A content delivery network (CDN) is a large distributed system of servers deployed in multiple data centers in the Internet. The goal of a CDN is to serve content to end-users with high availability and high performance.
Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet. - en.wikipedia.org/wiki/URI
Border Gateway Protocol (BGP) is the protocol which is the core routing decisions on the Internet. It maintains a table of IP networks or 'prefixes' which designate network reach-ability - en.wikipedia.org/wiki/BGP
The multiprotocol extensions of BGP has been used to carry many types of information. I stumbled across a great progression on the idea from this NANOG presentation from the guys at Comcast.
Here's their packet capture screenshot. Notice the Address Family - URI.