for AS/A Level Computer Science (for 2024 exam) The network topology is a physical layout of the network devices. The most common network topologies are: Bus topology: All devices are connected to a single cable. Star topology: All devices are connected to a central hub or switch. Mesh topology: All devices are connected to each other. The star topology is the most common network topology because it is simple and reliable. The central switch acts as a traffic controller, directing data packets between the devices on the network. The router is responsible for routing data packets between different networks. In this case, the router is routing data packets between the home network and the internet. Here is a more detailed description of the network topology diagram: Computer 1: This computer is connected to the switch using an Ethernet cable. Computer 2: This computer is connected to the switch using an Ethernet cable. Computer 3: This computer is connected to the switch using an Ethernet cable. Computer 4: This computer is connected to the switch using an Ethernet cable. Switch: The switch is a central hub that connects all of the devices on the network. Router: The router is responsible for routing data packets between different networks. The network topology diagram also shows the flow of data packets between the devices on the network. For example, if Computer 1 wants to send a data packet to Computer 2, the data packet will be sent to the switch. The switch will then forward the data packet to Computer 2. If Computer 1 wants to send a data packet to the internet, the data packet will be sent to the switch. The switch will then forward the data packet to the router. The router will then route the data packet to the internet. Network topology diagrams are useful for understanding how networks are designed and how data flows between the devices on a network. In a thin client and thick client network, the thin clients are connected to the central server using a network cable. The server hosts the operating system and applications that the thin clients use. When a user on a thin client wants to use an application, the thin client sends a request to the server. The server then sends the application to the thin client. The thin client then displays the application to the user. Thin client and thick client networks have a number of advantages: Reduced costs: Thin clients are less expensive to purchase and maintain than thick clients. This is because thin clients do not require their own processing power and storage. Improved security: Thin clients are more secure than thick clients because they do not store any data locally. All data is stored on the central server. This makes it more difficult for hackers to steal data. Increased scalability: Thin client and thick client networks are more scalable than traditional networks. This is because it is easier to add new thin clients to a network than it is to add new thick clients.

1. Computer Science
Prepared by: Merbert J. Jeruela, Brainworks-Total International School
Based on 2024-2025 9618 AS/A Level Computer Science Syllabus

2. Chapter 2: Communication
2.1: Networking
By the end of the lesson students will be able to:

3. Chapter 2: Networks Including the Internet
2.1: Networking
By the end of the lesson students will be able to:

4. Chapter 2: Networks Including the Internet
2.1: Networking
By the end of the lesson students will be able to:

5. Chapter 2: Networks Including the Internet
2.1: Networking
By the end of the lesson students will be able to:

6. For topics 2.1.1-2.1.7, please refer to the
presentation prepared by different group of
students. See Google Classroom.
This presentation covers 2.1.8, 2.2.1-2.2.6 only.
Note

7. 2.1.8: Bit Streaming Chapter 2: Networks Including the Internet
Bit Streaming
Is a contiguous sequence of digital bits sent over the internet or
a network that requires a high speed data communication link
(such as fast broadband).

8. 2.1.8: Bit Streaming Chapter 2: Networks Including the Internet
Bit Streaming
requires…
High speed data
communication link
Data compression Buffering
Buffer is a temporary storage area of a computer (usually in RAM).

9. 2.1.8: Bit Streaming Chapter 2: Networks Including the Internet
A good reference about bit streaming:
• https://learnlearn.uk/alevelcs/bit-streaming/#google_vignette

10. 2.1.8: Bit Streaming Chapter 2: Networks Including the Internet
Bit streaming can be either:
On demand Real time

11. 2.2.1: The difference between the internet and the World Wide Web Chapter 2.2: The Internet
World Wide Web The Internet
• Collection of multimedia web
pages and other documents
stored on websites which are
accessed by web browsers.
• https protocol is written using
html.
• URL specify the location of all
web pages.
• Uses the internet to access
information from servers and
computers.
• Massive network of networks (the
internet is not a WAN).
• Stands for Interconnected
Network.
• Use of Transmission Control
Protocol/Internet Protocol
(TCP/IP).

