Wilamowski B.M., Irwin J.D. The Industrial Electronics Handbook. Second Edition: Industrial Communication Systems

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57-1

57.1 Introduction

OPC. Unied. Architecture. (OPC. UA). is. the. new. standard. of. the. OPC. Foundation. [1]. providing.

inte

roperability

.(e.g

.Micr

oso

.DCOM.tech

nology

.is.not.used.anymo

re)

.in.proc

ess

.auto

mation

.and.

beyo

nd.

.By.den

ing

.abst

ract

.serv

ices,

.OPC.UA.prov

ides

.a.serv

ice-oriented

.arch

itecture

.(SOA

)

.for.

indu

strial

.appl

ications

.from.fact

ory-oor

.devi

ces

.to.ente

rprise

.appl

ications.

.Sinc

.the.rst.intr

oduc-

tion

.of.OPC.in.1996

.OPC.UA.repr

esents

.a.trem

endous

.achi

evement,

.whic

.star

ted

.at.the.end.of.

2003

.that.prop

oses

.to.inte

grate

.the.die

rent

.avo

.of.the.form

.OPC.spec

ications

.(DA,.HDA,.DX,.

XML-

DA…)

.into.a.uni

ed address space accessible with a single set of services including IT security.

 is.chap

ter

.give

.an.over

view

.over.the.arch

itecture

.of.OPC.UA,.its.addr

ess

.spac

.mode

.and.its.ser-

ices,

.as.well.as.die

rent

.impl

ementation

.avo

rs.

.For.an.in-d

epth

.stud

.of.OPC.UA,.it.is.advi

sed

.to.

get.the.spec

ications

.from.the.OPC.Foun

dation

.Web.site.[2],.whic

.oer

.a.lot.of.info

rmation

.abou

impl

ementations

.and.pro

duct

.ava

ilability.

.It.is.int

eresting

.to.kno

.tha

.the.OPC.Fou

ndation

.is.wor

ing

.with.bodi

.such.as.MIMO

.[3],.ISA.[4],.and.OMAC.[5].to.exte

.the.UA.stan

dard

.to.batc

asse

.mana

gement,

.and.othe

.area

.Anot

her

.impo

rtant

.thin

.to.know.is.that.OPC.UA.prov

ides

.sup-

ort

.for.the.elec

tronic

.devi

.desc

ription

.lang

uage

.(EDD

.[6].so.that.it.is.poss

ible

.to.make.devi

data.para

meters

.avai

lable

.to.a.larg

.doma

.of.appl

ications

.thro

ugh

.OPC.UA..In.this.way,.it.give

.an.

alte

rnative

.to.the.Web.Serv

ices

.for.Devi

ces

.(WS4

.init

iative

.[7].that.prop

oses

.to.spec

ify

.and.impl

ment

.WS4D.usin

.the.Devi

ces

.Pro

.for.Web.Serv

ices

.(DPW

.spec

ication

.[8].that.is.the.succ

essor

of.the.Univ

ersal

.Plug.and.Play.(UPn

.prot

ocol.

Typical

.use.of.OPC.UA.conc

erns

.the.midd

leware

.serv

ices

.that.oer.an.abst

raction

.laye

.betw

een

devices.(e.g.,.programmable.logic.controller.[PLC],.sensors,.actuators,…).and.plant-oor.applications.

(SCA

DA,

.MES

,…),

.as.sho

.in.Fig

ure

.57.

OPC UA

57.1. Introduction.....................................................................................57-1

57.2

. Over

view

.of.OPC.UA.Sys

tem

.Arc

hitecture................................. 57-2

UA.Client.Application.Architecture. •. UA.Server.Architecture

57.3. Overview.of.UA.AddressSpace...................................................... 57-5

57.4

. Over

view

.of.UA.Ser

vices................................................................ 57-7

General.Services. •. Discovery.Service.Set. •. SecureChannel.Service.

Set. •. Session.Service.Set. •. NodeManagement.Service.Set. •. View.

Service.Set. •. Query.Service.Set. •. Attribute.Service.Set. •. Method.

