My reading ... i.e. the configuration needed for the inclusion or removal of company sites is fully decentralised.

-

--------------------------------------------------
Note added at 25 mins (2008-07-20 00:31:05 GMT)
--------------------------------------------------

MEANT TO SAY ÁT´ THE EDGE OF THE NETWORK

Second, although it may be a futile gesture, each of these innumerable government IP addresses must be heavily defended not only """at the edge of the network"""" but also on every connected PC and server. Yet a vast organization such as the Defense Department has never had, and never will have, 100 percent compliance with all of the patches, upgrades, installations and configurations required to defeat recognized threats—much less those of a knowledgeable opponent.
http://www.afcea.org/signal/articles/templates/Signal_Articl...

A network can be segmented at the network layer to create an end-to-end VPN in numerous ways. In Part I we described a controlled route leakage approach that attempts to perform the segregation only """at the edge of the network""", using route advertisement control to ensure that each connected network received a view of the network (only peer networks). We pick up the description at this point in this second part of the article.
http://www.cisco.com/web/about/ac123/ac147/archived_issues/i...

The "edge of the network" is where the end user is.

"On-demand applications are driving increased needs for network capacity closer to the edge of the network, or closer to the end user..."
http://lw.pennnet.com/display_article/332029/13/ARTCL/none/n...

"QoS at the edge of the network ensures that traffic is classified, prioritized, and congestion is avoided at the first possible opportunity..."
http://www.cisco.com/warp/public/cc/general/bulletin/lan/171...
(An announcement from the network equipment manufacturer Cisco)

"Efficiency Gains at the Edge of the Network"
PDF! http://www.sun.com/products/networking/whitepapers/edge.pdf

"Stanford University law professor Larry Lessig talks about innovation at the edge of the network..."
http://bpastudio.csudh.edu/fac/lpress/471/audio/lessigedges....
(Larry Lessig may be a law professor, but he also often discusses Internet issues.)

"Caching at the Edge of the Network"
PDF! http://www.cmswatch.com/Trends/65-Caching-at-the-Edge-of-the...

"Storage at the Edge of the Network"
http://www.isaserver.org/articles/Storage_at_the_Edge_of_the...

"Further, the value is added at the edge of the network, outside of telephone company purview..."
http://netparadox.com/



--------------------------------------------------
Note added at 27 mins (2008-07-20 00:32:59 GMT)
--------------------------------------------------

Regarding "trunk" versus "backbone":

"The Internet backbone refers to the main 'trunk' connections of the Internet. It is made up of a large collection of interconnected commercial, government, academic and other high-capacity data routes and core routers that carry data across the countries, continents and oceans of the world."
http://en.wikipedia.org/wiki/Internet_backbone

To me, this sounds like "backbone" is much bigger than "trunk," and gives me the impression that only a major company or a sovereign nation would provide part of the Internet "backbone" - whereas a smaller country would provide a "trunk."