The different possible BigBlueButton conference types cause different network and CPU loads. However, this affects not only the BBB server, but also the participants who use very different Internet providers and who have to share the connections with family members and neighbors. Remember that the whole of Germany is in the "home office" during the Corona crisis. BigBlueButton allows you to combine different communication options:
pdf, ppt, jpg and png files can be uploaded to the server, automatically converted into the svg graphic format and distributed to the conference participants. This happens once when the presentation is activated and is done in a few seconds even for participants with poor network connections. Then only the signal to turn the page and the position of the cursor have to be transmitted during the lecture. Both can almost be neglected.
All audio signals must be collected on the BBB server and mixed together before they are passed on to all participants. If there are N subscribers with M microphones switched on, the server must process M × 0.04 MBits/sec and send N data streams to the subscribers, each with 0.04 MBits/sec. The mixing of the data streams is very CPU-intensive, so the participants' microphones should be muted as a matter of principle.
With video, the network connection of each individual participant and especially that of the server is stressed. Depending on the resolution, a rate R of up to 0.25 Mbit/sec must be estimated for each video data stream. For N participants with V cameras switched on, the server must receive a rate of V × R and send a rate of (N-1) × V × R and manage N × V data streams.
For the participants it should be noted that the upload speed is usually much lower than the download speed. Approximately 0.3 Mbit/sec must be estimated for the camera and voice signals.
Screen sharing takes the most bandwidth. The actual bandwidth for desktop sharing depends on the size of the area chosen by the presenter (full screen and region) and how often their screen updates. At the low end, if the presenter’s screen is largely idle, the screen sharing application will transmit about 0.2 Mbits/sec; at the high end, if the presenter’s screen is updating frequently, the BigBlueButton server could transmit 1.0 Mbits/sec. For a session with N users, BigBlueButton server would also transmit N desktop sharing streams (the presenter gets a stream as well for their Screen Sharing Preview window).
The following possible combinations are ordered by the server load caused. Of course, you can switch between the options during an event and all conference types are authorized. In a classic digital lecture, however, constantly transmitting the audio and video signal of all participants is not expedient.
- Presentation mode + audio transmission of the speaker.
- Presentation mode + audio and video transmission of the speaker.
- Screen sharing + audio transmission of the speaker.
- Screen sharing + audio and video transmission of the speaker.
- In addition to 1.-4 .: audio and / or video transmission of one participant posing question.
- Audio conference: all participants have switched on the microphone and speak alternately.
- Panel discussion: a few participants share audio and video signals, all others only watch and listen.
- Video conference: all participants share the audio and video signals.