Service.Set. •. MonitoredItem.Service.Set. •. Subscription.Service.Set

57.5. Implementations.and.Products................................................... 57-10

57.6

. Conc

lusion...................................................................................... 57-10

References................................................................................................... 57-10

Tuan Dang

EDF Research and

Deve

lopment

Renaud Aubin

EDF Research and

Deve

lopment

57-2 Industrial Communication Systems

57.2 Overview of OPC Ua System architecture

OPC.UA.soware.architecture.is.designed.using.the.ve-layer.model,.as.shown.in.Figure.57.2..Business.

information.models.(e.g.,.EDDL,.MIMOSA,.ISA…).and.vendor.information.model.are.typically.built.on.

top.of.OPC.UA.Base.Services,.which.also.provide.the.foundation.for.rebuilding.existing.OPC.information.

models.(DA,.A&E,.HDA…).

.release.1.01.of.OPC.UA.addresses.a.wide.range.of.target.applications:

•

. Supervisory.control.and.data.acquisition.(SCADA).and.human.machine.interface.(HMI).or.more.

generally.human.system.interface.(HSI).

•

. Advanced.control.in.distributed.control.system.(DCS):.Commands.may.be.sent.to.devices.and.

programmable.logic.controller.(PLC).

Panel PC

PLC

OPC UA

client

OPC UA

server

and

OPC UA

client

OPC UA

client

Embedded

OPC UA

server

Embedded

OPC UA

server

Embedded

OPC UA

client

Plant-oor

Sensors/actuators

SCADA

MES

ERP

FIGURE 57.1 Example.of.OPC.UA.application.

EDDL, MIMOSA, ISA...

OPC information model

All necessary services

OPC UA basis components

OPC UA transport

(Web services, UA binary TCP)

OPC UA data model

OPC UA base services

DA A&E HDA CMDs

Vendor information model

Information model speciﬁcations

FIGURE 57.2 OPC.UA.soware.architecture.

OPC UA 57-3

•. Manufacturing.execution.system.(MES).that.is.usually.deployed.in.the.supervisory,.simulation,.

and.scheduling.of.batch.processes.(e.g.,.pharmaceutical.process).

•

. Middleware.that.serves.intra-plant.applications.and.extra-plant.(enterprise.wide).applications.

(Figure.57.3).

Middleware

.is.a.piece.of.soware.that.serves.to.“glue.together”.or.mediate.between.two.separate.and.

usually.already.existing.programs..Middleware.is.sometimes.called.plumbing.because.it.connects.two.

sides.of.an.application.and.passes.data.between.them..Middleware plays a crucial role in enterprise

applications

.by.integrating.system.components,.allowing.them.to.interoperate.correctly.and.reliably,.

and.facilitating.system.management.and.evolution.. is.is.a.very.important.domain.of.applications.that.

OPC.UA.is.aimed.at,.bridging.the.industrial.information.systems.with.the.enterprise.one.

.system.architecture.of.OPC.UA.is.based.on.the.well-known.concept.of.client–server.interaction..

Each.system.may.contain.multiple.clients.and.servers..Each client may interact concurrently with one

or more servers,

.and.each server may interact concurrently with one or more clients..An.application.may.

combine.server.and.client.components.to.allow.interaction.with.other.servers.and.clients,.as.shown.in.

Figure.57.3..Peer-to-peer interactions between servers are also possible,.as.shown.in.Figure.57.4:

client

server

client

server

Enterprise

semantics

Process

semantics

“Aggregating” UA Servers

extract and process data

from lower level “Device”

UA Servers.

Data is recast using

different information models

appropriate for the clients at

the higher level.

Device

semantics

server

client

Enterprise network

Operations network

Plant floor

network

FIGURE 57.3 Chaining.of.UA.servers.and.UA.clients.

UA server

Client

interface

Client

interface

Server

interface

Server

interface

IP network

UA Binary TCP

SOAP XML over HTTP

FIGURE 57.4 Peer-to-peer.interactions.between.UA.servers.

57-4 Industrial Communication Systems

57.2.1 Ua Client application architecture

To.write.an.OPC.UA.client.application,.one.typically.needs.to.use.the.OPC.UA.client.application.

programming.interface.(API),.which.exposes.standard.services.that.should.be.used.to.send.and.receive.

