1.5 NETWORK TOPOLOGIES,
PROTOCOLS AND LAYERS 1
© OCR 2016
Thought for the day – IP Typo
© OCR 2016
The Big Picture:
Network topologies, protocols and layers
 Star and mesh network topologies
 Networks using wifi and ethernet
 Wi-fi : frequency and channels
 Encryption
 The uses of IP addressing, MAC addressing, and
commonly used protocols
• The concept of layers
• Packet switching
© OCR 2016
Learning Objectives
By the end of today’s lesson, you will understand:
• Compare Wi-Fi and Ethernet
• Understand and explain what encryption is and
why it is required
• Understand the main internet protocols and what
they do
© OCR 2016
Starter: Recap
1. What is an IP address?
2. Are you likely to have a dynamic or static IP
address on your tablet when connected to your
PAN at home?
3. How does an IP address differ from a MAC
address?
4. What is the difference between IPv4 and IPv6?
5. Give an example of an IPv4 IP address.
6. What does a router do? (in networking)
© OCR 2016
IP Address
192.168.1.23
• Data travelling on a Network are sent as packets
• Each device on the internet has a unique IP address
which is sent with the packets to identify which computer
to send the data to.
• The address is broken down into four numbers which can
represent a number between 0 and 255 separated by a
full stop.
• Routers route the data packets from one router to the
next
© OCR 2016
MAC address
• The MAC address is embedded into the device
when it is manufactured and the owner cannot
change it.
• A MAC address is a unique code which is built into
the Network Interface Card (NIC)
• Each address is individual and is made up of 48
bits, usually written in hexadecimal. (why?)
AA-34-G4-44-23-F1
© OCR 2016
Starter: Acronyms (more later!)
© OCR 2016
Wired vs Wireless
• You will be given a
selection of cards that
show the advantages
and disadvantage's of
Wired and Wireless
networks (Ethernet
and WiFi)
• Sort them into groups
• Compare you answers
with other students.
© OCR 2016
Answers
© OCR 2016
WiFi vs Wired
• Compare wi-fi and wired connections. Consider:
bandwidth, installation, cost, security,
interference, mobility of devices once
connected.
Eg: WiFi uses radio waves to transmit data packets
without the need for wires.
© OCR 2016
Cables (wired)
There are two main types of cable which can transport data between computers.
Ethernet Cables
These are made up of copper wires with the data being transported via electrical
signals. Because they carry electrical signals, they can suffer from interference.
Fibre Optic Cables
These are made up of glass fibres with the data being transported via light signals.
Fibre optic cables are more effective…nothing travels faster than the speed of light!
They also do not suffer from interference.
They are however more expensive that Ethernet cables.
© OCR 2016
Wi-Fi (wireless)
Wi-Fi allows network access to portable devices by using radio waves to send data
(not wires!).
Wi-Fi is a ‘standard’. This means that all Wi-Fi devices using the same standard
technology.
In particular they send and receive data using standard radio frequency bands:
2.4 GHz Band (frequencies between 2.4GHz & 2.5GHz)
5 GHz Band (frequencies between 5.725GHz & 5.875GHz)
0GHz
1GHz
2GHz
3GHz
4GHz
5GHz
6GHz
Furthermore, each band is split into channels that cover smaller frequency ranges,
within the band.
CH1
Ch2
Ch3
Ch4
Ch5
Ch6
Ch7
2.40GHz
2.41GHz
2.42GHz
2.43GHz
2.44GHz
2.45GHz
2.46GHz
© OCR 2016
Wi-Fi (wireless)
This is so that if two devices are sending signals using the same band
(e.g. 2.4GHz)…
0GHz
1GHz
2GHz
3GHz
4GHz
5GHz
6GHz
…they can each use different channels and therefore slightly different
frequencies (e.g. 2.41GHz and 2.45GHz)…
…so that they do not suffer from interference with one another.
CH1
Ch2
Ch3
Ch4
Ch5
Ch6
Ch7
2.40GHz
2.41GHz
2.42GHz
2.43GHz
2.44GHz
2.45GHz
2.46GHz
© OCR 2016
Craig and Dave
• https://youtu.be/Svm06j2_x5w?list=PLCiOXwirraUA
vkTPDWeeSqAKty3LAG37-
© OCR 2016
Encryption
• Encryption is used to protect data in case it has been
hacked or access illegally.
