Distributed Topology Construction of Bluetooth Personal Area Networks

1
Distributed Topology Construction of Bluetooth
Personal Area Networks

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

2
Objective of Study

• Multiple channels in an ad-hoc network
• Which subgroup of nodes share a common channel
  and which act as forwarding nodes
• Bluetooth Topology Construction Protocol
  Asynchronous distributed protocol for
  constructing scatternets

3
Introduction to Bluetooth

• Cable replacement technology
• Range is 10 meters so is targeted for personal
  area networks
• Based on a frequency hopping physical layer

4
Bluetooth Piconet

• A group of devices sharing a common channel
• Piconet consists of a Master and up to 7 slave
  devices

5
Bluetooth Piconet (contd.)

• Within a piconet channel is shared using TDD
  protocol
• Multiple piconets can co-exist using different
  hopping sequences
• Piconets interconnected via bridge nodes to form
  scatternets
• Bridge nodes are capable of timesharing between
  multiple piconets

6
Scatternet

• Scatternet with a shared Bridge node

7
Bluetooth Protocol Stack
Applications
SDP
RFCOMM
Audio
L2CAP
Link Manager
Baseband
RF
8
Functional Overview

• Standby
• Waiting to join a piconet
• Inquire
• Ask about radios
• to connect to
• Page
• Connect to a specific radio
• Connected
• Device is active on a piconet (master or
  slave)
• Park/Hold
• Low power connected states

Standby
Inquiry
Page
Transit Data
Connected
Park
Hold
Sniff
9
Connection Setup
Inquiry - scan protocol To learn about the clock
offset and device address of other nodes in
proximity
10
Addressing

• Bluetooth device address (BD_ADDR)
• 48 bit IEEE MAC address

• Active Member address (AM_ADDR)
• 3 bits active slave address
• assigned by Master

• Parked Member address (PM_ADDR)
• 8 bit parked slave address

11
Link Establishment in Bluetooth

• Inquiry procedure
• senders discover and collect neighborhood
  information
• Paging procedure
• senders connect to receivers
• Frequency Synchronization delay
• Time until sender transmits at the frequency
  receiver is listening to

12
Asymmetric Protocol for Link Formation

• Random Backoff Delay
• Receiver backs off for an amount of time
  between 0 639.375 ms on receiving IAC packet
• Link formation delay
• 2FS RB
• Initial FS delay until the sender hits frequency
  receiver is listening to and second FS delay
  after a second IAC packet is received from sender

13
Bluetooth Asymmetric Link Formation Protocol
Target
Initiator
IAC
1.Start Inquiry state
2.Start Inquiry state
3.Go to Sleep
IAC
4.Wake up
FHS
6.Enter Page state
5.Respond and enter Page Scan state
DAC
DAC
7.Connection Established
7.Connection Established
FHS
DAC
14
A Symmetric Protocol for Link Formation

• Forms connections in an ad hoc manner without any
  explicit sender or receiver role pre-assignment
• Nodes alternate between the sender (INQUIRY
  state) and receiver (INQUIRY SCAN state)

S
I
S
I
I
S
I
S
15
Connection Establishment Protocol

• Node has no initial knowledge about the other
  devices in the room
• Protocol must guarantee a connected scatternet
• Network setup delay should be minimized to the
  end user

16
BTCP A Distributed Scatternet Formation Protocol

• BTCP is based on a leader election process
• A bridge node may connect only two piconets
• The resulting scatternet should consist of
  minimum number of piconets
• Scatternet should be fully connected
• Two piconets share only one bridge

17
Phase I Coordinator Election

• Election of a coordinator node
• Two nodes that discover each other compare their
  VOTES variable
• Node with larger VOTES variable is selected
  winner
• Loser tears down connection and enters PAGE SCAN
  state
• Winner node increases its VOTES by VOTES (loser)

18
Phase II Role Determination

• Coordinator elected during Phase I has FHS
  packets of all the nodes
• Coordinator decides role that each node performs
  in scatternet
• Coordinator has a connectivity list set
  (SLAVESLIST(x), BRIDGELIST(x))
• Temporary piconet is formed with the coordinator
  as the Master

19
Phase III Connection Establishment

• Each Master pages and connects to the slaves and
  bridges
• Bridge node waits to be paged by a second master
  and then sends a CONNECTED notification

20
State Alternation Timeout ALT_TIMEOUT

• ALT_TIMEOUT expires
• Node assumes it is the elected coordinator
• Large ALT_TIMEOUT
• Node having won the competition continues to
  alternate
• Small ALT_TIMEOUT
• More than one nodes assume they are the
  coordinator and result in a disconnected
  scatternet

21
Protocol Performance

• Network connection setup delay and the
  probability of protocol correctness
• A large ALT_TIMEOUT period will satisfy the
  correctness condition with higher probability
  but will cause a larger overhead
• A small ALT_TIMEOUT period will result in more
  than one coordinators

22
Conclusions and Discussion

• Nodes which are not within communication range of
  each other
• Separate topology maintenance and optimization
  protocol in order to take into account mobility
  and nodes entering and leaving the network

23
Meet King Harald Bluetooth

• 10th Century Viking King
• King Harald united Denmark and Norway. Bluetooth
  of today will unite the world of computers and
  telecom