OPC.UA.service.requests.and.responses.to.the.OPC.UA.server,.as.shown.in.Figure.57.5.. e.API isolates

the client application code from an OPC UA communication stack

.that.may.be.chosen.between.dier-

ent

.avors:.UA Binary over TCP.and.SOAP XML/Text over HTTP.. e.OPC.UA.communication.stack.

converts.OPC.UA.Client.API.calls.into.messages.and.sends.them.through.the.underlying.communica-

tions

.entity.to.the.server.at.the.request.of.the.client.application.. e.OPC.UA.communication.stack.also.

receives.responses.and.notication.messages.from.the.underlying.communications.entity.and.delivers.

them.to.the.client.application.through.the.OPC.UA.Client.API,.as.shown.in.Figure.57.5.

57.2.2 Ua Server architecture

 e. realization. of. an. UA. server. application. requires. more. eorts.. One. has. to. implement. the. UA

AddressSpace,

.as.dened.in.Part.3.of.the.UA.specications..UA.AddressSpace.is.used.to.represent.real.

objects,.their. denitions. and.their. references.to. each.other..Real. objects. are. physical. (i.e.,. physical.

devices).or.soware.objects.(e.g.,.alarm.counters).that.are.accessible.by.the.OPC.UA.server.application.

or.that.it.maintains.internally.(e.g.,.internal.data.objects).. e.UA.AddressSpace.is.modeled.as.a.set.of.

Nodes.accessible.by.UA.client.applications.using.OPC.UA.services.(interfaces.and.methods)..A.View.is.

a.subset.of.the.AddressSpace..Views.are.used.to.restrict.the.Nodes.that.the.server.makes.visible.to.the.

client,.thus.restricting.the.size.of.the.AddressSpace.for.the.service.requests.submitted.by.the.client.. e.

default View.is.the.entire.AddressSpace..Servers.may.optionally.dene.other.Views..Views.hide.some.of.

the.Nodes.or.References.in.the.AddressSpace..Views.are.visible.via.the.AddressSpace.and.clients.are.able.

to.browse.Views.to.determine.their.structure..Views.are.oen.hierarchies,.which.are.easier.for.clients.to.

navigate.and.represent.in.a.tree.

.server.application.uses.the.OPC.UA.Server.API.to.send.and.receive.OPC.UA.Messages.from.OPC.

UA.client.applications.. e.OPC.UA.Server.API.isolates.the.server.application.code.from.an.OPC.UA.

communication.stack,.as.shown.in.Figure.57.6.

OPC-UA client

OPC UA client API

Client application

OPC-UA stack

Requests to

send service

requests

Requests to

send

publishing

requests

Delivery of

received

service

responses

Delivery of

received

notiﬁcations

To OPC-UA

server

From OPC-UA

server

From OPC-UA

server

To OPC-UA

server

Req Msg Rsp Msg Notif MsgPubl Msg

FIGURE 57.5 UA.client.architecture.

OPC UA 57-5

To.nish.the.implementation,.one.has.to.realize.publisher/subscriber.entities,.which.oer.a.com-

munication

. mechanism. for. informing. a. data. change. or. an. event/alarm. occurrence. that. is. mod-

eled

.by.MonitoredItems..MonitoredItems.are.entities.in.the.server.created.by.the.client.that.monitors.

AddressSpace.Nodes.and.their.real-world.counterparts..When.they.detect.a.change.or.an.alarm.occur-

rence,

.they.generate.a.Notication.that.is.transferred.to.the.client.by.a.Subscription..A.Subscription.is.an.

endpoint.in.the.server.that.publishes.Notications.to.clients..Clients.control.the.rate.at.which.publishing.

occurs.by.sending.Publish.Messages.

57.3 Overview of Ua addressSpace

AddressSpace.is.an.important.concept.in.OPC.UA..It.provides.a.standard.way.for.UA.servers.to.

represent.objects.to.UA.clients..The.OPC.UA.object.model.(Figure.57.7).defines.objects.in.terms.

of.Variables.and.Methods..It.also.allows.relationships.to.other.objects.to.be.expressed,.as.shown.in.

Figure.57.7.

.elements.of.this.model.are.represented.in.the.AddressSpace.as.Nodes..Each.Node.is.assigned.to.a.

NodeClass.and.each.NodeClass.represents.a.dierent.element.of.the.object.model.. e.Node.Model.that.

is.used.to.dene.a.NodeClass.is.illustrated.by.Figure.57.8:

Attributes

.are.data.elements.that.describe.Nodes..Clients.can.access.Attribute.values.using.Read,.

