Bluetooth: Introduction

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Bluetooth Introduction

• Reference Chapter 15, Wireless Communications
  and Networks, by William Stallings, Prentice Hall

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Overview

• Initially developed by Ericsson in 1994
• Using 2.4 GHz band (up to 720 kbps, 10m)
• Provide consumer with the ability to do
• 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
• Set up home networks
• Call home from a remote location to turn
  appliances on and off, set the alarm, and monitor
  activity

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Overview (cont)

• Bluetooth Applications
• Data and voice access points
• Cable replacement
• Ad Hoc networking

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Protocol Architecture
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Core Protocols

• Radio
• Details of the air interface, including
  frequency, the use of frequency hopping,
  modulation scheme, and transmit power
• Baseband
• Concerned with connection establishment within a
  piconet, addressing, packet format, timing and
  power control
• Link manager protocol (LMP)
• Responsible for link setup between BT devices and
  ongoing link management
• Security aspects authentication and encryption
• Control and negotiation of baseband packet sizes

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Core Protocols (cont)

• Logical link control and adaptation protocol
  (L2CAP)
• Adapts upper-layer protocols to the baseband
  layer
• Provide both connectionless and
  connection-oriented services
• Service discovery protocol (SDP)
• Device information, services, and the
  characteristics of the services can be queries to
  enable the establishment of a connection between
  two or more BT devices

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Bluetooth Protocols

• RFCOMM
• Cable replacement protocol
• RFCOMM presents a virtual serial port that is
  designed to make replacement of cable
  technologies as transparent as possible
• Provides for binary data transport and emulates
  EIA-232 control signals over the BT baseband
  layer
• Telephony control protocol (TCS BIN)
• Defines the call control signaling for the
  establishment of speech and data calls between BT
  devices

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Usage Model
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Usage Model (cont)
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Usage Model (cont)
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Piconets

• Piconet
• Basic unit of networking in BT
• Consisting of a master and from 1 to 7 active
  slave devices
• The radio designated as the master makes the
  determination of the channel and phase that shall
  be used by all devices on this piconet
• A slave may only communicate with the master and
  may only communicate when granted permission by
  the master
• A device in one piconet may also exist as part of
  another piconet and may function as either a
  slave or master in each piconet

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Master/Slave Relationships
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Wireless Network Configurations
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Wireless Network Configurations
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Radio Baseband Parameters
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Radio Specification
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Baseband Specification
1600 hops per second
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Baseband Specification (cont)
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Baseband Specification (cont)

• Physical links
• Synchronous connection oriented (SCO)
• Allocates a fixed bandwidth between a
  point-to-point connection involving the master
  and a single slave
• The master maintains the SCO link by using
  reserved slots at regular intervals
• The basic unit of reservation is two consecutive
  slots (one in each transmission direction)
• The master can support up to 3 simultaneous SCO
  linkes, while a slave can support 2 or 3 SCO
  links
• SCO packets are never retransmitted

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Baseband Specification (cont)

• Asynchronous connectionless (ACL)
• A point-to-multipoint link between the master and
  all the slaves in the piconet
• In slots not reserved for SCO links
• The master can exchange packets with any slave on
  a per-slot basis
• Only a single ACL link can exist
• For most ACL packets, packet retransmission is
  applied

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Baseband Specification (cont)
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Baseband Specification (cont)
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Baseband Specification (cont)
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Baseband Specification (cont)

• Packet format
• Access code used for timing synchronization,
  offset compensation, paging and inquiry
• Three types of access codes
• Channel access code (CAC) identifies a piconet
• Device access code (DAC) used for paging and its
  subsequent response
• Inquiry access code (IAC) used for inquiry
  purposes
• Header used to identify packet type and to carry
  protocol control information
• Payload contains user voice or data, and in most
  cases a payload header

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Baseband Specification (cont)

• Packet Header
• AM_ADDR
• 3-bit AM_ADDR contains the active mode address
  (temporary address assigned to this slave in this
  piconet) of one of the slaves
• A transmission from the master to a slave
  contains that slaves address
• A transmission from a slave contains its address
• The value 0 is reserved for a broadcast from the
  master to all slaves in the piconet
• Type
• Identifies the type of packet
• For SCO HV1, HV2, HV3
• For ACL DM1, DM3, DM5, DH1, DH3, DH5

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Baseband Specification (cont)

• Flow
• Provides a 1-bit flow control mechanism for ACL
  traffic only
• ARQN
• Provides a 1-bit acknowledgement mechanism for
  ACL traffic protected by a CRC
• If the reception was successful, an ACK (ARQN1)
  is returned otherwise a NAK (ARQN0) is returned
• SEQN
• Provides a 1-bit sequential numbering scheme
• HEC (Header Error Control)
• An 8-bit error detection code used to protect the
  packet header

