University of Pennsylvania
Bluetooth:
The Universal Radio Interface for
Ad hoc, Short-Range Connectivity
CIS 642
Maria Adamou
Overview
University of Pennsylvania
 Introduction
 Bluetooth Air Interface
 Architecture
 Connection Establishment
 Piconets and Scatternets
 Power Management
 Security
 Competing technologies
 Issues facing Bluetooth
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Introduction
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 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
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 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
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 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
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
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
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 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
University of Pennsylvania

License-free, globally available frequency band: IndustrialScientific-Medical (ISM) band, at 2.45 GHz in most countries in
the world

Frequency-hopping (FH) spread spectrum to better support lowcost, 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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University of Pennsylvania
Packet Definition
72 bits
Access code
54 bits
0 - 2745 bits
Packet
Header
Payload
3
4
1
M_ADDR
TYPE
FLOW
1
ARQN
1
SEQN
8
HEC

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
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 Two types of links to support multimedia applications:
o Synchronous Connection-Oriented (SCO) link
o Asynchronous Connectionless Link (ACL)
 SCO links support symmetrical, circuit-switched point-topoint connections typically used for voice
o 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
o 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
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 Controls the unit’s 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
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 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)
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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)
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 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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University of Pennsylvania
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
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
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
o TCS BIN: defines the call control signaling for the
establishment and release of calls between units
o TCS AT Commands: transmitting control signals for telephony
control

Adopted protocols
o PPP
o 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.
o WAP
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Connection Establishment
University of Pennsylvania
 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 unit’s 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
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 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
University of Pennsylvania

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:
o HOLD mode, where no communication is possible for a specified
hold time
o SNIFF mode, where the slave listens only to some slots
(depends on the application)
o PARK mode, where the slave listens to the master’s 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
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Security
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 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:
o a challenge-response routine – for
authentication
o stream cipher – for encryption
o session key generation – session keys can be
exchanged during a connection
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Competing Technologies
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 Infrared Data Association (IrDA) vs Bluetooth
 IEEE 802.11b vs Bluetooth
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IrDA vs Bluetooth

University of Pennsylvania
Wireless Standard
o IrDA already proven standard (50 million units)
o Bluetooth still in development

Data Transfers
o IrDA up to 4Mbps; 16Mbps( under development)
o Bluetooth 1Mbps(max) 721Kbps(average)

Range
o IrDA – 3 feet
o Bluetooth - 30 feet (or more)

Line of Sight
o Required for IrDA, can be advantage in crowded situations
o Not required for Bluetooth (penetrates walls)

Cost of Implementation
o IrDA - Currently $2
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o Bluetooth-
Initially $20
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IEEE 802.11b vs Bluetooth
University of Pennsylvania
IEEE 802.11b high rate
Bluetooth
Market
Home, school, and enterprise WLAN
Wireless cable
Technology
2.4 GHz, ISM, DSSS
FHSS, 1,000 hops/sec
Data rate
11 Mbps
1 Mbps
Power
20 dBm
0 dBm, 20 dBm
Range
50 m
1 to 10 m, 50 m
Topology
128 devices, CSMA/CA
8 devices, Piconet
Security
Optional WEP*
Encryption, authentication
Separate voice channel
Optional
Yes
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IEEE 802.1b vs Bluetooth
University of Pennsylvania
 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
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 Implementation Issues
 Cost
 Interoperability
 Performance
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Future of Bluetooth
University of Pennsylvania
 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
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