Write,.Query,.and.Subscription/MonitoredItem.services.. ese.services.are.detailed.in.Part.4.of.the.UA.

specications..Attributes.are.elementary.components.of.NodeClasses..Each.Attribute.denition.consists.

of.an.attribute.id1,.a.name,.a.description,.a.data.type,.and.a.mandatory/optional.indicator.. e.set.of.

Attributes.dened.for.each.NodeClass.shall.not.be.extended.by.UA.clients.or.servers.

When

.a.Node.is.instantiated.in.the.AddressSpace,.the.values.of.the.NodeClass.Attributes.are.pro-

vided.

. e.mandatory/optional.indicator.for.the.Attribute.indicates.whether.the.Attribute.has.to.be.

instantiated.

OPC UA server

Server application

OPC UA AddressSpace

Node

Monitored

item

Subscription

OPC UA Server API

Real

objects

OPC UA stack

Rsp Msg

To OPC UA

client

From OPC UA

client

To OPC UA

client

From OPC UA

client

Req Msg Notif Msg Publ Msg

Node

View

FIGURE 57.6 UA.server.architecture.

57-6 Industrial Communication Systems

References.are.used.to.relate.Nodes.to.each.other.. ey.can.be.accessed.using.the.browsing.and.

querying. services.. Like. Attributes,. they. are. dened. as. fundamental.components. of.Nodes.. Unlike.

Attributes,.References.are.dened.as.instances.of.ReferenceType Nodes..ReferenceType.Nodes.are.visible.

in.the.AddressSpace.and.are.dened.using.the.ReferenceType NodeClass.

.Node.that.contains.the.Reference.is.referred.to.as.the.SourceNode.and.the.node.that.is.referenced.

is.referred.to.as.the.TargetNode.(see.Figure.57.9).. e.combination.of.the.SourceNode,.the.ReferenceType,.

TargetNode

SourceNode

Attributes

ReferenceName

(name of the

reference’s

ReferenceType)

FIGURE 57.9 UA.reference.model.

Object

References to

other objects

Data change

notifications

Read/write

Invoke

Event

notifications

Variables

Methods

FIGURE 57.7 UA.object.model.

Node

References

Attributes

Attributes describe a Node

References define relationship

to other Nodes

FIGURE 57.8 UA.AddressSpace.node.model.

OPC UA 57-7

and.the.TargetNode.are.used.in.OPC.UA.services.to.uniquely.identify.References.. us,.each.Node.can.

refe

rence

.ano

ther

.Nod

.wit

.the.sam

.Ref

erenceType

.onl

y once.

.Targ

etNode

.of.a.refe

rence

.may.be.in.the.same.Addr

essSpace

.or.in.the.Addr

essSpace

.of.anot

her

OPC.UA.serv

er.

.Targ

etNodes

.loca

ted

.in.othe

.serv

ers

.are.iden

tied

.in.OPC.UA.Serv

ices

.using.a.combi

nation

.of.the.remo

te server name

.and.the.iden

tier

.assig

ned

.to.the.Node.by.the.remo

.serv

er.

.OPC.UA.

does.not.req

uire

.tha

.the.Tar

getNode

.exi

sts,

.thu

.Ref

erences

.may.poi

.to.a.Nod

.tha

.doe

.not.exi

st!

57.4 Overview of Ua Services

 is.section.contains.a.summary.of.the.description.of.UA.services.presented.in.Part.1.of.the.UA.

spec

ications.

.For.a.deta

iled

.desc

ription

.of.UA.Serv

ices,

.it.is.advi

sed

.to.read.Part.4.of.the.UA.spec

i-

cations.

.Tabl

.57.1.list

.die

rent

.part

.of.the.UA.spec

ications.

57.4.1 General Services

Request/response services.are.services.invoked.by.the.UA.client.application.through.the.OPC.UA.service.

inte

rface

.to.perf

orm

.a.spec

ic

.task.on.one.or.more.Node

.in.the.Addr

essSpace

.and.to.retu

.a.resp

onse.

Publisher Services

.are.serv

ices

.invo

ked

.thro

ugh

.the.OPC.UA.serv

ice

.inte

rface

.for.the.purp

ose

.of.

peri

odically

.send

ing

.Noti

cations

.to.UA.clie

nts.

