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ITC242 – Introduction to Data Communications Wireless Network Week 7

ITC242 – Introduction to Data Communications Wireless Network Week 7. Last Class. Topic 10 - Ethernet Describe the characteristics of Ethernet networks Discuss the operation of CSMA/CD Discuss the operation of bridges, hubs, and switches

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ITC242 – Introduction to Data Communications Wireless Network Week 7

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  1. ITC242 – Introduction to Data CommunicationsWireless NetworkWeek 7

  2. Last Class Topic 10 - Ethernet • Describe the characteristics of Ethernet networks • Discuss the operation of CSMA/CD • Discuss the operation of bridges, hubs, and switches • Describe the characteristics of fast Ethernet standards.

  3. Topic 11 – Wireless LANs Learning Objectives • Describe the basic components and uses of Wireless LANs • Describe the key components of the IEEE 802.11 wireless LAN standards • Explain the basic components of Bluetooth and Bluetooth usage models.

  4. The global goal integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics regional vertical handover metropolitan area campus-based horizontal handover in-house

  5. Applications I • Vehicles • transmission of news, road condition, weather, music via DAB( Digital Audio Broadcasting) • personal communication using GSM(Global System for Mobile communications ) • position via GPS(Global Positioning System ) • local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy • vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance • Emergencies • early transmission of patient data to the hospital, current status, first diagnosis • replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc. • Crisis, war, etc.

  6. History Info Applications II • Traveling salesmen • direct access to customer files stored in a central location • consistent databases for all agents • mobile office • Replacement of fixed networks • LANs in historic buildings • Entertainment, education, ... • outdoor Internet access • intelligent travel guide with up-to-datelocation dependent information • ad-hoc networks for multi user games • Distributed computing, mesh, sensor...

  7. Pager • receive only • tiny displays • simple text messages • PDA • graphical displays • character recognition • simplified WWW • Laptop/Notebook • fully functional • standard applications Sensors, embedded controllers • Palmtop • tiny keyboard • simple versions of standard applications • Mobile phones • voice, data • simple graphical displays www.scatterweb.net performance Mobile devices

  8. Wireless Spectrum (1) • Broadcast TV • VHF: 54 to 88 MHz, 174 to 216 MHz • UHF: 470 to 806 MHz 30 MHz 300 MHz 3 GHz 30 GHz • FM Radio • 88 to 108 MHz • Digital TV • 54 to 88 MHz, 174 to 216 MHz, 470 to 806 MHz

  9. Wireless Spectrum (2) • 3G Broadband Wireless • 746-794 MHz, 1.7-1.85 GHz, 2.5-2.7 GHz 30 MHz 300 MHz 3 GHz 30 GHz • Cellular Phone • 800-900 MHz • Personal Communication Service (PCS) • 1.85-1.99 GHz

  10. Wireless Spectrum (3) • Wireless LAN (IEEE 802.11b/g) • 2.4 GHz • Wireless LAN (IEEE 802.11a) • 5 GHz 30 MHz 300 MHz 3 GHz 30 GHz • Bluetooth • 2.45 GHz • Local Multipoint Distribution Services (LMDS) • 27.5-31.3 GHz

  11. Wireless vs. Mobile • Two aspects of mobility: • user mobility: users communicate (wireless) “anytime, anywhere, with anyone” • device portability: devices can be connected anytime, anywhere to the network • Wireless vs. mobile Examples stationary computer  notebook in a hotel wireless LANs in historic buildings  Personal Digital Assistant (PDA) • Integration of wireless networks into existing fixed networks is needed: • local area networks: IEEE 802.11 • Internet: Mobile IP extension of the internet protocol IP • wide area networks: e.g., internetworking of GSM (Global System for Mobile communications ) and ISDN

  12. Wireless vs. fixed networks • Restrictive regulations of frequencies • frequencies have to be coordinated, useful frequencies are almost all occupied • Low transmission rates • local some Mbit/s, regional currently, e.g., 53kbit/s with GSM/GPRS • Higher loss-rates due to interference • emissions of, e.g., engines, lightning • Higher delays, higher jitter • connection setup time with GSM in the second range, contention • Lower security, simpler active attacking • radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones • Always shared medium • Performance guarantees and secure access mechanisms important

