How are feeds received - newbie

Hi
fair warning, this is a noob question. I’m not a programmer, but I have ideas on how to use Jitsi, and I need some basic info.

So. When there are 10 participants (lets assume all with HD cameras, full res), do all 10 receive the full HD stream form the rest - so 9xHD streams all the time? If they select full screen of one talker, and the rest is on the filmstrip, shown as a small thumbnail, does their browser still receive all full streams, and create the view (downsizing the images) locally, or its requesting the view as such from the server, and sent as one HD image?

Thanks

The jvb is the one forwarding hd for the participant on stage and low quality for thumbnails, this is tganks to simulcast, clients sending multiple resolutions of same feed

thanks. Does this mean that in filmstrip view only the thumbnail resolution is requested from the server, or the clients get all the HD and thumbnail streams too for every participant?

meaning if I have 10 people with lets say 2KBpbs upstream each for HD (and 0.1 for thumbnail), and I view them in filmstrip, do I have to get 21KBps data (10x2+10x0.1) or 1x2KBps+9x0.1KBps?

The second one