Introduction
Currently, networking technology is experiencing its third major
wave of revolution. The first was the move from circuit-switched
mode to packet-switched mode, and the second from hardwired to
wireless mode. The third revolution, which we 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
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