Re: distribution layer confusion

[Kobus van der Merwe <kobus@research.att.com>]

Is content replication not a special case of content signaling as
you described it? Special because in addition to telling the CDN
about the content (i.e. expiration times, origin server etc), you want the
content to be replicated immediately. For example, in the streaming
CDN example you used you could conceivably only tell the CDN
where to obtain the media files from and then have it "replicated"
on-demand. (Unless of course the CDN is working in an exclusive
push model in which case you have to replicate it beforehand.)

Kobus

brad cain wrote:

> The comments below are really an attempt to better describe what
> I believe the distribution architectural layer is really about.  I think
> there has been some confusion between what we have been calling
> request routing and distribution.  [Note that these comments are not
> about protocols but about the architecture]
>
> Please comment as I think we should iron this out soon...
>
> -brad
>
> My belief is that the "distribution layer" is really divided into
> two straightforward parts:
>         1. content replication
>         2. content signaling
>
> Content replication: this is the actual replication of specific
> pieces of content between CDNs through distribution peering.
> A protocol is used to negotiate and advertise which content
> should be replicated between the peers. [note: There may
> be a negotiation phase but I'm a little worried about a complicated
> request response model.  A simple negotiation may be needed to
> negotiate content types.]  The key thing here is that this is
> about copying content from one CDN to another.
>
> Example:
>
> CDN A is peered with CDN B.  CDN A advertises a set of URIs
> which should be replicated on CDN B.  In this advertisement
> a location is sent as to where the content should be obtained
> from (i.e. a surrogate or origin server).  A real world example
> would be for distribution of streaming media files: CDN A
> would advertise to CDN B which files should be copied and
> from where.
>
> Content signaling: This is the distribution of content freshness
> information between CDNs.  An example would be the WCIP protocol.
> These signals are used to purge content or to update the expiration
> times of the content.  Content signals may also be used to update
> other metadata associated with the content (this is probably more
> future oriented).
>
> Example:
>
> CDN A is the "root" or main CDN for content provider B.  CDN A is
> peered with CDN C.  When content from provider B is changed, CDN A
> relays a content signal to CDN C so that it is expired from its
> surrogates.