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WLAN standards
The IEEE 802.11b standard published by the IEEE (Institute of Electrical and Electronics Engineers) in 1999 is the predominant WLAN technology. 802.11b

provides for a full Ethernet like data rate of 11 Mbps over DSSS. Like all IEEE 802 standards, the 802.11 standard focuses on the bottom two levels of the OSI model which are the physical layer and the data link layer. Any LAN application, NOS, or protocol, including TCP/IP, will run on 802.11 compliant WLANs as easily as they run over Ethernet.

Since its release, the 802.11b high-rate standard has been adopted by almost all of today's wireless vendors. Consequently, wireless network adapter card prices dropped an average of 200 percent in the past 12 months.

802.11a: Just as the market warmed up to the possibilities of WLAN using 802.11b, a new standard called 802.11a is already here. The IEEE has developed 802.11a, which represents the next generation of enterprise-class WLANs. It provides greater scalability, better interference immunity, and higher speed than the current technologies. It also allows higher bandwidth applications to be run simultaneously and supports more users.

Devices utilizing 802.11a are required to support speeds of 6, 12, and 24 Mbps. Optional speeds go up to 54 Mbps, but will also typically include 48, 36, 18, and 9 Mbps. These differences are the result of implementing different modulation techniques and FEC levels. In cases of both 802.11b and 802.11a, when the client device travels farther from its access point, the connection remains intact but speed decreases. However, 802.11a has a significantly higher signaling rate than 802.11b

HiperLAN2 - HiperLAN2 technology takes advantage of the latest developments in wireless technology as well as the media access protocol to try and deliver greater efficiency, QoS (Quality of Service), radio resource management, power savings, and plug-and-play capabilities. The HiperLAN2 architecture provides connections to multiple types of network infrastructures like Ethernet, IP, ATM and PPP (Point to Point Protocol). Security features include authentication and encryption. It will also offer automatic frequency management, which is supposed to simplify deployment.

HiperLAN2 has a very high transmission rate. At the physical layer it extends up to 54 Mbps and on layer three up to 25 Mbps. It uses OFDM (Orthogonal Frequency Division Multiplexing) to transmit the analog signals. It operates over the dedicated spectrum in the 5GHz band. A cell of a HiperLAN2 typically extends to approximately 30 to 150 meters.

802.11a's similarities and compatibility with other specifications
802.11a is similar to HiperLAN2 at the physical layer. HiperLAN2 also uses OFDM technology, and operates in the 5 GHz frequency band. While 802.11a uses CSMA-CA (Carrier Sense Multiple Access with Collision Avoidance), HiperLAN/2 utilizes TDMA (Time Division Multiple Access)

While 802.11a and 802.11b share the same MAC layer technology, there are significant differences at the physical layer. 802.11b transmits in the 2.4 GHz range, while 802.11a transmits in the 5 GHz range. Since their signals travel in different frequency bands they will not interfere with each other. A related consequence, therefore, is that the two technologies are not compatible. There are various strategies for migrating from 802.11b to 802.11a, or even using both on the same network concurrently.

WLAN standards to watch out for 802.11g - The IEEE standards board has approved a project within IEEE 802.11 to enhance the data rate of WLANs operating in the 2.4GHz band. It is expected that the WLAN data rates will be increased to greater than 20 Mbps from the current 11 Mbps as part of this project. The project will be managed by IEEE 802.11, which will form a new Task Group called TGg for the development of the new project.

802.11e - This draft specification from IEEE creates the industry's first true universal wireless standard. It offers seamless interoperability between business, home and public environments like airports and hotels. It adds QoS (Quality of Service) features and multimedia support to the existing 802.11b and 802.11a wireless standards, while maintaining full backward compatibility with these standards.

802.11i - This specification is currently under consideration. It features security and mobility enhancements to the existing standards.

802.11f - This specification is also under consideration. It involves the IAPP (Inter Access Point Protocol) task group.

Soutiman Das Gupta can be reached at soutimand@networkmagazineindia.com

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