Networking and connectivity

Course Content stand-alone or networked LAN or internet National 4 National 5 stand-alone or networked LAN or internet Wired or wireless peer-to-peer, client/server media: wired, optical, wireless.

Stand-alone or networked A stand-alone computer is not part of a network A network is a linked set of computers Capable of :- sharing programs and data Sending messages Two types of network (depending on the distance between the computers) :- Local Area Network Wide Area Network – the internet

Local area network Covers a small area e.g. a room or building Owned by a person or organisation e.g. our school

LAN features Computers called stations Has a special station called the file server File server stores :- shared programs user’s data files list of authorised users

What is the Internet? A wide area network that lets computers all over the world communicate Lots of networks connected together Made up of :- Large, well-organised networks e.g. Governments, universities, multi-national corporations Small company networks networks e.g. schools and little companies People at home using Internet Service Providers

What is an Internet Service Provider? A company that provides a host computer that subscribers connect to. The host computer:- sends and receives data for the subscriber to they can use the internet to communicate Stores the following for the subscribers:- electronic mail web pages files

Questions 1 Describe a network of computers Why does our school have a network Where would you find a local area network (apart from at school)? Which ISP do you use at home? Carry out some research and write a note about the key features and monthly cost of your ISP.

Graphic of the Internet How does it work?

Connectivity Transmission media – carries data on a network E.g. Wired (cables) or wireless (WiFi) Bandwidth – the amount of data that can be carried by a communications channel at any one time. On a network – “data transfer speed” means the same as “bandwidth” Measured in Mbps – Megabits per second – or Gbps – Gigabits per second.

Transmission media for LAN Wires or wireless technology (owned by the organisation) can connect stations Two types of cable may be used:- Unshielded twisted pairs of copper wires (UTP) Optical fibre

UTP cable facts Carries electrical signals Cheaper than optical fibre Interference can affect electrical signals Can be tapped i.e. someone else can read the signals carried by the cable Can corrode (rust) Can carry power to a device along with data Lower bandwidth than optical fibre – carries less data at a time Carry data over a shorter distance than optical fibre

Optical fibre cable facts Made of lots of very fine stands of glass Beams of light travel along cable More expensive than UTP Secure data transmission – no-one else can read the signal Does not corrode Higher bandwidth than UTP Can carry data over a longer distance than UTP

Questions 2 What type of cables are used in our classroom? Answer “UTP” or “Optical Fibre” for each of the following:- Higher bandwidth More secure Can carry power and data Carries data over longer distance Affected by interference Less expensive

Wired transmission for LANs Bandwidth - 1 Gbps (Gigabit Ethernet) At 1 Gbps a DVD-quality, full-length Hollywood movie it could take 30 seconds to download This would take several hours over a typical internet broadband connection

Wireless transmission for LANs - Bluetooth Uses radio waves that pass through walls so devices don’t need to point at each other Temporary short-range link between personal devices e.g. mobile phones and headsets Palmtop Laptop Range 10m Bandwidth is between 1 and 3 Megabits per second (Mbps) Wireless mice and keyboards typically use Bluetooth® transmission.

Wireless transmission for LANs - WiFi Wireless Fidelity Alliance - allows an electronic device to exchange data wirelessly over a Local Area Network Used in:- laptop computers wireless routers mobile phones some games consoles Minimum range (inside) 60m, (outside) 200m Data transfer rate – at least 600 Mbps

WiFi security Protect your home WiFi with a hard-to-guess password, to prevent other people from using your bandwidth Using someone else’s bandwidth may lead to prosecution Someone else using your internet connection to do something illegal may result in you being held responsible - unless you can prove otherwise

Advantages and Disadvantages of Wireless Technology Easy to install Easy to add more computers Portability – a laptop can be used anywhere that the signal can be received Not as secure as a network with wires

Questions What units are used to measure bandwidth? Give an example of where blue tooth transmission is used. Why is WiFi not used for a home network? Give an example of where WiFi is used. Describe how can someone “use your bandwidth” and how you can prevent it from happening.

