Higher Computing – Unit 3

Transcript Higher Computing – Unit 3

Higher Computing – Unit 3

Topics 5-8, 2, 9 Networking

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Topic 5 : Implications of WWW - Pre-Requisite Knowledge

Before studying this topic you should know what kind of services are provided by the Internet. You should know that an Internet Service Provider (ISP) is needed before you can connect a computer or a network to the Internet. You should be aware of the existence of E-commerce, and its implications for home and business users. You should be able to describe the main features of the Regulation of Investigatory Powers Act.

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Topic 5 : Implications of WWW – Learning Objectives After studying this topic you should be able to: • Describe the implications of the World Wide Web (WWW) for E-commerce • Understand the social ethical and legal implications of the WWW • Describe the current legislation which affects users of the WWW

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Topic 5 : Implications of WWW – Revision Q1: What is E-commerce?

a) The ability to use the Internet for communication b) The ability to use the Internet for economic transactions c) Downloading music from the Internet d) Using Electronic Funds Transfer (EFT) Q2: Which of these is not covered by The Regulation of Investigatory powers Act?

a) Employer monitoring their employees emails b) Government monitoring a telephone line c) Buying goods over the Internet d) Using encryption to hide details of a crime Q3: Why is an Internet Service Provider (ISP) needed before you can connect a computer to the Internet?

a) Every computer connected to the Internet needs a unique IP address and ISPs provide these.

b) You need a telephone connection which ISPs can supply.

c) ISPs control the Internet.

d) Connecting a computer to the Internet is very complicated and only ISPs can do this.

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Topic 5 – Implications of WWW - Introduction The World Wide Web has implications for: •the way people communicate with each other, •how societies are organised, •how information is shared, •and how we are governed.

Many of the changes which the WWW has been responsible for have not yet been realised by everyone, and many governments are only just waking up to its benefits and dangers.

This topic explores some of the commercial, social, ethical and legal issues which the existence of the WWW raises.

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Topic 5 – Implications of WWW – E-Commerce E-commerce - buying and selling products or services over the Internet Electronic Funds Transfer (EFT) - we now take it for granted that we can use ATMs and pay for goods in shops and on-line, all over the world, using a credit or debit card.

This is only possible because of the networked banking systems. On-line purchasing has led to fears about security of credit card details and the difficulty of receiving compensation if goods or services do not arrive or are not what they are advertised to be.

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Topic 5 – Implications of WWW – E-Commerce There are 3 different types of e-commerce: 1. Business to consumer e-commerce is the sale of goods or services to the general public via the internet.

2. Consumer-to-consumer e-commerce allows consumers to purchase goods from one another. An example of this is an online auction, such as Ebay.

3. Business-to-business e-commerce is when businesses provide goods and services to other businesses. Services may consist of online advertising, job recruiting, credit, sales, market research, technical support, web hosting, and different types of training.

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Topic 5 – Implications of WWW – Purchasing Software from WWW Software is often distributed via the Internet, with be locked, or set to expire after a period of time unless it is registered. Payment of a fee results in the code to unlock the software being sent by email.

Pay as you go software will be possible when sufficient bandwidth is available! Because everyone would be using the same version of the software, software companies would be able to save on technical support and distribution costs. They would also be able to offer services such as data backup, offering many of the advantages of a Local Area Network. Software distributed over the Internet can often be cheaper because developers can save on distribution costs and reach a very wide market. are prepared to pay a small amount for software it may prepared to pay a large amount.

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Topic 5 – Implications of WWW – Purchasing Software from WWW Mass Markets - Even if a product is very specialised or allows vendors to target their product to a particular audience, world wide.

Purchasing Services over the Internet

Eg Access to an Internet connection, a certain amount of bandwidth and sometimes networked storage facilities for file transfer and web hosting. Allows training and on-line courses over the web eg Scholar using an ID and password. Content providers can sell access to information on the Internet eg up to date stock market prices, detailed satellite data, photographic images, on-line training, news feeds and other services. Entertainment services are services, which are likely to become subscription based services.

Advertising fees allow content to be provided "free" to users in the same way that advertising is able to fund

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Topic 5 – Implications of WWW – Advantages of E-commerce The advantages of E-commerce to the customer are: • Goods and services can be purchased at any time of day or night • Goods and services can be purchased from anywhere in the world • E-commerce uses Electronic Funds Transfer (EFT) so no cash needs to be used • Consumers are able to research a product and its competitors more thoroughly • before purchase and compare prices from different retailers • Goods purchased arrive by post or courier so reducing

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Topic 5 – Implications of WWW – Advantages of E-commerce The advantages of E-commerce to the merchant are: • Dealing directly with the customer means no profit taken by retailers or "middlemen" • Your customer base is no longer restricted to those who can travel to your nearest outlet • You do not need to pay for expensive high street retail outlets • EFT means no security problems handling cash • You can automate the packing and delivery of your product • Your on-line profile does not depend on the physical size of your organisation • Stock control, order tracking and funds transfer can be automated and linked directly to e-transactions

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Topic 5 – Implications of WWW – Disadvantages of E-commerce The disadvantages to the consumer are: • If you purchase goods or services from a company in another country then you may have difficulty recovering funds if goods do not arrive or are not what was advertised.

• You rely on the security procedures of the firm you are dealing with to keep your credit card details secure.

• You may pay more for delivery or packing than it would cost you otherwise • Local businesses may suffer if you purchase on-line from larger firms • If you purchase goods from supplier in another

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Topic 5 – Implications of WWW – Disadvantages of E-commerce The disadvantages to the merchant are: • Since customers may be anywhere in the world you need to have good security in place to avoid credit card fraud • You need to employ someone to keep your web-site and catalogue up to date • You need to make sure your web site is secure and that your servers are protected from hacker attack

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Topic 5 – Implications of WWW – Disadvantages of E-commerce - Fraud Security on the Internet is of particular concern eg financial transactions in banking or the stock market. Concerns that credit card details being transmitted over the Internet could be intercepted or stolen from company servers are widespread. Anyone using an on line bank account needs to be reassured that the system they are using to access their financial details is as secure as possible.

Most e-commerce sites use the HTTPS (HTTP over a Secure Socket Layer) protocol to ensure that credit card data cannot be intercepted when it is being transmitted over the Internet. The HTTPS protocol browsers will display a padlock icon or similar when using this protocol, so that users are aware that data is being encrypted.

you think it is working?

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Topic 5 – Implications of WWW – Disadvantages of E-commerce - Fraud "Phishing" is a recent scam which involves extracting from people by sending them emails which pretend to come from their bank or credit card company. These emails direct them to a fake web-site where they are asked to enter their details.

Many credit card companies are using Artificial Intelligence systems to spot unusual card activity such as very large purchases or sudden increases in transactions to try and spot the use of stolen card details. This is necessary because a customer might only become aware that their card details are being used fraudulently when they receive their statement at the end of the month.

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Topic 5 – Implications of WWW – Social Implications

The Information-Rich and the Information-Poor

Many people feel that the Internet has accentuated the difference between the rich and the poor. People in western countries are described as "Information rich" whereas most people in the Third World are "Information poor", since connecting to the Internet requires expensive equipment and access to a networking infrastructure which does not exist in many poor countries. Many rich countries also have sections of their populations which are Information Poor. This may be for a variety of reasons such as poverty, geographical isolation or poor education. Many governments are concerned that the Information Poor will be unable to access government support and information services, will be unable to participate in the knowledge industry job market, and will increasingly become more dependent on welfare and be less

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Topic 5 – Implications of WWW – Social Implications

Social Isolation

There is a fear that the increased use of electronic communication will mean that many people will become physically more isolated from each other. The Internet encourages the creation of global communities, but may result in neighbours not seeing each other for weeks on shops less and meet together less as a result. Tele commuting means that people work from home instead facebook rather than meeting up for a chat.

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Topic 5 – Implications of WWW – Social Implications

Employment and Taxation

Tele-working has revolutionised the way in which firms utilise their employees. Tele-working can mean working from home instead of travelling to an office every day, using communications technology to keep in touch with your employer. Work is sent/received electronically. Tele-working can also mean working in a different country from your employer or even not ever meeting your co-workers or collaborators because they are all living in different parts of the world.

Advantages for the employee:

Save on travel time and transport costs; As long as you produce the required results, it does not matter where or when you work. If you are self employed, you can deliver your work to your customers electronically.

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Topic 5 – Implications of WWW – Social Implications

Disadvantages for the employee:

You can get a feeling of isolation, missing out on office gossip or possible promotion prospects; You may actually work harder and put more hours in than you would if you were working in an office, feeling you have to prove you work hard; You will need space in your home to work, and you may have to insure your employer’s computer equipment.

Advantages for the employer:

You can save money on office space , employees use their homes; Tele-workers often work harder than if they were working in an office; You can save money on wages as you can employ people in parts of the world where wages are low. For instance, many Western software companies are now looking to the Far East to employ programmers and data processing workers.

