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Networks Illustrated: Principles without Calculus

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Princeton University

Networks Illustrated: Principles without Calculus

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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

Routing Traffic through the Internet

It is hard to overstate the impact that the Internet has had on society. In this lesson, we will overview the fundamental concepts behind the way the Internet is designed. We will also take a look at routing, which is the process of determining how packets of information are transported.

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Christopher Brinton
Lecturer
Electrical Engineering
Mung Chiang
Professor
Electrical Engineering

So, ARPANET eventually evolved into NSFNET not too quickly after ARPANET

started, but let's look at some more of a time line here.

1974 TCP and IP TCP stands for transmission control protocol.

IP stands for internet protocol.

that was really invented in 1974, and that

was invented by Robert Kahn and Vinton Cerf.

And TCP/IP really is the foundation for the modern internet,

and even though many of the other parts of the internet have changed quite

a bit TCP/IP has remained relatively unchanged

even from back when it was invented.

so we'll talk about IP in this chapter, TCP deals more

with end-to-end connectivity and we'll talk about that in the next lecture.

so a protocol is a language for devices, so each of these,

TC, Transmission Control is a protocol and the internet is a protocol.

And so it's really a language that devices

speak so that they all understand and they're all, they all know

kind of what to read in the messages as they're sending them across.

And so that's the idea of protocol very important to understand.

and TCP/IP is really a very scalable way to connect hosts.

And, what we mean by scalability, and this will become

evident as we talk more about the Internet, but is that

you can add more, and more, and more hosts to

the network, and it'll remain TCP/IP won't have to be changed,

right.

So, you don't have to change the protocol when you add

more people to the network, which is a very, very good thing.

Thing about TCP/IP.

it became part of the internet not until 1983, actually.

So ARPANET had a previous scheme that they

used, and in 1983 became part of the internet,

when ARPANET was still around, but it had actually

already become a subset of the quote, unquote, internet.

So, 1985, 1995.

the National Science Foundation took over the development

of the Internet really and then NSFNET came out.

And it was an Academic research network.

Part of the reason the NSFNET came out,

actually, was because under ARPANET it was very hard.

It was a very tightly controlled and regulated, so it was really hard

to actually buy into the ARPANET if you wanted to add a host.

So, NSFNET, they came out and said okay, well as long as

you're doing academic research you can add a hub onto this network.

and it wasn't until the 1990s actually that you were allowed to do anything with

commercial ventures on the Internet.

so they did allow, for instance, companies to have who

used the internet, but only as it was related to research.

Right, so you could obviously you know share

files with other companies to do research related activities.

It wasn't until the until much later that we were

able to do things for fun and entertainment on the internet.

It was originally just for purely for research.

And so this NSFNET had the idea, it was really a three

tiered structure.

This was when it came out, and that extends really

to the modern day, even though they're not called these anymore.

At the lowest end, we had campus networks, right.

They're, they're so, that's how you know, your it, your, whatever

campuses run NSFNET at this time would be at the lowest level.

they would all be connected in what's called,

to a regional network, which is one step above.

And then, the entire backbone would connect the entire thing together.

So it's really kind of a tree

structure, right?

Where this is the roots and it comes out to the leaves.

That you can say the campus networks really form the leaves of that tree.

and so this is the idea, this is

that three tiered structure campus, regional, and backbone.

so the backbone by 1991 already had 14 nodes.

Just to give you an idea of how large it had become, even by then.

The the backbone notes are showing up at the top here.

they're all

showing and connected.

And then at the bottom, these are either a regional or a campus-level nodes.

So, you can see how many nodes there were. It really extended, not always the United

States, but also, abroad, to even different countries as well by 1991.

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