The Structure of the Internet

In this lesson we will…

• Examine the difference between the Internet, the Web and the Intranet.

• Cover packet switching and how the Internet enables the Web.

Starter Activity

What do you do online?

OMG

How would you feel if you couldn’t do any of this?

How would you cope?

Internet

Web

Intranet The Internet houses the Web but why does the intranet overlap both?

How do these intercept? What are their functions?

The Internet, the Web and the Intranet

Activity 1

Now we are going to fill in the gaps …

The Internet • This is a global system of networks which are connected

together using a particular protocol called the TCP/IP . This is a procedure which controls how computers send information to each other. One important feature of this system is its decentralised structure. Because there is no central point on which communications depend, the system can continue to function well even when some connections break down.

The World Wide Web • This application, which was created in 1989, sits on top of the

Internet. It contains information resources in many forms (documents written in HTML, images, music, video, etc.) which can be linked together. Users can access information via a browser (which helps them find information, entertainment or services), or navigate between documents by clicking on hyperlinks.

• Each information resource has a unique URL and these resources

can be transferred using another protocol called HTTP.

Intranet • Many companies want to take advantage of the

networking capabilities of computers, but also need to keep their information restricted and secure. For this reason they often use a internal network to help them communicate, share information, provide computing services, or create internal websites. Employees of organisations can access the information in these systems, but external access is controlled or blocked.

The Internet…

The Resilience of the Internet

Communication and the Internet…

• Protocols: Set of rules for communication

• Transmission Control Protocol (TCP) and Internet Protocol (IP): Protocols for communicating across the Internet

TCP and IP

• TCP: underlying layer of the Internet ensuring delivery of information

• IP: Responsible for providing addresses for sending information

IP Packets

• Items that are transferred across the networks• IP Packet:

HeaderActual Data

• Source IP Address, • Destination IP Address, • Packet Number, • Number of packets that make up

that item

• Foundations of communicating across the Internet:– Protocol are a set of rules– TCP: delivering the information– IP: Providing the addresses– Information is broken into IP Packets

Questions?

So far…

Now to get your brains working that little bit more….

Post Office Analogy

• When you send a Letter in the Post what is the process…

Digital Post Office

• Write the Letter• Sign the Letter• Put it in an envelope• Write the Address of Destination on Envelope• Place a Stamp on the Envelope• Place Letter in Post Box• Local Post Man picks up letter amongst others from post

box• Letter goes through Sorting Office• New local Post Man delivers letter to destination

Activity 2

Together, organise the slips which represent the steps for packet switching into the correct order – think about the post office analogy to help you

Packet Switch Networks - 1

Moving a File from A to B

Packet SwitchingPoint A

Point B

Now Lets Give it a Go….

Packet SwitchingPoint A

Point B

Packet Switch Networks - 2

Routing around missing servers

Packet SwitchingPoint A

Point B

Packet Switch Networks - 3

Packet order

Packet SwitchingPoint A

Point B

HE LL O

Packet Switch Networks - 4

Time-To-Live (TTL)

Packet Time To Leave (TTL)

• Data packets have TTL number • TTL is number of server-to-server hops before

the packet is no longer forwarded (hop limit).• A server receiving a packet reduces TTL by 1

before passing it on.• A server receiving a packet with TTL discards it

and sends a re-send message to the originating server (i.e. send packet again)

Point A

Point B

HE LL O

10

9

8

7

6

9

9

5 4 3 2 1

8

7 6 5

4

3

8 7 6 5

4

3

2

1

Packet Switching

0Request new packet

9

8

7 6 5 4

3

10

IP Address

• A unique label assigned to each device in a computer network that uses the Internet Protocol.

• Does anyone know what is the most common form of IP Address and what is the newer IP Address?

IPv4

• Most common Internet Protocol• Limited number of IP addresses• IPv6 – newer version (to be discussed at a

later date)

IPv4

• 32-bits (4 bytes)

= 2^32 different values (this is binary which will cover at a later date)

Bits/Bytes

• If 32 bits = 4 bytes, so how many bits are there in 1 byte?

Fun Fact…

Half a Byte (4 bits) is called a Nibble!

IP Addresses

0 to 255 0 to 255 0 to 255 0 to 255

192 192 158 1581 chunk

1 byte1 chunk1 byte

1 chunk1 byte

1 chunk1 byte

IP Addresses

192 192 158 158Network Identifier Host Identifier

IP Addresses

Are these IP addresses on the same network?

1) 126.203.123.123 and 126.203.100.100

2) 126.203.123.123 and 123.123.126.203

3) 126.203.97.54 and 126.203.123.123

IP Addresses

Are these IP addresses on the same network?

1) 126.203.123.123 and 126.203.100.100 - YES

2) 126.203.123.123 and 123.123.126.203 - NO

3) 126.203.97.54 and 126.203.123.123 - YES

Summarise…

• Can you individually write 4 or 5 points that you have learnt and can take away with you today…

• Internet is the foundation• Web uses the Internet• Intranets are private networks• Communicating across the Internet:– Protocol are a set of rules– TCP: delivering the information– IP: Providing the addresses– Information is broken into IP Packets

• Methodology used for communicating IP Packets across the Internet is called Packet Switching

To Summarise…

To Summarise…

• IP Addresses are used to identify a device on a network

• IPv4 is most commonly used IP Address• IP Addresses are made up of 4 chunks, 32-bits– First 2 Chunks = Network Identifier– Second 2 Chunks = Host Identifier

*Key Terms Handout

Any Questions?