OPC Unified Architecture

OPC UAOPC UA
Ch. Vishwa MohanCh. Vishwa Mohan
Freelance Software Consultant &Freelance Software Consultant &
Corporate TrainerCorporate Trainer

AgendaAgenda
IntroductionIntroduction
Information ModellingInformation Modelling
MappingMapping
ServicesServices
ArchitectureArchitecture
System and InfrastructureSystem and Infrastructure
SecuritySecurity
Technology MappingTechnology Mapping
Migration from Classic OPC to OPC UAMigration from Classic OPC to OPC UA
Performance, Profiling and TuningPerformance, Profiling and Tuning 22

Introduction to OPC UAIntroduction to OPC UA

IntroductionIntroduction
OPC UA is a standard for communication and Information
modeling in Automation industries.
OPC UA supplements existing OPC industry standard with
important features such as Platform Independency, Scalability,
High Availability and Internet Connectivity.
OPC Foundation provides stacks, wrappers and proxies.
OPC UA specifications are standardized as IEC 62541.
OPC UA allows the implementation of servers in embedded
systems.
OPC Foundation definesOPC Foundation defines howhow the data is transferred whereasthe data is transferred whereas
cooperating organizations (cooperating organizations (ISA, MIMOSA, PLCOpenISA, MIMOSA, PLCOpen, etc.,), etc.,)
definesdefines whatwhat data and information is transferred.data and information is transferred.
44Ch.Vishwa MohanCh.Vishwa Mohan

OPC UA BasisOPC UA Basis
ArchitectureArchitecture
Designed for FederationDesigned for Federation
Information ModelingInformation Modeling
Complex DataComplex Data
SecuritySecurity
Enterprise IntegrationEnterprise Integration
Robustness and ReliabilityRobustness and Reliability
CommandsCommands
Companion StandardsCompanion Standards
Web StandardsWeb Standards
Optimized for Internet (Performance)Optimized for Internet (Performance)

OPC UA in Embedded DevicesOPC UA in Embedded Devices
OPC UA allows the implementation of servers in embedded
systems, thus opening the doors to new automation concepts

OPC UA allows multi-platform communication between applications
Multi Platform CommunicationMulti Platform Communication

Limitations of Classic OPCLimitations of Classic OPC
Closely tied toClosely tied to MicrosoftMicrosoft WindowsWindows and its base technologyand its base technology
COM / DCOMCOM / DCOM..
Configuration requires expensive expertise and complicatesConfiguration requires expensive expertise and complicates
the use of OPC.the use of OPC.
Lack of following features:Lack of following features:
Security supportSecurity support
Protection against data lossProtection against data loss
Redundancy capabilitiesRedundancy capabilities
Support for complex data types.Support for complex data types.
Internet capabilities.Internet capabilities.

Advantages of OPC UAAdvantages of OPC UA
Simplification by Unification.
Standardized communication over Internet & across firewalls.
Protection against unauthorized data access.
Data Security and Reliability.
Platform independency and scalability.
Simplified use across computers
Quick and easy engineering through embedded OPC UA
Support of complex data structures
Optional redundancy capabilities
High Performance.

OPC UA defines anOPC UA defines an integrated address spaceintegrated address space and anand an
information modelinformation model in which in whichin which in which process dataprocess data,, alarmsalarms,,
historical datahistorical data andand programs callsprograms calls can be represented.can be represented.
Simplification By UnificationSimplification By Unification

Is OPC will become Obsolete ?Is OPC will become Obsolete ?

OPC UA SpecificationOPC UA Specification
OPC UA multipart specifications categorized into threeOPC UA multipart specifications categorized into three
groups.groups.

OPC UA FrameworkOPC UA Framework
The following three concepts inThe following three concepts in OPC UA FrameworkOPC UA Framework makesmakes
complex.complex.
The Query capabilities of OPC UA.The Query capabilities of OPC UA.
The Publish mechanism.The Publish mechanism.
Connection Establishment.Connection Establishment.

Typical application composed of three software layers :Typical application composed of three software layers :
OPC UA Software LayersOPC UA Software Layers

OPC UA Stack LayerOPC UA Stack Layer
OPC UA defines three Stack layers and different profiles for
each layer.
Message Encoding LayerMessage Encoding Layer
Message Security LayerMessage Security Layer
Message Transport LayerMessage Transport Layer

Protocol BindingsProtocol Bindings
At present OPC UA defines four (4) protocol bindings.At present OPC UA defines four (4) protocol bindings.
Native UA Binary (Native UA Binary (mandatorymandatory))
HTTPS with UA BinaryHTTPS with UA Binary
HTTPS with SOAP and XML encodingHTTPS with SOAP and XML encoding
HTTP with SOAP &WS-SecureConversation and XML Encoding.HTTP with SOAP &WS-SecureConversation and XML Encoding.

