Post Order based Scheduling

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 m1 is atmost a level higher than node m.
• Message of node m is always above that of node
  m1 at any time t.
• gt 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.