Wireless Local Area
Networks
Standards
Overview of IEEE
802.11
The
IEEE (Institute of Electrical and Electronic Engineers) finalized the initial
standard for wireless LANs, called IEEE 802.11, in June 1997. This initial
standard specified a 2.4 GHz operating frequency with data rates of 1 and 2
Mbps. With this standard you could
opt between using frequency hopping or direct sequence, two non-compatible forms
of spread spectrum modulation. Because
of relatively low data rates (as compared to Ethernet), products based on the
initial standard did not flourish as many had hopped.
In
late 1999, the IEEE published two supplements to the initial 802.11 standard:
802.11a and 802.11b. The 802.11a
standard specifies operation in the 5 GHz band with data rates up to 54 Mbps.
The advantages of this standard (compared to 802.11b) are much higher
capacity and less RF interference with other types of devices (e.g., Bluetooth),
and products are just now becoming available throughout 2002.
802.11a isn’t compatible with the 802.11b and 802.11g products,
however.
Like
the initial standard, 802.11b operates in the 2.4 GHz band, but it includes 5.5
and 11 Mbps in addition to the initial 1 and 2 Mbps. The 802.11b standard only
specifies direct sequence modulation, but it is backward compatible with the
initial direct sequence wireless LANs. The IEEE 802.11b standard is what most
companies choose today for deploying wireless LANs.
The
802.11 working group is currently working on extending the data rates in the 2.4
GHz band to 54 Mbps using OFDM (orthogonal frequency division multiplexing),
which is the 802.11g standard. This standard will hopefully become ratified by
the end of 2002. Companies should be able to easily migrate their existing
802.11b products to become 802.11g compliant through firmware upgrades. This
enables companies having existing 802.11b infrastructures to scale up their
network via relatively simple cost-effective changes.
To
address interoperability among different wireless LANs, semiconductor companies
are currently releasing single integrated chipsets that combine both 802.11a and
802.11b/g. This will enable makers of radio NICs and access points to develop
interoperable products. For example, a radio NIC based on the dual-standard
technology will eventually be able to sense the type of wireless LAN access
point (either 802.11a or 802.11b/g) and automatically communicate using the
applicable frequency and protocol.
In
addition to performance, IT organizations are deeply concerned about security of
wireless LANs. The existing 802.11 security mechanism, WEP (wired equivalent
privacy), is very easy to compromise. As a result, the 802.11 working group is
developing upgrades to the standard to include stronger encryption and dynamic
key exchange. These changes should become available by the end of 2002.
Jim
Geier provides independent consulting
services to companies developing and deploying wireless networks. He is the
author of the book, Wireless LANs (2nd Edition), and regularly
instructs workshops on
wireless LANs.
By
Jim Geier, Independent
Consultant
Recommended
Reference Book
"Wireless
LANs"
by Jim Geier,
published by
SAMS,
ISBN 0-672-32058-4
