Demonstrate an Understanding of the Principles of the Internet and the World-Wide-Web

DEMONSTRATE AN UNDERSTANDING OF THE PRINCIPLES OF

THE INTERNET AND THE WORLD-WIDE-WEB 115391

PURPOSE OF THE UNIT STANDARD People credited with this unit standard are able to:  Explain the principles of the internet and the world-wide-web  Explain how the world-wide-web incorporates the various internet applications  The performance of all elements is to a standard that allows for further learning in this area.

LEARNING ASSUMED TO BE IN PLACE AND RECOGNITION OF PRIOR LEARNING The credit value of this unit is based on a person having prior knowledge and skills to:  Demonstrate PC competency skills (End-User Computing unit Standards, at least up to NQF level 3.)

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INDEX

Competence Requirements Page Unit Standard 115391 alignment index Here you will find the different outcomes explained which you need to be 23 proved competent in, in order to complete the Unit Standard 115391. Unit Standard 115391 25 Explain the principles of the internet and the world-wide-web 27 Explain how the world-wide-web incorporates the various internet applications 41 Self-assessment Once you have completed all the questions after being facilitated, you need to check the progress you have made. If you feel that you are competent in the areas mentioned, you may tick the blocks, if however, you feel that you require 49 additional knowledge, you need to indicate so in the block below. Show this to your facilitator and make the necessary arrangements to assist you to become competent.

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Unit Standard 115391 – Alignment Index

SPECIFIC OUTCOMES AND RELATED ASSESSMENT CRITERIA SO 1 EXPLAIN THE PRINCIPLES OF THE INTERNET AND THE WORLD-WIDE-WEB. AC 1 The explanation outlines the origins and history of the internet 112 AC 2 The explanation identifies the major applications of the internet 115 AC 3 The explanation demonstrates the use of major internet applications 121 The explanation describes the history and development of the world-wide- AC 4 web 112 EXPLAIN HOW THE WORLD-WIDE-WEB INCORPORATES THE VARIOUS INTERNET SO 2 APPLICATIONS. The explanation provides a comprehensive understanding of the physical AC 1 context of web pages 126 The explanation identifies how the world-wide-web can be applied in an AC 2 intranet and extranet 132 The explanation describes the latest internet applications, including web- AC 3 based email, instant messaging and Voice-over-IP (VoIP) 127

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CRITICAL CROSS FIELD OUTCOMES UNIT STANDARD CCFO IDENTIFYING Identify, solve problems and make decisions in relation to the current systems development environments

UNIT STANDARD CCFO ORGANISING Organise and manage him/herself and his/her activities responsibly and effectively

UNIT STANDARD CCFO COMMUNICATING Communicate effectively using visual, mathematical and or language skills in the modes of oral and/ or written persuasion when engaging with systems development

UNIT STANDARD CCFO CONTRIBUTING Contribute to his/her full personal development and the social and economic development of the society at large by being aware of the importance of: reflecting on and exploring a variety of strategies to learn more effectively, exploring education and career opportunities and developing entrepreneurial opportunities.

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All qualifications and unit standards registered on the National Qualifications Framework are public property. Thus the only payment that can be made for them is for service and reproduction. It is illegal to sell this material for profit. If the material is reproduced or quoted, the South African Qualifications Authority (SAQA) should be acknowledged as the source.

SOUTH AFRICAN QUALIFICATIONS AUTHORITY REGISTERED UNIT STANDARD: Demonstrate an understanding of the principles of the internet and the world-wide- web SAQA US ID UNIT STANDARD TITLE 115391 Demonstrate an understanding of the principles of the internet and the world-wide-web ORIGINATOR SGB Computer Sciences and Information Systems FIELD SUBFIELD Field 10 - Physical, Mathematical, Computer and Life Information Technology and Computer Sciences Sciences ABET UNIT PRE-2009 NQF NQF LEVEL CREDITS BAND STANDARD LEVEL TYPE Undefined Regular- Level 4 NQF Level 04 3 Fundamental REGISTRATION STATUS REGISTRATION REGISTRATION SAQA DECISION START DATE END DATE NUMBER Reregistered 2015-07-01 2018-06-30 SAQA 10105/14 LAST DATE FOR LAST DATE FOR ACHIEVEMENT ENROLMENT 2019-06-30 2022-06-30 In all of the tables in this document, both the old and the new NQF Levels are shown. In the text (purpose statements, qualification rules, etc), any reference to NQF Levels are to the old levels unless specifically stated otherwise. This unit standard does not replace any other unit standard and is not replaced by any other unit standard

