1. Scheduling Mechanism in IEEE 802.15.4e
SPEAKER: CHUN-WEI CHANG
ADVISOR: DR. HO-TING WU
DATE: 2017/11/10

2. Outline IEEE 802.15.4e Review Distributed Scheduling
Centralized Scheduling
Autonomously Scheduling
Reference

3. IEEE e Review

4. IEEE 802.15.4e Time Slotted Channel Hopping (TSCH)
Absolute Slot Number (ASN)
The total number of timeslots that has elapsed.
Links

5. Slotframe Slotframe is a collection of timeslots repeating in time.
ASN 1 2 3 4 5 6 7 8 TS
C→B
B→A
Slotframe
length
Slot offset

6. Slotframe Global View ASN 1 2 3 4 5 6 7 8 TS C→B B→A For A ASN 1 2 3 41 2 3 4 5 6 7 8 TS
C→B
B→A
For A
ASN 1 2 3 4 5 6 7 8 TS
OFF RX
For B
ASN 1 2 3 4 5 6 7 8 TS RX TX
OFF

7. Multiple Slotframes Note: TX > RX
ASN 1 2 3 4 5 6 7 8
Slotframe 1
5 slots
Slotframe 2
3 slots
Note:
TX > RX
Lower slotframeHandler > higher slotframeHandler

8. Channel
𝑓=𝐹{ 𝐴𝑆𝑁+𝑐ℎ𝑂𝑓 𝑚𝑜𝑑 𝑛 𝑐ℎ }

9. Cell Type
Shared slots
Dedicated slots

10. Distributed Scheduling

11. Distributed Scheduling
Goal:
Motes and it’s neighbors work together to obtain schedules
Faster reaction time

12. IETF 6TiSCH 6top
Cell Model
Transmit
Receive
Shared
Timekeeping

13. 6top Transaction

14. 6top Command Adding cells Deleting cells Relocating cells
Counting cells
Listing cells
Clear the schedule
6 top provide a protocol to exchange message between mote. However scheduling method is not defined in 6top

15. 6TiSCH 6top Scheduling Function Zero (SF0)
SF0 dynamically adapts the number of scheduled cells between neighbor nodes, based on the amount of currently allocated cells and the neighbor nodes' cell requirements.

16. SF0 Cell Estimation Algorithm
Collect the current number of used cells to the neighbor
Calculate the new number of cells to be scheduled to the neighbor by adding the current number of used cells plus an OVERPROVISION number of cells
Transfer the request to the allocation policy as REQUIREDCELLS

17. SF0 Allocation Policy

18. SF0 Analysis
On-the-Fly Bandwidth Reservation for 6TiSCH Wireless Industrial Networks

19. Simulation Results

20. Simulation Results
Motes only start generating data at
packetPeriod/2

21. Simulation Results

22. Centralized Scheduling

23. Centralized Scheduling
A central place to manage all motes’ scheduling
Once scheduling table have been calculated, need a way to notify all mote their new scheduling table.
mote
mote
Network Manager
mote
mote
mote

24. Traffic Aware Scheduling Algorithm
Local Queue (LQ) = packets need to transmit in one slotframe
Global Queue (GQ) = the total number of LQ of the nodes belonging to the given sub-tree
root B C A D E F
LQ:1
GQ:2
LQ:1
GQ:1
LQ:1
GQ:3
LQ:1
GQ:1
LQ:1
GQ:1
LQ:1
GQ:1
Traffic Aware Scheduling Algorithm for reliable low-power multi-hop IEEE e networks

25. TASA Algorithm Find the largest GQ with LQ > 0 and without conflict
Assign link to mote
For sender, LQ - 1, GQ – 1
For receiver, LQ +1
Find link’s conflict
Continue to next channel and go to 1
Continue to next slot and go to 1

26. TASA Algorithm root B C A D E F 1 2 3 C->root Slot Offset 01 2 3
C->root
Slot Offset 0
Channel Offset 0
root B C A D E F
LQ:1
GQ:2
LQ:1
GQ:1
LQ:1
GQ:3
LQ:0
GQ:2
LQ:1
GQ:1
LQ:1
GQ:1
LQ:1
GQ:1

27. TASA Algorithm root B C A D E F 1 2 3 C->root D->A Slot Offset 01 2 3
C->root
D->A
Slot Offset 0
Channel Offset 1
root B C A D E F
LQ:2
GQ:2
LQ:1
GQ:2
LQ:1
GQ:1
LQ:0
GQ:2
LQ:0
GQ:0
LQ:1
GQ:1
LQ:1
GQ:1
LQ:1
GQ:1

28. TASA Algorithm root B C A D E F 1 2 3 C->root A->root D->A1 2 3
C->root
A->root
D->A
Slot Offset 1
Channel Offset 0
root B C A D E F
LQ:1
GQ:1
LQ:2
GQ:2
LQ:1
GQ:1
LQ:0
GQ:2
LQ:0
GQ:0
LQ:1
GQ:1
LQ:1
GQ:1

29. TASA Algorithm root B C A D E F 1 2 3 C->root A->root D->A1 2 3
C->root
A->root
D->A
E->C
Slot Offset 1
Channel Offset 1
root B C A D E F
LQ:1
GQ:1
LQ:1
GQ:1
LQ:0
GQ:2
LQ:1
GQ:2
LQ:0
GQ:0
LQ:0
GQ:0
LQ:1
GQ:1
LQ:1
GQ:1

30. TASA Algorithm root B C A D E F 1 2 3 4 5 C->root A->root1 2 3 4 5
C->root
A->root
B->root
D->A
E->C
F->C
root B C A D E F
LQ:0
GQ:0
LQ:0
GQ:0
LQ:0
GQ:0
LQ:0
GQ:0
LQ:0
GQ:0
LQ:0
GQ:0

31. TASA Problem
After scheduling calculation, need to find a way to tell all motes to follow the schedule result.
In our experiment, we use CoAP messages to send scheduling table to motes.

