about the type of CODEC used for voice compression in your particular case (as noted in JimLynch's answer), as well as the packet frequency, so that the calculation will have validity.  Hopefully this will help you ensure you have sufficient bandwidth for good voice quality.  Be certain that you have enough bandwidth, because if you don't you will get packet loss, and as soon as that happens, your going to get IMs/emails/calls from everyone from the CEO to the janitor.  Don't ask me how I know!  Good luck!

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