Computer Network Definition, Types and Topology

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Last Updated on November 23, 2020 by admin


DEFINITION OF NETWORK

Network literally means a collection of a large and widely distributed group of people or things such as stores, colleges, or offices that communicate with one another and work together as a unit or system.
A Computer Network,  simply referred to as a network, can be defined as a system of two or more computers, terminals and communication devices linked by wires, cables, or telecommunication system in order to exchange data. The network may be limited to a group of users in a local area (LAN), or  it could be global in scope just like the Internet. The major reason network exist is to enable sharing of resources and information among interconnected devices.
TYPES OF NETWORK:
(i)  Ethernet
(ii)  Token Ring
(iii)  Arcnet
Ethernet:
Ethernet is a family of computer networking technologies for Local Area Networks (LANs), it is a protocol that controls the way data is transmitted over a Local Area Network. This network which was commercially introduced in 1980 uses wires (i.e. it is not a wireless technology) in form of either a bus or star topology and supports data transfer rates of about 10Mbps. 
Token Ring:
A Token ring is a type of computer network in which all the computers are arranged in a circle (see diagram below). A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then allows it continue to travel around the network. It uses a special three-byte frame called a token that token that around the ring. Physically, when implemented, the computers are connected through cables to a ‘HUB’, which manages the network in a ring topology manner.
A token ring prevents the collision of data when more than one computer in a network attempts to send messages simultaneously. It is the second most popular type of Local Area Network protocol.
Arcnet:
ARCnet ( an acronym from Attached Resource Computer Network) is defined as a group of nodes that communicates to one another over a geographically-limited area usually within one building or a campus of buildings. It was developed John Murphy at Datapoint Corporation in the late 1970s.It was the simplest and least expensive type of Local Area Network, which uses token ring architecture, supported data rates of 2.5Mbps, and connected up to 255 computers. A special advantage of ARCnet is that it permitted various types of transmission media to be mixed on the same network.
NETWORK TOPOLOGY
In Computer Networking, topology refers to the layout of connected devices. It is the plan or model in which two or more computing devices are connected in a network. There are two types of network topology, Physical Topology and Logical Topology.
The Physical Topology of a network refers to the layout or arrangement of the cables and network devices.
The Logical Topology refers to the method of communication of the network devices.
Network Topologies are categorized into the following basic types:
(i)  Point to Point Topology
(ii)  Star Topology
(iii)  Bus Topology
(iv)  Ring Topology
(v)  Mesh Topology
STAR TOPOLOGY
Star Network is a local area network in which each device (node) is connected to a central computer in a star-shaped configuration (topology); commonly, a network consisting of a central computer (the hub) surrounded by terminals. The central point may be a hub, a switch or a router, and all the individual network devices communicate with the central point which manages and control all functions of the network.
An example of star network topology is the ARCNET.
Advantages of Star Topology
  • A star network is reliable in the sense that a node can fail without affecting any other node on the network.
  • Easy to install and wire
  • Easy to detect faults and remove parts
Disadvantages of Star Topology
  • Failure of the central computer results in a shutdown of the entire network.
  • If the hub, switch, or concentrator fails, nodes attached are disabled
  • Since each node is individually wired to the hub, cabling costs can be high.
BUS TOPOLOGY
Bus network topology uses a common backbone (a cable) to connect all devices. The backbone is a shared communication medium that all devices are attached or connected. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted.An example of bus network is the Ethernet.

Advantages of Bus Topology

  • Easy to connect a computer or peripheral
  • Inexpensive to implement when compared to other topologies because it requires less cable
Disadvantages of Bus Topology
  • Entire network shuts down if there is a break in the main cable
  • Terminators are required at both ends of the backbone cable
  • Difficult to identify the problem if the entire network shuts down.

RING TOPOLOGY

It is a local area network in which devices (nodes) are connected in a closed loop, or ring. Messages in a ring network pass in one direction, from node to node. As a message travels around the ring, each node examines the destination address attached to the message. If the address is the same as the address assigned to the node, the node accepts the message; otherwise, it regenerates the signal and passes the message along to the next node in the circle. Such regeneration allows a ring network to cover larger distances than star and bus networks. It can also be designed to bypass any malfunctioning or failed node.

 

Advantages of Ring Topology
  • They can span larger distances than other types
  • It can also be designed to bypass any malfunctioning or failed node.

 

Disadvantages of Bus Topology
  • Failure in one of the network connection results in breakdown of the entire network.
  • new nodes can be difficult to add.

MESH TOPOLOGY

In Mesh network topology, each computer includes everything it needs to serve as a relay point for sending information to any

NETWORK DEVICES

The network devices are the nodes of the network. They are devices that aid connection and communication. The common network devices are:
(i)  The Hub
(ii)  The Network Interface card
(iii)  The Switch
(iv)  The Router
(v)  The Modem
The Hub:
A Hub is a device that connects all the other devices in a star network together, thus making them act as a single network segment. Due to the fact that the hub broadcast messages, any message sent by the hub is received by all the devices because the hub is not able to identify the device that owns the message.
Modems:
A Modem, which means Modulator-Demodulator, is a device or program that enables a computer to transmit digitally stored data over telephone or cable lines. A modem converts between analogue and digital waves.Modem transmit data at different speeds, measured by the number of bits of data they send per second. For example, a 28.8 Kbps modem sends data at 28,800 bits per second. A 56 Kbps modem is twice as fast, sending and receiving data at a rate of 56,000 bits per second.
 
The Switch:
Literally, a switch means a mechanical or electronic device that opens, closes or changes the connections in an electrical circuit. Examples are the ones used to turn light on or machine on or off. In computing, a switch is a programmed technique for indicating which alternative path to take at a decision point in a program’s logic. They are key components of computer networks which could connect multiple PCs, printers, servers, and other hardware.
Unlike the hub, the switch is intelligent because it does not broadcast but channels the data to the specific destination.

Routers:

A Router is a network device that connects networked computers to the internet, allowing multiple users to share a connection. A Router acts as a dispatcher, choosing the best route (passage) for information to travel, so that it is transmitted as efficiently as possible.
Network Interface Card:
A Network Interface Card (referred to as network adapter, LAN adapter or card) is an expansion board inserted into a computer so as to be connected to a network. Networked computers communicate with each other using a given protocol for transmitting data packets between the different machines, known as nodes.

 

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