Definition of terms
i) Network
A colection of independent entities that are arranged in such a manner to exchange data,
information or resources e.g Road networks, telephone networks.
ii) Computer networks
A collection of computers linked together using transmission media for the purpose of communication and resource sharing

iii) Transmission Media
is a physical and non-physical link between two or more computers and in which a signal can be made to flow from source to destination

iv) Resource Sharing
Is the sharing of the resources that are attached to the network for access by users eg file, printers , data, application programs etc

v) Data Communication
A process of transmitting data signal from one point to anothe through the network

vi) Telecommunication
The communication i.e. transferring of data and information over significant distances is known as telecommunication.

Advantages of computer network are:

• Data and software of computer can be shared with other computer on the network.
• Only the authorized user of a network can use the facilities of the network.
• Computers on the network can communicate with each other.

The disadvantages of computer network are:

• Data and information may be stolen by computer hackers if the security of network is not reliable.
• If any computer in a network gets affected by computer virus, there is high chance of spreading computer viruses on the other computer.
• Computers on the network have to depend on the server computer for resources.
• This sharing of information may leak the privacy of other clients.

Explain how computer network reduce expences in an office.
- Computer Networks can allow businesses to reduce expenses and improve efficiency by sharing data and common equipment, such as printers, among many different computers. At the same time, the network may be connected through cables, telephone lines, infrared beams etc, which is cheaper and helps to reduce the expenses.

TERMS USED IN DATA COMMUNICATION
i) Data siganal
Is a voltage signal level in the circuirt which represents the flow of data. This can be either Analog or
Digital in nature
ii) Signal mgnaodulation and Demodulation
Is a process of converting data signal to and from a form that is suitable for transmission over a
transmition medium.
MODEM - Converts digitl signal by superimposing it on an analog carrier signal which is trnsmitted
over analog telephone line. A process known as Modulation
A modem at the receiving end converts the analog signal into digital form a process called
Demodulation.

iii) Multiplexing
Is a process of sending multiple data signals over the same medium e.g a wire conductor can carry several data signal either simultenously or at differenet times.
Demultiplexing
A preocess of seperating the multiplexed signals at the receiving end.



iv) bandwidth
- Is a maximun amount of data that the trnsmission medium can carry at any one time. e.g a cable having a bandwidth of 100 mbps.
v) Basesband
- A digiltal signaal that is generated and applied to transmission medium directly without modulation.
- It utilises the full capacity of transmission medium hence at any time, only one signal can be sent unless they are multipled.

vi) Attenuation/ Signal loss
- Is the decrease in magnitute and energy as a signal progressively move along a transmission medium. The signal is not boosted, it will totally be lost along the way and may never reach the destination.
- It corrected by placing a signal amplifier ( repeater station) along the medium at appropriate distances in order to receive the wek signal, clean it, amplify it then restart it.

MODES OF DATA COMMUNICATION
There are three modes of data communication
i) Simplex
ii) Half Duplex
iii) Full Duplex

1. Simplex
Communication in only one direction e.g radio broadcast. The listener cannot communicate back through radion receiver



2. Half Duplex
- Communication in both direction but one direction at a time e.g sender sends informtion then the receiver can reply e.g radio call


3.Full Duplex
- Communication occurs in both directions simultenouesly e.g a computer sending and receiving data on anetwork.


TYPES OF COMPUTER NETWORKS
Types of computer networks are classified acoording to size. There are three common networks
1. Local Area Network


2. Metropolitant Area Network



3. Wide Area Network


TYPES OF NETWORK TOPOLOGIES
- Refers to the way which computers and other devices have been arranged or how data is passed from one computer to another in a network
- Topology is viewed in two ways
1. Logical Topology/ Signal Topology
- Deals with the way data passes from one device to the next in the network e. g Ethernet and Token Ring


2. Physical Toplogy
- Refers to the physical layout or arrangement of cmponents on the network e.g Star, Bus, Ring, Mesh, Tree/Hierachical Topologies

1. Bus Topolgy
Alternatively referred to as a line topology, a bus topology is a network setup in which each computer and network device are connected to a single cable or backbone. The following sections contain both the advantages and disadvantages of using a bus topology with your devices.

Advantages of bus topology

• It works well when you have a small network.
• Easiest network topology for connecting computers or peripherals in a linear fashion.
• Requires less cable length than a star topology.

Disadvantages of bus topology

• Difficult to identify the problems if the whole network goes down.
• It can be hard to troubleshoot individual device issues.
• Not great for large networks.
• Terminators are required for both ends of the main cable.
• Additional devices slow the network down.
• If a main cable is damaged, the network fails or splits int

2. Ring Topology
A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet.













Advantages of ring Topology

• Very orderly network where every device has access to the token and the opportunity to transmit
• Performs better than a bus topology under heavy network load
• Does not require a central node to manage the connectivity between the computers
• Due to the point to point line configuration of devices with a device on either side (each device is connected to its immediate neighbor), it is quite easy to install and reconfigure since adding or removing a device requires moving just two connections.
• Point to point line configuration makes it easy to identify and isolate faults.
• Reconfiguration for line faults of bidirectional rings can be very fast, as switching happens at a high level, and thus the traffic does not require individual rerouting.

Disadvantages of Ring Topology

• One malfunctioning workstation can create problems for the entire network. This can be solved by using a dual ring or a switch that closes off the break.
• Moving, adding and changing the devices can affect the network
• Communication delay is directly proportional to number of nodes in the network
• Bandwidth is shared on all links between devices
• More difficult to configure than a Star: node adjunction = Ring shutdown and reconfiguration

3. Star Toplogy

Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central node, typically a switch or hub, which acts as a conduct to transmit messages. In star topology, every node (computer workstation or any other peripheral) is connected to a central node. The switch is the server and the peripherals are the clients.^[1]

Advantages

• If one node or its connection breaks it doesn’t affect the other computers and their connections.^[3]
• Devices can be added or removed without disturbing the network

Disadvantages

• An expensive network layout to install because of the amount of cables needed^[3]
• The central hub is a single point of failure for the network

4. Mesh Topology
A mesh network is a network topology in which each node relays data for the network. All mesh nodes cooperate in the distribution of data in the network. It can be applied to both wired and wireless networks.

Advantages of Mesh topology

1) Data can be transmitted from different devices simultaneously. This topology can withstand high traffic.
2) Even if one of the components fails there is always an alternative present. So data transfer doesn’t get affected.
3) Expansion and modification in topology can be done without disrupting other nodes.

Disadvantages of Mesh topology

1) There are high chances of redundancy in many of the network connections.
2) Overall cost of this network is way too high as compared to other network topologies.
3) Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.








Switch Bridge Packet forwarding in Switches are performed using ASICs (Application Specific Integrated Circuits). Packet forwarding in Bridges are performed using software. Work at higher speed. Work at lower speed. Switches have more ports. Bridges have less port. Switches can operate on half and full duplex mode. Bridges can operate on half duplex mode only.

Router Gateways Coordinates data transfer within internal network. Coordinates data transfer from internal network to internet. All the functionalty of gateways are in router. Gateways are integrated into the router. Always have to have a hardware to function. Some softwares also can perform as gateways.

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