Towards theInternet of Relevant Things
The IEEE 802.15.4e Standard
G. Anastasi, S. Brienza, D. De Guglielmo
Pervasive Computing & Networking Lab (PerLab)
Dept. of Information Engineering, University of Pisa
Website: www.iet.unipi.it/~anastasi/

PerLabACM SAC 2016 | Pisa, Italy, April 4‐8, 2016

Overview
PerLab Introduction
 IEEE 802.15.4 standard
 limitations

 IEEE 802.15.4e
 802.15.4e DSME mode literature survey
 open issues

 802.15.4e TSCH mode literature survey
 open issues

 IoT with 802.15.4e TSCH
 The 6TiSCH initiative

 Conclusions
Towards the Internet of Relevant Things2References
PerLab D. De Guglielmo, S. Brienza, G. Anastasi, IEEE 802.15.4e: a Tutorial andSurvey, Computer Communications, accepted with minor revision.
 G. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE
802.15.4e: a Step towards the Internet of Things, Chapter 10 in Advances
onto the Internet of Things, pp. 135‐152, January 2014. Springer

Towards the Internet of Relevant Things3

Internet of Things
PerLab“The next logical step in the technological revolution connecting people anytime,
anywhere is to connect inanimate objects. This is the vision underlying theInternet of things: anytime, anywhere, by anyone and anything”(ITU, Nov. 2005)

More than 26 billion devices will
be wirelessly connected to theInternet of Things by 2020

 computers and communication devices
 cars, robots, machine tools persons, animals, and plants
 garments, food, drugs, etc.

Towards the Internet of Relevant Things4Wireless Sensor & Actuator Networks (WSANs)
PerLab“WSANs will behave as a digital skin for the IoT
providing a virtual layer through which any
computational system can interact with the physicalworld”

C. Alcaraz, P. Najera, J. Lopez, R. Roman, Wireless Sensor Networks and the Internet of Things: Do we need a Complete
Integration? Proc. International workshop on the Security of The internet of Things (SecIoT 2010), Tokyo, Japan, 2010.
Towards the Internet of Relevant Things

5Standards for WSANs
PerLab IEEE 802.15.4/802.15.4e
 ZigBee Bluetooth WirelessHART ISA‐100.11a
 6LoWPAN IPv6 over Low power WPAN

 RPL
 Routing Protocol for Low powerand Lossy networks

 CoAP
 Constrained Application Protocol
Towards the Internet of Relevant Things

6IEEE 802.15.4 Standard
Reference technology for WSANs
Expected to be a major enabling technology
also for IoT

IEEE 802.15.4 standard
PerLab

 Standard for Personal Area Networks (PANs)
 low‐rate and low‐power
 PHY and MAC layers

 Main features transceiver management
 channel access PAN management
Towards the Internet of Relevant Things

8802.15.4 Network Topologies
PerLab

Ed Callaway, Paul Gorday, Lance Hester, Jose A. Gutierrez, Marco Naeve, Bob Heile, Home Networking with IEEE 802.15.4: DevelopingStandard for Low‐Rate Wireless Personal Area Networks, IEEE Communications Magazine, August 2002.
Towards the Internet of Relevant Things

9Channel frequencies
PerLabEuropeUSA(20 Kbps)(40 Kbps)(250 Kbps)

Ed Callaway, Paul Gorday, Lance Hester, Jose A. Gutierrez, Marco Naeve, Bob Heile, Home Networking with IEEE 802.15.4: DevelopingStandard for Low‐Rate Wireless Personal Area Networks, IEEE Communications Magazine, August 2002.
Towards the Internet of Relevant Things10802.15.4 MAC protocols
PerLab

 Two different channel access methods Beacon‐Enabled duty‐cycled mode
 Non‐Beacon Enabled mode (aka Beacon Disabled mode)

Non-beacon enabled

Beacon enabled
Superframe Structure

Contention based

Contention based

Contention free

Unslotted CSMA-CA

Slotted CSMA-CA

Reserved time slot

Towards the Internet of Relevant Things

11802.15.4 Beacon Enabled mode
PerLab

ActiveBeaconBeacon

GTS

CAP

GTS

Inactive

CFP

SD = aBaseSuperFrameDuration*2SO sym
BI = aBaseSuperFrameDuration*2BO sym

Towards the Internet of Relevant Things

12CSMA-CA: Beacon-Enabled mode
PerLab

NB=0, CW=2, BE= BE=macMinBE

At each trial the backoff‐
window size is doubled
Yes

Only a limited number ofattempts is permitted(macMaxCSMABackoffs)

No

No

No

Yes

Towards the Internet of Relevant Things

Yes

13

CSMA-CA: Non-Beacon Enabled mode
PerLab
Un-slotted CSMA

NB = 0,BE = macMinBE

Delay forrandom(2BE - 1) unit
backoff periods

At each trial the backoff‐
window size is doubled

Perform CCA

Channel idle?

Only a limited number ofattempts is permitted(macMaxCSMABackoffs)

Y

N
NB = NB+1,
BE = min(BE+1, aMaxBE)

N

NB>
macMaxCSMABackoffs?

Y
FailureTowards the Internet of Relevant Things

Success14

Acknowledgement Mechanism
PerLab Optional mechanism Destination Side ACK sent upon successful reception of a data frame Sender side Retransmission if ACK not (correctly) received within thetimeout At each retransmission attempt the backoff window size isre‐initialized Only a maximum number of retransmissions allowed(macMaxFrameRetries)

Towards the Internet of Relevant Things

15Limits of IEEE 802.15.4 MAC
PerLab

 Reliability and scalability issues
 Unbounded latency
 Due to contention‐based CSMA‐CA algorithm

 No guaranteed bandwidth Unless GTS is used
 GTS only provides a limited service (7 slots)

 No built‐in frequency hopping technique Prone to failures due to interferences and multi‐path fading

G. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE 802.15.4e: a Step towards the Internet of Things,
Chapter 10 in Advances onto the Internet of Things (S. Gaglio, G. Lo Re, Editors), pp. 135‐152. January 2014. Springer
Towards the Internet of Relevant Things16Performance of CSMA-CA in BE mode
PerLab

G. Anastasi, M. Conti, M. Di Francesco, A Comprehensive Analysis of the MAC Unreliability Problem in IEEE 802.15.4 WirelessSensor Networks, IEEE Transactions in Industrial Informatics, Vol. 7, N. 1, Feb 2011.
Towards the Internet of Relevant Things

17Limits of IEEE 802.15.4 MAC
PerLab

 Reliability and scalability issues
 Unbounded latency
 Due to contention‐based CSMA‐CA algorithm
 No guaranteed bandwidth Unless GTS is used
 GTS only provides a limited service (7 slots)
 No built‐in frequency hopping technique Prone to failure due to interferences and multi‐path
fadingG. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE 802.15.4e: a Step towards the Internet of Things,
Chapter 10 in Advances onto the Internet of Things (S. Gaglio, G. Lo Re, Editors), pp. 135‐152. January 2014. Springer
Towards the Internet of Relevant Things18Limits of IEEE 802.15.4 MAC
PerLab

 Reliability and scalability issues
 Unbounded latency
 Due to contention‐based CSMA‐CA algorithm
 No guaranteed bandwidth Unless GTS is used
 GTS only provides a limited service (7 slots)
 No built‐in frequency hopping technique Prone to failure due to interferences and multi‐path
fadingG. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE 802.15.4e: a Step towards the Internet of Things,
Chapter 10 in Advances onto the Internet of Things (S. Gaglio, G. Lo Re, Editors), pp. 135‐152. January 2014. Springer
Towards the Internet of Relevant Things

19Channel Hopping
PerLab

 Subsequent packets are sent at a different frequency
 following a pseudo‐random hopping pattern If a transmission fails
 retransmission will happen on a different frequency

 Greater chance of successful transmission
 than if the retransmission happened on the same channel
 Since a different frequency means different effects of multi‐path fading
and interference Increased security
 Against Selective Jamming attack

 Channel Hopping used in Bluetooth WirelessHart
Towards the Internet of Relevant Things

20

Key Question
How to do in real‐life
critical scenarios?