PURPOSE OF THE UNIT STANDARD People credited with this unit standard are able to:  Explain the principles of the internet and the world-wide-web  Explain how the world-wide-web incorporates the various internet applications The performance of all elements is to a standard that allows for further learning in this area.

Specific Outcomes and Assessment Criteria: SPECIFIC OUTCOME 1 Explain the principles of the internet and the world-wide-web. ASSESSMENT CRITERION 1 The explanation outlines the origins and history of the internet ASSESSMENT CRITERION 2 The explanation identifies the major applications of the internet ASSESSMENT CRITERION 3 The explanation demonstrates the use of major internet applications ASSESSMENT CRITERION 4

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The explanation describes the history and development of the world-wide-web

SPECIFIC OUTCOME 2 Explain how the world-wide-web incorporates the various internet applications. ASSESSMENT CRITERION 1 The explanation provides a comprehensive understanding of the physical context of web pages ASSESSMENT CRITERION 2 The explanation identifies how the world-wide-web can be applied in an intranet and extranet ASSESSMENT CRITERION 3 The explanation describes the latest internet applications, including web-based email, instant messaging and Voice-over-IP (VoIP)

UNIT STANDARD ACCREDITATION AND MODERATION OPTIONS The relevant Education and Training Quality Authority (ETQA) must accredit providers before they can offer programs of education and training assessed against unit standards Moderation Process: Moderation of assessment will be overseen by the relevant ETQA according to the moderation guidelines in the relevant qualification and the agreed ETQA procedures

UNIT STANDARD ESSENTIAL EMBEDDED KNOWLEDGE 1. Performance of all elements is to be carried out in accordance with organisation standards and procedures, unless otherwise stated. Organisation standards and procedures may cover: quality assurance, documentation, security, communication, health and safety, and personal behaviour. An example of the standards expected is the standards found in ISO 9000 Certified Organisations. 2. Performance of all elements complies with the laws of South Africa, especially with regard to copyright, privacy, health and safety, and consumer rights. 3. All activities must comply with any policies, procedures and requirements of the organisations involved, the ethical codes of relevant professional bodies and any relevant legislative and/ or regulatory requirements.

Critical Cross-field Outcomes (CCFO): UNIT STANDARD CCFO IDENTIFYING Identify, solve problems and make decisions in relation to the current systems development environments UNIT STANDARD CCFO ORGANISING Organise and manage him/her self and his/her activities responsibly and effectively UNIT STANDARD CCFO COMMUNICATING Communicate effectively using visual, mathematical and or language skills in the modes of oral and/ or written persuasion when engaging with systems development UNIT STANDARD CCFO CONTRIBUTING Contribute to his/her full personal development and the social and economic development of the society at large by being aware of the importance of: reflecting on and exploring a variety of strategies to learn more effectively, exploring education and career opportunities and developing entrepreneurial opportunities.

THE PRINCIPLES OF THE INTERNET AND THE WORLD WIDE WEB TIME: 120 MINUTES ACTIVITY: SELF AND GROUP

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(SO1-AC1/4) ne of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together Oin many different ways to form the single entity that we know as the Internet. In fact, the very name comes from this idea of interconnected networks.

Since its beginning in 1969, the Internet has grown from four host computer systems to tens of millions. However, just because nobody owns the Internet, it doesn't mean it is not monitored and maintained in different ways.

The Internet Society, a non-profit group established in 1992, oversees the formation of the policies and protocols that define how we use and interact with the Internet.

Every computer that is connected to the Internet is part of a network, even the one in your home. For example, you may use a modem and dial a local number to connect to an Internet Service Provider (ISP).