12. 2.2.2: Hardware and software needed to support the internet Chapter 2.2: The Internet
Requirements for connecting to the internet…
Device
Telephone line
connection
A router ISP Web browser

13. 2.2.2: Hardware and software needed to support the internet Chapter 2.2: The Internet
Public Switched Telephone Network (PSTN)
• Used to connect devices and LANs between towns and cities.
• Before, PSTN uses coppers wires, now, it uses fiber optic to allow for greater
bandwidth and faster data transfer.
• Fiber optic telephone networks identified as fast broadband which allowed
WLANs to be developed using WAPs.

14. 2.2.2: Hardware and software needed to support the internet Chapter 2.2: The Internet
Internet Calling
User’s voice is converted to digital packages using VOIP.
• Data is split into packages and sent over to the network via the fastest route.

15. 2.2.2: Hardware and software needed to support the internet Chapter 2.2: The Internet
PSTN vs Internet when making phone call
Classwork 1: Comparison of Internet from PSTN Calling
a. Complete the T Diagram (See page 55-56). [6]

16. 2.2.2: Hardware and software needed to support the internet Chapter 2.2: The Internet
Cellular networks and satellites
Homework 1:
a. Explain what is trilateration. [3]
b. Explain why satellites are needed (See page 56). [2]

17. 2.2.3: IP Addresses Chapter 2.2: The Internet
TCP/IP protocols
Protocols can be divided into TCP
layers.
Note: This will be covered in detail in
chapter 14.
So, we will consider internet protocol
for now.
Internet Protocols define
the rules that
must be agreed
by sender and
receiver on the
internet

18. 2.2.3: IP Addresses Chapter 2.2: The Internet
TCP/IP protocols determines how data should be
Internet
Broken down
Addressed
Transmitted
Routed
Received
TCP
TCP
TCP
IP
IP

19. 2.2.3: IP Addresses Chapter 2.2: The Internet
Internet Protocol (IP)
IPv4 addressing IPv6 addressing

20. 2.2.3: IP Addresses Chapter 2.2: The Internet
Internet Protocol (IP)
• All hosts within a single network share the same network address. Each host also has an address that
uniquely identifies it.
• Depending on the scope of the network and the type of device, the address is either globally or
locally unique.
• Devices that are visible to users outside the network (webservers, for example) must have a globally
unique IP address.
• Devices that are visible only within the network must have locally unique IP addresses.
• IP addresses are assigned by a central numbering authority called the Internet Assigned Numbers
Authority (IANA). IANA ensures that addresses are globally unique where needed and has a large
address space reserved for use by devices not visible outside their own networks.
• IANA a division of the Internet Corporation for Assigned Names and Numbers (ICANN).
Did you know?

21. 2.2.3: IP Addresses Chapter 2.2: The Internet
Internet Protocol (IP) IPv4 addressing
• Most common type
of addressing on the
internet
• Based on 32 bits
giving 232 (4, 294,
967, 296) possible
addresses.
How to check your windows
computer IP Address?
• Open the Start menu and type cmd to
open the Command Prompt.
• Type ipconfig into the Command
Prompt and press Enter.
• The tool will return a set of data that
includes your IP address.

22. 2.2.3: IP Addresses Chapter 2.2: The Internet
Internet Protocol (IP)
The IPv4 is divided into 4 groups of 8 bits:
Example IP: 254.0.128.77
1 2 3 4
IPv4
IPv4 uses the group of bits to define:
• network (netID)
• Network host (hostID)

23. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4
netID hostID
• Allows for initial transmission
to be routed according to the
netID.
• Is looked at by the receiving
network.
Example IP Address: 190.15.25.240

24. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Classes of Networks

25. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Classes of Networks

26. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Classes of Networks

27. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Classes of Networks
Find the class of the given IP Addresses

28. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 explained

29. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 explained
How would the host know which portion of 32-bit
(IPv4) is a network and which is a host?
It knows using the Subnet Mask

30. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 IPv4 address and subnet mask. Explained…
1. When IP host is configured, a subnet mask is assigned along with the IP address.

31. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 IPv4 address and subnet mask. Explained…
Can we change subnet mask? Yes
Why do we change a Subnet Mask?
• It is a recommended procedure for increasing a DHCP scope when the
current scope has entirely consumed the current subnet mask.
More info about subnet mask: https://www.youtube.com/watch?v=s_Ntt6eTn94

32. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 IPv4 address and subnet mask. Explained…
2. Like IPv4 address, subnet mask is also 32-bit long .
255.255.255.0
3. Subnet mask signifies which part of IPv4 address is network and host.
network host
11111111.11111111.11111111.00000000
to binary…

33. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 So, how subnet mask can tell?
Example:
IPv4 address: 192.168.123.132 Subnet mask: 255.255.255.0
IPv4: 11000000. 10101000. 01111011. 10000100
Subnet Mask: 11111111. 11111111. 11111111. 00000000
to binary…
Network Address: 11000000. 10101000. 01111011. 00000000
so,
Which is 192.168.123.0 in denary.
Host Address: 00000000. 00000000. 00000000. 10000100
Which is 000.000.000.132 in denary.

34. 2.2.3: IP Addresses Chapter 2.2: The Internet
What is CIDR?
Homework 2:
a. Define what CIDR is[1].
b. Why is it needed in IPv4 address using a Class C network? [2]
c. Explain how it is used. [2]

35. 2.2.3: IP Addresses Chapter 2.2: The Internet
Extension Activity: Network Address Translation (NAT) removes the needs
for each IP Addresses to be unique.
Find out more…
Recommended Video Reference:
https://www.youtube.com/watch?v=FTUV0t6JaDA
CW2:
Note: While watching, complete the note-taking template.

36. 2.2.3: IP Addresses Chapter 2.2: The Internet
Short presentation
In a team of 3-4, you are tasked to read, discuss and present your understanding of the
following topics without using PowerPoint presentation:
a. IPv6 (Team Alpha)
b. Zero Compression (Team Bravo)
c. Sub-netting (Team Charlie)
d. Private and Public IP addresses(Team Delta)

37. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4

38. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv6
More information about IP Addresses: https://community.fs.com/blog/ipv4-vs-ipv6-whats-the-difference.html

39. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network Classes and CIDR value

40. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
default subnet mask
255 . 255. 255. 0

41. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
Example:
New subnet mask

42. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting

43. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting

44. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting

45. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
Another Example:

46. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
Another Example:

47. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
How many network can be created?

48. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
How to find the number of IP Address on each network?

49. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
How to find the number of host in each network?

50. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting

51. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting

52. 2.2.3: IP Addresses Chapter 2.2: The Internet
IPv4 Network and Subnetting
Do it your own:

53. 2.2.4: URLs Chapter 2.2: The Internet
• Web browsers are software that allow users to access and display web pages on
their screens.
• They interpret HTML sent from websites and display the results.
• Web browsers use uniform resource locators (URL) to access websites; these are
represented by a set of four numbers, such as 109.108.158.1.
• But it is much easier to type this into a browser using the following format:
protocol://website address/path/filename
Uniform Resource Service (URLs)

54. 2.2.4: URLs Chapter 2.2: The Internet
• Protocol is usually http or https
• Website address is
» domain host (www)
» domain name (name of website)
» domain type (.com, .org, .net, .gov, and so on)
» (sometimes) a country code (.uk, .de, .cy, .br, and so on).
• Path is the web page (if this is omitted then it is the root directory of the website)
• Filename is the item from the web page
For example: https://www.hoddereducation.co.uk/computerscience/networking
protocol://website address/path/filename

55. 2.2.4: Domain Name Service Chapter 2.2: The Internet
• The domain name service (DNS) (also known as domain name system) gives
domain names for internet hosts and is a system for finding IP addresses of a
domain name.
• Domain names eliminate the need for a user to memorize IP addresses.
• The DNS process involves
• converting a host name (such as www.hoddereducation.co.uk) into an IP
address the computer can understand (such as 107.162.140.19).
• Often, DNS servers contain a database of URLs with the matching
IP addresses
Domain Name Service (DNS)

