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Week 3 Lesson 1 Computer Networks – data packets Computer Networks – data transfer across the Internet This lesson, we’ll be investigating the highlighted questions … • How does the internet work? • How does data get from one computer to another? • How do emails get sent? • How does the data/emails know Partial map of the Internet. Each line is drawn between two nodes, representing two IP addresses. The length of the lines give an idea of the delay of data transfer between those two nodes. In today’s lesson: Lesson Objectives • Understand how data is transmitted across networks, including the internet • To model how internet packets travel across the world via routers Success Criteria ALL: Understand that data is transferred in packets over the internet/networks MOST: Successfully explain how data is transferred across the internet/networks SOME: Successfully explain using technical terms how data is transferred and describe some of the problems that may arise during data transfer Literacy -Today’s key words Here is part of the London tube system. Imagine you want to go from Paddington to Victoria. In pairs, decide…. How could you get there? Which colour lines would you choose and where would you change? Trains from Wigan & Preston arrive at Euston. My sister lives in Shepherd’s Bush. How can I get there? Which colour lines should I choose and where would I change? Trains from Wigan & Preston arrive at Euston. My sister lives in Shepherd’s Bush. Problem – Tottenham Court Road tube station is closed due to a mouse on the line. No trains are passing through. How can I get to Shepherd’s Bush now? This time, you want to go from London Bridge (where you’ve been to see the Bridge) to Oxford Circus where you want to go shopping on Oxford Street. How could you get there? Which colour lines would you choose and where would you change? There’s a problem!!! Bank Station is shut, you can’t get off there but trains are still passing through. You may not have used this station before, but you definitely can’t use it now. Find an alternative route to Oxford Circus. So how does this link to the internet? • Just like taking a tube around London, we saw last lesson that: – the stations are like the servers which simply pass the data on, the ‘data’ is the tube trains and everyone on them. – when data (the trains & people on them) is passed around the internet – the network of networks – it travels around the world (rather than London) – when data is passed around, instead of going from station to station, it goes from IP address to IP address – There are sometimes problems with the routes the data is due to take, and another route has to be found. Internet Rules Now think about using the tube in Japan, you probably don’t speak Japanese, you’re not sure if their ‘rules’ for travelling on the tube are the same as ours, and you have certainly never seen people being pushed onto the trains in London when the station is getting full!! But happens in Tokyo! Each country has its own particular set of rules or customs for traveling on tube • Ifthe the data is travelling across the world, how does it get transferred between computer systems in different countries without too many problems? • To get around this potential problem, we have internet protocols which are a set of rules and instructions to be followed by a computer (anywhere) when sending and receiving messages from other computers. Data packets • When data is sent from one machine to another over a network, either through the internet or over a LAN, it needs to be collected together in bundles called packets. Packets = bundles of data ready to be transmitted. • The size of the ‘message’ doesn’t matter as packages are a standard size, the bigger the message the more packets sent. • A data packet consists of several parts or labels Source Address Where the file Is coming from Destination Address Where it is going to Packet Sequence Number DATA Which part of The data itself the file it is Error Checking (Checksum) Ensuring it is the same as original and not corrupted Data packets • The router will pick up any packets addressed to a destination outside the LAN – for example, a Google search from your computer rather than you opening a file which is stored on our network. • Protocols – rules – will define how each packed is packed in a series of “envelopes” so they can be unpacked in the correct order when they arrive. These rules are: TCP = Transmission Control Protocol and IP = Internet Protocol • It will then send the packets out to the wider network and hopes that all the other routers on the internet will work out how to deliver them to their final destination. • The packets might take different routes to get to their destinations. We saw last week these could be 1000s of miles away! Packet switching • The transfer of data in packets is called packet switching • Each packet finds its own way from the sender to the receiver • This means that unavailable or congested routes can be avoided • Different users/data can share parts of the same route • Lost or damaged packets can be resent and may take different routes to the first time to get to their destination Packet switching • Routers send the packets along their journey and communicate with each other. • They calculate the shortest and quickest path, taking into account “traffic conditions” so the packets that pass through them get to their destination as quickly as possible. • There is no set route which means that intercepting data is harder. A packet’s tale • https://www.youtube.com/watch?v=WwyJGzZmBe8 Data Transfer, Packets and Switching Learning Check … On your whiteboard, • Write the 3 important or interesting things you have learned about how data is transferred around the internet in today’s lesson. • Write down 1 question you’d still like to know the answer to. Be ready to share your points with the class • If you finish, on the other side, see if you can draw a diagram to show packet switching. ‘Unplugged’ data transfer 1 ** Make sure you have a whiteboard and a working pen** • At the top, put TO and write the name of person who is going to receive your data. They should not be next to you or within 3 people of where you are. Under this, put FROM and write your name. This is the “header” • Next write a short, sensible question (as if you were googling something) about something we covered today or on this topic (so the person receiving it should actually be able to answer it!!!) • When everyone is ready, you are going to pass the white boards around from person to person until they arrive at their correct destination. • The receiver is going to use the other side of the board, put the header information and write their answer • The data will then be sent back to the sender when everyone is ready ‘Unplugged’ data transfer 2 ** Make sure you still have a whiteboard and a working