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VoIP Bandwidth

Posted on 2009-12-22
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Last Modified: 2013-12-27
I am trying to figure out the necessary bandwidth for good quality VoIP calls. The situation is our company has International branches that use IP phones and in some areas (ie. Countries in Africa) the QoS is poor. These countries only use 1 IP phone. I do not know their bandwidth/ISP situation, but I do understand it relies heavily on available/dedicated bandwidth.

What I need is a general overall guidance of the bandwidth needed per IP Phone connection (ie. 100 kbps) and some of the factors that can deteriorate the QoS (ie. weather, equipment, web browsing etc.). I also need to pass this info to non-technical people so they will know what they have/can do to improve IP voice calls.

We will be improving our Voice communications sometime in the new year, but I need an interim solution.

Thanks.
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Question by:ILSI
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Expert Comment

by:Lazarus
ID: 26108937
Here is a handy link to figure out your VOIP Bandwidth: http://www.bandcalc.com/
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by:feptias
ID: 26111856
Most IP phones support the G.729 codec and it uses considerably less bandwidth than the standard uncompressed G.711 A-Law/u-Law. However, you need to check that G.729 is supported by the equipment at the other end. For example, if using Asterisk, you need to purchase a license for G.729 and install it on the Asterisk server.

Internet connections are often asymmetric - i.e. they provide more download bandwidth than upload. VoIP useage is symmetric so don't make the mistake of only looking at download bandwidth/speed. Web browsing over the same Internet line as you are using for voice would therefore have less impact than uploading a large file. However, it is always best to avoid simultaneous shared use of a low speed Internet connection for both data and voice. VoIP speech quality over an Internet connection may be influenced by factors beyond shared use within your own location because there is usually some wider sharing of equipment further upstream - e.g. you will see reduced access speed when other subscribers are accessing the Internet.

An alternative to the very handy bandwidth calculator suggested by lazarus98, is this comparison table:
http://www.ozvoip.com/voip-codecs/
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by:ILSI
ID: 26114600
So feptias are you suggesting for example that 100 kbps for 1 voice connection may only be the download speed? And that it will require double that? Or that 100 kbps is for symmetric usage (50up/50down)? I am asked to throw out a number '384 kbps' that is needed for voip. I am not sure where this number came from and if it included the factors you mentioned and that I have found in my research.
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by:Lazarus
Lazarus earned 164 total points
ID: 26115036
We allocate about 90k fo ours. Vonage VOIP call needs about 90K, but a G.729 will use only about 35Kbps bandwidth for a call. We error on teh high side for qualities sake.
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by:ILSI
ID: 26115050
lazarus98 - is that 98k total bandwidth (both ways)?
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by:feptias
ID: 26115140
The bandwidth requirements are each way. So if you are using the G.711 codec it will need 72kbps upload and another 72kbps download. However, Internet service providers usually quote the download speed - they do not add their max download and upload speeds together so you don't need to add them together when you are comparing.
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by:Lazarus
ID: 26115181
The 90Kbps is for both, yes.
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feptias earned 168 total points
ID: 26118669
Don't get over concerned about adding upload to download requirements - the sum is irrelevant. The critical factor is to know which one is slowest - usually it is the upload speed that is slowest. So if your client device is on an Internet connection that has 0.5Mbps download and only 125kbps upload, then you need to be concerned about Codec choices with respect to the 125kbps limit. Once you hit that limit, the speech quality in one direction will be degraded.

However, if the Internet connection is used for both voice and data then you may find the data (e.g. web browsing) is using up some of the download bandwidth, but very little of the upload. In this case it is possible that the download bandwidth will all be used up before the upload is. VoIP requires equal amounts of bandwidth in each direction. If using silence suppression then bandwidth is only used when one party is speaking, but the requirement for peak demand remains the same.

Is that 384kbps figure for just one call? If so it is hard to see how they arrived at such a figure.
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by:CoreyMac
CoreyMac earned 168 total points
ID: 26280790
~90Kbps for G.711 and ~32Kbps for G.729.  The codec data rates being quoted as much lower are not taking into account the other overhead in getting the packets from point A to point B.  There are several factors that will affect voice quality:

The actual CODEC used (G.729, G.711) - Latency, Jitter, Bandwidth and Packet-Loss

You can push one of these to the design limit and not really destroy the call, but you cannot push them all and keep a usable voice call.  You should learn about all of these parameters and investigate what your environment can realistically support before you can know how things will behave and what you need to do.

It is worth noting that most people cannot hear the difference between G.729 and G.711 for voice calls on good, clean and fast connections.  Music (on hold) and FAXing is another story entirely...  You cannot generally FAX except using G.711 and even then you should slow the FAX down to 14.4Kbps (or even 9600bps) at a maximum.  Music is only barely tolerable on hold for G.711.  G.729 is awful for constant tones like music.

Here is more detail that you likely want, but it is excellent for reference.

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml
the PDF
http://www.cisco.com/application/pdf/paws/7934/bwidth_consume.pdf

For the Internet to carry voice, Jitter and Latency are usually more of a problem than just bandwidth.
Take a look at Ping Plotter Pro (http://www.pingplotter.com) to help measure what is going on and also seriously consider setting up a QOS endpoint in each location as part of the infrastructure so you can keep track of the state of things.  Almost any low-end Cisco router will do things like this as will some others.

Here are some more bandwidth discussions:
http://www.hh.se/download/18.59906e3a11ee92e66ac80009684/2_4_Calculating_Bandwidth.pdf

http://www.cisco.com/en/US/docs/ios/solutions_docs/voip_solutions/TA_ISD.html

Here is a calculator available online:

http://www.voip-info.org/wiki/view/Bandwidth+consumption

http://www.voip-calculator.com/calculator/lipb/

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