56. 2.2.4: Domain Name Service Chapter 2.2: The Internet
An example of a Domain Name Service (DNS) process

57. 2.2.4: Domain Name Service Chapter 2.2: The Internet
① The user opens their web browser and types in the URL
(www.hoddereducation.co.uk) and the web browser asks the DNS server (1) for the
IP address of the website.
② The DNS server can’t find www.hoddereducation.co.uk in its database or its
cache and sends out a request to DNS server (2).
③ DNS server (2) finds the URL and can map it to 107.162.140.19; the IP address is
sent back to DNS server (1) which now puts the IP address and associated URL into its
cache/database.
An example of a Domain Name Service (DNS) process

58. 2.2.4: Domain Name Service Chapter 2.2: The Internet
④ This IP address is then sent back to the user’s computer.
⑤ The computer now sets up a communication with the website server
and the required pages are downloaded. The web browser interprets the
HTML and displays the information on the user’s screen.
An example of a Domain Name Service (DNS) process

59. 2.2.4: Domain Name Service Chapter 2.2: The Internet
End of Chapter Revision (CW4-Peer Revision)

60. 2.2.4: Domain Name Service Chapter 2.2: The Internet
End of Chapter Revision (CW4-Peer Revision)

61. 2.2.4: Domain Name Service Chapter 2.2: The Internet
End of Chapter Revision (CW4-Peer Revision)

62. Chapter 2 Revision Chapter 2.2: The Internet
By the end of the lesson, students will be able to:
• Explain in three parameters, why in terms of data transfer rate, fiber
optic cable transmits data faster than wi-fi.
• Describe what is FHSS and explain how it works.
• List 3 advantages and 2 disadvantage of using FHSS (HW5).
Objectives

63. Chapter 2 Revision Chapter 2.2: The Internet
In terms of data transfer rate, why fiber optic cable is still faster than Wi-
Fi although light waves and electromagnetic waves travel at the same
speed (speed of light)?
Explain in three parameters:
• Medium and Signal Interference
• Bandwidth
• Dedicated Connections
Activity 1: Tell me what you know!

64. Chapter 2 Revision Chapter 2.2: The Internet
You presentation as a team, will be assessed based on the
following criteria:
1. Accuracy of information presented [10].
1-2 (poor), 3-4 (weak) ,5-6 (good), 7-8 (very good) ,10 (excellent)
2. Manner of the Delivery [3].
1 (poor), 2 (good), 3 (excellent)
3. Evidence of Collaboration [3].
1 (poor), 2 (good), 3 (excellent)
Activity 1: Tell me what you know!

65. 2.2.4: Domain Name Service Chapter 2.2: The Internet
Parked Question
In terms of data transfer rate, why fiber optic cable is still faster than Wi-Fi although
light waves and electromagnetic waves travel at the same speed (speed of light)?
1. Medium and Signal Interference:
• Fiber optic cables use glass or plastic fibers to transmit data using light signals. These
fibers are highly efficient at transmitting light over long distances without significant
signal loss or interference.
• In contrast, Wi-Fi uses radio waves, which can be susceptible to interference from
various sources such as walls, electronic devices, and other wireless networks.
Interference can degrade the signal quality and reduce data transfer rates in Wi-Fi.

66. 2.2.4: Domain Name Service Chapter 2.2: The Internet
Parked Question
In terms of data transfer rate, why fiber optic cable is still faster than Wi-Fi although
light waves and electromagnetic waves travel at the same speed (speed of light)?
2. Bandwidth:
• Fiber optic cables offer significantly higher bandwidth compared to Wi-Fi. This
means they can transmit a much larger volume of data simultaneously. Fiber optics
can support multiple channels of data transmission, allowing for faster data rates.
• Wi-Fi networks, on the other hand, share the available bandwidth among multiple
devices connected to the same access point. As more devices connect to a Wi-Fi
network, the available bandwidth per device decreases, potentially leading to slower
data transfer rates, especially in crowded environments.