Some Real-life Scenarios
PerLab Smart Cities
 Smart Buildings Smart Homes
 Industrial Settings ....
Requirements
 M. Dohler, T. Watteyne, T. Winter, and D. Barthel, Routing Requirements for Urban Low‐Powerand Lossy Networks, IETF ROLL Std. RFC5548, May 2009.
 J. Martocci, P. De Mil, N. Riou, andW. Vermeylen, Building Automation Routing Requirements in
Low‐Power and Lossy Networks, IETF ROLL Std. RFC5867, June 2010.
 A. Brandt, J. Buron, G. Porcu, Home Automation Routing Requirements in Low‐Power and Lossy
Networks, IETF ROLL Std. RFC5826, April 2010
 K. Pister, P. Thubert, S. Dwars, and T. Phinney, Industrial Routing Requirements in Low‐Powerand Lossy Networks, IETF ROLL Std. RFC5673, Octobert 2009.
Towards the Internet of Relevant Things

22Requirements
PerLab Energy Efficiency
 Target battery lifetime: 5 years, or more

 Scalability Large network sizes Timeliness Alert applications, process monitoring, ...

 Reliability Wire‐like reliability may be required, e.g., 99.9% or better

Towards the Internet of Relevant Things

23

IEEE 802.15.4e
PerLab IEEE 802.15 Task Group 4e
 chartered to define a MAC amendment to the existing
standard 802.15.4‐2006.
 The intent of this amendment was to enhance and add
functionalities to the 802.15.4‐2006 MAC
 better support the industrial markets
 increase robustness against external interference On February 6, 2012 the IEEE Standards Association
Board approved the IEEE 802.15.4e MAC Enhancement
Standard document for publication.
 http://www.ieee802.org/15/pub/TG4e.html
Towards the Internet of Relevant Things24Major Changes
PerLab General functional improvements
 not tied to any specific application domain

 MAC Behavior Modes support of specific application domains

Remarks:
Many ideas borrowed from previous industrial
standards
 WirelessHART and ISA 100.11.a
 slotted access, shared and dedicated slots, multi‐channel
communication, and frequency hopping.

Towards the Internet of Relevant Things

25General Functional Improvements
PerLab

 Low Energy (LE) Information Elements (IE)
 Enhanced Beacons (EB) Multipurpose Frame MAC Performance Metrics
 Fast Association (FastA)

Towards the Internet of Relevant Things

26

MAC Behavior Modes
PerLab Radio Frequency Identification Blink (BLINK) item and people identification, location, and tracking

 Asynchronous Multi‐Channel Adaptation (AMCA)
 application domains where large deployments are required (e.g., process
automation/control, infrastructure monitoring, etc.)

 Deterministic & Synchronous Multi‐channel Extension (DSME)
 industrial and commercial applications with stringent timeliness andreliability requirements

 Low Latency Deterministic Network (LLDN) applications requiring very low latency requirement (e.g., factory
automation, robot control) Time Slotted Channel Hopping (TSCH)
 application domains such as process automation

Towards the Internet of Relevant Things

27

IEEE 802.15.4e DSMEDeterministic &Synchronous
Multichannel Extension

IEEE 802.15.4e DSMEPerLab Target Application Domains
 Industrial applications
 Commercial applications
 Healthcare applications

 Provides
 Flexibility Robustness
 High reliability
 Deterministic latency
 Scalability
 Efficiency
Towards the Internet of Relevant Things

29

Main Features
PerLab Multi‐channel, multi‐superframe
 Mesh extension to GTS
 Two channel diversity modes channel adaptation
 channel hopping Distributed beacon scheduling Distributed slot allocation
 Group acknowledgments
 Many topologies
 Star, cluster‐tree and peer‐to‐peer
Towards the Internet of Relevant Things

30

Multi superframe structure
PerLabWhen CAP reduction is enabled, only the first superframe in the multi‐
superframe has the CAP

Towards the Internet of Relevant Things

31Enhanced Beacons (EBs)
PerLab

 Sent by each coordinator at regular intervals
 At the beginning of superframes

 Contains parameters
 To regulate the multi‐superframe structure Indicates the enabled options
 Used for global time synchronization
 Each node associates with a coordinator (i.e., its time synchronization
parent) and tracks its EBs
 In order to join the network, a node performs a passive channel scanover a given list of channels
Towards the Internet of Relevant Things

32

Beacon Scheduling
PerLabEach coordinator transmits its EBs during a
superframe Distributed scheduling algorithm Beacon schedule information shared through EBs
 A bitmap sequence indicates the usage of beacon slots by its one‐hop
neighbors
 A bit in the bitmap is set to one if the corresponding beacon slot isalready used for EB transmission

 A prospective coordinator searches for a vacant slot in thebitmaps of all the received EBs
 Once the new device finds a vacant beacon slot, it uses the slot
as its own beacon slot

Towards the Internet of Relevant Things

33Channel Diversity
PerLab

 Channel Adaptation
 Two neighboring nodes can communicate using any of the freeavailable channels
 The channel is decided basing on the quality estimated by nodes
 The channel used in a DSME‐GTS does not change over time unless its quality degrades Channel Hopping Nodes change the communication channel at each DSME‐GTS
 The series of channels used is referred to as Hopping Sequence Each node has a Channel Offset
 an integer indicating the starting position in the Hopping Sequence A transmitting node has to switch to the channel used by thereceiverTowards the Internet of Relevant Things

34Channel Adaptation
PerLab

Towards the Internet of Relevant Things

35Channel Hopping
PerLabChannel number C at the given DSME‐GTS Slot ID i in SDIndex j, shallbe determined as follows:

Towards the Internet of Relevant Things

36

Data Structures (1/2)
PerLab

ALLOCATION COUNTER TABLE (ACT) A table containing an entry for each Guaranteed TimeSlot
allocated to the node
 Each entry stores the following information:
 Superframe ID
 Slot ID
 Channel ID
 Direction Address

Towards the Internet of Relevant Things

37

Data Structures (2/2)
PerLabSLOT ALLOCATION BITMAP (SAB) A bitmap used to store which GTSs in themulti‐superframe are allocated to thenode and its neighbors
 The SAB contains a bit for each possible
pair [ch, ts], indicating whether thechannel ch, during timeslot ts, is used (1)or not (0).

