Post Order based Scheduling Post Order traversal of
Post Order based Scheduling Post Order traversal of a Tree • Visit parent after visiting children 12 5 3 1 4 2 11 9 6 7 10 8
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 = 2 p sec, node 2 fires – At t = kp sec, node k fires & so on • What is p ?
An Example 12 5 3 1 11 4 2 6 9 7 10 8
Why should it work ? Simultaneous transmissions taking place all over the tree. What about collisions ? Ø Node m+1 is atmost a level higher than node m. Ø Message of node m is always above that of node m+1 at any time t. => Messages cannot collide ! 12 5 11 3 4
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.
Implementation Stages ü Post Order Number assignment. Fully implemented and tested for a multi hop network. ü Time Synchronization. • Initiation and maintenance.
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
T=0 13
T=1 12 8
T=2 11 7 5 8
T=3 10 6 4 3 7 5 8
T=4 9 5 3 2 6 4 3 7 4 8
T=5 8 4 2 1 5 3 2 6 3 4 7 6
T=6 7 3 1 4 2 2 3 Size 1 0 1 6 5 1 4 5
T=7 6 2 3 5 4 Size 2 0 1 1 Size 1 0 0 2 3 Size 1 0 1 4
T=8 5 1 2 Size 2 0 0 4 3 Size 1 0 1 2 Size 1 0 0 3
T=9 4 Size 5 0 1 3 2 Size 3 0 0 0 0 1 0 2
T = 10 3 Size 1 0 0 2 1 Size 1 0 0 0 0 0 1
T = 11 2 Size 6 0 0 1 0 Size 1 0 0 0 0 0
T = 12 1 Size 2 0 0 0 0
T = 13 0 0 0 0
Pros and Cons • Pros – Power Efficiency – Faster approach, lower query time • Cons – Need for large message sizes – Possible interference due to simultaneous communication
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
Future Schedule • First CVS snapshot of GUI to be completed by 15 th 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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