An important ingredient in the Technology of Cyberspace is the ability to let any user communicate with any other user or service. How do we wire 5 billion people on the planet? That's an engineering problem - to design a network capable of handling such numbers over such a wide geographic area. We are going to talk about the engineering aspects of such network design for next two lectures.

In the field of telecommunications, a Clos network is a kind of multistage circuit switching network, first formalized by Charles Clos in 1952,[1] which represents a theoretical idealization of practical multi-stage telephone switching systems. Clos networks are required when the physical circuit switching needs to exceed the capacity of the largest feasible single crossbar switch.