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Chapter 11: Wireless LANs Business Data Communications, 5e Wireless LAN Applications • • • • LAN extension Cross-building interconnect Nomadic access Ad hoc networks Business Data Communications, 5e 2 LAN extension • Originally targeted to reduce cost of wiring, but new buildings now have sufficient wiring in place • Still useful in buildings where wiring is problematic – buildings with large open areas, – historical buildings with insufficient twisted pair – small offices wired LANs are not economical • Typically, a wireless LAN will be linked into a wired LAN on the same premises Business Data Communications, 5e 3 Single-Cell Wireless LAN Business Data Communications, 5e 4 Cross-building interconnect • Connect LANs in nearby buildings, be they wired or wireless LANs • Point-to-point wireless link is used between two buildings (e.g. two microwave or infrared transmitter/receiver units can be placed on the rooftops of two buildings within the line of sight of each other) • Devices are typically bridges or routers. Business Data Communications, 5e 5 Nomadic Access • Provides a wireless link between a LAN hub and a mobile data terminal (e.g. laptop computer) • Examples – Enable an employee returning from a trip to transfer data from a personal portable computer to a server in the office. – Access in an extended environment such as a campus or a business operating out of a cluster of buildings. – In both of these cases, users may wish access to the servers on a wired LAN from various locations Business Data Communications, 5e 6 Ad hoc networks • A peer-to-peer network (no centralized server) set up temporarily to meet some immediate need • For example, a group of employees, each with a laptop or palmtop computer, may convene in a conference room for a business or classroom meeting. The employees link their computers in a temporary network just for the duration of the meeting Business Data Communications, 5e 7 Wireless LAN Requirements • • • • • • • • • • Efficient throughput Support for multiple nodes Connection to backbone LAN Broad service area (~ 100-300m) Allows for reduced power consumption while not using the network (e.g. sleep mode) Transmission robustness and security Co-located network operation License-free operation Handoff/roaming Dynamic and automated addition, deletion, and relocation Business Data Communications, 5e 8 Wireless LAN Technology • Infrared (IR) LANs – Individual cells are limited to a single room, because infrared light does not penetrate opaque walls • Spread spectrum LANs – In most cases, these LANs operate in the ISM (Industrial, Scientific, and Medical) bands so that no FCC licensing is required for their use in the U.S. • Narrowband microwave – Do not use spread spectrum. Some of these products operate at frequencies that require FCC licensing, while others use one of the unlicensed ISM bands Business Data Communications, 5e 9 IEEE 802.11 Architecture Business Data Communications, 5e 10 IEEE 802.11 Services • • • • • Association Reassociation Disassociation Authentication Privacy Business Data Communications, 5e 11 IEEE 802.11 Medium Access Control • Reliable Data Delivery – Basic data transfer mechanism involves an exchange of two or four frames (data, ACK, and optional CTS/RTS) • Access Control – DFWMAC (distributed foundation wireless MAC) Business Data Communications, 5e 12 IEEE 802.11 Protocol Architecture Business Data Communications, 5e 13 IEEE 802.11 Physical Layer • 802.11 (1997) – MAC layer and three physical layer specifications; two 2.4-GHz band, one infrared, all operating at 1 and 2 Mbps • IEEE 802.11a (1999) – operates in the 5-GHz band at up to 54 Mbps • IEEE 802.11b (1999) – operates in the 2.4-Ghz band at 5.5 and 11 Mbps. • IEEE 802.g (2002) – extends IEEE 802.11b to higher data rates Business Data Communications, 5e 14 Original 802.11 Physical Media Definitions • Direct-sequence spread spectrum (DSSS) operating in the 2.4 GHz ISM band, at data rates of 1 Mbps and 2 Mbps • Frequency-hopping spread spectrum (FHSS) operating in the 2.4 GHz ISM band, at data rates of 1 Mbps and 2 Mbps • Infrared at 1 Mbps and 2 Mbps operating at a wavelength between 850 and 950 nm • All of the original 802.11 products were of limited utility because of the low data rates Business Data Communications, 5e 15 IEEE 802.11b • Extension of the IEEE 802.11 DSSS scheme, providing data rates of 5.5 and 11 Mbps (higher data rate is achieved with more complex modulation) • Apple Computer was first, with AirPort wireless networking, followed by other vendors • Wireless Ethernet Compatibility Alliance created to certify interoperability for 802.11b products Business Data Communications, 5e 16 Problems with 802.11 and 802.11b • Original 802.11 and 802.11b may interfere with other systems that operate in the 2.4GHz band – Bluetooth – HomeRF – other devices--including baby monitors and garage door openers • Limited data rate results in limited appeal Business Data Communications, 5e 17 Higher-Speed 802.11 Options • 802.11a – Uses 5-GHz band. – Uses orthogonal frequency division multiplexing (OFDM) rather than spread spectrum – Possible data rates are 6, 9, 12, 18, 24, 36, 48, and 54 Mbps • 802.11g – Higher-speed extension to IEEE 802.11b. – Combines physical layer encoding techniques used in 802.11a and 802.11b to provide service at a variety of data rates Business Data Communications, 5e 18 Bluetooth • Always-on, short-range radio hookup that resides on a microchip • Low-power short-range wireless standard for a wide range of devices • Uses 2.4-GHz band (available globally for unlicensed low-power uses) • Two Bluetooth devices within 10 m of each other can share up to 720 kbps of capacity Business Data Communications, 5e 19 Examples of Bluetooth Capability • Make calls from a wireless headset connected remotely to a cell phone • Eliminate cables linking computers to printers, keyboards, and the mouse • Hook up MP3 players wirelessly to other machines to download music • Set up home networks to remotely monitor air conditioning, appliances, and Internet surfing • Call home from a remote location to turn appliances on and off, set the alarm, and monitor activity. Business Data Communications, 5e 20 Bluetooth Applications • Up to eight devices can communicate in a small network called a piconet; ten of these can coexist in the same coverage range of the Bluetooth radio • Three general application areas – Data and voice access points – Cable replacement – Ad hoc networking Business Data Communications, 5e 21 Bluetooth Standards • Core Specifications – Describes layers of the protocol architecture, from radio interface to link control • Profile Specifications – Discusses the use of the technology defined in the core specifications to implement a particular usage model – General access profile specifies how the baseband architecture should be used between devices that implement one or multiple profiles – Other profiles fall into one of two categories: cable replacement or wireless audio Business Data Communications, 5e 22 Bluetooth Protocol Architecture • Core Protocols • Cable Replacement Protocol (RFCOMM) – presents a virtual serial port that is designed to make replacement of cable technologies as transparent as possible • Telephony Control Protocol (TCS BIN) – a bit-oriented protocol that defines the call control signaling for the establishment of speech and data calls between Bluetooth devices • Adopted Protocols Business Data Communications, 5e 23 Bluetooth Core Protocols • • • • Radio Baseband Link manager protocol (LMP) Logical link control and adaptation protocol (L2CAP) • Service discovery protocol (SDP) Business Data Communications, 5e 24 Bluetooth Adopted Protocols • • • • PPP TCP/UDP/IP OBEX WAE/WAP Business Data Communications, 5e 25 Bluetooth High-Priority Usage Models • • • • • • File Transfer Internet Bridge LAN Access Synchronization Three-in-one Phone Headset Business Data Communications, 5e 26 Piconets and Scatternets Business Data Communications, 5e 27