ks4 networks - stem€¦ · •describe the four-layer internet protocol suite •identify specific...

KS4 NetworksThe Internet Protocol Suite

Who are we?

•David Zendle• University of York,

Computer Science Department• Associate Lecturer

• Computing at School Regional Centre (CRC) for Yorkshire and the Humber• Regional Co-Ordinator

Who are we?

•Paul Willcox• University of York,

Computer Science Department• Associate Lecturer

• Computing at School Regional Centre (CRC) for Yorkshire and the Humber• Regional Co-Ordinator

CAS regional centre

(CRC)

The CAS Regional Centre

• Where’s the CRC?• Computer Science

department, University of York

• What’s the CRC for?• CAS is dedicated to

providing support for teaching computing

• The CRC for Yorkshire and the Humber is dedicated to specifically supporting you (teachers in the region).

The CAS Regional Centre

• How can the CRC support you in teaching computing?

• We…1. Support and organise local

CAS Hubs2. Run larger CAS Regional

Meetings3. Support and organise local

Master Teachers4. Act as a POC for teachers5. Arrange and deliver a

variety of CPD

#1: We Support and organise local CAS

Hubs•A CAS Hub is a group of teachers who meet up once or twice a term to:• Network• Discuss computing• Share best practice• Receive computing CPD

• The CRC supports Hubs• Setting up hubs• Running hubs• Publicising hubs

#1: We Support and organise local CAS

Hubs• Interested in attending a

hub?• There are some running in

York next week!• Ask us!• casyork@computingatschoo

l.org.uk

• Interested in starting your own hub?• Ask us!• casyork@computingatschoo

l.org.uk

Hubs are not the

only events we

organise…

#2: We Run larger CAS Regional Meetings

• We support CAS Hubs• Local

• We also organise termly Regional Meetings, which are a lot like Hubs• Teachers meeting up• Networking• Sharing best practice• CPD• But on a regional level across

Yorkshire and the Humber, not a local one.

• Interested?• Ask us!• [email protected]

#3: We support Master Teachers

• Master Teachers are experienced and high-performing teachers of computing

• MTs provide CPD and mentoring support to teachers in their local area

• The CRC• Helps excellent teachers become MTs• Connects MTs with teachers in their

local area who need support or mentoring

• Interested• In becoming a MT?• In being put in touch with a MT?• Ask us!• [email protected]

#4: We act as a point of contact for

teachers

•Teaching computing can be:• Scary

• Confusing

•Need help?

•Need support?

•Ask us!• [email protected]

#5: We organise CPD

• Want someone to:• Come into your school / cluster

and deliver some computing training?

• Upskill you in some particular aspect of the curriculum?

• Organise some CPD which you want to run?

• Ask us!• [email protected]

• That’s what I’m here today to do!

• Today I’ll be delivering a bit of CPD on networks

mailto:[email protected]

Order of presentation

• 40 minute lecture• “The Internet Protocol Suite”• Subject knowledge• Led by David

• 10 minute workshop• Turning that knowledge into a lesson• Led by Paul

• 10 minute feedback• Share ideas

Okay, let’s get

started!

What are communication protocols?

• I’m here to talk about protocols• But what are protocols?

• Like most technical terms, the concept underlying the word is quite simple

•Protocols are sharedsets of rules.

What are communication protocols?

• In the case of networks, these sets of rules govern:• How data is transmitted across a network

• What is done with that data by the various devices on a network

Today I’m going to talk about

• A whole bunch of protocols:• TCP• IP• FTP• HTTP• ARP

• How they fit together to define communication over the internet• Internet Protocol Suite• TCP/IP Model

OF INTERNET

PROTOCOLS

But David, why

would I care about

that?

A couple of reasons for caring about this

1. It’s pretty cool• We use the internet all the time

• It’s fun to find out how it actually works

2. It’s assessed explicitly in the new September 2016 specs

• For Edexcel

• For AQA

• For OCR

Edexcel, OCR, AQA

If you find that

exciting, you’ll be

thrilled to learn

that…

Quick event plug

OCR will present on their

new CS GCSE spec and how

to meet it at the NSTEMC

on Monday @ 4.30Sign up here:

https://goo.gl/OK3TcM

https://goo.gl/OK3TcM

Objectives

• So, under new GCSE specs, you need to know about some specific content• To be precise• The layered protocol model

on which the internet runs

• This can be problematic• Why?• This content can be pretty

confusing

Case and point?

By the end of today,

you should understand

why this is unhelpful

Objectives

•By the end of the session, you will be able to:• Describe the four-layer Internet Protocol Suite

• Identify specific protocols from within this suite

• Explain the functionality provided by these protocols

• Teach this content with confidence

layered protocols

Let’s start off with

a game!

Here’s a game for us to play!

• Here’s a particular network topology

• Each node is connected to nodes on the left and right

• You’re all sitting in a row• I hope• So let’s pretend you’re a network

with this particular topology• Let’s also pretend this piece of

paper is some data to pass across your network

• And let’s assign each of you a location on this network

Rules of the game

•Object of the game:• Get a piece of data from

source to destination

• Have that piece of data read out at the destination

•What kind of rules will we need to play this game?

