Wireless LANs  

Wireless Local Area Networks


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 isnít 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

  Copyright annor Ltd   2004