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Topic 5 – Implications of WWW – Social Implications

Disadvantages for the employer:

Train your tele-workers and pay for communications costs and computer equipment; you want your employees to be able to log into your company network from home; You may have less control of the quality of service your country.

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Topic 5 – Implications of WWW – Social Implications Video conferencing allows a number of people to share data such as text and graphics even though they are thousands of miles apart. Video conferencing requires a high bandwidth connection and is expensive, but can be dramatically cheaper than flying several

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Topic 5 – Implications of WWW – Ethical Implications

Personal Privacy

The monitoring of individuals’ Internet and email use is a contentious issue. Many governments would like to have access to this sort of information. Many individuals would not like them to have this kind of access. With modern communications networks it is theoretically possible to trace the movements of any individual around the world - they use cash machines, pay with credit cards, use the Internet, use mobile phones, appear on surveillance cameras, and may use electronic road tolling systems. All of these systems could be combined to track an individual’s movements. Even organisations who manage LANs are becoming concerned about the security and employment issues surrounding email, and some are monitoring all email activity on their networks to make sure that their employees are not divulging company secrets or using the network

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Topic 5 – Implications of WWW – Ethical Implications

Cookies

Cookies are small data files which web servers send to your machine along with web pages. HTTP is a "stateless" protocol, which means that the web server has no way of knowing which machine or user a request for a web page has come from. This can be a problem if you are using e-commerce, as the server needs to be able to track a transaction between different web pages. One solution is to store a session number in a cookie which is sent to your machine - when you go to the checkout the server requests the cookie so that it knows which transaction belongs to you. Cookies are also used to store details of personalisation which people have applied to web pages. Unfortunately cookies can also be used to track your activity on web pages, which adverts you have responded to etc, and to customise on line advertising accordingly. Many people regard this as an invasion of their privacy. They can hold passwords so should be regularly deleted.

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Topic 5 – Implications of WWW – Ethical Implications

Encryption

Encrypting data is a method of coding it, in order to make it difficult or even impossible for someone to read it unless they have authorisation from you. Some governments make encrypting data illegal, others regard it as an individual right. As with all security systems, there is a trade-off between security and convenience. The more secure you make a communication system, the more inconvenient it is to use.

At the moment email on most networks is un-encrypted and insecure, as messages are sent as plain ASCII text.

Netiquette

There are several conventions and a whole new vocabulary which has developed with regard to how you should behave on Internet newsgroups, using email, etc. Simple rules such as not sending "Spam" (unsolicited commercial email), not privacy may seem obvious, but it is easy to make mistakes without realising it. The best policy when subscribing to a newsgroup or joining a list server is to "listen" quietly for a submit any contributions yourself.

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Topic 5 – Implications of WWW – Ethical Implications

Misrepresentation

The ability to post messages on newsgroups or discussion lists anonymously means that offensive statements can be made without the person making them being held to account.

Chatrooms – popular, world wide, real-time communication. It’s an area on internet where users type messages, messages are available to all connected to server. Communication slow as you need to type messages, but real-time application makes it popular. One problem with chatrooms is that there is no way of who they say they are. They may have lied about their with you. Paedophiles use chatrooms!

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Topic 5 – Implications of WWW – Ethical Implications

Censorship and Pornography

What is legal in one country may not be legal in another. Not all governments encourage the free debate of political subjects and many governments try to block access to opinions or political debate which is critical of them. Many people believe that children should be protected from violent, pornographic or extreme political material, though of course what is considered to be extreme in one society is not always considered to be extreme in every society. From the point of view of those wishing to impose censorship, the world-wide nature of the Internet makes it very difficult if not impossible to control. An international standard of "rating" web pages for violent or sexual content has been developed by the Internet Content Rating Association (ICRA) which makes controlling access easier.

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Topic 5 – Implications of WWW – Internet Regulation

Taxation

Buying and selling on the Internet makes it very difficult indeed to impose taxes, import duties or other fees, particularly if the item purchased such as software, music, or access to information can be transmitted electronically and does not have to be physically delivered to the purchaser. If you work in one country but are employed in another, where should you pay tax? Who should pay for your National Insurance? Which country’s employment laws should apply?

The Copyright, Designs and Patents Act 1988 - On line distribution of software is cheap and easy, but the distribution of illegal copies of software is just as easy. Software piracy is a major problem in many parts of the world. Many people argue that software piracy increases the cost of software because software distributors need to charge more to recover the cost of research and development if only a percentage of those using the

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Topic 5 – Implications of WWW – Internet Regulation In addition to conventional software licensing, there are existence, including shareware, ad ware and even freeware. On-line distribution reduces costs and increases the market-share. There is also concern over copyright concerning images and other data available on the Internet. The fact that this data is on a web page and anyone can access it does not make it freely available for anyone to take for themselves and publish it under their own name.

Peer to Peer file sharing software enables users to share music or other files which may be subject to copyright legislation. In the US, the Recording Industry Association of America (RIAA) is conducting a legal campaign to stop users from sharing music files in this way .

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Topic 5 – Implications of WWW – Internet Regulation The Computer Misuse Act 1990 - covers using computers to damage or steal data. The Computer Misuse Act covers crimes such as hacking, ie breaking into computer systems or networks to destroy or steal data and propagating viruses which destroy or damage information or computer systems. Before this act was passed, people breaking into computer systems were often only able to be prosecuted for mundane offences such as "stealing electricity".

The Data Protection Act (1998) describes the duties and responsibilities of those holding data on individuals (Data Users). It also describes the rights of these individuals (Data Subjects). In general, it is the duty of those holding data on individuals to register with the Data Protection Registrar, to keep the information secure, make sure it is accurate, and to divulge it only to those persons who are authorised to view it. It is the right of an individual who has data stored concerning them to view that information and to have it changed if it is inaccurate. There are a number of organisations which may be given exemption from this act namely the Police, Customs, National Security and Health Authorities.

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Topic 5 – Implications of WWW – Internet Regulation

The Regulation of Investigatory Powers Act (RIP Act)

The Regulation of Investigatory Powers Act (2000) gives government and employers wide rights to monitor employees e-mails and telephone calls to ensure that they relate to work. It has been condemned as an invasion of privacy but the government argues it is necessary to crack down on internet crime and There are two main areas of controversy in the RIP act. They concern collection of data and the use of

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Topic 5 – Implications of WWW – Internet Regulation

First Concern:

Security services, eg MI5, will be able to monitor people’s internet habits by recording the websites and chatrooms they visit and the addresses of emails they send and receive. Currently all telephone numbers are logged and some telephone companies are required to enable security services to intercept calls (this is legal). Internet activity is different however as web addresses show exactly what people have been looking at and enable the security services to build up detailed profiles of where people go online and who they communicate with. The act also allows employers to intercept emails and internet use by their staff, on grounds such as monitoring for computer viruses, checking inappropriate use of company email, or counteracting industrial espionage.

Many people think that this law is disproportionate to the problem it is trying to tackle, and that it allows an

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Topic 5 – Implications of WWW – Internet Regulation Under RIP, some UK internet service providers (ISPs) capability". This would mean that they would be required to install a device enabling the security services to monitor the flow of data. Critics say that these devices will be hugely expensive and will have difficulty keeping pace with fast-changing internet technology as well as the ever-growing volume of internet traffic.

The Home Office claims that the power of interception is rarely used and would need approval from Home Secretary. Only used if national security was threatened or serious crime was suspected.

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Topic 5 – Implications of WWW – Internet Regulation Second Concern: The legislation’s reverse burden of proof - if intercepted communications are encrypted, the act will force people to surrender the decryption keys on pain of jail sentences of up to two years. The government says decryption keys will only be required in special circumstances and promises that the security services will destroy the decryption keys as soon as they are finished with.

Human rights campaigners argue that the act reverses the burden of proof in UK law as the person sending or receiving the communication must prove their innocence rather than the authorities proving their guilt. Stiff prison sentences are a threat if a decryption key is lost/forgotten.

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Topic 5 – Implications of WWW – Internet Regulation From the How to Pass Book

Regulation of Investigatory Powers Act 2000

The Government has the powers to: • Intercept communications • Acquire communications data (eg billing data) • Set up intrusive surveillance (on private property/vehicles) • Set up covert surveillance in the course of specific operations • User covert human intelligence sources (agents, informants, undercover officers) • Access encrypted data

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Topic 5 – Implications of WWW – Internet Regulation But, the government must do all of the above while • Government can demand a tele-comms company to intercept an individual’s communications • Interception warrants’ can be used where national security is at risk, or preventing/detecting serious crime/safeguarding economic welfare of the UK. Eg intercepting communications between a UK businessman and a foreign company • Home Secretary can intercept all data flowing to/from a PC by contacting the ISP, or surveillance of an person/building • Government can insist an ISP fit surveillance equipment to their systems, or leave a ‘back-door’ to systems open (ISP is then vulnerable to hackers) • Government can demand a decryption key • Government can access internet traffic data eg emails, ftp, web site accesses, chatrooms, newsrooms and e-groups

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Topic 5 – Implications of WWW – Internet Regulation

Why are these powers needed

• To maintain national security • To prevent/detect crime • In the interests of the UK’s economic well-being • In the interests of public safety • Protection of public health • Tax assessment and collection • Preventing death/injury/damage to a person’s health in the event of an emergency • The Home Secretary has wide ranging powers and give the Government increased power to monitor

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Topic 5 – Implications of WWW – Internet Regulation

Summary

E-commerce is the buying or selling of goods or services on-line Advantages - customer - convenience and increased choice Advantages - retailer - economies of scale, ↑ markets and Automation Disadvantages for both Social problems ↑ gulf between Information Rich/Poor and Tele-working - improve peoples lives by reducing the need to travel and allowing them to work in their own home in their own time.

