Hasan SÖZER1 Data Scheduling and SAR for Bluetooth MAC Manish Kalia, Deepak Bansal, Rajeev Shorey IBM India Research Laboratory

Hasan Sözer2 Outline Medium Access Control in Bluetooth Problems & Restrictions faced in Bluetooth MAC Goals, Assumptions & Approaches Priority Policy (PP) K-Fairness Policy (KFP) Scheduling Data in Presence of Voice Bluetooth SAR Policy & Possible Improvements Results & Conclusion

Hasan Sözer3 Medium Access Control in Bluetooth TDD slot structure with strict alternation of slots between the Master and the Slaves Single point of coordination (at Master) Polling based A slave transmits packets in the reverse slot only after the Master polls the slave in a forward slot Thus, Bluetooth is a Master driven, polling based TDD standard

Hasan Sözer4 Problems & Restrictions Conventional scheduling policies such as Round Robin (RR) does not perform well Bluetooth MAC enforces tight coupling of uplink & downlink, which leads to slot wastage TDD structure also restricts the packet size (1,3 or 5)

Hasan Sözer5 Goals, Assumptions & Approaches Parameters of interest: system throughput packet delays fairness packet drop probability simplicity satisfying the low cost objective of Bluetooth standard. conflicting objectives

Hasan Sözer6 Goals, Assumptions & Approaches (Continues...) Criterias that an efficient scheduling policy would depend on: state of the queues at the Master and the Slaves traffic arrival process at these queues packet length distributions

Hasan Sözer7 Goals, Assumptions & Approaches (Continues...) N queues at the Master for a piconet with N slaves Each slave has a queue for its connection with the Master Binary information is used in order to represent the state of the queues: 1 : has data to send0: has no data awaiting State of the queue at the Slave is available at the Master (requires only 1 bit of information to transfer)

Hasan Sözer8 Priority Policy (PP) There are four possibilities for the state of the queues regarding a connection: 1-1: Both Master and Slave have data to send 1-0 or 0-1: Only one side has data awaiting 0-0: Neither of them has data to send PP assigns different priorities to these: 1-1 > 1-0 = 0-1, 0-0 is not scheduled It is also argued that it could be 1-0 > 0-1 (*) * Master:1 – Slave:0 > Master:0 – Slave:1

Hasan Sözer9 K-Fairness Policy (KFP) Beyond optimization and system throughput: Having a strict fairness bound qmax: Master-Slave queue pair that has received maximum excess service (service sacrified to it) qmin: Master-Slave queue pair that has sacrificed maximum service to other connections (Services of qmax – Services of qmin) can be at most K When K = 0, KFP tuns out to be pure Round Robin In order to prevent more sacrifices: Change 1-0 into 1-1

Hasan Sözer10 Scheduling Data in Presence of Voice Extend PP (to HOL-PP) & KFP (to HOL-KFP) Consider slot utilization by using Head-of-the-line (HOL) packets (higher utilization -> higher priority)

Hasan Sözer11 Bluetooth SAR Policy & Possible Improvements Bluetooth Segmentation and Reassembly (SAR): naive SAR is random: assigns data packet sizes (1, 3 or 5) probabilistically. Instead, data arrival rates at the Master and Slave queues can be used -> Intelligent SAR (ISAR) (?): Initially all queues have packet size of 1 Packet sizes change according to the differences in arrival rates at the Master and Slave Binary information represent high/low data rates

Hasan Sözer12 Results & Conclusion Simulation results (K=500 & P=4, for 5000 TDD slots): KFP > PP > RR in throughput KFP < PP < RR in average delay (units of slots) KFP gives better throughput than PP with more fairness ISAR > SAR by means of throughput Keep It Simple and Stupid!

Hasan Sözer13 Interconnecting Bluetooth-like Personal Area Networks Godfrey Tan MIT Laboratory of Computer Science

Hasan Sözer14 Outline Conclusion Challenges of Interconnecting Bluetooth-like PANS & proposed solutions for each: Scatternet topology formation Packet routing Channel or link scheduling

Hasan Sözer15 Scatternet Formation Decentralized and self-healing algorithm Unique address for each node that are connected in a tree structure (constructed incrementally) Loop-free No packet overhead No periodic routing messages New nodes join with search announcements (root or the new node can choose among possible points of attachement)

Hasan Sözer16 Scatternet Formation (Continues...) 0N0N 0* 10 N-1 1*11* 110 N-2 10* 101* 100* 1010 N * 1010* N-4 b k = k b’s, where b = 0 or 1 Each node holds the portion of the address space allocated to each child

Hasan Sözer17 Packets Relaying & Channel Scheduling Relaying of packets are accomplished by means of a technique that is similar to forwarding of IP packets makes use of longest-prefix match Channel scheduling problem is declared to be similar to the maximal matching problem for bi-partite graphs An upper-bound of ceiling(d/2)*MaxDegree (*) is given for an algorithm of which details are not given * MaxDegree = depth of the tree, d = distance in hops

Hasan Sözer18 Conclusion It is declared that the algorithms are implemented in ns-2 and give good performance but simulation results are not presented The key idea is to construct the scatternet as a tree makes other problems easy to keep track of If the root is the one that hadle new attachements, it would have large overhead Enforcement of tree structure may cause deficiencies

Hasan Sözer19 Scatternet Structure and Inter-Piconet Communication in the Bluetooth System Manish Kalia, Sumit Garg, Rajeev Shorey IBM India Research Laboratory

Hasan Sözer20 Outline Piconet models and possible scatternet structures Single Piconet Model (SPM) Scatternet Model Two-Level Hierarchy of Piconets (TLP) Shared Slave Piconets (SSP) Performance Comparisons & Conclusion

Hasan Sözer21 Single Piconet Model (SPM) Single piconet is used even if there exists more then seven slaves Model uses the “Park mode” Timestamps are used in order to determine the period in which a slave remained parked/unparked Periodically, parked Slave with the oldest timestamp is unparked and active Slave with oldest timestamp is parked Each Slave remains unparked for the same time period

Hasan Sözer22 Scatternet Model Notion of a “Communicating Group” (CG): A group of mobile devices which have frequent data transfer in between When forming scatternets try to make members of a CG reside in the same piconet Start with a SPM, structure the scatternet by collecting traffic flow patterns Master can observe destination addresses (Efficient policies for discovering and updating CGs are not investigated)

Hasan Sözer23 Two-Level Hierarchy of Piconets (TLP) Centralized design Notion of root & leaf piconets Masters of leaf piconets periodically become slaves of the root piconet (temporary Masters can be assigned)

Hasan Sözer24 Shared Slave Piconets (SSP) Decentralized structure A Slave in between, periodically switchs to the hopping pattern of two different Masters. Better load balancing & robust Routing is more complex

Hasan Sözer25 Performance Comparisons & Conclusion Simulation results with to piconets: System throughput: SSP > TLP > SPM Average System Delays SPM >> TLP > SSP Scatternet allows simultaneous communication in different piconets In TLP leaf piconets periodically suspend communication SPM can be improved by considering backlogged data at the Slave queues