Introduction to Networks

Objectives

• The purpose and uses of networks• The Key components of a computer network• The Different types of network and the

advantages and disadvantages of them

The Importance of Networks

Networking is a way of connecting hardware together so that software, data, files and peripheral devices can be shared.

Networks allow users to have access to lots of hardware devices from their personal terminal.

What is the Internet• The internet is a network of networks that

connects governments, people and companies all over the world

Where did it Begin?

• The ancestor of the Internet was the ARPANET, a project funded by the U.S. Department of Defence (DOD) in 1969.

• Later in the 1980’s American Universities used something similar to communicate between them.

• In 1991 British born scientist Tim Berners-Lee created the World Wide Web that used the HTML language to communicate with. This made it possible for people to use the Internet from home.

• The World Wide Web (www) was developed to make Browsing (viewing) easier through http (Hypertext Transfer Protocol)

• http is a set of standards that allows web browsers and servers to communicate.

Network Components - Modems

A modem stands for Modulator-demodulator. They connect computers to the Internet or distant networks by converting the digital, binary signals into an analogue signal that can be transmitted down telephone lines.

Old modems converted digital information to an audio signal which sounded like screeching.

Modern modems are built into computers and use DSL or ADSL technology. These use much higher transmission frequencies which allows for faster data transfer.

Network Components – Network Cards

• In order for a computer to function as part of a network, it has to have a special piece of equipment installed to give it this capability.

• This is called a Network Interface Card or NIC. It has a port for a network cable to be connected.

• NICs are still fairly common, but increasingly people are using wireless network cards or wireless USB adapters.

Ethernet and Alternatives

• Ethernet is the name given to the most common method of networking computers. Although other methods exist, Ethernet has been the standard since 1990’s.

• Ethernet uses CAT 5 cables to connect the computers together

HubsHubs are devices that are used to

connect multiple computers on a network. An ethernet cable connects each computer’s Network Interface card (NIC) to the hub which allows the computers to start sharing data. Hubs are inexpensive, but any data transmitted to the hub is transmitted to all computers (whether they are the intended recipients or not). This process can slow the network down or even make it crash.

Switches

Switches connect multiple computers together on a network. Switches are more ‘intelligent’ than hubs but also more expensive. Data is sent from one computer to the switch. The switch reads the data and locates the computer or device where it needs to be sent. It then forwards it to that location. This frees up brandwidth, meaning that the network is not as clogged up. This improves performance and speed.

RoutersRouters are also connection devices

but they work at a network level whereas switches and hubs work at a device level. Routers allow one or more LANs to connect to a WAN. The router joins the networks and sends the incoming and outgoing data to the correct places. Routers with built in modems are popular for home users but business routers tend to be far more complex. Routers are used in many homes to connect home LAN to the Internet.

Network AddressEach computer on a network has a network address so that devices can recognise where the data needs to go. Software breaks down data into small parts so they can be directed by the quickest route to their destination. These small parts are called packets and will be reassembled when they arrive at the right destination.

Similarly, computers connected to the internet have their own IP address to allow these to arrive at the right location.

Cables

There are many types of network cable.Twisted pair cables are he most common. This cabling

is often called ethernet cabling. Category 5 (Cat5) twisted-pair cables can carry 100Mb per second over distances of up to 100metres.

Coaxial cable is better at resisting interference and can be run for longer lengths, but it is not as flexible and is not used much now.

Fibre optic cable can transfer data at higher speeds over longer distances and can be used outside buildings, but is it much more expensive. It has a central core made of glass and transmits the signals using light.

Wireless Networks

With improvements in radio technology, it has become possible to connect computers on a LAN network (Local Area Network) without using wires.

A wireless network card is similar to a standard NIC, but has a transmitter/receiver for sending signals via radio waves.

Wireless networks are popular as they allow the user much more freedom, such as working outdoors.

Wi-Fi Hotspots

Wi-Fi technology allows users to wirelessly connect to the Internet. Access points are set up at various locations from which users can connect to a wireless network and access the Internet.

Many cafes and bars offer wireless hotspots, allowing users to work where they please.

What benefits and drawbacks might establishments face when offering Wi-Fi access?

Mobile Networks

It is now incredibly common to use mobile devices to access a network. Most modern mobiles allow Internet access via 3G (third generation) networks.

It’s not just mobiles though. Tablet computers, PDA’s, E-readers and even gaming devices like Nintendo DS are all being created with the ability to connect to local area networks (LANs) or wide area networks (WANs) without the need for cables.

URLs

The Domain Name system links the IP address (eg. 217.27.240.45) with the text name or web address (eg. www.bbc.co.uk). This means that users only have to remember a short name instead of lots of numbers.

URLs

URLs are usually made up of these parts:• www, standing for World Wide Web• An organisation name (bbc)• A top level domain (.co)• A country (.uk)• There are many top level domains, for instance .com, .org

(organisation), .sch (school) and .ac (university).• When you are deciding whether the information from a

website is reliable, take a look at the URL. It will give you some idea about the source of the information.

Speaking the Same LanguageTo allow different types of computers in

different parts of the world to interact, there has to be some agreement about how they communicate.

These standards are called protocolshttp is the first part of many web

addresses – it stands for hypertext transfer protocol and states the protocol that the site will use to communicate.

HTML stands for Hypertext Markup Language and it is the standard language for writing webpages.Do you know what HTTPS stands for?