6. HTTP is the protocol for retrieving web pages, HTML is the language used to tell a browser how to display data on a web page.

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1 Topic1: Common Network Protocols 1. A network protocol is a set of rules which describe exactly how communication is to occur between two computers. They are needed because otherwise there would be no agreed standard way in which one machine could send data to another. 2. a. SMTP is the protocol for sending s to a mail server b. HTTP is the protocol for retrieving web pages from a server c. POP3 is the protocol for retrieving s from a mail server d. FTP is for transferring files between computers 3. user_name@domain_name 4. TCP/IP is actually made up of two protocols. The Transmission Control Protocol (TCP) which provides a reliable end-to-end link between hosts, and the Internet Protocol (IP) which defines a common method for exchanging packets among a wide collection of networks. TCP is responsible for splitting the data into these packets and adding a header to each one. This header includes a sequence number which allows the file to be recreated at the receiving end by re-assembling the packets in the correct order. TCP is also responsible for re-transmitting packets if it does not receive an acknowledgment that a packet has been received. The IP protocol is responsible for taking each packet and adding its own header to allow the packet to be routed around between networks 5. This works because the domain mysite.co.uk is actually identified by a unique IP address. The Domain Name Service converts the friendly name to the numeric IP address whenever you type in the domain name. 6. HTTP is the protocol for retrieving web pages, HTML is the language used to tell a browser how to display data on a web page. 7. FTP is used to transfer files between computers files can be transferred in both directions and the connection remains open until closed. An HTTP connection only remains open while the file is being transferred, and files can only be transferred in one direction, from server to client. 8. POP3 and SMTP 9. The domain name

2 Topic 2: The OSI Network Model 1. a. The Application Layer is the top layer of the OSI model. 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 client, or an Internet browser. b. The Transport layer breaks up the file into segments for transport to the network, and combines incoming segments into a contiguous file. The Transport layer is responsible for creating and maintaining the basic end-to-end connection between communicating systems. The transport layer guarantees an error free connection between two hosts. 2. Transparency means that From the point of view of each layer on a network, it behaves as if it is communicating directly with the equivalent layer on the receiving network. This means that from the user s point of view, the application layer on one network appears to pass information to the application layer on the other. 3. Describing the layers as hierarchical means that each layer is responsible to the layer above and below it for ensuring that the data it receives and transmits remains intact. 4. HTTP and POP3 operate on the Application layer 5. From the point of view of the Application layer, the client is transferring a message to the equivalent mail server on the computer it is connected to. As 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.

3 Topic 3: IP addresses and the Domain Name Service 1. A domain name is needed so that the company can have a website which is identifiable with their company name. 1. The Domain Name Service converts names of computers into IP addresses. 2. A Class C IP address range only has 255 addresses. A Class B IP address range has addresses 3. Public IP addresses are used to uniquely identify computers on the Internet and can be accessed from anywhere. Private IP addresses are used in private networks and can only be accessed from within their network. 4. Static IP addressing is where a computer has a permanent IP address. A dynamic IP address may be allocated to a computer while it is connected to a network, but can be used by another computer when it disconnects.

4 Topic 4: The World Wide Web (WWW) 1. A structure tag identifies a structural part of a web page like the header or the body. A text tag is used to switch a text effect on or off. For example the <head> and </head> tags identify the header of a web page <u> and </u> switch underlining on and off. 2. XHTML (Extensible Hypertext Markup Language) has stricter rules for tags and this allows its pages to be used with XML tools. 3. The benefit of using stylesheets is that they allow the developer to separate content from design in a web page. Changing the stylesheet can change the look of all the web pages based on it without having to change each page individually. 4. A microbrowser allows WAP pages to be viewed on a mobile phone. 5. HTML is not optimised for small screens or low bandwidth connections. Whereas HTML was designed for creating documents, WML was designed for creating applications. Users of WAP enabled devices need short menus and easily read questions in order to find what they need. Users want to be connected for as little time as possible. 6. Crawler based search engines have databases which are selected and built by computer robot programs called spiders. These programs "crawl" the web in their hunt for pages to include, They find the pages for potential inclusion by following the links in the pages they already have in their database, but also rely on contributors submitting their web pages to be indexed. The software "crawls" through the web indexing pages as it goes, using the content of pages, their titles, and content HTML tags as a means of building the index. Directories are human powered indexing facilities which are built up by users and editors working for the directory company. Users submit a short description to the directory for their entire site, or editors write one for sites they review. When a query is entered, the search engine only looks for matches in the descriptions submitted. 7. Meta tags provide information about the page itself such as the author, the date of creation and the type of information it contains.

5 Topic 5: The Implications of the WWW 1. The advantages of E-commerce to the customer are: Goods and services can be purchased at any time of day or night, 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 the need to travel The advantages of E-commerce to the retailer are: Dealing directly with the customer means no profit taken by retailers or middle-men Your customer base is no longer restricted to those who can travel to your nearest outlet and you do not need to pay for expensive high street retail premises 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 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 country, you may be liable to pay import tax The disadvantages to the retailer 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

