[PPT] - Open-Source Cyber-Physical Network Infrastructure Tobias Betz PowerPoint Presentation

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Chair of Network Architectures and Services Department of Informatics Technical University of Munich

Open-Source Cyber-Physical Network Infrastructure

Tobias Betz

2017-12-13 Chair of Network Architectures and Services Department of Informatics Technical University of Munich

SLIDE 2

Motivation

Open standards: 6TiSCH network stack
Open-source firmware: OpenWSN
Open hardware: OpenMote

IEEE 802.15.4 PHY IEEE 802.15.4e TSCH MAC 6TiSCH 6top 6LoWPAN adaptation layer IPv6 UDP ICMPv6 CoAP RPL

[1]

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Background — IEEE 802.15.4e TSCH

TSCH: Time-Slotted Channel Hopping A B C D E

A → B B → C B → C D → C E → B B → ∗

101 timeslots ≈ 10ms 16 channels

Synchronized timeslots
Scheduled transmissions
Channel hopping
Energy-efficient
Deterministic MAC behavior
Robust

against interference / multi-path fading

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Background — 6TiSCH

IETF working group: "IPv6 over TSCH mode of IEEE 802.15.4e"

IEEE 802.15.4 PHY IEEE 802.15.4e TSCH MAC 6TiSCH 6top 6LoWPAN adaptation layer IPv6 UDP ICMPv6 CoAP RPL A B C D E

A B

ADD 2 [x,y] SUCCESS [x,y]

6top Protocol (6P)

Send requests to L2 neighbors to add / delete / relocate cells in the shared schedule [2]. Allows nodes to dynamically adapt their TSCH schedules.

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Background — 6TiSCH Scheduling function

Runs on each 6TiSCH node, monitors traffic requirements, and triggers 6P transactions [3]. If more bandwidth is needed, a 6P ADD request is sent including the locations of the candidate cells. The default implementation (SF0) chooses random cell locations, which seems inconsistent with deterministic MAC behavior. ⇒ Main work: make SF0 more efficient and deterministic

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New Implementation — hashSF

Modifications from SF0: M.1: Use the addresses of both nodes to generate a hash that maps to a determin- istic sequence of cell locations ⇒ determinism M.2: Use spare candidate cells in 6P requests ⇒ efficiency M.3: Let the RPL parent choose cell locations ⇒ efficiency

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Modification M.1 — Hashed cell locations

hash(A B) = 0xb35f... 0xb3 mod (nrChannels · nrTimeslots) = 3 0x5f mod (nrChannels · nrTimeslots) = 95 ...

0a → 0b 0a → 0b

1

0a → 0b

2

0a → 0b

5

0a → 0b

6

0b → 0d 0e → 0b 0c → 0e 0a → 0e

1 2 3 4 5 15 channelOffset 1 2 3 4 5 10 slotOffset

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Modification M.2 — Spare cells in 6P transactions

A B

ADD 1 [x,y,z] SUCCESS [y]

Send a larger list of cells in the 6P requests to allow the neighbor to choose from more cell locations. ⇒ 6P requests are more likely to succeed

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Modification M.3 — Let RPL parent choose cell locations

A B

ADD 2 [] SUCCESS [x,y] CONFIRM [x,y]

Child node has less busy schedule than parent ⇒ chosen cell locations might not be free in parent’s schedule Use 3-step 6P transactions to let RPL parent choose cells ⇒ more likely to succeed

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Measurements (1/2)

Compare chosen candidate cells for SF0 and M.1 ⇒ determinism

n1 n2 n3 n4

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Results — Chosen cell locations — SF0

n1 n2 n3 n4

1 2 3 4 5 6 7 8 9 10 Order of most frequent cell locations at parent n1 1 2 3 4 5 Frequency [%]

5.0% 133 3.8% 108 3.3% 171 3.3% 104 2.9% 120 2.9% 67 2.9% 141 2.9% 69 2.5% 174 2.5% 77

RPL child n2

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Results — Chosen cell locations — M.1

n1 n2 n3 n4

1 2 3 4 5 6 7 8 9 Order of most frequent cell locations at parent n1 5 10 15 20 25 30 Frequency [%]