.Noti

cations

.incl

ude

.Even

ts,

.Alar

ms,

.Data.Chan

ges,

and.Pro

gram

.Out

puts.

57.4.2 Discovery Service Set

 is.service.set.denes.services.used.to.discover.OPC.UA.servers.that.are.available.in.a.system..It.also.

prov

ides

.a.mann

.in.whic

.clie

nts

.can.read.the.secu

rity conguration

.requ

ired

.for.conn

ection

.to.the.

Serv

er.

. e.Disc

overy

.serv

ices

.are.impl

emented

.by.indi

vidual UA servers

.and.by.dedi

cated Discovery

servers.

.Well

-known

.dedi

cated

.Disc

overy

.serv

ers

.prov

ide

.a.way.for.clie

nts

.to.disc

over

.all.regi

stered

.OPC.

UA.ser

vers.

57.4.3 SecureChannel Service Set

 is.service.set.denes.services.used.to.open.a.communication.channel.that.ensures.the.condentiality.

and.inte

grity

.of.all.mess

ages

.exch

anged

.with.the.UA.serv

er.

.More.deta

ils

.abou

.the.base.conc

epts

.for.UA.

secu

rity

.are.de

ned

.in.Par

.2.of.the.UA.spe

cications.

TABLE 57.1 List.of.the.UA.Specications

OPC.UA.Part.N° Description Status

Part

.1 Over

view

.and.concep

.1.01.spe

cication Released

Part

.2 Sec

urity

.mode

.1.01.spe

cication Released

Part

.3 Addres

.space.mode

.1.01.spe

cication Released

Part

.4 Serv

ices

.1.01.spe

cication Released

Part

.5 Info

rmation

.mode

.1.01.spe

cication Released

Part

.6 Map

pings

.1.00.spe

cication Released

Part

.7 Pro

les

.1.00.spe

cication Released

Part

.8 Dat

.access.1.01.spe

cication Released

Part

.9 Ala

rms

.dra.0.62.spe

cication Dra

Part

.10 Prog

rams

.1.00.spe

cication Released

Part

.11 Historical.access.1.00.specication Released

57-8 Industrial Communication Systems

 e.SecureChannel.services.are.unlike.other.services.because.they.are.typically.not.implemented.by.

the.UA.app

lication

.dir

ectly.

.Ins

tead,

.the

.are.pro

vided by the communication stack

.tha

.the.UA.app

lica-

tion

.is.bui

.on..For.exa

mple,

.a.UA.ser

ver

.may.be.bui

.on.a.SOA

.sta

.tha

.all

ows

.app

lications

.to.est

ab-

lish

.a.Sec

ureChannel

.usin

.the.WS-

SecureConversation

.spe

cication.

.In.the

.cas

es,

.the.UA.app

lication

simp

.nee

.to.ver

ify

.tha

.a.WS-

SecureConversation

.is.act

ive

.whe

never

.it.rec

eives

.a.mes

sage.

.Par

.6.of.

the.UA.spe

cications

.des

cribes

.how.the.Sec

ureChannel

.ser

vices

.are.imp

lemented

.wit

.di

erent

.typ

of.co

mmunication

.st

acks.

57.4.4 Session Service Set

 is.service.set.denes.services.used.to.establish.an.application-layer.connection.in.the.context.of.a.session.

on.beh

alf

.of.a.spec

ic

.user

57.4.5 NodeManagement Service Set

 e.NodeManagement.service.set.allows.clients.to.add,.modify,.and.delete.Nodes.in.the.AddressSpace..

.se

rvices

.pr

ovide

.an.in

terface

.fo

.th

.co

nguration

.of.UA.Se

rvers.

57.4.6 View Service Set

Views.are.publicly.dened,.UA.server-created.subsets.of.the.AddressSpace.. e.entire.AddressSpace.is.

the.def

ault

.Vie

.and.the

refore,

.the.Vie

.ser

vices

.are.cap

able

.of.ope

rating

.on.the.ent

ire

.Add

ressSpace.

Ser

vices

.to.cr

eate

.cl

ient-dened

.Vi

ews

.ma

.be.sp

ecied

.in.fu

ture

.ve

rsions

.of.OP

.UA

.Vie

.ser

vice

.set.all

ows

.cli

ents

.to.dis

cover

.Nod

.in.a.Vie

.by.bro

wsing.

