Business data communications 5e by stallings chapter 11

Chapter 11: Wireless LANs Business Data Communications, 5e... Nomadic Access• Provides a wireless link between a LAN hub and a mobile data terminal e.g.. IEEE 802.11 Medium Access Contro

Chapter 11:

Wireless LANs

Business Data Communications, 5e

Wireless LAN Applications

• LAN extension

• Cross-building interconnect

• Nomadic access

• Ad hoc networks

– 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

Single-Cell Wireless LAN

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

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

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

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

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

IEEE 802.11 Architecture

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)

IEEE 802.11 Protocol Architecture

IEEE 802.11 Physical Layer

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

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

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

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

• 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

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.

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

– 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

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

Bluetooth Core Protocols

• Radio

• Baseband

• Link manager protocol (LMP)

• Logical link control and adaptation

protocol (L2CAP)

• Service discovery protocol (SDP)

Bluetooth Adopted Protocols

• PPP

• TCP/UDP/IP

• OBEX

• WAE/WAP

Bluetooth High-Priority Usage Models

Piconets and Scatternets