Download - Wireless Networking 802.11b. Wireless Networking 802.11b 802.11 1-2 Mbps Adopted June 1997
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Wireless Networking802.11b
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Wireless Networking 802.11b
• 802.11
• 1-2 Mbps
• Adopted June 1997
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Wireless Networking 802.11b
• September 1999 802.11b adopted
• 11Mbps
• Actual throughput under 5.5 Mbps
• Also called Wi-Fi
• Uses CSMA/CA
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Wireless Networking 802.11b
• Here are some illustrations of how a wireless network is put together
• http://www.homenethelp.com/802.11b/index.asp
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Wireless Networking 802.11b
• CSMA/CA mostly copies 802.3’s CSMA/CD
• Wireless can’t use collision detect because it can’t sense and transmit at the same time
• Uses a backoff timer and active handshaking- RTS/CTS
• Addresses “hidden node” problem
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Wireless Networking 802.11b
SendingWorkstation
ReceivingWorkstation
RTS (including length)(Everybody hears it)
CTS
Data
ACK with CRC
Wireless MAC802.11X
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Wireless Networking 802.11b
Laptop A Laptop B Laptop C Laptop D
Hidden Node
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Wireless Networking 802.11b
• Uses direct sequence spread spectrum in the 2.4 GHz band
• Go to http://www.wireless-nets.com/articles/whitepaper_spread.htm for a clearer understanding of DSSS and a comparison with frequency hopping spread spectrum
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Wireless Networking 802.11b
• Eleven 30Mhz overlapping channels available in the US.
• Europe uses channels 1-13
• Japan uses channel 14 only
• Is compatible with 802.11
• Falls back to lower speed with distance and noise
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Wireless Networking 802.11b
• 5 MHz between channels
• 30 MHz bandwidth channels
• Spread spectrum allows overlap, but causes problems
• Compare with usual guard band
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Wireless Networking 802.11b
• Channel 1 starts at 2.412 GHz and channels progress at 5MHz intervals.
• Ch2= 2.417GHz, Ch3=2.422GHz, etc.
• If you want no overlap, use Channels 1, 6, and 11
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Wireless Networking 802.11b
1 2 3 4 5 6 7 8 9 10 11
Channel Distribution
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Wireless Networking 802.11b
• 802.11 2 Mbps
• 802.11a 54 Mbps at 5 GHz (not WiFi)
• 802.11b 11 Mbps at 2.4 GHz (also WiFi)
• 802.11e adds QoS to a and b
• 802.11g 54 Mps at 2.4 GHz (meets WiFi)
• 802.11h is a European standard like g
• 802.11i provides added security options
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Wireless Networking 802.11b
• Hubs called Access Points
• They function as bridges, isolating the MAC layer functions
• NICs have radios and antennas
• APs are physically wired to the rest of the network
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Wireless Networking 802.11bNIC
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Wireless Networking 802.11b
• Range is 200 to 500 feet in an open office (claimed), 100 feet or less in closed offices
• Designed to be used with laptops• Adapters for desktop computers were largely
ineffective because of shielding problems • Site surveys determine antenna placement
http://www.wi-fiplanet.com/tutorials/article.php/2243911
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Wireless Networking 802.11b
• Wireless networks are designed by doing a Site Survey to measure signal strength.
• There are built-in tools with every AP, but a Spectrum Analyzer does a much better job
• Spectrum Analyzers can display all of the frequencies within the range you are going to use, but they’re several thousand dollars.
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Wireless Networking 802.11b
• Troubleshooting wireless networks can be difficult.
• Use network analyzers designed specifically for Wireless networks.
• Sniffer Wireless by Network Associates $10,000
• Airopeek by Wildpackets, $3500
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Wireless Networking 802.11b
• WEP is the security method (Wired Equivalent Privacy)
• Uses encryption. Weak, and causes a big impact on network speed
• Security is a major concern
• Biggest problem, most don’t implement any security at all
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Wireless Networking 802.11b
• Here’s a little article about how to use WEP and the alternatives.