Towards the Internet of Relevant Things

38

DSME-GTSs
PerLab A DSME‐GTS is used for communication between a specificsource device and a specific destination device.
 A DSME‐GTS is allocated by the destination device,basing on requirements specified by the source node in the request
 current slot availability

 DSME‐GTSs are allocated on a
FCFS basis
 Three‐step allocation(during CAP)

Towards the Internet of Relevant Things

39

DSME-GTSs: Allocation (1/3)
PerLab• In this example, B wants to allocate a DSME‐GTS with C

A

B

C

D

 B sends a REQUEST in unicast to C
 The REQUEST indicates the available slots for allocation
 After transmission, node B waits for a REPLY from node C If the REPLY frame is not received in time, the allocation isassumed to be failed (i.e., a Timeout occured)
Towards the Internet of Relevant Things

40

DSME-GTSs: Allocation (2/3)
PerLabA

B

CD

 Once the REQUEST has been received, C search in its
bitmap for free GTSs in common with B If they are found, C updates its own data structures
 C sends a REPLY in Broadcast, indicating the newly
allocated GTSs
Towards the Internet of Relevant Things

41

DSME-GTSs: Allocation (3/3)
PerLabA

B

CD

 Upon receiving the REPLY, B updates its data structures
 B broadcasts a NOTIFY message to inform its neighbors
 When receiving a REPLY/NOTIFY, A and D check if they
already use the just allocated GTS:
• If not, they update their SAB• Otherwise, they send a error message to the sender
Towards the Internet of Relevant Things

42IEEE 802.15.4e DSME
Literature Review

Performance Evaluation
PerLab

 W.C. Jeong, J. Lee, Performance evaluation of IEEE 802.15. 4e DSME MAC protocol for
wireless sensor networks, In Proceedings of the first IEEE Workshop on Enabling
Technologies for Smartphone and Internet of Things (ETSIoT), Seoul, South Korea, 18
June 2012.
 T. Paso, J. Haapola, J. Iinatti, Feasibility study of IEEE 802.15.4e DSME utilizing IR‐
UWB and S‐Aloha, In Proceedings of the 24th IEEE International Symposium on
Personal Indoor and Mobile Radio Communications (PIMRC), London, United Kingdom,
8‐11 September 2013.
 J. Lee, W.C. Jeong, Performance analysis of IEEE 802.15.4e DSME MAC protocol under
WLAN interference, In Proceedings of the IEEE International Conference on ICT
Convergence (ICTC), Jeju Island, South Korea, 15‐17 October 2012.
 G. Alderisi, G. Patti, O. Mirabella, L. Lo Bello, Simulative assessments of the IEEE
802.15.4e DSME and TSCH in realistic process automation scenarios, In Proceedingsof the 13th IEEE International Conference on Industrial Informatics (INDIN),
Cambridge, United Kingdom, 22‐24 July 2015.

Towards the Internet of Relevant Things44802.15.4e DSME vs. 802.15.4 BE
PerLab DSME always offers a minimum throughput
 only limited by the number of available DSME‐GTSs

 In 802.15.4 BE the delivery ratio decreases when the # of nodes
increases
 DSME guarantees a deterministic delay it is unpredictable in 802.15.4 CSMA‐CA (or S‐Aloha)

 DSME shows a significant lower consumption
 as collisions cannot happen and CCA are not needed DSME is much more resistant toexternal interferences, thanks to its channel diversity
mechanisms

Towards the Internet of Relevant Things45

802.15.4e DSME vs. TSCH
PerLab

 Both are robust against channel noise assuring high reliability

 TSCH offers lower delays
 when the number of nodes is limited
 the DSME multi‐superframe structure does not adapt to the network size

 TSCH needs larger timeslots
 to accommodate ACKs DSME can benefit from the Group ACK option

 DSME exhibits lower delays
 when the number of nodes grows
 more DSME‐GTSs in the multi‐superframe are used.

G. Alderisi, G. Patti, O. Mirabella, L. Lo Bello, Simulative assessments of the IEEE 802.15.4e DSME and TSCH in realistic process
automation scenarios, Proc. IEEE International Conference on Industrial Informatics (INDIN 2015), Cambridge, UK, July 2015
Towards the Internet of Relevant Things46

General Enhancements (1/2)
PerLab

 ELPIDA (Enhancements for Low‐Power Instrumentation DSME Applications) Aims at making DSME more energy efficient in cluster‐tree
networks
 Limits the time spent by leaf nodes radio in RX state (e.g.
during CAP)
 Introduces three main changes to DSME: CAP Wake‐up
 DSME‐GTS Wake‐up Beacon Look‐up

 ELPIDA decreases the energy consumption of end devices
 up to a factor 7, if compared with standard DSMES. Capone, R. Brama, F. Ricciato, G. Boggia, and A. Malvasi, Modeling and Simulation of Energy Efficient Enhancements for IEEE
802.15.4e DSME, Proceedings of Wireless Telecommunications Symposium (WTS), Washington, DC, USA, 9‐11 April 2014.
Towards the Internet of Relevant Things

47

General Enhancements (2/2)
PerLab

 EFastA (Enhanced Fast Association)
 Addresses the association phase Many collisions may occur with the association proceduredescribed in the standard Many Beacon Intervals can be necessary to associate all the nodes
to the network

 In EFastA, nodes do not sent association requests
immediately after the EB reception
 Nodes wait for a randomly selected superframe inside themulti‐superframe Simulations show that EFastA reduces association time up to about 90%, with respect to FastA
X. Liu, X. Li, S. Su, Z. Fan, G. Wang, Enhanced Fast Association for 802.15.4e‐2012 DSME MAC Protocol, Proceedings of the
2nd International Conference on Computer Science and Electronics Engineering (ICCSEE), Hangzhou, China, 22‐23 March 2013.
Towards the Internet of Relevant Things48

Beacon Scheduling (1/3)
PerLab The DSME Beacon Scheduling algorithm presents a numberof limitations
 long waiting time for network construction
 storage wastage
 variable and growing length of EB frame size
 potential beacon collision issues

Towards the Internet of Relevant Things49

Beacon Scheduling (2/3)
PerLab

 E‐DSME (Enhanced DSME) Exploits a distributed permission notification mechanism
 A node waits for a Permission Notification to complete theallocation
 Only the coordinator that has transmitted the latest beacon cansend permission notifications

 CAP is divided into Allocation Contention Periods (ACP) andPermission Notification Periods (PNP)
 Simulation results show that E‐DSME allows
 to achieve very high success ratio (near to 100%)
 to avoid beacon collisions even in complex networks

K. Hwang, S. Nam, Analysis and Enhancement of IEEE 802.15.4e DSME Beacon Scheduling Model, Journal of Applied
Mathematics.
Towards the Internet of Relevant Things

50

Beacon Scheduling (3/3)
PerLab DFBS (Distributed Fast Beacon Scheduling) many problems are caused by the use of a bitmap torepresent slot allocation data The bitmap is replaced by a single integer, namely RINSD(Representative Indicator of Neighbor Superframe Duration)
 It represents the index of the superframe to be used to send EBs
 Each node maintains its own RINSD

