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

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

IEEE 802.15.4e Review

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

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

Slotframe Global View ASN 1 2 3 4 5 6 7 8 TS C→B B→A For A ASN 1 2 3 4 1 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

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

Channel 𝑓=𝐹{ 𝐴𝑆𝑁+𝑐ℎ𝑂𝑓 𝑚𝑜𝑑 𝑛 𝑐ℎ }

Cell Type Shared slots Dedicated slots

Distributed Scheduling

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

IETF 6TiSCH 6top Cell Model Transmit Receive Shared Timekeeping

6top Transaction

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

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.

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

SF0 Allocation Policy

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

Simulation Results

Simulation Results Motes only start generating data at packetPeriod/2

Simulation Results

Centralized Scheduling

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

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 802.15.4e networks

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

TASA Algorithm root B C A D E F 1 2 3 C->root Slot Offset 0 1 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

TASA Algorithm root B C A D E F 1 2 3 C->root D->A Slot Offset 0 1 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

TASA Algorithm root B C A D E F 1 2 3 C->root A->root D->A 1 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

TASA Algorithm root B C A D E F 1 2 3 C->root A->root D->A 1 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

TASA Algorithm root B C A D E F 1 2 3 4 5 C->root A->root 1 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

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.

TASA Simulation

Autonomously Scheduling

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

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

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

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)

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

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

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

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

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

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

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

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

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

Orchestra Performance Analysis 20 nodes One packet per 500 ms

Orchestra Evaluation

Orchestra Evaluation Upward in Indriya PRR (Packet Reception Rate)

Orchestra Evaluation Random link failure

Conclusion

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

Reference – Distributed “ 6top Protocol (6P).” [Online]. Available: https://tools.ietf.org/html/draft-ietf-6tisch-6top-protocol-08. “6TiSCH 6top Scheduling Function Zero (SF0).” [Online]. Available: https://tools.ietf.org/html/draft-ietf-6tisch-6top-sf0-05. 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.

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 802.15.4e networks,” 2012 IEEE 23rd International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC), 2012.

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

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