Pstn/ss7

Does anyone know if there are good training resources for how the PSTN works? It seems like voip is interdependent in alot of scenarios with the PSTN out in the real world and all of the old school telephony stuff is just a big black void of ignorance for me (I don't get it).
Climb a mountain, tell no one.
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Training Courses on DVD Video: Telecommunications, Data Communications, Networking, TCP/IP, IP Security, VoIP, SIP, MPLS
[h=1]Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services (Networking Technology) [Hardcover][/h]
Amazon.com: Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services (Networking Technology) (061947205040