CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND
Early computer networks carried continuous bit streams over physical links in a technique called
circuit switching. This was well suited for transmitting voice or real time data from a single
sender to a single receiver (Unicast communication). In this kind of network, a single physical
link failure had dramatic consequences, leading to the interruption of all communications that
was using the failed link, popularly known as circuit switched network (Andrew, 2011; Stallings,
2007).
The Internet today is a datagram packet-switched network that addressed the drawback of the
circuit switched network by cutting data into small chunks called packets. These packets are
individually routed through the network, such that two packets from the same communication
network are individually handled in the network. Therefore, if a link fails, packets can be
rerouted to avoid the failed link and communications are not interrupted, this feature of a packet
switched network is called resilience because it hides network failure from the end users
(Andrew, 2011; Stallings, 2007).
The Internet uses Transmission Control Protocol / Internet Protocol (TCP/IP) suites of protocols
as in Figure 1.1 to transport traffic over the network and the Internet, this suite of protocols was
designed by Department of Defense (DoD) from United States of America to ease
communications between troops in the war field and later being adopted into all other means of
communication and data sharing. Many protocols consist of a suite (or group) of protocols
stacked into layers, these layers depend on the operation of the other layers in the suite to
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function properly. TCP/IP consists of four layers that perform functions necessary to prepare
data for transmission over a network (Lammle, 2012).