OPC UA Toolkit architecture :
OPC UA Tool KitOPC UA Tool Kit

Information ModelInformation Model

What is an Information ModelWhat is an Information Model
OPC UA not only addresses data communication but also
provides a meta model allowing standardized information
model built on top of it.
OPC UA provides a framework that can be used to represent
complex information as Objects in the address space.
Objects consists of differentObjects consists of different NodesNodes connected byconnected by referencesreferences..
An Information Model Defines:
NodesNodes
Type Definitions, Reference types and Data types.Type Definitions, Reference types and Data types.
Modeling Rules.Modeling Rules.
Standard Properties and methods.Standard Properties and methods.
Standard Objects and ViewsStandard Objects and Views
ConstraintsConstraints 1919Ch.Vishwa MohanCh.Vishwa Mohan

OPC UAOPC UA defines graphical symbols for all NodeClasses and
how References of different types can be visualized.
OPC UA notation is actually stereotyped UML.
All Nodes in OPC UA would be mapped to instances of UML.
The OPC UA NodeClasses would be mapped to UML-Classes.
In OPC UA ObjectTypes become instances of that UML-Class.
OPC UA Graphical NotationOPC UA Graphical Notation

NodeClass Graphics ElementsNodeClass Graphics Elements
OPC UA defines eight node classes. Each node in the address
space is an instance of one of these node classes.

NodeClass & AttributesNodeClass & Attributes

Data Types HierarchyData Types Hierarchy

Base Information ModelBase Information Model
ContentContent

ContentContent
Attributes & DescriptionAttributes & Description

Node ClassNode Class
Used to define nodes in the UA Address Space.Used to define nodes in the UA Address Space.
Node classes are use to represent the following three types ofNode classes are use to represent the following three types of
objects:objects:
Define instances.Define instances.
Define types for instances.Define types for instances.
Define data types.Define data types.
All nodes are derived fromAll nodes are derived from BaseBase node class.node class.
No references are specified forNo references are specified for BaseBase node class.node class.
Attributes of Base Node class are:Attributes of Base Node class are:
NodeidNodeid,, NodeClassNodeClass,, BrowseNameBrowseName,, DisplayNameDisplayName,, DescriptionDescription,,
WriteMaskWriteMask,, UserWriteMaskUserWriteMask..

Object Node ClassObject Node Class
ThisThis ObjectObject Node class is used to define real-world objects,Node class is used to define real-world objects,
software objects and system components.software objects and system components.
TheThe ObjectObject node class derived fromnode class derived from BaseBase node class.node class.
Attributes defined byAttributes defined by ObjectObject Node class:Node class: EventNotifierEventNotifier..
Object node is represented as rectangle including textObject node is represented as rectangle including text
represents string part ofrepresents string part of DisplanyNameDisplanyName attribute as below:attribute as below:
If the Object is created based on an instance declaration, it
shall have the same BrowseName as its instance declaration.
In addition all nodes referenced with hierarchical reference in
forward direction shall have unique BrowseName value in the
context of this Object. 2828Ch.Vishwa MohanCh.Vishwa Mohan

Ch.Vishwa MohanCh.Vishwa Mohan
Variable Node ClassVariable Node Class
TheThe VariableVariable node class used to define variables. Two types ofnode class used to define variables. Two types of
variables are defined:variables are defined:
PropertiesProperties
Data VariablesData Variables
VariableVariable nodenode never appear themselvesnever appear themselves in the address space.in the address space.
Always they are defined asAlways they are defined as propertiesproperties andand data variablesdata variables ofof
other nodes.other nodes.
Clients may read or write Variable values, or monitor them for
value changes.
This node has at most oneThis node has at most one HasModelingRuleHasModelingRule referencereference
pointing topointing to ModelingRuleModelingRule node.node.
It can have at mode oneIt can have at mode one HasModelingParentHasModelingParent reference.reference. 2929

Variable Node ClassVariable Node Class
PropertiesProperties are defined usingare defined using VariableVariable node class. Representsnode class. Represents
characteristics of a node.characteristics of a node.
DataVariablesDataVariables node represents the content of an object. It alsonode represents the content of an object. It also
defined usingdefined using VariableVariable node class.node class.
Addition toAddition to BaseBase node attributes it supports following attributesnode attributes it supports following attributes
ValueValue
DataValueDataValue
ValueRankValueRank
ArrayDimensionsArrayDimensions
AccessLevelAccessLevel
UserAccessLevelUserAccessLevel
MinimumSamplingIntervalMinimumSamplingInterval
HistorizingHistorizing 3030

Type DefinitionsType Definitions
Type definition describes theType definition describes the semanticssemantics andand structurestructure of itsof its
instance Nodes.instance Nodes.
OPC UA definesOPC UA defines ObjectObject andand VariableVariable type definitions aretype definitions are
ObjectTypeObjectType andand VariableTypeVariableType..
To link an instance with its type definitionTo link an instance with its type definition HasTypeDefinitionHasTypeDefinition
reference used.reference used.
For any data variable type definition not available then serverFor any data variable type definition not available then server
will usewill use BaseDataVariableTypeBaseDataVariableType as its type definition.as its type definition.
PropertyType used as type definition for all properties.
It is possible to subtype a type definition.

