Video Conferencing Network Bandwidth Requirements

Video conferencing has been around for over two decades and the associated technologies have evolved dramatically. Corporations, big or small, use video conferencing on a daily basis. It is an important technology that is coined as a business enabler as well as a tool for interactive, face to face communication. In old days video conferencing was merely about setting up a connection so that all participants could see each other, waive their hands and say “Hi, I can see you OK. Can you see me OK?”.  That was the old time experience. Today users demand supreme quality, seamless “virtually there” experience. The good news is, we have the technology to meet that demand.

This article talks about the network requirements to achieve a practical and truly successfully video conferencing implementation that your users will have no hesitation in using.

I am assuming you have bought the right video conferencing equipment which includes the codec, the camera and the professional display (or projector in certain implementation) and you have a conference room which is sufficiently designed for conducting video conferencing. Now let’s get down to the network budgeting part.

When it comes to video quality there are two factors that you have to consider: resolution (number of pixels in the image) and frame rate (how quickly the image refreshes). Your network bandwidth requirement has a direct relationship with these two factors. Nowadays video compression techniques and advanced codecs do a good job in terms of reducing bandwidth consumption but as we understand every video compression algorithm has its limit.

Take a look at this example. An HD720 video call carrying 24-bit image color depth that refreshes 30 times every second (i.e. 30 frames per second or fps) generates about 664Mbps of video traffic (1280 x 720 x 24 x 30). After compression by the highly efficient codec it comes down to between 2Mbps and 3Mbps when it is transmitted over the network. The table below summarizes the bandwidth requirement against various video qualities.

Resolution / Bandwidth Relationship

What determines a good image? The answer is resolution. The higher the resolution the better the image. However, in a typical video conferencing situation, the key is to display the participants as sharp and vivid as they can be. How much detail we can get about a person’s outlook is determined by the number of pixels of the image that is transmitted. Depending on the number of participants in the room, the maths are calculated differently. Take a look at the pixel requirements:

One-person video conferencing

Let’s take CIF quality as an baseline. A full screen CIF image delivers 101,376 pixels. In a typical single person call, the face, shoulders and upper chest area usually occupies 25% of the screen. This gives 25,344 pixels. To run a CIF call you need at least 384Kbps of bandwidth.

Four-people video conferencing

Let’s assume we want to achieve the same detail, i.e. same number of pixels per person. Based on the CIF baseline, we need to deliver 101,376 pixels in total. In a four-people call the face, shoulders and upper chest area per person typically occupies 10% of the screen. This gives a total screen pixel requirement of 1.013,760 which means we need an HD720 call to delivery the same pixel requirement per person. This equates to a bandwidth requirement of at least 2Mbps.

Now you can see the difference between a single and a multiple participants call.

Frame Rate / Bandwidth Relationship

Frame Rate is a measure of how often the image gets refreshed (from one frame to another). This has a direct impact on the “vividness” of the image and how the participants perceive the video conferencing quality. Video codecs will dynamically adjust the frame rate based on the motion in the room but for a typical video call involving constant movement of the participants, 30 fps is considered the minimum standard. Anything lower than 30 fps, participants may perceive an unsteady or unnatural video. In any practical implementation we should not sacrifice frame rate for a lower bandwidth requirement.

Dual Video

Many video conferencing calls nowadays involve PC presentation. This is handled by the H.239 data protocol which embeds the PC screen in the video call so that you don’t need to set up a separate web conferencing session. This is a handy feature. H.239 protocol also handles the sound coming from the PC so it is ideal for a multi-media presentation. When there is a PC screen embedded in a call, your primary image (the participants) may be degraded because the codec will dynamically lower the resolution (number of pixels) that is being sent across. The percentage that is assigned to the PC screen can usually be capped by a configuration setting on the codec.

Concurrent Video Calls

Some video codecs support multi-site feature. This means a single codec can act as a bridge to connect two or more concurrent video calls. You’d need to take this into consideration when calculating the overall bandwidth requirement.

Conclusion

When calculating the bandwidth budget for your video conferencing implementation, it is important to look into the two factors that affect the quality of the call:  resolution and frame rate. Higher resolution and higher frame rate require higher bandwidth. It is also necessary to consider the dual video and concurrent call situations.