Bluetooth: The Universal Radio Interface for Ad hoc, ShortRange Connectivity

1
Bluetooth The Universal Radio Interface for Ad
hoc, Short-Range Connectivity

• CIS 642
• Maria Adamou

2
Overview

• Introduction
• Bluetooth Air Interface
• Architecture
• Connection Establishment
• Piconets and Scatternets
• Power Management
• Security
• Competing technologies
• Issues facing Bluetooth

3
Introduction

• In February 1998 five major telecom and PC
  companies Ericsson, Nokia, IBM, Toshiba, and
  Intel- formed a Special Interest Group (SIG) to
  create a standard radio interface for short-range
  connectivity between electronic devices
• The radio interface was named Bluetooth after a
  Danish Viking king Harald Bluetooth who united
  Denmark and Norway during 10th century
• This group was further expanded in December 1999
  with 3Com, Lucent, Microsoft and Motorola
• Today more than 2000 companies have joined as
  adopters of the Bluetooth technology

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What is Bluetooth

• Bluetooth is a universal standard radio interface
  for short-distance, point-to-multipoint voice and
  data transfer between portable devices
• Its nominal link range is from 10 cm to 10 meters
  but can be extended to 100 meters by increasing
  the transmission power
• Printers, desktops, fax machines, cellular phones
  and virtually any other digital device can be
  part of the Bluetooth system and form ad hoc
  groupings that replace cables

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Goals

• The system must operate globally
• The system must support peer connectivity,
  connections are made on an ad hoc basis
• The connection must support voice and data
• Ability to withstand interference from other
  sources
• The radio transceiver must be small and operate
  at low power, to fit into small, portable
  devices, such as mobile phones, headsets, PDAs
  etc
• Low cost, short-range

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User Scenarios

• 3-in-1 phone At home, portable phone (fixed line
  charge), when on the move, mobile phone (cellular
  charge), and when your phone comes within range
  of another mobile phone a walkie-talkie (no
  telephony charge)
• Ultimate Headset Connect your wireless headset
  to your mobile phone, mobile computer or any
  wired connection
• Interactive Conference in meetings and
  conferences
• Automatic Synchronizer Automatic synchronization
  of your desktop, PDA, notebook and your mobile
  phone.
• Internet Bridge use of a mobile telephone or
  cordless modem device that provides modem
  services to a PC, to enable cordless access for
  dial-up networking services.
• LAN access use of a device that acts as a LAN
  access point (LAP) providing Bluetooth access
  services to one or more data terminals.
• many others...

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Definitions

• Piconet a collection of (up to eight) devices
  connected via Bluetooth technology in an ad hoc
  fashion. Each piconet is identified by a
  different frequency hopping sequence and all
  hosts on the same piconet are synchronized
• Scatternet two or more independent and
  non-synchronized piconets that communicate with
  each other
• Master unit the device in a piconet whose clock
  and hopping sequence are used to synchronize all
  other devices in the piconet
• Slave units all devices in a piconet that are
  not the master (up to 7 active units for each
  master)

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Bluetooth Air Interface

• License-free, globally available frequency band
  Industrial-Scientific-Medical (ISM) band, at 2.45
  GHz in most countries in the world
• Frequency-hopping (FH) spread spectrum to better
  support low-cost, low-power radio implementations
  with maximum immunity to interference
• Channels use a Frequency-Hopping/ Time Division
  Duplex (TDD) scheme the channel is divided into
  slots of 625ms giving 1600hops/sec and subsequent
  slots are alternately used for transmitting and
  receiving (TDD)
• One packet can be transmitted per slot
• The channel makes use of 79 equally spaced 1-MHz
  channels (from 2,402 MHz to 2,480 MHz), frequency
  shift keying (FSK) modulation
• 1 Mb/s transmission/reception rate
• 2 power levels 0dBm for 10 meters or 20dBm (100
  meters)

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Packet Definition
0 - 2745 bits
54 bits
72 bits
Access code
Packet Header
Payload
3
4
1
1
1
8
ARQN
TYPE
FLOW
SEQN
HEC
M_ADDR

• 72-bit access code unique for the channel, used
  for packet identification and synchronization,
  derived from the master
• Header 3-bit slave address, packet type, flow
  control bits, ARQ bit, sequence number,
  Header-Error-Check fields
• Payload 0-2745 bits
• Multislot packets have been defined a packet may
  cover one, three or five slots, sent on a single
  hop channel

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Links supported

• Two types of links to support multimedia
  applications
• Synchronous Connection-Oriented (SCO) link
• Asynchronous Connectionless Link (ACL)
• SCO links support symmetrical, circuit-switched
  point-to-point connections typically used for
  voice
• Reservation is carried out by the master and the
  slave
• ACL links support packet-switched
  point-to-multipoint connection typically used for
  bursty data transmission
• Master units use a polling scheme to control ACL
  connections a master-to-slave packet or a POLL
  packet poll the slave. Collisions are avoided.
• All SCO and ACL traffic is scheduled by the master

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Architecture
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RF and Baseband

• Controls the units synchronization and
  transmission frequency hopping sequence,
  compresses and puts data into packets, assigning
  identifiers etc
• The two link types SCO and ACL are also managed
  by this layer
• Takes care of retransmissions and transmission
  error detection and recovery

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HCI

• Provides a uniform interface method for accessing
  the Bluetooth hardware capabilities
• It contains a command interface to the Baseband
  controller and link manager and access to the
  hardware status

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Link Manager Protocol (LMP)

