Fixing the Unfairness of TCP Congestion Control

duncan99 writes "George Ou, Technical Director of ZDNet, has an analysis today of an engineering proposal to address congestion issues on the internet. It's an interesting read, with sections such as "The politicization of an engineering problem" and "Dismantling the dogma of flow rate fairness". Short and long term answers are suggested, along with some examples of what incentives it might take to get this to work. Whichever side of the neutrality debate you're on, this is worth consideration."

Comments

Not all sessions experience the same congestion

[thehickcoder]

The author of this analysis seems to have missed the fact that each TCP session in a P2P application is communicating with a different network user and may not be experiencing the same congestion as other sessions. In most cases (those where the congestion is not on the first hop) It doesn't make sense to throttle all connections when one is effected by congestion.

Re:Not all sessions experience the same congestion

[smallfries]

Even if that is true, the congestion won't be correlated between between your streams, if it occurred on the final hops (and hence different final networks). There is a more basic problem than the lack of correlation between congestion on separate streams - the ZDnet editor, and the author of the proposal have no grasp of reality.

Here's an alternative (but equally effective) way of reducing congestion - ask p2p users to download less. Because that is what this proposal amounts to. A voluntary measure to hammer your own bandwidth for the greater good of the network will not succeed. The idea that applications should have "fair" slices of the available bandwidth is ludicrous. What is fair about squeezing email and p2p into the same bandwidth profile?

This seems to be a highly political issue in the US. Every ISP that I've used in the UK has used the same approach - traffic shaping using QoS on the routers. Web, Email, VoIP and almost everything else are "high priority". p2p is low priority. This doesn't break p2p connections, or reset them in the way that Verizon has done. But it means that streams belonging to p2p traffic will back off more because there is a higher rate of failure. It "solves" the problem without a crappy user-applied bandaid.

It doesn't stop the problem that people will use as much bandwidth for p2p apps as they can get away with. This is not a technological problem and there will never be a technological solution. The article has an implicit bias when it talks about users "exploiting congestion control" and "hogging network resources". Well duh! That's why they have have network connections in the first place. Why is the assumption that a good network is an empty network?

All ISPs should be forced to sell their connections based on target utilisations. Ie here is a 10Mb/s connection, at 100:1 contention, we expect you to use 0.1Mb/s on average, or 240GB a month. If you are below that then fine, if you go above it then you get hit with per/GB charges. The final point is the numbers, 10Mb/s is slow for the next-gen connections now being sold (24Mb/s in the UK in some areas), and 100:1 is a large contention ratio. So why shouldn't someone use 240GB of traffic on that connection every month?

Weighted TCP solution

[esocid]

Under a weighted TCP implementation, both users get the same amount of bandwidth regardless of how many TCP streams each user opens...Background P2P applications like BitTorrent will experience a more drastic but shorter-duration cut in throughput but the overall time it takes to complete the transfer is unchanged.

I am all for a change in the protocols as long as it helps everybody. The ISPs win, and so do the customers. As long as the ISPs don't continue to complain and forge packets to BT users I would see an upgrade to the TCP protocol as a solution to what is going on with neutrality issues, as well as an upgrade to fiber optic networks so the US is on par with everyone else.