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 channelsin 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 IP Control Data Applications SDP RFCOMM Audio L2CAP Link Manager Baseband RF

8. Functional Overview Standby • 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 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 • Pagingprocedure “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