Business data communications 5e by stallings chapter 11

Chapter 11: Wireless LANs Business Data Communications, 5e Wireless LAN Applications • • • • LAN extension Cross-building interconnect Nomadic access Ad hoc networks Business Data Commun ications, 5e 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 Commun ications, 5e Single-Cell Wireless LAN Business Data Commun ications, 5e 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 Commun ications, 5e 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 Commun ications, 5e 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 Commun ications, 5e 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 Commun ications, 5e 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 Commun ications, 5e IEEE 802.11 Architecture Business Data Commun ications, 5e 10 IEEE 802.11 Protocol Architecture Business Data Commun ications, 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 and 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 Commun ications, 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 Mbps and Mbps • Frequency-hopping spread spectrum (FHSS) operating in the 2.4 GHz ISM band, at data rates of Mbps and Mbps • Infrared at Mbps and 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 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 Commun ications, 5e 23 Bluetooth Core Protocols • • • • Radio Baseband Link manager protocol (LMP) Logical link control and adaptation protocol (L2CAP) • Service discovery protocol (SDP) Business Data Commun ications, 5e 24 Bluetooth Adopted Protocols • • • • PPP TCP/UDP/IP OBEX WAE/WAP Business Data Commun ications, 5e 25 Bluetooth High-Priority Usage Models • • • • • • File Transfer Internet Bridge LAN Access Synchronization Three-in-one Phone Headset Business Data Commun ications, 5e 26 Piconets and Scatternets Business Data Commun ications, 5e 27 ... foundation wireless MAC) Business Data Commun ications, 5e 12 IEEE 802 .11 Protocol Architecture Business Data Commun ications, 5e 13 IEEE 802 .11 Physical Layer • 802 .11 (1997) – MAC layer and... Authentication Privacy Business Data Commun ications, 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,... others use one of the unlicensed ISM bands Business Data Commun ications, 5e IEEE 802 .11 Architecture Business Data Commun ications, 5e 10 IEEE 802 .11 Services • • • • • Association Reassociation