It seems like there're quite many players who're struggling with packetloss in quakeworld. I'd say it's rather odd since I'd say we had less packetloss problems a few years ago. There're even some packetloss between qw-proxies.
Is it something to do with with QW using UDP instead of ICMP?

Rikoll suggested changing upstream channel as a fix to pl, I changed mine but it didn't help. http://www.quakeworld.nu/forum/viewtopic.php?id=4832

Any other ideas or fixes?

Mine still isn't solved! But getting a new ISP so eventually it should be fixed :-)

The only way I got my problem completely solved eventually, was through a friend of mine that works at the ISP I'm using. He had some tech guy a bit up in the hierarchy (not one of those coming to your appartment telling everything is fine). He discovered that the node I was connected to was heavily overloaded, and did whatever he did to equalize that.

Even though changing Upstream Channel ID seemed to help me temporarly, my ISP kept changing it back to its original state and it wasn't really a usable solution after all.

So, I'd say its possible to fix this, but it seems you gotta know, or at least get in touch with the right people. If your isp throws out cheap 100mbit lines to everyone, there probably isn't much hope tho.

The problem is basically that cable sucks for quake. I was with Virgin (the UK's HFC provider) for a couple of weeks to give it a test and had the same issues as described in that other thread. Cable usually has much more jitter because of the nature of the shared upstream. Here is a nice happy ADSL graph (sync@14/1):

Here was my Virgin graph (this was 30/3)

A little "trick" that works at the moment on our ISP is hrping related again. To get rid of jumpy ping and packetloss, I need to spam ICMP packets out and in. So when I go playing QW, i launch:
hrping -t -w 50 -s 50 <somecloseiphere>
Reduces jumpy ping to stable one, decreases PL. Can't say if this fools my ISP's packet filtering or my router. But it works. Using this for a couple of months now.

Also, this suggests that ISP's in the US might soon have to disclose how they filter / prioritize their packets. Or maybe I misunderstood it. But would be great. Finally could be able to choose proper ISP for QW, or at least ask the existing one why they are dropping my QW packets.

johnny: where do I launch this? command prompt seeing hrping as a bad command. Sorry for beeing noob!

Well, regular ping would maybe do just fine, but for various reasons I just prefer hrping. http://www.cfos.de/hrping-v312.zip

thnx johnny, gotta try this, 10pl is crap =\

One other thing to try out:
Start a proxy on a server on port 53 (DNS resolution) instead of 30000. Then connect through this proxy to play. Unfortunately i have not found out yet how to start qw proxy on other ports than 30000.

that pinging thing didn't help me, it actually lagged shit out of my pc :-)

bps just download hrping somewhere, it's freeware.

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I think my problem is just that there's too much traffic on my ISP. One hour ago I had 30ms and ~5 pl on local server and now I've 12ms and 0 pl.

didn't help neither grisling nor razor.

burps: isn't it possible to set "-port 53" i proxy cmd line?

It's not that big an issue from what I can see, and I'd be very surprised if it was affecting QW specifically and not just a problem in general. Typical issues include:

Cable: Overloaded local nodes, like Driz a few years ago I had a UK cable ISP which gave 40-80% pl at peak times
ADSL: If SNR margin drops very low (say <5db) you can sometimes get packetloss, usually rebooting your router to force it to connect at a slightly lower rate will fix this.
Internal network: Some people use wireless, I'd always recommend using a wired connection for testing purposes even if you've used wireless for years without issue as it could be that an interfering device has recently arrived
Other traffic on same connection: Really obvious stuff but make sure you don't have any other devices (other computers, smartphones, consoles etc etc) connected to your router during testing
ISP Prioritisation: ISPs use different sorts of traffic shaping and it may be that some even prioritise specific port ranges.

One solution you could look at is using Qizmo which supports the resending of packets, it can send C2S up to 3x and S2C up to 5x iirc. Not sure what affect this could have on latency though and obviously you'd need a serverside qizmo where you want to play.

This seems to be the issue for all of us. :-)

I think it's ridiculous that we're living 2010 and I've packetloss, wtf? I didn't have packetloss 2000

Is there a external program like the netgraph, where you could really see if you have packet loss with high traffic ? cmd ping.exe does not work proberly. The problem is, if you call the service help of your ISP they try to tell you that everythings is normal, because they do not really stress test your network connection like a quake do it.

Better get back into the DeLorean man!