  13. Wireless Link Characteristics Differences from wired link …. • decreased signal strength: radio signal attenuates as it propagates through matter (path loss) • interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well • multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “difficult”

  14. wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility network infrastructure Elements of a wireless network

  15. base station • typically connected to wired network • relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers, 802.11 access points network infrastructure Elements of a wireless network

  16. network infrastructure Elements of a wireless network wireless link • typically used to connect mobile(s) to base station • also used as backbone link • multiple access protocol coordinates link access • various data rates, transmission distance

  17. infrastructure mode • base station connects mobiles into wired network • handoff: mobile changes base station providing connection into wired network network infrastructure Elements of a wireless network

  18. Elements of a wireless network ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves

  19. Characteristics of selected wireless link standards 200 802.11n 54 802.11a,g 802.11a,g point-to-point data 5-11 802.11b 802.16 (WiMAX) 3G cellular enhanced 4 UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO Data rate (Mbps) 1 802.15 .384 3G UMTS/WCDMA, CDMA2000 2G .056 IS-95, CDMA, GSM Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km

  20. Wireless network taxonomy multiple hops single hop host may have to relay through several wireless nodes to connect to larger Internet: mesh net host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet infrastructure (e.g., APs) no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET, VANET no infrastructure no base station, no connection to larger Internet (Bluetooth, ad hoc nets)

  21. 802.11b 2.4-5 GHz unlicensed spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps 802.11n: multiple antennae 2.4-5 GHz range up to 200 Mbps IEEE 802.11 Wireless LAN • all use CSMA/CA for multiple access • all have base-station and ad-hoc network versions

  22. AP AP Internet 802.11 LAN architecture • wireless host communicates with base station • base station = access point (AP) • Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: • wireless hosts • access point (AP): base station • ad hoc mode: hosts only hub, switch or router BSS 1 BSS 2

  23. 802.11: Channels, association • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies • AP admin chooses frequency for AP • interference possible: channel can be same as that chosen by neighboring AP! • host: must associate with an AP • scans channels, listening for beacon frames containing AP’s name (Service Set Identifier-SSID) and MAC address • selects AP to associate with • may perform authentication • will typically run DHCP to get IP address in AP’s subnet

  24. 4 3 2 3 2 2 1 1 1 802.11: passive/active scanning BBS 1 BBS 1 BBS 2 BBS 2 AP 1 AP 1 AP 2 AP 2 H1 H1 • Active Scanning: • Probe Request frame broadcast from H1 • Probes response frame sent from APs • Association Request frame sent: H1 to selected AP • Association Response frame sent: H1 to selected AP • Passive Scanning: • beacon frames sent from APs • association Request frame sent: H1 to selected AP • association Response frame sent: H1 to selected AP

  25. B A C C C’s signal strength A’s signal strength B A space IEEE 802.11: multiple access • avoid collisions: 2+ nodes transmitting at same time • 802.11: CSMA - sense before transmitting • don’t collide with ongoing transmission by other node • 802.11: no collision detection! • difficult to receive (sense collisions) when transmitting due to weak received signals (fading) • can’t sense all collisions in any case: hidden terminal, fading • goal: avoid collisions: CSMA/C(ollision)A(voidance)

  26. DIFS data SIFS ACK IEEE 802.11 MAC Protocol: CSMA/CA 802.11 sender 1 if sense channel idle for DIFS (Distributed Inter-frame Space) then transmit entire frame (no CD) 2 ifsense channel busy then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (Short Inter-frame Spacing) (ACK needed due to hidden terminal problem) sender receiver

  27. H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning: switch will see frame from H1 and “remember” which switch port can be used to reach H1 router 802.11: mobility within same subnet hub or switch BBS 1 AP 1 AP 2 H1 BBS 2

  28. P P P P P M M Master device Slave device Parked device (inactive) S S S S 802.15: personal area network • less than 10 m diameter • replacement for cables (mouse, keyboard, headphones) • ad hoc: no infrastructure • master/slaves: • slaves request permission to send (to master) • master grants requests • 802.15: evolved from Bluetooth specification • 2.4-2.5 GHz radio band • up to 721 kbps radius of coverage

