said by Smokey:... some of those links have been upgraded ...
I'm not too surprised. That diagram was from a May 2004 Cox VoIP whitepaper »
www.fcc.gov/oet/tac/7.28 ··· aper.pdf which likely used an even earlier diagram. At the time of it's writing, VoIP was still only being trialed in Roanoke, VA.
I'm sure at least some of those OC-3s and OC-12s were upgraded and/or re-routed to support the recent speed increases and ongoing VoIP roll-outs, and to eliminate "single-threading" to some of those markets. (e.g. Tucson AZ, Cleveland OH, and Gainesville FL)
Got any more current info?