wireless networking 802.11b. wireless networking 802.11b 802.11 1-2 mbps adopted june 1997

Wireless Networking802.11b

Wireless Networking 802.11b

• 802.11

• 1-2 Mbps

• Adopted June 1997


• September 1999 802.11b adopted

• 11Mbps

• Actual throughput under 5.5 Mbps

• Also called Wi-Fi

• Uses CSMA/CA


• Here are some illustrations of how a wireless network is put together

• http://www.homenethelp.com/802.11b/index.asp

http://www.homenethelp.com/802.11b/index.asp

http://www.homenethelp.com/802.11b/index.asp


• 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


SendingWorkstation

ReceivingWorkstation

RTS (including length)(Everybody hears it)

CTS

Data

ACK with CRC

Wireless MAC802.11X


Laptop A Laptop B Laptop C Laptop D

Hidden Node


• 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


• 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


• 5 MHz between channels

• 30 MHz bandwidth channels

• Spread spectrum allows overlap, but causes problems

• Compare with usual guard band


• 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


1 2 3 4 5 6 7 8 9 10 11

Channel Distribution


• 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


• 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

Wireless Networking 802.11bNIC


• 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


• 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.


• 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


• 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


• 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

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


• 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.


• 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


• 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.


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


• 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/

http://www.personaltelco.net/index.cgi/PortlandWirelessCommunities

http://www.personaltelco.net/index.cgi/PortlandWirelessCommunities

http://www.wififreespot.com/


• 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

http://www.internetnews.com/wireless/article.php/10799_2197391

http://www.internetnews.com/wireless/article.php/10799_2197391


• 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


• Commercial wireless hot spots are becoming more common, but profit seems to be elusive.

Directional Antenna 24 dB 8 degree

Directional Antenna12dB Gain


• 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


• 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

http://wifinetnews.com/

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


• A great source for information about 802.11 is http://www.netstumbler.com/


• 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


• 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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wireless networking 802.11b. wireless networking 802.11b 802.11 1-2 mbps adopted june 1997

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