New Quake 2 Lithium server in Europe

[Jay Dolan]

i notice if you play around with the rate, say 100 (which is 100 bytes) game gets yellow bars in the netgraph and plays choppy. changing the FPS however does something similiar which allows players to go through some objects not normally able to. (q2ctf1)

Sure, if you set the rate to anything lower than what the game actually requires to communicate (4000 on a small average server, 8000 on a busy map), then the server will actually skip frames (updates) that it would otherwise send to you, to try to limit your downstream bandwidth to your requested rate. This is possible because the server keeps a buffer of exactly what state has been sent to each and every client. So if you miss one frame, the server can still prepare a delta update for you at the next iteration of its big loop. It's the same mechanism the protocol uses to recover from lost packets.

https://github.com/jdolan/quake2/blob/master/src/server/sv_send.c#L548

Those yellow bars on your netgraph are frames that were dropped due to requested rate limiting on your behalf. Similarly, pegging your framerate to an artificially low number will also limit opportunities for your client to process updates from the server. Rather than never receiving a given update due to rate limiting, multiple updates (packets) pile up, and end up effectively buffered by your operating system. Your client then reads and processes several server updates in a single client frame in order to catch up. It doesn't mind doing this, and reading server frames is hardly the expensive portion of the client's main loop (drawing the world is). But what you end up seeing, of course, is entities flying across your screen or snapping into or out of existence.

https://github.com/jdolan/quake2/blob/master/src/client/cl_main.c#L2464