Any good source of getting study material regarding PSDN (Packet Switeched Digital Network)......?

Answer 1

I assume you would like it for WAN activitiies so check out http://www.cisco.com/public/support/tac/documentation.html

also another good site to check out is http://www.networkworld.com/details/647.html?def

Search for terms like Packet Switching... It's always gona be digital... so don't need to include it.. Circut Switching is the other way around from packet...