Bluetooth

 What is Bluetooth?
 Goals
 Requirements
 Usage Models
 Bluetooth Architecture
 Security

 Bluetooth is a new standard developed by a
group of electronics manufacturers that will
allow any sort of electronic equipment -- from
computers and cell phones to keyboards and
headphones -- to make its own connections,
without wires, cables or any direct action from
a user.
 A key difference with other existing wireless
technologies is that bluetooth enables
combined usability models based on
functions provided by different devices.

 The Bluetooth Special Interest Group
comprises more than 1000 companies.The
major companies who created the technology
include
 Intel
 3 com
 Ericcson
 IBM
 Motorola
 Nokia
 Toshiba

The Name –Bluetooth?
 The name is attributed to Harald Bluetooth
was king of Denmark around the turn of the
last millennium.
 Choosing this name for the standard
indicates how important companies from the
Baltic region (nations including Denmark,
Sweden, Norway and Finland) are to the
communications industry

 Present wireless technology like infra red
data communication has two problems –
1)Line of Sight 2) One to One
 Using data synchronizing – e.g. hot syn
on a PDA --- problem of using the right
cradle and cable.
 BLUETOOTH OVERCOMES THESE
PROBLEMS

 It provides agreement at the physical level --
Bluetooth is a radio-frequency standard.
 Provides agreement at the data link level
where products have to agree on
 when bits are sent
 how many will be sent at a time
 how the parties in a conversation can be
sure that the message received is the same
as the message sent

The Basic Idea
 Bluetooth is a standard for a small , cheap
radio chip to be plugged into computers,
printers, mobile phones, etc
 Bluetooth chip is designed to replace
cables.Information normally carried by
the cable, is transmitted at a special
frequency to a receiver Bluetooth chip.
 These devices can form a quick ad-hoc
secure “piconet” and start communication.
 Connections in the “piconets” can occur even
when mobile.

“Piconet”
 A collection of devices connected via
Bluetooth technology in an ad hoc fashion.
 A piconet starts with two connected
devices, and may grow to eight connected
devices.
 All Bluetooth devices are peer units and
have identical implementations. However,
when establishing a piconet, one unit will
act as a Master and the other(s) as
slave(s) for the duration of the piconet
connection.

Requirements
 Low cost as cables – chip $5
 Secure as cables – must support authentication and
encryption
 Must support both data and voice.
 Must connect to a variety of devices.
 Must be able to function in a noisy environment.
 Data rates – 721kbps , using the 2.45Ghz radio
frequency band –I.S.M (Industrial, scientific and
medical)
 Must support many simultaneous and private
“piconets”.
 Must be low power, compact and global.

Usage Models- Voice/Data Access Points
 Connecting a computing
device to a communicating
device.
 Allows any device with a
bluetooth chip to connect to
the internet while located
within the range of the
access point.
 Example- a notebook could
link to the internet using a
mobile phone as an access
point.
 Envisions public data access
points

Usage models-Peripheral Interconnects
 Standard peripheral devices
like keyboard, mice,
headsets etc working over a
wireless link.
 The same device can be
used in multiple functions e.g
a headset can access
phones while in the office and
can interface with a cellular
phone when mobile.

Usage model- Personal Area Networking.(PAN)
 Allows dynamic
formation and
breakdown of
“PICONETS”--ad-
hoc personal
networks.

Bluetooth Architecture
 Core Specification
-Deals with the lower
layers of the
architecture and
describes how the
technology works.
 Profile Specification -
Focuses on how to build
interoperating devices
using the core
technology.

RF Layer
 The Radio (layer) is the lowest defined
layer of the Bluetooth specification.
 It defines the requirements of the
Bluetooth transceiver device operating
in the 2.4GHz ISM band.

 In order to minimize interference the nominal
antenna power is 1 mW which can be
extended to 100mW.
 The low power limits the range to about 10
centimeters to 10 meters. With higher power
of 100mW range of 100meters can be
achieved.
 It uses a packet switching protocol based on
a technology called spread-spectrum
frequency hopping to spread the energy
across the ISM band.

Spread-Spectrum frequency
hopping
 A device will use 79 individual randomly chosen
frequencies within a designated range, changing from
one to another on a regular basis.
 The designated range is from 2.402GHz to
2.480GHz, in steps of 1MHz.
 The frequency hopping is done at a rate of 1600
times a second.
 This allows more devices to use the limited time slice
and secondly reduces the chance of two transmitters
being on the same frequency at the same time.

 Baseband layer – This layer defines the
timing, framing, packets and flow control on
the link.
 Link Manager – Responsible for managing
connection states(authentication &
encryption), enforcing fairness among slaves
& power mangt.
 Logical Link Layer – Handles multiplexing,
segmentation and reassembly of large
packets and device discovery.
 Audio – The audio data is directly mapped to
the baseband layer.

Bluetooth Frame
 Each frame consists of a transmit packet and
a receive packet.
 Each packet may have either 1, 3 or 5 slots of
625ùs.
 Single slot packet – max data rate of 172Kbps
 Multislot frames support higher rates–
721Kbps or a max. of 3 voice channels .