At work, you may be part of a local area network (LAN), but you most likely still connect to the Internet using an ISP that your company has contracted with.

When you connect to your ISP, you become part of their network. The ISP may then connect to a larger network and become part of their network. The Internet is simply a network of networks.

Most large communications companies have their own dedicated backbones connecting various regions. In each region, the company has a Point of Presence (POP). The POP is a place for local users to access the company's network, often through a local phone number or dedicated line.

The amazing thing here is that there is no overall controlling network. Instead, there are several high-level networks connecting to each other through Network Access Points or NAPs. The Internet Backbone The National Science Foundation (NSF) created the first high-speed backbone in 1987. Called NSFNET, it was a T1 line that connected 170 smaller networks together and operated at 1.544 Mbps (million bits per second). IBM, MCI and Merit worked with NSF to create the backbone and developed a T3 (45 Mbps) backbone the following year.

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Backbones are typically fiber optic trunk lines. The trunk line has multiple fiber optic cables combined together to increase the capacity. Fiber optic cables are designated OC for optical carrier, such as OC-3, OC-12 or OC-48. An OC-3 line is capable of transmitting 155 Mbps while an OC-48 can transmit 2,488 Mbps (2.488 Gbps).

Compare that to a typical 56K modem transmitting 56,000 bps and you see just how fast a modern backbone is. Today there are many companies that operate their own high-capacity backbones, and all of them interconnect at various NAPs around the world.

In this way, everyone on the Internet, no matter where they are and what company they use, is able to talk to everyone else on the planet. The entire Internet is a gigantic, sprawling agreement between companies to intercommunicate freely.

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“Who controls everything..?” It is often said that there is no central control, administration, or management of the Internet. While this is generally true, there are several well-known organizations that work together in a relatively well structured and roughly democratic environment to collectively participate in the research, development, and management of the Internet, shown with inter- relationships in the chart below.

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Internet Network Example (SO1-AC2) Here's an example. Imagine that Company A is a large ISP. In each major city, Company A has a POP. The POP in each city is a rack full of modems that the ISP's customers dial into.

Company A leases fiber optic lines from the phone company to connect the POPs together (see, for example, this UUNET Data Centre Connectivity Map).

Imagine that Company B is a corporate ISP. Company B builds large buildings in major cities and corporations locate their Internet server machines in these buildings. Company B is such a large company that it runs its own fiber optic lines between its buildings so that they are all interconnected.

In this arrangement, all of Company A's customers can talk to each other, and all of Company B's customers can talk to each other, but there is no way for Company A's customers and Company B's customers to intercommunicate. Therefore, Company A and Company B both agree to connect to NAPs in various cities, and traffic between the two companies flows between the networks at the NAPs.

In the real Internet, dozens of large Internet providers interconnect at NAPs in various cities, and trillions of bytes of data flow between the individual networks at these points. The Internet is a collection of huge corporate networks that agree to all intercommunicate with each other at the NAPs. In this way, every computer on the Internet connects to every other.

o Internet Addresses Because the Internet is a global network of computers each computer connected to the Internet must have a unique address. Internet addresses are in the form nnn.nnn.nnn.nnn where nnn must be a number from 0 - 255. This address is known as an IP address. (IP stands for Internet Protocol; more on this later.)

The picture below illustrates two computers connected to the Internet; your computer with IP address 1.2.3.4 and another computer with IP address 5.6.7.8.

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The Internet is represented as an abstract object in-between. (As this paper progresses, the Internet portion of Diagram 1 will be explained and redrawn several times as the details of the Internet are exposed.)

Diagram 1

If you connect to the Internet through an Internet Service Provider (ISP), you are usually assigned a temporary IP address for the duration of your dial-in session. If you connect to the Internet from a local area network (LAN) your computer might have a permanent IP address or it might obtain a temporary one from a DHCP (Dynamic Host Configuration Protocol) server. In any case, if you are connected to the Internet, your computer has a unique IP address.

