Multicast Traffic on Backbones

David Schwartz davids at webmaster.com
Sat Jun 16 01:16:28 UTC 2001



> "David Schwartz" <davids at webmaster.com> wrote

> > You mean one packet traverses *TWO* networks, don't you?

> probably - but you will still charge on this scheme if both sender and
> recipient are your customers, won't you?

	Some people do, some people don't. It depends. The company I work for does
not charge for traffic within a POP.

	If you expect this to be a large fraction of your traffic, you should
definitely negotiate a contract where you don't have to pay more for this.
If you expect this to be the usual percentage of your traffic, then you
should just understand that it's figured into the price.

	If you pay, say, $200 per megabit per second per month for traffic over
your DS3, this price is based upon the average your ISP expects your traffic
to cost it. Some traffic will be very cheap, perhaps going to a machine in
the same POP as your DS3 terminates. Some will be very expensive, requiring
them to haul it far over their backbone or pay high rates to get it to/from
someone else.

	When your ISP sets the rates you pay for your traffic, it's (at least
usually) based upon their expected costs for providing that traffic.

	If your usage breaks that model, either generally being more expensive (as
multicast can be) or generally being cheaper (say all your company's offices
use the same ISP with lots of VPN traffic) then you or your ISP should
negotiate for a different price or pricing model.

	If an ISP insisted on charging you much less than your traffic actually
costs it, it would go out of business. If an ISP insisted on charging you
much more, you would go elsewhere.

	An important point is that there is absolutely no meaningful difference
between the following statements:

	1) Both the sender and the recipient pay for the traffic, thus being double
billed.

	2) Both the sender and the recipient contribute to the cost of the traffic
between them.

	3) The sender pays to bring the traffic from him to some point and the
recipient pays to bring the traffic from that point to him.

	The simplest way to put it is that passing a packet from an origin to a
destination creates costs from the beginning to the end of that path. The
agreements covering the various links that packet flows over work out how
thoses costs will be borne. The parties at both ends of the link must find
the agreement covering the exchange of that traffic divides the costs
reasonably fairly or the link wouldn't exist.

	DS




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