Business Data Communications and Networking 10 th Edition

Business Data Communications and Networking 10 th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons, Inc Dwayne Whitten, D. B. A Mays Business School Texas A&M University Copyright 2010 John Wiley & Sons, Inc 7 -1

Chapter 7 Wireless Local Area Networks Copyright 2010 John Wiley & Sons, Inc 7

Chapter 7: Outline • Introduction • WLAN Components • WI-FI • WIMAX • Bluetooth • Best practice WLAN Design • Improving WLAN Performance • Management Implications Copyright 2010 John Wiley & Sons, Inc 7 -3

Wireless LANs (WLANs) • Use radio or infrared frequencies to transmit signals through the air (instead of cables) • Basic Categories – Use of Radio frequencies (FOCUS of this chapter) • 802. 1 x family of standards (aka, Wi-Fi) – Use of Infrared frequencies (Optical transmission) • Wi-Fi grown in popularity – Eliminates cabling – Facilitates network access from a variety of locations – Facilitates for mobile workers (as in a hospital) – Used in 90 percent of companies Copyright 2010 John Wiley & Sons, Inc 7 -4

Principal WLANs Technologies • WI-FI – IEEE 802. 11 b • Standardization started after. 11 a, but finished before, more commonly used than. 11 a – IEEE 802. 11 a • First attempt to standardization of WLANs; more complicated than. 11 b – IEEE 802. 11 g • WIMAX • Bluetooth – Also an IEEE standard 802. 15 Copyright 2010 John Wiley & Sons, Inc 7 -5

Components of WLANs • Network Interface Cards – Many laptops come with WLAN cards built in – Also available as USB cards – About 100 -300 feet max transmission range • Access Points (APs) – Used instead of hubs; act as a repeater • Must hear all computers in WLAN • Some use power over Ethernet (POE) Copyright 2010 John Wiley & Sons, Inc 7 -6

Antennas used in WLANs • Omni directional antennas – Transmit in all directions simultaneously – Used on most WLANs • Dipole antenna (rubber duck) – Transmits in all direction (vertical, horizontal, up, down) • Directional antennas – Project signal only in one direction • Focused area; stronger signal; farther ranges – Most often used on inside of an exterior wall • To reduce the security issue – A potential problem with WLANs – Antennas can be made from Pringles, etc. cans and are called “Cantennas” Copyright 2010 John Wiley & Sons, Inc 7 -7

Types of Antennas Copyright 2010 John Wiley & Sons, Inc 7 -8

WLAN Radio Frequencies • WLANs use radio transmissions to send data between the NIC and the AP • Most countries use the 2. 4 GHz range and the 5 GHz range • The larger the frequency range, the greater the bandwidth, or capacity • It is important to ensure that APs do not conflict with each other • Therefore, each AP is set up to transmit on a different part of the 2. 4 or 5 GHz frequency range Copyright 2010 John Wiley & Sons, Inc 7 -9

More on the APs and NICs • 3 separate channels available for 802. 11 b – All devices using an AP must use the same channel • WLAN functions as a shared media LAN – Reduces the interference – Users can roam from AP to AP • Initially NIC selects a channel (thus an AP) – Based on “strength of signal” from an AP • During roaming, if NIC sees another AP with a stronger signal, attaches itself to this AP • Usually a set of APs installed to provide geographical coverage and meet traffic needs – NICs selects a less busy channel if its current channel becomes busy (too many users) Copyright 2010 John Wiley & Sons, Inc 7 - 10

A WLAN Using Different Channels Copyright 2010 John Wiley & Sons, Inc 7 -

WLAN Topology Same as Ethernet • Physical star • Logical bus Use the same radio frequencies, so take turns using the network 10 Base-T or 100 Base-T Uses a NIC that transmits radio signals to the AP A wireless Access Point (AP) connected into an Ethernet Switch Copyright 2010 John Wiley & Sons, Inc 7 - 12

