Distributed Topology Distributed Topology Construction of Bluetooth Construction of Bluetooth Personal Area NetworksPersonal Area Networks

Theodoros Salonidis, Pravin Bhagwat, Theodoros Salonidis, Pravin Bhagwat, Leandros Tassiulas and Richard LaMaireLeandros Tassiulas and Richard LaMaire

Objective of StudyObjective of Study

Multiple channelsMultiple channels in an ad-hoc networkin an ad-hoc network

Which subgroup of nodes share a common Which subgroup of nodes share a common channel and which act as forwarding nodeschannel and which act as forwarding nodes

Bluetooth Topology Construction ProtocolBluetooth Topology Construction Protocol Asynchronous distributed protocol for Asynchronous distributed protocol for constructing scatternetsconstructing scatternets

Introduction to BluetoothIntroduction to Bluetooth

Cable replacement technologyCable replacement technologyRange is 10 meters so is targeted for Range is 10 meters so is targeted for

personal area networkspersonal area networksBased on a frequency hopping physical Based on a frequency hopping physical

layerlayer

Bluetooth PiconetBluetooth Piconet

A group of devices A group of devices sharing a common sharing a common channelchannel

Piconet consists of Piconet consists of a Master and up to a Master and up to 7 slave devices7 slave devices

Bluetooth Piconet Bluetooth Piconet (contd.)(contd.)

Within a piconet channel is shared using Within a piconet channel is shared using TDD protocolTDD protocol

Multiple piconets can co-exist using Multiple piconets can co-exist using different hopping sequencesdifferent hopping sequences

Piconets interconnected via bridge nodes to Piconets interconnected via bridge nodes to form scatternetsform scatternets

Bridge nodes are capable of timesharing Bridge nodes are capable of timesharing between multiple piconetsbetween multiple piconets

ScatternetScatternet

Scatternet with a shared Bridge nodeScatternet with a shared Bridge node

Bluetooth Protocol StackBluetooth Protocol Stack

RF

Baseband

AudioLink Manager

L2CAP

Data

SDP RFCOMM

IP

Con

trol

Applications

Functional OverviewFunctional Overview StandbyStandby Waiting to join a piconet InquireInquire Ask about radios to connect to Page Page Connect to a specific radio ConnectedConnected Device is active on a piconet

(master or slave) Park/HoldPark/Hold Low power connected states

Standby

Inquiry Page

Transit

Data Connected

Park Hold Sniff

Connection SetupConnection Setup

Inquiry - scan protocolInquiry - scan protocol

To learn about the To learn about the clock offset and clock offset and device address of device address of other nodes in other nodes in proximity proximity

AddressingAddressing

Bluetooth device address (BD_ADDR)Bluetooth device address (BD_ADDR)– 48 bit IEEE MAC address48 bit IEEE MAC address

Active Member address (AM_ADDR)Active Member address (AM_ADDR)– 3 bits active slave address3 bits active slave address– assigned by Masterassigned by Master

Parked Member address (PM_ADDR)Parked Member address (PM_ADDR)– 8 bit parked slave address8 bit parked slave address

Link Establishment in Link Establishment in BluetoothBluetooth

Inquiry procedureInquiry procedure “ “senders” discover and collect senders” discover and collect

neighborhood informationneighborhood informationPagingPaging procedureprocedure “ “senders” connect to receiverssenders” connect to receiversFrequency Synchronization delayFrequency Synchronization delay Time until sender transmits at the frequency Time until sender transmits at the frequency

receiver is listening toreceiver is listening to

Asymmetric Protocol for Link Asymmetric Protocol for Link FormationFormation

Random Backoff DelayRandom Backoff Delay

Receiver backs off for an amount of time Receiver backs off for an amount of time between 0 – 639.375 ms on receiving IAC packetbetween 0 – 639.375 ms on receiving IAC packet

Link formation delayLink formation delay

2FS + RB2FS + RB

Initial FS delay until the sender hits frequency Initial FS delay until the sender hits frequency receiver is listening to and second FS delay after a receiver is listening to and second FS delay after a second IAC packet is received from sendersecond IAC packet is received from sender

Bluetooth Asymmetric Link Bluetooth Asymmetric Link Formation ProtocolFormation Protocol