 To join the network, a node performs an Active Association
 Simulation results show that allows to solve the highlighted beacon collision problems
 reduces the network construction time (up to 75% with 25 nodes)
W. Lee, K. Hwang, Y.A. Jeon, S.S. Choi, Distributed Fast Beacon Scheduling for Mesh Networks, Proceedings of the 8th IEEE
International Conference on Mobile Adhoc and Sensor Systems (MASS), Valencia, Spain, 17‐22 October 2011.
Towards the Internet of Relevant Things

51

IEEE 802.15.4e DSMEOpen Issues

Open Issues (1/2)
PerLab A complete implementation of DSME is still missing Current works do not consider mesh topologies
 Many aspects are left to implementers How to choose the DSME‐GTSs to be allocated How to accommodate traffic in GTSs
 How to select the communication channel when using
channel adaptation
 The beacon scheduling algorithm is presented without any
concrete outline and implementation details
 …
Towards the Internet of Relevant Things

53Open Issues (2/2)
PerLab More attention should be devoted to the energy topic
 DSME conceals a number of security issues
 The distributed DSME‐GTS allocation mechanism assumes
that all nodes are trustworthy

 Feasibility of the integration with the upper layers of
the network stack should be investigated with reference to the Internet of Things protocols,such as 6LoWPAN, RPL, and CoAP.

Towards the Internet of Relevant Things

54

IEEE 802.15.4e TSCH
Time Slotted
Channel HoppingTime Slotted Channel Hopping (TSCH)
PerLab

 Time slotted access, multi‐channel communication andchannel hopping Particularly suitable for multi‐hop mesh networks

 Time‐slotted access Predictable and bounded latency
 Guaranteed bandwidth Multi‐channel communication
 More nodes can communicate at the same time (i.e., same slot) using
different channels (identified by different channel offsets)
 increased network capacity

 Channel hopping
 mitigates the effects of interferences and multipath fading improves reliability

 No CAP in TSCH
Towards the Internet of Relevant Things

56Periodic Slotframe
PerLab

Towards the Internet of Relevant Things

57

TSCH Link
PerLab Link = Pairwise assignment of a directed communication
between devices in a specific slot, with a given channel offset
 t chOfslot in the slotframe
channel offset

Dedicated links

Shared link

Channel Offset

4

L→B
B→ A

3
H→ D

2
1
0

I→ D
E→ C
G→C

0

D→ A
C→ A

1

2

3

timeslot
Towards the Internet of Relevant Things

58

Dedicated vs. Shared Links
PerLab Dedicated links
 Deterministic traffic Periodic transmissions
 One transmitter – One
receiver Direct accessTowards the Internet of Relevant Things

 Shared links
 Sporadic, unpredictabletraffic
 Discovery and routing
messages Multiple
transmitters/receivers
 CSMA‐CA based access

59

TSCH CSMA-CA for Shared Links
PerLab

Towards the Internet of Relevant Things

60

TSCH CSMA-CA vs. 802.15.4 CSMA-CA
PerLab

 Backoff mechanism
 is activated only after the node has experienced a collision (toavoid repeated collisions) Backoff unit duration
 TSCH: a shared slot
 802.15.4: 320 sec

 Clear Channel Assessment (CCA) CCAs are not used to prevent collisions among nodes, but to avoid
transmitting a packet if a strong external interference is detected Packet dropping a packet is dropped only if it reaches the maximum number ofretransmissions
D. De Guglielmo, B. Al Nahas, S. Duquennoy, T. Voigt, G. Anastasi, Analysis and Experimental Evaluation of IEEE 802.15.4e TSCH
CSMA‐CA Algorithm, IEEE Transactions on Vehicular Technology, to appear.
Towards the Internet of Relevant Things

61TSCH Link
PerLab Link=Pairwise assignment of a directed communication
between devices in a specific slot, with a given channel offset
 t chOfslot in the slotframe
channel offset

Channel Offset

4

L→B
B→ A

3
H→ D

2
1
0

I→ D
E→ C
G→C

0

D→ A
C→ A

1

2

3

timeslot
Towards the Internet of Relevant Things62Frequency Translation - Channel Hopping
PerLab

The channel offset of a Link = (t, chOf ) is translated in
an operating frequency f

 ASN: total # of slots elapsed since the network was
deployed nch: number of used physical channels
 F is implemented as a look‐up‐table containing the setof available channels
Towards the Internet of Relevant Things

63

TSCH: Multi-channel + Frequency Hopping
PerLabchannelOffset

ASN 1

2

3 4 5

6 7

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

15

1
0
slotOffset
Slotframe0 1

2 3 0 10Channel (f)2 3 0 1

2

1
5

2 3

9

0 1

2 3 0 1313

2 3 0 12 3 0 1

2 3

t

4
1

5

9

13

Slotframe size and nch should be relatively prime
Each link rotates through the nch available channels over nch slotframes.
Towards the Internet of Relevant Things

64Literature Review
PerLab

A lot of attention by the research community
 Researches mainly focused on: Performance Evaluation of TSCH mode Network formation
 Link scheduling Network synchronization

 IETF 6TiSCH Initiative Integration of TSCH with IoT protocols
 Use of IPv6 on top of 802.15.4e TSCH
Towards the Internet of Relevant Things

65IEEE 802.15.4e TSCH
Performance
Evaluation

Performance Evaluation of TSCH Mode
PerLab S. Zats, R. Su, T. Watteyne, K. Pister, Scalability of Time Synchronized
Wireless Sensor Networking, Proceedings of Annual Conference on IEEE
Industrial Electronics Society (IECON 2011), November 7‐10, 2011.
 S. Chen, T. Sun, J. Yuan, X. Geng, C. Li, U. Sana, M. Abdullah Alnuem,
Performance Analysis of IEEE 802.15.4e Time Slotted Channel Hopping for
Low‐Rate Wireless Networks, KSII Transactions on Internet and Information
Systems, Vol. 7, N. 1, 2013.
 D. De Guglielmo, G. Anastasi, and A. Seghetti, From IEEE 802.15.4 to IEEE
802.15.4e: A Step Towards the Internet of Things, Chapter in Advances onto
the Internet of Things, pp. 135–152, 2014. Springer.
 X. Vilajosana, Q. Wang, F. Chraim, T. Watteyne, C. Tengfei, K. Pister, A
Realistic Energy Consumption Model for TSCH Networks, IEEE Sensors
Journal, 14 (2), 482‐489, Feb. 2014.
 T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e
Networks: Performance and Trade‐offs, Proceedings of IEEE International
Conference on Communications (ICC 2015), June 8‐12, 2015.
 ....
Towards the Internet of Relevant Things

67

802.15.4e TSCH vs. 802.15.4 CSMA-CA
PerLab

 Comparison
 802.15.4 CSMA‐CA in BE and NBE mode
 802.15.4e in TSCH mode

 Star Network
 Periodic Reporting 1 packet every T (BI in BE mode) TSCH: single channel used