ObjectType Node ClassObjectType Node Class
ThisThis ObjectTypeObjectType node class provides definition for objects.node class provides definition for objects.
In addition toIn addition to BaseBase node attribute it supports additionalnode attribute it supports additional
IsAbstractIsAbstract attribute.attribute.
TheThe ObjectTypeObjectType node class supports following references:node class supports following references:
HasComponentHasComponent
HasPropertyHasProperty
HasSubtypeHasSubtype
GeneratesEventsGeneratesEvents
Its notation is a shadowed rectangle including textIts notation is a shadowed rectangle including text
representing string part ofrepresenting string part of DisplayNameDisplayName attribute.attribute.
ObjectsObjects are always based on anare always based on an ObjectTypeObjectType. (. (i.e., they havei.e., they have
HasTypeDefinitionHasTypeDefinition reference pointing to itsreference pointing to its ObjectTypeObjectType).). 3232Ch.Vishwa MohanCh.Vishwa Mohan

DataType Node ClassDataType Node Class
Used to define simple & complex data types.Used to define simple & complex data types.
Each Variable and VariableType node is pointing with its
DataType attribute to a node of the DataType node class:
EachEach DataTypeDataType can have several data type encoding andcan have several data type encoding and
encoding type shown by pointing toencoding type shown by pointing to DataTypeEncodingTypeDataTypeEncodingType..
Its notation in address space is shadowed hexagon includingIts notation in address space is shadowed hexagon including
text representstext represents DisplayNameDisplayName attribute.attribute.
It deinfes only single propertyIt deinfes only single property IsAbstractIsAbstract.. 3333

This node class is used to provide type definition for variablesThis node class is used to provide type definition for variables
VariableVariable node usesnode uses HasTypeDefintionHasTypeDefintion reference point to itsreference point to its
VariableTypeVariableType..
TheThe VariableTypeVariableType defines following attributes:defines following attributes:
Value,Value,
DataTypeDataType
ValueRankValueRank
AArrayDimensionrrayDimension
IsAbstractIsAbstract
This node class represented with shadowed rectangle with
rounder corner included with DisplayName attribute.
The VariableType node also defines HasProperty,
HasComponent, GenerateEvents references. 3434
VariableType Node ClassVariableType Node Class

ReferencesReferences
References allows nodes to be connect together.
All the References have ReferenceType that specify the
semantics of the relationship.
References can be Hierarchical or Non-Hierarchical.
HiHierarchical references are used to create the structure of Objects.
Non-hierarchical are used to create arbitrary associations .
Applications can define their own ReferenceTypes by creating
subtypes of the existing ReferenceType.
Each node can reference another node with the same
ReferenceType only once.

References NotationReferences Notation
References between Nodes are represented by lines between
them. Arrows expose the direction.

Reference Model HierarchyReference Model Hierarchy

EventsEvents
OnlyOnly ObjectObject andand ViewView nodes class used to subscribe events.nodes class used to subscribe events.
TheseThese two nodes havetwo nodes have EventNotifierEventNotifier attribute.attribute.
Event subscription usesEvent subscription uses MonitoringMonitoring andand SubscriptionSubscription services.services.
The OPC UA server’sThe OPC UA server’s ServerServer Object supports server specificObject supports server specific
events.events.
In OPC UA all events are derived fromIn OPC UA all events are derived from BaseEventTypeBaseEventType..
All event types exposed in the server are need to present inAll event types exposed in the server are need to present in
Address space.Address space.
Type definition of event is represented withType definition of event is represented with ObjectTypeObjectType node.node.
Event types can beEvent types can be subtypedsubtyped butbut can’t extendcan’t extend an existingan existing
event type.event type. 3838Ch.Vishwa MohanCh.Vishwa Mohan

Event Type HierarchyEvent Type Hierarchy

MethodsMethods
In OPC UA methods are light weight functions.In OPC UA methods are light weight functions.
Scope is bounded by an owningScope is bounded by an owning ObjectObject oror ObjecTypeObjecType..
Each method is described by a node ofEach method is described by a node of MethodMethod node class.node class.
NodeNode contains method metadata.contains method metadata.
Method are represented by aMethod are represented by a OvalOval including text representingincluding text representing
the string part of thethe string part of the DisplayNameDisplayName attribute ofattribute of MethodMethod node.node.
Methods are invoked by usingMethods are invoked by using CallCall service.service.
Method invocations always run to completion.
Each method is invoked in the context ofEach method is invoked in the context of existing sessionexisting session..
Methods areMethods are statelessstateless. But it can affect the state of owning. But it can affect the state of owning