Check It Out - The Ping Program

If you're using Microsoft Windows or a type of Unix and have a connection to the Internet, there is a handy program to see if a computer on the Internet is alive. It's called ping, probably after the sound made by older submarine sonar systems.1 If you are using Windows, start a command prompt window. If you're using a flavour of Unix, get to a command prompt. Type ping www.yahoo.com. The ping program will send a 'ping' (actually an ICMP (Internet Control Message Protocol) echo request message) to the named computer. The pinged computer will respond with a reply. The ping program will count the time expired until the reply comes back (if it does). Also, if you enter a domain name (i.e. www.yahoo.com) instead of an IP address, ping will resolve the domain name and display the computer's IP address. More on domain names and address resolution later.

o o

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o Protocol Stacks and Packets So your computer is connected to the Internet and has a unique address. How does it 'talk' to other computers connected to the Internet? An example should serve here: Let's say your IP address is 1.2.3.4 and you want to send a message to the computer 5.6.7.8.

The message you want to send is "Hello computer 5.6.7.8!". Obviously, the message must be transmitted over whatever kind of wire connects your computer to the Internet.

Let's say you've dialled into your ISP from home and the message must be transmitted over the phone line. Therefore the message must be translated from alphabetic text into electronic signals, transmitted over the Internet, then translated back into alphabetic text.

How is this accomplished? Through the use of a protocol stack. Every computer needs one to communicate on the Internet and it is usually built into the computer's operating system (i.e. Windows, Unix, etc.). The protocol stack used on the Internet is referred to as the TCP/IP protocol stack because of the two major communication protocols used. The TCP/IP stack looks like this:

Protocol Layer Comments

Application Protocols Protocols specific to applications such as WWW, e-mail, Layer FTP, etc.

Transmission Control TCP directs packets to a specific application on a Protocol Layer computer using a port number.

Internet Protocol IP directs packets to a specific computer using an IP Layer address.

Converts binary packet data to network signals and Hardware Layer back. (E.g. ethernet network card, modem for phone lines, etc.)

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If we were to follow the path that the message "Hello computer 5.6.7.8!" took from our computer to the computer with IP address 5.6.7.8, it would happen something like this:

1. The message would start at the top of the protocol stack on your computer and work it's way downward.

2. If the message to be sent is long, each stack layer that the message passes through may break the message up into smaller chunks of data. This is because data sent over the Internet (and most computer networks) are sent in manageable chunks. On the Internet, these chunks of data are known as packets.

3. The packets would go through the Application Layer and continue to the TCP layer. Each packet is assigned a port number. Ports will be explained later, but suffice to say that many programs may be using the TCP/IP stack and sending messages. We need to know which program on the destination computer needs to receive the message because it will be listening on a specific port.

4. After going through the TCP layer, the packets proceed to the IP layer. This is where each packet receives it's destination address, 5.6.7.8.

5. Now that our message packets have a port number and an IP address, they are ready to be sent over the Internet. The hardware layer takes care of turning our packets containing the alphabetic text of our message into electronic signals and transmitting them over the phone line.

6. On the other end of the phone line your ISP has a direct connection to the Internet. The ISPs router examines the destination address in each packet and determines where to send

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it. Often, the packet's next stop is another router. More on routers and Internet infrastructure later.

7. Eventually, the packets reach computer 5.6.7.8. Here, the packets start at the bottom of the destination computer's TCP/IP stack and work upwards.

8. As the packets go upwards through the stack, all routing data that the sending computer's stack added (such as IP address and port number) is stripped from the packets.

9. When the data reaches the top of the stack, the packets have been re-assembled into their original form, "Hello computer 5.6.7.8!"

o Networking Infrastructure So now you know how packets travel from one computer to another over the Internet. But what's in-between? What actually makes up the Internet? Let's look at another diagram (on the following page):

Here we see Diagram 1 redrawn with more detail. The physical connection through the phone network to the Internet Service Provider might have been easy to guess, but beyond that might bear some explanation. The ISP maintains a pool of modems for their dial-in customers.

This is managed by some form of computer (usually a dedicated one) which controls data flow from the modem pool to a backbone or dedicated line router. This setup may be referred to as a port server, as it 'serves' access to the network. Billing and usage information is usually collected here as well.