.Bro

wsing

.all

ows

.cli

ents

to.nav

igate

.up.and.dow

.the.hie

rarchy,

.or.to.fol

low

.Ref

erences

.bet

ween

.Nod

.con

tained

.in.the.Vie

.In.

thi

.ma

nner,

.br

owsing

.al

lows

.cl

ients

.to.di

scover

.th

.st

ructure

.of.th

.Vi

ew.

57.4.7 Query Service Set

 e.Query.service.set.allows.users.to.access.the.UA.AddressSpace.without.browsing.and.without.knowl-

edge

.of.th

.lo

gical

.sc

hema

.us

.fo

.in

ternal

.sto

rage

.of.th

.da

ta.

Querying

.all

ows

.UA.Cli

ents

.to.sel

ect

.a.sub

set

.of.the.Nod

.in.a.Vie

.bas

.on.som

.cli

ent-provided

lt

.cr

iteria.

. e.No

des

.se

lected

.fr

.th

.Vi

.by.th

.qu

ery

.st

atement

.ar

.ca

lled

.a.re

sult set.

Notice:

.UA.ser

vers

.may.nd.it.di

cult

.to.pro

cess

.que

ries

.tha

.req

uire

.acc

ess

.to.run

time

.dat

.suc

as.dev

ice

.dat

.tha

.inv

olves

.res

ource-intensive

.ope

rations

.or.sign

icant

.del

ays.

.In.the

.cas

es,

.the.UA.

ser

ver

.ma

.n

.it.ne

cessary

.to.re

ject

.th

.qu

ery.

57.4.8 attribute Service Set

 e.Attribute.Service.Set.is.used.to.read.and.write.Attribute.values..Attributes.are.primitive.charac-

teristics

.of.Nod

.tha

.are.de

ned

.by.OPC.UA.. ey.may.not.be.de

ned

.by.UA.Cli

ents

.or.UA.Ser

vers.

Att

ributes

.are.the.onl

.ele

ments

.in.the.Add

ressSpace

.per

mitted

.to.hav

.dat

.val

ues.

.A.spe

cial

.Att

ribute,

the.Va

lue

.At

tribute

.is.us

.to.de

ne

.th

.va

lue

.of.Va

riables.

57.4.9 Method Service Set

Methods.represent.the.function.calls.of.Objects.. ey.are.invoked.and.return.aer.completion,.whether.

suc

cessful

.or.uns

uccessful.

.Exe

cution

.tim

.for.Met

hods

.may.var

.dep

ending

.on.the.fun

ction

.the

.are.

per

forming.

.A.Met

hod

.is.alw

ays

.a.com

ponent

.of.an.Obje

ct.

.Dis

covery

.is.pro

vided

.thr

ough

.the.bro

wse

OPC UA 57-9

and.query.services..UA.clients.discover.the.Methods.supported.by.an.UA.server.by.browsing.for.the.

own

ing

.Ob

jects

.th

.id

entify

.th

eir

.su

pported

.Me

thods.

Notice:

.Bec

ause

.Met

hods

.may.con

trol

.som

.asp

ect

.of.pla

.ope

rations,

.Met

hod

.inv

ocation

.may.dep

end

on.use.cas

.con

ditions.

.For.exa

mple,

.one.may.att

empt

.to.re-

invoke

.a.Met

hod

.imm

ediately

.ae

.it.has.

com

pleted

.exe

cution.

.Con

ditions

.tha

.are.req

uired

.to.inv

oke

.the.Met

hod

.may.not.yet.hav

.ret

urned

.to.

the.sta

.tha

.per

mits

.the.Met

hod

.to.sta

.aga

in.

.In.add

ition,

.som

.Met

hods

.may.be.cap

able

.of.sup

port-

ing

.co

ncurrent

.in

vocations,

.wh

ile

.ot

hers

.ma

.ha

.a.sin

gle

.in

vocation

.ex

ecuting

.at.a.gi

ven

.ti

me.

57.4.10 MonitoredItem Service Set

 e. MonitoredItem. service. set. is. used. by. the. UA. client. to. create. and. maintain. MonitoredItems.

MonitoredItems

.mon

itor

.Var

iables,

.Att

ributes,

.and.Eve

ntNotiers.

. ey.gen

erate

.Not

ications

.whe

the

.det

ect

.cer

tain

.con

ditions.

