ECE 6160: Advanced Computer Networks Wireless LAN and Bluetooth

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ECE 6160 Advanced Computer NetworksWireless
LAN and Bluetooth

• Instructor Dr. Xubin (Ben) He
• Email Hexb_at_tntech.edu
• Tel [phone]

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Prev

• multimedia applications and requirements
• making the best of todays best effort service
• scheduling and policing mechanisms
• next generation Internet Intserv, RSVP, Diffserv

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Why Wireless?

• Human freedom
• Portability v. Mobility
• Objective anything, anytime, anywhere
• Mobility
• Size, weight, power
• Functionality
• Content
• Infrastructure required
• Cost
• Capital, operational

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Wireless Links

• The wave of the future for networking wireless
  links
• Examples of end systems
• Portable PCs, PDAs, airport hubs, wireless
  telephony (such as the cellphone pictured)
• Future appliances may include cameras,
  automobiles, pets, security systems, kitchen
  appliances, and plants.
• IEEE 802.11b most popular standard wireless
  LANs
• Bluetooth new standard that allows devices to
  communicate with each other

• Three classifications
• Power, range, data rate
• Bluetooth low, short, low
• 802.11 high, medium, high

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Wireless LAN Configurations
CLIENT AND ACCESS POINT
WIRELESS PEER-TO-PEER
BRIDGING WITH DIRECTIONAL ANTENNAS
MULTIPLE ACCESS POINTS ROAMING
UP TO 17 KM !
SOURCE PROXIM.COM
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Wireless Standards

• 802.11b (2.4 GHz 300 radius 11 Mbps)
• 802.11a (5 GHz 54 Mbps incompatible with b)
• 802.11g (2.4 GHz 54 Mbps backward compatible with
  b)
• 802.20 (1 Mbps _at_250 kph)
• BlueTooth (2.4 Ghz 30 radius)
• GSM (9.6 Kbps) GPRS (28.8 Kbps up to 60 Kbps )
• 3G (UMTS 1.1 Mbit/s shared typically giving 80
  Kbit/s )
• 4G 2010? (10 Mbs? )
• UWB potential to deliver 500 Mbps over short
  distances

SOURCE JOHN DOWNARD
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IEEE 802.11 Wireless LAN

• 802.11b
• Currently most popular form of wireless LAN
  wireless Ethernet, Wi-Fi
• 2.4 GHz unlicensed radio spectrum
• up to 11 Mbps
• physical layer and Media Access Control (MAC)
  layer for wireless local area network
• direct sequence spread spectrum (DSSS) in
  physical layer
• all hosts use same chipping code
• widely deployed.

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IEEE 802.11 Wireless LAN

• Other wireless LAN standards
• 802.11a operates on 5.1-5.8GHz range and uses
  OFDM (orthogonal frequency-division
  multiplexing), Speeds can get up to 54Mbps
• 802.11g operates at 2.4GHz, Speeds up to 54Mbps
• All use CSMA/CA for multi-access and have base
  stations and ad-hoc network versions

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Base station approach (Infrastructure)

• Wireless host communicates with a central base
  station (AP)
• Basic Service Set (BSS) (a.k.a. cell) contains
• wireless hosts (wireless stations)
• access point (AP) central base station
• BSSs combined to form distribution system (DS)

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Ad Hoc Network approach

• No AP (i.e., central base station)
• wireless hosts communicate with each other
• to get packet from wireless host A to B may need
  to route through wireless hosts X,Y,Z
• Applications
• laptop meeting in conference room, car
• interconnection of personal devices
• battlefield
• IETF MANET (Mobile Ad hoc Networks) working
  group

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IEEE 802.11 multiple access

• Collision if 2 or more nodes transmit at same
  time
• CSMA makes sense
• get all the bandwidth if youre the only one
  transmitting
• shouldnt cause a collision if you sense another
  transmission
• Collision detection doesnt work hidden terminal
  problem

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IEEE 802.11 MAC Protocol CSMA/CA

• 802.11 CSMA sender
• - if sense channel idle for DISF sec.
• then transmit entire frame (no collision
  detection)
• -if sense channel busy then binary backoff
• 802.11 CSMA receiver
• - if received OK
• return ACK after SIFS
• (ACK is needed due to hidden terminal problem)

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Collision avoidance mechanisms

• Problem
• two nodes, hidden from each other, transmit
  complete frames to base station
• wasted bandwidth for long duration !
• Solution
• small reservation packets
• nodes track reservation interval with internal
  network allocation vector (NAV)

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Collision Avoidance RTS-CTS exchange

• sender transmits short RTS (request to send)
  packet indicates duration of transmission
• receiver replies with short CTS (clear to send)
  packet
• notifying (possibly hidden) nodes
• hidden nodes will not transmit for specified
  duration NAV

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Collision Avoidance RTS-CTS exchange

• RTS and CTS short
• collisions less likely, of shorter duration
• end result similar to collision detection
• IEEE 802.11 allows
• CSMA
• CSMA/CA reservations
• polling from AP

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More Info

• Wireless Communications and Networks, by William
  Stallings, Part Four, Prentice Hall, 2002
• Wireless LANs Status Today and Visions for
  Future, by Anand R. Prasad, Lucent.
• Wireless Glossary

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A word about Bluetooth (802.15)

• Interference from wireless LANs, digital cordless
  phones, microwave ovens
• frequency hopping helps
• MAC protocol supports
• error correction
• ARQ

