The committee for IEEE 802 standards formed a working
group for wireless local network standards 802.11 in 1990. This
group undertook development of the general standard for radio equipment
and networks working at 2.4 GHz, with access time of 1 and 2 Mbps
(Megabits-per-second). The works on development of the standard
were completed in 7 years, and in June 1997 the first specification
of the 802.11 was ratified. The IEEE 802.11 is the first standard
for WLAN products from an independent international organization
developing the most of standards for wired networks. But the first
established data rate in a wireless network didn't meet the requirements
of users by that time. And the developers had to create a new standard
to make the Wireless LAN technology popular, cheap and attractive
for modern tough business applications.
In September 1999 the IEEE ratified the extension
of the previous standard. The new IEEE 802.11b extension (also known
as 802.11 High rate) defines a standard for products of wireless
networks working at 11 Mbps (similar to Ethernet), what allows using
these devices in large organizations. The compatibility of products
from different manufacturers is ensured by an independent organization
named Wireless Ethernet Compatibility Alliance (WECA). It was founded
by the leaders of wireless communication industry in 1999. At present
it includes more than 80 companies such as Cisco,
Lucent, 3Com,
IBM, Intel,
Apple, Compaq,
Dell, Fujitsu,
Siemens,
Sony, AMD
etc. On the WECA's
site you can look through the products which meet the requirement
of Wi-Fi (the WECA's term for IEEE 802.11b).
The need in wireless access to local networks grows
with the number of mobile devices such as notebooks and PDAs, as
well as with the desire of users to be connected to a network without
dealing with a network cable. According to forecasts, in 2003 there
will be more than a billion of mobile devices, and the WLAN market
is estimated to be more than two billion of dollars by 2002.
IEEE 802.11 standard and its extension
802.11b
Like all IEEE 802 standards, the 802.11 works
on two lower levels of the ISO/OSI model: a physical and a channel
one (fig. 1). Any network applications, a network operating system
or a protocol (e.g., TCP/IP) will work perfectly in the 802.11 network
as in the Ethernet.
Fig. 1. Levels of the ISO/OSI model and their correspondence
with the 802.11 standard.
The basic architecture, peculiarities and services
of the 802.11b are defined in the initial standard 802.11. The specification
of the 802.11b touches only the physical level, adding only higher
access speeds.
Operating modes of the 802.11
The 802.11 deals with two types of equipment -
a client which is a computer equipped with a wireless Network Interface
Card (NIC), and an Access point (AP) which serves a bridge between
a wireless and wired networks. An access point usually contains
a transceiver, a wired network interface (802.3) and software for
data processing. ISA, PCI or PC Card network cards in the 802.11
standard or integrated solutions (e.g. telephone garniture of the
802.11) can serve a wireless station.
The IEEE 802.11 standard has two operating modes
of a network - "Ad-hoc" and Client/Server (or infrastructure mode).
In the client/server mode (fig. 2) a wireless network consists of
at least one access point connected to a wired network, and a set
of wireless terminal stations. Such combinations are called Basic
Service Set (BSS). Two or more BSSs which make a single subnetwork
form an Extended Service Set (ESS). Since the most of wireless stations
require an access to file servers, printers, Internet available
in a wired LAN, they will work in the client/server mode.
Fig. 2. Architecture of the "client/server" network.
The "Ad-hoc" mode (
