ITC242

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ITC242 Introduction to Data Communications
Wireless NetworkWeek 7
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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.

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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.

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

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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...

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Mobile devices
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Wireless Spectrum (1)

• Broadcast TV
• VHF 54 to 88 MHz, 174 to 216 MHz
• UHF 470 to 806 MHz

30 MHz
30 GHz
3 GHz
300 MHz

• FM Radio
• 88 to 108 MHz

• Digital TV
• 54 to 88 MHz, 174 to 216 MHz, 470 to 806 MHz

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Wireless Spectrum (2)

• 3G Broadband Wireless
• 746-794 MHz, 1.7-1.85 GHz, 2.5-2.7 GHz

30 MHz
30 GHz
3 GHz
300 MHz

• Cellular Phone
• 800-900 MHz

• Personal Communication Service (PCS)
• 1.85-1.99 GHz

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Wireless Spectrum (3)

• Wireless LAN (IEEE 802.11b/g)
• 2.4 GHz

• Wireless LAN (IEEE 802.11a)
• 5 GHz

30 MHz
30 GHz
3 GHz
300 MHz

• Bluetooth
• 2.45 GHz

• Local Multipoint Distribution Services (LMDS)
• 27.5-31.3 GHz

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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

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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

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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

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Elements of a wireless network
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Elements of a wireless network
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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

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Elements of a wireless network
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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

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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
UMTS/WCDMA, CDMA2000
3G
2G
.056
IS-95, CDMA, GSM
Indoor 10-30m
Outdoor 50-200m
Mid-range outdoor 200m 4 Km
Long-range outdoor 5Km 20 Km
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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)
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IEEE 802.11 Wireless LAN

• 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

• 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

• all use CSMA/CA for multiple access
• all have base-station and ad-hoc network versions

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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
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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 APs 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 APs
  subnet

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802.11 passive/active scanning
BBS 1
BBS 1
BBS 2
BBS 2
AP 1
AP 2
AP 1
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

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IEEE 802.11 multiple access

• avoid collisions 2 nodes transmitting at same
  time
• 802.11 CSMA - sense before transmitting
• dont 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)
• cant sense all collisions in any case hidden
  terminal, fading
• goal avoid collisions CSMA/C(ollision)A(voidance
  )

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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 if sense 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
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802.11 mobility within same subnet

• 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

hub or switch
BBS 1
AP 1
AP 2
H1
BBS 2
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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
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Cellular Internet Access Components of cellular
network architecture
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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

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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
Dont drown in a bowl of alphabet soup use
this for reference only
IS-136
IS-95
GSM
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Cellular standards brief survey

• 2.5 G systems voice and data channels
• for those who cant 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

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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)

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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

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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

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Cellular Multiple Access Schemes
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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

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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.

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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

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

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GSM indirect routing to mobile
GSM Global system for mobile communications
home network
correspondent
Public switched telephone network
mobile user
visited network
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GSM handoff with common MSC

• 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 doesnt mandate why to perform handoff
  (policy), only how (mechanism)
• handoff initiated by old BSS

new routing
old routing
old BSS
new BSS
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GSM handoff with common MSC
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
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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
(a) before handoff
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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