Network Topology
 All units have a unique global ID(BD_Addr)
address( 48 bits)
 The unit that initializes the connection is
assigned as the master which controls the
traffic of the connection.
 A master can simultaneously connect upto
seven slaves.
 The master/slave roles can be swapped.
 A device can be a master in only one
“piconet” at a time.

Forming a piconet
 Needs two parameters --- a) Hopping pattern
of the radio it wishes to connect. b) Phase
within the pattern i.e. the clock offset of the
hops.
 The global ID defines the hopping pattern.
 The master shares its global ID and its clock
offset with the other radios which become
slaves.
 The global ID and the clock parameters are
exchanged using a FHS (Frequency Hoping
Synchronization) packet.

 Devices not connected to a piconet are in STANDBY
mode, using low power.
 A connection is made by either a PAGE command if
the address is known or by the INQUIRY command
followed by a PAGE
 When a radio sends an INQUIRE command, all the
listening radios respond with their FHS packets,
which tells the inquiring radio of all the radios in the
area.
 All listening radios perform a page scan and/or an
inquiry scan every 1.25 seconds.
 The master radio sends an FHS to the paged radio.

 Shows a bunch of
bluetooth devices
in proximity of
each other.
 Each device has
its own ID and its
clock offset

 Radio A has
become the master
and has formed a
piconet with B and C
as the slaves.
 Both B and C now
share A’s ID and
and clock offset.

 When a radio joins a piconet it is assigned a 3
bit Active Member Address(AMA).
 Once the piconet has eight radios, the master
assigns puts a radio into the PARK mode.
 This is one of the low power states, in which
the radio releases its AMA for a 8 bit PMA
(Passive Member Address).
 The freed AMA can be assigned to another
radio wishing to join the piconet.
 Though upto 256 radios can actively reside
on a piconet, only 8 of them with AMA’s can
transfer data.

Inquiry Scan
 One radio performs a page function on a
special Inquiry ID global address.
 Listening radios perform an inquiry scan on a
unique sequence of 32 channels.
 The radio will listen every 1.25 seconds on
each of these 32 channels for 10ms and will
then repeat the same for the next channel.
 The inquiring radio issues a number of pages
on the inquire channels and then listens for a
response for 1.25 seconds for 16 of the 32
channels.

 If a listening radio was doing a page scan on
one of these inquire channels it will respond
with its FHS packet.
 The sequence is repeated for the second set
of 16 channels.
 After an inquire scan is performed the
inquiring radio will have a list of all the FHS
packets of all the radios within its range.

Page Scan
 A page scan is done by a radio in the Standby mode
if the address of the device to connect is known.
 Each radio has a unique sequence of 32 paging
frequencies and 32 response frequencies based on
its Global ID.
 The radio will listen for a page of its global ID on each
of the 32 paging frequency for 10ms, changing
frequency every 1.25 seconds.
 The paging radio will continuously page using the
paged radio’s Global ID on one of the set of 16
paging frequency for 1.25seconds.

 The paging radio estimates the 16 frequencies on
which to start paging based on the last known clock
offset.
 If the paging radio receives no response then it will
page on the remaining 16 frequencies for the next
1.25 seconds.
 Connecting time α Clock offset
 Clock offset α how recently were they were
connected.

 Once a radio joins the piconet and has an
AMA it can direct data to other devices on the
piconet.
 In order to remain in the connected state
within a piconet, the radio needs to maintain
the frequency hopping pattern and offset
while consuming low power.
 To achieve this the connected radios can be
placed in either PARK, HOLD or SNIFF
modes.

HOLD MODE
 When data needs to be transmitted very infrequently,

thus conserving power.
 In this mode only an internal timer is running.

 No data is transferred when in HOLD mode.

 The master can put slaves on HOLD mode.

SNIFF MODE
 A slave device listens to the piconet at a reduced
rate.
 The SNIFF interval is programmable.
 In both the HOLD and SNIFF states the device
retains its AMA.

PARK MODE
 The device has given up the AMA and

has become passive.
 The parked device will occasionally

listen to see if the master has sent any
broadcast data asking it to become
active.

Types of Links and Packets
Synchronous Connection Oriented(SCO)
 Point to point full duplex link.

 Typically used for voice data.

 These packets do not use CRC and are

not retransmitted.
 Needs an asynchronous connectionless

(ACL) type link to be first established.

Asynchronous Connectionless Link
 This is a packet switched link between a

master and slave.
 Supports both isochronous and

asynchronous data.
Error Correction Schemes
 Forward error correction(1/3 and 2/3)

 Automatic Repeat Request scheme.

Security
 Authentication and
encryption is provided
at the Link Manager
layer.
 The PIN is translated
into a 128 bit link key
which is used for
authentication.
 After authentication the
radios will settle on a
suitable length
encryption key to be
used.
 Bluetooth relies on PIN
codes to establish
trusted relationships
between devices.

References
 Bluetooth Architecture Overview
James Kardach
 www.bluetooth.com
 www.palowireless.com

Bluetooth

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