
How Wi-Fi Works - sharjeelsayed
http://www.verizoninternet.com/bookmark/how-wifi-works/
======
andrenotgiant
This is (good) SEO linkbait. Someone at Verizon got $10k to spend getting it
created by saying it will boost organic search traffic to Verizon. Right now
(during link-building phase) they keep the page completely separate from rest
of site. Later, (after most links are created) they'll change it. Not sure
whether the goal is just to generally build authority to VerizonInternet, or
to get this URL ranking for wifi keywords. (Seems more likely the former.)

~~~
ejo3
That page probably cost a lot more than 10K.

~~~
moondev
Absolutely. They did a great job too

~~~
bigbugbag
Browser could not initialize WebGL For more info visit
blend4web.com/doc/en/problems_and_solutions.html#problems-upon-startup

Maybe they could have done a good job instead of a great job and this page
would actually work.

Not mention the font size issues and overlapping text, luckily they provide
images at the bottom that do not have the problem.

When you have to provide images at the bottom as a workaround, it usually
means you know there are issues with the page and the job is not that great.

Then again, as pointed in other comments here some of the technical
information is incorrect or just plain wrong.

------
mrb
As hatsunearu said, the radio modulation described is grossly incorrect. WiFi
never uses 8-PSK (encoding 3 bits per symbol). 802.11n and 11ac encode
1/2/4/6/8 bits using a BPSK/QPSK/16-QAM/64-QAM/256-QAM symbol (256-QAM is for
11ac only). The modulation scheme is negotiated based on signal quality. Here
is a quick reference: [http://mcsindex.com/](http://mcsindex.com/) (MCS =
modulation coding scheme) On Linux you can find the MCS negotiated with "iw
dev wlan0 link | grep -i mcs"

14 channels are defined in the 2.4GHz band. For example channel 6 is centered
on 2437 MHz. Each channel is 20MHz wide and divided in 52 "data" subcarriers,
each occupying a different frequency and spaced out by 312.5 kHz (52 × 312.5
kHz is less than 20 MHz because there are "control" subcarriers and additional
spacing.) So 52 different symbols can be sent in parallel at the same time,
which is what we call OFDM
[https://en.wikipedia.org/wiki/Orthogonal_frequency-
division_...](https://en.wikipedia.org/wiki/Orthogonal_frequency-
division_multiplexing) (basically, I'm simplifying!)

Remember this is for just 1 channel. So with 14 channels each composed of 52
subcarriers, we could have 728 symbols transmitted at the same time. If they
are 256-QAM symbols that's basically 728 × 8 = 5824 bits being transmitted at
the same time in the air. And they will all be received and demodulated
independently. This high level of parallelism of OFDM is how WiFi can achieve
very high throughput.

Then, with wide channels of 40 MHz, which basically aggregate two 20 MHz
channels, we get a few more data subcarriers because we don't need as many
control subcarriers so a few of them become used as data subcarriers. Hence a
40 MHz channel will have not 52 × 2 = 104 but actually 108 data subcarriers.
And 802.11ac defines 80 MHz and 160 MHz channels with respectively 234 and 468
data subcarriers.

Let's calculate the maximum usable throughput of a single 802.11ac 160 MHz
channel using 256-QAM modulation... It sends 468 symbols at the same time on
468 data subcarriers. Each symbol encodes 8 bits and takes in the best case
3.6us to be transmitted: 3.2us for the actual symbol + a short guard interval
of 0.4us (the GI is normally 0.8us but can be a short GI of 0.4us if
negotiated). The raw physical bitrate is:

1/3.6e-6 × 468 × 8 = 1.04 Gbit/s

However there is a mandatory error correction which is 5/6 in the best case so
the actual usable bandwidth is:

1.04 × 5/6 = 866.67 Mbit/s

