RE: hard questions: request routing

[Oliver Spatscheck <spatsch@research.att.com>]

Abbie,

	I think we are fighting over terminology at this point. Let me try to make
an example:


If I understand you right the DSP is building a content tree.
The content tree is managed by the authoritative CDN which has
a global view of the content tree.

For example: 

- CDN A is authoritative for a particular customer
- All CDN's B C D have business arrangements with each other

So possible content trees are, for example:

I.)

  A
  |
  B
  |
  C
  |
  D

or 

II.)

   A
   |\
   C B
     |
     D

or ....

What I meant with "you are constraining the topology at some early stage"
is that the authoritative DPS has to decide early on if the
content tree has topology I.) or II.). And it also has to
assure that the content tree is actually a tree and not a graph.
For example, the business relationship allows for a
content graph of

	+A-B-C-D+
	|-------|

which would be disallowed by the authoritative DPS since a loop does not make
any sense in terms of distributing content.

Is that true?

What I meant "deals not very well with CDN failures" was now that
if the DPS has chosen topology I.) early on a failure of 
CDN B will be preventing the use of CDN C and D, while 
topology II does still allow the use of CDN C even if CDN B fails.
(I think this is also the direction Hillary's comment is targeting.)

You could now argue that the DPS would recover from this
failure by choosing another content tree. This is what
I call an atomic update since all participants
have to have the same view of the content tree to
prevent request routing loops (since routing is a path
in the content tree). It actually uses CDN A's CDP as
arbiter to administer that update. 

Does my terminology makes more sense now or am I still off?

If I make sense this solution has similar drawbacks as the 
arbiter solution proposed by Brad. I guess we would have
to agree if it is a requirement to reveal all current
business relationships to the authoritative CDN for
a particular piece of content. There was some opposition
to that idea during the IETF meeting.

Oliver