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Calculating VoIP Bandwidth

One of the first things an organization has to do when considering VoIP deployment - whether on premise or hosted services - is to calculate how much bandwidth is required for VoIP calls. Bandwidth consumption has to be estimated early on as that will determine if the business needs to increase Internet speeds or otherwise optimize their network.

There are many online tools that will automatically calculate VoIP bandwidth and any service provider will be able to provide a table showing bandwidth consumption per call on their service. However it is better for the enterprise to know how these figures are calculated, since unscrupulous vendors can try to trick clients with misleading calculations.

What Affects VoIP Bandwidth Consumption? Some of the factors that influence VoIP bandwidth include:

Codec and compression used (G.711, G.729, G.722 or any other proprietary formats)
Header compression - (RTP + UDP + IP for instance),this is generally optional
Individual packet size - anywhere from 10 to 320 bytes
Layer 2 protocols such as Frame Relay or Point-To-Point Protocol
Voice detection or silence suppression technology

Calculating VoIP bandwidth consumption is an essential step in preparing a business network for the addition of voice traffic. Bandwidth consumption reduces if compression is used. This means that codecs like G.729 will use less bandwidth as compared to G.711. When longer packets are used, bandwidth consumption drops since the overhead is reduced i.e. space taken up by the header. If the voice is being compressed, it is better to compress the header data as well to offer maximum savings. Packet size is usually between 20 to 30 ms on different services.

Calculating VoIP Bandwidth

Suppose the service provider uses G.729 codec on their network. If the size of each voice packets is 20 bytes and uses MP headers, the calculation will be as follows:

Total packet size = header of 48 bits + compressed IP/UDP/RTP header of 16 bits + voice payload of 160 bits = 224 bits
PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps
Bandwidth per call = voice packet size (224 bits) * 50 pps = 11.2 Kbps

This final figure gives us the bandwidth required on a per call basis. To get a rough idea of the maximum bandwidth consumption, the business needs to multiply this number with the highest number of concurrent calls they expect. Calculating VoIP IP bandwidth is pretty simple once you know the factors and how they influence the final calculation.

Bhagwad is an expert consultant on Business VoIP Explained

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