32. TASA Simulation

33. Autonomously Scheduling

34. Autonomously Scheduling
Goal:
Quicker scheduling calculation
Less message exchange
Each mote maintain their own schedules
Reliable
Orchestra

35. Orchestra: Robust Mesh Networks Through Autonomously Scheduled TSCH
No message exchange to maintain MAC schedule
Relies on existing network stack information
PRL

36. RPL - Review root B C A D E F In RPL Non-Storing mode
Parent is chosen by child
Parent does not know who is his child
root B C A D E F
In RPL Storing mode
Parent is chosen by child
Parent know who is his child

37. Orchestra Slot Types Four types of slots:
Common Shared Orchestra Slots (CS)
Receiver-based Shared Orchestra Slots (RBS)
Sender-based Shared Orchestra Slots (SBS)
Sender-based Dedicated Orchestra Slots (RBD)

38. Common Shared Orchestra Slots (CS)
Used by both Rx & Tx
Installed at fixed coordinates (time and channel offset)
Similar to slotted ALOHA
TSCH use exponential back-off to resolve contention
Allowing RPL to discover neighbor

39. CS Example root B C A D E F CS slotframe length: 11 Slot offset: 0 1 21 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 CS V

40. Receiver-based Shared Orchestra Slots (RBS)
Communication between two neighbors
From properties of the receiver
Each mote have:
One Rx slot (based on node itself)
One Tx slot per neighbor (based on neighbors)
Can work on RPL Storing & Non-Storing mode
TSCH use exponential back-off to resolve contention

41. Slot Coordinate Method
𝑠𝑙𝑜𝑡𝑂𝑓𝑓𝑠𝑒𝑡=𝑢𝑛𝑖𝑞𝑢𝑒𝐼𝑑𝑒𝑛𝑡𝑖𝑓𝑒𝑟%𝑠𝑙𝑜𝑡𝑓𝑟𝑎𝑚𝑒𝐿𝑒𝑛𝑔𝑡ℎ
𝑢𝑛𝑖𝑞𝑢𝑒𝐼𝑑𝑒𝑛𝑡𝑖𝑓𝑒𝑟 can obtained by hard-coded or use a hash of the node’s MAC address.
Example: A688
𝐻𝑎𝑠ℎ 𝐴688 =88
𝑠𝑙𝑜𝑡𝑂𝑓𝑓𝑠𝑒𝑡=88%11=0

42. A does not know his children
RBS Example
Slotframe length: 13
If A want to send to receiver root:
root have coordinate at 0
->Tx at slot offset 0
If A want to receive from other:
A have coordinate at 1
-> Rx at slot offset 1
root B C A D E F 1
A does not know his children 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 CS V
RBS Tx Rx

43. Sender-based Shared Orchestra Slots (SBS)
From properties of the sender
Each mote have:
One Tx slot (based on mote itself)
One Rx slot per neighbor (based on neighbor)
Can only work on RPL Storing mode
TSCH use exponential back-off to resolve contention

44. SBS Example root B C A D E F 1 4 Slotframe length: 13
If A want to send to receiver root:
A have coordinate at 1
->Tx at slot offset 1
If A want to receive from other (D):
D have coordinate at 4
-> Rx at slot offset 4
root B C A D E F 1
A know his children 4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 CS V
RBS Tx Rx
SBS

45. Sender-based Dedicated Orchestra Slots (SBD)
In SBS we use uniqueID % slotframeLength If
slotframe length is long enough for all transmit
unique identifier are available
SBS can become SBD
Can only work on RPL Storing mode

46. Orchestra Performance Analysis
Contention Rate
In network with N nodes:
Average traffic load on slot with Poisson distribution
Slotframe length

47. Orchestra Performance Analysis
20 nodes
One packet per 500 ms

48. Orchestra Evaluation

49. Orchestra Evaluation
Upward in Indriya
PRR (Packet Reception Rate)

50. Orchestra Evaluation
Random link failure

51. Conclusion

52. Conclusion Distributed Centralized Autonomously Coordinated by
Between motes
Central manager (SPF)
Mote itself
Reaction time to traffic changed
Fast
Slow No
Reaction time to topology changed
Fastest
Message exchange to create schedule
Medium
(between motes)
High
(mote and manager)
None
Controllability
Low
Change On-The-Fly
Yes

53. Reference – Distributed
“ 6top Protocol (6P).” [Online]. Available:
“6TiSCH 6top Scheduling Function Zero (SF0).” [Online]. Available:
M. R. Palattella, T. Watteyne, and Q. Wang, “On-the-Fly Bandwidth Reservation for 6TiSCH Wireless Industrial Networks,” IEEE SENSORS JOURNAL, VOL. 16, NO. 2, JANUARY 15, 2016.

54. Reference - Centralized
M. R. Palattella, N. Accettura, M. Dohler, L. A. Grieco, and G. Boggia, “Traffic Aware Scheduling Algorithm for reliable low- power multi-hop IEEE e networks,” 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC), 2012.

55. References - Autonomously
S. Duquennoy, B. A. Nahas, O. Landsiedel, and T. Watteyne, “Orchestra,” Proceedings of the 13th ACM Conference on Embedded Networked Sensor Systems - SenSys 15, 2015

56. Thanks for Listening