Transcript
Feature
The WLAN Roadmap Wireless Local Area Networking (WLAN) is a simple
More reading:
concept, but one that entails a wide, sometimes
The IEEE, and the 802.11 standards themselves
confusing, variety of standards, implementations, and
http://www.ieee.org/portal/index.jsp
future plans for development. This article provides a map,
http://www.ieee.org.groups/802/11/
so you can understand what the current standards are, how they relate to one another, and how they will develop
WiFi Alliance http://www.wifi.org/OpenSection/index.asp Toshiba "Technology trends"
into the standards and implementations of the future.
u What exactly is WLAN? Simply stated, wireless LAN is a local network of
to assist in the setup and configuration of wireless
devices that send and receive data via radio frequency
networks (such as Toshiba’s ConfigFree).
(RF), thus no longer requiring network cabling. Users benefit by gaining flexibility and mobility, though there is a tradeoff in terms of performance as today’s
A word about bandwidth and throughput
wireless 802.11 standards offer a maximum of 54
Bandwidth and throughput are two different
Mbps as compared to standard wired Ethernet rates of
things. In the world of wired networking, the
100 Mbps. Enhanced and emerging WLAN standards
differences between them in performance
aim to boost speeds and WLAN performance, thus
terms are not nearly as dramatic as in the
boosting wireless productivity even more.
wireless world.
Fundamentally, WLAN configurations consist of two
The bandwidth of a network represents the
essential network components: an access point (AP),
maximum performance offered by
and a station (STA). Access points act as network hubs
connections—you can think of it as the “size of
and routers. Typically, at the “back end”, an access
the pipe” through which data can flow.
point connects to a wider LAN, WAN, or even the
The throughput of a network represents the
Internet itself. At the “front end” the access point acts as a contact point for a flexible number of stations. A station moving into the effective broadcast radius of an
actual performance offered by connections— the rate of actual data flowing “through the pipe”.
access point can then connect to the local network Thus, the throughput rate can never be greater
served by the AP (all the other local stations and
than a system’s bandwidth; and, in nearly all
resources in the LAN) as well as the wider network
cases, throughput is significantly less than the
connected to the AP’s “back end”.
bandwidth (because of radiointerference, data The flexible (even adhoc) nature of WLAN
congestion, the number of stations vying for an
configurations means that managing them can be
APs resources, and so on).
much more complex than wired connections where you essentially configureonceandforget. To enhance wireless usage, some vendors provide software tools
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Feature u WLAN standards today WLAN standards in use today basically divide into three general groupings; foundational, leadingedge and enhanced. Next, we take a look at how these standards evolved.
WLAN Standard Description
802.11 Original, foundational networking
Transfer method
Frequency range
Supported Bandwidth
Typical Throughput
FHSS, DSSS, 2.4 GHz, IR
2 Mbps
< 1 Mbps
2.4 GHz
11 Mbps
~4 Mbps
5 GHz
54 Mbps
~22 Mbps
infrared
standard
802.11b Foundation networking standard, most
DSSS, HR DSSS
popular in home/business
802.11a Leading edge highspeed networking OFDM standard, most popular in medium/large business ~22 Mbps, ~4
802.11g Leadingedge, highspeed networking
DSSS, HR
standard, gaining acceptance in
DSSS, OFDM
Mbps when 2.4 GHz
54 Mbps
interoperating with 802.11b
home/business
components
Atheros
Performs on top of the existing
Enhanced wireless performance, 802.11 standard employed in
108 Mbps
~60 Mbps
based on the existing 802.11 the network. standards.
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Feature u Foundational WLAN standards
u Leadingedge WLAN standards
There are two foundational WLAN standards: 802.11,
Although ratified at the same time as 802.11b, 802.11a
and 802.11b. The original 802.11 standard is, today,
faced a much slower deployment, despite the fact that
almost entirely obsolete. Once equipment
it offered much greater performance (modern 802.11a
implementing 802.11b was made more widely
systems afford a fivefactor increase upon the
available, it quickly moved into use and propelled
performance of 802.11b in optimum situations). Several
growth of the WLAN industry itself. The cost of 802.11
factors limited widespread adoption:
equipment was not attractive for the bandwidth it
·
supported: 2 megabits per second (2 Mbps)
products were slower to come to market, starting in about 2001
bandwidth, with an effective throughput of half that, or ·
less.
acceptance was much delayed in Europe (especially the UK) where 802.11a’s operation in
802.11b increased the available bandwidth, and
the regulated 5 GHz band could have caused
throughput, by a factor of five with only a marginal
problems with military and government
difference in cost. 802.11b equipment quickly made its
communications
way into small businesses and homes: the flexibility of ·
WLAN combined with the useful data rates now
operating in the regulated 5 GHz band rather
available made it very attractive for people to set up
than the unregulated 2.4 GHz band meant
smalluse networks. For the most part, small
higher costs for 802.11a equipment
businesses and home networks have adopted and
·
a tighter broadcast radius (more access points
continue widely to use 802.11b. Reasons for the
required, hence more expensive to implement
continued popularity of 802.11b include:
over a larger area)
·
ratified in 1999, 802.11b networks are widely
·
poorer penetration through walls and floors.
implemented already In the wideopen spaces of the modern office building ·
satisfactory performance
used by medium to largesized companies, 802.11a
·
economical price
systems proved popular, particularly because:
·
a system designed to cope with the
·
higher as to be a deterrent
architectural space (lots of walls and floors
·
cost was less of an issue and not so much
between APs and STAs)
·
the architecture of the space suited the system
widely available, meaning that mobile
·
high performance was very important.
connectivity with this standard is easily One of the primary leading edge WLAN standards in
accessible.
use today is 802.11g (ratified in 2003). This standard This despite the drawback that 802.11b’s use of the
achieves highperformance by using the transmission
2.4 GHz band places the networks in a situation where
protocols (Orthogonal Frequency Division Multiplexing,
it must cope with interference from other devices
or OFDM) employed by 802.11a; however, it also uses
inhabiting the same band (Bluetooth devices, cordless
the 2.4 GHz band and underlying protocols of (Direct
phones, microwave ovens, for example).