 Performance Metrics
 Delivery Ratio Average Latency
 Energy per Delivered Packet
G. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE 802.15.4e: a Step towards the Internet of Things, Chapter
10 in Advances onto the Internet of Things (S. Gaglio, G. Lo Re, Editors), pp. 135‐152. January 2014. Springer
Towards the Internet of Relevant Things

68802.15.4e TSCH vs. 802.15.4 CSMA-CA
PerLabSimulation Results

G. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE 802.15.4e: a Step towards the Internet of Things, Chapter
10 in Advances onto the Internet of Things (S. Gaglio, G. Lo Re, Editors), pp. 135‐152. January 2014. Springer
Towards the Internet of Relevant Things

69

Scalability
PerLab

 Network composed of 10,000 nodes deployed in an area of 0.1 km2
 E.g., oil refinery where miles of piping are equipped with 100‐1000
temperature, pressure, level and corrosion sensors, deployed in a
relatively small geographical area 50 Access Points
 i.e., special nodes that collect data generated by sensor nodes
 Multi‐hop communication towards the AP– routes are constructed using the upstream algorithm of RPL– with a metric which introduces load‐balancing between APs

 Periodic data generation
 1 packet every 10s

S. Zats, R. Su, T. Watteyne, K. Pister, Scalability of Time Synchronized Wireless Sensor Networking, Proceedings of Annual
Conference on IEEE Industrial Electronics Society (IECON 2011), November 7‐10, 2011.
Towards the Internet of Relevant Things

70Scalability
PerLab Results
 delivery ratio above 99.9%
 end‐to‐end latency of 2.25 s
 network lifetime of 8.4 years if 2200mAh AA batteries are used

 Conclusions
 By tiling 100 of these networks, the same results hold for a
network with 1 million nodes deployed in 10 km2
 using 5,000 APs.
S. Zats, R. Su, T. Watteyne, K. Pister, Scalability of Time Synchronized Wireless Sensor Networking, Proceedings of Annual
Conference on IEEE Industrial Electronics Society (IECON 2011), November 7‐10, 2011.
Towards the Internet of Relevant Things71Suitability to Real-life Applications
PerLabGoal
 exploring the capabilities and performance of a
TSCH network under different conditions
 trade‐off between throughput, latency, reliability, andpower consumption for different scenarios

Use Cases Smart City
 Smart Building Industrial Setting
T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things72

Suitability to Real-life Applications
PerLabSmart City
 10‐100 thousands node with moderate density
 Low data rate (data reporting period often in the order of hours)
 Delay tolerant (a fraction of the reporting period)
 99% reliability
 Target battery lifetime: 10 years (or more)

Smart Building Large networks, but broken in application‐specific networks
 Moderate data rate (e.g., 1 packet every 1‐30 s)
 Maximum delay less than 1s for security or fire applications
 Higher reliability than in urban networks, e.g., 99.9% reliability
 Target battery lifetime: 5 years (or more)
T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things73Suitability to Real-life Applications
PerLabIndustrial Setting Process monitoring and control applications
 Harsh environment
 Network size typically smaller than in urban/building environments, butwith larger radius (i.e., # of hops)
 Low‐to‐moderate data rate
 1 data packet every 1‐60 s

 Delay tolerant for some monitoring applications, stringent requirements
for control applications
 99.9% (or better) reliability
 Target battery lifetime: 5 years (or more) Larger batteries can be used because of lower cost sensitivity

T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things74Suitability to Real-life Applications
PerLab Performance Estimator for TSCH networks
 Advanced model providing latency, power consumption andthroughput achieved by nodes
 assumes that topology, quality of wireless links, and traffic
demands are known Validation through experimental measurements
 based on SmartMesh IP

T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things75Suitability to Real-life Applications
PerLab Topology
 Multi‐hop mesh topology
 Up to 100 nodes per manager/gateway
 In a real environment many suchnetworks can be tiled to form alarge network

manager/gateway

 Common Parameters
 Packet size: 90 bytes

T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things76Suitability to Real-life Applications
PerLabSmart City
Parameters

Performance Nodes: 100
 Network Radius: 8 hops
 Similar # of nodes at eachhop
 Data report period: 3600 s
 No peer‐to‐peer traffic Ploss=20%
 Slotframe=1024
 10000 mAh battery Lifetime: 51 years
 Larger than 10‐year requirement

 Latency
 1‐hop nodes: 1.50 s
 Deep nodes: 12.0 s

T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things77Suitability to Real-life Applications
PerLabSmart Building
Parameters

Performance Nodes: 100
 Lifetime: 5.3 years
 Larger than 5‐year requirement Network Radius: 4 hops
 Latency
 40, 30, 20, 10 nodes per hop 1‐hop nodes: 0.92 s
 Data report period: 15 s
 Deep nodes: 3.7 s
 Peer‐to‐peer traffic anddownstream control
 Ploss=30%
 Slotframe=256
 2000 mAh battery (a pair of AA batteries)
T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things78Suitability to Real-life Applications
PerLabIndustrial Setting
Parameters

Performance Nodes: 100
 Network Radius: 20 hops
 5 nodes for each hop Data report period: 30 s
 Ploss=30%
 Slotframe=256
 10000 mAh battery

 Latency
 1‐hop nodes: 0.46 s
 Deep nodes: 9.2 s

T. Watteyne, J. Weiss, L. Doherty, J. Simon, Industrial IEEE802.15.4e Networks: Performance and Trade‐offs, Proceedings of IEEE
International Conference on Communications (ICC 2015), June 8‐12, 2015.
Towards the Internet of Relevant Things

79IEEE 802.15.4e TSCH
TSCH
Network Formation

Network Formation
PerLab Based on Enhanced Beacons (EBs) Regularly emitted by the PAN Coordinator and other nodes

 EBs are special frames containing
 Synchronization information
 allows new devices to synchronize to the network Channel hopping information
 allows new devices to learn the channel hopping sequence Timeslot information
 describes when to expect a frame transmission and when to send an
acknowledgment

 Initial link and slotframe information
 allows new devices to know:––

when to listen for transmissions from the advertising device
when to transmit to the advertising device

The EB advertising policy is not part of the 802.15.4e standard
Towards the Internet of Relevant Things81Network Formation
PerLab

 A joining device starts listening for possible EBs
 on a certain frequency

 Upon receiving an EB
 The MAC layer notifies the higher layer
 The higher layer initializes the slotframe and links
 Using information in the received EB message

 and switches the device into TSCH mode
 At this point the device is connected to the network

 Then, the device allocates communication resources
 (i.e., slotframes and links)

 and starts advertising, on its turnTowards the Internet of Relevant Things82Network Formation
PerLabCoordinator Node

EB

EB

EB

EB

Radio ON using frequency f2
Joining Node
LegendaTowards the Internet of Relevant Things

f0

f1

f2

f3
83

When to transmit EBs?
PerLabchannelOffset

15

2
1
0
0 1 2 310

Slotframe

Towards the Internet of Relevant Things

84Goals
PerLab

 Minimum Joining time
 Devices must keep the radio ON during the joiningphase EBs should be sent frequently

 Frequent EB transmissions
 Reduce communication resources Increase energy consumption at network nodes

