Technological advances in semiconductor products have essentially been the primary
driver for the growth of networking that led to improvements and simplification
in the long-distance communication infrastructure in the twentieth century.Two
major networks of networks, the public switched telephone network (PSTN) and the
Internet and Internet II, exist today. The PSTN, a low-delay, fixed-bandwidth network
of networks based on the circuit switching principle, provides a very high quality
of service (QoS) for large-scale, advanced voice services. The Internet provides
very flexible data services such as e-mail and access to theWorldWideWeb. Packetswitched
internet protocol (IP) networks are replacing the electronic-switched,
connection-oriented networks of the past century. For example, the Internet
is primarily based on packet switching. It is a variable-delay, variable-bandwidth
network that provides no guarantee on the quality of service in its initial phase.
However, the Internet traffic volume has grown considerably over the last decade.
Data traffic now exceeds voice traffic. Various methods have evolved to provide
high levels of QoS on packet networks – particularly for voice and other real-time
services. Further advances in the area of telecommunications over the last half a
century have enabled the communication networks to see the light. Over the 1980s
and 1990s, research into optical fibers and their applications in networking revolutionized
the communications industry. Current telecommunication transmission
lines employ light signals to carry data over guided channels, called optical fibers.
The transmission of signals that travel at the speed of light is not newand has been in
existence in the form of radio broadcasts for several decades. However, such a transmission
technology over a guided medium, unlike air, with very low attenuation
and bit-error rates makes optical fibers a natural choice for the medium of communication
for next-generation high-speed networks. The first major change with the
development of the fiber technology was to replace copper wires by fibers. This
change brought high reliability in data transmission, improved the signal-to-noise
ratio and reduced bit-error rates.