Scope
The scope of this paper is to research through the IEEE 802.11
wireless standards identifying range,
security, throughput, costs and the future prospects of this
technology. Since the number of specifications, ratified and draft
amendments to the 802.11 Prime is big, we will not include those that
are addressed to manufacturers, and we will cover 802.11 a/b/g/n
specifications (The book of wireless, p.32) referring to the rest
necessary amendments for the security section only.
Introduction
IEEE 802.11 Wireless Standard defines the technology used for local
area network (LAN) communications, using radio frequencies (RF).
Institute of Electrical and Electronics Engineers (IEEE) is the
professional society that creates and Maintains standards that we use
for communications (CWNA, p. 154). The original IEEE 802.11 standard
was published in
1999 and reaffirmed in 2003. The latest revision of the standard was
published in 2007. The publication date of the specifications to be
covered in this paper, are shown below:
- IEEE Std 802.11-1999 (R2003)
- IEEE Std 802.11a-1999
- IEEE Std 802.11b-1999
- IEEE Std 802.11g-2003
- IEEE Std 802.11n-2009
(IEEE Std 802.11™-2007 Revision of IEEE Std 802.11-1999)
“IEEE specifically defines 802.11 technologies at the Physical
layer and MAC sublayer of the Data-Link layer. By design, the 802.11
standard does not address the upper layers of the OSI model, although
there are interactions between the 802.11 MAC layer and the upper
layers for parameters such as quality of service”. (CWMA, p.155)
A brief comparison and overview of the IEEE 802.11 Legacy/a/b/g/n is
shown below, in order to be used as a visual reference thoughout the
rest of the paper.
|
|
802.11 Legacy |
802.11 a |
802.11 b |
802.11 g |
802.11 n |
|---|---|---|---|---|---|
|
Frequency
|
2.4 GHz ISM band
|
5 GHz UNII-1, UNII-2 and UNII-3 bands
|
2.4 GHz ISM band
|
2.4 GHz ISM band
|
2.4 GHz ISM band – 5 GHz UNII band
|
|
Spread Spectrum Technology
|
FHSS or DSSS
|
OFDM
|
HR-DSSS
(PBCC is optional)
|
ERP:ERP-OFDM and
ERP-DSSS.CKK are mandatory
ERP-PBCC and DSSS-OFDM are optional
|
HT MIMO with OFDM.
HR-DSSS, OFDM, ERP.
|
|
Data Rates
|
1, 2 Mbps
|
6,12 and 24 Mbps are madnatory.
Also supported are 9, 18, 36, 48 and 54 Mbps.
|
DSSS:1, 2Mbps
HR-DSSS:5.5 and 11 Mbps
|
ERP-DSSS/CCK: 1,2, 5.5 and 11 Mbps
ERP-OFDM:6, 12 and 24 Mbps are mandatory
Also supported are 9, 18, 36, 48 and 54 Mbps.
ERP-PBCC:22 and 33 Mbps
|
Data rates vary from 6,5 Mbps to 600 Mbps due to
different type of modulation and Channel width (20/40MHz)
(IEEE 802.11 n-2009 pages 345-354)
|
|
Backward Compatibility
|
N/A
|
None
|
802.11 DSSS only
|
802.11 HR-DSSS and 802.11 DSSS
|
|
(CWNA, p. 162, p.590 and IEEE 802.11 n-2009 pages 345-354)
Range
The coverage area of the standards above is related to
the part of the spectrum they operate, the Radio Frequency behaviors
of absorption, reflection, attenuation and multipath.
802.11a and 802.11n operate in 5 GHz Unlicensed National
Information Infrastructure (UNII-USA) spectrum. On the other hand
the 802.11 b/g/n (when operating in 2,4 GHz) operate in 2,4 GHz
Industrial, Scientific and Medical (ISM) band. This means that 802.11
b/g/n (when operating in 2,4 GHz) suffer from less attenuation
compared to the 5 GHz band, because of the longer wavelength. This
allows signal to reach theoretically further. Table 2 shows the
Attenuation Comparison of Materials for 2,4 GHz.
|
Material |
2,4 GHz |
|---|---|
|
Foundation wall
|
-15dB
|
|
Brick, concrete, concrete blocks
|
-15dB
|
|
Elevator or metal obstacle
|
-10dB
|
|
Metal Rack
|
-6dB
|
|
Drywall of Sheetrock
|
-3dB
|
|
Nontinted glass windows or door
|
-3dB
|
|
Wood door
|
-3dB
|
|
Cubicle wall
|
-2dB
|
Table 2. Attenuation Comparison of Materials (CWNA,
p.47)
Moreover
under the consideration that wireless networks are mostly used
indoors, the RF behavior of absorption affects the coverage area.
Further the 2,4 GHz band is not used exclusively by the 802.11
standards wireless devices, but it is used by other home appliances,
as well as bluetooth devices. This means
that there is danger of interference, since the channels may be
already used, leading to loss of packets, which need to be resent for
transmission to be acknowledged. This does not apply to the 5GHz
band.
