Communication Technologies for the IoT · Communication Technologies for the IoT Networking tiny devices. IACDM –Introduction to the course –Matteo Cesana, Paolo Rocco and Letizia

Communication Technologies for the IoT

Networking tiny devices

IACDM – Introduction to the course – Matteo Cesana, Paolo Rocco and Letizia Tanca

Connectivity in I4.0 – Why is it so different?

• A different environment• Strong electromagnetic interference• Harsh conditions (temperature, humidity, etc.)• High mechanical stress

• Different Requirements• Timeliness• Determinism• Reliability

IT/OT Check list: – What is the network size– Mobile or Fixed Nodes– Any service QoS constraint (throughput, latency)?– The “integration issue”– Any budget?

Connectivity


Who Needs to Communicate in I4.0?

• Higher Layer componentsamong themselves

• Controllers with higher layercomponents (MES, ERP, Data Bases, Data Lakes)

• Controllers with controllers(PLCs, SCADA)

• Sensors with controllers (PLCs, DCS)


What is the traffic in I4.0?

• Cyclic Traffic: periodic transfer of sensor measurementsand set points

Example: velocity control loop of a electrical enginerequires sending a set point (2 bytes) every 100us

• Acyclic Traffic: traffic generated by unpredictable eventsExample: alarm triggered by a failing component of the industrial process

• Multimedia Traffic: images/videoExample: intrusion detection systems, defectinspection

• Backhand Traffic: aggregated flows at enterprise level


Industrial Traffic KPIs [IEC 61784] - Throughput

Throughput (rate): number of bits (bytes) per second that can be sentacross a link (Unit measure: [bit/s] or [byte/s])

Depends on: link type

1 kbps (kb/s) = 103 bps1 Mbps (Mb/s) = 106 bps1 Gbps (Gb/s) = 109 bps

1 B = 8 bit1 kB = 103 B1 MB = 106 B1 GB = 109 B


Industrial Traffic KPIs [IEC 61784] – Delay KPIs

Delivery Time: time necessary to send one service data unit from source to destination (Unit measure: [s])Depends on: transmission time, propagation time, protocol executiontimeExample: link d meters long with a throughput R, source S to send L bits to D, wave propagation speed

S DR [b/s]d [m]

T = L/R+ d/⌫

S

D

0 0 1 0 1 0 1 0t

td/⌫

L/R

Propagation delay

Transmission time


Industrial Traffic KPIs [IEC 61784] – Delay KPIs

Minimum Cycle Time (MCT): minimum time required to execute a cyclein a control loop

Example: one controller, 2 sensors; control loop: PLC polls sensor 1, sensor 1 sends back reading, PLC does the same for sensor 2

PLC Sensor 1

Sensor 2

MCT = TPLC�S1 + TS1�PLC + TPLC�S2 + TS2�PLC


Industrial Traffic KPIs [IEC 61784] – Precision KPIs

Jitter: precision/reliability in performing periodic operations

Example: nominal required time to execute a generic control operation, P; actualcurrent time to execute the generic operation P̂

J =|P � P̂ |

P


Industrial Communication Technologies – Market Share

www.automazioneindustriale.it


Wireless is Gaining Momentum

Wired connectivity (Ethernet, field bus technology, etc.) is just fine for IIoT but wireless is on the hype

ON World/ISA Survey, Nov.2016 - 180 industrial end users, systems integrators, and service providers

62%80%

48%20%

2014 2016

No wireless

Some wireless

A primer on networking fundamentals


How to Define a Communication Technology?

1) Physical infrastructure: hosts (sensors/actuators, PLC, SCADA), links (fiberoptics, wireless, wired), network nodes (accesspoint, switch, router, gateway)

2) Network architectures/topologies

3) A set of communicationprotocols


Industrial Network Topologies


Communication Protocols

Human Comm Protocol Network Comm protocol

Hi

Hi

What’s the time?