Network Interface Card NIC Circuit board in computer to let it communicate with the network wired wireless

Transmission media for Wide Area networks Transmission media in a WAN are own by many different organisations Three types of media are used :- Copper cable Optical fibre Wireless – including microwave and satellite

Transmission media for WANs - Microwave transmission Used by the public phone service Organisations may use private installations to send data between important locations Dish aerials used – directional i.e. the dishes point in the direction that they send and receive on

Transmission media for WANs - Satellite links Public phone services use satellite links for international calls One channel carries lots of separate transmissions Use highly directional, narrow beam, two-way transmissions

Transmission media for WANs - Optical fibre Described earlier Remember – not affected by interference so optical fibre provides a reliable link

WAN and the internet: bandwidth Low bandwidth compared to a LAN Most common method of connecting a home computer to the internet is ADSL or Asymmetric Digital Subscriber Line A typical home computer may connect to a WAN such as the internet, at a data transfer speed of 8 Mbps using ADSL via a standard home telephone line This bandwidth is download (receiving data) only. Sending data (uploading) is at a much slower rate, for example 512 Kbps The bandwidth of a WAN connection may be greatly improved if your locality or home has a dedicated cable or optical fibre connection, rather than just a standard telephone line. Many urban areas have optical fibre connected to the cabinet in the street (Fibre To The Cabinet: FTTC), typically allowing bandwidth of between 40 and 100 Mbps. Higher bandwidth may be expected if your home has a direct optical fibre connection (Fibre To The Home: FTTH or Fibre To The Premises: FTTP)

Questions Why does a computer require a Network Interface Card? Describe a difference between microwave transmission and satellite links.

What is a peer-to-peer network Each computer has same status Each computer has its own set of application programs and backing storage devices i.e. hard disk and optical drives The user may log but the user’s data is stored locally, on the hard disk so... ... each user must always use the same computer Each user must back up their own data Resource sharing is available to users – e.g. can share a printer to avoid buying one for each computer

What is a client and server network? Clients (network stations) use resources available on server(s) Most clients are desktop computers Each client has a Network Interface Card that allows it to connect to the network

What is a server? A computer that deals with requests from other computer for data, e-mail and file transfers e.g. documents, programs and webpages

File server - hardware Central disk storage - holds programs and user’s data on a network Compared to a client it has:- faster processor or many processors to respond quickly to many users More hard disk space More RAM Better quality components as it runs 24 hours a day / 7 days a week A backup of files is essential – e.g. on magnetic tape

File server software Software organises user’s files and provides security for them Manages usernames and passwords to control access to files – users must log on to access their files Each user is given access permissions to control what files and software they can use Each user can be given a disk quota to control how much disk space they are allowed to use

Protecting the file server A File server should have an Uninterruptable Power Supply (UPS) This battery allows it to operate a short time when there is a power cut The file server will safely shut down if the power does not restart quickly

Printer Server Controls a printer so many client stations can use it Puts requests for hard copies in a queue Often large monochrome laser printers – as they are fast Colour laser are becoming common too Network printer has a processor and RAM to store the print jobs

Background printing If there is no printer server on a LAN print jobs are spooled to the workstation’s own local hard disk This allows the user to continue working while the print job is dealt with by background printing Background printing - the processor is shared between the user’s commands and sending the print job to the printer when it is ready for more data

Other servers CD-ROM server – client stations access a number of CD-ROMs (e.g. Encarta) Database server – centrally stores a database for client stations to access Web server – stores webpages that it provides to provides computers

Other servers Internet server – lets stations access the Internet Mail servers – transfers e-mail between computers e.g. POP3 or SMTP

Advantages of LAN Share data and programs Share peripherals e.g. Printers. Called “resource sharing” E-mail Passwords keep data secure Workgroup computing – many users can access a file at the same time Client server network advantages:- Flexible access – users access files from any station Different levels of access for users Central backups ensure all user’s data is safe

Client server disadvantages If the file server is not working no-one can access their files The file server and software are expensive

Questions 5 Which topology is used in our school network? Suggest two places that a multi-access computer system consisting of a mainframe computer and terminals be used How does a printer server cope when lots of users want a hard copy at the same time? Describe a client and a server in our network.