[opendtv] Re: News: TV Braces for the Apple Tablet

  • From: Kon Wilms <konfoo@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 1 Feb 2010 16:44:06 -0800

On Mon, Feb 1, 2010 at 4:01 PM, Manfredi, Albert E
<albert.e.manfredi@xxxxxxxxxx> wrote:
> Heh heh. That's exactly the same problem with regular wired ISPs' acceptance 
> of multicast, turns out. I think IP multicast gets used mainly by the 
> providers THEMSELVES, e.g. if they want to use IP to emulate a cable TV 
> service, but it requires many additional bells and whistles. There is an I-D 
> floating around about all this. They don't give the answer in this I-D, just 
> state the problem.

Well I would personally like to term those 'legacy distribution
networks'. As a CDN provider we don't make use of any IP multicast.
This threw me for a loop for a while since I spent so many years doing
exclusively IP multicast, but right now, distribution mechanisms are
far different for unicasting than they were years ago.

The preferred distribution mechanism for CDNs that I currently see
(and one we ourselves implement) is that of stream push over UDP to
various POPs, and from there, HTTP caching on edge servers (or stream
caching/splitting at the unicast level).

There is absolutely no benefit to implementing multicast in a switched
fabric since you pay for the packet distribution regardless. In fact,
you're probably at a disadvantage since one has to cope with erasure
correction, possible packet flooding, TTL tuning (lets not even go
there), and tunneling for security/legacy purposes.

> That's true, with faster and faster wired (fibered) backbone nets becoming 
> available. And then you can make every session VOD.

Right. We can scale quite easily to anywhere in the globe using HTTP
caching and TCP reflection on localized edge clusters.

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