After your packets traverse the phone network and your ISP's local equipment, they are routed onto the ISP's backbone or a backbone the ISP buys bandwidth from. From here the packets will usually journey through several routers and over several backbones, dedicated lines, and other networks until they find their destination, the computer with address 5.6.7.8. But wouldn't it would be nice if we knew the exact route our packets were taking over the Internet? As it turns out, there is a way...

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Check It Out - The Trace route Program

If you're using Microsoft Windows or a flavour of Unix and have a connection to the Internet, here is another handy Internet program. This one is called trace route and it shows the path your packets are taking to a given Internet destination.

Like ping, you must use trace route from a command prompt. In Windows, use tracert www.yahoo.com. From a Unix prompt, type trace route www.yahoo.com. Like ping, you may also enter IP addresses instead of domain names. Trace route will print out a list of all the routers, computers, and any other Internet entities that your packets must travel through to get to their destination.

(SO1-AC3) Internet Infrastructure The Internet backbone is made up of many large networks which interconnect with each other. These large networks are known as Network Service Providers or NSPs. Some of the large NSPs are UUNet, CerfNet, IBM, BBN Planet, SprintNet, PSINet, as well as others.

These networks peer with each other to exchange packet traffic. Each NSP is required to connect to three Network Access Points or NAPs.

At the NAPs, packet traffic may jump from one NSP's backbone to another NSP's backbone. NSPs also interconnect at Metropolitan Area Exchanges or MAEs. MAEs serve the same purpose as the NAPs but are privately owned. NAPs were the original Internet interconnect points.

Both NAPs and MAEs are referred to as Internet Exchange Points or IXs. NSPs also sell bandwidth to smaller networks, such as ISPs and smaller bandwidth providers. Below is a picture showing this hierarchical infrastructure.

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Diagram 4

This is not a true representation of an actual piece of the Internet. Diagram 4 is only meant to demonstrate how the NSPs could interconnect with each other and smaller ISPs.

None of the physical network components are shown in Diagram 4 as they are in Diagram 3. This is because a single NSP's backbone infrastructure is a complex drawing by itself.

Most NSPs publish maps of their network infrastructure on their web sites and can be found easily. To draw an actual map of the Internet would be nearly impossible due to its size, complexity, and ever changing structure.

o The Internet Routing Hierarchy So how do packets find their way across the Internet? Does every computer connected to the Internet know where the other computers are? Do packets simply get 'broadcast' to every computer on the Internet? The answer to both the preceding questions is 'no'.

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No computer knows where any of the other computers are, and packets do not get sent to every computer. The information used to get packets to their destinations are contained in routing tables kept by each router connected to the Internet.

Routers are packet switches A router is usually connected between networks to route packets between them. Each router knows about it's sub-networks and which IP addresses they use. The router usually doesn't know what IP addresses are 'above' it.

Examine Diagram 5 below. The black boxes connecting the backbones are routers. The larger NSP backbones at the top are connected at a NAP. Under them are several sub-networks, and under them, more sub-networks. At the bottom are two local area networks with computers attached.

Diagram 5

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When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks it's routing table.

If the network containing the IP address is found, the packet is sent to that network. If the network containing the IP address is not found, then the router sends the packet on a default route, usually up the backbone hierarchy to the next router.

Hopefully the next router will know where to send the packet. If it does not, again the packet is routed upwards until it reaches a NSP backbone.

The routers connected to the NSP backbones hold the largest routing tables and here the packet will be routed to the correct backbone, where it will begin its journey 'downward' through smaller and smaller networks until it finds its destination.

o Domain Names and Address Resolution But what if you don't know the IP address of the computer you want to connect to? What if you need to access a web server referred to as www.anothercomputer.com? How does your web browser know where on the Internet this computer lives?

The answer to all these questions is the Domain Name Service or DNS. The DNS is a distributed database which keeps track of computer's names and their corresponding IP addresses on the Internet.

Many computers connected to the Internet host part of the DNS database and the software that allows others to access it. These computers are known as DNS servers. No DNS server contains the entire database; they only contain a subset of it.

If a DNS server does not contain the domain name requested by another computer, the DNS server re-directs the requesting computer to another DNS server.