pen** • At the top, put the header information again, sending it to someone different this time, who is not sat immediately near or next to you. • Again, write a short, sensible question (as if you were googling something) about something we covered today or on this topic (so the person receiving it should actually be able to answer it!!!) • When everyone is ready, you are going to pass the white boards around from person to person • BUT this time, your teacher will choose a few points during the data transfer process and say that certain routers (certain people in the class!!) are not working & data will need to take an alternative route. • Once the destination is reached, the receiver puts the header information, answers the question and sends it back Problems – how can they be overcome? • What happens if one of the data packets doesn’t arrive & gets lost? • How would you know? • What would happen if they packets were numbered? • What is there is a data collision – several packets arrive at a router at the same time? • What happens if the header data is corrupted? Plenary – define today’s key words Week 3 Lesson 2 Computer Networks – sending emails Computer Networks – data transfer across the Internet This lesson, we’ll be investigating the highlighted questions … • How does the internet work? • How does data get from one computer to another? • How do emails get sent? • How does the data/emails know In today’s lesson: Lesson Objectives • Understand how emails are sent across the internet • To model how internet packets travel across the world via routers to send emails Success Criteria ALL: Understand that email data is transferred in packets over the internet/networks MOST: Successfully explain how emails are sent across the internet SOME: Successfully explain using technical terms how emails are sent, and understand the difference between the 2 main email protocols. Literacy -Today’s key words Starter Recap – complete on your whiteboards …. 1. 2. 3. 4. Data is divided into …… As it travels around the network it passes through ……… This is known as packet ………………. Different packets can take ………………… ………….. to arrive at the same destination 5. ………………… information tells the routers where the packets need to go. 6. Routers calculate the ………. and ………. path Starter Recap – check your answers 1. Data is divided into packets 2. As it travels around the network it passes through routers 3. This is known as packet switching 4. Different packets can take different routes to arrive at the same destination 5. Header information tells the routers where the packets need to go. 6. Routers calculate the quickest and shortest path Introduction to how emails are sent • Easy animation to introduce how emails are sent: http://www.bbc.co.uk/education/clips/zwp3r82 Intended for KS2 but very clear Email protocols – rules between computers when handling emails SMTP – Simple Mail Transfer Protocol SMTP is a set of guidelines for sending emails. First created in 1982. Used by all major email systems. You have a nice user friendly interface to write the email When you press SEND SMTP takes your email and breaks it into strings of text, using labels to identify different parts. These form the email header. The email is sent to your mail server which checks your user name and password . It uses the header informatio n to look up where the email should be sent The email is passed to the recipients mail server so it can be delivered Email protocols – rules between computers when handling emails There are 2 popular but very different protocols used to retrieve emails from the mail server. POP – Post Office Protocol • Downloads emails from a mail server • When downloaded, the emails are removed and stored locally • Not useful if viewing emails on several different devices as it is only on the one you read it on IMAP – Internet Message Access Protocol • Retrieves emails from a mail server but leaves a copy on the server, allowing multiple devices to access the same email • Can access emails anywhere on any device • Changes made eg creating a draft, deleting an email, are updated on mail server & all devices Email packets game • Last lesson we had a quick look at how data is sent around the internet in packets. • Today, we’re going to do a similar activity and model what happens when an email is sent from one email server to another • You’ll need a white board pen, a dice and a set of laminated cards • See separate instructions: email packet game Email packets – blank Make sure you have a whiteboard pen Demonstrate your learning • Now we’ve had some fun, it’s time to demonstrate what you’ve learned • You can choose from one of the 5 following tasks to present your understanding of the internet, packets, packet switching and how emails work. • This task will be assessed so you need to choose a task that suits your strengths and will enable you to show off what you’ve learned to the best of your ability Choose your task…. Presentation • Produce a presentation to explain to a Y7 student how data & emails are transferred around the internet Story • Write a descriptive and/or narrative story to explain a “packet’s tale” – you could write it from the point of view of a packet of data eg an email to describe how it travels around the world to get to its destination and everything that happens to it along the way Article • Write a factual article for a newspaper or magazine to explain how data or an email is transferred around the internet. You could write this in columns and format as a newspaper. Cartoon • IF you are a good artist, draw a cartoon strip to show how data/email is transferred around the internet, this should include some text to explain the illustrations Annotated Diagram • Using a detailed diagram which could by hand or on the computer, show how data/email is transferred around the internet. Success criteria for all tasks Whichever task you choose, remember this will be marked and assessed. You need to make sure your work: Is informative and factually accurate Teaches the reader/viewer about the topic in a way that is easily understood Is NOT copied and pasted! Needs to be YOUR work. Uses at least some technical / key words Shows some creativity or thought about how best to present quite a tricky topic Is well – presented, attractive, uses appropriate software and shows care and attention to presentation and SPAG Plenary: Peer evaluation ** Swap places or work with your partner ** • Look at their work carefully – – What do you think about what they have written/drawn/designed and how well it informs you about the topic? – What do you think about the way it has been presented. • On their work, write down: – 3 STARS – 3 things you think they’ve done really well – 1 WISH – 1 thing you think they could do better – 1 QUESTION – 1 question you’d like to ask them about the topic or their work. • If you spot any SPAG errors, mark these in green pen