> Again, this games claims to send 10-20mbps per client. The quadratic part would be the full outgoing from the server, those numbers are not the full outgoing. The full outgoing is claimed to be 10-20 gigabits per second.

Per-client bandwidth -> O(n), where n is the number of players. 10 - 20mbps for this game per-client. Let's say n=1000. O(n) because each client needs to receive state for n other players (yes, each client also receives state for its own local player too)

Total bandwidth sent from server -> O(n*n), where n is the number of players. Since the server sends 10-20mbps per-client, and there are 1000 clients the total bandwidth sent from the server is 1000 * 10-20mbps -> 10-20gbps.

Where the quadratic comes in: When you increase from n=100 to n=1000, per-client bandwidth increases by only 10X, but total bandwidth increases by 10*10=100X O(n*n), because packets are now being sent to 10X the clients, but ALSO and the bandwidth sent per-client is 10X (because each client now has 10X players it needs to receive state for).

Thus quadratic. FIN.