The Domain Name Service is structured as a hierarchy similar to the IP routing hierarchy. The computer requesting a name resolution will be re-directed 'up' the hierarchy until a DNS server is found that can resolve the domain name in the request.

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Diagram 6

Figure 6 illustrates a portion of the hierarchy. At the top of the tree are the domain roots. Some of the older, more common domains are seen near the top. What is not shown are the multitude of DNS servers around the world which form the rest of the hierarchy.

When an Internet connection is setup (e.g. for a LAN or Dial-Up Networking in Windows), one primary and one or more secondary DNS servers are usually specified as part of the installation.

This way, any Internet applications that need domain name resolution will be able to function correctly. For example, when you enter a web address into your web browser, the browser first connects to your primary DNS server.

After obtaining the IP address for the domain name you entered, the browser then connects to the target computer and requests the web page you wanted.

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USING THE WORLD WIDE WEB AND ITS’ APPLICATIONS TIME: 120 MINUTES ACTIVITY: SELF AND GROUP

(SO2-AC1) o Application Protocols: HTTP and the World Wide Web One of the most commonly used services on the Internet is the World Wide Web (WWW). The application protocol that makes the web work is Hypertext Transfer Protocol or HTTP. Do not confuse this with the Hypertext Mark-up Language (HTML). HTML is the language used to write web pages. HTTP is the protocol that web browsers and web servers use to communicate with each other over the Internet.

It is an application level protocol because it sits on top of the TCP layer in the protocol stack and is used by specific applications to talk to one another. In this case the applications are web browsers and web servers. HTTP is a connectionless text based protocol. Clients (web browsers) send requests to web servers for web elements such as web pages and images. After the request is serviced by a server, the connection between client and server across the Internet is disconnected. A new connection must be made for each request.

Most protocols are connection oriented. This means that the two computers communicating with each other keep the connection open over the Internet. HTTP does not however. Before an HTTP request can be made by a client, a new connection must be made to the server.

When you type a URL into a web browser, this is what happens: 1. If the URL contains a domain name, the browser first connects to a domain name server and retrieves the corresponding IP address for the web server. 2. The web browser connects to the web server and sends an HTTP request (via the protocol stack) for the desired web page. 3. The web server receives the request and checks for the desired page. If the page exists, the web server sends it. If the server cannot find the requested page, it will send an HTTP 404 error message. (404 means 'Page Not Found' as anyone who has surfed the web probably knows.) 4. The web browser receives the page back and the connection is closed.

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5. The browser then parses through the page and looks for other page elements it needs to complete the web page. These usually include images, applets, etc. 6. For each element needed, the browser makes additional connections and HTTP requests to the server for each element. 7. When the browser has finished loading all images, applets, etc. the page will be completely loaded in the browser window.

(SO2-AC3) o Application Protocols: SMTP and Electronic Mail Another commonly used Internet service is electronic mail. E-mail uses an application level protocol called Simple Mail Transfer Protocol or SMTP. SMTP is also a text based protocol, but unlike HTTP, SMTP is connection oriented. SMTP is also more complicated than HTTP. There are many more commands and considerations in SMTP than there are in HTTP.

When you open your mail client to read your e-mail, this is what typically happens: 1. The mail client (Netscape Mail, Lotus Notes, Microsoft Outlook, etc.) opens a connection to it's default mail server. The mail server's IP address or domain name is typically setup when the mail client is installed. 2. The mail server will always transmit the first message to identify itself. 3. The client will send an SMTP HELO command to which the server will respond with a 250 OK message. 4. Depending on whether the client is checking mail, sending mail, etc. the appropriate SMTP commands will be sent to the server, which will respond accordingly. 5. This request/response transaction will continue until the client sends an SMTP QUIT command. The server will then say goodbye and the connection will be closed.

o Transmission Control Protocol Under the application layer in the protocol stack is the TCP layer. When applications open a connection to another computer on the Internet, the messages they send (using a specific application layer protocol) get passed down the stack to the TCP layer. TCP is responsible for routing application protocols to the correct application on the destination computer.