. ey.mon

itor

.Var

iables

.for.a.cha

nge

.in.val

.or.sta

tus;

.Att

ributes

.for.a.

cha

nge

.in.va

lue;

.an

.Ev

entNotiers

.fo

.ne

wly

.ge

nerated

.Al

arm

.an

.Ev

ent

.re

ports.

Each

.Mon

itoredItem

.ide

nties

.the.ite

.to.mon

itor

.and.the.Sub

scription

.to.use.to.per

iodically pub-

lish Notications

.to.the.UA.cli

ent.

.Eac

.Mon

itoredItem

.als

.spe

cies

.the.rat

.at.whi

.the.ite

.is.to.be.

mon

itored

.(sa

mpled)

.and

.for.Var

iables

.and.Eve

ntNotiers,

.the.lt

.cri

teria

.use

.to.det

ermine

.whe

a.Not

ication

.is.to.be.gen

erated.

.Mor

.det

ails

.on.lt

.cri

teria

.for.Att

ributes

.are.des

cribed

.in.Par

.4.of.

the.UA.sp

ecications.

.sam

ple rate

.de

ned

.for.a.Mon

itoredItem

.may.be.fast

.tha

.the.pub

lishing rate

.of.the.Sub

scription.

For.thi

.rea

son,

.the.Mon

itoredItem

.may.be.con

gured

.to.eit

her

.que

.all.Not

ications

.or.to.que

.onl

the.la

test

.No

tication

.fo

.tr

ansfer

.by.th

.Su

bscription.

.In.th

.la

tter

.ca

se,

.th

.qu

eue

.siz

.is.on

MonitoredItem

.serv

ices

.also.de

.a.mon

itoring mode.

. e.mon

itoring

.mod

.is.con

gured

.to.dis

able

sam

pling

.and.rep

orting,

.to.ena

ble

.sam

pling

.onl

.or.to.ena

ble

.bot

.sam

pling

.and.rep

orting.

.Whe

.sam

pling

.is.ena

bled,

.the.UA.serv

.sam

ples

.the.ite

.In.add

ition,

.eac

.sam

ple

.is.eval

uated

.to.det

ermine

.if.a.

Not

ication

.sho

uld

.be.gen

erated.

.If.so,.the.Not

ication

.is.que

ued.

.If.rep

orting

.is.ena

bled,

.the.que

.is.

mad

.avai

lable

.to.the.Sub

scription

.for.tra

nsfer.

MonitoredItems

.can.be.con

gured

.to.tri

gger

.the.rep

orting

.of.oth

.Mon

itoredItems.

.In.thi

.cas

the.mon

itoring

.mod

.of.the.ite

.to.rep

ort

.is.typ

ically

.set.to.sam

pling

.onl

.and.whe

.the.tri

ggering

item.generates.a.Notication,.any.queued.Notications.of.the.items.to.report.are.made.available.to.the.

Sub

scription

.fo

.tr

ansfer.

57.4.11 Subscription Service Set

 e.Subscription.service.set.is.used.by.the.UA.client.to.create.and.maintain.Subscriptions. Subscriptions.

are.ent

ities

.tha

.per

iodically

.pub

lish

.Not

icationMessages

.for.the.Mon

itoredItem

.ass

igned

.to.the

. e.

Not

icationMessage

. con

tains

. a. com

mon

. hea

der

. fol

lowed

. by. a. seri

. of. Not

ications.

. e. for

mat

. of.

Not

ications

.is.spec

ic

.to.the.typ

.of.ite

.bei

.mon

itored

.(i.

e.,

.Var

iables,

.Att

ributes,

.and.Eve

ntNotiers).

Once

.cre

ated,

.the.exi

stence

.of.a.Sub

scription

.is.ind

ependent

.of.the.UA.cli

ent’s

.ses

sion

.wit

.the.UA.

ser

ver.

. is.all

ows

.one.UA.cli

ent

.to.cre

ate

.a.Sub

scription,

.and.a.sec

ond,

.pos

sibly

.a.red

undant

.UA.cli

ent,

to.re

ceive

.No

ticationMessages

.fr

.it

.pro

tect

.aga

inst

.non

use

.by.UA.Cli

ents,

.Sub

scriptions

.hav

.a.con

gured

.lif

etime

.tha

.UA.cli

ents

.per

odically

.ren

ew.