Towards the Internet of Relevant Things85When to transmit EBs?
Random Vertical

Random Horizontal

15

15

channelOffset

channelOffset

PerLab

2
1

2
1
0

0
0 1 2 310

Slotframe0 1 2 310

Slotframe

E.Vogli, G.Ribezzo, L.A.Grieco, and G.Boggia, Fast Join and Synchronization Schema in the IEEE 802.15.4e MAC, Proc. IEEE
Wireless Communications and Networking Conference Workshops (WCNCW 2015), 2015.
Towards the Internet of Relevant Things86Model-based Approach
PerLabModel of the Joining Phase Based on DTMC
 Analytical expression of joining time
 Avg. joining time depends on the EB transmission strategy

D. De Guglielmo, S. Brienza, G. Anastasi, A Model‐based Beacon Scheduling Algorithm for IEEE 802.15.4e TSCH Networks,
Proc. IEEE Int’l Symposium on a World of Wireless, Mobile, and Multimedia Networks (WoWMoM 2016), Coimbra, Portugal,
June 21‐24, 2016.
Towards the Internet of Relevant Things87Model-based Approach
PerLabModel of the Joining Phase Based on DTMC
 Analytical expression of joining time
 Avg. joining time depends on the EB transmission strategy

∑

1

,

2

,

1

,

1

∑

,

1

≡

D. De Guglielmo, S. Brienza, G. Anastasi, A Model‐based Beacon Scheduling Algorithm for IEEE 802.15.4e TSCH Networks,
Proc. IEEE Int’l Symposium on a World of Wireless, Mobile, and Multimedia Networks (WoWMoM 2016), Coimbra, Portugal,
June 21‐24, 2016.
Towards the Internet of Relevant Things88Model-based Approach
PerLab

Optimization Problem
min

∈


…

∀
are the unknowns‒ distances, in terms of timeslots, between successive EBs

 T: slotframe duration

D. De Guglielmo, S. Brienza, G. Anastasi, A Model‐based Beacon Scheduling Algorithm for IEEE 802.15.4e TSCH Networks,
Proc. IEEE Int’l Symposium on a World of Wireless, Mobile, and Multimedia Networks (WoWMoM 2016), Coimbra, Portugal,
June 21‐24, 2016.
Towards the Internet of Relevant Things

89Model-based Approach
PerLab Model‐based Sheduling Algorithm
 Given the total number of EBs to allocate
 provides the EB allocation strategy that minimizes thejoining timechannelOffset

15

2
1
0
0 1 2 310

Slotframe
Towards the Internet of Relevant Things90Performance Comparison
PerLab Model‐based Scheduling (MBS) Random (RD) Extended Random Vertical (ERV) Extended Random Horizontal (ERH)
Nb (# of EBs advertised per superframe) equal for all theconsidered options
Performance Index: Avg. Network Formation Timeaverage time (in # of timeslots) from when the PAN coordinator transmits thefirst EB to when the last node in the group joins the network
Towards the Internet of Relevant Things

91Simulation Results
PerLabScenarionodes willing to set up a network Random deployment over an areaof 80 80 m2
 Ploss = 0%

D. De Guglielmo, S. Brienza, G. Anastasi, A Model‐based Beacon Scheduling Algorithm for IEEE 802.15.4e TSCH Networks, Proc. IEEE
Int’l Symposium on a World of Wireless, Mobile, and Multimedia Networks (WoWMoM 2016), Coimbra, Portugal, June 21‐24, 2016.
Towards the Internet of Relevant Things

92IEEE 802.15.4e TSCH
TSCH
Link SchedulingLink Scheduling
PerLab Assignment of links to nodes for data transmissions
 Duplex‐conflict free
 A node cannot receive simultaneously from many senders
 A node cannot transmit and receive at the same time Interference‐conflict free neighboring nodes should not transmit in the same timeslot andwith the same channel offset

 Multi‐channel comm. makes link scheduling easier Optimal schedule is hard to find
 large networks with multi‐hop topology
 dynamic networks (mobility, power management, …)IEEE 802.15.4e does NOT specify how
to derive an appropriate link schedule
Towards the Internet of Relevant Things

94TDMA Scheduling
PerLab TDMA scheduling algorithms typically address
single‐channel networks
 recently, multi‐channel TDMA scheduling solutions havebeen proposed

 Most existing multi‐channel scheduling schemes are
not suitable for TSCH networks do not allow per‐packet channel hopping do not address resource‐constrained nodes
 e.g., they are not memory efficient do not consider the spatial reuse of channels

Towards the Internet of Relevant Things

95TSCH Scheduling
PerLab

 Centralized Scheduling Distributed Scheduling

Towards the Internet of Relevant Things

96TSCH Scheduling
PerLabCentralized Scheduling Link schedule computed and distributed by aspecial node Coordinator (Manager) node Based on information received by all the nodes of the network network topology
 traffic pattern Re‐computed dynamically Whenever a change in the operating conditions occurs

 Not appealing for dynamic networks (mobile nodes, power management) large‐scale networks
Towards the Internet of Relevant Things

97TSCH Scheduling
PerLabDistributed Scheduling No central entity
 Link schedule computed autonomously by each node based on local, partial information exchanged with its
neighbors.

 The overall schedule is typically non optimal
 Limited Overhead Suitable for energy‐constrained nodes

Towards the Internet of Relevant Things

98TSCH Centralized Scheduling
PerLab TASA (Traffic Aware Scheduling Algorithm) [1] [2] Tree network topology
 Converge‐cast communication model The coordinator has a single radio interface
 Heterogeneous traffic conditions

 MODESA (Multi‐channel Optimized Delay Slot Assignment) [3] Tree network topology
 Converge‐cast communication model The coordinator has multiple radio interfaces
 Homogeneous traffic conditions (heterogeneous conditions in [4])[1] M.R. Palattella, N. Accettura, M. Dohler, L.A. Grieco, G. Boggia, Traffic Aware Scheduling Algorithm for reliable low‐power multi‐hop IEEE
802.15.4e networks, Proc. IEEE Int’l Symposium on Personal Indoor and Mobile Radio Communications (PIMRC 2012), Sept. 12, 2012[2] M.R. Palattella, N. Accettura, L.A. Grieco, G. Boggia, M. Dohler, T. Engel. On Optimal Scheduling in Duty‐Cycled Industrial IoT Applications
Using IEEE802.15.4e TSCH, IEEE Sensors Journal, Vol. 13, N. 10, pp. 3655‐3666, October 2013
[3] R. Soua, P. Minet, E. Livolant, MODESA: An optimized multichannel slot assignment for raw data convergecast in wireless sensor
networks, Proc. IEEE International Performance Computing and Communications Conference (IPCCC 2012), Dec. 1‐3, 2012
[4] RSoua, E. Livolant, P. Minet, MUSIKA: A multichannel multi‐sink data gathering algorithm in wireless sensor networks, Proc.
International Wireless Communications and Mobile Computing Conference (IWCMC 2013), July 1‐5, 2013
Towards the Internet of Relevant Things

99TSCH Centralized Scheduling --TASA
PerLab

 Every node regularly updates the Manager with the list of other nodes it can hear
 the amount of data it generates