2:00

Richiesta di connessione TCP

Risposta diconnessione TCP

Get http://www.awl.com/kurose-ross

<file>

time

BrowserWeb Server

Web


Communication Protocols

Set of rules underpinning the exchange of information between twoentities• Message format• Connection set up procedures• Connection tear down procedures• Semantics

Industrial comm networks protocols exchange packets (like the Internet)

header dataReal informationEg. Sensor reading

Signalling informationEg, source and destination address


Layered Architecture

Multiple protocols are commonly layeredEach layer provides some services/funstionalities to upper layers

level 5

level 4

level 3

level 2

level 1

level 5

level 4

level 3

level 2

level 1


Layered Architecture

livello 5

livello 4

livello 3

livello 2

livello 1

5432

543

54

5 livello 5

livello 4

livello 3

livello 2

livello 1

5

54

543

5432

54321


Internet Protocol Stack

Physical

Data Link

Network

Transport

Application

Physical

Data Link

Network

Transport

ApplicationMessages

Segments

Packets

Frames

Bits

Communication Technologies for I4.0


Communication Technologies @ I4.0

M. Laeger, T. Sauter, and J .Jasperneite, The Future of Industrial Communication, IEEE Industrial Electronics Magazine, 2017

Bits over cables….


Fieldbus Generalities

• Mainly targeting the interconnection of control devices and fielddevices (sensors/actuators)

• Short frequently-exchanged messages• Tigth requirements in terms of delay and determinism

Application

Data Link

Physical

Semantics of the specific service

What links are used

How the physical link are accessed


Short Digression on Channel Access

Problem– To share a single communication medium (in our case a IEEE

802.15.4 frequency channel)Solutions

– Scheduled access (“I Tell You when to Talk”)• Transmissions on the channel are sequential with no conflicts• Polling schemes• Centralized scheduling schemes

– Random access (“You Decide when to Talk but be Wise in Recovering from Collisions”)• Transmission are partially uncoordinated and can overlap

(collision)• Conflicts are resolved using distributed procedures based on

random retransmission delay


Scheduled vs Random Access

Scheduled Access (e.g., GSM, Bluetooth, Wifi PCF)– PROs:

• “guaranteed” performance (bounded delay/throughput)– CONs:

• Coordination required (central node, synchronization, etc.) Random Access (e.g., WiFi DCF, Ethernet)

– PROs:• Easy to implement• Opportunistic access to the resources

– CONs:• Only “Statistical” guarantees on performance• Poor performance under heavy traffic (collisions kick in)


Fieldbus Example: the CAN Bus [ISO 11898-1, ISO 11898-2, ISO 11898-3]

Connectivity based on shared physical busEverybody receives everything transmitted on the BUS

Sensor 1

Sensor 2 Actuator 1

Sensor 3 PLC

CSMA to arbitrate collisions

Rate: 1 [Mb/s]


Fieldbus Example: The CAN bus

Carrier Sensing Multiple Accesssense the BUS before transmitting; if BUS free transmit otherwise

refrain and try later

Collissions

t

t

A

BC t

t

t

A

X ttVulnerability period


BUS Arbitration

• Each message has a priority (Lower identifier field means higherpriority)

• Each station monitors its own transmission and the status of the BUS• If a transmitting station overhears another transmission on the

channel at higher priority, then quits (e.g., B in the figure)

t

t

A

B

HIGHER PRIORITY

B quits transmission


Other Fieldbus technologies - PROFIBUS

BUS access managed through pollingMaster station «tells» who can talk

MasterSlave

Slave

Slave

Slave

Rate: up to 12 [Mb/s]


Ethernet/IP

Concept:– Bringing the Internet to industry– Automation/Enterprise information to converge

Rate: up to [Gb/s]


Ethernet Topologies

Hosts (I4.0 devices)Repeaters/hubSwitches

Physical BUSLogical BUSStar of stars

HUB SWITCH


SWITCHtrame

HUBbit bit by bit relaying

Store & Forward

Hub and Switches


CSMA/CD

Carrier Sensing Multiple Accesssense the BUS before transmitting; if BUS free transmit otherwise

refrain and try laterCollision Detect

If collision detected all the transmissions are aborted after a while

t

t

A

B

!

!