67. 2.2.4: Domain Name Service Chapter 2.2: The Internet
Parked Question
In terms of data transfer rate, why fiber optic cable is still faster than Wi-Fi although
light waves and electromagnetic waves travel at the same speed (speed of light)?
3. Dedicated Connections:
• Fiber optic cables often provide dedicated point-to-point connections, ensuring
that the full bandwidth of the cable is available for the connected devices.
• In Wi-Fi, multiple devices share the same radio spectrum, leading to contention and
potential slowdowns when multiple devices are actively using the network.

68. Extended Topic Chapter 2.2: The Internet
A quick look at Electromagnetic Wave and Frequencies

69. Extended Topic Chapter 2.2: The Internet
A quick look at Electromagnetic Wave and Frequencies

70. Extended Topic Chapter 2.2: The Internet
A quick look at Electromagnetic Wave and Frequencies
The two big differences between these upending internet technologies, 2.4 GHz
and 5 GHz Wi-fi connections are - speed and range.
A wireless transmission at 2.4 GHz provides internet to a larger area but
sacrifices the fast internet speed, while 5 GHz provides faster speeds but
restricts itself to a smaller area.
2.4 GHz vs 5 GHz as Wi-fi Frequencies

71. Extended Topic Chapter 2.2: The Internet
When you listen to
your favorite radio
station or watch TV
show.
Frequency Hopping Spread Spectrum (FHSS as used in Bluetooth)
You tune in
into a fixed
channel.
Which is a traditional
narrow-band radio
and TV
communications.
This fixed
frequency has 3
problems.
Interference
(unintentional
forms of
disruption
during wireless
communication)
Jamming
(deliberate
forms of
disruption or
blocking)
Interception
(monitoring and
listening to
communication
without the
knowledge of the
person making the
communication)

72. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
Fixed
frequency
problems
interference jamming
In wireless
communication,
Slows down
transmission
interception
A security
problem

73. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
Suppose, we use a 2.4
GHz band to send and
receive data.
Check here for usage of this band: https://www.screenbeam.com/wifihelp/wifi-networking/2-4ghz-vs-5ghz-wifi/
As you observed, it
can get easily
intercepted/hacked
as data travel though
one channel only.
To address this issue, signal modulation methods are needed, hence the FHSS.

74. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
What is FHSS?
Uses spread spectrum technology by which a signal generated with a particular
bandwidth is deliberately spread within the frequency band.
To reduce
Interference
Jamming
Interception

75. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
How does FHSS work?
1. Divide the (2.4GHz)
frequency band into
79 narrow frequency
channels.
• Each channel is 1
MHz wide.
We will use 6 narrow channels to demonstrate how FHSS works.

76. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
How does FHSS work?
2. Divide the data travel
time into smaller time
units or segments.
We label them with T1, T2, T3,...
Each tiny segment is called hop time.

77. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
How does FHSS work?
3. Let’s assume a data
packet is moving from a
sender to a receiver.
• During a certain time
period, data packet
will not travel
through one fix
channel. Instead, it
will hop up and
down to multiple
different channels. We label them with T1, T2, T3,...
Each tiny segment is called hop time.

78. Extended Topic Chapter 2.2: The Internet
Frequency Hopping Spread Spectrum (FHSS)
How does FHSS work?
3. Let’s assume a data
packet is moving from a
sender to a receiver.
• During a certain time
period, data packet
will not travel
through one fix
channel. Instead, it
will hop up and
down to multiple
different channels. We label them with T1, T2, T3,...
Each tiny segment is called hop time.

79. Extended Topic Chapter 2.2: The Internet
Wrap-up Activity
3-2-1
List 3 things you did not know before.
List 2 things you know now.
List 1 thing you want to learn more.

80. Extended Topic Chapter 2.2: The Internet
Homework 5
Extension Activity
1. Discuss 2 advantages and 2 disadvantages of
FHSS. [4]
2. Explain how Direct Sequence Spread Spectrum
is used in wireless transmission using Wi-fi. [5]
link: https://www.youtube.com/watch?v=-1mxYWvfVWQ