Main kinds of rules

•Rules governing where to pass the data

•Rules governing what to do with the data

Rules of the game

•What to do with the data when you receive it:• Open up the piece of paper

• Read what’s inside it

• Check the destination number on the outside. If you’re the destination, read the words aloud

•Where to pass the data next:• If the destination is on your left, pass left

• Else If the destination is on your right, pass right

How could we make

that process

faster?

Not all protocols should be used all the

time•Most of you didn’t need to open the data and process what was inside it•Your job was just to pass it on•You should never have needed to use that protocol at all!• Using it was inefficient


time

•Similarly, some devices on networks only need to pass data around

•They’re don’t need to actually interpret that data• They just need to know where it’s going next

•So these devices should only use some protocols• Otherwise, waste occurs

There’s a good analogy to postmen here


time

•This is where layered protocol models come in• These approaches

(unsurprisingly) work by separating protocols out into different layers.

• Devices only use protocols from necessary layers

Okay, let’s do the

same exercise, but

this time let’s layer

our protocols…

Rules of the game from before

•What to do with the data when you receive it:• Open up the piece of paper

• Read what’s inside it

• If you’re the destination, read the words aloud

•Where to pass the data next:• If the destination is on your left, pass left

• Else If the destination is on your right, pass right

• Else If you’re the destination, don’t pass

Rules of the game

Layer 1. Work out where the data should go• Check the outside of the message

• Are you the destination?

• If not, you don’t need to care about what the data is. Pass the data towards the destination.• Do not go on to Layer 2.

Layer 2. Interpret the data• If you are the destination, (and only if you’re the

destination) open up the paper and read what’s inside!

A lot more

efficient, huh?

A very simple layered protocol model

•We’ve essentially defined a very simple layered protocol model:• Layer 1: ‘Passing Paper Layer’: All people need to care

about this layer, to determine where to pass next

• Layer 2: ‘Reading Paper Layer’: Most people don’t need to care about this layer!

• The key point to put across about layered protocol models is that they work because nodes in a network often don’t need to use all the layers

The internet protocol suite

•The model which is mentioned in GCSE specifications is the Internet Protocol Suite• This is often

confusingly called the TCP/IP model, but it really shouldn’t be (in my opinion).


•The simple layered protocol model we defined earlier governed our communications in the room

•The Internet Protocol Suite governs communications across the internet


• This model consists of four layers of protocols:• Application Layer• Transport Layer• Internet Layer• Link Layer

•Word to the wise• These are sometimes

called by other names! (See image)

Just like in our

example earlier, each

of these layers

handles different

functionality

The internet protocol suite: Summary

I’ll briefly summarise each of the layers:

• Application Layer• defines protocols for how applications talk to each other

• Transport Layer• Defines protocols for segmenting data from a sending host and

reassembling that data on a receiving host (‘host to host’); error control; flow control.

• Internet Layer• Defines protocols for packaging data and routing it across a network

• Link Layer• Defines protocols for handling low-level communication between

individual devices


•This model consists of four layers of protocols:

1. Application Layer2. Transport Layer3. Internet Layer4. Link Layer

Application Layer

Applications and the application layer

•What do application-layer protocols do?

•The clue’s in the name!

•We’ve all used applications at one time or another• I hope!

•Lots of these applications communicate with other applications via networks:


•Web browsers• Talk to web servers• “Hey! Give me some

data!”• “Hey! Upload this data

for me!”

•When an application receives a message from another application • It needs to know how to respond to that message

What should I do with this?

•Does this message mean that they want some data from me?

•Does this message mean that they want me to do something with their data?

•How do I handle this message?


•Application-layer protocols help with this problem. They:• Interpret data so that the application can use it

• Prepare data so that it can be understood by an application using the same protocol ‘at the other end’

Example?

•HTTP

•Hypertext Transfer Protocol

•Defines common rules for how to:• Request resources from a server

• Interpret requests for resources

• Request that a server do something with a resource

• Interpret requests that something should be done with an incoming resource

Here’s a quick

outline

Say my web server

receives a request

What does http do?

•HTTP provides a common set of rules for applications to talk to each other

• Aha! The ‘get’ command tells me that they want that specific resource… I’d better go get that for them!

Acting out HTTP

•Here’s a scenario:

•There are two applications in different locations on a network• These applications can make requests for resources

• These applications can receive requests for resources

I would like to

GET that

yellow sphere

resource

GET Yellow Sphere!

Aha! A GET

request for the

Yellow Sphere

resource!

That’s pretty

simple!

But wait… doesn’t

it skip out a few

steps?

A few steps are missing

• Remember that message which used the HTTP protocol?

• It doesn’t mention IP addresses anywhere

• But IP addresses define where things are on the internet

• How can these applications talk to each other without knowing who they’re talking to?

