How Much Bandwidth Does VoIP Use?

How much bandwidth does VoIP use? In general, businesses have two ways of improving VoIP call quality – either allocate more bandwidth to VoIP calls or optimize QoS settings directly on the hardware running the network.

Since all kinds of data – files, audio, video, documents etc. – are being transferred over the same network, all of them are fighting to be first in line.

QoS settings take care of this to an extent, since it ensures that VoIP traffic receives the highest priority regardless of what other applications are using bandwidth at the moment.

Nevertheless there is only so much that optimizing can do. Sometimes the enterprise just has to increase the available bandwidth. In order to assess whether more bandwidth needs to be allocated, it is necessary to know exactly how much is being consumed by VoIP on your network.

Bandwidth consumption calculations are also necessary when evaluating the robustness of the network before VoIP deployment.

Calculating how much bandwidth is used by VoIP is not a difficult or arduous task, but you are required to have a basic knowledge of the various factors that influence consumption. Generally VoIP vendors are willing to provide a table showing consumption per call on their service to prospective clients.

While those calculations may indeed be right, it is always better to double check. The document will also provide all the other details such as codec, header type etc. that are necessary to calculate bandwidth consumption.

Factors Influencing Bandwidth Consumption

Overhead

Since VoIP transmits voice calls over the Internet, the voice signals have to be packaged into data packets just like other forms of media. There are usually multiple wrappers required for each packet that contain details such as the origin, destination etc.

These wrappers are collectively referred to as overhead and allow the packet to be routed correctly. Each layer of packaging such as RTP, UDP, IP and Ethernet contributes to the overall bandwidth consumption. Overhead can range from 25 to 35 kbps, depending on the optimization settings.

Codec

VoIP uses codecs to convert voice signals into digital data that can be transmitted over the Internet. Most codecs can be roughly divided into two categories – those that prioritize quality at the expense of bandwidth and vice versa. For example, the G.729 codec utilizes compression algorithms to reduce the size of the audio packets.

This results in less than the best audio quality, although it is generally not noticeable. On the other hand, G.711 does not use compression which results in high quality calls but it uses a lot of bandwidth. The difference might be as much as 50-60 kbps. It might not seem much on a per call basis but when multiplied with the thousands of calls made by an enterprise during a typical week, bandwidth consumption can add up significantly.

Packet size

The size of the individual packets is somewhat related to overhead. Each data packet typically contains overhead plus the actual voice data and the size can vary greatly. Hosted VoIP vendors use either 20ms or 30ms for the most part.

Using larger data packets minimizes overhead consumption but can result in missing sections if an individual packet is lost. Smaller package sizes will have more overhead but can tolerate dropped or missed packets.

Taking the above factors into consideration, a one-hour VoIP call using the G.711 codec can take up to 85 MB of data. On the other hand, the same call may consume just 35 MB if the G.729 codec is used.

VoIP bandwidth consumption is a trade-off between voice quality and bandwidth availability. The right decision for an organization will depend on their priorities, requirements, costs and other business considerations.