~~~
azernik
Note that, although the 2.4GHz spectrum is formally divided into 12-14
channels (depending on local regulations), these are very _narrow_ channels;
in practice there are only 3 non-overlapping 20MHz-wide channels. This is a
small fraction of the width of the 5GHz band.

~~~
aexaey
There are 3 non-overlapping 2.4Ghz channels (1,6,11) for 802.11b, because of
the channel spectrum shape. Not only "b" uses 22Mhz channels with is just a
bit too wide, but also, due to the way how single-carrier PSK modulation
works, especially on older hardware, "b" has considerable amount of spurious
emissions adjacent to the main carrier that widen it even more - could be seen
here as smaller "hills" to the left and right [1],[2].

802.1g/n/ac can easily have _4_ non-overlapping channels (1,5,9,13) because
(thanks to OFDM) channel spectrum is much neater with rather square 20 (40)
Mhz channels with practically no energy outside [3].

Yet, everybody's stuck with 1,6,11 channel scheme which is wasting precious
bandwidth. [4] (middle graph) Notice gaps between the channels that could be
eliminated by moving 6->5 and 11->9, and gap on the right where channel 13 can
fit after that.

[1] [https://villagetelco.org/2009/11/rf-
hacking/](https://villagetelco.org/2009/11/rf-hacking/)

[2]
[http://ecee.colorado.edu/~ecen4242/wlanb/index_files/image02...](http://ecee.colorado.edu/~ecen4242/wlanb/index_files/image029.gif)

[3]
[http://rfmw.em.keysight.com/rfcomms/n4010a/n4010aWLAN/online...](http://rfmw.em.keysight.com/rfcomms/n4010a/n4010aWLAN/onlineguide/transmitter_spectral_mask_test__\(802.11n\).htm)

[4] [https://www.codify.com/wp-content/uploads/2009/07/Central-
Ro...](https://www.codify.com/wp-content/uploads/2009/07/Central-Room-A-
Spectrum.png)

~~~
kees99
> Yet, everybody's stuck with 1,6,11

Reminds me of:

[https://blog.xkcd.com/2009/09/02/urinal-protocol-
vulnerabili...](https://blog.xkcd.com/2009/09/02/urinal-protocol-
vulnerability/)

------
princekolt
"How Wi-Fi Works" \--> 503 Service Unavailable

Seems about right.

~~~
Kenji
Hahaha, I was about to post just that. Made me laugh. Reminds me of my time at
university... during breaks and boring lectures, WiFi was impossible to use
because of the load. You could probably measure how boring a lecture is by
recording WiFi latency and stability parameters.

------
Ajedi32
Getting a 404 now. Any idea where the page went? (Here's an archive link:
[https://web.archive.org/web/20170723145452/http://www.verizo...](https://web.archive.org/web/20170723145452/http://www.verizoninternet.com/bookmark/how-
wifi-works/))

~~~
glenneroo
Are you sure it was a 404? I'm getting a 503 (Service Temporarily
Unavailable). Not that it really matters...

------
sshanky
This is beautiful, but probably still too complex for most of their customers.
I wonder what their motive in putting this together was, as it must have been
very expensive.

~~~
crispyambulance
Yeah, it is beautiful.

Unlike their overcomplicated phone plans and billing statements which are
deliberately obscure and their customer service which they run like a 2-bit
boiler room operation.

~~~
lhuser123
Specially obscure. Which is like scamming, because most people won't try to
understand it.

------
notgood
Just a reminder that Verizon its the biggest lobbyist against Net
Neutrality[0] and if you do support it then it's probably wise to stay away
from their services as far as possible.

[0] [https://www.dailydot.com/layer8/lobbyists-net-neutrality-
fcc...](https://www.dailydot.com/layer8/lobbyists-net-neutrality-fcc/)

------
jonathanbull
Mirror:
[http://webcache.googleusercontent.com/search?q=cache:http://...](http://webcache.googleusercontent.com/search?q=cache:http://www.verizoninternet.com/bookmark/how-
wifi-works/)

~~~
gruez
google cache doesn't do the page justice. most of the value is in its
visualizations.

~~~
dotancohen
The cache now has the images, though it didn't when first posted. Honestly,
the Google cache is _better_ than the original as it doesn't have the CPU-
killing animations.

~~~
emilfihlman
No images for me :/

------
bdcravens
Speaking of how wifi works, I learned something interesting about wifi and
Verizon's partner in many things, Comcast: Last night I notified my home
Internet acting funny, and learned that the admin interface for my Comcast
router had username "admin", password "password". SMH.

~~~
rayiner
I mean, I just got a 10-gig router,[1] and the stock username/password was
"ubnt"/"ubnt." It's always the installer's job to set up a new
username/password.

