Currently, networking technology is experiencing its third major wave of revolution. The first was the move from circuit-switched mode to packet-switched mode, the second from hardwired to wireless mode, and finally the third revolution, which we will examine in this book, is the move from hardware to software mode. Let us briefly examine these three revolutions, before focusing more particularly on the third, which will be studied in detail in this book.

I.1. The first two revolutions

A circuit is a collection of hardware and software elements, allocated to two users – one at each end of the circuit. The resources of that circuit belong exclusively to those two users; nobody else can use them. In particular, this mode has been used in the context of the public switched telephone network (PSTN). Indeed, telephone voice communication is a continuous application for which circuits are very appropriate.

A major change in traffic patterns brought about the first great revolution in the world of networks, pertaining to asynchronous and non-uniform applications. The data transported for these applications make only very incomplete use of circuits, but are appropriate for packet-switched mode. When a message needs to be sent from a transmitter to a receiver, the data for transmission are grouped together in one or more packets, depending on the total size of the message. For a short message, a single packet may be sufficient; however, for a long message, several packets ...

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