MethodMethod
TheThe MethodMethod node class inherits fromnode class inherits from BaseBase node class.node class.
MethodMethod node defines the following attributes.node defines the following attributes.
ExecutableExecutable
UserExecutableUserExecutable
Properties are defined on method usingProperties are defined on method using HasPropertyHasProperty referencereference
Predefined propertiesPredefined properties InputArugmentsInputArugments andand OutputArguementsOutputArguements
are array ofare array of ArugmentArugment type.type.
To specifyTo specify modeling rulemodeling rule on a method it can useon a method it can use HasModelRuleHasModelRule
property.property.
Method can useMethod can use GenerateEventsGenerateEvents reference to identify thatreference to identify that
method can generate eventsmethod can generate events of specified event type or subtype.of specified event type or subtype.

Attributes SummaryAttributes Summary

BitMask forBitMask for
WriteMask and UserWriteMaskWriteMask and UserWriteMask

Information ModelInformation Model
Information Model uses OO concepts and allow full-meshed
network of nodes related by multiple types of references.
AllAll information in an OPC UA server will be composed of the
standard OPC UA Object types (ServerTypes, EventTypes,
VariableTypes, BaseTypes, etc., )
EEvery OPC UA server will have an OPC UA Root object.
Every OPC UA server will have at least one Server Object.
Every OPC UA server will support at least one View Object

Object in UA Address SpaceObject in UA Address Space
A simpleA simple ReservationReservation object in UA Address space:object in UA Address space:
Relationship betweenRelationship between ObjectObject and itsand its Type definitionType definition::

Diagnostic Information ModelDiagnostic Information Model

Data Access Information ModelData Access Information Model

Definition of “Definition of “AnalogMeasurementAnalogMeasurement” type and its instance.” type and its instance.
Type Definition & InstancesType Definition & Instances

NamespacesNamespaces
Namespaces in OPC UA have a globally unique string called a
NamespaceURI and a locally unique integer called a
NamespaceIndex.
NNamespaceIndex is unique only within the context of a Session.
Two types of values in OPC UA are qualified with NamespacesTwo types of values in OPC UA are qualified with Namespaces
NodeId
QualifiedNamesQualifiedNames
OPC UA Information Models generally define globally unique
NodeIds for the TypeDefinitions defined by the Information
Model.

OPC UA MetaModelOPC UA MetaModel
The OPC UA meta model is represented by UML classes and
UML objects marked with the stereotype <<TypeExtension>>.
Stereotyped UML objects represent data types or reference types.
In Object Diagram, OPC Attributes are represented as UML
attributes without data types and marked with the
stereotype <<Attribute>>.
OPC references are represented as UML associations marked with
5050

Nodes UML DiagramNodes UML Diagram

UML Meta Model forUML Meta Model for
ReferenceTypesReferenceTypes

UML Meta Model forUML Meta Model for
Method Node ClassMethod Node Class

BaseObjectTypeBaseObjectType
TheThe BaseObjectTypeBaseObjectType is used as type definition whenever thereis used as type definition whenever there
is anis an ObjectObject having no concrete type definition available.having no concrete type definition available.
All otherAll other ObjectTypesObjectTypes are directly or indirectly derived from theare directly or indirectly derived from the
BaseObjectTypeBaseObjectType..
The following types are derived from BaseObjectType. TheseThe following types are derived from BaseObjectType. These
are called special (tree group) types.are called special (tree group) types.
ModellingRuleType: Used as type for modeling rule.
FolderType : Used to organize the Address Space into hierarchy
of nodes.
DataTypeEncodingType: Used as type for data type encodings.
DataTypeSystemType: Used as type for data type systems.

OPC UA Address Space is structured as a
hierarchy, with the top levels standardized
for all servers.
RootRoot browse entry point for Address Spacebrowse entry point for Address Space
ViewsViews browse entry point for views.browse entry point for views.
ObjectsObjects browse entry point for Objects.browse entry point for Objects.
ReferenceTypes: It will be used as filters in
the browse Service and in queries, the
server shall provide all its ReferenceTypes.
DataTypes: Entry point for all data types
that server wishes to expose in Address
space.
Standard Address Space StructureStandard Address Space Structure

Unified Object ModelUnified Object Model
OPC UA enables DA, AE and HDA data to be accessed by a
single OPC Server. Similarly OPC UA unifies and simplifies
access to Process Data, Events, Historical Data & Programs.

