bluetooth and bluez

8/4/2019 Bluetooth and BlueZ

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BLUETOOTH

Hemant Singh Chauhan


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About Bluetooth

Open wireless Technology

Uses Short Wavelength Radio Technology (SWRT)

Create PANs

Managed by BSIG

Uses ISM band at 2.4 GHz


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How It Works

Uses Radio Technology FHSS

FHSS chops data and transmit it :

Up to 79 channels

1600 hops per sec

Data and Voice Transmission :

ACL Data Connection

SCO Voice Channels

Piconet and Scatternet Topology

Packet Based protocol and Master-Slave Structure


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Piconet

active slave

master parked slave

standby

Star Topology

Master:

determines hopping

scheme and timing

Administers piconet

(polling)

Logical Channels

Asynchronous, packetoriented

Synchronous Connection-

Oriented


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Operational States

Master

P

SB

SB

SB

Operational States

Slave

Parked*

Standby*

* Low power states

A piconet

M

S

S

S

S


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Forming a Piconet - I

Initially, devices know only about themselves

No synchronization

Everyone monitors in standby mode

All devices have the capability of serving as master or

slave

D AE

B

CF

KJ

H

G

I

M

NL

P

O

Q


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Forming a Piconet - II

Unit establishing the piconet automatically becomes themaster

It sends an inquiry to discover what other devices are out

there

Addressing

Active devices are assigned a 3-bit active member address(AMA)

Parked devices are assigned an 8-bit parked member address(PMA)

Standby devices do not need an address


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Connection Establishment

INQUIRY PAGE CONNECTION


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States

disconnected

connecting

active

detach

standby

inquiry page

TransmitAMA

ConnectedAMA

ParkPMA

HoldAMA

SniffAMA

low power

Typical = 2s

Typical = 0.6s

AMA = Active Member Address

PMA = Parked Member Address

Typical = 2ms


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Connecting to a Piconet

Device in standby listensperiodically

If a device wants to establish apiconet, it sends an inquiry,

broadcast over all wake-up carriers It will become the master of

the piconet

If inquiry was successful, device

enters page mode Devices in standby may respond to

the inquiry with its device address

It will become a slave to thatmaster

standby

inquiry page

TransmitAMA

ConnectedAMA

ParkPMA

HoldAMA

SniffAMA


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Page and Connect States

After receiving a response from

devices, the master can connect to

each device individually

An AMA is assigned Slaves synchronize to the

hopping sequence established

by the master

In active state, master and slaveslisten, transmit and receive

A disconnect procedure allows

devices to return to standby

mode

standby

inquiry page

TransmitAMA

ConnectedAMA

ParkPMA

HoldAMA

SniffAMA


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Low Power States

Sniff state Slaves listen to the piconet at a

reduced rate

Master designates certain slotsto transmit to slaves in sniff state

Hold state

Slave stops ACL transmission, butcan exchange SCO packets

Park state

Slave releases its AMA

Still FH synchronized and wakesup periodically to listen tobeacon

standby

inquiry page

TransmitAMA

ConnectedAMA

ParkPMA

HoldAMA

SniffAMA


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Scatternet


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Features

Piconets with overlapping coverage use differenthopping sequences

Collisions may occur when multiple piconets use the same

carrier frequency at the same time Devices can participate in multiple piconets

simultaneously, creating a scatternet

A device can only be the master of one piconet at a time

A device may serve as master in one piconet and slave inanother

A device may serve as slave in multiple piconets


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Bluetooth Architecture

Hardware layer

Radio, Baseband and Link Manager

Access through the Host Controller Interface

Standards for USB and UART

Host protocols

L2CAP, RFCOMM, BNEP, AVDTP etc.

Application profiles

Serial Port Profile, Dialup, PAN, A2DP, HID etc.


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Bluetooth Stack


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Complex View


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Baseband

Responsible for channel coding/decoding, timing

and managing a Bluetooth link.

Master/slave

Devices in a connection are either master or slave.

Communication is only possible between a master

and its slaves. A master and the slaves are named piconets.

Scatternet; multiple piconets connected together.


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The Link Manager

Responsible for establishing, supervising and tear down

connections and logical links.

Link controller states introduced to carry out thesetasks.

States:

Standby

Inquiry / Inquiry Scan

Page / Page Scan

Connection


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The Link Manager (cont.)

Inquiry

Used to detect all devcies in an unknown environment.

Page / Page Scan Describes how connection is established.

Have to know the address of the other devices. Is usually

achieved through inquiry.

Connection Master and slaves are synchronized.

Connection is established.


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Bluetooth and linux

Many Implementations

Embedded and non-free Protocol Stack

Four major known Bluetooth Stacks : OpenBT, BlueDrekar, BlueZ and Affix

Official Protocol stack is BlueZ

Released May, 3rd 2001 Integrated to Linux kernel 2.4.6


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BlueZ

Core Layers Real hardware abstraction over HCI

Generic interface for drivers

Support of multiple devices


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BlueZ Protocols

Kernel modules for core protocols

Use of the BSD socket interface

Management sockets

Stream or sequential packet sockets


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Bluetooth Network

Dialup and LAN access

RFCOMM terminal emulation

Using of PPP and AT commands

LAN access using PPP

Personal Area Networks (PAN)

Linux TCP/IP with BNEP

Use bridging, netfilter, NAT etc.

Access to ISDN

CAPI integration with CMTP


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Summary Of BlueZ

BlueZ is qualified by the Bluetooth SIG

Full access to all Bluetooth host layers

Native integration into many projects

Active development


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THANK YOU

bluetooth and bluez

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