So WiFi is officially called IEEE 802.11 and that's a technical attribute
standard. And if you look there, you will see the
specifications for WiFi. So the 802 part is for Local Area
Networks or LANs and LANs can either be wireless, like in this case or they can
also be wire line. Like in the case of an Ethernet local
area network. You may have heard of Ethernet before if
you have an Ethernet can able /g, if you're not connecting via WiFi to your
internet right now, then you're, might be connecting directly with an Ethernet
cable. And the .11 part is for wireless.
So 802, as we said, is for local area networks, and then .11 specifies that
it's a wireless Local area network. But nobody really wants to look around
say IEEE 802.11 so people just coined the better term WiFi which stands for
Wireless Fidelity. So, for a while up until around 1999
there were no real standards. Even on WiFi, or nobody was, people would
walk around and say that their devices were WiFi that didn't necessarily conform
to the WiFi standards. So in 1999, the WiFi alliance was set up
to ensure interoperability, and we looked at the word in the last section when we
talked about Europe and adopting GSM as the global standard for over in Europe
for cellular networks. in this case, we mean interoperability
among devices for WiFi. And so if they stamp this symbol on your
device, it means that it conforms the WiFi standard, or a specific WiFi
standard. And what do we mean by specific WiFi
standard? Well, there's more than just 802.11 we
actually cook some of an alphabet soup if you want to look at it that way.They're a
lot of different standards and you may have heard of some of these before:
there's 802.11B, 802.11A, 802.11G, 802.11N.
And these are just four of them, right so WiFi started maybe around 1997 when it
was officially called WiFi. and it came around in a frequency band of
2.4 GHz at first and supported a maximum speed of 2 Mbps.
You can see over the years, the maximum speed has improved, and so let's stop
there for a second and let's say, what do you mean by speed, well We measure speed
in what's called a megabit per second.So, what does that exactly mean?
Well, when we talk about speed, when you're driving your car, you say, miles
per hour, kilometers per hour, meters per second, or however you say it.
What you're saying there, you're saying that you go a certain distance in a
certain amount of time or on average, that's kind of how you're driving right
now. And when we measure speed in a network,
we measure the number of bits that we're sending per second.
So your device will transmit at a certain number of bits per second, and we talked
about how a bit, in the last lecture, is either a zero or a one, just a logical
zero or one. Like in computer code and so when we talk
about bits per second or bps for short, we're saying the number of bits that are
going over the network in one second and that's on average.
So you're sending a number of bits over the network and then in one second you're
just basically probing and saying, well, how many bits are going to pass through
here in one second on average? And we measure in mega bits per second,
because its many, many and many its per second.
Because bit is small little piece and we transmit millions of them in each second
and gigabits per second and now what we can handle, and so we set mega bits per
second with in millions and just like when we say megahertz we meant millions
of hertz, and, and so on. And so, then in 1999 we went to 802.11b
and that was the first official [UNKNOWN] standard still at 2.4 gigahertz and went
up to 11 megabits per second. And so, these are mostly in alphabetical
order, there's a little variation there, for the most part it is, but here's one
example. b came out and then actually a came out
with an even higher data rate of 54 Mbps at a different frequency range, in the
same year, so they found out they could transmit much, much higher in that
frequency range, and then g came out in 2003.
And that was still at 54, but it was down then at the 2.4 GHz range and then as of
2009, we have 802.11n, which is the most commonly used right now, and that's in
both 2.4 and around 5 GHz range, and that supports up to a maximum speed of 100
Mbps. And, clearly that will vary, as we will
see, so you're not always going to get 100 Mbps, it'll depend on who else is on
the network, and so on. And so, as the data rates improved over
the years, the number of devices that wanted to access WiFi went way up.
So back in 2009, when IEEE 802.11n came out so 802.11n came out, we had somewhere
around 600 million devices, and then by 2015, it's projected that that's going to
go up to 2.2 billion. So as the data rates go up, there's more
and more of a demand. We saw a very similar trend with cellular
networks.
Christopher BrintonLecturer
Mung ChiangProfessor