 The Manager
 draws the connectivity graph …
 Based on information received from nodes

 assigns slots to different links in the graph …
 Conflict‐free schedule taking an iterative approach Based on a combination of matching and vertex coloring techniques informs each node about links it is involved in If the connectivity graph changes
 the manager updates its schedule and informs affected nodes
Palattella, M. R., Accettura, N., Dohler, M., Grieco, L. A., & Boggia, G., Traffic Aware Scheduling Algorithm for reliable low‐power
multi‐hop IEEE 802.15. 4e networks, Proc. IEEE International Symposium on Personal Indoor and Mobile Radio Communications(PIMRC 2012), pp. 327‐332, 2012
Towards the Internet of Relevant Things

100

TSCH Centralized Scheduling
PerLab TASA (Traffic Aware Scheduling Algorithm) [1] [2] Tree network topology
 Converge‐cast communication model The coordinator has a single radio interface
 Heterogeneous traffic conditions

 MODESA (Multi‐channel Optimized DElay Slot Assignment) [3] Tree network topology
 Converge‐cast communication model The coordinator has multiple radio interfaces
 Homogeneous traffic conditions (heterogeneous conditions in [4])[1] M.R. Palattella, N. Accettura, M. Dohler, L.A. Grieco, G. Boggia, Traffic Aware Scheduling Algorithm for reliable low‐power multi‐hop IEEE
802.15.4e networks, Proc. IEEE Int’l Symposium on Personal Indoor and Mobile Radio Communications (PIMRC 2012), Sept. 12, 2012[2] M.R. Palattella, N. Accettura, L.A. Grieco, G. Boggia, M. Dohler, T. Engel. On Optimal Scheduling in Duty‐Cycled Industrial IoT Applications
Using IEEE802.15.4e TSCH, IEEE Sensors Journal, Vol. 13, N. 10, pp. 3655‐3666, October 2013
[3] R. Soua, P. Minet, E. Livolant, MODESA: An optimized multichannel slot assignment for raw data convergecast in wireless sensor
networks, Proc. IEEE International Performance Computing and Communications Conference (IPCCC 2012), Dec. 1‐3, 2012
[4] RSoua, E. Livolant, P. Minet, MUSIKA: A multichannel multi‐sink data gathering algorithm in wireless sensor networks, Proc.
International Wireless Communications and Mobile Computing Conference (IWCMC 2013), July 1‐5, 2013
Towards the Internet of Relevant Things

101TSCH Centralized Scheduling --MODESAPerLab Basic idea selecting one node at each iteration …
 … and choosing a link to accommodate one of its required
transmissions
 The execution terminates when the transmissions of allnodes in the network have been accommodated

 Node selection
 based on dynamic priority
 depending on the number of packets still to transmit

R. Soua, P. Minet, E. Livolant, MODESA: An optimized multichannel slot assignment for raw data convergecast in wirelesssensor networks, Proc. IEEE International Performance Computing and Communications Conference (IPCCC 2012), Dec. 1‐3, 2012
Towards the Internet of Relevant Things

102

TSCH Centralized Scheduling --MODESAPerLab

MODESA Algorithm
Iterates over the set of nodes with data to transmit
 and having an available interface with their parent in that slot
 Sorted according to their priorities

 Picks the node with the highest priority
 Schedules its first transmission
 on that timeslot
 on the first channel offset

 Then, selects another node
 If the node is in conflict with a previously scheduled node its transmissionis allocated on a different channel offset
 otherwise, the same channel offset is used

 Continues until transmissions of all nodes have been scheduled
R. Soua, P. Minet, E. Livolant, MODESA: An optimized multichannel slot assignment for raw data convergecast in wirelesssensor networks, Proc. IEEE International Performance Computing and Communications Conference (IPCCC 2012), Dec. 1‐3, 2012
Towards the Internet of Relevant Things

103

TSCH Centralized Scheduling --MODESAPerLab MODESA has been shown to be optimal
 For linear and balanced‐tree topologies

 Performance is close to that of an optimal algorithm
 Also for random network topologies

 Impact of # of communication channels
 Drastically reduce the schedule length Similar trend when increasing the # of interfaces at the coordinator Guidelines
 It is useless to equip the coordinator with a number of interfaces greaterthan the number of its children
 It is pointless to use a number of channels higher than the number ofcoordinator interfaces.
R. Soua, P. Minet, E. Livolant, MODESA: An optimized multichannel slot assignment for raw data convergecast in wirelesssensor networks, Proc. IEEE International Performance Computing and Communications Conference (IPCCC 2012), Dec. 1‐3, 2012
Towards the Internet of Relevant Things

104

TSCH Distributed Scheduling
PerLabDistributed
Scheduling

Non‐Energy
Constrained Nodes

Energy‐constrained
Nodes

Single Sinks

Multiple Sinks

D. De Guglielmo, S. Brienza, G. Anastasi, IEEE 802.15.4e: a Survey, Computer Communications, Accepted with minor revision.
Towards the Internet of Relevant Things

105IEEE 802.15.4e TSCH
Summary &Open Issues

Summary
PerLab

TSCH combines
 Time‐slotted access multi‐channel communication
 frequency hopping Energy efficiency
 Reliability
 Guaranteed bandwidth Limited and predictable delay Scalability (high aggregate throughput)
 Support for multi‐hop mesh communication
Towards the Internet of Relevant Things

107Open Issues
PerLab

 Communication Model Most of the previous studies have considered a convergecast
scenario Node‐to‐node communication needs to be investigated In the perspective of the Internet of Things Lightweight scheduling and routing solutions for quickly
establishing node‐to‐node paths

 Network Formation
 Currently available solutions may be inefficient for Mobile Objects  Frequent joins and leaves
 Nodes operating on a duty cycle

Towards the Internet of Relevant Things

108Open Issues
PerLab Security
 TDMA networks are typically prone to Selective Jamming(SJ) attacks
 An attacker can easily identify slots assigned to victim node and destroy all communications by that node Frequency Hopping and Secure Beacons should make TSCH
networks more secure How robust is a TSCH network against SJ attacks?