Bits in the Air…


The Race to the Smart object

Mobile Radio Networks– RAN and CN Evolutions

Cellular IoT Operators– Low Power Long Range Technology

Hot Spot Networks– Short/medium range + backhauling

Field Network

Backend Servers

Backhauling Network

PLC

WiFi

Ethernet

3G/4G

Field Network

Backend Servers

Radio Access Network Core Network

SGW

MME

PGW

PCRF


Wireless Connectivity Offer

Wi-Fi HaLow


Hot Spot Networks

Highly fragmented technologies/standards/protocolsFine for small-scale, hot spot coverageThe “Gateway Problem”


Several Solutions available

Classification Guidelines

– Proprietary (WirelessHART) vs open standard (WiFi, ZigBee, 6LowPAN, THREAD)

– Application specific vs application agnostic• ZWAVE for home automation, WirelessHART for industrial

applications; 6LowPAN/THREAD for everything

– IP-compliant vs non-IP-compliant


WiFi

Standardized within IEEE working group 802.11It’s a «Wireless Ethernet»Different dialects at the physical and upper layers


WiFi Architectures

BSS: Basic Service SetAP: Access Point

Centralized interconnection

BSS

AP

Distributed ad hoc mode

BSS


WiFi: architettura di rete

BSS (Basic Service Set)

BSS

Distribution System

ESS (Extended Service Set)


Frame format: Frame Control Field

Up to 4 addresses per frame

Numero di sequenza necessario perché ogni trama viene riscontrata

(non c’è CSMA/CD)

E’ indicata la durata temporale (!") delle trasmissione della trama

(usato per aiutare meccanismo anti-collisioni)

Frame Control: versione protocollo, tipo di trama, gestione energetica

dei dispositivi, frammentazione, etc.

FrameControl

Duration Addr 1 Addr 2 Addr 3 Addr 4SequenceNumber CRCFrame

Body

2 2 6 6 6 62 0-2312 4

802.11 MAC Header

Bytes:


A New Communication Stack Needed

Ethernet, 802.3, 802.11

IP

TCP / UDP

HTTP / FTP / SNMP

XML

Routing Tiny Disconnecteddevices

Heavy Protocols undesirable

Extremely tight to applicationscenario

?

Tight Coupling with PHY- Energy efficiency


WirelessHART vs ISA100a for Industrial Automation

Similarities– Requirements: guaranteed delays below 100[ms] – network topology: meshed star-of-stars– PHY and MAC Layers based on hacks of IEEE802.15.4


Zigbee: Communication Stack

PHY LAYER2.4 GHz 915MHz 868 MHz

MAC LAYERMAC LAYER

NETWORK LAYERStar/Cluster/Mesh

APPLICATION INTERFACE

APPLICATIONS

SiliconApplication ZigBee Stack

Customer

IEEE802.15.4

ZigBee Alliance

SECURITY


802.15.4: Types of Devices

Full Function Device (FFD):– Can send beacons– Can communicate with other FFDs – Can route frames– Can act as PAN coordinator– Typically features power supply

Reduced Function Device (RFD):– Cannot route frames– Cannot communicate with other RFDs– Can communicate with FFD– Runs typically on batteries

PAN Coordinator– Is responsible of a Personal Area Network (PAN)– Manages PAN association/de-association


Supported Topology: Stars

PAN Coordinator

Full Function Device

Reduced Function Device


PAN Coordinator



Supported Topology: Mesh


PAN Coordinator



Supported Topology: Cluster-Tree (not in 802.15.4 standard)


802.15.4:PHY

3 channels available in 868MHz bands30 channels available in the 915MHz bands16 channels available in the 2.4GHz bands


MAC: Functional Description

Two operation modes are defined:

– Beacon Enabled

• PAN coordinator periodically transmits beacons

• Usually adopted in star topologies

• Slotted CSMA/CA + scheduled transmissions

– Non Beacon Enabled

• Uncoordinated access through unslotted CSMA/CA


802.15.4 Channel Access

The resource to be shared is timeA Mixture of Scheduled and Random AccessScheduled Access implemented through PAN Coordinator (only beacon-enabled mode)Random Access allowed between RFDs and between RFD/FFD and PAN Coordinator (allowed in both operation modes)