Layers are specialised

•Application layer protocols• Just define rules for applications to talk to each other

• Don’t handle other things!

• Leave those to the other layers…

The transport layer

The internet protocol suite: Summary

•Application Layer• defines protocols for how applications talk to each

other

•Transport Layer• Defines protocols for segmenting data from a sending

host and reassembling that data on a receiving host (‘host to host’)• error control

• flow control

Example? TCP

•TCP is a Transport-layer protocol• Transmission Control Protocol

•What does it do? Amongst other things:• Provides a protocol for splitting one big piece of data

into several smaller packets for easy travel• Provides a protocol for reassembling packets into a

message• Provides a way of checking that all packets have

been received

Acting out TCP

•Can I have a volunteer from the audience please!• Step up!

• Don’t be shy!

•You are going to act out the role of a machine which has just requested some data using TCP

Acting out TCP

• I’m going to send you some packets of data, labelled 1-6

•Here are the rules which our transport-layer protocol gives us:• If you receive a packet out of order, you can reorder

the packet

• If you think you’re missing a packet overall you can request that packet

So… that’s the transport

layer! Shared rules for

making sure data gets

transported between hosts

The Internet Layer

Defines protocols for

packaging data and

routing it across a

network

Hmmm… that sounds

a lot like the

transport layer!

Transport layer vs. internet layer

•Transport Layer handles things like:• Splitting data into packets at one end

• Reassembling those packets at the other end

• Making sure host machines have all the right packets

•The Internet layer handles things like:• Putting addresses on those packets that say where

they’re going to and coming from

• Determining how those packets get across a network

We’re on more solid

ground here, I think

Example? IP

• IP• Internet Protocol

•What does it do? •Defines rules for:

• Attaching a header to some data which says where the data should go

• Reading a header and using that information to send data somewhere else

The Link Layer

Defines protocols for

handling low-level

communication

between individual

devices

Example? ARP

• ARP is a protocol in the Link layer• Address Resolution Protocol

• When is it used?• When we have some data with an IP address and we want to

know where physically to send that data.

• What does it do? • Defines rules for:

• Asking local devices what the physical address (MAC address) of an IP address is

• Replying to requests asking for MAC addresses for IP addresses

Still confused?

Here’s a little demo

MAC: AA

IP: 2

MAC: BB

IP: 3

Computers making ARP requests

• Oh! I have a piece of data for IP address 3.

• But I don’t know where that physically is in the network.

• Hello! Everyone in the network! Are any of you mapped to IP address 3?

• Sure thing!

• Hi! Yeah, that’s me!

• My MAC Address is BB

• Can you send that data over?

Still confused?

•An IP address is like a street address• E.g. 20 Lowther Drive

• It tells you where something is

•So, where in the world is 20 Lowther Drive?

•Can you cycle from here to 20 Lowther Drive?• You can’t tell me

• Even though that address identifies a specific place

• You can’t tell from that address where in the physical world that place is

IP-MAC == Street Address-GPS

• ARP defines rules for turning an IP into a MAC Address

• This is like mapping Street Address to GPS co-ordinates• It’s defining where that thing

physically is

• This is the kind of thing the Link Layer handles• Low-level rules for defining

ways for physical things to talk to each other

Putting it all together

Remember how we

modelled simple

protocols in a human

line network?

Here’s a game for us to play!

• Here’s a particular network topology

• Each node is connected to nodes on the left and right

• You’re all sitting in a row• I hope• So let’s pretend you’re a network

with this particular topology• Let’s also pretend this piece of

paper is some data to pass across your network

• And let’s assign each of you a location on this network

How might we model

the internet protocol

suite in a human line

network?

Let’s model these layers in our line

network again: application layer

Application Layer

•Rules for applications to talk to each other

•You could show how the application layer tells applications ultimately what to do with data• Sources: Fold your data up neatly

• Destinations: Unfold the data and read aloud


network again: transport layer

Transport Layer

•Rules for host to host communication e.g. segmentation

•You could show how the transport layer segments data into packets• Sources: Cut your data up and put it in numbered

envelopes• Destinations: Arrange the envelopes in the right order• Destinations: Open up the envelopes and sellotape the

data together


network again: Internet and link layer

Internet Layer

•Rules for transporting data across the network• Work out where to pass each envelope next

Link Layer

• Low-level rules for communication between individual pieces of hardware• Use your eyes to work out what direction to physically to

pass the envelope in order to get to the address specified at the layer above

Objectives

•By the end of the session, you will be able to:• Describe the four-layer Internet Protocol Suite

• Identify specific protocols from within this suite

• Explain the functionality provided by these protocols

• Be confident in teaching this content

Workshop

What now?

•Now what?

•Let’s have a chat

•How might you teach this content?

I know how I’d

teach this at

University

Roughly like this!

Workshop

•How have you taught similar content in the past?

•How would you teach this content without using computers?

ks4 networks - stem€¦ · •describe the four-layer internet protocol suite •identify specific...

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