6 2. Advantages for the employee: Because you are working from home you can save on travel time and transport costs, and if you are self employed, you can deliver your work to your customers electronically. As long as you produce the required results, it does not matter where or when you work. This means that you can save on child-minding or other expenses such as high housing costs; Disadvantages for the employee: Because you are not in touch with your fellow employees, 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 because you worry that your employers may think you are having an easy time of it at home; 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 because your workers are using their own homes as their work-space; Tele-workers often work harder than they would 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. Disadvantages for the employer: You will need to train your tele-workers and pay for communications costs and computer equipment; There may be security issues you will need to consider if 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 work-force provide if your workers are in a foreign country. 3. Cookies are used to store details of your preferences when you view a web page they are also used to transmit data back to the web server when you purchase online. 4. Misrepresentation is pretending to be a different age or a different sex when you are communicating online with someone else. 5. 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. 6. The Regulation of Investigatory Powers Act (2000) gives government and employers wide rights to monitor employees s and telephone calls to ensure that they relate to work. Under RIP, some UK internet service providers (ISPs) will be asked "to maintain a reasonable intercept capability". This would mean that they would be required to install a device enabling the security services to monitor the flow of data If intercepted

7 communications are encrypted, the act will force people to surrender the decryption keys on pain of jail sentences of up to two years

8 Topic 6: Network Security 1. A group policy allows security settings to be allocated to a large number of users in one go. 2. Set passwords to be more than 8 letters, but not to expire. You don t want pupils to be endlessly forgetting their passwords, but they need to be secure 3. Encryption is classified by the number of bits needed for the key used to encode the data. The more bits that are used, the longer it takes for the code to be cracked. 4. Lock up servers, add hardware security to computer rooms such as swipe cards or fingerprint recognition. Use switches instead of hubs when installing the network infrastructure. Avoid wireless networks unless they are secure. 5. A virus is a destructive piece of code which attaches itself to another program. A worm is similar to a virus, but it is a program in its own right. Often it is not necessarily destructive, although its prime concern is to propagate itself as efficiently as possible, often consuming machine resources in the process. A Trojan is software which once installed allows someone else to take control over or monitor activity on the host machine. 6. A proxy server protects a network by presenting a single IP address to the outside world, hiding the network of machines with private IP addresses using NAT (Network Address Translation) 7. A Walled Garden approach only allows certain domains to be accessed from inside a network. Conventional internet filtering uses a list of banned domains and IP addresses to restrict access. A walled garden is safer, but restricts legitimate access to useful material. Conventional filtering will never block out everything which needs to be blocked, and has to be kept up to date.

9 Topic 7: Denial of Service Attacks and Disaster Recovery 1. A Denial of Service attack is an attempt to deny legitimate users access to a web site or internet service by some means 2. Resource starvation is usually achieved by flooding a server with irrelelvant or invalid requests for data. 3. DoS attacks might occur as part of an extortion attempt, commercial sabotage or political or malicious attacks 4. I would recommend: a. Make regular backups, and keep them safe and secure b. Install anti virus software and keep it up to date c. Install a firewall d. Keep duplicates of crucial equipment such as hard disks, switches and backup tape drives

10 Topic 8: Data Transmission 1. 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 the bit and transmission speed is measured in Megabits per second (Mbps) or Kilobits per second. 2. Bandwidth is the amount of data which can be transmitted per second. Higher bandwidth means that resource hungry applications like video conferencing or voice over IP can run on a network. 3. Asynchronous data transmission (where the sending and receiving machine are not synchronised) uses a transmission system where each byte is sent individually with its accompanying stop and start bits. Asynchronous data transmission (where the sending and receiving machine are not synchronised) uses a transmission system where each byte is sent individually with its accompanying stop and start bits. 4. Circuit switching is where there is a direct connection established between the two networks. All data follows the same physical path during the communication. Packet switching is a system where the data to be exchanged is broken up into blocks of data called packets. These packets are given a destination address and a sequence number, and this information is used to re-assemble the communication when it reaches its destination. Circuit switching is expensive, but delivers a very high bandwidth connection. Packet switching is usually much cheaper than circuit switching because it does not need a dedicated connection. 5. 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. Unicast transmission is where a packet is sent from a single source to a specified host. Packets must be acknowledged and retransmitted if lost. 6. A MAC address is fixed buy the Network Interface Card. An IP address is controlled by software. 7. CSMA/CD: In order to transmit a frame on an Ethernet network, any node can transmit, but must first check that no other machine is transmitting at the same time (This is the Carrier Sense Multiple Access part). If there is no other transmitting node, then the transmission is started. Once the transmission has started, if a collision is detected, (the Collision Detection part) then transmission stops, and the machine waits for a short random time before attempting to re-transmit. If a collision is detected again during this re-transmission, then the machine will wait for a longer random time before re-trying. 8. Applications which depend on accurate timing are inappropriate because connection speeds depend on the amount of network traffic which may vary over time. 9. Parity is a system of error detection. An extra bit called a parity bit is added to each unit of information (usually a single character) which is transmitted. If odd parity is used then the parity bit will be set so that the number of 1s in the transmitted data is always an odd number. The receiver counts the number of bits whose value is 1. If this comes to an odd number then it assumes that the data has been transmitted correctly. If it comes to an even number then it will request that the data be retransmitted. 10. Error detection just detects errors. Error correction uses additional information to reconstruct lost data if it has been corrupted in transit.

11 11. PPP and SLIP are both protocols used for dialup internet connections, though SLIP is an older one and is not used much 12. Both ADSL and Cable are services which use contention to share bandwidth between a number of users 13. ISDN and leased lines both have a fixed guaranteed bandwidth 14. Video conferencing and Voice over IP

12 Topic 9: Wireless Data Applications 1. Bluetooth is used to create a Wireless Personal Area Network (WPAN) 2. Security is difficult to implement on a WLAN because it is difficult to stop people connecting to a wireless network since the connection is available all around the transmitters. 3. A WPAN has a range of a few metres, a WLAN may have a range of several hundred metres a. Use the built in Wired Equivalent Privacy (WEP).to encrypt wireless traffic. b. Use the MAC address to authenticate connections. c. Use Virtual Private Networking

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