Alleged Netflix “deliberate throttling” conspiracy is normal congestion
The folks at breakitdownblog.com have accused Netflix of deliberately throttling their users to 480 Kbps (60 KB/sec). Their proof? Downloading a video stream using 10 TCP flows is 10 times faster than downloading videos using the normal single flow. The blogger at breakitdownblog.com concludes that this must mean Netflix is intentionally throttling their users because they assume that there must be extra available bandwidth that Netflix is keeping from their customers. Unfortunately, this is often what passes as credible news these days and the blog has been slashdotted so they’re probably getting on the order of 40,000 hits or so.
Well I hate to break the news to breakitdownblog.com, but this is normal congestion behavior. In fact, they’ve accidentally discovered the multi-flow cheat that works around Jacobson’s TCP congestion control algorithm which rations bandwidth on a per-flow basis and not per-user basis. Even if the server’s capacity is completely filled, asking for 10 times more TCP connections will allow a client to pull nearly 10 times more bandwidth at the expense of other normal clients who are only asking for one TCP connection. Peer-to-peer (P2P) applications employ the same technique to accelerate its own performance at the expense of other users.
So what this sounds like is that the particular Netflix server they’re connecting to is running out of streaming capacity and it can’t handle this many users. This may still be bad on Netflix’s part if the performance problems are consistent, but let’s not attribute occasional inadequacy to malice. I can’t imagine this being frequent since Netflix’s support lines would be ringing off the hook. I also just ran a quick test with my Netflix account and verified that everything is working fine. I’m not suggesting that the alleged problems don’t exist, but we need to have a rational discussion about them.
George,
I may not have made it clear enough in the post (I’ll take a look in a bit) but the indicator to us of the throttling behavior was the very different experience we were seeing during streaming on the Xbox 360 (started in under a minute) and the PC video player (~2hrs of buffering and a capped speed at 50 kb/sec — not enough to stream anything).
These are two Netflix-enabled devices on the same network, providing *much* different behaviors. Please note that the entire 2nd half of the article clarifies that Netflix is providing a much-improved QoS to the Xbox 360 Netflix integration at the cost of PC streaming by throttling those connections — *that* is the claim, now that in general Netflix throttles everything, all the time.
I’d also point out that the section of the article that opens up 10 connections and gets exactly (Cap x 10) bandwidth would indicate there is no congestion or overloading on the server’s side as you mention in your last paragraph. I would have expected the connection speed to scale non-linearly if that were the case, maybe capping out at 200 KB/sec… but to increase the connections to 10, and get exactly 10x the performance indicates there is very intentional throttling occurring here.
Hope that clarifies our position — more comments and thoughts are absolutely welcome. Thanks!
Well, of course they’re doing “evil” throttling. After all, bandwidth is free, right? And all ISPs are evil…. Not.
"but to increase the connections to 10, and get exactly 10x the performance indicates there is very intentional throttling occurring here."
This is NATURAL throttling here. This is Jacobson’s algorithm in effect. I would suggest you read this article in case this blog wasn’t clear enough for you. http://blogs.zdnet.com/Ou/?p=1078.
And does Netflix’ contract give you the right to stream 10 movies at once? I doubt it. Bandwidth is expensive, Netflix isn’t a charity. It has a right to set limits.