• Responsible for
• Connection set-up
• Generation, exchange and control of link and
  encryption keys for Authentication and Encryption
• Link mode negotiation and set-up, e.g. data or
  data/voice
• Sending and receiving of data
• Management of power modes, power consumption and
  state of a unit

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Logical Link Control and Adaptation Protocol
(L2CAP)

• L2CAP is an interface between upper layer
  protocols and baseband and operates in parallel
  to LMP
• Multiplexing L2CAP must support protocol
  multiplexing, since a number of protocols (e.g.
  SDP, RFCOMM and TCS Binary) can operate over
  L2CAP.
• Segmentation and Reassembly Data packets
  exceeding the Maximum Transmission Unit, MTU,
  must be segmented before being transmitted. This
  and the reverse functionality, reassemble, is
  performed by L2CAP.
• Quality of Service The establishment of an L2CAP
  connection allows the exchange of information
  regarding current Quality of Service for the
  connection between the two Bluetooth units

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Service Discovery Protocol (SDP)

• Defines how a Bluetooth client's application
  shall act to discover available Bluetooth
  servers' services (like printing, file transfer,
  synchronization) and their Bluetooth
  characteristics.
• Defines how a client can search for a service
  based on specific attributes without the client
  knowing anything of the available services.
• Provides means for the discovery of new services
  becoming available when the client enters an area
  where a Bluetooth server is operating.
• Provides functionality for detecting when a
  service is no longer available

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Other protocols

• RFCOMM - Cable replacement protocol emulates
  serial port to cover applications that use serial
  ports of the kind used in PCs and provides
  transport capabilities for upper level services
• Telephony Control Protocols
• TCS BIN defines the call control signaling for
  the establishment and release of calls between
  units
• TCS AT Commands transmitting control signals for
  telephony control
• Adopted protocols
• PPP
• TCP/UDP/IPThe TCP/UDP/IP standards are defined to
  operate in Bluetooth units allowing them to
  communicate with other units connected, for
  instance, to the Internet.
  
• WAP

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Connection Establishment

• When units are not connected they are in STANDBY
  mode, where they listen to 32 unique (for each
  unit) wake-up channels, for page or inquiry
  messages, for about 10ms each
• Wake-up interval ranges between 0 to 3.84s
  (usually 1.28s)
• A unit enters the PAGE or INQUIRY state in which
  it broadcasts page or inquiry messages
• If the paging unit knows the identity of the unit
  to which it wants to connect, it knows the
  wake-up sequence and transmits the units access
  code every 1.25ms to 16 different hop frequencies
  defined for the slave unit (total 10ms period)
• If the pager does not know the identity of the
  unit, it broadcasts an inquiry message according
  to a common inquiry sequence, every 0 to 2.56s

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Connection Establishment
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Piconets and Scatternets

• Two or more Bluetooth units that share a FH
  channel form a piconet. At most 1 master and 7
  slaves can be in one piconet
• Any unit can become a master, but by definition
  the paging unit that establishes the piconet is
  the master
• The master identity and clock specify the channel
  parameters
• All devices in a piconet are synchronized to the
  same FH sequence
• Up to 10 piconets can co-exist with overlapping
  coverage areas and form a scatternet
• A unit can be a master in one piconet and a slave
  in another, or slave in several piconets

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Power Management

• Frequency-hopping mechanism provides
  synchronization between master-slaves therefore
  no dummy packets have to be exchaged
• A receiver can quickly decide whether a packet is
  present or not, by the access code and the header
  and sleep for the rest of the slot
• Power-save modes
• HOLD mode, where no communication is possible for
  a specified hold time
• SNIFF mode, where the slave listens only to some
  slots (depends on the application)
• PARK mode, where the slave listens to the
  masters beacon at large intervals to
  re-synchronize, does not have a MAC address and
  does not participate in the traffic

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Modes of operation
23
Security

• As radio signals can be easily intercepted,
  Bluetooth devices have built-in security to
  prevent eavesdropping or falsifying the origin of
  messages (spoofing)
• The main security features are
• a challenge-response routine for authentication
• stream cipher for encryption
• session key generation session keys can be
  exchanged during a connection

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Competing Technologies

• Infrared Data Association (IrDA) vs Bluetooth
• IEEE 802.11b vs Bluetooth

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IrDA vs Bluetooth

• Wireless Standard
• IrDA already proven standard (50 million units)
• Bluetooth still in development
• Data Transfers
• IrDA up to 4Mbps 16Mbps( under development)
• Bluetooth 1Mbps(max) 721Kbps(average)
• Range
• IrDA 3 feet
• Bluetooth - 30 feet (or more)
• Line of Sight
• Required for IrDA, can be advantage in crowded
  situations
• Not required for Bluetooth (penetrates walls)
• Cost of Implementation
• IrDA - Currently 2
• Bluetooth- Initially 20

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IEEE 802.11b vs Bluetooth
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IEEE 802.1b vs Bluetooth

• The 802.15.2 task group deals with Co-existence
  and interoperability between Bluetooth and
  802.11b
• Bluetooth offers ubiquity and low price
• Both technologies can co-exist reasonably well
  Bluetooth will function as an aid to a
  larger-scale network

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Issues facing Bluetooth

• Implementation Issues
• Cost
• Interoperability
• Performance

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Future of Bluetooth

• Conservative estimates foresee several hundred
  million Bluetooth-enabled devices in the next
  five years
• By 2004, 75 of all mobile devices will support
  Bluetooth
• Communications companies will no longer have to
  build external cables and PC cards to enable
  their wireless phones and network cards to
  interface with computers
• Bluetooth will provide the "glue" for the merger
  of wireless and computers.

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References