Chapter 11 Wireless LANs Business Data Communications 6

Chapter 11: Wireless LANs Business Data Communications, 6 e

Wireless LAN Applications • • LAN extension Cross-building interconnect Nomadic access Ad hoc networks 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 3

Single-Cell Wireless LAN 4

Multiple-Cell Wireless LAN 5

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. 6

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 7

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 8

Wireless LAN Requirements • • • Efficient throughput Support for multiple nodes Connection to backbone LAN Broad service area (~ 100 -300 m) 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 9

Wireless LAN Technology • 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. • OFDM LANs – For higher speeds; this is known as orthogonal frequency division multiplexing and is superior to spread spectrum. • Infrared (IR) LANs – Individual cells are limited to a single room, because infrared light does not penetrate opaque walls 10

IEEE 802. 11 Architecture 11

IEEE 802. 11 Services Service Provider Used to Support Association Distribution system MSDU delivery Authentication Station LAN access and security Deauthentication Station LAN access and security Disassociation Distribution system MSDU delivery Integration Distribution system MSDU delivery Station MSDU delivery Privacy Station LAN access and security Reassociation Distribution system MSDU delivery 12

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) 13

IEEE 802. 11 Protocol Architecture 14

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. 11 a (1999) – operates in the 5 -GHz band at up to 54 Mbps • IEEE 802. 11 b (1999) – operates in the 2. 4 -Ghz band at 5. 5 and 11 Mbps. • IEEE 802. g (2002) - operates in the 2. 4 -Ghz band 54 Mbps • IEEE 802. n – operates in the 2. 4 -Ghz band hundreds of Mbps 15

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 16

IEEE 802. 11 b • 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 Air. Port wireless networking, followed by other vendors • Wireless Ethernet Compatibility Alliance created to certify interoperability for 802. 11 b products 17

Problems with 802. 11 and 802. 11 b • Original 802. 11 and 802. 11 b may interfere with other systems that operate in the 2. 4 GHz band – Bluetooth – Home. RF – other devices--including baby monitors and garage door openers • Limited data rate results in limited appeal 18

Higher-Speed 802. 11 Options • 802. 11 a – 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. 11 g – Higher-speed extension to IEEE 802. 11 b. – Combines physical layer encoding techniques used in 802. 11 a and 802. 11 b to provide service at a variety of data rates 19

Higher-Speed 802. 11 Options • 802. 11 n – Uses both the 2. 4 GHz and 5 -GHz band. – Improves data transmission and effective throughput – Uses Multiple Input Multiple Output (MIMO) antenna architecture – Uses channel bonding , allowing for 2 X as many subchannels, doubling the transmission rate – Uses orthogonal frequency division multiplexing (OFDM) rather than spread spectrum – Aggregates multiple MAC frames into a single block for transmission 20

IEEE 802. 11 Security Considerations • Workstations are not physically connected to the network • Privacy concerns since any station in range can receive data • Wi_Fi Protected Access (WPA) used to address these concerns 21