Video conferencing - reduces the need for travel, but currently needs special equipment and a high bandwidth connection Ethical implications of the WWW include the problem of personal privacy, the ability of others to track your use of the internet and the increased use of encryption to disguise illegal activities paedophiles is also an ethical concern.

Computers and the Internet are regulated by a number of acts of parliament in the UK. These include the Copyright Act, the Data Protection Act, the Misuse Of Computers Act and the Regulation of Investigatory Powers Act ↑ fraud, ↑ need advanced technology ↑

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Topic 6 – Network Security - Pre-Requisite Knowledge Before studying this topic you should know about the basic software security measures on a network such as the requirement for ID and password. You should know about physical measures which can be employed such as restricting access to certain workstations. You should know what encryption is and what are the advantages of using it. You should know why Internet filtering is needed in schools and other organisations.

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Topic 6 – Network Security - Pre-Requisite Knowledge After studying this topic you should be able to: • Describe types of threat to network security and how they can be counteracted • Describe a number of hardware and software solutions to protecting networks • Explain the benefits of encryption • Explain the benefits of monitoring and logging activity on a network • Describe different approaches to Internet filtering • Describe the functions of a network firewall

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Topic 6 – Network Security - Pre-Requisite Knowledge Q1: Why should network users have an ID and password to log on?

a) Because you need to charge people for using a network b) Because it is against the law to use network resources without one c) Because the network software needs to know who you are in order to give you access to networked resources d) Because all software needs an ID and password before you can use it Q2: What does it mean when we say a file has been encrypted?

a) Compressing the file so that it takes up less space on the hard disk b) Encoding the file so that it can only be decoded if you have the correct password c) Making the file unreadable by any other operating system.

Q3: Why is Internet access filtered in schools?

a) Because pupils could find answers to exam questions on it b) Because the Internet can only be used at certain times c) Because it costs money to use the Internet d) Because there may be material unsuitable for young people on the Internet

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Topic 6 – Introduction to Network Security Security on a network is a compromise between security and convenience. The security regime should reflect the importance of the data.

Too strict a security policy (eg forces users to change their passwords daily or to use mixtures of alphanumeric change them regularly.

and numerical characters) and the danger is that they write their passwords down. Allowing users to set their own passwords has the danger they will be easy to guess/don’t

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Topic 6 – Introduction to Network Security As well as internal security on a network, network from outside. Security from outside that there is only one connection between the applying security measures to that connection. Security from virus infection is best dealt with by installing virus protection software at the point where the network connects to the case users bring in infected disks or USB sticks. For this reason many organisations have connection of USB devices either.

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Topic 6 – Threats to Network Security The purpose of security on a network can be • Protecting data on the network • Protecting the network software and resources • Protecting the users of the network Protecting these three areas can be done by: • Imposing network security on users and on network hardware • Additionally installing virus protection and a firewall • Filtering Internet content On any network, all three of these security precautions are normally in place.

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Topic 6 – Protecting Data on the Network Students/pupils – guessing passwords Hackers – malicious – virus/trojan installs Employees – accessing confidential files Disgruntled ex-employees – sabotaging network system by gaining admin access Accountants – embezzling money Fraudsters – stolen credit cards used to make purchases Hackers/Spies – Tapping into wireless networks using radio listening equipment

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Topic 6 – Software Solutions Network Authentication - Log-in using network ID and password, the network operating system checks the combination of ID and password against an encrypted database and if they match, the user is given access to the files and resources which they have the permissions to use, otherwise they are denied.

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Topic 6 – Software Solutions Network operating systems can enforce password security using rules: • The password must be more than a set number of characters eg 8.

• Password must contain at least one number or character such as ? : } / ; • The password must not be one already used before eg in the last year.

• The password must not be a word which appears in the dictionary (Password cracking programs can match passwords quickly); • The password must be changed every set number of days. Eg 30.

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Topic 6 – Software Solutions A networking OS can restrict a user to a particular PC, by time of day, or by location, or both.

Every file and directory on the network will have permissions set by the network operating system. These permissions are checked when a user attempts to access a file or resource. Normally a user would have •full read-write access to their own files on the network; •read only access to shared files; •no access to network operating system files.

The networking OS checks the users ID against the Access Control List (ACL) for that file/folder. Users are assigned to groups and permissions are given to groups. Eg the pupil group is more restricted that the staff group in school.

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Topic 6 – Encryption Network traffic created by a logon ID and password is normally encrypted in case it is intercepted by an unauthorised machine on the network. Encryption can be used to protect data from prying eyes within a network as well as from outside.

Encryption simply lengthens the time it takes the data to be deciphered! It is not full-proof!

128-bit encryption is common. Increasing processing power of computers reduces time taken to crack the code. So encryption bit length needs to keep getting bigger.

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Topic 6 – Hardware Solutions Lock network servers in secure rooms. Physical access to the server can often allow a skilled hacker to get hold of the encrypted password file (which can then be compared with dictionary words encrypted using the same algorithm in order to extract passwords). Backup tapes and emergency repair disks are also a security risk unless they are protected by lock and key.

Magnetic swipe cards, smart key entry or 4-digit key code entry can be used to physically secure rooms. Biometric security systems such as fingerprint, face or iris pattern recognition systems can also be used. They can be used along with User ID and password to increase security.

Hardware resources on the network such as printers can also be restricted to certain users by time, workstation location or security level.

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Topic 6 – Hardware Solutions Using switches instead of hubs for the network cabling infrastructure increases security because switches direct network packets to the specific machine they are destined for rather than to every machine on their segment. Since a Network Interface Card (NIC) receives every packet on its segment and can be can be set to display their contents on the machine they are fitted in, a hacker could use a laptop equipped with a "packet sniffer" plugged into the network to extract ID and password information from network traffic.

Wireless networks are particularly prone to this sort of attack as there is no physical connection needed, and many wireless networks can be accessed from outside the building they are installed in. Wireless networks need to be configured so that the packets transmitted over them are encrypted.

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Topic 6 – Human Engineering Since the ID and password on a network is effectively the key to much of its security, it is this area which inevitably attracts most of the efforts of those trying to break in. Use of: fake logon screens which then save ID and password details keystroke loggers which can be inserted in between a keyboard and a computer case. These devices log every key press, and this data can be trawled through at leisure once the hacker removes the device.

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Topic 6 – Protecting the Network Software and Resources The network itself needs to be protected as well as the data which it contains. These attacks can come in the form of software such as viruses and worms or human in the form of hackers.

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Topic 6 – Anti Virus Software Viruses and worms are software, they can damage data on a network or network software. They can also make the network unusable by their attempts to propagate (spread) themselves to other machines or other networks. They are usually small sections of code which hide themselves inside legitimate applications. When the user runs the application the extra code may delete files, infect other applications or attempt to propagate itself to other machines. Viruses may lie dormant until a particular date or set of circumstances. They may attempt to disguise themselves from anti-virus software and may change themselves as they propagate.

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Topic 6 – Anti Virus Software A worm is similar to a virus although its prime concern is to propagate itself as efficiently as possible, often consuming machine resources in the process.

Worms have been designed to install trojan software on user’s machines, allowing the hacker access to the machine without the owner’s knowledge either to extract information eg bank account data for fraud, or to use the machine as a host to send spam email which would otherwise be blocked by spam filters.

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Topic 6 – Anti Virus Software Protecting a network against viruses, trojans and worms is usually achieved by installing anti-virus software on to the network file servers and stations. The software installed on the servers is responsible for checking every file which is run/created on the server. Although this affects network systems performance that is preferable to a virus attack. Suspect files are either repaired/quarantined.

The anti-virus server is also responsible for downloading the latest virus signatures from the anti-virus software vendor and for updating itself and all the stations with this information, normally at least weekly.

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Topic 6 – Proxy Servers As well as enabling private IP addresses to be used on a Local Area Network, a proxy server is also a convenient way of helping to secure a network because the private internal IP addresses are hidden from the outside world, using a system known as Network Address Translation (NAT). This protects these internal machines from external attack because without knowing the IP address of a machine, a hacker cannot access it in order to control it. This is what we do in school, our IP address are all in the range 10.5.11.0 or 10.5.10.0, but these addresses do not exist on the Internet side of our network.

