descentchampions.org

This made me jump like a little girl!



From the game:



My question is how does the packet loss work for the display (% next to the ping.) A lot of the times I see the skipping but no packet loss will be shown or he says he can see packet loss but on my said it shows nothing. I am a bit confused about that.

When you set the PPS for a game, you're setting the rate at which ship positions update. The game uses those packets to measure loss. Those packets are given serial numbers, and the game knows how many to expect at what times, since they're sent at a regular rate. It looks back over the last 100 packets (which is about 3 seconds at 30 PPS) and counts how many are missing -- that's your downstream loss number.

Ping packets are send out once per second. They have timestamps attached, and the replies come with those same timestamps. So the ping displayed means you really did just send a packet and get a reply, and it really did just take that long. Those numbers are pretty solid.

Ping packets also include the measured downstream loss (from the other guy's perspective), which is where your upstream loss number comes from.

One of the glitches with the system right now is that the numbers only update when you get a packet. If the traffic goes totally dead, the upstream loss meter is never updated by incoming pings, and the downstream loss just cheerfully waits for the next (long delayed?) position update to arrive, and doesn't see any holes in the sequence in the mean time. So the system doesn't do a good job of alerting you when the connection has gone really sideways.

I've seen it behave oddly at other times, too. Sometimes it'll spaz out and count up to 100% loss, even though the other guy is clearly and smoothly flying around. I think it's getting confused about where it is in the sequence? Regardless, it seems to sort it out pretty quickly.

I haven't seen skipping with no loss reported (other than what I mentioned above), but I don't doubt that others might have. If there's some sort of intermittent interruption or delay in the connection, that would do it.

No doubt the system could be improved.

That teleport was pretty nasty. With an intermittent lag spike up around 1000 ms . . . something that bad can happen.

Thanks for the information Drakona. Yeah, I was confused due to watching side by side videos where one person will show loss while the other person does not show anything. Does anyone have a basic chart for which pps to use for each ping (not really EACH number?) Right now I mainly stick with 20 which is pretty good because most people I get around 100-150ish ms. I guess in the case of the video we probably should have went up to 30 pps which even in some of the cases it would not of helped. Also, I have not looked around yet but is there a log that tracks the network traffic? I know I can do it with 3rd party software but if its already in place that would be good to know.

I do see dropped packets in the gamelog.txt file.

17:06:13 Dropped UPID_PDATA: out-of-order packet 14 (last received 19).

That is that big burst from the video but that's the only one that it tracked. It does not show all the other times.

If you run Descent with the -netlog command line option, it dumps all network traffic to a somewhat-human-readable file, netlog.txt. I use it for debugging. The file's usually pretty big, but I have some visualization tools I use to help make sense of it. And it does have timestamps, so if you want to look up something specific, you can do it by eye.

The PDATA packets are the position packets I mentioned. The game does drop them when they're received out of order. If you got a lot of out of order packets, something really wonky happened to your connection. I can't remember if it counts out-of-order packets as loss, or if it just doesn't tell you about them, or what.

I can't really give you any expert advice about what to set the PPS to. The internet's a weird place. I just try things and see what seems to work on a given connection, on a given day. As a general rule, though, I run at 30 unless Icewolf's in a game, in which case I run at 20 (apparently Descent can run up against his upstream bandwidth limit in a large game). 30's nice and smooth, but it isn't a big enough difference from 20 that I really notice it. 10 is noticably choppy; I don't run with that.