4. Networks and the effects of using them Flashcards
What is a computer network?
A computer networks consists of 2 or more computers or electronic devices such as printers that have been linked together
What do networks enable us to do?
Share files
Send emails to each other
Share resources
How are networked computers joined together?
Cables
Radio signals
Telephone lines and satellites
Advantages of computer networks
Resources such as printers, scanners and internet can be shared
Files and data can be shared
Easy to communication with people on the network
Access our data from any computer
Data can be backed up to a separate computer for security
Access huge amount of information and files
Disadvantages of computer networks
If part of the network fails, the whole network can break down
Viruses can spread across the network very easily and quickly
If a computer on the network is hacked into then all other computers are prone to attack
What are the two types of computers that make up a network?
Servers
Clients
What is a server computer?
Powerful computers that provide ‘services’ to the client computers on the network.
Services provided by server computers
Providing central storage
Sharing devices
Providing network security
Sharing internet connections
Different types of servers
File servers
Application servers
Printer servers
Proxy servers
What is a client computer?
A normal computer that is used to perform everyday tasks and to access info and programs from the server.
What are the types of computer networks?
LAN
WLAN
WAN
Bluetooth
LAN
Local Area Network
Usually located in a single room or small building.
Private and can only be accessed by people in the room/building.
e.g. a school network is only used by students of that school.
Ads + disads of LAN
Ads:
Save money as each computer can share resources
Files and data can be shared easily
Files and data can be accessed from any computer within the server
Data can be sent around very fast
Can be monitored easily
Disads:
Viruses can spread very quickly
Security can be an issue
The network can become unusable if the main server computer breaks down
Slow internet connections
High initial cost
WLAN
Wireless Local Area Networks
Similar to LANs but they connect computers together wirelessly without cables.
e.g. home networks
Ads + disads of WLANs
Ads:
physically safer as no cables are needed
cheaper to set up than a WLAN
easier to add more computers
devices such as printers and scanners can be connected to the network easily
computers and devices can be used anywhere in the building
Disads:
some areas might not be able to pick up the signal
security can be an issue
wireless signals can be unreliable
data transfer is slower than LAN
signal range is limited, so useless in a large building
WAN
Wide Area Network
made up of computers and devices that are connected in a large geographical area
created by connecting lots of LANs and individual computers together
computers and devices can connect to a WAN using telephone lines, fibre-optic cables and satellite signals
need a router or a modem
e.g. the internet
Ads and disads of WANs
Ads:
computers can be connected over wide areas
files and data can be shard over a large area
users can communicate very quickly, over large areas
e-commerce
computers and devices can be used anywhere
Disads:
security can be an issue
easy to accidentally download viruses
data is transferred across a WAN is a lot slower than a LAN
monitoring a WAN is difficult
Bluetooth (WPAN)
Wireless Personal Area Network (WPAN)
devices can connect to each other between 1 and 100 metres away from each other
ads + disads of bluetooth
ads:
very easy to connect
not easy to disrupt
works wirelessly so no messy cables
very little power needed
disads:
limited signal range
slow data transfer
very secure
Internet
a computer network that connects computers worldwide
Intranet
a private network within a company and it is only available to staff members of the organisation
Local area networks (LAN) - describe
Not over a large geographical area (e.g. in one building)
Typical LAN will consist of a number of computers and devices
Devices and computers will be connected to hubs or switches.
One of the hubs or switches will usually be connected to a router and modem to allow the LAN to connect to the internet
LAN - Ads and Disads?
Advantages of Networking using LAN
The sharing of resources
Communication between users
Network administrator can control and monitor all aspects of the network
Disadvantages of Networking using LAN
Easier spread of viruses throughout the whole network
Increased security risk
If main server breaks down, usually the networks will no longer function.
Different topologies
Star
Bus
Ring
Wireless LANs (WLANs) - describe
Do not involve any wiring or cabling
Provide wireless network connection overs a short distance
They use radio or infrared signal’s instead of cables
Devices known as Access Points (APs) are used for a larger range
APs usually use spread spectrum technology (larger range)
Wireless LANs (WLANs) - Ads and disads?
Advantages
All computers can access the same services and resources
No cabling is involved
The system is more flexible
Adding new computers and devices is very easy
Cost is reduced and safety is improved
Disadvantages
Security is an issue
Problems and interference can affect the signal
The data transfer is slow than in the wired LAN
Wi-Fi - describe
Any system which allows you to connect to a network or computer through wireless communication
Examples :
o WLANs
o Tablets
o Laptop computers
o Peripheral devices such as printers
Wi-Fi Hotspots - describe
Wi-Fi systems rely on AP (radio frequency technology) to enable the device to receive and send signals
Wi-Fi hotspots are places where you can access Wi-Fi (free or paid)
Hotspots are found in public places like Airports, hotels and cafés
Bluetooth - describe
Bluetooth is an example of wireless personal area networking (WPAN) technology
Spread spectrum transmission (radio waves) is used to provide wireless links between to devices such as mobile phones and allow connection to the internet
A small home network can be created with this system
Used to transfer photos from camera to a mobile phone. It behaves like a mini-LAN
Wide area networks - describe
WAN is formed by a number of LANs being connected together through a router or a modem e.g. the Internet is a WAN
Some companies set up Private WANs, it is expensive however it comes with a much enhanced security
It is common to use an Internet service provider (ISP) for connections to the internet and communicate via this network system
Additional hardware is needed for a WAN: Routers, modems and proxy servers
Modems - describe
It stands for modulator demodulator.
Converts computer’s digital signals (modulates it) into analogue for transmission through telephone
lines.
Reverse this process- analogue signal from a telephone line into digital for a computer to process the data. (demodulates it)
The main use it to connect to computer networks over long distances using existing telephone lines.
