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Copyright 2010 John Wiley & Sons, Inc7 - 1 Business Data Communications and Networking 10th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons,

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Presentation on theme: "Copyright 2010 John Wiley & Sons, Inc7 - 1 Business Data Communications and Networking 10th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons,"— Presentation transcript:

1 Copyright 2010 John Wiley & Sons, Inc7 - 1 Business Data Communications and Networking 10th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons, Inc Dwayne Whitten, D.B.A Mays Business School Texas A&M University

2 Copyright 2010 John Wiley & Sons, Inc7 - 2 Chapter 7 Wireless Local Area Networks

3 Copyright 2010 John Wiley & Sons, Inc7 - 3 Chapter 7: Outline Introduction WLAN Components WI-FI WIMAX Bluetooth Best practice WLAN Design Improving WLAN Performance Management Implications

4 Copyright 2010 John Wiley & Sons, Inc7 - 4 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) 802.1x 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

5 Copyright 2010 John Wiley & Sons, Inc7 - 5 Principal WLANs Technologies WI-FI –IEEE 802.11b Standardization started after.11a, but finished before, more commonly used than.11a –IEEE 802.11a First attempt to standardization of WLANs; more complicated than.11b –IEEE 802.11g WIMAX Bluetooth –Also an IEEE standard 802.15

6 Copyright 2010 John Wiley & Sons, Inc7 - 6 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)

7 Copyright 2010 John Wiley & Sons, Inc7 - 7 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”

8 Copyright 2010 John Wiley & Sons, Inc7 - 8 Types of Antennas

9 Copyright 2010 John Wiley & Sons, Inc7 - 9 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

10 Copyright 2010 John Wiley & Sons, Inc7 - 10 More on the APs and NICs 3 separate channels available for 802.11b –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)

11 Copyright 2010 John Wiley & Sons, Inc7 - 11 A WLAN Using Different Channels

12 Copyright 2010 John Wiley & Sons, Inc7 - 12 WLAN Topology A wireless Access Point (AP) connected into an Ethernet Switch Same as Ethernet Physical star Logical bus Use the same radio frequencies, so take turns using the network Uses a NIC that transmits radio signals to the AP 10Base-T or 100Base-T

13 Copyright 2010 John Wiley & Sons, Inc7 - 13 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”)

14 Copyright 2010 John Wiley & Sons, Inc7 - 14 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)

15 Copyright 2010 John Wiley & Sons, Inc7 - 15 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 and 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

16 Types of Wi-Fi IEEE 802.11a IEEE 802.11b IEEE 802.11g IEEE 802.11n Copyright 2010 John Wiley & Sons, Inc7 - 16

17 Copyright 2010 John Wiley & Sons, Inc7 - 17 IEEE 802.11a 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.11b Reduced range because of higher speed –50 meters ( 150 feet) –Highest speed achievable within 15 meter

18 Copyright 2010 John Wiley & Sons, Inc7 - 18 IEEE 802.11b Moderate speed networking in the 2.4GHz 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 802.11b suffers less attenuation than 802.11a Designed to connect easily to Ethernet

19 Copyright 2010 John Wiley & Sons, Inc7 - 19 IEEE 802.11g Designed to combine advantages of 802.11a and 802.11b –Offers higher data rates (up to 54 Mbps) in 2.4 GHz band (as in.11b) with longer ranges –Backward compatible with 802.11b.11b devices can interoperate with.11g APs Price to pay: when an.11g AP detects an.11b device, it prohibits.11g devices from operating at higher speeds Uses the same topology as.11b –Provides 3-6 channels (depending on configuration) –54 Mbps rate obtained within 50 meter range

20 Copyright 2010 John Wiley & Sons, Inc7 - 20 802.11g Media Access Control Almost the same media and error control protocols as.11b –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.11a and.11b

21 Copyright 2010 John Wiley & Sons, Inc7 - 21 IEEE 802.11n 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

22 Copyright 2010 John Wiley & Sons, Inc7 - 22 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

23 Copyright 2010 John Wiley & Sons, Inc7 - 23 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: –802.16d –802.16e

24 IEEE802.16d 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, Inc7 - 24

25 IEEE802.16e 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, Inc7 - 25

26 Copyright 2010 John Wiley & Sons, Inc7 - 26 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

27 Copyright 2010 John Wiley & Sons, Inc7 - 27 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

28 Copyright 2010 John Wiley & Sons, Inc7 - 28 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

29 Copyright 2010 John Wiley & Sons, Inc7 - 29 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 802.11b –Potential interference problems (especially if many Bluetooth devices present close to.11b devices)

30 Copyright 2010 John Wiley & Sons, Inc7 - 30 Best Practice Recommendations Select best one, cost permitting Adopt 802.11g or n –Will replace 802.11b and.11a –Prices of.11g and n NICs and APs coming down Wireless vs. Wired Similar data rates for low traffic environment When mobility important  802.11g 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

31 Copyright 2010 John Wiley & Sons, Inc7 - 31 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

32 Copyright 2010 John Wiley & Sons, Inc7 - 32 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

33 WLAN Design Specs for 802.11g Copyright 2010 John Wiley & Sons, Inc7 - 33

34 Copyright 2010 John Wiley & Sons, Inc7 - 34 Multistory WLAN Design Must include –Usual horizontal mapping, and –Vertical mapping to minimize interference from APs on different floors

35 Copyright 2010 John Wiley & Sons, Inc7 - 35 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

36 Copyright 2010 John Wiley & Sons, Inc7 - 36 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

37 Copyright 2010 John Wiley & Sons, Inc7 - 37 Types of WLAN Security, cont’d Wi-Fi Protected Access (WPA) –new standard –longer key, changed for every packet 802.11i –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

38 Copyright 2010 John Wiley & Sons, Inc7 - 38 Improving WLAN Performance Similar to improving wired LANs –Improving device performance –Improving wireless circuit capacity –Reducing network demand

39 Copyright 2010 John Wiley & Sons, Inc7 - 39 Improving WLAN Performance Similar to improving wired LANs –Improving device performance Upgrade devices to 802.11g or n Buy high-quality cards and APs –Improving wireless circuit capacity Upgrade to 802.11g 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

40 Copyright 2010 John Wiley & Sons, Inc7 - 40 Improving Wireless Circuit Capacity Upgrade to 802.11g 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)

41 Copyright 2010 John Wiley & Sons, Inc7 - 41 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

42 Copyright 2010 John Wiley & Sons, Inc7 - 42 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

43 Copyright 2010 John Wiley & Sons, Inc7 - 43 Copyright 2010 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein.


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