WiFi Deployment

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Del curso dictado por Princeton University

Networks Illustrated: Principles without Calculus

39 calificaciones

Princeton University

Networks Illustrated: Principles without Calculus

39 calificaciones

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. Please note that per Princeton University policy, no certificates, credentials or reports are awarded in connection with this course.

De la lección

Random Access in Wifi Networks

In this lesson, we will investigate WiFi, another type of wireless network. Rather than having stringent power control algorithms as we saw for cellular, WiFi relies on "random access" methods to manage interference among users in the same location.

Unlicensed Spectrum5:01

Traffic Analogy4:43

WiFi Standards5:34

WiFi Deployment6:24

Accessing WiFi10:55

Interference7:49

Controlled vs. Random Access6:49

Random Access Protocols & ALOHA7:00

ALOHA Successful Transmission5:15

ALOHA Throughput7:12

ALOHA Inscalability8:19

CSMA Carrier Sensing5:54

CSMA Backoff7:49

CSMA vs. ALOHA5:41

Conoce a los instructores

Christopher Brinton
Lecturer
Electrical Engineering
Mung Chiang
Professor
Electrical Engineering

Let's now take a look at the technical WiFi deployment and the text and terms

that we see when we look at deployment. So, we'll refer to this diagram

throughout this slide. So, the first thing we'll see is what's

called a basic service set and we can draw analogies here to sign their

networks because though WiFi and cellular have very different ways of actually

sharing the medium and different devices when we look at the technical way of that

It's done. Their topology is the way that they're

laid out are actually very similar. So a basic service set is similar to the

idea of a cell. And we call that a BSS for short.

And Basic Service Set has a bunch of components in it.

So this is a BSS, one of these circles in here.

obviously devices like your laptops, or Your smartphone which can access the

internet. An Access Point or an AP, we call it for

short, that's similar to the idea of a bay station.

So that's what's going to actually give your device access to the internet

through WiFi. And each access point is identified by

what's called a service set identifier or an SSID.

And what an SSID really is or those things that you see on your screen like

when you go into your settings, you know to connect to your WiFi network you may

see some different SSIDs and if your in public you'll see Probably more of them

than if you're sitting in your house you're probably going to see one or maybe

your neighbor's as well. But when you see these names, these catch

phrase names like Optimum WiFi or other network and then you see your signal

strength next to it. And so you could connect to these SSIDs

and it'll put you on a different access This point so which access point will

have a different SSID. And some of those SSIDs are locked so,

you can't get on a network if it's protected and you don't have a password

if you're not a paying subscriber of whatever network it is that you're

looking at. So then there's the idea beyond just the

basic service set, which just practice out is that in general we can also have

what are called extended service sets or ESSs.

So, we still have your basic service set. An ESS is you can look at it like a

collection of basic service sets which have more than one access point within

them. And they support roaming capabilities.

So, if your device could maybe move from here into here and then it could also

access, get onto this access point. or that access point would actually

broadcast the same SSID. So, these two if they were going to form

an extended service set. And ESS, they would broadcast the SSID.

And so in a house or in a home you would only have one basic service set typically

or in a Starbucks or anywhere that you're going to go.

'Cause there's probably only one access point.

But if you go to a hotel or a large building there may be multiple access

points that support roaming, so you don't actually notice even when you switch

between them. But then if you move over to this service

set over here, which is an extended service set you can actually then connect

to this other device. So, an ESS is a collection of basic

service sets that readily support roaming capabilities, and then beyond the basic

service sets they're all really tethered to the backhaul.

And there's a backhaul network up there, that's typically ethernet, that's

probably a common name that you hear for a backhaul network which then goes up

into what's called the access network and the access network is the bridge between

the backhaul and the rest of the internet.

So we won't really distinguish, right now at least, between the backhaul, and the

access, and we won't look at that much in this course.

But we will focus a lot on the internet in later chapters, and just know that

between the basic service sets, there's a few more sets that you'd go before you

get to the quote, unquote. Internet cloud up here and, so now where

is WiFi? Lets, lets take a look at a few examples

and first is in a home and we can look at a typical home declaimer just to give you

more of an idea what do these terms really mean, so in your house you Have a

router. And it's your router if it supports WiFi

it was called to the via Wifi Router or Wireless Router.

And then basically you form a BSS of all the devices in your house that have WiFi

on it. So, any device that's connected to the

WiFi will become part of this basic service set.

And then this is the access point. The WiFi Router becomes the access point.

This point and all your devices in here and the WiFi Router itself though it may

also not just have wireless devices like your desktop computers or if your laptop

if it's connected directly in would be over ethernet or a wired connection.

So, Ethernet the standard wired protocol. And that's roughly speaking you would say

that the ethernet protocol runs on the wires.

But we really call them Ethernet cables and common speech, and then beyond the

Wifi router it connects back to a modem. And actually more and more today even

routers and modems are in one device, so you may actually have one of these boxes,

but then you're connecting to a modem, and then outside of your house you have

the access network then, and the access network would be for instance cable, or

it could be fiber so fiber is common. For instance, if you have FIOS or you

could have DSL or anything along those lines.

So, those are all access network names. So another place beyond the home is in

hotspots. For instance in June 2012 something,

interesting, US providers, five major cable providers in the US.

Agree to quote unquote join forces and actually connect all their hotspots into

a single service. You can actually look more up on that if

you want and you can blog or write a Wikipedia article on it, that would be a

good thing to look into, and in addition to hotspots even street corners nowadays

in certain countries. For instance, in Korea, Seoul plans to

have their entire city covered, the entire city of Seoul, all the street

corners, everywhere that you go should be able to have WiFi they claim by 2015.

So we em at home, we see them at hotspots, even more and more now we're

seeing them at street corners. Eventually you have to wonder will

everywhere be covered by WiFi if we wanted.

So will we have the choice between WiFi or cellular where ever we go.

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