Virgin (and most other ISP's) actually perform Traffic management / packet filtering / throttling at two specific points - on your link, and on the backbone.

Users on the VM 10 & 20 mb services experience throttling on thier connections if they hit a specific volume of traffic inside a given period of time. As it suggests, this artifically restricts the throughput of thier connection down to 5mb or 2.5mb. This is automatically controlled by rules configured on an endpoint router close to thier home, and automatically lifted after a given period per the same set of rules. It doesnt affect specific types of traffic, all its doing is reducing the size of the pipe that traffic has to squeeze through. Game traffic is not actually that signficant (compared to the volume of traffic downloading a movie generates for example) so doing nothing except playing WoW on a 2.5mb connection should not be any problem.

The recent issues with VM as recognised by many WoW players (along with users playing other games or accessing services with similiar network traffic characteristics) is not due to user specifc throttling, but due to recently introduced Traffic Management measures on Virgins backbone network. This affects all thier users, even those on the 50mb connection offering who are not affected by throttling

VM have recently introduced a large raft of QoS (Quality of Service) rules to traffic passing accross thier core network. QoS is essentially a mechanism whereby traffic flagged as "important" (in Virgin media's case, they is likely to mean HD video and audio content from thier commercial web partners) is given the highest priority over thier congested network - this ensures in most cases that when the network is busy (i.e. at peak times) that users of that "important" traffic will see it perform especially well. Think of a bus-lane on the motorway... when the road is busy buses can still get form A to B quickly, the same applys to "priority" traffic on Virgins core network.

At the other end of the spectrum, VM also specifically flag certain types of network traffic as "low priority" - for the most part this will include P2P, email and more recently - Usenet traffic. VM deem this traffic to be of less importance to its users. Traffic which is flagged as low priority is effectively a second class citizen on VM's network - it gets constantly shoved to the back of the queue, behind both the high-priority and all other regular traffic. To use a similiar motorway analogy... at peak times all "low priority" traffic is forced to use the outside lane, regardless of how quiet the rest of the lanes actually are...

Now - specifically in relation to WoW - what has happened is that as Blizzard have changed the way the network traffic "looks" with the 4.0.1 patch - VM's automatic Traffic Management tools are now recognising it as P2P traffic (and flagging it as low priority), which is where the terrible ingame performance comes from.

Virgin do not "prioritise" game traffic normally - but neither do they intentionally de-prioritise it. At present, the newly 4.0.1 tweaked WoW traffic is being incorrectly flagged as low-priority, hence all the problems players are witnessing. Virgin need to identify what new style WoW network traffic looks like, and reconfigure thier traffic management software to leave it as "normal" priority. They claim a headsup from Blizzard would have allowed them to do this before the patch hit, and could thus have avoided the issue altogether.

The root of the problem is therefor twofold - partially Virgin Media's fault (for using overzealous automatic traffic management tools on thier core network) but also partially Blizzards (for not making information changes to the network traffic profile of their flagship and massively popular online game available in advance to major ISP's to prepare for).

I have endevoured to avoid being judgemental in this post - whether you believe that Virgin Media are being underhand by failing to explain the throttling is not the same thing as traffic shaping, or that Blizzard are in the wrong for changing the way thier game transfers traffic accross the web at the drop of a hat, the outcome is the same - unplayable performance for the end user.

The solution? Well... in the long term Blizzard needs to give ISP's a very clear headsup on expected changes to thier traffic fingerprints, or ISP's need to stop utilising arbritary traffic shaping tools to compensate for thier horribly overcommitted networks. In the short term, either Blizzard need to revert thier traffic to work in the same way as 3.3.5, or Virgin etc need to quickly identify the new style traffic and rush through some Traffic Management rules exceptions to stop WoW traffic being incorrectly mangled.

#Wonderdog

PS - Let me make this clear - performing a traceroute or Ping test to your realm server WILL NOT demonstrate or help you to asist diagnosis this problem. ICMP (ping) traffic is NOT being actively "managed" by VM, and any packet loss etc you see on a ping test is NOT relevent or related to the traffic shaping (it could well be due to another ISP related issue though!). Only live game traffic is affected by the Traffic anagement system, hence the variably awful performance we are all seeing in game.