[1] [https://community.ubnt.com/t5/EdgeMAX-Stories/EdgeRouter-
Inf...](https://community.ubnt.com/t5/EdgeMAX-Stories/EdgeRouter-Infinity-XG-
New-kid-on-the-block-taking-EdgeMax-to/cns-p/1879930)

~~~
jstimpfle
Why not generate a long password and print it on the backside? My DSL provider
can do it (for my DSL router)

~~~
suprfnk
People might be less inclined to change it. And they should change it, because
some firm knowing your password isn't safe either.

~~~
cbhl
It's worth noting that all the ISPs that encourage you to change your password
have a separate maintenance account ("backdoor") with its own password.

------
deepsun
Does anyone know, if I'm on a WPA2-PSK wi-fi, do other devices that are also
on the same network can "sniff" my traffic. For unprotected networks it's
obvious, but what about protected?

~~~
detaro
Yes, if you know the PSK (=password) and can capture the initial handshake
(which is easy, since you can just force-disconnect a client so it has to do a
new one) you can decrypt it. (If I remember correctly, Wireshark has this
built in, so you can try it for yourself if you are curious)

~~~
voltagex_
I'm assuming you mean a malicious device can force a deauth on another client
(or more usually, all other clients) and then capture the packets as they
reconnect. If so, is there a way to detect this? Is there any way to protect
against this? I'm assuming client isolation makes it more difficult.

~~~
mort96
Well, the easiest way to protect against it is making sure an attacker doesn't
know your wifi password.

~~~
deepsun
Of course, but I'm working in a big office with office-private wi-fi with one
password. And who knows what viruses my colleagues have.

Also, I have a pretty special audience of hackers here, so I wouldn't be
surprised if someone actually tries it.

Same goes for various events and conferences.

------
pier25
I had to disable the ad blocker to get the nice web gl graphics.

From a front end perspective I think this it's awesome. No so sure about the
content though.

------
arikrak
I was looking at this and thought it looked nice but then my computer froze so
maybe they overdid the 3D graphics a bit?

~~~
dotancohen
Try the Google cache, it now has the images but not the animations:
[http://webcache.googleusercontent.com/search?q=cache:http://...](http://webcache.googleusercontent.com/search?q=cache:http://www.verizoninternet.com/bookmark/how-
wifi-works/)

------
hatsunearu
the radio stuff is pretty wrong; one glaring one is that PSK is pretty much
not used anymore, it's all OFDM.

~~~
rayiner
OFDM is orthogonal to PSK (hah). PSK is a modulation--a way of representing
bits on a carrier wave. Another type of modulation is QAM. OFDM is a way of
combining multiple sub-carriers (each modulated with PSK or QAM) into one
signal in order to deal with multi-path distortion:
[https://www.csie.ntu.edu.tw/~hsinmu/courses/_media/wn_11fall...](https://www.csie.ntu.edu.tw/~hsinmu/courses/_media/wn_11fall/ofdm_new.pdf).

~~~
mrb
Still, hatsunearu is correct. The page is grossly wrong, absolutely no modern
WiFi modulation technique uses 8-PSK. Have a look at
[http://mcsindex.com/](http://mcsindex.com/) 11a/11n/11ac all use BPSK, QPSK,
16-QAM, 64-QAM, and (for 11ac only) 256-QAM.

~~~
m-j-fox
I know. And not a word on forward-error correction, trellis codes, automatic
gain control, beam steering or MU-MIMO. Is this for babies? They don't even
touch on low-noise amplifiers. Much less DAC and ADC performance. Where's the
link a primer on FFT?

------
nvahalik
Can someone explain the natural resonance of walls of talked about with
regards to 5Ghz?

------
Piccollo
Why did CSS stop working

------
founderguy
Pretty sure that domain isn't owned by Verizon. Looks like an authorized
seller creating content to try to build authority.

~~~
andrenotgiant
Looks like it is actually owned by Verizon, see email contact on WHOIS
[http://whois.domaintools.com/verizoninternet.com](http://whois.domaintools.com/verizoninternet.com)

------
Web1Dollar
wi-Fi is a best device! but is can work slow than wire.
[https://www.webhostingonedollar.com/](https://www.webhostingonedollar.com/)
visit for getting more detail about hosting plan.

------
KozmoNau7
TL;DR: It doesn't.

------
srtjstjsj
website crashes chrome on windows after a few seconds.

------
Yizahi
In my experience it doesn't. My every attempt at improving this shit ends up
in laying more wires everywhere.

------
anilakar
Stopped reading at "Wi-Fi antennas send information". Antennas don't send
anything, they just match the impedance of the feedline into that of the
medium.

