Copyright © 2007 Heathkit Company, Inc. All Rights Reserved PC Fundamentals Presentation 50 – The Wireless LAN

2 Objectives At the end of this presentation, you will be able to:

3 Define wireless LAN, WLAN, wireless access point (AP), A, b, and g. Specify the speed, access methods, topology, and media of wireless LANs. Given a troubleshooting scenario involving a wireless LAN, identify the cause of the problem.

4 The Wireless LAN can be defined as: A data communication system that uses electromagnetic or infrared waves, rather than wired connections, as a communications medium. Designed to augment or replace a wired LAN.

5 Wireless LAN Makes the LAN portable. Reduces the need for connecting cables. Adds flexibility and convenience while reducing costs.

6 Applications of wireless LANs Hospitals – Medical information on patients is available to doctors and nurses Schools – Facilitates information transfer to students Warehouses – Gives portable access to inventory, storage locations, quantities, turns ratio, etc. Executives – Gives portable access to the company LAN from a variety of locations.

7 Benefits of WLANs Mobility - Provides users with access to information anywhere in their organization. Flexibility – New clients can be quickly and effortlessly added to the system or moved from one location to another. Simplicity of installation – No cables to run. Reduced total cost of ownership – Installation expense is lower. Scalability – Easily sized to meet new needs.

8 Wireless Medium Spread Spectrum Radio Frequency (RF) Infrared

9 Spread Spectrum RF Frequency Power

10 Frequency-Hopping Spread Spectrum (FHSS) Frequency Power

11 Frequency Hopping Spread Spectrum (FHSS) Frequency Power

12 Frequency Hopping Spread Spectrum (FHSS) Frequency Power

13 Direct-Sequence Spread Spectrum (DSSS) Frequency Power

14 Wired Ethernet LAN Hub Copper Cables

15 Wireless LAN (WLAN) Access Point (AP)

16 IEEE Standards IEEE A IEEE B IEEE G IEEE N

17 A vs B vs G B802.11A802.11G Speed (Max)11Mbps54Mbps Frequency2.4GHz5GHz2.4GHz Range

18 A vs B vs G B802.11A802.11G Speed (Max)11Mbps54Mbps Frequency2.4GHz5GHz2.4GHz Range

19 A vs B vs G B802.11A802.11G Speed (Max)11Mbps54Mbps Frequency2.4GHz5GHz2.4GHz Range

20 A vs B vs G B802.11A802.11G Speed (Max)11Mbps54Mbps Frequency2.4GHz5GHz2.4GHz Range

21 The ISM Band Industrial, Scientific, Medical Unlicensed band that may be used for many purposes. 2.4 GHz to 2.5 GHz Used by B and G

22 Independent Basic Service Set (IBSS) Independent Basic Service Set (IBSS)

23 Basic Service Set (BSS) Access Point (AP)

24 Extended Service Set (ESS) AP BSS-1 BSS-2

25 AP BSS-1 AP BSS-2 AP

26 Carrier Sense Multiple Access (CSMA) Methods Ethernet uses Collision Detection or CSMA/CD Wireless uses a variation of this technique called Collision Avoidance or CSMA/CA. Collision Avoidance adds a level of handshaking to the basic Collision Detection model.

27 Review of CSMA/CD Carrier Sense means that each node listens before transmitting. Multiple Access means that each node is free to transmit when ever it has data to send. Collision Detection refers to the ability of each node to detect when two nodes transmit at once.

28 Collision Detection does not work well with wireless. The transmitted signal drowns out the received signal. It is much harder to detect collisions. Wireless adds a handshaking arrangement to the Collision Detection scheme.

29 Carrier Sense Multiple Access/ Collision Avoidance (CSMA/CA) Node listens until channel is clear. Node transmits a Request to Send (RTS) signal. If no one less is transmitting, the access point sends back a Clear to Send (CTS) signal. This tells the node that it is okay to transmit its data.

30 Collisions still occur Nodes listen until channel is clear. Two nodes transmits a Request to Send (RTS) signal simultaneously. The AP detects the collision and does not send the Clear to Send (CTS) signal.

31 Throughput vs. Distance Range and throughput vary inversely b automatically adjusts for interference and weak signal strength by dynamically down shifting the transmission rate.

32 Typical Operating Range Indoor – 50 11Mbps – 5.5 Mbps – Mbps – Mbps Outdoor – Mbps – Mbps – Mbps – Mbps

33 Wireless Security Extended Service Set Identity (ESSID) Access Control Lists Remote Authentication Dial-In User Service (RADIUS) Protocol Wired Equivalent Privacy (WEP) Encryption

34 Remote Authentication Dial-In User Service (RADIUS) Protocol A client/server security protocol defined by IETF. Centralizes authentication and permissions into a single server. Authenticates MAC addresses Associate clients with keys or passwords Secures the wireless LAN against hackers.

35 Wired Equivalent Privacy (WEP) Two levels of encryption: 64-bit & 128-bit All devices must use the same encryption level. Authorized Users have a “key” that allows them to unscramble the encrypted incoming transmissions and to scramble their own outgoing transmissions. The default for these schemes is “encryption disabled.”

36 What is 40-bit WEP encryption? A different name for 64-bit WEP encryption 40-bit secret key with a 24-bit initialization vector ( = 64) Wireless vendors may use either term. We will call it 64-bit encryption.

37 Wireless Components Wireless Access Point Wireless NIC Wireless Laptop PCMCIA Card

38 Wireless Network Access Point Power LinkAct To Wired LAN To Wireless LAN To Wireless LAN

39 Power LAN Configuration Port Configuration Port

40

41

42 Competing Technologies Bluetooth – Speed:780KBps – Range:10 Meters HomeRF – Speed:1.6 MBps – Range:150 Feet

43 Troubleshooting the WLAN Isolate the trouble to the WLAN. Use general LAN troubleshooting techniques. Use techniques specific to the WLAN. – Same channel – Same ESSID – Same encryption level – Within range

Copyright © 2007 Heathkit Company, Inc. All Rights Reserved PC Fundamentals End