21.1 Introduction
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is usually accomplished by the user having a hand-held
terminal or laptop that has
an RF interface card installed inside the terminal or through the PC card slot of
the laptop. The client connection from the wired LAN to the user is made through
an access point (AP) that can support multiple users simultaneously. The AP can
reside at any node on the wired network and acts as a gateway for wireless users’
data to be routed onto the wired network.
The range of a WLAN depends on the actual usage
and environment of the
system. It may vary from 100 feet inside a solid walled building to several thou-
sand feet in an outdoor environment with direct line-of-sight. Much like cellular
phone systems WLANs are capable of roaming from the AP and reconnecting to
the network through other APs residing at other points in the network. This can
allow the wired LAN to be extended to cover a much larger
area than the existing
coverage by the use of multiple APs.
An important feature of WLANs is that they can be used independently
of wired networks. They can be used as stand-alone networks anywhere to link
multiple computers together without having to build or extend wired networks.
The network communications take place in a part of the radio spectrum that is
designed as
license free.
In
this band, 2.4–2.5 GHz, users can operate without a
license so as long as they use equipment that has been of the type approved for use
in the license-free band. The 2.4–2.5 GHz band has been designated as license free
by the international telecommunications Union (ITU),
and is available as license
free in most countries of the world.
Standard WLANs are capable of operating at speeds in the range of 1–2 Mbps
depending on the actual system; both of these speeds are supported by the stan-
dard for WLANs defi ned by the IEEE. The fastest WLANs use 802.11b high-rate
standard to move data through air at a maximum speed of 11 Mbps.
The IEEE
established the 802.11b standard for wireless networks and the wireless compat-
ibility Ethernet alliance to assure that WLAN products are interoperable from
manufacturer to manufacturer. Any LAN application,
network operating systems,
or protocol, including transmission control protocol/Internet protocol (TCP/IP)
will run on 802.11b-compliant WLANs as easily as they run over the Ethernet.
