3.1 Network Basics

3.1.1 Basic Concept of Network

---

What is meant by Network?

Network is collection of computers and devices(also known as nodes) connected together via communications devices and media. For example:-

• PCs
• Printers and plotters
• Scanners
• Communication hardware(modems, hub, switches) 

The purpose of network is to share data, information and resources. 

  

Communication Device is known as any type of hardware capable of transmitting data, instructions and information between a sending device and a receiving device.

Computer Communications is known as a process in which two or more computers or devices(communication device) transfer data instructions and information.

Things needed to communicate successfully are:-

• a sending device (communication device)
• Transmission media
• a receiving device (communication device) 

Type	Modem	Network Card	Wireless Access Point	Router	Hub/Switch
Function	Convert digital signals to analog signals and analog signals to digital signals, so that data can travel along an analog telephone line.	Enables a computer or device that does not have built-in networking capability to access a network.	A central communications device that allows computers and devices to transfer data wirelessly among themselves or to transfer data wirelessly to a weird network.	Connects multiple computers or other routers together and transmits data to its correct destination on a network.	Provides a central point for cables in a network, receives data from many directions and then forwards it to one or more destinations.

 Transmission Media

Definition: Materials that capable of carrying one or more signal from one system to another.

Types of Transmission Media:

1. Physical Transmission Media: use wire, cable and other tangible materials to send communications signals.
   
2. Wireless Transmission Media: send communications signals through the air or space using radio, micro wave and infrared signals.

3.1.2 Network Architecture

Network architecture is defined the design or configuration of computers, devices and media in a network. 

 Type of Network Architecture are:

1. Client/Server

1. Centralized control by the server can be more efficient at administering the whole network.
2. Network professionals are normally needed to manage and maintain the whole network.
3. Cost to install and manage the network can be expensive.
4. Only servers have high responsibilities and capabilities.

 2. Peer-to-peer

1.  Every user is taking care of his/her own machine so could be difficult to administer the network.
2. Easy to install and configure for the computers in the network.
3. Cost to install and maintain network is inexpensive.
4. Each computer has equal responsibilities and capabilities.

ADVANTAGES

Client/Server	Peer-to-peer
All files are stored in a central location Network peripherals are controlled centrally Backups and network security is controlled centrally Users can access shared data which is centrally controlled	No need for a network operating system Much easier to set upthan a client-server network - does not need specialist knowledge Does not need an expensive server because individual workstations are used to access the files.

 DISADVANTAGES

Client/Server	Peer-to-peer
A specialist network operating system is needed. The server is expensive to purchase  Specialist staff such as a network manager is needed If any part of the network fails a lot of distruption can oc	Files and folders cannot be centrally backed up Ensuring that viruses are not introduced to the network is the responsibility of each individual user Because each computer might be being accessed by others it can slow down the performance for the user

3.1.3 Network Topology

Network topology is defined as a network topology refers to the layout of the computers and devices in a communications network.

Bus 

Physical Description	Consists of a single central cable(backbone/bus), to which all computers and other devices connect Each device is connected to the single bus cable through T-connecter A terminator is required at each end of the bus cable to prevent the signal from bouncing back and forth on the bus cable
Logical Description	Data is sent to all computers, but only the destination computer accepts it. Only one computer at a time can send data on a bus network
Advantages	Use less cable than other topologies Can easily add more workstations Failure of one device usually doesn not affect the rest of the bus network
Disadvantages	If backbone breaks, the whole network down Difficult to isolate problems Access time and network performance degrades as devices are added to the network.

Star

Physical Description	All the computers and other devices on the network connect to a central device, thus forming a star. Devices that provide a common central connection point for nodes on the network are a hub and a switch.
Logical Description	All data that transfers from one node to another passes through the hub or switch. The hub/switch takes a signal that comes from any device and passes it along to all the other devices in the network.
Advantages	Easy to add devices as the network expands Hub provides centralised management Easy to find device and cable problems
Disadvantages	A star network requires more cable than a ring or bus network. Failure of the central hub(router/hub) can bring down th entire network.

Ring

Physical Description	A cable forms a closed loop(right) with all computers and devices arranged along the ring. Each device takes a turn sending and receiving data through the use of a token.
Logical Description	Data transmitted on a ring network travels from device to device around the entire ring, in one direction. Each device takes a turn sending and receiving information through the use of a token. Only the device with the token is allowed to send data. All other devices must wait for the token to come to them.
Advantages	Cable faults are easily located, making troubleshooting easier. The uses of token passing enable all devices in a ring topology to share the network resources fairly.
Disadvantages	A failure in any cable or device breaks the loop and can take down the entire network. A ring netwrork can apan a larger distance than bus network, but it is more difficult to install.

3.1.4 Network Classification

Definition :-

LAN(Local Area Network)

• Networks that connects computers and devices in a limited geographical area.

MAN(Metropolitan Area Network)

• A high-speed network that connects local area networks in a metropolitan area.

WAN(Wide Area Network)

• Networks that connects computers and devices in a large geographical area.

Criteria	LAN	MAN	WAN
Size/Area	Confined to a single building.	Cover multiple buildings in a city area(metropolitan city).	Cover any size geographical area(country wide or worldwide).
Ownership	Controlled and managed by a single person or organization	Single entity such as government body or large corporation	Own by any organization which exist under distibuted ownership and   management over long distance
Example	-Network in a Computer Lab -Network in a home	-Traffic light system in metropolitan city -Network used for banks in metropolitan city	-The Internet

3.2 The Internet
The Internet is a worldwide collection of networks that links millions of businesses, government agencies, educational institutions and individuals.

Advantages of using Internet

1. Faster communication - People can communicate in a fraction of second with a person who is in the other part of the world.
2. Entertainment - There are numerous games that can be downloaded for free
3. Online services - With numerous online services people can now perform all their transactions online.

Disadvantages of using Internet

1. Theft of Personal Information - User of Internet for online banking, social networking or other services, may risk theft of personal information such as name, address, credit card number etc.
2. Spamming - Spamming refers to sending unwanted e-mails in bulk. Such illegal activities makes your Internet slower and less reliable.
3. Virus Threat - Computers connected to the Internet are very prone to targeted virus attacks and may end up crashing.

Intranet	Extranet	Internet
Intranet access is private-is restricted to an organization	Extranet access is semi private-used for the purpose of data sharing between closely trusted organization.	Internet access is public-everyone can use the Internet.

Two types of Internet connection: 

• Dial-up - is a fixed Internet connection that uses a voiceband modem and telephone lines

• Broadband - offers high-speed Internet access in terms of data transmission, upload and download times and connectivity.

Type of broadband

1. Cable Internet Srvice
2. Digital Subscriber Line (DSL)
3. Fiber to the Premises (FTTP)
4. Fixed Wireless
5. Cellular radio Network
6. Wi-fi
7. Satellite Internet Service