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Topic 6 – Firewalls and Routers A firewall is a piece of software installed on the machine which controls access to the outside world. It will normally block network traffic by examining each packet as it passes through. A firewall may be installed on a dedicated machine, or may be part of a proxy server. Each packet can be identified by its source address, its destination address and the port number it is using. A firewall can block traffic on all incoming and outgoing ports except the ones which the network manager knows are for legitimate use of protocols such as HTTP, FTP, SMTP and POP3.

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Topic 6 – Firewalls and Routers A router can perform many of the blocking functions of a firewall, but are often more difficult to configure. Routers can be set up to block traffic from particular IP addresses, although they are primarily designed to route packets between networks. The best combination is to have both a router and a firewall in place. This means that any individual trying to break in will have two separate hurdles to jump instead of just one.

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Topic 6 – Protecting Resources against External Attack There are a number of reasons why a hacker might wish to gain access to a network: • to make illegal use of the network resources, eg hard disk space and bandwidth - storing and distributing pirated software/pornography or using the mail server to distribute spam or to propagate a virus, • to deface the company web site or compromise the web server so that it can be used as a secure platform for an attack on another system.

A hacker will also want to hide their tracks as far as possible by removing any trace of their activities.

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Topic 6 – Monitoring and Logging Network Activity It is always wise to monitor and keep logs of network activity. Monitoring software can be set to inform the network manager of unusual activity which might signify a problem. Logs of network activity such as logins, file activity, network traffic etc can help a network manager to track down the source of an intrusion or the route by which network security was breached.

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Topic 6 – Internet Content Filtering This can restrict the web sites which network users can access. Companies/schools filter internet content to prevent employees/pupils from using company bandwidth/employee time to surf the web for their own entertainment, or to protect their students from accessing unsuitable material. Home internet filtering may allow parents to protect their children from unsuitable Internet material. Too strict filtering can restrict legitimate research.

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Topic 6 - Filtering Software Filtering software takes the approach of letting the user access anything on the web other than those sites which have been identified as being unsuitable. •By type of internet service – allowing access to web sites but blocking access to FTP sites/chat rooms •By using lists of URLs – web page addresses that are banned are stored in a DB. When a user requests a web page that is in the DB of banned sites access is denied.

•By examining the words on web pages – access to web pages containing a ‘forbidden word’ are denied •By checking the content rating of a web site – eg includes rating on objectionable language, violence, or porn Filtering software can often be combined with a logging system which automatically logs attempts to access banned material.

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Topic 6 – Walled Garden The "Walled Garden" approach only allows users to access certain parts of the WWW. The software will only allow users to access a web site if its IP address matches one of those on the list of permitted ones. This list may be supplied by the software vendor, or may be complied by the organisation themselves. Normally sites can be added or removed from the list. While this approach is very effective at filtering content, it is very restrictive and considerably reduces the functionality of the WWW.

A firewall can be: • Software running on an individual machine • Software running on servers across a network (distributed firewalls) • Hardware based – ie firewall software runs on server. These are faster, more reliable as it’s all they do!

• Provided by managed firewall service providers

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Topic 6 – Summary • Network security is always a compromise between security and convenience • The purpose of network security is to protect data on the network, the network itself, and users of the network • Threats to network security can be from both inside and outside an organisation • Security inside a network is primarily enforced by user ID and password • Security from outside is primarily enforced by ensuring that there is only one point of contact with the outside world • The hardware and software resources which a user has access to are determined by the restriction policy linked to their ID

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Topic 6 – Summary • Encrypting data files on a network can add a further level of security • Hardware solutions to security concerns include physically locking up workstations, servers and backup tapes. User IDs can also be linked to biometric security systems • Using a switched network, and making sure that wireless networks are secure reduces the chances of Ethernet packets being intercepted by someone who has managed to connect a rogue machine into the network.

• Wireless networks need to be configured to make them secure.

• Network servers and stations need to be protected from virus attack using antivirus software. The anti-virus software should be kept up to date with virus signatures • A firewall is software which blocks attack from outside, and restricts the transfer of packets from inside a network by examining the source and destination IP address and port number of every packet which passes through it

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Topic 7 – Denial of Service Attacks and Disaster Recovery

Pre-requisite knowledge

You should know why backups are necessary and why there needs to be a strategy in place to make sure that backups are effective. You should know that a network topology can be described in terms of nodes and channels, and the effect of failure of a node or a channel on different topologies.

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Topic 7 – Denial of Service Attacks and Disaster Recovery

Learning Objectives

After studying this topic you should be able to: • Understand what a Denial of Service attack is • Describe different types of Denial of Service Attack and why they occur • Describe the effects of a Denial of Service attack • Describe the hardware and software approaches to disaster avoidance

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Topic 7 – Denial of Service Attacks and Disaster Recovery - Revision Q1: Which of the following are true of a sensible backup strategy?

A) Make regular backups B) Re-use backup tapes daily C) Test the backup frequently D) Keep all backups in a safe place a) A, B and C b) A and B c) A C and D d) A,B and D

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Topic 7 – Denial of Service Attacks and Disaster Recovery - Revision Q1: Which of the following are true of a sensible backup strategy?

A) Make regular backups B) Re-use backup tapes daily C) Test the backup frequently D) Keep all backups in a safe place a) A, B and C b) A and B c) A C and D d) A,B and D Q2: What is the effect of a channel failure on a single segment network with a bus topology?

a) All the nodes on the segment fail b) The node nearest to that channel fails c) The nodes on that segment slow down d) No effect

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Topic 7 – Denial of Service Attacks and Disaster Recovery - Revision Q3: What is the effect of a channel failure on a network with a star topology?

a) All the nodes on the network fail b) The nodes connected to that channel fail c) The nodes on that segment slow down d) No effect Q4: What is the effect of a channel failure on a network with a mesh topology?

a) All the nodes on the network fail b) The nodes connected to that channel fail c) The nodes on that segment slow down d) No effect

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Topic 7 – Denial of Service Attacks and Disaster Recovery - Revision Avoiding disaster – 2 main types: a deliberate attack - such as Denial of Service (DoS) attack or virus infection natural forces - equipment failure, fire, flood etc.

Both sorts of disaster require similar strategies in order to protect the network in the first place and recover afterwards should the worst happen.

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Topic 7 – Passive and Active Attacks Passive Attacks are not designed to destroy or damage network resources, but merely to intercept the data. “Packet sniffers” are used where data on a network is intercepted by the hacker. The best defence for this type of attack is encryption of the data.

Active Attacks – this type of attack is designed to actively cause damage to a system. In this type of attack the hacker breaches the network security then alters the data stream entering the network eg by diverting the data through another computer to corrupt it before sending it back to the network again. DoS attacks are examples of Active Attacks.

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Topic 7 – Denial of Service (DoS) Attacks A Denial of Service attack is an attack on a network server which significantly reduces the capacity of that server to provide resources to legitimate users. Denial of Service attacks are not normally launched from within a network, as such an attack would be easy to trace and to counteract. Denial of Service attacks are almost always launched from outside an organisation, and are directed towards the services which the network is providing to the external users of that network. Denial of Service attacks may be designed to put a competitor out of business, to bring down a high profile organisation or just to cause trouble.

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Topic 7 – Types of (DoS) Attacks Physical Attack: The simplest form of physical DoS attack is to cut the cables between the company providing the service and their customers. This kind of attack is rare, and is relatively easy to protect against.

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Topic 7 – Types of (DoS) Attacks Exploitation of Software flaws: Operating Systems and Server Software can be released for use prior to all the bugs being found and fixed. The remaining bugs and loopholes are an easy way for hackers to gain access to a system.

Attacks which were devastating when unleashed sending that included e-mails had attachments with 256-character file names to Netscape and Microsoft mail programs, or the Ping of Death, where a ping message larger than the permitted size was sent to a server. In both these cases the software suffered a buffer overflow. Usually when a buffer overflow attack is successful the application that has been attacked crashes in a way which allows the hacker to gain control of a system or execute code as the system crashes.

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Topic 7 – Types of (DoS) Attacks Resource starvation: This means using up a network resource to the point that legitimate users can’t access it. Eg if the M8 motorway was filled with cars with no people in them then legitimate commuters would not be able to get on to the motorway for legitimate journeys. A DoS attack may send badly assembled packets to a server of workstation. The server or workstation can’t deal with the packets so keep them in their buffers, buffers fill up jamming the network.

Bandwidth consumption – Flood the network with useless traffic. If you flood an email server with useless traffic it will crash to simply stop legitimate users being able to send/receive emails. “I Love You” was of this type.

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Topic 7 – Types of (DoS) Attacks Attacking Routers – these are vulnerable to ping attacks. Ping attacks are used to test the integrity and operating speed of a network. Corrupted packets mean the ping attacks divert routers from their normal function of routing data around the network.

Viruses or worms can also be regarded as DoS attacks as they consume bandwidth in an attempt to propagate themselves. Some DoS attacks have been propagated by viruses which install server software on unsuspecting users machines. Port scanning software is then used to identify the infected machines and use them as a platform to mount a resource starvation attack on a server.

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Topic 7 – Types of (DoS) Attacks DNS attacks: This type of attack disrupts network access by filling the cache on Dame Name Servers with name lookup information about non-existent hosts. This causes legitimate requests to be dropped. This is a specific type of resource starvations.