• On an open or public WiFi network anyone can join and
sniff out packets of data from other users.
• Therefore encryption is used. If intercepted the data will
have no meaning (although this doesn’t stop the actual
hacking it just means the data is unreadable)
• In order to read the data the user is required to decrypt
the data using the key.
© OCR 2016
Secure shopping
• When you are using a secure site for example
your bank, or purchasing on Amazon, encryption
is applied to keep your details safe
• The encryption method used is called 'SSL'
(Secure Socket Layer).
• A tiny padlock appears in your browser window,
usually on the left hand side of the address bar
and the website address starts with HTTPS://
© OCR 2016
Secure communications egTwitter
• Twitter users a HTTPS when you log in, why?
• What’s app encrypts messages.
• Why does the data need to be encrypted?
• What could happen if it was not encrypted?
• But – what about if the police or security services need
access to someone’s messages…..and they are
encrypted….and can’t be accessed……
http://www.bbc.co.uk/news/uk-39396578
© OCR 2016
Encryption videos
• https://www.youtube.com/watch?v=w0Qbn
xKRD0w
• https://youtu.be/TImdsUglGv4
© OCR 2016
Key terms
Plaintext – the orginal
message to be encrypted
Ciphertext – the encrypted
message
Encryption – the process of
converting plaintext into
cipher text
Key – a sequence of numbers
used to encrypt or decrypt
often using a mathematical
formual
Encryption algortiim – the
mehod for encrypting the
plain text
© OCR 2016
Encryption task
http://www.cryptoclub.org/
© OCR 2016
Protocols
• Network protocols are a set of rules or conventions which
control the communication between devices on a network.
• If one computer transmits a stream of binary to another,
the receiving computer needs to know what the rules are.
• Protocols are rules and standards that define how devices
communicate and make it possible for the to ‘talk’ to each
other,
• Without these international standards,
devices from different manufacturers
wouldn’t be able to interact with each other
across networks.
© OCR 2016
Key Protocols
• TCP/IP (Transmission Control Protocol/Internet
Protocol)
• HTTP (Hyper Text Transfer Protocol)
• HTTPS (Hyper Text Transfer Protocol Secure)
• FTP (File Transfer Protocol)
• POP (Post Office Protocol)
• IMAP (Internet Message Access Protocol)
• SMTP (Simple Mail Transfer Protocol)
© OCR 2016
Key Protocols - Files
• TCP/IP (Transmission Control Protocol/Internet Protocol) –
error free transmission of packets between 2 IP address on
a WAN
• HTTP (Hyper Text Transfer Protocol) – client server method
of requesting HTML filems
• HTTPS (Hyper Text Tranffer Protocol Secure) – encryption
and authtication of clier-server deata from web pages eg
transfer a username and password from a web pagetext
entry box to web server to log in
• FTP (File Transfer Protocol) – sending files between
compuers Typical use would be for uploading web pages
and associated firles to the server for hosting
© OCR 2016
Key Protocols - Mail
• SMTP – simple mail transfer protocol – sends mail
to a mail server
• POP (Post Office Protocol) – used by email clients
to get email from a mail server
• IMAP (Internet Message Access Protocol) – used
by email clients to get mail from a mail server and
to manage remote mail boxes. More advancee than
pop
• SMTP (Simple Mail Transfer Protocol)
© OCR 2016
Show your understanding
• Complete the worksheet on today’s topics
• Log into Moodle
• ICT & Computing > GCSE Computer Science >
Computer Systems
• Scroll down to 1.5
• 5. 1 Folder
• Download, save and complete Wifi, encryption
and protocols.docx
© OCR 2016
Explanation Videos
•
•
•
•
•
An Overview:
https://www.youtube.com/watch?v=WmymBI-X7Tc
IP
https://www.youtube.com/watch?v=zyL1Fud1Z1c
IMAP vs POP3:
https://www.youtube.com/watch?v=BK4ng6Gcits
© OCR 2016
Plenary
Stretch yourself!
• Investigate the Caesar shift cipgher
• Devise a simple encryption program eg
shift left 3
• Code an encryption program using a
programming language of your choice.
© OCR 2016