Query re request routing

[Steve Rudkin <srudkin@jungle.bt.co.uk>]

In the case of broadband streamed media on-demand, surrogates need to be as
close to the edge of the network as possible and content will mostly likely
be pushed to the surrogates in advance. 
In this situation, I would therefore expect that
- with respect to any given request, all candidate surrogates will be within
the same CDN, (referred to as the destination CDN)
- the origin could well be operated by a different CDN though, (referred to
as the source CDN)

Whilst there is a need to interconnect distribution systems of the source
and destination CDNs (and any intermediaries) and to do the same for
accounting systems,  is it necessary for the RRS of the destination CDN to
interact with other RRSs? If so, why? If not, should the statement that
there is a single authoritative RRS for each *content unit* be
modified/qualified in some way. Would it be better to say there is a single
authoritative RRS for each *request* ?

Thanks,
Steve Rudkin