Circuit Switched Networks Revisited:In the beginning there was a monolithic hierarchy based on analog signals and FDMA…Simple hierarchyThen came PCM, TDMA and the digital hierarchy…
A brief introduction to network propocols
Schematic Multiloop Network
DWDM channels - 100 GHz separation
An extended discussion of SONET
Internetworking Technology Overview: extensive and uthoritative information on internet issues from Cisco Systems.
Data Communication Networks and Distributed Systems: a quite extensive set of lecture notes by Saleem N. Bhatti, University College London.
Nortel TutorialsTelephony 101: (pdf) A basic introduction to how public network telephone services are provided in North America.Frame Relay: a vitual textbook by John H. Petrangelo at Worcester Polytechnical Institute
SONET 101: (pdf) An introduction to synchronous optical networks.
Introduction to SONET Networking: A tutorial handbook of advanced SONET networking concepts.
Long Distance 101: An introduction to how long distance service is delivered in North America, and opportunities for network providers in the long distance arena.
on the subject of Frame Relay
Tutorials and Technical Notes from Sangoma Technologies
Tutorials fron Scan Technologies