Lecture 2.3: Protocol Stack

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Из курса от партнера University of California, Irvine

Introduction to the Internet of Things and Embedded Systems

3187 оценки

University of California, Irvine

Introduction to the Internet of Things and Embedded Systems

3187 оценки

Курс 1 из 6 — Specialization An Introduction to Programming the Internet of Things (IOT)

The explosive growth of the “Internet of Things” is changing our world and the rapid drop in price for typical IoT components is allowing people to innovate new designs and products at home. In this first class in the specialization you will learn the importance of IoT in society, the current components of typical IoT devices and trends for the future. IoT design considerations, constraints and interfacing between the physical world and your device will also be covered. You will also learn how to make design trade-offs between hardware and software. We'll also cover key components of networking to ensure that students understand how to connect their device to the Internet. Please note that this course does not include discussion forums. Upon completing this course, you will be able to: 1. Define the term “Internet of Things” 2. State the technological trends which have led to IoT 3. Describe the impact of IoT on society 4. Define what an embedded system is in terms of its interface 5. Enumerate and describe the components of an embedded system 6. Describe the interactions of embedded systems with the physical world 7. Name the core hardware components most commonly used in IoT devices 8. Describe the interaction between software and hardware in an IoT device 9. Describe the role of an operating system to support software in an IoT device 10. Explain the use of networking and basic networking hardware 11. Describe the structure of the Internet 12. Describe the meaning of a “network protocol” 13. Explain MANETs and their relation to IoT

Из урока

Networking and the Internet

An important aspect of the Internet of Things is that devices are networked in some way, and often connected to the Internet. Networking enables devices to communicate with other IoT devices and larger cloud-based servers. IoT devices can often be thought of as small parts of a much larger collective system which includes large servers based in the cloud. This module will introduce the basics of networking and the Internet protocol in particular. Eventually, most IoT devices are connected to the Internet, so understanding the protocols associated with the Internet is important to the design of IoT devices. We will also introduce the concept of a Mobile Ad Hoc Network, or MANET, which describes small, local networks of IoT devices.

Lecture 2.1: Internet Structure6:10

Lecture 2.2: Protocols8:10

Lecture 2.3: Protocol Stack6:20

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Ian Harris
Professor
Department of Computer Science

[MUSIC]

This lecture we'll talk about what a protocol stack is,

really define that term.

We will go into a little bit of detail,

little bit of information about how a protocol stack is defined.

Now remember though, that in practice certainly in this specialization,

in practice you're not gonna be writing a protocol stack,

making a protocol stack, but you can use a protocol stack.

So you at least would wanna know what this term is because it gets

thrown around, right.

If you want to make a new embedded system you say, well I need to be networked,

you know Internet, which protocol stack am I going to use, right?

Which implementation of the protocol stack will I use?

You need to know what that term means,

because it gets used a lot when you're actually coding things.

You should know basically what it means.

So not all the details that I'm talking about will be important in the long run,

but you should see it all at once because it'll

give you a better context about what you're using.

So OSI Layer Concept.

So the idea about taking these protocols and making a stack,

different layers of protocol, is that you've got these multiple layers,

different tasks, different networking tasks that you have to handle.

These tasks are associated with different layers of protocol stack.

And each layer is implemented usually in software,

actually some of the lower layers are implemented in hardware.

So some are in hardware, some are in software.

The difference doesn't matter

too much to us right now certainly the top layers are in software, but

the idea is that a message, say you want to send a message okay.

So you make this message, we got our picture up here, this message M.

M is our message, and that's maybe just the pay load okay.

That is what the data we want to send.

So then that is basically an input to a layer.

Let's talk about the first layer,

layer R let's say is the first layer, the top layer.

So that goes into it and into the code, so that code takes the message,

it makes some kind of a decision, whatever decisions are made at that layer, and

then it puts the results of that decision into the header of the message

producing a new message, M prime down there, which is now bigger.

It has whatever was inside M and

it has additional header on the outside of that, right?

So at every level every level that happens.

So, the first level, for

instance here, let's see this level is performing routing.

So the goal of this level is to take a message and figure out a sequence of

machines that it will hop through to get to its destination.

So at this level it takes a message, it finds the route,

it says okay you need to go through machines A, B, C, and D.

All right, that sequence.

So it can take a sequence, that whole sequence of nodes,

put that into the header of the message, and then output this new message, M prime.

Which is the same old message,

but now with this extra routing message contained inside the header.

So that's the general idea, that at every layer the code, or the hardware,

or whatever it is that's implementing the protocol, will make some decisions like

routing information, arbitration information, flow control information.

And then the results of that it'll put into the header, or

some of the results, it'll put directly into the header,

and you'll get a new message out, which is bigger than the original one, right?

Which now has its new header data.

This is on the sending side.

So this is the idea, and you have a stack of these layers.

So that's what they mean by protocol stack, you have layer after layer and

they call that a stack.

Now, encapsulation is used to mean that the protocols

they're separated from one another, in some sense.

So, each layer, each protocol layer is separated.

So, all these different tasks that need to be performed, say routing.

That is mapped to a particular layer.

That is performed by the protocol information stack at this layer and

other layers do not have to deal with it.

So it is encapsulated, it's separating the different layers.

And the whole point of that is to make it simpler to understand and

also to write code.

All right, so as a programmer, if you're dealing with the layer that deals with

routing, then that's all you have to think about, you don't have to think about flow

control because flow control is dealt with at another layer.

So that's what encapsulation generally means.

And a protocol stack is the implementation of all the different layers put together.

So a transmission, when want to send a message,

basically the messages start at the top layer and then they go down.

So you put the messages into the top layer protocol.

It makes its decisions, adds to the header, passes it to the next layer,

which adds, makes some decisions, adds to the header and

continues, until you get to the bottom layer.

Now the bottom layer is called the physical layer, and

at that layer it actually takes the data and puts it on to an electrical

mechanism, a transmission mechanism, some kind of medium.

So that means one of two things, either wire, so

a physical layer, it codes the data onto physical wires, or

it encodes it onto wireless broadcasts, radio broadcasts, so one of the two.

So always at the bottom layer there's this physical layer,

which actually transmits the signal either by wire or through the air through radio.

Now, at the receiving end, the message comes in.

Remember, it's sent physically, right?

So it's on wires, it's a bunch of electrical signals on wires, or

it's sent through the radio.

So at this end, the messages go up through the same protocol stack.

So that means when it's received, it's received at the physical layer, right?

Because it's physical signals, either wired or wireless.

They come in,

and then they have to get basically recoded back to the original data.

So now at the receiving end,

these messages are going through the protocol stack up, from bottom up.

So the opposite of what happened on transmission happens here.

At every layer, the message gets received, the appropriate header

information is read and used, and then the new message that's produced is actually

smaller than the first message, minus that header information, right?

And then it goes up to the next layer, which takes the header information

at that layer it uses that and then produces a new message which is smaller.

And so by the end at the top all you have is the actual payload and

all the header information has been stripped off.

So that what happens at the receiving end and

it's the reverse of what happens at the transmission side.

Thank you.

[MUSIC]

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