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Topic 7 – Effects of (DoS) Attacks The effects of a DoS attack can be devastating for a company, particularly if they are high profile or rely on 24 hour connectivity. Apart from the loss of business, there is the loss of confidence by users, the cost of repair and response, and the disruption to the organisation.

Denial of Service attacks became world news in August 2000 when Yahoo, Amazon.com and other web sites were hit by attacks lasting for several hours. As with most DoS attacks, these attacks just simply overran the target web sites with streams of poorly formed IP packets.

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Topic 7 – Effects of (DoS) Attacks

Why do DoS attacks occur?

There are a variety of reasons why DoS attacks occur. In September 2003 a number of anti spam web sites which supply spam blocking lists were hit by DoS attacks perpetrated by hackers who had been hired by spammers. Business competition may well become a more common reason for DoS attacks in the future. Some DoS attacks are merely malicious, though this does not make them any less annoying or inconvenient. DoS attacks may also be politically motivated, one example being the attacks on the US White House web site after the Chinese embassy in Belgrade was accidentally bombed. (Disgruntled ex-employees of a firm etc).

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Topic 7 – Effects of (DoS) Attacks

Avoiding Disaster

Disaster can come in a number of guises, such as virus or hacker attack, or physical disasters such as fire flood, theft or even just deleing crucial files by accident. The most important thing to remember as far as disaster avoidance and recovery is concerned is that the data held on a computer system is many times more valuable than the physical equipment itself. Obviously avoiding hardware failure is a sensible strategy, but it always makes sense to build redundancy into a system by having replacement parts, backup servers etc available even though they may never be used.

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Topic 7 – Effects of (DoS) Attacks

Software Solutions

Make regular backups, keep them in a safe and secure place. A backup schedule is an automatic system which runs at a specific time every day (usually in the middle of the night when network activity is at its minimum). A backup strategy minimises data loss in the event of a disaster. A simple backup strategy – backup servers every night to tape, the tapes are taken off site to a secure location the next day. Tapes are used because they are cheap and portable, although tape drives are expensive.

Do daily backups, but also do a backup once a week. Weekly tapes are kept for at least a month. Daily ones are rotated every 5 days.

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Topic 7 – Software Solutions Backup versions available for every weekday up to a week before plus every Friday up to a month before. Backups can be made over a network connection if there is sufficient bandwidth.

There are various types of backup: Full Backup – backup all data on drives irrespective of changes since last backup, slow, for an end of week backup.

Differential Backup – backup only data files that have changed since the last full backup. End of day - saves time/space.

Incremental Backup – backs up all files changed since the last backup of any type. Fastest to do, restoring data slow.

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Topic 7 – Software Solutions In a situation where servers are destroyed additional redundant servers would be utilised. Such identical systems make it easier to recover from a disaster. Backup strategies will vary according to the size of the organisation and the importance of the data to its survival. Backup are either made to DAT tape, DLT tape of Super DLT tape. However backups can be made over the internet if bandwidth is sufficient. This saves tapes having to be removed and stored off-site.

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Topic 7 – Hardware Solutions

1. Regular maintenance

2. Fault Tolerant Components: This is simply making sure to install components which have duplication built in so that if one part fails, the other can take over. Many servers are fitted with dual power supplies for this reason. Or an organisation has 2 servers, switch to backup server if main server fails.

3. Hardware Redundancy: Duplicates of crucial equipment like servers, switches and routers, so that if one of these fails, it can be quickly replaced without waiting for a supplier to deliver. A failsafe strategy would ensure that the spare equipment was always configured with the latest version of the current network software and data. This is likely to be the most expensive but most effective precaution against disaster.

4. Uninterruptible Power Supplies (UPS): An Uninterruptible power supply is a device which contains a battery with enough capacity to supply a server for a short power cut, and to shut down the server gracefully in the event of a longer problem. Usually a UPS will communicate with the server via a serial cable and will be able to instruct it to shut down when the remaining capacity is nearing its end. A UPS can also act as a "filter" for erratic or dirty power supplies, avoiding large changes in voltage or frequency which might damage a server.

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Topic 7 – Hardware Solutions 1. Disk Mirroring and RAID: An alternative and/or a complementary strategy to tape backup is to use a disk mirroring system or a server which runs a Random Array of Inexpensive Disks (RAID). The best versions of RAID enable the recreation of the data on a failed hard disk from the information on the other disks in the array, "hot-swapping" means the server doesn’t need to shut-down or rebooted if the disk fails. Another option is simply to write to two hard disks simultaneously, so that in the event of a failure of one, the data will always be duplicated on the other. This is called disk mirroring.

2. Network Topology: Different network topologies can have different tolerances to failures. Channel failures will normally only affect the node which they are connected to unless that channel is one from server to switch or router. In general, bus topologies are the least tolerant to channel failure. Star and tree topologies are better as a channel failure only affects the node which it serves unless the channel which fails is the one which serves the node at the centre. Node failure can be much more serious if the node concerned is a server, switch or router.

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Topic 7 – Hardware Solutions

Summary

• Denial of Service attacks are attempts to reduce the resources available to legitimate users of a server.

• DoS attacks can be physical attacks, or exploitation of careless network management.

• An example of the exploitation of software flaws is where the hacker crashes the server and then gains access via a debug mode.

• Resource starvation is where the server is flooded with ping messages or attacked with a virus or a worm • DNS attacks are where DNS servers are used to launch a resource starvation attack.

• The effects of a DoS attack are loss of business, loss of trust, inconvenience and expense.

• The reasons for a DoS attack may be political, economic or malicious.

• Disaster can be avoided by keeping regular and reliable backups and making sure that a robust backup strategy is in place.

• Backup tapes should normally be taken off site and kept in a secure location.

• Hardware solutions include duplicate equipment, uninterruptible power supplies, and disk mirroring or RAID servers.

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Topic 8 – Data Transmission – Pre-Requisite Knowledge You should know that telecommunications networks are used for voice and data transmission. You should know about the infrastructure required for an Ethernet network including cabling, hubs, switches and Network Interface Cards. You should know that there are a number of different types of Internet connection available including dialup modem, Asymmetric Digital Subscriber Line (ADSL), Integrated Subscriber Digital Network (ISDN), Cable modem, and leased line. You should know about the different types of transmission modes: unicast, broadcast and multicast.

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Topic 8 – Data Transmission – Pre-Requisite Knowledge

Learning Objectives

• After studying this topic you should be able to: • Understand the units of measurement used in data transmission • Describe the difference between synchronous and asynchronous data transmission • Describe the difference between circuit and packet switching • Understand the Ethernet standard and its use of CSMA/CD • Describe a Network Interface Card and why it needs a MAC address • Describe error checking methods including parity and CRC • Understand the different types of Internet connection and where they might be used

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Topic 8 – Data Transmission – Revision Q1: Which of the following technologies would not be suitable for a company needing a high bandwidth network connection?

a) ADSL b) ISDN c) Dialup modem d) Cable modem Q2: Which one of the following transmission modes describes streaming video?

a) Unicast b) Simplex c) Broadcast d) Duplex

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Topic 8 – Data Transmission – Revision

Q3: What is the major benefit of VOIP

(Voice over IP) a) Phone calls don’t cost anything because they are transmitted over the Internet b) Phone calls are connected more quickly c) Phone call quality is better d) Phone calls are faster

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Topic 8 – Data Transmission – Introduction The Data Link Layer of the OSI model is responsible for putting data into frames/packets and providing an error free data transfer from one node to another. This topic looks at Ethernet, which implements the Data Link Layer in many Local Area Networks. We also look at a number of other types of network connection available to the home and business user such as dialup or ADSL where the Data Link Layer performs a similar function and compare them in terms of speed and bandwidth.

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Topic 8 – Data Transmission – Units of Measurement It is important to be aware of the units used in computer networking. Firstly we need to distinguish carefully between a bit and a byte. A bit is a single unit of information, on or off, represented as a 1 or a 0. A byte is 8 bits, originally used to represent a single character in ASCII code. Since transmitting data over networks often involves sending extra bits in order to cope with error detection, error correction and the information needed to identify where a message starts and where it stops, the unit for measuring the quantity of data transmitted is measured in Kilobits per second (Kbps) or Megabits per second (Mbps). It is important to distinguish these units from MB (Megabytes) and KB (Kilobytes) which are normally used to measure file size and storage capacity.

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Topic 8 – Data Transmission – Asynchronous/Synchronous Data Trans.

Asynchronous data transmission (where

the sending and receiving machines are not synchronised) uses a transmission system where each byte is sent individually with its accompanying start and stop bits. Asynchronous data transmission is normally used for low speed transmission and the protocols used do not normally include any error checking.

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Topic 8 – Data Transmission – Asynchronous/Synchronous Data Trans.