.If.any.UA.cli

ent

.fai

.to.ren

.the.lif

etime,

.the.lif

etime

.exp

ires

.and.the.Sub

scription

.is.clo

sed

by.the.serv

er.

.Whe

.a.Sub

scription

.is.clo

sed,

.all.Mon

itoredItems

.ass

igned

.to.the.Sub

scription

.are.del

eted.

Subscriptions

. inc

lude

. fea

tures

. tha

. sup

port

. det

ection

. and. rec

overy

. of. los

. mes

sages.

. Eac

Not

icationMessage

.con

tains

.a. seq

uence number

.tha

.all

ows

.UA. cli

ents

.to. det

ect

.mis

sed

. mes

sages.

Whe

.the

.are.no.Not

ications

.to.sen

.wit

hin

.the.kee

p-alive

.tim

.int

erval,

.the.UA.ser

ver

.sen

.a.kee

alive

.message.that.contains.the.sequence number.of.the.next.NoticationMessage.sent..If.a.UA.client.

fai

.to.rec

eive

.a.mes

sage

.ae

.the.kee

p-alive

.int

erval

.has.exp

ired,

.or.if.it.det

ermines

.tha

.it.has.mis

sed

.a.

mes

sage,

.it.ca

.re

quest

.th

.UA.se

rver

.to.re

send

.on

.or.mo

.me

ssages.

57-10 Industrial Communication Systems

57.5 Implementations and Products

 e.OPC.Foundation.has.released.the.OPC.UA.SDK.(soware.development.kit).and.Java.SDK.for.

conc

ept

.veri

cation

.test

. e.UA.SDK.prop

oses

.a.set.of.inte

rfaces,

.libr

aries,

.and.exec

utables

.that.

allo

.deve

lopers

.to.quic

kly

.crea

.UA.appl

ications

.usin

.C/C#.lang

uages

.with.the..NET.prog

ram-

ming

.envi

ronment.

. e.Java.SDK.is.targ

eted

.for.the.deve

lopment

.of.UA.appl

ications

.with.the.Java.

envi

ronment.

Companies

.like.Advo

sol,

.Uni

.Auto

mation

.GmbH

.and.Techn

osoware

.AG,.are.amon

.the.sowa

vend

ors

.that.have.anno

unced

.OPC.UA.prod

ucts

.avail

ability.

57.6 Conclusion

OPC.UA.is.the.next.generation.of.the.well-known.OPC.technologies.from.the.OPC.Foundation..It.is.a.

plat

form-independent

.stan

dard

.thro

ugh

.whic

.vari

ous

.kind

.of.syst

ems

.and.devi

ces

.can.comm

unicate

by.send

ing

.mess

ages

.betw

een

.clie

nts

.and.serv

ers

.over.vari

ous

.type

.of.netw

orks.

. e.OPC.UA.spec

i-

cations

.are.laye

red

.to.isol

ate

.the.core.desig

.from.the.unde

rlying

.comp

uting

.tech

nology

.and.netw

ork

tran

sport.

. is.allo

.OPC.UA.to.be.mapp

.to.futu

.tech

nologies

.as.nece

ssary,

.with

out

.nega

ting

.the.

core.desi

gn.

references

. 1.. W..Mahnke,.S.-H..Leitner,.and.M..Damm,.OPC Unied Architecture,.Springer.Verlag,.Berlin/Heidelberg,.

Germ

any,

.2009

.ISBN

.978-

3-540-68898-3.

. 2.. Abou

.OPC.pag

.OPC.Foun

dation,

.Augus

.2010,.htt

p://www.opcfoundation.org

. 3.. What.is.MIMOSA?,.Welco

.pag

.Augus

.2010,.htt

p://www.mimosa.org

. 4.. Abou

.ISA.pag

.Augus

.2010,.htt

p://www.isa.org

. 5.. Abou

.OMAC.pag

.Augus

.2010,.htt

p://www.omac.org

. 6.. Abou

.EDDL.pag

.Augus

.2010,.htt

p://www.eddl.org

. 7.. Abou

.WS4D.pag

.Augus

.2010,.htt

p://www.ws4d.org

. 8.. S..Chan.et.al.,.Devices.Pro

.for.Web.Services,.May.2005,.http://s

pecs.xmlsoap.org/ws/2005/05/

devprof/devicesprole.pdf