1. © OCR 2016 1.5 NETWORK TOPOLOGIES, PROTOCOLS AND LAYERS 2

2. © OCR 2016 Thought for the day – Networks transfer and receive a lot of data!! The amount of traffic on the internet is incredible! Click on the link in the resources sidebar to see for yourself

3. © 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

4. © OCR 2016 Learning Objectives By the end of today’s lesson, you will understand: Know what layers are and their role Be able to explain the role of each layer Understand the concept of Packet Switching

5. © OCR 2016 Starter: Do you know your Protocols? TCP/IP HTTP HTTPS FTP POP IMAP SMTP

6. © OCR 2016 Do you know your Protocols? - Answers 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)

7. © OCR 2016 Quick recap: How DNS works 123.45.67.89 174.25.46.77 322. 55.24.12 www.bbc.co.uk 1. 2. 3. 1. You can’t remember the IP address of the computer which hosts the BBC website, so you type in the URL into the browser. 2. The URL is sent to your ISP and they look up the URL in their DNS ‘address book’. They find it and send back to you the website’s URL address or passes it on to another DNS server to see if that can find it. 3. Now you can communicate with the computer which hosts the website on the internet, directly.

8. © OCR 2016 Packet Switching Imagine that you have a large LEGO model to post through a letter box but, it does not fit. What could you do? What if you could take the model apart and then post it through the letter box and then reassemble it? This is packet switching

9. © OCR 2016 Packet Switching Now image you want to email a photo, first it is broken down into small packets of data Each packet is then given a header which contains the IP address of the network and device that it is being sent to. It also contains the IP address of the network that it was sent from

10. © OCR 2016 Packet Switching The header also contains the packet number as well as the total number of packets, for example packet 4 of 60, packet 45 of 60. When the packets arrive at the destination this information is used to reassemble the data. Packets can be lost so sometimes the computer request the packet to be sent again, if a packet never arrives then it is deleted by the router.

11. © OCR 2016 Data Packets When files are sent over the internet they are split into millions of data packets. –Packets get sent by different routes according to availability. –When you send a file online, the parts of the file might travel one way around the world and the other parts may go in the opposite direction! –Packets are reassembled at receiving end. Typical packet structure: Data Packet Header Destination Address Return AddressSequence No. Error Check

12. © OCR 2016 Data Packets Data Packet Header Destination Address Return AddressSequence No. Error Check This this the data itself. The Header contains 3 pieces of information: Sequence Number Return Address Destination Address. As data is split into packets, the sequence number allows the file to be rebuilt by putting the packets back together in the correct order. When data arrives, the computer which sent the data can be notified that it arrived safely. And if a packet arrives corrupted, the computer which sent the data can be asked to send it again. Obviously a data packet needs a destination address so that it can be routed to the correct location. An error check is an important aspect of a data packet. This aspect of the packet is a ‘checksum number’. A checksum made up of a calculation and its correct answer. Once the packet has been received by the destination computer, If the calculation is run and still produces the correct answer, then we know the data hasn’t been corrupted on its journey.

13. © OCR 2016 The amazing way that data is sent across the internet!

14. © OCR 2016 Packets Header Contains instructions about the data being carried. These instructions may include: the length of the packet; packet number; position of this packet; protocol address; originating IP address. Body This is the actual data that the packet is delivering to the destination. Also called the payload Footer Contains a parity bit/checksum to error check and ensure that the complete packet has been delivered intact, and couple of bits that tell the receiving device that the end of the packet has been reached.

15. © OCR 2016 Which protocol …? 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.

16. © OCR 2016 Understanding a Packet Research one of the parts of the packets that you do not know. Explain it to another students.

