Chapter 11: Wireless LANs

Chapter 11: Wireless LANs

Business Data Communications, 5e


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Wireless LAN Applications

• LAN extension

• Cross-building interconnect

• Nomadic access

• Ad hoc networks


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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


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Single-Cell Wireless LAN


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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.


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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


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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


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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


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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


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IEEE 802.11 Architecture


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IEEE 802.11 Services

• Association

• Reassociation

• Disassociation

• Authentication

• Privacy


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IEEE 802.11Medium 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)


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IEEE 802.11Protocol Architecture


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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


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Original 802.11Physical 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


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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


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Problems with 802.11 and 802.11b

• Original 802.11 and 802.11b may interfere with other systems that operate in the 2.4-GHz band– Bluetooth– HomeRF– other devices--including baby monitors and

garage door openers

• Limited data rate results in limited appeal


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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


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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


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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.


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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


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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


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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


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Bluetooth Core Protocols

• Radio

• Baseband

• Link manager protocol (LMP)

• Logical link control and adaptation protocol (L2CAP)

• Service discovery protocol (SDP)


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Bluetooth Adopted Protocols

• PPP

• TCP/UDP/IP

• OBEX

• WAE/WAP


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Bluetooth High-Priority Usage Models

• File Transfer

• Internet Bridge

• LAN Access

• Synchronization

• Three-in-one Phone

• Headset


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Piconets and Scatternets

Documents

Chapter 11: Wireless LANs