In
addition, 802.11n standard multiple input-multiple output (MIMO)
amendment to the standard allows it to take advantage of the
reflection of waves in furniture, halls, corridors etc converting the
multipath RF behavior form enemy to asset.
Outcome:
802.11
b/g/n (operating in the 2,4 GHz band) provide a larger coverage area
comparing them to the ones operating under the 5 GHz band. They are
even more effective when we have knowledge about the surrounding
transmitting devices (home appliances and neighbor wireless devices)
and the channels they operate. Channels 1-6-11 are recommended for
the 2,4 GHz band because they do not interfere with one another. (The
book of wireless, p.35) A practical coverage area for these standards
should be estimated approximately to 17m (~50ft) (Wireless Networks
for Dummies, p.30)
Security
802.11a/b
standards where published
in 1999 using the Wired Equivalent Privacy (WEP) as their
cryptographic solution for security. WEP provides authentication,
ensuring that information is accessible only to those authorized to
have access and encryption, meaning that the data is intact and that
no one has tampered with it, with 40 to 128 bit key length. It uses
RC4 algorithm for confidentiality and CRC algorithm for integrity.
CRC-32 is a hash function whose goal is to prevent accidental
changes, but since no authentication exists for the AP any
intentional intervention from an intruder is not detected. This makes
WEP key insecure for replay attacks. Replays attacks are repeat
transmission of valid data, previously intercepted by a valid user by
a man-in-the-middle during a conversation. Replay attacks aim in
gaining authentication credentials or session initialization
messages.
Table 4.
WEP key basic vulnerabilities
|
1 |
AP
are not authenticated |
|
2 |
There
are patterns in the final key production making it predictable |
|
3 |
Key
is the same for all mobile nodes |
|
4 |
Intentional
intervention in packets is not detectable |
|
5 |
Keys
are not updated automatically |
Result
of the weaknesses above was the WPA (1.0 with TKIP and WPA 2 keys
introduced with 802.11i in July 2004.
Even
though compatibility issues have been taken under consideration,
firmware updates are required to old devices, in order to implement
the new directives of the 802.11i standard. However, such updates are
not always an option, narrowing the security level.
Finally,
802.11 g/n standards have protection mechanisms that implement the
backward compatibility with older devices, allowing Access Points to
support different standards at the same time.
Throughput
Data rates for each of the standards are shown in Table
1. Even though these data rates are the theoretical speed they can
give us a visual comparison for the throughput taking in
consideration that the “aggregate throughput is typically one-half
or less of the available data rate speed” (CWNA, p.156).
Moreover, it must be stated that protection mechanisms
that for compatibility issues, allows the 802.11 b/g/n to coexist at
the same time affects the throughput as well. “An 802.11 b/g access
point with a data rate of 54 Mbps might see a decrease in aggregate
throughput from 20Mbps down to as little as 8 Mbps the instant the
protection mechanism is enabled.” (CWNA, p. 161)
Costs - Future prospects of this technology
Devices supporting IEEE 802.11b were the first to be
widely accepted in market. Their success is shown in by the backward
compatible standards IEEE 802.11g/n. It is obvious that new devices
are more expensive and even though new standards offer improvements,
they come with a price as well. The upgrade to new devices for
companies depends on the value for money they offer and according to
certain needs they cover, since it is part of a bigger plan that is
affected by the current infrastructure.
Taking under consideration different scenarios and
different variables such as compatibility, battery consumption for
smartphones-tablets and data rates, devices that support different
802.11 standard can find their place in the market. For example
802.11b offers lower power consumption, but 802.11n devices,
implement a new technology that offers more and better services with
backward compatibility.
Trends so far have shown that it takes a while for a
standard to gain its part in the market after it has been published.
This gives time to older devices, while offering more time for
testing and debugging the new ones.
Conclusion
Since there is no given scenario to which we must adapt
our comparisons and provide a solid direction towards which standard
is better, it must be stated that each IEEE 802.11 standard can be
presented as the best solution according to certain given facts. We
should filter our needs through the basic guidelines above, in order
to reach to a conclusion.
References
- The book of Wireless 2nd Edition, John Ross, No Strach Press, 2008
- CWNA, Certified Wireless Network Administrator, Official Study Guide, David Coleman, David Westcott, Wiley 2009
- IEEE Std 802.11™-2007 (Revision of IEEE Std 802.11-1999) as found at http://standards.ieee.org/getieee802/download/802.11-2007.pdf on 30 Oct 2011.
- IEEE Std 802.11n™-2009 (Amendment to IEEE Std 802.11™-2007 as amended by IEEE Std 802.11k™ -2008, IEEE Std 802.11r™-2008, IEEE Std 802.11y™-2008, and IEEE Std 802.11w™-2009) as found at http://standards.ieee.org/getieee802/download/802.11n-2009.pdf on 30 Oct 2011.
- Wireless networks for Dummies, Barry D. Lweis, Peter T. Davis, Wiley, 2004
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