Layered Protocol Stack

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Networks Illustrated: Principles without Calculus

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Princeton University

Networks Illustrated: Principles without Calculus

40 оценки

What makes WiFi faster at home than at a coffee shop? How does Google order its search results from the trillions of webpages on the Internet? Why does Verizon charge $15 for every GB of data we use? Is it really true that we are connected in six social steps or less? These are just a few of the many intriguing questions we can ask about the social and technical networks that form integral parts of our daily lives. This course is about exploring the answers, using a language that anyone can understand. We will focus on fundamental principles like “sharing is hard”, “crowds are wise”, and “network of networks” that have guided the design and sustainability of today’s networks, and summarize the theories behind everything from the social connections we make on platforms like Facebook to the technology upon which these websites run. Unlike other networking courses, the mathematics included here are no more complicated than adding and multiplying numbers. While mathematical details are necessary to fully specify the algorithms and systems we investigate, they are not required to understand the main ideas. We use illustrations, analogies, and anecdotes about networks as pedagogical tools in lieu of detailed equations. All the features of this course are available for free. It does not offer a certificate upon completion.

Из урока

Controlling Congestion in the Internet

The Internet has many important tasks to manage, like routing packets (discussed in the last module) and controlling congestion. This workload is modularized into different functional layers, each responsible for performing a different set of functions, as we will see in this lesson. We will also look at the principles of congestion control, managed at the transport layer.

Divide And Conquer2:10

Layered Protocol Stack4:13

Transport & Network Layers4:42

Processing Layers2:17

Controlling Congestion4:03

Traffic Jam & Bucket Analogy3:02

Sliding Window2:36

Cautious Growth of Window Size6:51

Inferring Congestion5:46

Congestion Control Versions2:16

Loss-Based Congestion Inference5:19

Delay-Based Congestion Inference: Part I6:43

Delay-Based Congestion Inference: Part II5:33

Delay-Based Congestion Inference: Part III4:51

Distributed Congestion Control5:14

Познакомьтесь с преподавателями

Christopher Brinton
Lecturer
Electrical Engineering
Mung Chiang
Professor
Electrical Engineering

So the notion of modularization in that,

created what's called the Layered Protocol Stack.

And this is an idea of one of them is a five layer stack, it's the 5-layer model

of the, really important to note the labeling on

the start down at the bottom of layer one.

And we'll work our way up layers two, three,

four, to five and not the other way around.

so this is a 5-layer model, there are 7-layer models for

instance the OSI model is a 7-layer and it takes the

top layer here actually and extends it up.

But, let's look at this model, because it gets the main ideas across.

So down at the physical layer, that's really the network medium itself.

Right so it's like, fiber, wireless, whatever it happens to be.

If it's copper, anything else, the

physical transmission of information, as bits,

as ones and zeros, digital transmission, that's all down at the Physical layer.

Then, we'll look at the Network layer next.

The Link layer, we won't concern ourselves with the details of that one

too much, but it's more about how we actually get onto the link.

It controls access to the networking medium, but you can almost look at

those Physical and Link layer for our purposes kind of as one layer.

Then the Network layer is really what we looked at last time, this handles routing.

And the dominate protocol in the networking layer is

IP or Internet Protocols as we saw with IP addresses.

So the network layer is where

IP addresses are handled. That does hop by hop routing.

Then if we go one step above that to the Transport layer,

that's going to be our focus in the second portion of this lecture.

We look at that's really TCP, also UDP is another protocol

there, but mainly TCP is the dominant one that you'll hear.

This deals with end to end management, right,

and as we've said TCP is the dominant protocol.

So, the Network layer does

hop by hop routing, and the Transport

layer's where, what's actually managing the connections, right?

It's managing the end-to-end connections.

It's saying that we have one session which is

which consists of one user connected to other user.

And then out of the top is the Application

layer and this is really what we interact with, right.

So you know Netflix, Facebook, those are all applications and

the dominant protocol there is HTTP, Hyper Text Transfer Protocol.

So each layer provides service to the layer

above and uses some service in layer below.

So that's one of the important points here to see is, for instance,

the Transport layer sets up those end to end connections as we've said, right.

So we have two users that are connected

to one another and a Transport layer is dealing

with the end to end connection itself, so,

that provides a service to the Application layer, right.

Because the Application layer needs

things like packet reordering, the session

establishment to actually run the application

on top of this, for instance if we're talking to each other.

we have like two Facebook sessions open and

we're each talking to each other over Facebook.

The application is you know what we're typing in

and the Transport layer is providing end to end connectivity.

So, the Application layer is using information from the Transport

layer the Transport layer provides information to the Application layer.

additionally, the Networking

layer will provide information to the Transport layer, and the Transport

layer will use service from the Network layer, and so on,

all the down the line, although we get, when we get

down to the Physical layer, which is just the actual transmission itself.

these horizontal lines here, don't get

confused, they're, they're actually really complicated objects,

and they, they represent limitations of what different layers can do and see.

But these, horizontal lines and how you'd define

really what layers are allocated and which is

not is not an easy task to do because

there's a lot of art that goes into designing this.

And it's also not a clear-cut division, for instance, error control.

There's some amount of error control that goes on really at every layer.

So even down at the Physical layer we

have some sort of methods of correcting for errors,

and all the way up the Application layer

we might run some error correction mechanisms as well.

And that's, that's not a mistake, right.

So it's not that certain functions

are not only confined to one layer and the reason for that is robustness.

So if maybe my Physical layer technique for detecting errors doesn't get all the

errors, well then, maybe I'll put the Networking layer when I'm doing check sum.

Or I'm going to have the Transport layer when I'm using my

error correction mechanism there, maybe one of them will catch it.

So that's the idea, is to have the robustness

and some of the functions allocated to multiple layers.

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