A number of different types of connections to Transcoding Conferencing Nodes are required for a conference to take place, or for a gateway call to be made.
A connection can be a call or presentation from an endpoint to a Virtual Meeting Room or Virtual Auditorium, a backplane between Transcoding Conferencing Nodes, or a call into or out of the Infinity Gateway. In this context, a connection is analogous to a port. In some situations, a single conference participant such as a WebRTC or Skype for Business client requires two connections (one for the video call, and one for presentation content).
When a connection is proxied via a Proxying Edge Node, the proxying node also consumes connection resources in order to forward the media streams on to a Transcoding Conferencing Node. A transcoding node always consumes the same amount of connection resources regardless of whether it has a direct connection to an endpoint, or it is receiving the media streams via a proxying node.
Each connection to a Transcoding Conferencing Node requires a certain amount of resource, or capacity.
In general, when compared to a single high definition HD 720p call:
- a Full HD 1080p call uses twice the resource
- an SD standard definition call uses half the resource
- an audio-only call uses one twelfth of the resource.
However, note that:
- A WebRTC call using the VP8 codec uses the same amount of resource as H.264, and the VP9 codec uses around 25% more resource, so VP9 at 720p uses the equivalent of 1.25 HD resources, and VP9 at 1080p uses the equivalent of 2.5 HD resources. Note that within the same conference some participants may use VP9 (if they are connected to a Conferencing Node using the AVX2 or later instruction set) while other participants may use VP8 (if they are connected to a Conferencing Node on older hardware).
- Conferences that use the Adaptive Composition layout consume additional Conferencing Node resources. The actual amount of additional resource depends on many factors, but as a guide, it uses an additional 0.5 HD of resource for each video participant that is on stage (up to 13 participants per conference). This is regardless of the call quality / resolution of the conference itself and each individual participant's connection (codec, bandwidth and so on).
- H.323 audio-only calls are treated the same as video calls for resource usage purposes.
If you want to limit video calls to specific resolutions (and limit the transcoding node resources that are reserved for calls), you should use the Maximum call quality setting
The following rules determine how hardware resources are allocated and consumed by conference and gateway calls in a Pexip Infinity deployment. They are measured in terms of HD resources, and assume that the Maximum call quality of the conference is set to HD (more or less resources are used for Full HD and SD respectively, as described above):
Standards-based endpoints (SIP or H.323) participants:
- Each participant uses 1 HD resource.
- They do not require an additional connection resource when sending or receiving presentation. Presentation is sent and received using the call connection.
Skype for Business / Lync participants:
- Each participant uses 1 HD resource.
- They each require 1 additional HD resource when sending or receiving presentation.
WebRTC VP8/VP9 participants:
- VP8 participants use 1 HD resource and VP9 participants use 1.25 HD resources for main video.
- They use 0.5 HD resources for sending presentation content. This is always 0.5 HD resources, regardless of the Maximum call quality of the conference, the codec, and whether it is sending images, PDFs or screensharing.
- They use no additional resources to receive normal (still images) presentation, and use 1 additional HD resource (regardless of codec) when receiving full motion presentation.
- If an endpoint is restricted due to bandwidth limitations to a lower resolution than the conference's maximum call quality, the transcoding node will use the appropriate lower level of resource for that endpoint's connection. For example, if it is limited to an SD connection it will use 0.5 HD resources.
Each conference instance on each Transcoding Conferencing Node reserves a backplane connection at a resource level corresponding to the conference's Maximum call quality setting, to allow the conference to become geographically distributed if required. The exceptions to this are:
- Deployments with a single Conferencing Node. In such cases, no backplanes will ever be required, so capacity is not reserved.
- Conferences that are audio-only (in other words, where the conference has its Conference capabilities set to Audio-only). In such cases, capacity equivalent to one audio connection is reserved for the backplane.
- Only one backplane connection is used for each conference on each Transcoding Conferencing Node, regardless of the number of other transcoding nodes that are involved in the conference. Note that on the Administrator interface, backplanes are displayed as unidirectional, so a single link between two nodes is shown with two backplanes, one in each direction. Likewise, a conference between three nodes is shown with six backplanes. However, for resource allocation purposes each node would require just one backplane connection.
Pexip Infinity always tries to optimize gateway calls:
- A gateway call does not reserve resource for a backplane, but will use one if required (for example, if the participants are connected via different Transcoding Conferencing Nodes).
- If both of the participants in a gateway call are connected to the same node, and at least one of the participants is either a WebRTC VP8/VP9 client or a Skype for Business / Lync client, and there is currently no presentation being sent by either participant, Pexip Infinity reserves a backplane connection on the node to which the participants are connected. This is in case either participant starts sending presentation and that presentation is handled on a different node to the node to which the participants are connected, thus requiring a backplane to be created between the two nodes.
- For a gateway call to Google Meet, the connection to Google Meet always uses 1 HD resource (it uses VP8) for main video. The resources required for the VTC leg of the connection depend upon the type of endpoint and the Maximum call quality setting. If the VTC endpoint starts to present content then an extra 1 HD resource is used for the connection from Pexip Infinity to Google Meet. However, no additional resources are required if presentation content is sent from Google Meet.
- For a gateway call to a Microsoft Teams meeting, the connection to Teams uses 1.5 HD of resource if Maximum call quality is SD or HD, otherwise it uses 1.5 Full HD resources. The resources required for the VTC leg of the connection depend upon the Maximum call quality setting. No additional resources are required for the connection from Pexip Infinity to Teams for presentations to or from the Teams meeting.
- For a gateway call to a Skype for Business meeting, the connection to SfB uses 1 HD of resource for main video and will use another 1 HD of resource if either side starts presenting. The resources required for the VTC leg of the connection depend upon the Maximum call quality setting.
- If an API participant is the first participant to join a conference, it will reserve a backplane for the conference.
When a connection is proxied via a Proxying Edge Node, the proxying node also consumes connection resources in order to forward the media streams on to a Transcoding Conferencing Node.
A proxying node uses approximately the equivalent of 3 audio-only resources to proxy a video call (of any resolution), and 1 audio-only resource to proxy an audio call.