33.0% 1 32.2% 6 25.7% 9 6.7% 17 0.9% 12 0.7% 21 0.4% 5 0.2% 7 0.2% 3

RPL child n2

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Measurements (2/2)

Compare timestamps of network formations events and ratio of denied 6P requests (SF0,

M.1+M.2, M.1+M.3) ⇒ efficiency of 6P transactions

n1 n3 n2 n4

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Results — Timestamps

10 20 30 40 Elapsed time [s]

Time spent in SF

SF0 M.1, M.2 M.1, M.3

Median SF0 1.40 s M.1, M.2 2.14 s M.1, M.3 2.30 s

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Results — Timestamps

50 100 150 200 Elapsed time [s]

Time until reachable

SF0 M.1, M.2 M.1, M.3

Median SF0 59.23 s M.1, M.2 61.91 s M.1, M.3 55.58 s

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Results — Ratio of successful 6P transactions

SF0 M.1, M.2 M.1, M.3 20 40 60 80 100 Ratio of successful requests [%]

81.6% 88.9% 98.7%

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Conclusion

Deterministic cell locations can be achieved by hashing the nodes’ addresses
Efficiency of 6P transactions can be increased by proposing more candidate cells (M.2) or

by letting the busier node choose the cells (M.3)

Faster scheduling function does not significantly affect network formation time
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Bibliography

[1] WoTT OpenMote. http://wott.tlc.unipr.it/site/images/nodes/OpenMote.png. [2]

Q. Wang, X. Vilajosana, and T. Watteyne.

6top Protocol (6P), 2017. https://tools.ietf.org/html/draft-ietf-6tisch-6top-protocol-07. [3] Diego Dujovne, Luigi Alfredo Grieco, Maria Rita Palattella, and Nicola Accettura. 6TiSCH 6top Scheduling Function Zero (SF0), 2017. https://tools.ietf.org/html/draft-ietf-6tisch-6top-sf0-05. [4] Simon Duquennoy, Beshr Al Nahas, Olaf Landsiedel, and Thomas Watteyne. Orchestra: Robust Mesh Networks Through Autonomously Scheduled TSCH. In Proceedings of the 13th ACM Conference on Embedded Networked Sensor Systems, SenSys ’15, pages 337–350, New York, NY, USA, 2015. ACM.

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Backup — Chosen cell locations — M.1

n1 n2 n3 n4

1 2 3 4 5 Order of most frequent cell locations at parent n2 20 40 60 80 Frequency [%]

84.5% 1 10.7% 11 3.6% 17 1.2% 33 89.3% 2 6.0% 5 2.4% 17 1.2% 35 1.2% 11

RPL child n3 n4

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Backup — Timestamps

rebooted sync parent_found cell_added reachable Timestamp 50 50 100 150 200 250 Time [s] SF0 M.1, M.2 M.1, M.3

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Backup — Timestamp differences

rebooted 40 30 20 10 10 20 Time [s] diff_sync 25 50 75 100 125 150 175 diff_parent_found 2 4 6 8 10 diff_cell_added 10 20 30 40 SF0 M.1, M.2 M.1, M.3 diff_reachable 50 100 150 200

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Backup — Autonomous Scheduling Function (ASF)

#1 #2 #3 #4

(a) Topology

#3 #2 #1 #4

Time

RxTxS RxTxS RxTxS RxTxS RxTxS RxTxS RxTxS RxTxS

6 slots slotframe (b) Rendez-vous Time

#3 #2 #1 #4

Rx Rx TxS Rx TxS Rx TxS Rx TxS Rx TxS Rx TxS Rx

6 slots slotframe (c) Receiver-based

#3 #2 #1 #4

TxS Rx TxS Rx TxS Rx Rx TxS Rx Rx TxS TxS TxS TxS

Time 6 slots slotframe (d) Sender-based

Three types of slotframes as defined in ASF . The network topology consists of four nodes. The cell types are labeled as Tx (transmit), Rx (receive), and S (shared), from [4]

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