Beacon Enabled: functional description

Beacon Enabled

Frame Length: from 15[ms] to 252[s] (15.38ms*2n where 0 £n £ 14)RFD associated to PAN coordinator are aligned with the frame structureRandom access through CSMA/CA in CAPGuranteed Time Slot statically assigned by PAN coordinator through beacons

GTS GTS Inactive

Beacon BeaconCAP CFP

0 1 2 3 4 5 6 7 8 9 10 11 12 13 1514


ISA100a vs WirelessHART for Industrial Automation

Differences– From network layer on– WirelessHART has its own protocol stack ”rules”– ISA100.a is IPv6 compliant


Facts and Trends

Gateway-based interoperability solutions still at the top

Shift towards an all-IP communication is continuing (slowly)

Focus on ecosystems, alliances and interoperability

Mission• Advocate for open standards• Influence standard development• Create testbed for specific verticals


Mobile Radio Networks

Few Applications

throughput-bound

HighEnd Terminals

Fragmented Applications

Many clients – Low Traffic

Simple (cheap) terminals

OLD SCHOOL MOBILE IoT-Enabled Mobile


Mobile Radio Networks


5G is coming to Industry

Industry-compliant 5G nice features: – mmWave access, Massive MIMO – Network Densification– Slicing– Mobile Edge Computing (MEC)

Enabled/Boosted Applications– Immersive reality/virtual reality– Autonomous vehicles – Collaborative Robotics

Tactile Internet• Hig Access Speed [Gb/s] • low latency


Low Power Long Range Technologies

Common Features– Low TCO– Energy efficiency– plug&play connectivity– Capillary Coverage ON World/ISA Survey, Nov.2016

What is your strategy with LPWAN?


LPWAN: “cable replacement” or more?

What are you doing with LPWAN?What LPWAN do you trust most?

New applications mostly related to large-scale capillary logistics


LoraWAN Architecture

Association-less, cellular-like architectureEnd devices: field devicesGateways: receive and forward messages from end devices (and network server)Network server: where all the intelligence is

– Remove duplicate messages, manages ACKs, manages radio link parameters, etc. A Technical Overview of LoRa and LoraWAN, LoraAlliance


LoraWAN Protocol Stack

Region-specificCarrier frequency [MHz]

ProprietaryBy SemTechTM

Open source

Rb = SF4

4+CR2SF

BW

[b/s]

How fast can LoRaWAN go?


How to Choose?

Two contrasting objectives:– Rate: “I want to go fast” (low SF)– Reliability: “I want to go safe” (high SF)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

6 7 8 9 10 11 12

SF

R b[b

/s]

SF

-134 -133 -132 -131 -130 -129 -128 -127 -126 -125 -124 -123

6 7 8 9 10 11 12

P min

[dBm

]


LoraWAN End Devices

Class A:– Downlink “slots” following uplink

transmissions– ALOHA-like access in the uplink

Class B:– “extra” downlink ”slots” available

in a scheduled fashion

Class C:– Almost continuous downlink

“slots”

DLLatency

Energyconsumption

Class A

Class B

Class C


LoraWAN Class A Devices

In EU: RX_delay_1 = 1[s]; RX_delay_2= RX_delay_1 + 1[s]If a preamble is detected during one of the receive windows, the radio receiver stays active until the downlink frame is demodulated If frame detected, demodulated and received during the first receive window, the end-device does not open the second receive window

RX window1

RX window2

RX_delay_1

RX_delay_2

Uplink Transmission


And the Winner is….

Cellular IoT Operators– “first mover” advantage wrt to classical operators– mid term advantage on cost/flexibility

Mobile Radio Networks– Advantages in terms of global reach, maintenance/support,

bandwidth/capacity, scaleCapillary Multi-hop Networks

– Fine for hot-spot-like coverage, indoors, personalcommunications

Documents

Communication Technologies for the IoT · Communication Technologies for the IoT Networking tiny devices. IACDM –Introduction to the course –Matteo Cesana, Paolo Rocco and Letizia