Synchronous data transmission (where the sending and receiving machine are synchronised) uses a start frame to tell the receiving station that a packet is on its way and is used to synchronise the receiving station with the transmitting one. Synchronous transmission is much more efficient because a start and stop frame is only needed at the beginning and end of a block of characters which can be up to 8Kb in length, whereas with asynchronous data transmission, start and stop bits need to be transmitted with every byte. Error checking information can be included in the block. Synchronous transmission is more difficult and expensive to implement than asynchronous transmission, since it requires the transmitter and receiver clocks to be synchronised. It is used with higher transfer rates of communication: such as 100Mbps Ethernet.

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Topic 8 – Data Transmission – Circuit/Packet Switching Connections between nodes on different networks can be achieved either by circuit switching or packet switching. Circuit switching is where there is a direct connection established between the two networks (sender and receiver). All data follows the same physical path during the communication. Circuit switching is expensive because it means dedicating a particular connection for the time that the communication is occurring. It is used for transmitting video, audio, and computer data over the same network, and makes sure that no single type of data monopolises the line. Used to connect networks over a leased telephone line. This is expensive, particularly if large distances are involved, but provides a high bandwidth connection.

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Topic 8 – Data Transmission – Circuit/Packet Switching In packet switching the message is broken up packets are given a destination address and a to re-assemble the communication when it into packets means that packets may follow different routes between the transmitter and the receiver, but is extremely efficient because the network hardware can decide on the most usually much cheaper than circuit switching because it does not need a dedicated switching.

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Topic 8 – Data Transmission – Unicast, Broadcast, Multicast

Unicast Transmission

Unicast is the term used to describe communication where a packet is sent

from a single source to a specified host.

Unicast transmission is still the main form of transmission on LANs and on the Internet and uses the TCP and UDP protocols which are implemented on the Transport Layer.

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Topic 8 – Data Transmission – Unicast, Broadcast, Multicast

Broadcast Transmission is a method of

delivering a packet to every host on a particular network or group of hosts on the Internet. Broadcast transmission does not retransmit dropped packets or wait for acknowledgement of their delivery, so the protocol used is UDP. Examples of broadcast technology in action are streaming audio or video.

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Topic 8 – Data Transmission – Unicast, Broadcast, Multicast

Multicast Transmission is where packets

are sent from one or more points to a set of other points. In this case there are maybe one or more senders, and the information is distributed to a set of receivers. One example of an application which may use multicast is a video server sending out a number of different TV channels.

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Topic 8 – Data Transmission – Ethernet The Ethernet standard was developed by the Xerox Corporation, DEC and Intel. Ethernet is a networking system where all nodes are connected together on a common bus but where only one node can transmit at any one time. The system used for making sure that only one machine is transmitting at a time is called

Carrier Sense Multiple Access / Collision

Detection (CSMA/CD). The Ethernet standard operates on the Data Link Layer of the OSI model. Ethernet is currently the most commonly used technology for Local Area Networks.

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Topic 8 – Data Transmission – Ethernet

Ethernet frames and transmission rates

When data is being passed between two computers on the same Ethernet segment, the computers are identified by their

MAC addresses. The actual data to be

transmitted is packaged up into a frame. The frame contains the destination address, the source address, the data itself, error detection information and some additional information necessary for successful transmission.

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Topic 8 – Data Transmission – Ethernet This table shows the structure of an Ethernet frame.

The original Ethernet transmission rate was 10Mbps, but the common standard is now 100Mbps with 1Gbps and 10Gbps available for applications which require a particularly high bandwidth such as the connections between servers.

A collision is when two devices transmit simultaneously on an Ethernet segment. The propagation delay of a network is the time it takes for a signal to travel from one end of a segment to another.

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Topic 8 – Data Transmission – CSMA/CD

Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

In order to transmit a frame on an Ethernet network a node should “listen before talking”. This means it should “listen” to the line (carrier sense), make sure it is not transmitting a message, then it can “talk”, ie transmit a message. Once the transmission has started, if a collision is detected, (the Collision Detection part) then transmission stops, and both machines wait for a short random time before attempting to re-transmit. If a collision is detected again during this retransmission, then both machines will wait for a longer random time before re-trying. On a busy network with lots of collisions, this delay can reduce network performance considerably.

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Topic 8 – Data Transmission – CSMA/CD

Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

•View the video demos:-

C03demo5 C03demo6

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Topic 8 – NIC and MAC Address Every Ethernet network interface card (NIC) has its own unique Media Access Control (MAC) address which identifies it on the network. It is this address which is used by the Ethernet protocol to direct data around the network from one host to another. The data to be transmitted is packaged into a frame. The frame contains the destination MAC address, the source MAC address, error detection and transmission information along with the actual data.

NIC on Ethernet networks receives all frames, only accepts: • Frames with the destination as its own MAC address • Frames with the destination as the broadcast address (address is all 1s) • Frames with the destination as a multicast address • All frames if it has been put into promiscuous mode.

It passes to its host machine only the frames which it accepts

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Topic 8 – NIC and MAC Address The last item in this list is why a switched network is more secure than one which uses multiport repeaters (hubs) and why unsecured wireless networks are a particular security risk. Someone wishing to break into an Ethernet network could connect a laptop with the NIC set to promiscuous mode, and use software to read all the packets on that particular segment. Any traffic where passwords and IDs were sent in unencrypted form would be a security risk.

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Topic 8 – Data Transmission – Identifying a machine

Machine Identification – MAC/IP/Computer Name

All nodes on a network (servers or clients) have a unique identity. The type of identity will be determined by the protocols running on the network. The Ethernet standard requires that every network interface card has a MAC address in the form of a 6 byte number. The TCP/IP protocol used for access to Internet services requires that every node has its own IP address in the form of a 4 byte number. In addition to these identifiers, nodes on a network may also have a user friendly name which identifies them to users on the network. The network operating system is responsible for making sure that all of these different ways of identifying a machine are mapped to the same unique entity.

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Topic 8 – Practical Tasks

Practical Exercise: Setting up a Local Area Network

For this exercise you will need to have access to at least two machines which do not have the kind of restrictions applied to them which machines connected to a school or college LAN would normally have. Initially you should set the machines up as a peer to peer network.

Allocating an IP address:

Do the practical task, Setting a Static IP address.

Setting Up a Temporary Network using Bluetooth Devices

Using your own mobile phone connect to another user in the class. Show this connection to your teacher. This forms part of the practical NAB for the Networking Unit.

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Topic 8 – Error Detection and Correction Error detection is the business of determining whether an error has occurred during the transmission of data from one machine to another. If an error is detected, then the only solution is to ask the transmitting machine to retransmit the data. If error correction is in place, then depending on the amount of extra data sent with the original, the errors may be able to be corrected without asking for it to be re transmitted.

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Topic 8 – Error Detection and Correction - Parity Parity – to detect errors in the transmission of single characters. An extra bit called a parity bit is added to each unit of information. Odd parity - the parity bit will be set so keep number of ones odd. Receiver counts the 1s, if odd, no errors. If even then it will request a retransmission.

Eg, As ASCII is a 7-bit code the 8th bit (128) can be used as a parity bit. When sending the letter A (A=65), and using odd parity, the data sent would be: Odd Parity 64 32 16 8 4 2 1 A=65 1 1 number of ones.

0 0 0 0 0 1 The parity bit set to 1 ensures the data sent has an odd

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Topic 8 – Error Detection and Correction - Checksums A checksum is used when blocks of data are being transmitted. A checksum is generated by performing a calculation on the data - usually by performing a calculation involving the numerical value of all the bits in the block. The checksum is transmitted along with the data and an identical calculation is done by the machine at the receiving end. If the results match, then it is assumed that the data has been transmitted correctly. If the results do not match then a re transmission of the data is requested.

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Topic 8 – Error Detection and Correction – Cyclic Redundancy Check A Cyclic Redundancy Check (CRC) uses more complicated maths than a checksum, although the principle is similar. A calculation is done on the data to be transmitted resulting in additional data which is added to the packet. The receiving machine performs the same calculation and if it gets the same answer, then the data is presumed to be error free.

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Topic 8 – Error Correction Error correction is possible if the data being transmitted is encoded in a way which allows for potentially redundant information to be transmitted along with it. If the difference between two character codes is sufficiently great, then the corruption of one or even two bits may still leave the character recognizable. A parallel with written communication would be the fact that you can often still read text which has faded or has had some part of the letter erased, because they can be recognized without all of the letter needing to be visible. Inevitably the extra data required to be transmitted for error correction to work must be traded off against the time taken to re-transmit the data if error detection alone is implemented. A good example of where error correction as opposed to error detection is worthwhile would be where there is a large time delay between transmission and receipt of data such as in communications with robotic spacecraft on planetary exploration missions.

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Topic 8 – Types of Internet Connection - Dialup A modem converts the digital signal from a computer into a modulated analogue signal that can be transmitted down a telephone line and vice versa. Modem is a short name for "modulator / demodulator". The current maximum bandwidth available is 56Kbps. Typically dialup takes 15 to 20 seconds to connect.