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Baseband Specification (cont)

• Payload format
• Payload header
• An 8-bit header is defined for single-slot
  packets, and a 16-bit header is defined for
  multislot packets
• Payload body user information
• CRC 16-bit CRC code on data payload
• Payload header
• L_CH identifies the logical channel
• Flow used to control flow at the L2CAP level
• Length the number of bytes of data in the
  payload, excluding the payload header and CRC

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Baseband Specification (cont)

• Error correction
• 1/3 rate FEC (forward error correction)
• Used on the 18-bit packet header
• For the voice field in an HV1 packet
• Simply sending three copies of each bit
• A majority logic is used
• 2/3 rate FEC
• Used in all DM packets, in the data field of the
  DV packets, in the FHS packet, an in the HV2
  packet
• Hamming code
• Can correct all single errors and detect all
  double errors in each codeword

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Baseband Specification (cont)

• ARQ (automatic repeat request)
• Used with DM and DH packets, and the data field
  of DV packets
• Similar to ARQ schemes used in data link control
  protocols
• 1. Error detection
• 2. Positive acknowledgement
• 3. Retransmission after timeout
• 4. Negative acknowledgement and retransmissions

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Baseband Specification (cont)

• Logical Channels
• Five types of logical data channels designed to
  carry different types of payload traffic
• 1. Link control (LC)
• Carries low level link control information ARQ,
  flow control, payload characterization
• The LC channel is carried in every packet except
  in the ID packet, which has no packet header
• 2. Link manager (LM)
• Transports link management information between
  participating stations
• Support LMP traffic and can be carried over
  either an SCO or ACL link

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Baseband Specification (cont)

• 3. User asynchronous (UA)
• Carries asynchronous user data normally carried
  over the ACL link
• 4. User isochronous (UI)
• Carries isochronous user data normally carried
  over the ACL link but may be carried in a DV
  packet on the SCO link
• 5. User synchronous (US)
• Carries synchronous user data
• This channel is carried over the SCO link

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Baseband Specification (cont)

• State diagram

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Baseband Specification (cont)

• Inquiry procedure
• The first step in establishing a piconet is for a
  potential master to identify devices in a range
  that wish to participate in the piconet
• Once a device has responded to an Inquiry, it
  moves to the page scan state to await a page from
  the master in order to establish a connection
• Page procedure
• Once the master has found devices within its
  range, it is able to establish connections to
  each device, setting up a piconet

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Baseband Specification (cont)

• Channel state
• Standby
• The default state, low-power state
• Connection
• The device is connected to a piconet as a master
  or a slave
• Page
• Device has issued a page
• Used by the master to activate and connect to a
  slave
• Master sends page message by transmitting slaves
  device access code (DAC) in different hop
  channels
• Page scan
• Device is listening for a page with its own DAC

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Baseband Specification (cont)

• Master response
• A device acting as a master receives a page
  response from a slave
• Slave response
• A device acting as a slave responds to a page
  from a master
• Inquiry
• Device has issued an inquiry, to find the
  identity of the devices within range
• Inquiry scan
• Device is listening for an inquiry
• Inquiry response
• A device that has issued an inquiry receives an
  inquiry response

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Baseband Specification (cont)

• Connection state
• Active
• The slave actively participates in the piconet by
  listening, transmitting and receiving packets
• The master periodically transmits to the slaves
  to maintain synchronization
• Sniff
• The slave does not listen on every receive slot
  but only on specified slots for its message
• The slave can operate in a reduced-power status
  the rest of the time

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Baseband Specification (cont)

• Hold
• The device in this mode does not support ACL
  packets and goes to reduced power status
• The slave may still participate in SCO exchanges
• Park
• When a slave does not need to participate on the
  piconet but still is to be retained as part of
  the piconet, it can enter the park mode, which is
  a low-power mode with very little activity
• The device is given a parking member address
  (PM_ADDR) and loses its active member (AM_ADDR)
  address
• With the use of the park mode, a piconet may have
  more than seven slaves

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Link Manager Specification
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Link Manager Specification (cont)
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L2CAP
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L2CAP Formats
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L2CAP Signaling Command Code
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L2CAP Quality of Service

• Flow specification
• Service type
• Token rate (bytes/second)
• Token bucket size (bytes)
• Peak bandwidth (bytes/second)
• Latency (microseconds)
• Delay variation (microseconds)

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L2CAP Quality of Service