A Brief Introduction

In order to start our journey to the world of Data Networks, it is mandatory to have some definitions.

A message is the information/data that a user wants to transmit to another user. It can contain any kind of data, including text, sound and images. Each message is cut up to packets in order to be transmitted over the media. 

A packet is the fundamental unit of information that is transmitted over packet-switched networks.

Packet switching is the process of the division of messages into packets before they are sent, transmitting each packet individually, and then reassembling them into the original message since all of them have arrived at the destination. Packet switching shares available network bandwidth between multiple communication sessions. The advantage of Packet switching is that network resources are managed by statistical multiplexing or dynamic bandwidth allocation in which a channel is effectively divided into an arbitrary number of logical variable bit rate channels or data streams. In other words, a channel is occupied only when a user transmits packets. Otherwise it is available to others users to transmit.

In a packet switching network, packets can follow different routes from the source to destination.

Contrary, Circuit switching is a process of implementing a communication network in which two nodes establish a dedicated channel (circuit) through the network before the nodes may communicate. The advantage of Circuit switching is that delay is constant during a connection but each channel cannot be used by other users until the circuit is released and a new connection is set up. Even if no actual communication is taking place, the channel remains unavailable to others users.

Channel is a physical transmission medium such as a Fiber Fiber or a logical connection over a multiplexed medium such as a radio channel. It is used to convey data from one or several sources (transmitters) to one or several destinations (receivers). A channel has a certain capacity for transmitting information that is measured by its bandwidth.

Bandwidth is the data transmission capacity of a channel. The greater a channel’s bandwidth, the more information it can carry per unit of time.

It is expressed in bits/second or multiplies of it (kilobits/sec, megabits/sec).