Sequence Spread Spectrum, or DSSS), and is
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Feature constructed to be fully backwards compatible with
u Mapping WLAN into the future
802.11b equipment.
The future of WLAN performance has many aspects; in
As a result of this compatibility and price
this section, we describe some of the most important
competitiveness with 802.11a equipment, 802.11g
standards you should know about to understand the
solutions are swiftly achieving widespread
map of WLAN’s future directions.
acceptance. Home and business users are adopting the 802.11g components piecemeal, replacing their existing 802.11b. Vendors have made this transition
802.11e provides Quality of Service (QoS) As the need for highspeed, asynchronous data transfers increases, a standard for determining QoS in
especially easy with the falling prices of wireless routers (access points) and including WLAN capability
the network also becomes increasingly important. QoS is particularly important for realtime, streaming video
in a wider and wider range of computer offerings
and audio data. Ensuring consistent performance is
(desktops and laptops) and peripheral components
especially important for the viewer/listener. Whether for
(printers and scanners). Purchasers can buy an
a VoWLAN telephone call or a highdefinition video
802.11g AP that can support their existing 802.11b computers, knowing that sometime in the near future,
streamed wirelessly, it is important that the experience be seamless.
they can replace their computers at their natural obsolescence point with one that supports the higher
802.11e describes standards for APs and STAs to
performance AP. Finally, some vendors are offering
determine the quality of a wireless connection. APs and
802.11a/g dualmode devices. Dualmode APs and
STAs can then use this data to dynamically adjust their
STAs can support connections to both 802.11a and
connections to optimize behaviour. For example,
802.11g (and therefore 802.11b) networks, ensuring
detecting a high rate of errors in packet transmission,
wireless connectivity for all of today’s standards.
the system could slow down the attempted transfer rate and switch to a slower, but more effective, system
u Enhanced WLAN standards
of error checking and retransmission.
A number of vendors build on the existing 802.11
802.11h makes 802.11a safe in Europe
standards providing various kinds proprietary extensions to provide performance enhancements.
The 802.11h standard enhances 802.11a, adding
Atheros’ SuperG™ system is a useful example of this:
specifications for support of Transmission Power
SuperG™ components are fully compatible with
Control (TPC) and Dynamic Frequency Selection (DFS).
standard 802.11 components, but in combination with
These extensions ensure that 802.11h equipment can
other Super G™ components, they employ a series of
function in the 5 GHz band without interfering with European government and military communications.
techniques to offer much greater performance. For example, Super G™ components can provide
802.11i provides more robust security
datacompression in the networking hardware, so that
One of the knocks against the foundational 802.11
more data can be sent over the network in the same
systems was their attention to network security.
time. Super G™ systems can also bond two network
Complex configuration combined with relatively weak
channels together and use them both in a single AP
ciphering on the connections themselves resulted in a
STA connection, achieving twice the effective
widespread problem of insecure wireless LANs (for
bandwidth over plain 802.11g or 802.11a systems.
example, leading to the practice of “war driving”: roaming around with wireless equipment looking for
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Feature vulnerable wireless systems whose network connection resources could be appropriated). 802.11i describes fundamental standards for implementing robust network security on top of 802.11
WLAN Standard Description
networks, and will doubtless become important in the
802.11e
future. However, 802.11i will require adjustments to the wireless hardware; it cannot be implemented solely in
Quality of Service
software, and will therefore be phased in more slowly
802.11h
as people will have to replace their equipment.
802.11n offers another fivefactor increase in performance Although still in very early stages, 802.11n represents
Mitigation measures for 802.11a
802.11i Security
802.11n
the next generation in wireless networking. The shapers of this standard hope that this new standard will provide a basis for another fivefold increase in performance: effective throughput in excess of 100
Faster WLAN (throughput in excess of 100 Mbps)
Ratification Date
Anticipated Benefit
Pending (some time in 2005)
Improved voice and video over wireless (VoWLAN)
September 2003
Safer operation of 802.11a in European 5 GHz band.
June 2004
Enhanced wireless security
Currently only in proposal phase; expected ratification not yet sets
Greatly enhanced throughput to support rich media data
Mbps, with bandwidths over 200 Mbps. Current estimates place equipment in the field in a year or two, and this would mean a performance improvement of ©2004. Toshiba Europe GmbH. While Toshiba has made every effort at the time of publication to ensure the accuracy of the information provided herein, product specifications, configurations, prices, system/component/options availability are all subject to change without notice. For the most up-to-date product information about your computer, or to stay current with the various computer software or hardware options, visit Toshiba’s Web site at pcsupport.toshiba.com.
two orders of magnitude over the initial 802.11 standard in ten years’ time. Currently, discussions are still ongoing as to exactly what protocols and technologies will form 802.11n. However, everyone seems to be agreed that one technique used will be “Multiple Input, Multiple Output” (MIMO): the employment of multiple antennae and multiple channels to increase the effective bandwidth of a connection. One immediate and obvious disadvantage to MIMO systems is the increase in spectrum used which implies an increase in the number of components used, the complexity of the components, and the power those component use. Since WLAN and portable computing are a natural fit, vendors are working hard to improve MIMO systems to simplify them, reducing cost, complexity, and power consumption so that future generations of portable devices can continue to drive WLAN development as they have to this point.
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