The original protocol used for dialup connections was Serial Line Internet Protocol (SLIP) which was designed to allow IP packets to be transmitted using a modem. A more secure protocol called Point to Point Protocol (PPP) is now used, which includes features like Address Notification which allows a server to inform a dial-up client of its IP address, password authentication and better compression.

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Topic 8 – Types of Internet Connection – ISDN

The Integrated Services Digital Network (ISDN) -

digital transmission over telephone copper wire. A single ISDN line has two 64 Kbps B-channels which can carry data or voice, and one 16 Kbps D-channel used for transmitting control information. T The two channels can be used independently (one for analogue or digital telephone, one for internet access) or can be combined together to provide a single digital connection. Both channels used for internet = 128 Kbps connection. ISDN can be combined together giving 128Kbps per line. Need ISDN Terminal Adapter, max 5.5km tel exchange.

ISDN lines are often used for one to one video conferencing if a high bandwidth IP connection is not available – this is expensive.

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Topic 8 – Types of Internet Connection – ADSL An ADSL connection requires a special ADSL modem but uses a normal copper telephone line. ADSL2/2+ as per the advert below, allows data transfer speeds of 20Mbps downstream and up to 2Mbps upstream. ADSL is well suited for web browsing, video on demand and some client-server applications.

ADSL is an "always on" connection which means that users will have a static IP address which makes them much more vulnerable to hacker attack (and more attractive as they have access to higher bandwidth).

Users of ADSL connections need to make sure that they have a reliable firewall installed

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Topic 8 – Types of Internet Connection – Cable Transmitting TV over a cable connection is common due to the spread of optical cable network infrastructure. A cable modem is needed. Although the possible bandwidth for Internet services over a cable TV line can be up to 27Mbps, since this bandwidth will be shared by a substantial number of other users on the line (and the total bandwidth available will also be limited by the bandwidth which the cable company has leased from the telecommunications provider) the actual bandwidth available to the home user is usually only slightly higher than that available using ADSL.

Like ADSL, cable is also an "always on" connection so users need to make sure that they have a reliable firewall installed.

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Topic 8 – Types of Internet Connection – Leased Line A leased line is an agreement with a communications company to provide a permanent dedicated circuit between two points.

The cost of the line is usually based on the distance between the locations. The traditional telephone system utilises the same lines for many different conversations by using packet switching whereas leased lines maintain a single open circuit at all times. Leased lines most commonly are rented by businesses to connect branch offices, because these lines guarantee bandwidth for network traffic. Leased lines are expensive to set up and expensive to maintain. A leased line is often called a T1 connection. A T1 connection is sometimes referred to as a Symmetric Digital Subscriber Line (SDSL) (to distinguish it from ADSL).

Because they provide a permanent switched circuit between two points, leased lines often transmit video and audio as well as computer data.

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Topic 8 – Benefits of High Bandwidth A high bandwidth connection provides a number of benefits to an organisation using Voice Over IP (VOIP).

The saving in telephone charges for an organisation which has a number of branches distributed around the world is very large indeed, if they are able to use a system where their Internet connection provides a telephone service, as the connection is already being paid for through the ISP. Video Conferencing is another service which a high bandwidth connection can provide, again saving telephone charges or travelling costs. Both of these applications need a guaranteed bandwidth to work successfully, so any system which uses contention to share a connection is likely to be unsuitable.

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Topic 8 – Summary Bandwidth = Kilobits per sec Kbps / Megabits per sec Mbps Asynchronous data transmission transmits one byte at a time along with start and stop bits Synchronous data transmission more efficient as larger blocks of data and less control information included Circuit switching maintains a fixed connection between two points while data is being transferred Packet switching is "Connectionless" because data is routed in packets which may take different routes The Ethernet standard uses Carrier Sense Multiple Access / Collision Detection (CSMA/CD) to reduce collisions. A switched Ethernet network has less collisions and is more secure because the switch effectively divides the network up into a number of separate segments Every Network Interface Card (NIC) has a unique MAC address to identify it. This is separate from the IP address which is controlled by software.

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Topic 8 – Summary Error detection using Parity, Checksums and Cyclic Redundancy Checks means extra data is transmitted Dialup connection, modem, maximum speed of 56Kbps An ISDN line and terminal adapter provides two 64Kbps digital channels and one 16Kbps control line An ADSL line is programmed to operate between two specific locations and can provide 2Mbps download and 128Kbps upload bandwidth. ADSL bandwidth may be shared between a number of users.

A Cable modem provides similar bandwidth to an ADSL line but uses Television distribution cable to provide the connection A leased line provides a guaranteed 1.54 Mbps digital connection between two specific locations but is by far the most expensive option

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Topic 2 – The OSI Network Model – Pre-Requisite Knowledge Before studying this topic you should know the difference between a node and a channel on a network. You should be familiar with the functions of a hub (multiport repeater), a switch and a router on a network. You should be familiar with the idea of a network protocol, and the fact that different protocols operate at different levels - for instance the SMTP protocol operates at the level of an application such as an email client, whereas the TCP/IP protocol operates at the level of a node on the network. A host on a network usually means a node which provides a service - in effect a machine which can act as a server.

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Topic 2 – The OSI Network Model – Pre-Requisite Knowledge After studying this topic you should be able to: • Name and describe the functions of the 7 layers in the OSI Network model • Understand the reasons for dividing network functions into a hierarchy of different layers • Understand the reasons for Independence and transparency in network layers

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Topic 2 – The OSI Network Model – Review Q1: What is a node in a network?

a) A device on a network with a unique IP address b) A connection between two computers c) An Internet link d) A type of communications software Q2: What is a channel on a network?

a) A device on a network with a unique IP address b) A connection between two nodes c) An Internet link d) A type of communications software

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Topic 2 – The OSI Network Model – Review Q3: Which of these statements is false?

a) A hub just retransmits packets to every node on the network b) A switch selectively retransmits packets according to the IP address of the destination machine c) A hub cannot reduce the number of collisions on a local area network d) A switch cannot reduce the number of collisions on a local area network

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Topic 2 – Introduction to Network Architecture The Open Systems Interconnection (OSI) model was developed to ensure that communications equipment and networking software would be compatible, irrespective of manufacturer. The OSI model divides data transfer across a network into 7 layers. The layers are hierarchical with each layer having a specific task to perform. The top layer is the Application layer which is the layer you are using when you send an email using an email client or view a web page using a web browser. The lowest layer is the Physical layer which is concerned with the cabling and physical characteristics of the network. Each layer has been designed with a particular task in mind and communicates with the layers above and below it in the hierarchy. Each layer is independent.

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Topic 2 – Introduction to Network Architecture The OSI model is often referred to as the OSI network architecture. There are several good reasons for using this hierarchical layered model:

Transparency:

The complexities of each layer are hidden from the user. Layers simply pass data to the layer above/below. The user makes a request on their computer and it appears to communicate directly with the other computer (but the 7 layers must communicate to transfer the data on each computer)

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Topic 2 – Introduction to Network Architecture Hierarchy: Imagine sending an email or accessing a web page (application layer). When the data is transmitted the data is passed by one layer to the layers below, these files are split into smaller segments, each with that layer’s headers, error correction and sequence information added to them, until the data becomes a stream of bits transmitted via the physical layer. The reverse process takes place at the receiving end with the headers getting stripped out, segments reassembled until the application layer presents the user with the transmitted file. Each layer is responsible to the layer above and below it for ensuring that the data it receives and transmits remains intact.

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Topic 2 – Introduction to Network Architecture

Independence:

Because the layers are independent, it is possible to replace or upgrade one layer with another software version without having to change how the other layers communicate with it. This modularity means that parts of the system can be upgraded independently without changing the entire system.

James Bond

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Topic 2 – Introduction to Network Architecture An easy way to remember the order of the layers is: All People Seem to Need Domino’s Pizza

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Topic 2 – Application Layer The Application Layer is the top layer of the OSI model and is concerned with specific applications eg browsers, e-mail, file transfer, database access. It provides a set of interfaces for applications to obtain access to networked services as well as access to the kinds of network services that support applications directly such as an email client, or an Internet browser.

Application Layer protocols include HTTP, FTP, SMTP and POP3. Examples of software used: Email client, browser.

How to Pass Book:

Concerned with specific applications eg it supports applications such as mail transfer, database access and file transfer.

Controls how applications access the network Connects user applications with network functionality.

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Topic 2 – Presentation Layer Handles data format information for networked communications. Converts data into a standardised format that can be understood by both sides, character code conversion, compression or encryption. Controls file locking and security at the user level - this is why if a file is already open for writing on a network drive, another user cannot also open it for writing. Standards such as HTML, GIF, ASCII might be used at this layer.

How to Pass Book: Manages data represented to enable 2 way comm. Converts data - from application to network (Defines data format so application receives suitable data).

Encrypts the data, Compresses data

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Topic 2 – Session Layer Manages log on procedures and password recognition. Permits two parties to hold ongoing communications called a session across a network. It performs Domain Name Resolution.

How to Pass Book:

Synchronizes the exchange of data Defines how connections can be established, maintained and terminated. Performs name resolution functions turning the text names for web pages into IP addresses. Domain Name Resolution.

