WiFi - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 171

The WiFi Protocol
Wi-Fi standard devices use a wireless local area network (LAN). The technology
is managed by the Wi-Fi Alliance, a group of some of the leading companies in
wireless and networking products that did not actually create the technology
itself.
In 1985, the U.S. Federal Communication Commission opened up part of the
wireless spectrum for unlicensed use. The original wireless protocol was called
WaveLAN, developed by NCR for cashier systems. The radio portion was hid-
den from operating systems, and to the drivers, WaveLAN cards were talking
together via wired systems, making installation and use extremely easy.
Its successor, 802.11, was created in 1997. It had a data-rate of either 1 or 2
megabits per second and a communications distance of 60 feet. Interoperability
problems were detected, notably because the Institute of Electrical and Electronics
Engineers (IEEE for short) creates standards but does not test them for certii -
cation. The original 802.11 was not widely embraced, but a new version was:
802.11b. With the birth of 802.11b came the Wireless Ethernet Compatibility
Alliance (WECA), which proposed rigorous certii cation programs. All devices
sold with a Wi-Fi logo were compatible, and consumers loved the technology.
WECA later changed its name to the Wi-Fi Alliance.
802.11b gave much faster data rates: 1, 2, 5.5, and 11 megabits per second.
Although these speeds were good for browsing the web, they were not fast
enough for video streaming or heavy data transfer. 802.11g proposed data rates
of up to 55 Mbit/s, while retaining 802.11b compatibility. (When talking to an
802.11b device, the speed would be at a maximum of 11 Mbit/s). Newer versions
provide even faster data rates; 802.11n can go as fast as 150 Mbit/s; 802.11ac can
go up to 866.7 Mbit/s; and 802.11ad can transfer data at a staggering 6.75 Gbit/s.
Topology
Wi-Fi works with several network topologies, but there are two main types that
are used: ad-hoc and infrastructure.
Ad-hoc mode is an unmanaged, decentralized mode. Wireless peers are free to
connect to other peers, and the network is managed by all the peers. Wireless
devices maintain network connectivity by forwarding packets to other devices
when needed. All network peers have an equal status, and the network is only
as reliable as the parameters of the hosts (transmit power, interference, and
link-length). Ad-hoc networks are often closed networks; peers cannot always
communicate outside the network.