1. GCSE COMPUTER SCIENCE
Communication
3.1 Networks

2. What is a Network?
A network is two or more hardware devices that are connected together.
Devices can include personal computers, tablets, smartphones and peripherals such as printers and scanners.
ACTIVITY
Write this definition in your exercise book.

3. What activities do networks make possible?
Advantages of Networks
What activities do networks make possible?
Below are some common advantages of networks
Share printers and other devices
Allow users to hot-desk
Automated central-backup
Use site-software licenses
Allows for easier communication
Security can be controlled centrally
..and many more.

4. Disadvantages of Networks
Below are some common disadvantages of networks
Purchasing the cables, server and other infrastructure can be expensive.
Managing a large network is complex, need extra staff such as a network administrator.
If the server breaks, it could take out the whole network.
Malware can spread easily on a network.

5. Advantages and Disadvantages
Activity 1
Advantages and Disadvantages
Create an information sheet outlining the pros and cons of a network.
Networks
Advantages
Disadvantages
Use Word or Powerpoint.
Format it like the diagram on this slide.
Use an image to represent each point you are making.
A4 Landscape
HELP
Use BBC Bitesize and Teach-ICT.

6. LANs and WANs Watch this video to find out more about LANs and WANs.
Link:

7. Activity 2a
Fill in the blanks
A network is a collection of interconnected __________. The network allows users to __________ resources. In a __________ network there is no server but in a client-server network all the __________ can be saved on the server and so can be easily __________. Also __________ and access-rights can be handled centrally. A LAN is a __________ Area Network whereas a network spanning the world such as the __________ is called a __________.
Words to use: WAN, peer-to-peer, security, backed up, devices, Local, Internet, files, share.

8. Activity 2b
Computer Networks are categorised according to their geographic coverage.
Type of Network
Description
Example
Wide Area Network (WAN)
Connect computers over a large area such as a town, city or country.
Company creating a private WAN to connect different parts of their business securely.
Local Area Network (LAN)
Connect computers over a building or a site.
School network.
Personal Area Network (PAN)
Connect the computers or devices used by one person.
Bluetooth headset connected to a mobile phone.
Virtual Private Network (VPN)
User encryption and special ‘tunnelling’ network protocols to enable them to connect securely over the internet.
Company using a VPN to connect different parts of their business without having to build their own network infrastructure.

9. Typical Question and Model Answer
Activity 3
Typical Question and Model Answer
Question
Answer
A railway company has 30 railway stations. Each station has a LAN that connects the ticket machines, barriers and information points.
Each station is connected to the railway company head office where the main servers are located.
Evaluate the use of a private WAN and a VPN for this purpose and recommend which would be most suitable for the railway company.
A private WAN would allow the company to keep their data and information more secure. However, a WAN would be the most expensive option because they would have to buy all the hardware associated with a WAN for each station.
A VPN would allow the company to connect each of their stations using the internet, this saves lots of money compared to a WAN. However, the Internet is much less secure than a private WAN so would be more susceptible to a security breach.

10. Network Media
There are three main types of network media that are used to connect computers together in a network.
Copper Cable
Fibre Optic Cable
Wireless

11. Transmission Speed (Fastest, Medium, Slowest)
Activity 4
Copy and complete this table.
Type of Media
Range in m
Transmission Speed (Fastest, Medium, Slowest)
Security
(Good, Medium, Poor)
Copper Cable
50-100
Medium
Fibre Optic Cable
600 – 2000
Fastest
Good
Wireless
Less than 30
Slowest
Poor

12. Time = size of file in bits / network speed in bits
Transmission Speed
Data transmissions speeds are measured in bits per second (bps).
Data storage is measured in bytes (1 byte = 8 bits)
We use this formula to calculate how long it will take to transfer a file.
Time = size of file in bits / network speed in bits
ACTIVITY
Write this formula in your exercise book.

13. Activity 5 Scenario Calculation File size: 2 KB Speed: 5 Mbps
File size in bits: 2 * 1024 * 8 = 16,384
Speed in bits: 5 * 1024 * 1024 = 5,242,880
Transmission Time: 16,384 / 5,242,880 = seconds
File size: 3 KB
Speed: 1 Mbps
File size in bits: 3 * 1024 * 8 = 24,576
Speed in bits: 1 * 1024 * 1024 = 1,048,576
Transmission Time: 24,576 / 1,048,576 = seconds
File size: 10 MB
Speed: 2 Mbps
File size in bits: 10 * 1024* 1024 * 8 = 83,886,080
Speed in bits: 2 * 1024* 1024 = 2,097,152
Transmission Time: 83,886,080 / 2,097,152 = 40 seconds
File size: 1 KB
Speed: 4 Mbps
File size in bits: 1 * 1024 * 8 = 8,192
Speed in bits: 4 * 1024 * 1024 = 4,194,304
Transmission Time: 8,192 / 4,794,304= seconds
File size: 20 MB
Speed: 150 Mbps
File size in bits: 20 * 1024 * 1024 * 8 = 167,772,106
Speed in bits: 150 * 1024 * 1024 = 157,283,400
Transmission Time: 167,772,106 / 157,283,400 = seconds