OPC Interface UnificationOPC Interface Unification
OPC UA ServerOPC UA Server embodies the functionality of existingembodies the functionality of existing OPCOPC
ServersServers using a single set of servicesusing a single set of services..
Features of UA Server are:Features of UA Server are:
Service Oriented Architecture (SOA)Service Oriented Architecture (SOA)
Integrated with DA, AE, Commands, ComplexData, etc.,Integrated with DA, AE, Commands, ComplexData, etc.,
Single Set of Services Query, Read, Write, Subscribe, etc.,Single Set of Services Query, Read, Write, Subscribe, etc.,
Named/Typed relationship between Nodes.Named/Typed relationship between Nodes.
Platform Independent.Platform Independent.
Communication architecture is a 3-Tier.Communication architecture is a 3-Tier.

MappingMapping
Classic OPC can be mapped to OPC UA without losing
information.
Mapping from OPC UA to Classic OPC is possible but may
lead to loss of information.

Most of OPC UA servers needed to implement the complete OPC
DA functionality are contained in the base specifications of OPC UA.
The implementation functionalities are categorizedThe implementation functionalities are categorized Address SpaceAddress Space
andand Access InformationAccess Information..
Mapping from OPC DA to OPC UAMapping from OPC DA to OPC UA

Mapping fromMapping from OPC DAOPC DA toto
OPC UAOPC UA containscontains FolderFolder,,
ObjectObject,, DataData VariableVariable,,
OrganizesOrganizes andand
HasComponentHasComponent
references.references.
OPC DA Address Space MappingOPC DA Address Space Mapping

OPC DA Access Information MappingOPC DA Access Information Mapping
OPC DAOPC DA toto OPC UAOPC UA
access informationaccess information
mappingmapping

OPC XML DA MappingOPC XML DA Mapping
OPC XMLDA uses the same Address Space concept like COM-
based OPC DA.

OPC Alarm & Event MappingOPC Alarm & Event Mapping
Simple and trackingSimple and tracking
eventsevents defined indefined in classicclassic
OPC A&EOPC A&E are easilyare easily
implemented inimplemented in OPC UAOPC UA
by using baseby using base
specifications.specifications.
For mappingFor mapping conditioncondition
EventsEvents thethe OPC UAOPC UA
Alarm & condition modelAlarm & condition model
is requiredis required..

OPC UA ServicesOPC UA Services
OPC UA defines totally 37 different services.
3 services deals with discovery.
6 services for connection handling.
28 services uses to access OPC UA data.
Independent ofIndependent of Transport protocolTransport protocol andand Program environmentProgram environment..
UsesUses Request-ResponseRequest-Response pattern.pattern.
By default all services areBy default all services are AsynchronousAsynchronous..
Each service haveEach service have Individual TimeoutIndividual Timeout..
Each Service contains the same headers for Request
Messages and for Response Messages..
UA services are designed inUA services are designed in SOASOA manner. (manner. (ProvidesProvides BulkBulk
operationsoperations to reduce round trips between client and serverto reduce round trips between client and server).). 6666

OPC UA Services SetsOPC UA Services Sets
OPC UA Services are grouped by functionalities:OPC UA Services are grouped by functionalities:
Discovery Service Set
Secure Channel Service Set
Session Service Set.
View Service Set
Attribute Service Set
Subscription Service Set
Monitored Item Service Set.
Method Service Set.
Query Service Set
Node Management Service Set.

Request & Response Header ParametersRequest & Response Header Parameters
Request HeaderRequest Header Parameters:Parameters:
AuthenticationTokenAuthenticationToken
RequestHandleRequestHandle
TimeStampTimeStamp
TimeoutHintTimeoutHint
ReturnDiagnosticReturnDiagnostic
AuditEntryIdAuditEntryId
ResponseResponse HeaderHeader Parameters:Parameters:
Service ResultService Result
RequestHandleRequestHandle
TimestampTimestamp
ServiceDiagnosticsServiceDiagnostics

Error InformationError Information
Two types ofTwo types of Error InformationError Information Used by OPC UA Services:Used by OPC UA Services:
Status CodeStatus Code
Diagnostic InformationDiagnostic Information
Status CodeStatus Code is 32-bit unsigned integer (is 32-bit unsigned integer (ExtendableExtendable).).
Most significant 16 bits numeric code value used to detect
specific errors or conditions.
Two most significant bits uses overall severity:Two most significant bits uses overall severity:
GoodGood
UncertainUncertain
BadBad
Least significant 16-bitsLeast significant 16-bits are bit flags that containare bit flags that contain additionaladditional
informationinformation. (. (But doesn’t effect the meaning ofBut doesn’t effect the meaning of StausCodeStausCode).). 6969Ch.Vishwa MohanCh.Vishwa Mohan

Diagnostic InformationDiagnostic Information
TheThe DiagnosticInformationDiagnosticInformation structure contains additionalstructure contains additional
information for ainformation for a StatusCodeStatusCode. It includes:. It includes:
Vendor Specific Error code.Vendor Specific Error code.
Localized Description of the Error.Localized Description of the Error.
Text field for Additional Information.Text field for Additional Information.

