Video conferencing/Bootlenecks

Regardless of the capacity of the available ones, the load for the server or server cluster may not be sufficient. The increased demand during the pandemic in schools and other educational institutions has increased significantly during COVID-19. If unregulated free capacity unrestricted access to the videoconferencing servers is possible, reliable access to the server infrastructure may not be possible for everyone. Especially for planned meetings or courses with interaction between the participants On the one hand the plannable reliable use of resources is important and on the other hand the administrative technical side has to avoid overloading the server infrastructure. If there is a load on the infrastructure, all or many users may be affected by this load. BigBlueButton is not equipped with a booking system. The use of a regular booking system for rooms e.g. in universities can be extended to digital rooms. Such a booking system at universities avoids double occupancy of available rooms and the physical conditions and legal requirements for fire protection and evacuation measures naturally require a capacity limitation for available physical rooms. Extension of this booking system to digital conference rooms also allows to control the maximum load for a server cluster. This way, known booking procedures and digital infrastructure can be transferred from physically available rooms to video conference rooms.

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Requirements Capacity Server

The test provides a limitation for the capacity of the server (see Video conferencing/Booking and Video conferencing/Testing). A booking / reservation mechanism helps to avoid to overload the capacity of the server.

Requirements on the clients

In general, clients participating in a videoconference with a growing number of video streams are exposed to an increased demand of CPU and memory resources for processing and decoding video signals. The capacities of the clients for parallel processed video streams vary dependend on the hardware used by the client. Therefore, all participants should use video streams only if they are actually necessary for the video conference meeting, so that no one is excluded from participating due to hardware constraints. Just like online music jam sessions it is recommended to have a wired cable connection to your network infrastructure at home or in the office to assure good connection.

Learning Task

• Old hardware used by the participant could lead to bottleneck, that the client could handle e.g. 4 simultaneous video streams only. Why is it difficult to understand for participants with recent hardware, that they cause the connectivity problems for the participant with old hardware, because they switch on their videostream. What are required information given to the participants by the moderator of the video conference, to avoid these problems for some participants with poor hardware.
• Network bandwidth is shared resource. Explain why switching off video streams (or even audio streams) are measures of a sustainble use of IT infrastructure and bandwith as a shared resource.

• (Cyclic Still Image Update - CIU) Analyze the principle of a cyclic still update (CIU) and explain how it can be used to reduce bandwidth and server bottlenecks on the server side (BigBlueButton) or bottlenecks in peer-to-peer connections (Jitsi-Meet).

Cyclic Still Image Update (CIU)

This feature is not necessarily implemented by video conferencing systems. It is a way to significantly reduce the bandwidth usage of a videoconference.

Framework condition

• 500 students are in a very large course,
• a lecturer would like to answer individual questions from the group of students or discuss aspects that arise in the context of an Inverted Classroom session after the students have watched the asynchronously provided teaching-learning video.
• Managing 500 video streams in parallel and making them visible to the lecturer on one screen does not offer any real added value for the lecturer,
• If one person is speaking (lecturer, student), this video stream should be distributed by the speaking person to all other participants at the standard frame rate of the video conferencing system (one-to-many)

Conversion

With 500 students and one teacher, there are 501 people in the video conference, of which a maximum of one video stream would have to be transmitted in standard video quality by a person speaking for a longer time (One-to-Many). All other video streams can be displayed with a cyclic still image update (CIU Cyclic Imaga Update). To put it simply

• 'a video stream with 25 frames per second used for this
• 25 single images of 25 participants to be updated in one second.

In the above example with 501 people in the videoconference, using the bandwidth of one video stream, all still images would be exchanged once every 20 seconds. Also, sending the video stream from client to server or in peer-to-peer connections between clients would be limited to sending one frame every 20 seconds if there are a large number of clients in a video channel, instead of distributing a video stream between the participants. When participants take over the speaker role, the CIU switches to the default video stream mode.

See also

• Online Music Jam Session