This course provides the fundamental concepts of digital switching systems with an emphasis on how the telephone exchange and packet switching systems operate. Topics covered in the lectures include: Introduction to telephony and networks, Strowger automatic telephone exchange, Crossbar switching, Logic circuit for crosspoint operation, Multistage interconnection networks, Call blocking probability of crossbar switches, Call congestion and time congestion, Clos network, Strictly non-blocking network, Rearrangeably non-blocking network, Cantor network, wide-sense non-blocking network, Packet switching, Input queued switch, Output queued switch, Banyan network, Delta network, and Buffered delta Network. (from nptel.ac.in)