Communication ContextCommunication Context
OPC UA services areOPC UA services are StatefulStateful. So to call a Service need to. So to call a Service need to
establish Communication context.establish Communication context.

OPC UA ServicesOPC UA Services
List of services to exchange information between OPC UA client &Server.List of services to exchange information between OPC UA client &Server.

Discovery ServicesDiscovery Services
OPC UA specifies a set of abstract services for performing the
discovery process.
Entities for Discovery process are:Entities for Discovery process are:
Session EndpointSession Endpoint
Discovery EndpointDiscovery Endpoint
Local Discovery ServerLocal Discovery Server
Global Discovery ServerGlobal Discovery Server
Service Related to Discovery Process are:Service Related to Discovery Process are:
RegisterServerRegisterServer
FindServersFindServers
GetEndpointsGetEndpoints
OPenSecureChannelOPenSecureChannel 7373

Discovery ProcessDiscovery Process
Discovery process performed by exchanging DiscoveryDiscovery process performed by exchanging Discovery
Messages. Discovery Process can be any one of the 3 forms:Messages. Discovery Process can be any one of the 3 forms:
Simple DiscoverySimple Discovery
Normal DiscoveryNormal Discovery
Hierarchical DiscoveryHierarchical Discovery

The OPC UA Server or Client consists 3 layers :The OPC UA Server or Client consists 3 layers :
StacksStacks are shipped by OPC Foundation.are shipped by OPC Foundation.
SDK’sSDK’s are provided by third parties.are provided by third parties.
OPC UA Application ArchitectureOPC UA Application Architecture

Stacks ArchitectureStacks Architecture
Functionalities of theFunctionalities of the StackStack accessed by higher layers:accessed by higher layers:
Stack ConfigurationStack Configuration
Managing Connection Establishment.Managing Connection Establishment.
Sending Messages.Sending Messages.
Message Receive Notification.Message Receive Notification.

Stack ArchitectureStack Architecture
ANSI C Stack supports UA Binary for the Encoding layer, UA Secure
Conversation for secure layer and UA TCP for transport layer.
The .NET Stack doesn’t have a Platform Layer. Different
configurations(Transport profiles or facets) of .NET stacks:
HTTP/SOAP, WS-SecureConversation, UA Binary
HTTP/SOAP, WS-SecureConversation, XML
HTTP/SOAP, WS-SecureConversation, UA Binary, and XML
UA TCP, UA-SecureConversation, UA Binary

SDKSDK
SDK’sSDK’s sits on top of Stacks and consists 3 parts:sits on top of Stacks and consists 3 parts:
UA Specific FunctionalityUA Specific Functionality
Common FunctionalityCommon Functionality
Client/ Server API (Interfaces)Client/ Server API (Interfaces)

SDK Providers.SDK Providers.
SDK’s consists two parts Client library and Server library.SDK’s consists two parts Client library and Server library.
C++ based UA SDKs for clients and servers also available.

System InfrastructureSystem Infrastructure

System ArchitectureSystem Architecture
OPC UA is designed to run on different platforms also
supports different architectural concepts at system level such
as redundancy, server-chaining, server-aggregation.
System Architectural Patterns:
Client-Server
Chain Server
Server –To- Server communication
Aggregating Servers

System ArchitectureSystem Architecture
Typical system architecture for large networks shown below:

Architectural PatternsArchitectural Patterns
Client-Server Pattern:Client-Server Pattern:
Chained Server Pattern:Chained Server Pattern:

Architectural PatternsArchitectural Patterns
Server to Server Communication:Server to Server Communication:

Aggregating ServersAggregating Servers
Aggregating server pattern normally used in MESAggregating server pattern normally used in MES

RedundancyRedundancy
Redundancy can be atRedundancy can be at serverserver side orside or clientclient side. Differentside. Different
Redundancy structuresRedundancy structures for client and server.for client and server.
Client RedundancyClient Redundancy: Uses TransferSubscription service.: Uses TransferSubscription service.

Server RedundancyServer Redundancy
It can beIt can be Transparent Server RedundancyTransparent Server Redundancy andand Non-Non-
transparent Server Redundancytransparent Server Redundancy..