• http://www.80211-planet.com/tutorials/article.php/2106281
• Here’s an article about the shortcomings of WEP. http://www.isaac.cs.berkeley.edu/isaac/wep-faq.html
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Wireless Networking 802.11
• 802.11a runs at 5 GHz range
• Not compatible with 802.11b
• 54 Mbps, but very short range
• Requires lots of power
• Not often implemented
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Wireless Networking 802.11
• 802.11a has not gained popularity because it’s expensive and incompatible with 802.11b. It also consumes a lot of power. However, at 54Mbps it’s fast.
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Wireless Networking 802.11
• 802.11g runs at 54 Mbps• 2.4 GHz band• Became a standard June 2003, shipping
since 2002• http://zdnet.com.com/2100-1105-
957229.html • Compatible with 802.11b• Also short range
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Wireless Networking 802.11
• 802.11g is slower than b in some tests
• Adding an 802.11b device to an 802.11g network slows the entire network.
• For commercial applications, you may want to wait for the hardware to stabilize before adoption.
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Wireless Networking 802.11
Prices, as of Fall 2003• 802.11b bridges cost about $70, cards $30
• 802.11b+ (non standard, 22Mbps, TI) cost about $100, cards $40
• 802.11G bridges cost about $140, cards $90
• Dual band 802.11a and g are ~$300
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Wireless Networking 802.11b
• Personal Telco Communities of Portland
• http://www.personaltelco.net/index.cgi/PortlandWirelessCommunities
• Privately funded, all volunteer
• Here is a national list of wireless “hot spots” http://www.wififreespot.com/
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Wireless Networking 802.11b
• Voice
• VoIP is moving ahead in the workplace, but the proliferation of 802.11 may begin to cut into the cellular telephone market as well.
• http://www.internetnews.com/wireless/article.php/10799_2197391
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Wireless Networking 802.11b
• London is planning to use 802.11 for their security cameras and for public workers like parking meter enforcers. Cisco is in this picture too.
• http://www.theregister.co.uk/content/59/30404.html
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Wireless Networking 802.11b
• Commercial wireless hot spots are becoming more common, but profit seems to be elusive.
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Directional Antenna 24 dB 8 degree
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Directional Antenna12dB Gain
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Wireless Networking 802.11b
• Overlapping WLANs is becoming a problem. • Service Set Identifiers, (SSID), are unique 32
character network identifiers that help make sure the proper network gets the data. The SSID is attached as a header to all packets. It is transmitted in the clear, so it doesn’t add to security.
• Also called the Network Name
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Wireless Networking 802.11b
• To stay current in this emerging technology, go to the WiFi Networking News at http://wifinetnews.com/
• Or 802.11 Planet at http://www.80211-planet.com/
• Check out a tutorial on 802.16. It has a range of 30 miles and a data rate of 70 Mbps
• http://networking.earthweb.com/netsp/article.php/3065261
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Wireless Networking Alternatives
• Check out a tutorial on 802.16 as an alternative to last mile coverage. It has a range of 30 miles and a data rate of 70 Mbps. It operates in from 10-66 GHz range.
• http://networking.earthweb.com/netsp/article.php/3065261
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Wireless Networking 802.11b
• A great source for information about 802.11 is http://www.netstumbler.com/
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Wireless Networking Alternatives
• CDMA2000 is a 3G wireless phone alternative. It operates at 144Kbps and is backward compatible with standard CDMA cell phones.
• Operates in the 800 MHz band
• Qualcomm chipset
• http://www.ericsson.com/cdmasystems/3gcdma2000.shtml
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Wireless Networking Alternatives
• Bluetooth was designed as an inexpensive, point-to-point wireless connectivity solution designed for low speed, very short range (30’) communication. It uses frequency hopping spread spectrum at low power in the unlicensed 2.4 GHz range.
• A comparison of 802.11b and Bluetooth is at:• http://www.wi-fiplanet.com/tutorials/article.php/
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