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?
How would you feel if you
couldn’t do any of this?
How would you cope?
The Internet, the Web and the Intranet
Internet
Web
How do these intercept?
What are their functions?
Intranet
The Internet houses the Web
but why does the intranet
overlap both?
Activity 1
Now we are going to fill in the gaps …
• This is a global system of networks which are
connected together using a particular protocol
called the
. This is a procedure which
controls how computers send information to
each other. One important feature of this system
is its
structure. Because there is no
central point on which communications depend,
the system can continue to
well even
when some
break down.
• This application, which was created in 1989, sits on top of
the
. It contains information resources in many
forms (documents written in
, images, music, video,
etc.) which can be
together. Users can access
information via a
(which helps them find
information, entertainment or services), or navigate
between documents by clicking on
.
• Each information resource has a unique
and these
resources can be transferred using another protocol called
.
• Many companies want to take advantage of the
capabilities of computers, but also need to
keep their information
and secure. For this
reason they often use a internal network to help them
, share information, provide computing
services, or create internal websites. Employees of
organisations can access the information in these
systems, but
access is controlled or blocked.
The Resilience of the Internet
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:
Header
•
•
•
•
Source IP Address,
Destination IP Address,
Packet Number,
Number of packets that make up
that item
Actual Data
So far…
• 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?
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 Switching
Point A
Point B
Now Lets Give it a Go….
Packet Switching
Point A
Point B
Packet Switch Networks - 2
Routing around missing servers
Packet Switching
Point A
Point B
Packet Switch Networks - 3
Packet order
HE
LL
O
Packet Switching
Point A
Point B
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)
Packet Switching
HE LL
O
Point A
10
9
8
9
9
8
8
8
7
6
5
4
7
6
5
4
7
6
5
7
6
5
2
Request new packet
1
0
3 31
3
3
4
2
Point B
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
192
192
158
1 chunk
1 byte
1 chunk
1 byte
1 chunk
1 byte
0 to 255
158
1 chunk
1 byte
IP Addresses
192
192
Network Identifier
158
158
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…
To Summarise…
•
•
•
•
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…
• 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?