> Cover Story> Full Story
IN THE SKY
802.11b: 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
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.
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
802.11f - This specification is also under consideration.
It involves the IAPP (Inter Access Point Protocol) task group.
Das Gupta can be reached at email@example.com