14. Typical Question and Model Answer
Activity 6
Typical Question and Model Answer
Question
Answer
At the end of each week, a photographer transfers the photographs from his camera’s memory card to his computer’s hard drive.
Explain how to calculate the time it will take to transfer 2000 photographs that are 5 MB each.
Step 1 Storage of each photograph: Each photograph size is 5 * 1024 * 1024 * 8 measured in bits.
Step 2 Total storage of all photographs: You would then need to multiply this by 2000 because that’s how many photographs there are.
Step 3 Speed of transfer: The transfer speed would depend on the speed on the photographers camera storage medium, such as an SD Card.
Step 4 Final calculation: You would then take the total size of the photographs (in bits) and divide by the transfer rate (in bits) to give a time (in seconds).

15. This program is six lines.
Activity 7
Develop a Python program that takes a file size in KB and a network speed in Mbps and output the time it would take to transfer a file.
This program is six lines.
User inputs the file size (in KB)
User inputs the network speed (in Mbps)
Calculation to convert file size to bits
Calculation to convert network speed to bits
Division calculation to work out the time
Output the result using print.
TASK HELP
Extension: Find a way of the program allowing other units of input such as Bytes (B), Megabytes (MB), Kilobits per second (Kbps) and Gigabits per second (Gbps). Hint: If, Elif and Else statements could be used.

16. Network Addressing
Watch this video to find out more about network addressing.
Link:

17. Activity 8
Fill in the blanks
Every computer on a network has an __________ address which is assigned when a user logs in. It also has a MAC address which is given to the network __________ when it is made. When data is transmitted, it is broken down into __________. Each one contains part of the data, the sender and recipient __________ and its position in the complete message. It also contains a __________ so the recipient can check that the message has arrived intact. On its journey it passes through a series of __________ which decides the route it should take, taking into account the current network __________. To communicate the computers must follow a set of rules or __________.
Words to use: packets, routers, checksum, IP, protocols, traffic, address, adaptor.

18. Packets
Packets are made up of:
Header
Contains instructions about the data being carried. These instructions may include: the length of the packet; packet number; protocol address; originating IP address.
Body
This is the actual data that the packet is delivering to the destination.
Footer
Contains a parity bit and couple of bits that tell the receiving device that the end of the packet has been reached.

19. TCP/IP
An internationally agreed protocol. It starts by establishing a ‘handshake’ to set up a connection between two devices. The data is then transferred as packets between the two devices. It specifies exactly how data must be transmitted.
Stands for: Transmission Control Protocol / Internet Protocol
ACTIVITY
Write this definition in your exercise book.

20. MAC Addresses
Like a house, every device on a network needs a unique address to ensure that data reaches the correct destination.
A MAC address is a unique number written into the network card (or adapter), composed of six pairs of hexadecimal characters.
00:10:5A:44:12:B5
An example of a MAC address.
ACTIVITY
Write this definition in your exercise book.

21. Write this definition in your exercise book.
Host Names
A host name is a human-readable label that is assigned to a network device.
ACTIVITY
Write this definition in your exercise book.

22. USE THIS CODE TO HELP YOU
Activity 9
Develop a Python program that asks the user ten questions about this topic and outputs a final score.
score = 0 #set the starting score to zero
#repeat the code below for each question
print(“Question 1!”)
answer = input(“Write question here”)
if answer == “Write answer here”: #no capital letters
print(“Correct!”)
score = score + 1
else:
print(“Wrong!”)
#after the final question output the total score
print(Your total score is “ + str(score) + “.”)
USE THIS CODE TO HELP YOU
EXAMPLE QUESTION
Q: What does IP stand for? A: Internet Protocol

23. Activity 10
Crossword
Create a crossword based on this topic using the online crossword generator linked below. It should have a minimum of 10 questions.
When you have finished, paste your crossword on to a Powerpoint slide and name it 3.1 Networks
Print out one copy (include your name) and stick it in your book.
puzzle maker criss-cross