Towards the Internet of Relevant Things

109Open Issues
PerLab

 TSCH and IoT integration
 IoT protocols rely on a flexible and dynamic paradigm
 E.g., the IPV6 Routing Protocol for Low‐Power and Lossy Networks(RPL) They assume that smart objects
 are always active
 can be added and removed dynamically

Combining a dynamic and flexible routing mechanism(e.g., RPL) with 802.15.4e TSCH introduces a number ofchallenges

Towards the Internet of Relevant Things

110IEEE 802.15.4e TSCH
TSCH andthe Internet of Things

The 6TiSCH Initiative
PerLab Working Group set up by IETF
 Name: IPv6 over the TSCH mode of IEEE 802.15.4e
 Acronym: 6TiSCH

 Goal defining mechanisms to combine the high reliability andlow‐energy consumption of IEEE 802.15.4e TSCH withthe ease of interoperability and integration offered by
the IP protocol

https://datatracker.ietf.org/wg/6tisch/Towards the Internet of Relevant Things

112

6TiSCH: Problem
PerLab

TSCH does not define policies to build and maintain the communication schedule mechanisms to match the schedule to the multi‐hop paths
maintained by RPL mechanisms to adapt the resources allocated between
neighbor nodes to the data traffic flows
 techniques to allow differentiated treatment of packets
 data packets generated at the application layer signaling messages needed by 6LoWPAN and RPL to discoverneighbors and react to topology changes

Towards the Internet of Relevant Things

113

6TiSCH Reference Architecture
PerLab

Towards the Internet of Relevant Things

114

6TiSCH Protocol Stack
PerLabProtocol stack fordeterministic IPv6‐enabled
wireless mesh networks
New sub‐layer for integrating
higher IETF layers with IEEE
802.15.4e TSCH
Under definition by the 6TiSCH WG

Towards the Internet of Relevant Things

115

6Top Sub-layer
PerLab

 Controls the TSCH schedule Through a Management Entity (ME) Adds/removes links (cells)

 Collects connectivity information
 useful for upper layers (e.g., RPL) Monitors the performance of links(cells) reschedules them if performance is not
as expected Both centralized and distributedscheduling supported

Towards the Internet of Relevant Things

116

6TiSCH Scheduling
PerLab

 Minimal Scheduling used during network bootstrap or when a better schedule is not available

 Centralized Scheduling Based on a central entity
 Path Computation Element (PCE) Distributed Scheduling distributed multi‐hop scheduling protocols
 neighbor‐to‐neighbor scheduling negotiation

Towards the Internet of Relevant Things

117

Minimal scheduling
PerLab

 Static scheduling Pre‐configured Learnt by the node at joining time Minimal 6Tisch configuration
X. Vilajosana and K. Pister, “Minimal 6TiSCH Configuration, draft‐ietf‐6tisch‐minimal‐00”, IETF, Fremont, CA, USA, 2013

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118Centralized Scheduling
PerLabPath Computation Element (PCE) Collects
 network state information
 traffic requirements from all nodes

 Builds
 Communication schedule Making sure that QoS requirements of all flows are met Installs
 The schedule on the network
6TiSCH will define the protocol to be used for message exchange between PCE
and network nodes
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119Distributed Scheduling
PerLab

 Nodes agree on a common schedule distributed multi‐hop scheduling protocol
 neighbor‐to‐neighbor scheduling negotiation

 Reservation protocol
 to transport QoS requirements along a certain path

 Negotiation phase at each hop, 6top starts a negotiation with the next hop which and how many cells allocate to satisfy the QoS requirementsof the path

6TiSCH WG is currently identifying protocols to be used for QoS requirements.
Strategies for cells allocation are also under definition
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IEEE 802.15.4e
Summary andConclusions

Summary
PerLab IEEE 802.1.5.4 standard
 limitations

 IEEE 802.15.4e
 802.15.4e DSME mode literature survey
 open issues

 802.15.4e TSCH mode literature survey
 open issues

 IoT with 802.15.4e TSCH
 The 6TiSCH initiative

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122Conclusions
PerLab 802.15.4e DSME mode
 Only partially investigated A lot of open issues

 802.15.4e TSCH mode
 A lot of work has been done Many open issues still remains
 Network Formation
 Security

 IoT with 802.15.4e TSCH
 Still a completely open issue
Towards the Internet of Relevant Things123References
PerLab D. De Guglielmo, S. Brienza, G. Anastasi, IEEE 802.15.4e: a Tutorial andSurvey, Computer Communications, accepted with minor revision.
 G. Anastasi, D. De Guglielmo, A Seghetti, From IEEE 802.15.4 to IEEE
802.15.4e: a Step towards the Internet of Things, Chapter 10 in Advances
onto the Internet of Things, pp. 135‐152, January 2014. Springer

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124Questions

IEEE 802.15.4e LLDN
Low Latency
Deterministic Network

Main Characteristics
PerLab

 LLDN Addresses the industrial automation application domain
 LLDN devices can be located on robots, cranes, and portable tools in theautomotive industry, …

 Common requirements are low latency and high cyclic determinism
 LLDN shall allow to transmit data from 20 different sensor nodes every 10 ms

 Designed for star topologies and periodic traffic
 Nodes use just one frequency channel
 Time is divided into superframes
 Nodes can access the medium in dedicatedtimeslots of the superframe, according to a time
division (TDMA) approach.
 Shared group timeslots can also be configured, toallow multiple access for groups of nodes (using a
CSMA protocol).

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127Transmission States
PerLab An LLDN network passes through three states in order tobecome operative (current state is announced throughbeacons).
1. DISCOVERY Devices scan channels to detect a beacon

2. CONFIGURATION Each node sends a frame to the
PAN coordinator, containing thenode’s requirements
 The PAN coordinator replies withthe configurations the node mustuse (e.g., the timeslots that havebeen assigned to the node).

3. ONLINE
 Nodes can transmit data and readings to the PAN coordinator
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Superframe Structure
PerLab Superframes have a fixed duration and are divided into timeslots:
 Beacon timeslots
 Management timeslots
 Uplink timeslots
 Bidirectional timeslots
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129

Literature Review
PerLab

 Improving communication reliability through Relay nodes
1.

Berger, M. Pichler, A. Springer and W. Haslmayr, Energy Efficient and Reliable Wireless Sensor Networks – An Extension
to IEEE 802.15.4e, EURASIP Journal on Wireless Communications and Networking, 9 August 2014.

2.

H. Kapil and C. S. R. Murthy, Rainbow product ranking based relay placement and adaptive retransmission scheme fora reliable 802.15.4e LLDN, In Proceedings of IEEE International Conference on Industrial Technology (ICIT), Seville, Spain,
17‐19 March 2015.

3.

A. Berger, A. Entinger, A. Potsch, and A. Springer, Improving IEEE 802.15.4e LLDN Performance by Relaying andExtension of Combinatorial Testing, In Proceedings of IEEE Emerging Technology and Factory Automation (ETFA),
Barcelona, Spain, 16‐19 September 2014.

 Extending the network coverage through Relay nodes
4.

G. Patti, G. Alderisi, and L. Lo Bello, Introducing multi‐level communication in the IEEE 802.15.4e protocol: The
MultiChannel‐LLDN, In Proceedings of IEEE Emerging Technology and Factory Automation (ETFA), Barcelona, Spain, 16‐
19 September 2014.

 Tackling node mobility
5.

Y. Al‐Nidawi, H. Yahya, and A. H. Kemp, Impact of mobility on the IoT MAC infrastructure: IEEE 802.15. 4e TSCH and
LLDN platform, in Proceedings of the 2nd IEEE World Forum on Internet of Things (WF‐IoT), December 2015.

6.

Y. Al‐Nidawi and H. Yahya and A. H. Kemp, Tackling Mobility in Low Latency Deterministic Multihop IEEE 802.15.4eSensor Network, IEEE Sensors Journal, 16 (5), March 2016.

 Analytical model for shared timeslots
7.

C. Ouanteur, D. Aïssani, L. Bouallouche‐Medjkoune, M. Yazid, and H. Castel‐Taleb, Modeling and performance
evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs, Wireless
Networks, 2016.

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