2.4GHz 11Mbps
unlicensed wireless computer networking and the IEEE 802.11 standard
from the UARC perspective in the year 2003
http://www.xmission.com/~c/uarc/ieee802
or http://www.qsl.net/kk7dv/uarc/ieee802
by Gary
Crum, [email protected]
last modified on
January 28, 2003
Introduction
This article is
about the radio-based wireless computer networking system defined by the
IEEE 802.11 standard. IEEE is the Institute for Electrical and
Electronics Engineers, and the use of equipment based on the 802.11b
standard is becoming a very inexpensive and popular way for computers to
communicate over radio, especially over short distances such as within
an office building. Access point routers and PCMCIA cards with
2.4GHz transceivers cost under $100 now. Data rates of wireless
802.11b networking can be 11Mbps (11000000 bits per second), which is
approximately that of the original wired ethernet 802.3 specification.
These rates are a good match for current use of Internet protocols
for computer networking.
IEEE 802.11b RF
transmission conforms to FCC Part 15 rules for unlicensed operation of
low-power devices, so this topic is somewhat analogous to discussing the
design and usage of cordless telephones. But, 802.11 allows large
numbers of computers to participate in a network, at data rates over a
megabit per second, so hopefully this topic is a little more interesting
than discussing cordless telephones.
The 802.11
standards are also given names such as Wi-Fi and AirPort. Existing
802.11b products use 2.4GHz spread-spectrum transceivers at power levels
less than 100 milliwatts for computer networking at data rates from 1 to
11 megabits per second. Newer specifications such as 802.11g
introduce higher data rates such as 54Mbps, and the use of radio
spectrum at 5GHz. Because of the popularity of 802.11 equipment,
the FCC is soliciting comments for future spectrum allocation for
similar specifications, and the ARRL has formed a working group for the
use of 802.11 specifications under Part 97 rules (with corresponding
modifications such as the possible use of higher power).
The timely
topics discussed below include:
- Links to web pages
with more information including specifications, reviews and analysis,
and engineering work in progress. This is the "core" content of
this article, since there is a great deal of information about 802.11 in
web pages.
- Internet access
from laptop computers at UARC meetings.
- A firsthand
throughput test result: 5Mbps FTP throughput using 802.11b -- 45%
efficiency.
Links
This is the core
content of this article; Computer networking, including 802.11, is
one topic on which there is a great deal of good information in web
pages.
http://www.palowireless.com/i802_11/tutorials.asp
A great collection of links, including tutorials on the subject of
802.11.
http://grouper.ieee.org/groups/802/11/
The IEEE site for 802.11, including standards documents.
http://www.intelligraphics.com/articles/80211_article.html
"Introduction to IEEE 802.11."
http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html
"Security of the WEP algorithm."
http://www2.arrl.org/hsmm/
An ARRL group working on 802.11 projects using Amateur Radio Part 97
rules.
http://home.satx.rr.com/wdubose/
A San Antonio radio club working on 802.11 projects.
http://www.turnpoint.net/wireless/has.html
http://www.oreillynet.com/cs/weblog/view/wlg/448
Homebrew 2.4GHz antennas used for 802.11, including the "Pringle's Can
Antenna."
http://slashdot.org/article.pl?sid=02/12/31/1943224&mode=thread
http://www.apple.com/airport/
New 802.11g hardware, with data rate of 54Mbps.
http://slashdot.org/article.pl?sid=02/12/22/2115207&mode=thread
http://www.linksys.com/splash/wsb24_splash.asp
http://www.hyperlinktech.com/web/amplifiers_2400.html
http://www.ydi.com/products/amp2441-amplifier.php
802.11b RF amplifier products.
http://www.tomshardware.com/network/20030117/index.html
http://www.techtv.com/freshgear/products/jump/0,23009,3395028,00.html
http://www.timhiggins.com/ProductGuides-Wireless.php
http://www.oreillynet.com/pub/a/wireless/2001/03/29/microwave.html
Some discussion of performance, price and
interference issues.
http://slashdot.org/article.pl?sid=02/12/12/1336258&mode=thread
http://hraunfoss.fcc.gov/edocs_public/attachmatch/DOC-229400A1.doc
"FCC
BEGINS INQUIRY REGARDING ADDITIONAL SPECTRUM FOR UNLICENSED DEVICES."
Internet access at UARC meetings
One fun
practical use of 802.11b wireless computer networking is the
availability of Internet access at UARC meetings, using laptop
computers. The University of Utah does have some 802.11b coverage
on campus, but it does not normally include the UARC meeting room, EMCB
101. Since there is a 10BaseT (wired) ethernet connection to the
campus network in the room, I have setup a temporary access point during
the last two UARC meetings, and I will probably continue to do so at the
UARC meetings I attend.
Since I
configure the network to be "public" and broadcast the W7SP network
name, the use of this network should be trivial; The setup can
even be completely automatic depending on network device driver
configuration. DHCP is used to assign a dynamic IP address along
with default gateway and nameserver information. These standards
are independent of operating system type, so this should certainly work
with common operating systems such as Linux, Windows, OS X and FreeBSD.
If there are any problems using the network, you are welcome to
contact me, Gary Crum, [email protected].
Throughput test
Here is the
result of a firsthand test of 802.11b throughput. I transferred a
10MB file from one computer named "d" to another named "b", in both
directions and over both an 802.11b wireless connection as well as a
10BaseT (wire) ethernet connection. The result was a throughput of
around 5Mbps over 802.11b, and a throughput of around 9Mbps over
10BaseT. This shows a much lower efficiency over 802.11b than over
ethernet (45% versus 90%), but the 5Mbps throughput over 802.11b is
still quite fast. In the case where the global Internet is being
accessed, the bottleneck limiting data throughput can often be a lower
speed link such as a 640Kbps DSL connection.
Incidently, another aspect of network performance is latency, and in
this area I have observed "ping" ICMP round-trip times down around 2
milliseconds, which is comparable to 10BaseT ethernet. Of course,
there are faster versions of wired ethernet; 100BaseT is a very
common standard providing 100Mbps data rates, and 1Gbps and 10Gbps
ethernet standards also exist. So, computer networking over copper
and fiber can be much faster than 802.11 RF data rates, but the original
10Mbps ethernet standard serves as a good baseline for performance
comparison.
Here is the raw data from my firsthand test:
wireless (11Mbps
802.11b link):
d->b
629 KB/s, 5.03
Mbps throughput, 45.7% efficiency
b->d
610 KB/s, 4.88
Mbps throughput, 44.4% efficiency
10BaseT ethernet:
d->b
1126 KB/s, 9.01
Mbps throughput, 90.1% efficiency
b->d
1117 KB/s, 8.94
Mbps throughput, 89.4% efficiency
Conclusion
IEEE 802.11 is a
popular specification for unlicensed wireless computer networking.
Whereas the bulk of amateur "packet" radio involved data rates of
1200 bits per second in the 2-meter band, 802.11 involves data rates
over 1000 times that in the 13-centimeter band. There is a lot of
online information about 802.11, and I hope this article is a convenient
survey of some current links. Certainly search engines such as http://www.google.com can be used to
find information with appropriate keywords such as "802.11" and "Wi-Fi".