Comcast blocking p2p uploads

Sean Figgins sean at labrats.us
Fri Oct 19 23:16:50 UTC 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
> not.

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.

  -Sean




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