North American Network Operators Group

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Re: Can P2P applications learn to play fair on networks?

  • From: Eric Spaeth
  • Date: Sun Oct 21 16:59:16 2007

Matthew Kaufman wrote:
Maybe Comcast should fix their broken network architecture if 10 users sending their own data using TCP (or something else with TCP-like congestion control) can break the 490 other people on a node.

That's somewhat like saying you should fix your debt problem by acquiring more money. Clearly there are things that need to be improved in broadband networks as a whole, but the path to that solution isn't nearly as simple as you make it sound.
Or get on their vendor to fix it, if they can't.

They have. Enter DOCSIS 3.0. The problem is that the benefits of DOCSIS 3.0 will only come after they've allocated more frequency space, upgraded their CMTS hardware, upgraded their HFC node hardware where necessary, and replaced subscriber modems with DOCSIS 3.0 capable versions. On an optimistic timeline that's at least 18-24 months before things are going to be better; the problem is things are broken _today_.
If that means traffic shaping at the CPE or very near the customer, then perhaps that's what it means, but installing a 3rd-party box that sniffs away and then sends forged RSTs in order to live up to its advertised claims is clearly at the "wrong" end of the spectrum of possible solutions.

On a philosophical level I would agree with you, but we also live in a world of compromise. Sure, Comcast could drop their upstream sync rate to 64kbps, but why should they punish everyone on the node for the actions of a few? From the perspective of practical network engineering, as long as impact can be contained to just seeding activities from P2P applications I don't think injected resets are as evil as people make them out to be. You don't see people getting up in arms about spoofed TCP ACKs that satellite internet providers use to overcome high latency effects on TCP transfer rates. In both cases the ISP is generating traffic on your behalf, the only difference is the outcome. In Comcast's case I believe for their solutions the net effect is the same; by limiting the number of seeding connections they are essentially rate limiting P2P traffic. It just happens that reset inject is by far the easiest option to implement.
Maybe Comcast's behavior will cause all 500 neighbors to find an ISP that isn't broken. We can only hope.

Broken is a relative term. If Comcast's behavior causes their heavy P2P users to find another ISP then those who remain will not have broken service. For $40/mo you can't expect the service to be all things to all people, and given the shared nature of the service I find little moral disagreement with a utilitarian approach to network management.