Network Hubs - describe
They are devices that can have multiple devices connected to them.
Main task is to receive data from different ports and send it to each device
The information will be received to the device whether its relevant, or not
Switches - describe
More efficient than hubs in distributing data.
Each device has an access control media address MAC which identifies it uniquely
MAC is a number unique to each device connected to the network (like fingerprints)
Data sent will have a mac address which tells the source and receiving device.
Bridges - describe
It connects 2 different types of networks together e.g. a bus and star network
It can only connect networks that use the same way for handling messages
They do this by changing the form of message to suite the different type of network
Routers - describe
Acts like a bridge, yet can link between two or more networks
Makes decisions on messages being passed between the networks
Formats the messages making it suitable for the new network
Reads information about the message and decides where the message should go and the best route for it to get there
Used to provide a connection between a network and the internet
You need an ISP account to have access to the internet (internet server provider)
HTTP Proxy Server - describe
Type of server that acts as a buffer between a WAN and a LAN.
Retrieves web pages and passes them onto the computer that made a request.
Stores any page retrieved on the server, which means that when a different computer requests the same page it would be available.
Speeds up the browsing process
The Internet - describe
The Internet is a worldwide collection of networks.
It allows for web browsing, gaming, file sharing, video and email.
User can access by web browser.
Websites - describe
Web is made up of millions of websites and web pages
Web pages are documents on a computer screen containing
Uniform Resource Locator (URL) - describe
Web browsers use URLs to retrieve files.
They are standard way of locating on the internet
Standard form: 4 numbers e.g. 194.106.220.19
Also alphanumeric form: protcol://site address/path/filename
Where; Protocol is usually http
Site address consists of: computer name, domain name, domain type, and country code
Path is the web page
Filename is the item on the page
ADSL modems - describe
Operate at 11,000 kilobits/sec.
Faster at downloading than uploading
They don’t tie up the line while accessing the internet
Intranets - describe
It is an internal website that is setup internally for companies and can be accessed by employees for the purpose of standard documents or information and many items of information and data. They use internet protocols i.e. a browser
Intranets - advantages
Safer and less chance of hacking
Possible to prevent employees from accessing unwanted sites
Companies ensure that info. available is specific to their needs
Easier to send sensitive messages that remain within a company
User IDs - describe
To log on to a network, a user must type in a user ID
User ID assigns user privilege once user logs in
The top level privilege for a network is an administrator: Able to set passwords and delete files from server etc.
User privilege may only allow to access their own work area
Passwords - describe
After typing in user ID, the user will be requested to type in their password.
Generally, it is a combination of letters and numbers
Passwords are shown as stars (***) so nobody overlooking can see it.
Many systems ask for password to be typed in twice as a verification check, in case of input errors
To help protect the system, user is has a finite number of attempts
If password is forgotten, administrator has to reset it
If password is forgotten on a website, it will be sent to your e-mail
Encryption - describe
The conversion of data to code by encoding it
Done by using encryption software
Since data is encoded, it appears meaningless to a hacker
This technique does not prevent illegal access
Necessary to use decryption software to decode the data
Used to protect sensitive data e.g. banking details
Encryption keys are complex algorithms which makes codes almost unbreakable
Describe authentication techniques
Biometric methods: finger print, retina scans, iris scans, face scans - using physical characteristics to authenticate access to systems
magnetic stripe cards
Fax -describe
A system that scans documents electronically and converts them into a bit map image (a bit is a binary digit and is a 1 or a 0)
Then transmitted as a series of electrical signals through the telephone network
Receiving fax machine converts the electronic image and prints it out on paper
It is also possible to generate fax signals from a computer to allow documents to be sent to a fax machine
This saves printing out the document first and then passing it through the fax machine
Fax/modem software in the computer converts the image into a form fax machines can recognise
Email - describe
A method for sending text and attachments from one computer to another over a network
Email - ads and disads?
Advantages
Speed of sending and receiving replies is quick
Low cost (no stamps, paper etc.)
Not needing to leave home to send the mail
Disadvantages
Possibility of virus threats and hacking
Need for the email address to be correct
Inability to send bulky objects via emails
Don’t always get immediate response
Video Conferencing - describe
This is a method of communication between people at 2 or more separate locations
It is done in real time and makes use of LAN, if internal, or WAN if through the internet.
Uses hardware like; webcam, microphones, speakers and monitors
It also uses special software like CODEC converts and compresses analogue data into digital data to send down digital lines.
How it works
Delegates at one end speak into a microphone and look into the webcam.
The other delegates can see them and hear them using speakers and monitors,
However there are several problems with these as the conference call often lags and quality is not always high. Also, as travelling tickets increase in price, terrorists can use this way of communicating with each other, increasing risk.
VOIP - describe
VOIP (Voice over internet protocol) is a method used to talk to people over internet
VOIP converts sound (picked up by a microphone) into discrete digital packets that can be sent to a destination via internet
The biggest advantage is that it is free and can be used all over the world
The biggest disadvantage is that sound quality is usually bad.
General security issues - describe
Identity and service theft
Viruses and malware
Spamming (sending junk mail)
Phishing attacks (the act of sending an email to a user falsely claiming to be an established legitimate enterprise in an attempt to scam user in different ways
What is LAN?
Local Area Network
What are the features of LAN?
PCs located usually in the same building
computers connected by cable
does not require a modem
requires a server
What is WAN?
Wide Area Network
What are the features of WAN?
the internet is the largest WAN
PCs connected by telecomunications or wireless
mormally spread over various distant areas
requires a modem
requires a phone/dedicated line
computers/LAN can be large distances apart
What is WLAN?
Wireless Local Area Netweork
