Re: Distribution CPG Protocol

[Stephen Thomas <stephen.thomas@transnexus.com>]

This is an interesting perspective that is quite different from the one 
I've been stuck on. I can't completely connect all the dots, but I'm 
willing to explore it a bit.

I would characterize the main difference between Dan's perspective and my 
own as one of peer-to-peer vs. client/server. My view of the CDN peering 
problem was very definitely a client/server one. One CDN has surrogates 
(it's the "server"), and another CDN (or the content provider itself) has 
content (it's the "client"). In that view, it cannot be "the pair that gets 
advertised" since only the 'server' knows its surrogates and only the 
'client' knows the content.

Now let me see if I can context-switch to a peer-to-peer perspective and 
ask intelligent questions.

At 05:48 PM 2001-01-12 -0800, Dan Li wrote:
>At 04:33 PM 1/12/01 -0800, Tomlinson, Gary wrote:
> >The fundamentals of advertising surrogates vs advertising content or both is
> >clouding my thought processes at the moment.
>
>It's both. Take domain name as a simplified representation for content 
>(URL is more elaborate but you see names like "images.foo.com" that encode 
>a class of content into a name). Then, content routing is the task of 
>mapping a name to a location, similar to routing a IP to a location. Then, 
>a surrogate is mere a location for a *set* of names it supports.
>
>So a route advertisement would have these two parts:

So, what is a "route advertisement"? Is it a content provider advertising 
its content? Or a CDN advertising content that it is distributing? I kind 
think the latter, but it doesn't hurt to check. If that is the case, I have 
a couple of questions:

1) This assumes that the content has already been distributed, right? I 
think that the issue I was dealing with was primarily how to get the 
content distributed in the first place? I guess, though, that a content 
provider with content on origin servers is a degenerate case.

2) This approach seems to imply that CDNs exchange content with each other. 
But, if a new CDN wants to acquire content to distribute, wouldn't it just 
grab the content from the origin servers? It might learn about the content 
from another CDN, but it sure would be more efficient to get the content 
directly from the origin. (I can think of security/business associations 
that might, at first, create some obstacles, but I think those are actually 
fairly easy to solve.)

>1. "route to content set X is via next hop M to content server A with 
>metrics K", where A is chosen (based on metrics K) among other possible 
>destinations B, C, D, which all advertise support for the same set X).

Okay, what is the difference between M and A? Which one is the surrogate? I 
think A is the surrogate, but then I don't know what M represents.

Do you think the metrics K are an intrinsic property of the surrogate only, 
or are they a property of both the surrogate and the particular content? I 
sure would like to see something concrete for these metrics.

Stephen