• Low-power, small radius, wireless networking
  technology
• 10 meters or so
• Interconnects gadgets
• 2.4-2.5 GHz unlicensed radio band
• up to 721 kbps

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Bluetooth

• A standard permitting for wireless
  connection of
• Personal computers
• Printers
• Mobile phones
• Handsfree headsets
• LCD projectors
• Modems
• Wireless LAN devices
• Notebooks
• Desktop PCs
• PDAs

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Bluetooth Devices
ALCATEL One TouchTM 700 GPRS, WAP
ERICSSON R520 GSM 900/1800/1900
ERICSSON BLUETOOTH CELLPHONE HEADSET
NOKIA 9110 FUJI DIGITAL CAMERA
ERICSSON COMMUNICATOR
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Bluetooth Application Areas

• Bluetooth provides support for 3 general
  application areas using short range wireless
  connectivity
• Data and voice access points
• Real-time voice and data transmissions
• Cable replacement
• Eliminates need for numerous cable attachments
  for connection
• Ad hoc networking
• Device with Bluetooth radio can establish
  connection with another when in range

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Profiles Bluetooth usage models

• Set of protocols to implement a particular
  Bluetooth-based application, defined as profile.
• File transfer
• Internet bridge
• LAN access
• Synchornization phone book, task lists
• Three-in-one phone
• Headset act as a remote devices audio I/O

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The ultimate headset

• Bluetooth removes the cable between the headset
  and the telephone.
• The user of a headset is not physically tied to
  the audio device and is free to roam about the
  area.
• The same headset can be used with multiple
  devices.
• The same headset used with
• a telephone might also be used
• with a cordless telephone base
• station and could be used for
• audio interaction with computers.
• Using voice recognition it may
• be possible to place telephone
• calls using only headset as
• the user interface.

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The three in one phone

• The three in one usage model allows a mobile
  telephone to be used
• as a cellular phone in the standard manner.
• As a cordless phone connecting to a voice access
  point.
• As a an walkie-talkie for direct phone-to-phone
  communication with another device in proximity
  (why to use it when you can shout ?).

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File Transfer

• In an interactive conference room scenario,
  business cards and files could be exchanged among
  the participants.

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Dial-up networking

• Todays usage models for dial-up networking
  require a cable between the computer and
  telephone.
• Even when a mobile telephone is used, a cable
  between a computer and the mobile telephone is
  required.
• If computer and telephone support dial-up
  networking profile the connection can be wireless.

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Direct network access

• It is possible to implement LAN bridges where one
  port has Bluetooth interface instead of the wired
  serial access.

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Piconets and Scatternets

• Piconet
• Basic unit of Bluetooth networking
• Master and one to seven slave devices
• Master determines channel and phase
• Scatternet
• Device in one piconet may exist as master or
  slave in another piconet
• Allows many devices to share same area
• Makes efficient use of bandwidth

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Scatternet
Piconet B
Piconet A
Active slave A1
Active slave B1
Master B
Active slave A2 Active slave B3
Master A
Active slave B2
Active slave A3
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Master and Slave roles in piconet

• A given master may communicate with up to 7
  active slaves and up to 255 parked slaves.
• All slaves communicating with a single master
  form a piconet.
• There can be only one master in a single piconet.
• In the higher protocol layers, devices operate
  as peers

Slave1
Master
Slave2
piconet
Slave3
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Communications topology

• The Bluetooth network model uses peer-to-peer
  communications based on proximity.
• The slaves within the area of proximity can form
  a piconet.

Proximity sphere
Active slave
Standby slave
Parked slave
Master
sniff slave
Standby slave
hold slave
Active slave
Piconet
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Communications topology

• It is possible for a device to take part in more
  than one piconet.
• When two or more piconets at least partially
  overlap in time and space a scatternet is formed.
• Each piconet has its own hopping pattern
  determined by the master.
• A slave could participate in multiple piconets by
  establishing connections with different masters
  in proximity.
• A single device might act as a slave in one
  piconet but be the master in another piconet.

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Physical Links between Master and Slave

• Synchronous connection oriented (SCO)
• Allocates fixed bandwidth between point-to-point
  connection of master and slave
• Master maintains link using reserved slots
• Master can support three simultaneous links
• Asynchronous connectionless (ACL)
• Point-to-multipoint link between master and all
  slaves
• Only single ACL link can exist

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Bluetooth Packet Fields

• Access code used for timing synchronization,
  offset compensation, paging, and inquiry
• Header used to identify packet type and carry
  protocol control information
• Payload contains user voice or data and payload
  header, if present

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Frequency Hopping in Bluetooth

• Provides resistance to interference and multipath
  effects
• Provides a form of multiple access among
  co-located devices in different piconets

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Frequency Hopping

• Total bandwidth divided into 1MHz physical
  channels
• FH occurs by jumping from one channel to another
  in pseudorandom sequence
• Hopping sequence shared with all devices on
  piconet (FH channel)
• Piconet access
• Bluetooth devices use time division duplex (TDD)
• Access technique is TDMA
• FH-TDD-TDMA

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ARQ Scheme Elements

• Error detection destination detects errors,
  discards packets
• Positive acknowledgment destination returns
  positive acknowledgment
• Retransmission after timeout source retransmits
  if packet unacknowledged
• Negative acknowledgment and retransmission
  destination returns negative acknowledgement for
  packets with errors, source retransmits

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More info

• http//www.palowireless.com/bluetooth/
• http//www.bluetooth.org
• http//www.tutorial-reports.com/wireless/bluetooth
  /