WLAN Media Access Control • Uses CSMA/CA – CA collision avoidance – A station waits until another station is finished transmitting plus an additional random period of time before sending anything • May use two MAC techniques simultaneously – Distributed Coordination Function (DCF) • Also called “Physical Carrier Sense Method” – Point Coordination Function (PCF) • Also called “Virtual Carrier Sense Method” • Optional: (can be set as “always”, “never”, or “just for certain frame sizes”) Copyright 2010 John Wiley & Sons, Inc 7 - 13

Distributed Coordination Function • Relies on the ability of computers to physically listen before they transmit – When a node wants to send a message: • First listens to make sure that the transmitting node has finished, then • Waits a period of time longer • Each frame is sent using stop-and-wait ARQ – By waiting, the listening node can detect that the sending node has finished and – Can then begin sending its transmission – ACK/NAK sent a short time after a frame is received, – Message frames are sent a somewhat longer time after (ensuring that no collision will occur) Copyright 2010 John Wiley & Sons, Inc 7 - 14

Point Coordination Function (PCF) • Solves Hidden Node problem – Two computers can not detect each other’s signals • A computer is near the transmission limits of the AP at one end another computer is near the transmission limits at the other end of the AP’s range – Physical carrier sense method will not work • Solution – First send a Request To Send (RTS) signal to the AP • Request to reserve the circuit and duration – AP responds with a Clear To Send (CTS) signal, • Also indicates duration that the channel is reserved – Computer wishing to send begins transmitting Copyright 2010 John Wiley & Sons, Inc 7 - 15

Types of Wi-Fi • IEEE 802. 11 a • IEEE 802. 11 b •

IEEE 802. 11 a • Operates in a 5 GHz frequency range • Total bandwidth is 300 MHz – Faster data rates possible: Up to 54 Mbps • 6, 9, 12, 18, 24, 36, 48, and 54 Mbps • Uses the same topology as. 11 b • Reduced range because of higher speed – 50 meters ( 150 feet) – Highest speed achievable within 15 meter Copyright 2010 John Wiley & Sons, Inc 7 - 17

IEEE 802. 11 b • Moderate speed networking in the 2. 4 GHz range • Three channels for indoor use in the US, more or less in other parts of the world • Each channel has a maximum data rate of 11 Mbps, for users close to the center of the WLAN 6 -11 Mbps is the norm • 802. 11 b suffers less attenuation than 802. 11 a • Designed to connect easily to Ethernet Copyright 2010 John Wiley & Sons, Inc 7 - 18

IEEE 802. 11 g • Designed to combine advantages of 802. 11 a and 802. 11 b – Offers higher data rates (up to 54 Mbps) in 2. 4 GHz band (as in. 11 b) with longer ranges – Backward compatible with 802. 11 b • . 11 b devices can interoperate with. 11 g APs • Price to pay: when an. 11 g AP detects an. 11 b device, it prohibits. 11 g devices from operating at higher speeds • Uses the same topology as. 11 b – Provides 3 -6 channels (depending on configuration) – 54 Mbps rate obtained within 50 meter range Copyright 2010 John Wiley & Sons, Inc 7 - 19

802. 11 g Media Access Control • Almost the same media and error control protocols as. 11 b – Similar packet layout, except • Preambles and headers transmitted at slower speeds (up to a maximum of 11 Mbps) • Payload transmitted at higher speeds (up to a max of 54 Mbps) • Data Transmission in the Physical Layer – Same techniques in. 11 a and. 11 b Copyright 2010 John Wiley & Sons, Inc 7 - 20

IEEE 802. 11 n • Standard under development • Goal to provide high speed wireless networking • Uses both the 2. 4 and 5 GHz frequency ranges simultaneously • Current drafts propose speeds of 250 -300 Mbps, but 100 more likely • Backward compatible with a, b, and g Copyright 2010 John Wiley & Sons, Inc 7 - 21

