1 1.5 Network topologies, protocols and layers 1
2 Thought for the day – IP TypoIn May 2011, officers at South Yorkshire Police were informed by colleagues in Hertfordshire that they had identified an IP address from which more than 100 indecent images of children had been shared in April that year. The IP address passed on corresponded to an internet account held by Nigel's partner. But it had been typed incorrectly, with an extra digit added by mistake. When Nigel was arrested, all he could do was to repeatedly assure himself the police would discover the truth. "You say to yourself, 'Well they're going to find nothing and I haven't done anything, so I'll be alright.’ After three weeks, police returned Nigel's computers to him, and he had been found completely innocent. But the events had caused a deep psychological effect. "Because of what happened I felt unable to go back into the field of work I was working in," he says. His role as a drug recovery worker had involved helping teenagers. "It was the best job I'd had in my life, and I felt I was really good at it. "But I became fearful of working with young females in case any of them said I tried any sexual advances. It made me paranoid." 'Shouting my innocence' Eleven months after his arrest, and still without knowledge of why his home had been raided, Nigel began the search for answers - filing a complaint against South Yorkshire Police on grounds of racism and sexism Nigel decided to ask his solicitor to look deeper. The lawyer contacted Hertfordshire Police and discovered the truth of the incorrect IP address. Nigel received an apology, in writing, from Hertfordshire Police in 2014, which accepted responsibility for the error. 'Six years of fighting' Following Hertfordshire Police's admission, Nigel sought compensation for a breach of the Data Protection Act 1998, false imprisonment, police assault/battery, and trespass by police. In October 2016, Hertfordshire Police settled out of court. Nigel received damages of £60,000, plus legal costs.
3 The Big Picture: Network topologies, protocols and layersStar 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
4 Learning Objectives Compare Wi-Fi and EthernetBy 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
5 Starter: Recap What is an IP address?Are you likely to have a dynamic or static IP address on your tablet when connected to your PAN at home? How does an IP address differ from a MAC address? What is the difference between IPv4 and IPv6? Give an example of an IPv4 IP address. What does a router do? (in networking)
6 IP Address 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
7 IP Classes IP addresses also have different classes which identify the class of Network that the user is on. This indicates the number of total possible users and the purpose of the network
8 MAC address MAC addresses, or Media Access Control Addresses, uniquely identify a device on a network by identifying the network adapter that the device is using. This enables you to distinguish between different devices. Try this! On a windows computer you can locate your MAC address: Go to the start menu Type cmd Type ipconfig/ all The MAC address is listed as ‘Physical Address’
9 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-G F1
10 Starter: Acronyms (more later!)IP ISP DNS MAC URL WWW HTML
11 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.
12 Answers
13 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.
14 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.
15 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) Furthermore, each band is split into channels that cover smaller frequency ranges, within the band. 0GHz 1GHz 2GHz 3GHz 4GHz 5GHz 6GHz CH1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7 2.40GHz 2.41GHz 2.42GHz 2.43GHz 2.44GHz 2.45GHz 2.46GHz
16 Wi-Fi (wireless) This is so that if two devices are sending signals using the same band (e.g. 2.4GHz)… …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. 0GHz 1GHz 2GHz 3GHz 4GHz 5GHz 6GHz CH1 Ch2 Ch3 Ch4 Ch5 Ch6 Ch7 2.40GHz 2.41GHz 2.42GHz 2.43GHz 2.44GHz 2.45GHz 2.46GHz
17 Craig and Dave https://youtu.be/Svm06j2_x5w?list=PLCiOXwirraUAvkTPDWeeSqAKty3LAG37-
18 WiFi Frequency and Channelshttps://www.youtube.com/watch?v=3YHovkP1JC8
19 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.
20 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://
21 Secure communications egTwitterTwitter 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……
22 Encryption videos https://www.youtube.com/watch?v=w0QbnxKRD0whttps://youtu.be/TImdsUglGv4
23 Key terms Plaintext – the orginal message to be encryptedCiphertext – 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
24 Encryption task
25 Encryption task
26 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.
27 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)
28 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
29 Key Protocols - Mail SMTP – simple mail transfer protocol – sends mail to a mail server POP (Post Office Protocol) – used by clients to get from a mail server IMAP (Internet Message Access Protocol) – used by clients to get mail from a mail server and to manage remote mail boxes. More advancee than pop SMTP (Simple Mail Transfer Protocol)
30 Show your understandingComplete 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
31 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
32 Plenary Stretch yourself! Investigate the Caesar shift cipgherDevise a simple encryption program eg shift left 3 Code an encryption program using a programming language of your choice.