17. © OCR 2016 Layers When we write an email and send it, we have no idea what device it will be read on, what operating system, which software etc. It is an extremely complex process that is easier to deal with if broken down into layers of smaller more manageable parts. As a packet is prepared the data travels through layers where protocols manage it, adding or removing extra information as required so the packet can continue its journey. The layers must be able to work together exchanging information. Each layer performs specific tasks and interacts with adjacent layers – this is essential – that the layers can communicate with each other. Layering: rules organised into a distinct order in which they need to be applied

18. © OCR 2016 Why have layers? The benefits are: Simplifies things by dividing into parts Different layers can be combined in different ways as required One layer can be develop or changed without affecting others Makes it easier t identify networking errors and problems Is a universal standard for manufacturers to follow so all devices can communicate with each other For example, software for an Ethernet system can easily be adapted to a fibre-optic network by changing only the network layer – other layers are not affected

19. © OCR 2016 Layers and Protocols TCP/IP is an example of a layered protocol – it defines how data is transferred through a network for example over the internet or over a private network. The TCP/IP stack is a complete set of protocols covering the movement of data across the network. These include how the data should be formatted, addressed, routed and received. You need to know the protocols to be able to link them to the layers

20. © OCR 2016 Also called Network Layer TCP/Ip is set of protocols arranged in 4 layers, the names sometimes vary a little. Data to be transmitted or received must pass through the layers where packaging data is added or read. Also called Network Access Layer or Data Link Layer

21. © OCR 2016 Layers Stop here And watch the two videos below Before continuing

22. © OCR 2016 Internet Protocols and Layers All of the protocols which enable the internet to function correctly can be divided into ‘Layers of the Internet’. Each layer has a particular function and each layer provides a base for the layer above it – in other words, each layer does all the hard work for the layer above it! For example, if you are accessing a website (HTTP ), it requires data to be split into packets and sent across the internet (TCP / IP), which in turns requires the physical transport of data via cables (cables / Wi-Fi ) LayerExample ProtocolsLayer Purpose Application LayerFTP, HTTP, SMTPProvides user access to applications websites, files, email. Transport LayerTCPProvides transport of data between devices by splitting files into data packets and checking that they have been sent and received correctly. Network Layer Internet Layer IPProvides the routing of data across the network by making use of addressing. Data Link Layer & Physical LayerEthernetProvides the physical transport of data through electrical signals etc.

23. Application Layer I want to send a picture to my friend so I take it to the posting people.

24. Application Layer Transport Layer They cut the picture up into post cards and number each one. 12 34

25. Application Layer Transport Layer Internet Layer They then write the address which each card has to go to. 12 34

26. Application Layer Transport Layer Internet Layer The post cards are loaded into the post van and the van driver sets off. 1 2 34 Network Interface (Link) Layer

27. Application Layer Transport Layer Internet Layer The van driver uses the addresses on the post cards to drive to the destination specified. Network Interface (Link) Layer

28. Application Layer Transport Layer Internet Layer At the destination the post cards are removed and the address used to check they are in the right place. Unfortunately the van driver dropped card 3 which got washed down a drain. Network Interface (Link) Layer 1 2 34

29. Application Layer Transport Layer Internet Layer The delivered cards are checked and the missing number 3 is redelivered. The cards are passed in order to the delivery office. Network Interface (Link) Layer 12 4 3

30. Application Layer Transport Layer Internet Layer The cards are reassembled in order and given to my friend. They now have the original picture. Network Interface (Link) Layer 12 43

31. © OCR 2016 You need to remember the layers! LayerExample ProtocolsLayer Purpose Application Layer FTP, HTTP, SMTP Provides user access to applications websites, files, email. Transport Layer TCP Provides transport of data between devices by splitting files into data packets and checking that they have been sent and received correctly. Network Layer Internet Layer IP Provides the routing of data across the network by making use of addressing. Data Link Layer & Physical Layer Ethernet Provides the physical transport of data through electrical signals etc.

32. © OCR 2016

33. OCR Resources: the small print OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board, and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these resources. © OCR 2016 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work. OCR acknowledges the use of the following content: n/a Please get in touch if you want to discuss the accessibility of resources we offer to support delivery of our qualifications: resources.feedback@ocr.org.ukresources.feedback@ocr.org.uk