WI-FI as Public Internet Access • Wi-Fi was intended to be used for indoor mobile wireless access • Many providers have in airports and malls and other public places • Political issues, not technical, interfere with the large scale provision of Wi-Fi • Being offered by some towns as well as carriers Copyright 2010 John Wiley & Sons, Inc 7 - 22

WIMAX • Commercial name for family of IEEE 802. 16 standards • Two primary types: Fixed and mobile • Logical and physical topology same as 802. 11 and shared Ethernet • Uses controlled access with a version of 802. 11 point coordination function • Two types: – 802. 16 d – 802. 16 e Copyright 2010 John Wiley & Sons, Inc 7 - 23

IEEE 802. 16 d • Fixed point wireless access • Antennas 12 -18 inches • One central access point allows connection to fixed networks • Ideal – 70 Mbps and 30 mile range • Expect – 2 Mbps and 5 mile range Copyright 2010 John Wiley & Sons, Inc 7 - 24

IEEE 802. 16 e • For mobile users • Multiple channels, each with 28 Mbps • Effective rate of 5 Mbps • Effective range of 6 miles with line of sight • Effective range of 2½ miles without line of sight Copyright 2010 John Wiley & Sons, Inc 7 - 25

Issues to consider with WIMAX • WIMAX is a competitor to public access Wi -Fi and cellular phone service • WIMAX is incompatible with both • Has an effective range that offers benefits • Has controlled access, version of PDF • Considerably more distance covered with WIMAX over Wi-Fi Copyright 2010 John Wiley & Sons, Inc 7 - 26

Bluetooth (IEEE 802. 15) • A standard for Wireless Personal Area Network (WPAN) – Provides networking in a very small area • Up to 10 meters (current generation) • Up to 100 meters (next generation) – Includes small (1/3 of an inch square) and cheap devices designed to • Replace short distance cabling between devices – Keyboards, mouse, handsets, PDAs, etc – Provides a basic data rate of 1 Mbps • Can be divided into several voice and data channels Copyright 2010 John Wiley & Sons, Inc 7 - 27

Bluetooth Topology • Uses the term “piconet” to refer to a Bluetooth network – Consists of 8 devices • A “master” device controlling other devices, “slaves” – Acts like an AP – Selects frequencies and controls access – All devices in a piconet share the same frequency range Copyright 2010 John Wiley & Sons, Inc 7 - 28

Bluetooth Media Access Control • Uses Frequency Hopping Spread Spectrum (FHSS) – Available frequency range (2. 4000 -2. 4835) divided into 79 separate 1 -MHz channels – A data burst transmitted using one channel, next data burst uses the next channel, and so on. – Channels changed based on a sequence and established by the slave and the master prior to the data transfers • 1, 600 hops or channel changes per second – Also used to minimize interference • A noisy channel avoided eventually • Not compatible with 802. 11 b – Potential interference problems (especially if many Bluetooth devices present close to. 11 b devices) Copyright 2010 John Wiley & Sons, Inc 7 - 29

Best Practice Recommendations • Select best one, cost permitting • Adopt 802. 11 g or n – Will replace 802. 11 b and. 11 a – Prices of. 11 g and n NICs and APs coming down • Wireless vs. Wired • Similar data rates for low traffic environment • When mobility important 802. 11 g or n • Using WLAN as an “overlay network, ” or in conjunction with a wired LAN – WLANs installed In addition to wired LANs – To provide mobility for laptops – To provide access in hallways, lunch rooms, other sites Copyright 2010 John Wiley & Sons, Inc 7 - 30

Physical WLAN Design • More challenging than designing a traditional LAN – Use a temporary AP and laptop to evaluate placement of APs – Locations are chosen to provide coverage as well as to minimize potential interference • Begin design with a site survey, used to determine: – Feasibility of desired coverage • Measuring the signal strength from temporary APs – Potential sources of interference • Most common source: Number and type of walls – Locations of wired LAN and power sources – Estimate of number of APs required Copyright 2010 John Wiley & Sons, Inc 7 - 31

