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Re: Reducing Usenet Bandwidth

  • From: Toerless Eckert
  • Date: Sun Feb 03 19:20:41 2002

On Sun, Feb 03, 2002 at 03:00:03PM -0600, Chris Adams wrote:
> Okay, I'm with a (decent sized, although probably small by NANOG
> measures) ISP.  Why do I want to turn on multicast (what does it get me
> that I don't have today)?

Do you want a technical spin or the spin ?

The basis of the technical spin is that ip multicast is as much ip as ip
unicast and that as such it need to be provided for applications to leverage
all the benefits of the ip service. The basis of the  money spin is that
you as an ISP are making money (hopefully) by shuffling bits out onto links
(to customers) who are paying for the links, and you are paying for traffic
on backbone links where you connect to the core, and ip multicast allows
you to shuffle more bits out from your network on the links to customers
without linearly increasing the amount of bits on your uplinks.

Practically speaking, there a small but fair amount of ip multicast content
out on the network that you could have your customers receive, mostly
entertainment oriented, but you're not really limited by this. Given
that the primary purpose of ip multicast for you is to give you a savings in 
bandwidth, you might as well look into encouraging your customers to
put up content - especially if there are likely candidates that are
interesting to your regional customer space - after all, live content today
often does not exist at good quality because the need to use some existing
splitter technology drives up the cost to the content producer in such
a way that it's not feasible. Also, you could convert unicast content at
the uplink of your network into multicast so as to save pulling it in
multiple times into your network.

> And if I want to turn it on, where can I find the resources you mention?

There's a couple of books out there, but the config recommendation would
mostly come from your gear vendor like they'll probably come too for
most of the other features you've got on your routers.

If you use cisco gear, check out "", or ask
on Also, check out with your uplink ISPs,
you should easily be able to get up and running by having an ip multicast
enabled isp give you the config recommendation.

Getting ip multicast to run this way is not particularily challenging,
it is more the problem of getting the right cooking recipe and the three
pointers above should lead you there pretty well. 


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