To accomplish this, port numbers are used. Ports can be thought of as separate channels on each computer. For example, you can surf the web while reading e-mail. This is because these two applications (the web browser and the mail client) used different port numbers.

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When a packet arrives at a computer and makes its way up the protocol stack, the TCP layer decides which application receives the packet based on a port number.

TCP works like this:  When the TCP layer receives the application layer protocol data from above, it segments it into manageable 'chunks' and then adds a TCP header with specific TCP information to each 'chunk'. The information contained in the TCP header includes the port number of the application the data needs to be sent to.  When the TCP layer receives a packet from the IP layer below it, the TCP layer strips the TCP header data from the packet, does some data reconstruction if necessary, and then sends the data to the correct application using the port number taken from the TCP header.

This is how TCP routes the data moving through the protocol stack to the correct application TCP is not a textual protocol. TCP is a connection-oriented, reliable, byte stream service. Connection-oriented means that two applications using TCP must first establish a connection before exchanging data.

TCP is reliable because for each packet received, an acknowledgement is sent to the sender to confirm the delivery. TCP also includes a checksum in its header for error-checking the received data. The TCP header looks like this:

Notice that there is no place for an IP address in the TCP header. This is because TCP doesn't know anything about IP addresses. TCP's job is to get application level data from application to application reliably. The task of getting data from computer to computer is the job of IP.

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 43

Internet Protocol Unlike TCP, IP is an unreliable, connectionless protocol. IP doesn't care whether a packet gets to it's destination or not. Nor does IP know about connections and port numbers. IP's job is too send and route packets to other computers.

IP packets are independent entities and may arrive out of order or not at all. It is TCP's job to make sure packets arrive and are in the correct order. About the only thing IP has in common with TCP is the way it receives data and adds its own IP header information to the TCP data. The IP header looks like this:

Diagram 8 Above we see the IP addresses of the sending and receiving computers in the IP header. Below is what a packet looks like after passing through the application layer, TCP layer, and IP layer. The application layer data is segmented in the TCP layer, the TCP header is added, the packet continues to the IP layer, the IP header is added, and then the packet is transmitted across the Internet.

Diagram 9

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 44

Voice over Internet Protocol (VOIP) If you've never heard of VoIP, get ready to change the way you think about long-distance phone calls. VoIP, or Voice over Internet Protocol, is a method for taking analogue audio signals, like the kind you hear when you talk on the phone, and turning them into digital data that can be transmitted over the Internet.

How is this useful? VoIP can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free VoIP software that is available to make Internet phone calls, you're bypassing the phone company (and its charges) entirely.

VoIP is a revolutionary technology that has the potential to completely rework the world's phone systems. VoIP providers like Vonage have already been around for a while and are growing steadily. Major carriers like AT&T are already setting up VoIP calling plans in several markets around the United States, and the FCC is looking seriously at the potential ramifications of VoIP service.

Above all else, VoIP is basically a clever "reinvention of the wheel." In this article, we'll explore the principles behind VoIP, its applications and the potential of this emerging technology, which will more than likely one day replace the traditional phone system entirely. The interesting thing about VoIP is that there is not just one way to place a call. There are three different "types" of VoIP service in common use today:

ATA The simplest and most common way is through the use of a device called an ATA (analog telephone adaptor). The ATA allows you to connect a standard phone to your computer or your Internet connection for use with VoIP. The ATA is an analog-to-digital converter. It takes the analog signal from your traditional phone and converts it into digital data for transmission over the Internet.

You simply crack the ATA out of the box, plug the cable from your phone that would normally go in the wall socket into the ATA, and you're ready to make VoIP calls. Some ATAs may ship with additional software that is loaded onto the host computer to configure it; but in any case, it's a very straightforward setup.

IP Phones

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 45

These specialized phones look just like normal phones with a handset, cradle and buttons. But instead of having the standard RJ-11 phone connectors, IP phones have an RJ-45 Ethernet connector. IP phones connect directly to your router and have all the hardware and software necessary right onboard to handle the IP call. Wi-Fi phones allow subscribing callers to make VoIP calls from any Wi-Fi hot spot.

Computer-to-computer This is certainly the easiest way to use VoIP. You don't even have to pay for long-distance calls.