Physical WLAN Design • Begin locating APs – Place an AP in one corner – Move around measuring the signal strength – Place another AP to the farthest point of coverage • AP may be moved around to find best possible spot • Also depends on environment and type of antenna – Repeat these steps several times until the corners are covered – Then begin the empty coverage areas in the middle • Allow about 15% overlap in coverage between APs – To provide smooth and transparent roaming • Set each AP to transmit on a different channel Copyright 2010 John Wiley & Sons, Inc 7 - 32

WLAN Design Specs for 802. 11 g Copyright 2010 John Wiley & Sons, Inc

Multistory WLAN Design • Must include – Usual horizontal mapping, and – Vertical mapping

WLAN Security • Especially important for wireless network – Anyone within the range can use the WLAN • Finding a WLAN – Move around with WLAN equipped device and try to pick up the signal – Use special purpose software tools to learn about WLAN you discovered • Wardriving – this type reconnaissance • Warchalking – writing symbols on walls to indicate presence of an unsecure WLAN Copyright 2010 John Wiley & Sons, Inc 7 - 35

Types of WLAN Security • Service Set Identifier (SSID) – Required by all clients to include this in every packet – Included as plain text Easy to break • Wired Equivalent Privacy (WEP) – Requires that user enter a key manually (to NIC and AP) – Communications encrypted using this key – Short key (40 -128 bits) Easy to break by “brute force” • Extensible Authentication Protocol (EAP) – One time WEP keys created dynamically after login – Requires a login (with password) to a server Copyright 2010 John Wiley & Sons, Inc 7 - 36

Types of WLAN Security, cont’d • Wi-Fi Protected Access (WPA) – new standard – longer key, changed for every packet • 802. 11 i – EAP login used to get session key – uses AES encryption • MAC address filtering – Allows computers to connect to AP only if their MAC address is entered in the “accepted” list Copyright 2010 John Wiley & Sons, Inc 7 - 37

Improving WLAN Performance • Similar to improving wired LANs – Improving device performance • Upgrade devices to 802. 11 g or n • Buy high-quality cards and APs – Improving wireless circuit capacity • Upgrade to 802. 11 g or n • Reexamine placement of APs • Check sources of interference (other wireless devices operating in the same frequencies)) • Use different type of antennas – Reducing network demand Copyright 2010 John Wiley & Sons, Inc 7 - 39

Improving Wireless Circuit Capacity • Upgrade to 802. 11 g or n • Replace APs – Fewest walls between AP and devices – Ceiling or highly mounted to minimize obstacles – In halls, not in closets • Remove sources of interference – Other wireless devices operating in the same frequencies • Bluetooth devices, cordless phones, etc. • Use different type of antennas – Directional antennas in smaller range to get stronger signals (faster throughput) Copyright 2010 John Wiley & Sons, Inc 7 - 40

Reducing WLAN Demand • Never place a server in a WLAN – Doubles the traffic between clients and server, once from the client to the AP, and once from the AP to the server – Locate the server in the wired part of the network (ideally with a switched LAN) • Place wired LAN jacks in commonly used locations – If WLAN becomes a problem, users can switch to wired LAN easily Copyright 2010 John Wiley & Sons, Inc 7 - 41

Implications for Management • WLANs becoming common place – Access to internal data, any time, any place • Better protection of corporate networks – Public access through WLAN hotspots • Competition and overlap with cell phone technologies – New cell phone technologies (faster, longer ranges) – Drastic price drops of WLAN devices • Widespread Internet access via multiplicity of devices (PDAs, etc, ) – Development of new Internet applications • New companies created; some old ones out of business – Drastic increase in the amount of data flowing around Copyright 2010 John Wiley & Sons, Inc 7 - 42

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