Packet lossage

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The Purple Panzer
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Packet lossage

Post by The Purple Panzer » Sat Jul 07, 2012 3:26 pm

I've just moved from a somewhat flaky DSL line to a cable modem that's significantly faster (i.e., 10x). I see my lag on servers has gone *way* down, but now I'm seeing some percentage of packets being lost - the percentage being in the low single digits. I've never seen that before; does this mean that some UDP packets are just never arriving, or could they be arriving out of sequence? Given the increased speed/increased packet lossage (which I don't think I ever had before) am I better off, or not?

A second, perhaps related issue, though not with my connection. On of my admins mentioned that (on all the servers he plays on) the lag he gets from /lagstats doesn't subjectively match his play experience - which seems to him a lot more laggy than the numbers suggest. It wasn't clear if he had any significant jitter (I think not), but is there any mechanism by which this could be true? It seems to him that it's very significant, i.e. that when he's told the lag is 32 ms, his feeling is that it plays like about 200+ ms. It isn't just on my servers. I've never heard of anything like this either - does anyone have any thoughts? I can only think it might be delays in his video rendering, etc. I apologize for the vagueness of this second question - I will try to get his machine specifics, etc. - but thought it worth asking if anyone else has had this kind of experience, or might have some idea of what it might be.

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JeffM
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Re: Packet lossage

Post by JeffM » Sat Jul 07, 2012 4:52 pm

for item 1).

Yes UDP packets do get lost and do come out of order. Packet loss usually has nothing to do with speed, but how congested the routes are from your connection to your destination. So you may have more speed on the link from your house to your ISP, but one of the routes from the ISP to the game server is not able to deliver all the packets. Usually there is nothing you can do on your end about it. It is the nature of UDP communication.


for item 2).

That makes sense to me. The lagstats you see are a rolling average of the latency between you and the server. The playability of a game involves the latency of ALL players combined at every instant. If you have a lag of 30ms, and the guy you are shooting has a lag of 170ms, that ends up being 200ms latency when you try to shoot that one guy. If someone else has 45ms then you'd only have 75ms lag when interacting with her. BZFlag doesn't deal with latency in any way so they all just get drawn on your screen with no indication that those players are at radically different positions then you think they are.

So yeah, his statement sounds about normal, that's just what happens with how BZFlag works. It's a LAN game, it doesn't know how to handle lag or packet loss.
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