Some truth about Comcast - WikiLeaks style

Jon Lewis jlewis at
Wed Dec 15 15:51:19 CST 2010

On Wed, 15 Dec 2010, Mikel Waxler wrote:

> 1) "If you were a Comcast customer attempting to stream Netflix via this
> connection, the movie would be completely unwatchable."
> This is a false conclusion. Bandwidth is not allocated in static blocks on a
> first come first serve basis. It is shared across all users. So adding a
> single user only slows the speed of all connections proportionally. In a
> pool roughly 16 million customers (across all regions) a single new
> connection would not noticeably effect others.

When the pipes are full, and the latency is up closer to 1s vs a more 
reasonable 20-100ms, and you have a few percent packet loss, do movies 
continue to stream?  Where are they streaming from?  Over the TATA 
transit, a non-congested Level3 pipe, or on-net CDN servers?

> 2) "Comcast claims that a good network maintains a 1:1 "
> I have never heard them assert that. I have heard them assert that they have
> peering agreements with other providers. Those agreements assert that if the
> bandwidth ratio remains the same, or close that neither party will charge
> the other. For a end user network like comcast, that will never be 1:1. For
> a larger network connecting to Level3 or TaTa, that might be 1:1.

Ratios only make sense between peers.  When you're buying transit, you 
don't get to enforce ratios and tell your transit providers you're not 
going to pay (or they're going to pay you) because they're sending you too 
much traffic.  Back when I ran a dialup network, and our traffic profile 
was maybe 5:1 input vs output, UUnet would have laughed at me and shut us 
off if I told them "you're sending us traffic at a 5:1 ratio...because 
you're sending us so much more traffic than we send you, you're going to 
have to pay us to deliver that traffic."  Comcast can only get away with 
that because of their monopoly (captive userbase) and size.

> 3) You assert that the bandwidth is capped and if Comcast purchased more
> bandwidth it would not hit the cap.
> With 16 million customers and ~20mbit connections average they would need a
> 320 terabit connection to ensure that they never hit the cap.

That depends on your definition of 'never'.  You can oversell your network 
capacity...everyone does...and not run with the pipes full 99% or better 
of the time.  A responsible network keeps track of bandwidth trends and 
plans capacity upgrades as needed.  Comcast is allegedly intentionally 
running their transit at or beyond capacity (and removing bandwith 
capacity instead of adding it, to keep their transit full) and then 
bullying content providers into buying access to the Comcast network to 
avoid the congested transit links.

  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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