Networks

What is a Network?• Two or more computers linked together so they can send

and receive data.• We use them for sending e-mails, downloading files,

shopping, etc• They are divided into two types:

– Local Area Network (LAN)– Wide Area Network (WAN)

Local Area Network (LAN)• Cover a small area such as one room or building.

– The school has a LAN

• Each computer on a LAN is called a station

• One station is called the file server. – The file server is where

all the data & files are kept

Advantages of a LAN• Share data• Share peripherals (resource sharing e.g. Printers)• E-mail• Passwords keep data secure• Different levels of access

– stop unauthorised access• Flexible access

– Use any station connected to the LAN• Many users can use same document at the same

time (workgroup computing)

Transmission media for LAN• Stations can be connected by cables or

wireless technology• Cables:

• Unshielded Twisted Pair of copper wire (UTP)

• Uses electrical signals to transmit data• Cheaper but can get interference

• Optical fibre • Uses light beams to transmit data• Expensive but doesn't get interference

http://www.youtube.com/watch?v=WGvoJxIPAmw&feature=related

By changing the colour and wavelength of the light signals, we can send multiple pieces of data through the fibre cable at the same time. This is demonstrated with the 2 music clips from the video above.

Transmission media for LAN• Wireless

– Infrared communication• Like the TV controls

– Bluetooth• Range of about 10 metres

– WIFI (Wireless Fidelity Alliance)

• Range of about 12-50 metres

Bluetooth & WIFI use radio waves

Wide Area Networks (WAN)

• Connect computers across large distances • Spread across countries & cities worldwide

using telecommunications links• Similar advantages to LAN but on a bigger scale.

Transmission media for WANs• Telecommunications links

– The communication of information over a distance using:• Microwave transmission• Satellite links• Optical Fibre

Networking Modes• There are then two main networking modes

which affect how the network operates

• You can configure the network to be a • client-server network

or a• peer-to-peer network.

Client-Server Networks• In a client-server based network, the server is

a computer dedicated to managing the network resources.

• The server is the central part of the network, holding many resources in one place.

• Other computers, known as clients, then access this central server for applications, data, and hard disk space.

Client-Server Networks

Client-Server Networks

Server Description

Print

File Provides central storage and controls access levels for users

Web

Proxy

CD-ROM

Application

Mail

Peer-to-Peer Networks• In a peer-to-peer network, resources are not

located on a central computer but they are shared by the computer where the resources are stored.

Peer-to-Peer Networks

Services Provided by The Internet

• World Wide Web - On the web people can email, chat, browse, download, listen and do many more things.

• Email clients offer many features. As well as simply sending and receiving emails, you can attach files, create groups or mailing lists.

Services Provided by The Internet

• File Transfer Protocol (FTP) programs can be used for uploading or downloading files. This process can be anonymous or you may be required to log on with a user ID and password.

• Instant Messaging programs allow for real time communication. You may also share files or video conference using these programs.

Addressing on The Internet

• Every machine on a network including the Internet has a unique IP address

• This allows it to be identified by any other machine on the network. (like you have a home address)

• For ease of use, however, Domain Name Servers are used to translate numerical IP addresses to names which we can remember much more easily. (173.194.35.159) (212.219.209.216)

Addressing on The Internet

• Web sites typically have a domain name and a folder structure. You navigate through the folder structure to find particular pages.

• For example: http://www.bbc.co.uk/news/index.htm

• In this example, http is the protocol used to transfer the web page, www.bbc.co.uk is the domain name, news is the folder you are accessing and index.htm is the single page you are looking at.

Addressing on The Internet

• Similarly, email addresses have a naming convention.• For example: headmaster@trinity.sch.uk• Where headmaster is the user name or mail

recipient and trinity.sch.uk is the domain name. • The domain name consists of a registered name and

a top level domain identifier.• For example microsoft.com shows that Microsoft is

the company and .com shows that it is a commercial organisation.

Cloud Computing

• The term cloud is used as a metaphor for the Internet, based on the cloud drawing used to represent the Internet in computer network diagrams.

• Cloud computing refers to the delivery of applications and storage as services accessed remotely by users through web browsers or locally installed software/ mobile app.

• e.g. iCloud, GoogleDrive, SkyDrive, Glow, Jaycut…

Cloud Computing

Cloud Computing

• Advantages• Many services are free• No need to purchase software/

hardware• Accessible anywhere, anytime• Single point of storage ensuring

data integrity• Data backup provided by the

company providing the service

• Disadvantages• Limited functionality/ storage

unless you subscribe/ pay• Requires an internet connection• Can be slow• Entrusting someone else with

your data/ privacy