1. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Chapter 5 Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications, 7th edition May only be used by adopters of the book Wireless LANs (WLANs)

2. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Wireless LAN Technology –The dominant WLAN technology today –Standardized by the 802.11 Working Group 2 802.11 Wireless LAN (WLAN) Standards 802.11

3. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 3 802.11 Wireless LAN (WLAN) Operation The wireless access point connects the wireless client to the wired Ethernet LAN.

4. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 4 802.11 Wireless LAN (WLAN) Operation The LAN connection is needed to give clients access to servers and Internet access routers on the wired LAN.

5. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Large 802.11 WLANs –Organizations can provide coverage throughout a building or a university campus by installation of many access points. Speeds and Distances –Speeds up to 300 Mbps, but usually 10 to 100 Mbps –Distances of 30 to 100 meters 5 802.11 Wireless LAN (WLAN) Standards

6. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-6 5-3: 802.11 Wireless Access Points and NICs

7. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Wireless Transmission Concepts

8. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-8 5-4: Recap of Radio Propagation Concepts Frequency –Radio waves are measured in terms of frequency –Measured in hertz (Hz)—the number of complete cycles per second Most Common Frequency Range for WLANs: –High megahertz to low gigahertz range

9. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-9 5-4: Recap of Radio Propagation Concepts from Chapter 3 Propagation Problems –Electromagnetic interference –Rapid inverse-square law attenuation –Shadow zones (dead spots) –Multipath interference

10. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-10 5-6: Channel Bandwidth and Speed Channel Bandwidth –Channel bandwidth is the highest frequency in a channel minus the lowest frequency –An 88.0 MHz to 88.2 MHz channel has a bandwidth of 0.2 MHz (200 kHz) Higher-speed signals need wider channel bandwidths.

11. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Licensed and Unlicensed Bands

12. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-12 5-8: Licensed and Unlicensed Bands Licensed Radio Bands –If two nearby radio hosts transmit in the same channel, their signals will interfere –Most radio bands are licensed bands, in which hosts need a license to transmit –The government limits licenses to avoid interference –Television bands, AM radio bands, etc., are licensed –In cellular telephone bands, which are licensed, only the central transceivers are licensed, not the mobile phones

13. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-13 5-8: Licensed and Unlicensed Bands Unlicensed Radio Bands –Some service bands are set aside as unlicensed bands –Hosts do not need to be licensed to be turned on or moved –802.11 operates in unlicensed radio bands –This allows access points and hosts to be moved freely

14. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-14 5-9: 802.11 in the 2.4 GHz and 5 GHz Unlicensed Bands The 2.4 GHz Unlicensed Band –Defined the same in almost all countries (2.400 GHz to 2.485 GHz) –This sameness reduces radio costs –Propagation characteristics are good –For 20 MHz 802.11 channels, only three nonoverlapping channels are possible Channels 1, 6, and 11

15. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-15 5-10: Mutual Interference in the 2.4 GHz Unlicensed Band If two nearby access points operate on the same channel, the access points and their stations will interfere with each other

16. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-16 5-9: 802.11 in the 2.4 GHz and 5 GHz Unlicensed Bands The 5 GHz Unlicensed Band –Radios in the 5 GHz band are expensive because frequencies in different countries are different and because higher-frequency technology is more expensive than lower-frequency technology –Shorter propagation distance than in the 2.4 GHz band –Deader shadow zones because of higher frequencies

17. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-17 5-9: 802.11 in the 2.4 GHz and 5 GHz Unlicensed Bands The 5 GHz Unlicensed Band –More total bandwidth than 2.4 GHz, so between 11 and 24 non-overlapping 20 MHz channels –Allows different access points to operate on non- overlapping channels –Some access points can operate on two channels to provide faster service

18. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Typical Access Point Operation

19. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 19 WLAN Frames and Packets Sender puts a packet for the destination host into an 802.11 frame, then sends the frame wirelessly to the access point. Sender puts a packet for the destination host into an 802.11 frame, then sends the frame wirelessly to the access point.

20. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-20 5-14: Typical 802.11 Wireless LAN Operation with Wireless Access Points 802.11 and 802.3 have different frames 1. The access point receives an 802.11 frame carrying the packet 2. The access point removes the packet, places the packet into an 802.3 frame and passes the frame on The access point does NOT forward The 802.3 frame or convert the frame

21. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Does the 802.11 frame travel all the way to the destination host? Why or why not? Does the IP packet travel all the way to the destination host? 21 WLAN Frames and Packets

22. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-22 5-15: Hosts and Access Points Transmit in a Single Channel The access point and all the hosts it serves transmit in a single channel If two devices transmit at the same time, their signals will collide, becoming unreadable Media access control (MAC) methods govern when a device may transmit; It only lets one device transmit at a time

23. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-23 5-16: CSMA/CA+ACK in 802.11 Wireless LANs CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) –Sender listens for traffic 1. If there is traffic, the sender waits 2. If there is no traffic: –2a. If there has been no traffic for less than a present amount of time, waits a random amount of time, then returns to Step 1. –2b, If there has been no traffic for more than a preset amount of time, sends without waiting –This avoids collision that would result if hosts could transmit as soon as one host finishes transmitting Box

24. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-24 5-16: CSMA/CA+ACK in 802.11 Wireless LANs ACK (Acknowledgement) –Receiver immediately sends back an acknowledgement If sender does not receive the acknowledgement, retransmits using CSMA –CSMA/CA plus ACK is a reliable protocol Box

25. © 2009 Pearson Education, Inc. Publishing as Prentice Hall © 2011 Pearson Education, Inc. Publishing as Prentice Hall 25 5-17: Request to Send/Clear to Send

26. © 2009 Pearson Education, Inc. Publishing as Prentice Hall © 2011 Pearson Education, Inc. Publishing as Prentice Hall 26 5-17: Request to Send/Clear to Send 0 0

27. © 2009 Pearson Education, Inc. Publishing as Prentice Hall Other Local Wireless Technologies

28. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-28 5-30: Bluetooth Personal Area Networks (PANs) For Personal Area Networks (PANs) –Very-short-distance networks –To connect devices on a person’s body and nearby (mobile phone, PDA, notebook computer, etc.) –Devices around a desk (computer, mouse, keyboard, printer) –The goal: cable elimination

29. © 2009 Pearson Education, Inc. Publishing as Prentice Hall © 2011 Pearson Education, Inc. Publishing as Prentice Hall 29 8.11: Bluetooth  Cable Replacement Technology ◦ For example, with a Bluetooth phone, you can print wirelessly to a nearby Bluetooth-enabled printer ◦ Does not use access points ◦ Uses direct device-to-device communication

30. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-30 5-30: Bluetooth Personal Area Networks Disadvantages Compared with 802.11 –Short distance (10 meters) –Low speed (3 Mbps today with a slower reverse channel)

31. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-31 Figure 5-30: Bluetooth Personal Area Networks Advantages Compared to 802.11 –Low battery power drain, so long battery life between recharges –Application profiles Define how devices will work together without configuration work Sending print jobs to printers File synchronization Etc.

32. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-32 5-31: Emerging Local Wireless Technologies Ultrawideband (UWB) –Uses channels that are several gigahertz wide Each UWB channel spans multiple frequency bands! –Low power per hertz to avoid interference with other services –Wide bandwidth gives very high speeds –But limited to short distance –Wireless USB provides 480 Mbps up to 3 meters, 110 Mbps up to 10 meters

33. © 2009 Pearson Education, Inc. Publishing as Prentice Hall 5-33 5-31: Emerging Local Wireless Technologies ZigBee for almost-always-off sensor networks –Very low speeds (250 kbps maximum) –Very long battery life