There are several companies offering free or very low-cost software that you can use for this type of VoIP. All you need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like you would get through a cable or DSL modem. Except for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance. o Summary Now you know how the Internet works. But how long will it stay this way? The version of IP currently used on the Internet (version 4) only allows 232 addresses. Eventually there won't be any free IP addresses left. Surprised? Don't worry. IP version 6 is being tested right now on a research backbone by a consortium of research institutions and corporations.

After that? Who knows?

The Internet has come a long way since its inception as a Defence Department research project. No one really knows what the Internet will become. One thing is sure, however. The Internet will unite the world like no other mechanism ever has. The Information Age is in full stride and you should be proud to be a part of it!

(SO2-AC2)

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 46

ntranets and Extranets An intranet is a private network, operated by a large company or other organisation, which uses internet technologies, but is insulated from the global internet. An extranet is an intranet that is accessible to some people from outside the company, or possibly shared by more than one organisation. For decades, many organisations have used in-house networks to connect their computers and make applications available to their staff. These networks were often expensive and could be hard to use. When the internet became popular, its networking software became widely available and, usually, free. It therefore made sense for organisations to adopt the same software for internal use.

What intranets do: Intranets typically start by publishing web pages about company events, health and safety policies, and staff newsletters. Popular applications follow, such as forms to reclaim expenses or request holidays. All these help eliminate paperwork and speed up workflows. As more features are added, an intranet can become essential to the operation of an organisation. It becomes a portal that provides access to all the things workers need.

The intranet is protected from the global internet by firewalls and by the need to log on with a secure password. Staff working outside the organisation may be able to access the intranet by using a VPN (virtual private network). This means all communications between the intranet and the user’s personal computer are encrypted.

What extranets do: Extranets take this process a step further, by providing access to people who work for different organisations. For example, a company could provide access to a supplier for online ordering, order tracking and inventory management.

Instead of sending information to suppliers, it lets them fetch it on a self-service basis. Another example would be a hospital providing local GPs with access to a booking system so they can make appointments for their patients. An extranet should be more efficient because everyone has access to the same data in the same format. Because all extranet communications can be encrypted over a VPN, it should also be more secure than sending data over the public internet.

Potential drawbacks

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 47

In practice, there can be drawbacks to intranets and extranets. IT staff are not website developers - they don’t have to work with dozens of browsers on millions of different PCs, just the company standard. Also, in-house developers expect applications to last for many years, perhaps for decades, whereas websites can change every few months as web standards and fashions change. This means companies can get stuck with an obsolete browser, such as Microsoft’s Internet Explorer 6, because vital internal applications have not been tested against or adapted for more modern browsers.

Let’s recap: An intranet is a private network that is contained within an enterprise. It may consist of many interlinked local area networks and also use leased lines in the wide area network. Typically, an intranet includes connections through one or more gateway computers to the outside Internet.

The main purpose of an intranet is to share company information and computing resources among employees. An intranet can also be used to facilitate working in groups and for teleconferences.

An intranet uses TCP/IP, HTTP, and other Internet protocols and in general looks like a private version of the Internet. With tunnelling, companies can send private messages through the public network, using the public network with special encryption/decryption and other security safeguards to connect one part of their intranet to another.

Typically, larger enterprises allow users within their intranet to access the public Internet through firewall servers that have the ability to screen messages in both directions so that company security is maintained. When part of an intranet is made accessible to customers, partners, suppliers, or others outside the company, that part becomes part of an extranet.

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 48

You are now ready to go through a check list. Be honest with yourself

Tick the box with either a √ or an X to indicate your response

□ I am able to explain the principles of the Internet and the world-wide-web

□ I am able to explain how the world-wide-web incorporates the various internet applications

You must think about any point you could not tick. Write this down as a goal. Decide on a plan of action to achieve these goals. Regularly review these goals.

My Goals and Planning: ______

NC: IT: SYSTEMS DEVELOPMENT AUTHOR: LEARNER MANUAL REL DATE: 27/01/2020 REV DATE: 01/01/2023 DOC REF: 48872 LM MOD 5 V-1 PAGE 49