  29. connects cells to wide area net • manages call setup (more later!) • handles mobility (more later!) Mobile Switching Center Mobile Switching Center • covers geographical region • base station (BS) analogous to 802.11 AP • mobile users attach to network through BS • air-interface: physical and link layer protocol between mobile and BS Public telephone network, and Internet MSC cell wired network Cellular Internet Access Components of cellular network architecture

  30. time slots frequency bands Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum • combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots • CDMA: code division multiple access

  31. Cellular standards: brief survey 2G systems: voice channels • IS-136 TDMA: combined FDMA/TDMA (north america) • GSM (global system for mobile communications): combined FDMA/TDMA • most widely deployed • IS-95 CDMA: code division multiple access TDMA/FDMA CDMA-2000 EDGE GPRS UMTS Don’t drown in a bowl of alphabet soup: use this for reference only IS-95 IS-136 GSM

  32. Cellular standards: brief survey 2.5 G systems: voice and data channels • for those who can’t wait for 3G service: 2G extensions • general packet radio service (GPRS) • evolved from GSM • data sent on multiple channels (if available) • enhanced data rates for global evolution (EDGE) • also evolved from GSM, using enhanced modulation • data rates up to 384K • CDMA-2000 (phase 1) • data rates up to 144K • evolved from IS-95

  33. Cellular standards: brief survey 3G systems: voice/data • Universal Mobile Telecommunications Service (UMTS) • data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 Mbps • CDMA-2000: CDMA in TDMA slots • data service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps ….. more (and more interesting) cellular topics due to mobility (stay tuned for details)

  34. Multiple Access • Four ways to divide the spectrum among active users • frequency-division multiple access (FDMA) • time-division multiple access (TDMA) • code-division multiple access (CDMA) • space-division multiple access (SDMA) • FDMA and TDMA discussed in Chapter 17

  35. CDMA • Based on direct sequence spread spectrum (DSSS) • Provides immunity from various kinds of noise and multipath distortion. (The earliest applications of spread spectrum were military, where it was used for its immunity to jamming.) • Can be used for hiding and encrypting signals. • Several users can independently use the same (higher) bandwidth with very little interference

  36. Cellular Multiple Access Schemes

  37. Bluetooth • 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

  38. 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.

  39. 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

  40. MSC MSC MSC MSC MSC Components of cellular network architecture recall: correspondent wired public telephone network different cellular networks, operated by different providers

  41. Handling mobility in cellular networks • home network: network of cellular provider you subscribe to • home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network) • visited network: network in which mobile currently resides • visitor location register (VLR): database with entry for each user currently in network • could be home network

  42. home Mobile Switching Center Mobile Switching Center home MSC consults HLR, gets roaming number of mobile in visited network call routed to home network home MSC sets up 2nd leg of call to MSC in visited network HLR VLR 2 1 4 3 MSC in visited network completes call through base station to mobile GSM: indirect routing to mobile GSM: Global system for mobile communications home network correspondent Public switched telephone network mobile user visited network

  43. Handoff goal: route call via new base station (without interruption) reasons for handoff: stronger signal to/from new BSS (continuing connectivity, less battery drain) load balance: free up channel in current BSS GSM doesn’t mandate why to perform handoff (policy), only how (mechanism) handoff initiated by old BSS Mobile Switching Center VLR GSM: handoff with common MSC new routing old routing old BSS new BSS

  44. GSM: handoff with common MSC Mobile Switching Center 1 3 2 4 5 6 7 8 VLR 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released old BSS new BSS

  45. anchor MSC: first MSC visited during cal call remains routed through anchor MSC new MSCs add on to end of MSC chain as mobile moves to new MSC IS-41 allows optional path minimization step to shorten multi-MSC chain Home MSC home network MSC MSC MSC GSM: handoff between MSCs correspondent anchor MSC PSTN (a) before handoff

  46. Home MSC home network MSC MSC MSC GSM: handoff between MSCs • anchor MSC: first MSC visited during cal • call remains routed through anchor MSC • new MSCs add on to end of MSC chain as mobile moves to new MSC • IS-41 allows optional path minimization step to shorten multi-MSC chain correspondent anchor MSC PSTN (b) after handoff

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