IAC

FHS

1.StartInquiry state

6.EnterPage state

7.ConnectionEstablished

Initiator Target

7.ConnectionEstablished

IAC

DAC

DAC

DAC

FHS

2.StartInquiry state

3.Go to Sleep

4.Wake up

5.Respond and enter Page Scan state

A Symmetric Protocol for Link A Symmetric Protocol for Link FormationFormation

Forms connections in Forms connections in an ad hoc manner an ad hoc manner without any explicit without any explicit sender or receiver role sender or receiver role pre-assignmentpre-assignment

Nodes alternate Nodes alternate between the sender between the sender (INQUIRY state) and (INQUIRY state) and receiver (INQUIRY receiver (INQUIRY SCAN state)SCAN state)

S I

I S

S I

I S

Connection Establishment Connection Establishment ProtocolProtocol

Node has no initial knowledge about the Node has no initial knowledge about the other devices in the roomother devices in the room

Protocol must guarantee a connected Protocol must guarantee a connected scatternetscatternet

Network setup delay should be minimized Network setup delay should be minimized to the end userto the end user

BTCP: A Distributed BTCP: A Distributed Scatternet Formation ProtocolScatternet Formation ProtocolBTCP is based on a leader election processBTCP is based on a leader election processA bridge node may connect only two A bridge node may connect only two

piconetspiconetsThe resulting scatternet should consist of The resulting scatternet should consist of

minimum number of piconetsminimum number of piconetsScatternet should be fully connectedScatternet should be fully connectedTwo piconets share only one bridgeTwo piconets share only one bridge

Phase I: Coordinator ElectionPhase I: Coordinator Election

Election of a coordinator nodeElection of a coordinator node Two nodes that discover each other compare their Two nodes that discover each other compare their

VOTES variableVOTES variable Node with larger VOTES variable is selected Node with larger VOTES variable is selected

winnerwinner Loser tears down connection and enters PAGE Loser tears down connection and enters PAGE

SCAN stateSCAN state Winner node increases its VOTES by VOTES Winner node increases its VOTES by VOTES

(loser)(loser)

Phase II: Role DeterminationPhase II: Role Determination

Coordinator elected during Phase I has FHS Coordinator elected during Phase I has FHS packets of all the nodespackets of all the nodes

Coordinator decides role that each node Coordinator decides role that each node performs in scatternetperforms in scatternet

Coordinator has a connectivity list set Coordinator has a connectivity list set (SLAVESLIST(x), BRIDGELIST(x))(SLAVESLIST(x), BRIDGELIST(x))

Temporary piconet is formed with the Temporary piconet is formed with the coordinator as the Mastercoordinator as the Master

Phase III: Connection Phase III: Connection EstablishmentEstablishment

Each Master pages and connects to the Each Master pages and connects to the slaves and bridgesslaves and bridges

Bridge node waits to be paged by a second Bridge node waits to be paged by a second master and then sends a CONNECTED master and then sends a CONNECTED notificationnotification

State Alternation Timeout State Alternation Timeout ALT_TIMEOUTALT_TIMEOUT

ALT_TIMEOUT expiresALT_TIMEOUT expires

Node assumes it is the elected coordinatorNode assumes it is the elected coordinator Large ALT_TIMEOUT Large ALT_TIMEOUT

Node having won the competition continues to Node having won the competition continues to alternatealternate

Small ALT_TIMEOUTSmall ALT_TIMEOUT

More than one nodes assume they are the More than one nodes assume they are the coordinator and result in a disconnected scatternetcoordinator and result in a disconnected scatternet

Protocol PerformanceProtocol Performance

Network connection setup delay and the Network connection setup delay and the probability of protocol correctnessprobability of protocol correctness

A large ALT_TIMEOUT period will satisfy A large ALT_TIMEOUT period will satisfy the “correctness” condition with higher the “correctness” condition with higher probability but will cause a larger overheadprobability but will cause a larger overhead

A small ALT_TIMEOUT period will result A small ALT_TIMEOUT period will result in more than one coordinatorsin more than one coordinators

Conclusions and DiscussionConclusions and Discussion

Nodes which are not within communication Nodes which are not within communication range of each otherrange of each other

Separate topology maintenance and Separate topology maintenance and optimization protocol in order to take into optimization protocol in order to take into account mobility and nodes entering and account mobility and nodes entering and leaving the networkleaving the network

Meet King Harald BluetoothMeet King Harald Bluetooth

1010thth Century Viking Century Viking KingKing

King Harald united King Harald united Denmark and Norway. Denmark and Norway. Bluetooth of today Bluetooth of today will unite the world of will unite the world of computers and computers and telecomtelecom