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 managementSecurity aspects: authentication and encryption

Control and negotiation of baseband packet sizes

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Core Protocols (cont)• Logical link control and adaptation protoc

ol (L2CAP)– Adapts upper-layer protocols to the baseband l

ayer

– Provide both connectionless and connection-oriented services

• Service discovery protocol (SDP)– Device information, services, and the character

istics 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 establ

ishment 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 inquiryThree 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_ADDR3-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 slave’s address

A transmission from a slave contains its addressThe value 0 is reserved for a broadcast from the mas

ter to all slaves in the piconet

– Type Identifies the type of packetFor SCO: HV1, HV2, HV3For 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

– ARQNProvides a 1-bit acknowledgement mechanism for

ACL traffic protected by a CRC If the reception was successful, an ACK (ARQN=1) is

returned; otherwise a NAK (ARQN=0) is returned

– SEQNProvides 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 headerAn 8-bit header is defined for single-slot packets, an

d 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 FECUsed 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 ov

er 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

– StandbyThe default state, low-power state

– ConnectionThe device is connected to a piconet as a master or a

slave

– PageDevice has issued a pageUsed by the master to activate and connect to a slav

eMaster sends page message by transmitting slave’s

device access code (DAC) in different hop channels

– Page scanDevice 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 responseA device acting as a slave responds to a page from a

master

– InquiryDevice has issued an inquiry, to find the identity of

the devices within range

– Inquiry scanDevice is listening for an inquiry

– Inquiry responseA device that has issued an inquiry receives an

inquiry response

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Baseband Specification (cont)

• Connection state

– ActiveThe slave actively participates in the piconet by liste

ning, transmitting and receiving packets

The master periodically transmits to the slaves to maintain synchronization

– SniffThe slave does not listen on every receive slot but o

nly 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

– ParkWhen a slave does not need to participate on the pic

onet 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