Technical Summary
This document defines a protocol by which a downstream CDN (dCDN) may
query an upstream CDN (uCDN), in a CDN Interconnection (CDNI),
to retrieve metadata related to a specific content asset being
delivered by the dCDN, on behalf of the uCDN. The metadata
provides basic content delivery information, e.g., how to acquire
the content asset, as well as optional content delivery policy
information, e.g., geographic, time, and delegation restrictions.
Working Group Summary
The metadata is organized hierarchically, starting with the host
and further differentiated by URI path of the content.
There was a lot of discussion early on as to whether a generic
metadata interface was feasible or needed; there was concern
that the complexity of designing a generic metadata interface
would be prohibitive.
Much effort was put into defining how the metadata should be organized,
so as to allow inheritance and override within the hierarchy, as well
as metadata object reuse between hierarchies. There was broad discussion
in the WG on this topic. There were requirements for being able
to exchange core pieces of metadata (e.g., how to acquire content),
but there was also a desire to create an extensible protocol.
Multiple drafts were submitted and merged to arrive at the final design.
In addition to the extensible structure of the metadata, much discussion
and effort was put into making sure that transit CDNs, which may or may
not understand how to enforce the metadata, are able to safely
redistribute the metadata or are able to recognize when redistribution
of the metadata may violate content delivery policies.
The focus of the document is on providing metadata for delivering content
via HTTP. While the same metadata can be used to deliver content via HTTPS,
there is no metadata defined for conveying metadata specific to setting up
TLS connections between the dCDN and the end user. It was discussed within
the WG, but a secure solution was not deemed within the expertise of the WG.
Other solutions (e.g., LURK) could be used to address the TLS connection
setup problem, and a CDNI metadata extension could be added once such
a solution is available.
Document Quality
The document was well reviewed in the WG.
AppsDir review was performed by Matt Miller.
Personnel
The document shepherd is Francois Le Faucheur. The responsible
AD is Alexey Melnikov.