Server Failover ModesServer Failover Modes
Failover Mode can be three modes. (Failover Mode can be three modes. (Based onBased on modemode clientclient
need to perform some actions to supportneed to perform some actions to support redundancyredundancy).).
Cold
Warm
Hot
On Failover the client need to create a new session to a
backup server and transfer the subscription data of the
previous session to new session.
Transferring subscriptions two approaches:
Duplicating Subscription
Using TransferSubscription Service.

Transferring SubscriptionTransferring Subscription
Duplication SubscriptionDuplication Subscription: Here all subscriptions created on: Here all subscriptions created on
Active server also created on Backup server. But samplingActive server also created on Backup server. But sampling
and reporting only enabled on Active Server.and reporting only enabled on Active Server.

Transferring SubscriptionTransferring Subscription
TransferSubscription Service ApproachTransferSubscription Service Approach:: Proxy component on
the client only creates subscriptions on the active server.
Active server mirrors all created subscriptions to the backup server.
On Failover, proxy creates a new session on the backup server and
uses the TransferSubscription Service for getting the subscriptions.

Security in OPC UASecurity in OPC UA
Core Security features of OPC UA are:Core Security features of OPC UA are:
Authentication
Authorization
Confidentiality
Integrity
Auditability
Availability
OPC UA security uses:OPC UA security uses:
X.509 Certificates
OpenSSL Encryption
Username/Password
Access rights for each attribute. 9393Ch.Vishwa MohanCh.Vishwa Mohan

OPC UA has to provideOPC UA has to provide flexible security modelflexible security model need to thinkneed to think
tradeoff betweentradeoff between SecuritySecurity andand PerformancePerformance..
OPC UA Environment & SecurityOPC UA Environment & Security

Security ArchitectureSecurity Architecture
ContentContent

Connection EstablishmentConnection Establishment
The connection establishment of OPC UA includesThe connection establishment of OPC UA includes
Creating a Secure ChannelCreating a Secure Channel
Establishing a SessionEstablishing a Session
Activating the SessionActivating the Session
The following are messages related to connection:The following are messages related to connection:
GetEndpointsGetEndpoints
OpenSecureChannelOpenSecureChannel
CreateSesionCreateSesion
ActivateSesionActivateSesion
CloseSesionCloseSesion
CloseSecureChannelCloseSecureChannel

Connection EstablishmentConnection Establishment
Sequence diagram forSequence diagram for Secure Connection EstablishmentSecure Connection Establishment

To exchange data between applications OPC UA definedTo exchange data between applications OPC UA defined
Technology MappingTechnology Mapping addresses:addresses:
Data EncodingData Encoding
Securing CommunicationSecuring Communication
Transporting DataTransporting Data
OPC UA Application Function Layers shown below:OPC UA Application Function Layers shown below:

OPC UA Stack OverviewOPC UA Stack Overview
Mappings are organized intoMappings are organized into
three groups:three groups: DataEncodingsDataEncodings,,
SecurityProtocolsSecurityProtocols andand
TransportProtocolsTransportProtocols..
Different mappings combinedDifferent mappings combined
together to createtogether to create StackProfilesStackProfiles
OPC UA supports two types ofOPC UA supports two types of
datadata encodingencoding::
OPC UA BinaryOPC UA Binary
OPC UA XMLOPC UA XML

Data EncodingData Encoding
At present OPC UA supports two encodings XML and Binary.
As a pert of encoding OPC UA defined built in primitive types.
A special type container and common for all encoding type is
defined called ExtensionObject.
ExtensionObject is a container holds data & how it encoded.
OPC UA also defines Variant type.
Binary encoding for “OPCUA” string:
Sequence of UTF-8 Character is used beginning with length of string.Sequence of UTF-8 Character is used beginning with length of string.
No Null terminator.No Null terminator.
Exchange data with different types of systems XML Encoding best:

Two security protocols are defined for OPC UA:Two security protocols are defined for OPC UA:
WS-SecureConversationWS-SecureConversation
UA-SecureConversationUA-SecureConversation
WS-SecureConversationWS-SecureConversation is used in conjunction withis used in conjunction with WS-WS-
SecurityPolicySecurityPolicy..
The connection establishment in OPC UA requires creating
a Secure Channel and a Session.
UA-SecureConversation is a combination standards TLS
and WS-SecureConversation. (Defined for optimization).
Securing CommunicationSecuring Communication

Mapping ImplementationsMapping Implementations
Currently there are three stacks provided by OPC Foundation.Currently there are three stacks provided by OPC Foundation.
ANSI C StackANSI C Stack
C# StackC# Stack
Java StackJava Stack
ANSI C stacks currently provide UA Binary, UA-
SecureConversation, and UA TCP as mapping
implementations.
Possible to generate your own stack forPossible to generate your own stack for SOAP/HTTPSOAP/HTTP..

