A network is the interconnection of a set of devices capable of communication. In this definition,
a device can be a host (or an end system as it is sometimes called) such as a large computer,
desktop, laptop, workstation, cellular phone, or security system. A device in this definition can
also be a connecting device such as a router, which connects the network to other networks, a
switch, which connects devices together, a modem (modulator-demodulator), which changes the
form of data, and so on. These devices in a network are connected using wired or wireless
transmission media such as cable or air. When we connect two computers at home using a plugand-play router, we have created a network, although very small.
A network must be able to meet a certain number of criteria. The most important of
these are performance, reliability, and security.
Performance can be measured in many ways, including transit time and response time. Transit
time is the amount of time required for a message to travel from one device to another. Response
time is the elapsed time between an inquiry and a response. The performance of a network
depends on a number of factors, including the number of users, the type of transmission medium,
the capabilities of the connected hardware, and the efficiency of the software. Performance is
often evaluated by two networking metrics: throughput and delay. We often need more
throughput and less delay. However, these two criteria are often contradictory. If we try to send
more data to the network, we may increase throughput but we increase the delay because of
traffic congestion in the network.
In addition to accuracy of delivery, network reliability is measured by the frequency of
failure , the time it takes a link to recover from a failure, and the network's robustness in a
Network security issues include protecting data from unauthorized access, protecting
data from damage and development, and implementing policies and procedures for recovery
from breaches and data losses.