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Post Order based Scheduling

Assigning node numbers in post order traversal to schedule firing. Simultaneous transmissions, collision avoidance, and pros/cons outlined. Implemantation stages and alternates discussed.

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Post Order based Scheduling

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  1. Post Order based Scheduling Post Order traversal of a Tree • Visit parent after visiting children

  2. Description • Each node assigned a number according to its position in Post Order traversal. • At t = 0 , process begins • At t = p sec, node 1 fires • At t = 2p sec, node 2 fires • At t = kp sec, node k fires & so on • What is p ?

  3. An Example

  4. Why should it work ? Simultaneous transmissions taking place all over the tree. What about collisions ? • Node m+1 is atmost a level higher than node m. • Message of node m is always above that of node m+1 at any time t. => Messages cannot collide !

  5. Pros and Cons Pros • Time Period - proportional to number of nodes • Collision Avoidance guaranteed by theoretical model • Message Loss is tolerated by system. Cons • Power Consumption. • Time Synchronization.

  6. Implementation Stages • Post Order Number assignment. Fully implemented and tested for a multi hop network. • Time Synchronization. • Initiation and maintenance.

  7. The alter-ego : Store & Forward scheduling • Basic Idea : Collect information from children, add your own data, forward entire packet • Possibility of simultaneous queries in the network • Involves dynamic packet sizes

  8. T = 0 13

  9. T = 1 12 8

  10. T = 2 11 7 8 5

  11. T = 3 10 6 7 8 4 5 3

  12. T = 4 9 8 5 6 7 4 3 4 2 3

  13. T = 5 8 7 4 5 6 6 3 4 2 3 1 2

  14. T = 6 7 6 3 4 5 5 2 3 4 1 2 Size 1 1 0 1

  15. T = 7 6 5 2 3 4 Size 2 4 1 2 3 0 1 Size 1 Size 1 0 1 0 0

  16. T = 8 5 4 1 2 3 Size 1 Size 2 3 0 1 2 0 0 Size 1 0 0 0 0

  17. T = 9 4 Size 5 3 0 1 2 Size 3 2 0 0 1 0 0 0 0 0 0

  18. T = 10 3 Size 1 2 0 0 1 Size 1 1 0 0 0 0 0 0 0 0 0

  19. T = 11 2 Size 6 1 0 0 0 Size 1 0 0 0 0 0 0 0 0 0 0

  20. T = 12 1 Size 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0

  21. T = 13 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

  22. Pros and Cons • Pros • Power Efficiency • Faster approach, lower query time • Cons • Need for large message sizes • Possible interference due to simultaneous communication

  23. Implementation Status • Protocol coded, debugged and tested in very small scale networks • Need to test in a large multi-hop environment • Protocol is compatible with other stages in network setup

  24. Future Schedule • First CVS snapshot of GUI to be completed by 15th October • Scheduling protocols to be fully developed by end October • November : To be spent in optimizations. Ex. Improving radio stack, Using global counters for clock etc.

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