Transport ProtocolsTransport Protocols
OPC UA defined two transport protocolsOPC UA defined two transport protocols UA TCPUA TCP andand
SOAP/HTTPSOAP/HTTP..
UA TCP is a small set of protocol defined on top of TCP.
SOAP/HTTP is another transport communicates across the
networks.

Built-in TypesBuilt-in Types
105105

This encoding is developed for performance needs.This encoding is developed for performance needs.
This Encoding does not include any type or field name
information.
Binary encoding follows “little enedian” format.
All string values are encoded as a sequence of UTF8
characters without a null terminator and preceded by the
length in bytes.
The length in bytes encoded asThe length in bytes encoded as Int32Int32. A value. A value -1-1 for NULL string.for NULL string.
A DateTime value shall be encoded as a 64-bit signed integer.
An XmlElement is an XML fragment serialized as UTF-8 string
and then encoded as ByteString.
Enumerators are encoded as Int32 values.
OPC UA Binary EncodingOPC UA Binary Encoding

The encoding of a NodeId varies according to the contents of
the instance. The components of NodeId is given below:
A LocalizedText structure is given below:

Serialized form ofSerialized form of ExtensionObjectExtensionObject is given below.is given below.
In OPC UAIn OPC UA MessagesMessages are encoded asare encoded as ExtensionObjectsExtensionObjects..
TheThe TypeIdTypeId field contains the DataTypeEncoding identifier for
the message.
The Length field is omitted since the messages are defined by
the OPC UA specification.

Serialized form ofSerialized form of VariantVariant is given below. All OPC UAis given below. All OPC UA
standard built-in types are encoded inside variant.standard built-in types are encoded inside variant.

Serialized form ofSerialized form of DataValueDataValueis given below.is given below.
A DataValue is always preceded by a mask that indicates which
fields are present in the stream.

OPC UA XML EncodingOPC UA XML Encoding
Most of the built-in types are encoded into XML by using theMost of the built-in types are encoded into XML by using the
format defined in XML Schema Security Model Specification.format defined in XML Schema Security Model Specification.
The mappings between the OPC UA integer types and XML
schema data types are given below:
A Guid is encoded using the string its schema is given below:

A ByteString value is encoded as an xs:base64Binary value.
A NodeId value is encoded as a xs:string with the syntax:
ns=<namespaceindex>;<type>=<value>
A StatusCode is formatted in an xs:string as an 8 digit
hexadecimal number.
A LocalizedText value is encoded as a xs:complexType:

An ExtensionObject value is encoded as a xs:complexType
and its schema is given below:

Migration fromMigration from
Classic OPC to OPC UAClassic OPC to OPC UA

MigrationMigration
OPC UA provides migration strategies for different requirements
and levels of OPC UA adaption.
First LevelFirst Level : Doesn’t required any changes in existing products.: Doesn’t required any changes in existing products.
Using OPC UA providedUsing OPC UA provided WrappersWrappers andand ProxiesProxies are good enough.are good enough.
Second LevelSecond Level: Here mapping exposes the same features as in: Here mapping exposes the same features as in
the existing old OPC products with OPC UA.the existing old OPC products with OPC UA.

Wrappers & ProxiesWrappers & Proxies
OPC UA clients can instantly connect to existing OPC COM Servers.
UA Client Proxy to connect existing COM clients to new UA Servers.
Using UA proxy and wrappers to replace the DCOM .

Wrappers & ProxiesWrappers & Proxies
WrappersWrappers are used to alloware used to allow OPC UA ClientsOPC UA Clients to accessto access classicclassic
OPC ServersOPC Servers..
ProxiesProxies used to accessused to access UA serverUA server fromfrom COM clientCOM client..

Performance, Profiling & TuningPerformance, Profiling & Tuning

TitleTitle
ContentContent

OPC CertificationOPC Certification
OPC server and client products are tested atOPC server and client products are tested at OPC FoundationOPC Foundation
Certification LabCertification Lab. It will test the following :. It will test the following :
ComplianceCompliance
InteroperabilityInteroperability
RobustnessRobustness
EfficiencyEfficiency
UsabilityUsability
OPC Foundation also hosts workshop forOPC Foundation also hosts workshop for InteroperabilityInteroperability
testingtesting ((IOPIOP).).
OPC Foundation providesOPC Foundation provides OPC Compliance Test ToolOPC Compliance Test Tool ((CTTCTT).).
It isIt is a script based tool and can enhanced to create producta script based tool and can enhanced to create product
specific test cases.specific test cases.

Questions ?Questions ?
Ch. VishwaMohanCh. VishwaMohan
Freelance Software Consultant and TrainerFreelance Software Consultant and Trainer
Reach me @Reach me @
EmailEmail :: cvmohan@outlook.comcvmohan@outlook.com

OPC Unified Architecture

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