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Wireless Networks. Wireless Networking: Intangible Media. Depend on transmission at some kind of electromagnetic frequency, typically radio frequency, through the atmosphere to carry data transmissions from one networked device to another
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Wireless Networking: Intangible Media • Depend on transmission at some kind of electromagnetic frequency, typically radio frequency, through the atmosphere to carry data transmissions from one networked device to another • Appear most frequently in conjunction with wired networks
Capabilities of the Wireless World • Create temporary connections to existing wired networks • Establish back-up or contingency connectivity for existing wired networks • Extend a network’s span beyond the reach of wire- or fiber-optic-based cabling • Permit certain users to roam with their machines, within certain limits
Commercial Applications for Wireless Networking • Ready access to data for mobile professionals • Delivery of network access into isolated facilities • Access in environments in which layout and settings change constantly • Improved customer services in busy areas, e.g, 70% of Starbuck’s 4,000 stores were equipped with wireless LAN by 2003 • Network connectivity in facilities where in-wall wiring would be impossible to install or prohibitively expensive
Cities with Wireless Internet • Seoul • Taipei • Singapore • Hong Kong (being planned) • Mexico City (being planned) • Some cities in USA are given free wireless internet access (see http://ilovefreewifi.com/)
Questions • What are the major challenges to wireless networking when compared to wired networking?
Types of Wireless Networks • Local area networks (LANs) • Extended LANs • Mobile computing • Worldwide wireless LAN shipments is expected to grow from 1.7 million in 1999 to almost 12 million by 2004
Wireless LAN Applications • Still necessary to attach a network interface to a computer, but the interface attaches to an antenna and an emitter rather than to a cable • Requires an access point device (connected to a wired network) to bridge wireless components and the wired network
How Do WLANs Work? • Sending signals through the air between devices • Signal can be transmitted sometimes up to 1,000 feet • Dependent on the signal nature, a signal may be able to pass through nonmetal wall and barriers • WLAN cards are needed
Modes of communication • Device-to-device interaction • Access point (AP) connections to a wired LAN • APs are stationary devices usually installed in a ceiling (which is analogous to a tower in a cellular phone network)
Wireless LAN Transmission • Most common frequencies used • Radio: 10 KHz to 1 GHz • Microwave: 1 GHz to 500 GHz • Infrared: 500 GHz to 1 THz • Primary technologies used • Infrared • Laser • Narrowband, single-frequency radio • Spread-spectrum radio (most common)
Broadcast Medium Principles • Inverse relationship between frequency and distance (high frequency short distance) (when transmission power is ignored) • Direct relationship between frequency and data transfer rate and bandwidth • Higher-frequency technologies often use tight-beam broadcasts and require a clear line of sight between sender and receiver to ensure correct delivery
Infrared LAN Technologies • Use infrared light beams to send signals between pairs of devices • Have high frequency and bandwidth; work well for LAN applications • Require a line of sight between sender and receiver • Less reliable than the radio technologies
Kinds of Infrared LANs • Line-of-sight networks • Reflective wireless networks • Via a central hub (or transceiver) • Scatter infrared networks • Bounce transmission off walls and ceilings • Distance limited to ~30m • Tend to have a slow transmission • Broadband optical telepoint networks • Fastest of its kind
Laser-based LAN Technologies • Require a clear line of sight between sender and receiver • Devices are subject to many of the same limitations as infrared but are not as subject to interference from visible light sources; however, laser is much more sensitive to outside disturbances than infrared
Narrow-band, Single-frequency Radio LAN Technologies • Use low-powered, two-way radio communications • Require no line-of-sight between sender and receiver • Broadcast range is 5000 square meters and cannot go through steel or load-bearing walls
Spread-spectrum LAN Technologies • Address weaknesses of single-frequency communications • Use multiple frequencies simultaneously; improve reliability and reduce susceptibility to interference • Make eavesdropping more difficult • Two main kinds • Frequency-hopping • Direct-sequence modulation
Frequency-hopping Spread-spectrum • Frequency is divided into hops • Blocks of data are transmitted on different frequencies known to the intended receiver. The receiver gets the signals and puts the block in the right order. • Provides built-in security (but not error detection) because the frequencies hop around at undetermined times and frequencies and cannot be easily determined by potential hackers
Direct-sequence Modulation • Breaks a message into bits and modulates each bit by a redundant bit pattern (known as chip or chipping code) before each information bit is transmitted • Tends to use bandwidth inefficiently but transmissions are more reliable and secured • Chip may be used for error detection and correction purpose
Direct-sequence Modulation Example • Information bits to be transmitted • 1011 • Chipping code • 010 • Transmitted bits (modulo-2 addition) • 101010101101
Wireless Extended LAN Technologies • Wireless bridge • A pair of devices, typically narrow-band and tight beam, that relay network traffic from one location to another • Available using spread-spectrum radio, infrared, and laser technologies • Can span distances from hundreds of meters up to 25 miles
Microwave Networking Technologies • Can deliver higher transmission rates than radio-based systems • Transmitters and receivers must share a common, clear line of sight • Usually require FCC approval and licensing • More expensive than radio systems • Two types • Terrestrial • Satellite
Terrestrial Microwave • Uses line-of-sight communication between pairs of Earth-based transmitters and receivers to relay information • Expensive; usually positioned well above ground level
Satellite Microwave • Uses geosynchronous satellites to send and relay signals between sender and receiver • Usually leased for an exorbitant fee
Security issues (1/4) • Adopt an encryption mechanism • If possible, use Wi-Fi Protected Access (WPA) and WPA2 instead of wired Equivalent Privacy (WEP) • All clients and access points are to be configured with the same key for encryption and decryption (manually as there is no key management protocol)
Security issues (2/4) • Use a Service Set Identifier (SSID) • a case-sensitive string attached to all packets on a wireless network to identify each packet as part of that network • all wireless devices attempting to communicate with each other must share the same SSID • never use the default SSID given by the manufacturer • turn off SSID broadcasting
Security issues (3/4) • MAC addressing filtering • A list of client computers’ MAC addresses can be inputted into an Access Point so that only those computers will be allowed access. • This is a good method of security but only recommended for smaller networks as there is a high rate of work involved in entering each MAC address into every Access Point.
Security issues (4/4) • Restrict unnecessary traffic • If your router is equipped with a firewall, turn it on. • Change the default administrator password • Protect your PC with antivirus software and apply any new system patches timely
Summary (1/2) • Wireless networking • Provides cable-free LAN access • Extends span of LANs • Provides WAN links • Supports mobile computing needs • Uses a variety of electromagnetic frequency ranges • Narrow-band and spread-spectrum radio • Microwave • Infrared • Laser transmission
Summary (2/2) • Common security approaches • Wired equivalent privacy • Service set identifier • MAC address filtering
