Introduction
What is a wireless network? A technology that enables two or more entities to
communicate without network cabling
Different Wireless Networks
IrDA (Infrared Data Association) Uses beams in the infrared light spectrum
Bluetooth Uses 2.45 gigahertz radio waves, but emits weak
signals Limits distance to 10 feet, but travels through walls
HomeRF (SWAP) – developed by businesses 6 voice channels and 1 data channel Slow, and limited range, but cheap
Wireless Fidelity (Wi-Fi)
Essentially, this technology is a variation of the IEEE 802.11 specification known as 802.11b
Focuses on Direct-Sequence Spread Spectrum (DSSS)
High data rate (max of 11 Mbps) In the case of interference, speed drops in halves (11 Mbps
to 5.5 Mbps to 2 Mbps to 1 Mbps)
Wi-Fi
Advantages: Fast (11 Mbps) Reliable Long Range (up to 1000 ft outdoors, 400 ft indoors) Easy integration to wired networks Compatible with original 802.11 DSSS standard
Disadvantages: Speed may fluctuate
802.11a vs. 802.11b
Frequency 802.11b transfers at 2.4 gigahertz 802.11a transfers at 5 gigahertz
Coverage Distance 802.11b goes about 400 feet indoors 802.11a goes about 60 feet indoors
Need more access points to cover a location
Compatible to each other? Not yet.
ITL Wireless Equipment
2 Wireless Access Point Routers (with built in 4 port switch) Wired Equivalent Privacy (WEP) available
8 Wireless PCMCIA Cards4 ORiNOCO Gold 11 Mbps PC Cards4 3Com 11 Mbps PC Cards
Wireless Access Point
LINKSYS Model No. BEFW11S4 ver. 2 Supports
IEEE 802.3 (10BaseT) IEEE 802.3u (100BaseTX) IEEE 802.11b (Wireless)
Built-in router capability Obtains a Clarkson IP and uses DHCP
Built-in 4 port switch Fully-configurable through simple web interface
Wireless Cards
11Mbs 802.11b compatible 4 3Com Cards
Model No. 3CRWE62092A
4 ORiNOCO (Lucent) Cards Model No. 012352/G
Performance
Inside Range anywhere except in bathrooms Usually 11 Mbps connection
Outside Range To the SC lecture wing door (closest to ERC) Covers faculty lot next to ERC Half way to Rowley Connection slows as move away from access point
Summer Research
ProtocolMethod of Communication
Spoken Language Networked Programs (AIM) HTTP, Telnet, FTP
Two Main Protocols (Internet)
UDP (User Datagram Protocol) Fast, bare-bones, not reliable or friendly
Can lose data at any time
TCP (Transmission Control Protocol)Slower, many features, very reliable
All data will get to the other side
PCAttcp
Measuring tool for TCP and UDP Speed, Throughput, Time Amount of Data Sent vs. Amount Received
Our PCAttcp Controller
Enhanced UDP transfers Automated the entire process Created an easy way to compile results
and graphs using a spreadsheet for output Ran tests on various types of connections
References
http://www.howstuffworks.com/wireless-network.htm
http://www.80211-planet.com/columns/article/0,4000,1781_961181,00.html
http://www.80211-planet.com/columns/article/0,4000,1781_947661,00.html
http://www.pcausa.com
Different PCATTCP Trials
Same Host (same computer)
Same Switch (same lab)
LAN to LAN
(Clarkson to SUNY Potsdam)
LAN to Internet (Clarkson to a Roadrunner service)
Same LAN (inside Clarkson)
Note: LAN stands for “Local Area Network”
Bluetooth (cont)
spread-spectrum frequency hopping – a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis
When two Bluetooth devices come in contact with each other, they automatically conversate and form a personal-area network (PAN)
Spread spectrum
Spread-spectrum – data is sent in small pieces over a number of discrete
frequencies available for use at any time in the specified range
Frequency-hopping spread spectrum send a short burst of data, shift frequencies
(hop) and then send another short burst Since the FHSS devices that are communicating
agree on which frequencies to hop to, and use each frequency for a brief period of time (less than 400 milliseconds) before moving on, several independent FHSS networks can exist in the same physical area without interfering with each other
Direct-sequence spread spectrum splitting each byte of data into several
parts and sending them concurrently on different frequencies
DSSS uses a lot of the available bandwidth, about 22 megahertz (MHz).
The Basics
4 different types of wireless networks IrDA (Infrared Data Association)BluetoothHomeRF (SWAP)
“Shared Wireless Access Protocol”
WECA (Wi-Fi) “Wireless Ethernet Compatibility Alliance”
IrDA (Infrared Data Association)
Uses beams of light in the infrared spectrumRemote controls
Fairly reliable and low-cost Drawback: It is a “line-of-sight” technology
less interference Drawback: “one-to-one” technology
You can send data only between two things at once (but increased security?)
Bluetooth
The magic number: 2.45 gigahertz Radio-frequency also used by baby monitors,
garage door openers, and cordless phones
How do you avoid interference?Bluetooth sends weak signals of 1 milliwatt
Powerful cell phones use 3 watts
Bluetooth devices limited to 10 meters But they can go through walls better than others
HomeRF (SWAP)
Shared Wireless Access Protocol (SWAP) Developed by an alliance of businesses
6 voice channels and one data channel The data channel is the 802.11 wireless-Ethernet
specification by the IEEE
One drawback: SWAP can only be used with computers Printers and such need to be attached to a
computer and used as a resource
HomeRF (SWAP)
Advantages: Cheap, easy-to-install Allows multiple-networks in the same location Can encrypt data
Drawbacks: Not very fast (typically limited to 1 Mbps) Limited Range (75 to 125 ft) Physical obstructions (walls, large metal objects) cause huge
interference issues Difficult to integrate into existing wired networks