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Topic 2 – Transport Layer Breaks file into segments, combines incoming segments into a contiguous file. Creates/maintains end-to-end connection between systems, ensuring that the bits delivered are the same as bits transmitted; in the same order and without modification, loss or duplication. Guarantees an error free connection between two hosts.

The TCP protocol operates at this level.

How to Pass Book:

Sets up communication between users, controls the transmission between sending and receiving systems.

Sequences packets so that they can be reassembled at the destination in the correct order. Generates acknowledgements and retransmits packets.

Decompresses data

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Topic 2 – Network Layer Concerned with the path through the network. Responsible for routing, and controlling the flow of information between hosts. Adds network hardware source and destination addresses as a header. Does not guarantee the datagram will reach destination. The Network layer works in units of packets. The IP protocol is used at this layer. Network Routers operate at this level as they are responsible for routing packets between networks.

How to Pass Book:

Defines host addresses, for example IP addresses, creates packet headers and routes packets using routers.

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Topic 2 – Data Link Layer Puts data into frames or packets along with error checking data. In an Ethernet network it uses frames. Alternatively it transforms a stream of raw bits (0s and 1s) from the physical layer into a data frame, provides error-free transfer between nodes, allowing the layers above it to assume virtually error-free transmission. Is a firmware layer of the NIC where the Ethernet network standard is implemented. Network switches operate at this layer.

From How to Pass Book:

Organized stream of raw bits into frames (deals with size of packets) Sets up error detection and correction Deals with hardware addressing, eg MAC addresses.

Prevents 2 nodes transmitting at same time

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Topic 2 – Physical Layer Transforms bits in a computer system into electromagnetic (or equivalent) signals for a particular transmission medium (wire, fibre, ether, etc.) The Physical Layer defines items like the type of cabling (coax, twisted pair, etc.), the frequency of operation (10 Mbps, 100Mbps, etc.), voltage levels, and network topology (star, bus, ring, etc) The Physical layer functions in units of bits. Network hubs and repeaters operate at this layer.

How to Pass Book:

Defines the physical and electrical characteristics of the network interface Defines the bit synchronization, cabling topologies, how the NIC interfaces with the cabling.

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Topic 2 – Summary • The OSI model divides networks into seven layers • All People Seem To Need Domino’s Pizza • Layers are hierarchical, transparent, and independent • Application layer provides interfaces for network applications • Presentation layer handles data format information • Session layer manages log-on and password authentication • Transport layer breaks up file into segment for transport over a network and guarantees that these segments are not lost • Network layer routes packets • Data Link layer guarantees error free transmission • Physical layer transmits bits over physical medium

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Topic 9 – Wireless Data Applications – Pre-Requisite Knowledge You should know the difference between the following wireless communications methods: Wireless Personal Area Networks (WPAN) Wireless Local Area Networks (WWAN) Wireless Wide Area networks (WWAN)

Learning Objectives

• After studying this topic you should be able to: • Describe modern wireless communication methods • Describe a Wireless Personal Area Network (WPAN) and its applications • Describe a Wireless Local Area Network (WLAN) and its applications • Describe a Wireless Wide Area Network (WWAN) and its applications

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Topic 9 – Wireless Data Applications – Pre-Requisite Knowledge Q1: What is the range of a typical Bluetooth WPAN?

a) 100 Metres b) 50 Metres c) 10 Metres d) 1 Metre Q2: Which one of these is not a wireless technology?

a) Ethernet b) Bluetooth c) Microwave d) IEEE 802.11b

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Topic 9 – Wireless Data Applications – Pre-Requisite Knowledge Q3: What is the main difference between a WPAN and a WLAN?

a) A WLAN has multiple users a WPAN normally does not b) A WLAN does not need any cables whereas a WPAN does c) A WPAN has more potential connections than a WLAN d) A WLAN cannot share as many resources as a WPAN

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Topic 9 – Wireless Data Applications – Introduction There are a number of different wireless technologies available for the different applications we are going to look at: Bluetooth is a low power and low bandwidth technology for personal area networks, 802.11b, is a wireless networking standard for Local Area Networks (along with its companions, 802.11g, 802.11a and 802.11n) and there is a selection of wireless technologies available for Wireless Wide Area Networking including satellite, mobile phone networks and wireless broadband.

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Topic 9 – Wireless Data Applications – WPAN A Wireless Personal Area Network (WPAN) is a personal area network that permits communication within about 10 meters such as Bluetooth. A WPAN could interconnect all the ordinary computing and communicating devices that many people carry with them today such as mobile phone, mp3-player, laptop and Personal Digital Assistant (PDA).

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Topic 9 – Wireless Data Applications – WPAN Each bluetooth device has a unique 48-bit address. Devices are able to communicate when within range. Eg printing from bluetooth laptop to bluetooth printer. Using a system like this it should be possible to have all mobile and fixed computer devices totally coordinated. Bluetooth uses the radio waves in the frequency band of 2.4 GHz with a speed of up to 2Mbps. Bluetooth devices can function in two modes: circuit switched (for voice over land/wireless). This connection is asynchronous, speed of 57.6 Kbps to 721 Kbps.

packet switched (for Internet data, as well as for higher bandwidth mobile communication systems like the General Packet Radio Service (GPRS)). This connection is synchronous with at a speed of 64 Kbps.

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Topic 9 – Wireless Data Applications – WLAN A Wireless Local Area Network (WLAN) uses wireless signals and wireless network cards. Wireless networks are useful in creating temporary networks or where it is difficult or expensive to fit a cable infrastructure. A network station on a WLAN will be fitted with a wireless Ethernet card which communicates with a wireless base station (sometimes called a wireless hub).

The base station must be connected to the server in some way (often by cable, as the bandwidth available on cable is much greater than the bandwidth currently available over a wireless connection).

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Topic 9 – Wireless Data Applications – WLAN In a small network for the home user, the wireless hub may be replaced by a wireless router combined with an ADSL or cable modem. There may be a number of base stations throughout a building, since the range of wireless networks can be as little as 100 metres or less, and users can “roam” picking up different connections as they move through a building. The wireless protocol standards currently in use with their theoretical bandwidths are: 802.11b

up to 11 Mbps 802.11g

up to 54 Mbps 802.11n

up to 160 Mbps

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Topic 9 – Wireless Data Applications – Security on WLAN Securing a network which uses wireless workstations is more difficult as it is difficult to physically check which stations are connected to the network. The area within which a wireless laptop can connect is difficult to control and often will extend beyond the walls of the building it is installed in. Wireless technologies come equipped with encryption and other security features to restrict access to them.

Wireless networks are often referred to as Wi-fi networks. These are now popular in hotels, airports, coffee shops and even fast food outlets, where customers are attracted by the ability to surf the WWW from their wireless laptops etc. Some of these organisations will charge for the Wi-fi service.

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Topic 9 – Wireless Data Applications – Security on WLAN Wireless networks can be made secure by a number of strategies Using the MAC address of the wireless network card to authenticate legitimate users Use an encryption technology such as Virtual Private Networking (VPN) to ensure that signals which are intercepted cannot be used to extract information about the network which a hacker could use Use the IEEE 802.11b built in Wired Equivalent Privacy (WEP).to encrypt wireless traffic, although this should never be relied upon on its own as it is a relatively weak form of security.

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Topic 9 – Wireless Data Applications – WWAN There are a number of Wireless Wide Area Network (WWAN) solutions available. Use your mobile phone to connect your laptop to the telephone system – simple but expensive! A satellite modem is another very expensive but more effective solution if you want mobile connectivity, and has the added advantage of working anywhere in the world where the satellite can be accessed. Wireless Broadband is likely to be the most likely solution for rural and metropolitan areas if mobile connectivity is not required.

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Topic 9 – Wireless Data Applications – WWAN – Wireless Broadband Wireless broadband is currently under development.

WiMax (Worldwide Interoperability of Microwave Access) 802.16.

This is a broadband wireless access standard providing bandwidth in excess of 70Mbps.

service.

It services wide area and metropolitan (city) area networks. It has a theoretical maximum distance of 31 miles giving service equivalent to T1-level

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Topic 9 – Wireless Data Applications – Summary Wireless networking is still a relatively new technology and there are a wide variety of standards available to implement Personal, Local or Wide area networks.

Personal wireless area networks tend to be low bandwidth and short range and are used for linking portable communications equipment Wireless local area networks tend to be high bandwidth and medium range and are used for connecting portable machines to conventional cabled networks or replacing cabled networks Wireless wide area networks tend to be mid bandwidth and high range and are used to provide broadband services to users who do not have access to wired systems.

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Higher Computing – Unit 3

Transcript Higher Computing – Unit 3

Higher Computing – Unit 3

Topics 5-8, 2, 9 Networking

Q3: What is the major benefit of VOIP

Asynchronous data transmission (where

Unicast Transmission

from a single source to a specified host.

Broadcast Transmission is a method of

Multicast Transmission is where packets

Ethernet frames and transmission rates

MAC addresses. The actual data to be

Independence:

James Bond

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