North American Network Operators Group

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Re: Comcast blocking p2p uploads

  • From: Sean Figgins
  • Date: Fri Oct 19 19:24:28 2007

Martin Hannigan wrote:

O&M, etc. We already know that the givens are that it's generally
socially unacceptable to filter, but without Comcast's motivation
being know, it's hard to speculate as to the "why" they did it. Let's

It's not at all hard to imagine WHY. In fact, it's almost a given.

1) Comcast is an MSO. As such, their access (last mile) is over a coax or a HFC plant.
2) HFC has limitations on bandwidth. The frequencies that most MSOs use for data give it somewhere around a DS3's worth of return traffic. The forward traffic (to the customer) is greater.
3) The HFC plant almost always includes at least a few thousand customers per leg. These customers have to share the same return bandwidth.
4) With only 45 meg of return traffic, and a few thousand customers, it is pretty easy to see how a few high capacity customers could have a negative impact on the rest of the customers.

In addition to this, you have other applications, such as voip, that rides this same infrastructure. In many places there is no real ability to tag the voice traffic with a higher class service, so it has to contend just like everyone else.

You can add to this that in some markets, the only real bandwidth is via multiple T1 or DS3 due to it being more remote. You ever wonder why some places have cable modem but not DSL? That's usually because the telcos can't get the bandwidth there. Right or not, many MSOs will turn up markets on a handful of T1 circuits until they can get a DS3 or greater installed.

As to the SPECIFIC reason why Comcast is deploying the Sandvine instead of another architecture, or using another method of rate limiting... Well, I could probably comment on that as well, but I'm uncertain that my friends and associates at the MSOs and hardware vendors would look kindly on that. Since I no longer work for a MSO, I really no longer have any insight.

It's just a way that an MSO might manage their network in order to make 90% or more of their customers happy while reducing the need to deploy more hardware to split the plants.