JVB bandwidth

Dear All,
I would like to understand the relationship between the bandwidth of JVB / jitsi-meet client and the number of participants in one room.
I set up all the jitsi components (including prosody, jicofo, jvb and jitsi-meet) in the same server. In the config, I already set the lowest resolution as the following:
resolution; 180,
constraints: {
video:{
aspectRatio: 16 / 9,
height: {
ideal: 320,
max: 320,
min: 100
}
}
},
disableSimulcast: false,

At the server I can see the incoming ~ 13Mbps and the outcoming ~ 62Mbps
And at a jitsi-meet client I can see incoming ~ 7Mbps and the outcoming ~ 1.5Mbps
There were 30 participants at that moment.
It meant that even with the lowest quality, the average outcoming BW from client is already 1.5Mbps ?
And the incoming BW is necessarily as high as 7Mbps to joint the class of 30 persons ?
How can I understand the difference in the incoming and outcoming bitrate of the server ?
And why is the outcoming of client not equal to the incoming of the server multiplied by the number of participants?
Many thanks in advance for your explanation and guide to reduce these BWs

Client BW
ClientBW
Server BW
ServerBW

A client send 3 layers, server forwards the high resolution layer to a receiver only for the person on stage and the rest are the thumbnails.
If the receivers bandwidth is not so good it may not receive the highest resolution but the next one.
If all participants are sending 3Mbps but everyone are watching in tileview (180p depends on peoples screen size) you will see a big difference in in and out on server. Basically everyone sending HD and no one is watching it.

Thank you @damencho. Can I know what are the three layers sent out by a client? Can I modify these layers to fit better to the given network environment ?
Furthermore, during the meeting, sometimes I see people just disconnects, and I cannot see them again (sometimes they get back but sometimes not at all) if I dont refresh the browser with Ctl-Shift-R. My questions are do you have some logs to know more about the reason of disconnection ? How can we force the refreshing in a shorter and auto manner ?
Many thanks

This is browser implementation controlled by some parameters. Chrome is normally sending 180p, 360p, 720p if networks allow it so if you set your deployment resolutions to 360p I guess you will drop the HD layer.

This should be tracked form client-side logs through Nginx → prosody … If you are talking about signaling drops. If it is just media, in that case they can still chat with you but you don’t see or hear them than maybe checking jvb and its network.

Thank you @damencho.
Can I go down even lower resolution (then bitrate) than 180 ? The thumbnails video is less than 180 isn’t it? How can I just send the lowest resolution for the thumbnails video only.
Many thanks