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Abstract and Figures

Optimization of the industrial processes requires further research on the integration of machine-centric systems with human-centric cloud-based services in the context of new emerging disciplines, namely Industry 4.0 and Industrial Internet of Things. This research aims at working out a new generic architecture and deployment scenario applicable to this integration. The re-active interoperability relationship of the interconnected nodes is proposed to deal with the network traffic propagation asymmetry or assets' mobility. Described solution based on the OPC Unified Architecture international standard relaxes issues related to the real-time multi-vendor environment. The discussion addressing the generic architecture concludes that the embedded gateway archetype best suits all requirements. To promote separation of concerns and reusability, the proposed architecture of the embedded gateway archetype has been implemented as a composable part of an existing OPC UA PubSub framework. 2 OOI-Azure Interoperability The proposals are backed by proof of concept reference implementations confirming the possibility to interconnect selected cloud services with the cyber-physical system interconnected as one whole atop of the OPC UA by applying the proposed architecture and deployment scenario. It is contrary to interconnecting cloud services with a selected OPC UA server limiting the PubSub role to data export only.
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Object-Oriented Internet
Cloud Interoperability
Mariusz Post´o l1[0000000296690565] and Piotr Szymczak1 [0000000167903878]
Institute of Information Technology, Lodz University of Technology, od´z, Poland
mailto:mariusz.postol@p.lodz.pl
Abstract. Optimization of industrial processes requires further research
on the integration of machine-centric systems with human-centric cloud-
based services in the context of new emerging disciplines, namely the
fourth industrial revolution coined as Industry 4.0 and Industrial In-
ternet of Things. The following research aims at working out a new
generic architecture and deployment scenario applicable to that inte-
gration. A reactive interoperability relationship of the communication
parties is proposed to deal with the network traffic propagation asym-
metry or assets’ mobility. Described solution based on the OPC Unified
Architecture international standard relaxes issues related to the real-time
multi-vendor environment. The discussion concludes that the embedded
gateway software component best suits all requirements and thus has
been implemented as a composable part of the selected reactive OPC
UA framework which promotes separation of concerns and reusability.
The proposals are backed by proof-of-concept reference implementations
confirming the possibility of integrating selected cloud services with the
OPC UA based cyber-physical system by applying the proposed archi-
tecture and deployment scenario. It is contrary to interconnecting cloud
services with the selected OPC UA Server limiting the PubSub role to
data export only.
Keywords: Industry 4.0 ·Internet of Things ·Object-Oriented Internet
·Cloud Computing ·Industrial communication ·Reactive networking ·
Machine to Machine Communication ·OPC Unified Architecture ·Azure
1 Introduction
All the time, Information and Communication Technology is providing society
with a vast variety of new distributed applications aimed at micro and macro
optimization of the industrial processes. The design foundation of this kind of
application must focus primarily on communication technologies. Based on the
role humans take while using those applications they can be grouped as follows:
human-centric - information origin or ultimate information destination is
an operator,
machine-centric - information creation, consumption, networking, and pro-
cessing are achieved entirely without human interaction.
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Lecture Notes in Computer Science.
2 Mariusz Post´o l and Piotr Szymczak
A typical human-centric approach is a web-service supporting, for example,
a web user interface (UI) to monitor conditions and manage millions of devices
and their data in a typical cloud-based IoT approach [3,9, 13, 29]. In this case,
it is characteristic that any uncertainty and necessity to make a decision can be
relaxed by human interaction. Coordination of robot behaviors in a work-cell (au-
tomation islands) is a machine-centric example. In this case, any human inter-
action must be recognized as impractical or even impossible. The interconnection
scenario requires machine to machine communication (M2M) [10, 12,22, 25,28]
demanding the integration of multi-vendor devices.
From the M2M communication concept, a broader idea of a smart factory
can be derived. In this M2M deployment approach, the mentioned robots are
only executive assets of an integrated supervisory control system responsible for
macro optimization of an industrial process composed as one whole. Deployment
of the smart factory concept requires a hybrid solution and interconnection of
the above mentioned heterogeneous environments. This approach is called the
fourth industrial revolution and was coined as Industry 4.0. It is worth stress-
ing that interconnection of machines - or more general assets - is not enough,
and additionally, assets interoperability must be expected for the deployment of
this concept. In this case, multi-vendor integration makes communication stan-
dardization especially important, namely, it is required that the payload of the
message is standardized to be factored on the data-gathering site and consumed
on the ultimate destination site.
Highly-distributed solutions used to control any real-time process aggregating
islands of automation (e.g. virtual power plants producing renewable energy)
must, additionally, leverage public communication infrastructure, namely the
Internet. The Internet is a demanding environment for highly distributed process
control applications designed atop the M2M communication paradigm because
it is globally shareable and can be also used by malicious users. Furthermore, it
offers only non-deterministic communication making the integration of islands
of automation designed against the real-time requirements a demanding task.
Today both obstacles can be overcome, and as examples, we have bank ac-
count remote control and voice over IP in daily use. The first application must
be fine-tuned in the context of data security, and the second is very sensitive
concerning time constraints. Similar approaches could be applied to adopt the
concepts well known in process control industry, namely Human Machine In-
terface (HMI), Supervisory Control and Data Acquisition (SCADA), and Dis-
tributed Control Systems (DCS). It is worth stressing that, by design, all of
them are designed based on interactive communication. Interactive communica-
tion is based on a data polling relationship. If that is the case, the application
must follow the interactive behavioral model, because it actively polls the data
source for more information by pulling data from a sequence that represents the
process state in time. The application is active in the data retrieval process -
it controls the pace of the retrieval by sending the requests at its convenience.
After dynamically attaching a new island of automation the control application
(responsible for the data pulling) must be reconfigured for this interoperability
Object-Oriented Internet Cloud Interoperability 3
scenario. In other words the interactive communication relationship cannot be
directly applied because the control application must be informed on how to pull
data from a new source. As a result, a plug and produce scenario [16] cannot be
seamlessly applied. A similar drawback must be overcome if for security reasons
suitable protection methods have been applied to make network traffic propa-
gation asymmetric. It is accomplished using intermediary devices, for example,
firewalls, to enforce traffic selective availability based on predetermined security
rules against unauthorized access.
Going further, we shall assume that the islands of automation are mobile,
e.g. autonomous cars passing a supervisory controlled service area. Here, the
behavior of the interconnected assets is particularly important concerning the
environment in which they must interact. This way we have entered the Internet
of Things domain of Internet-based applications.
If we must bother with the network traffic propagation asymmetry or mobil-
ity of the asset network attachment-points the reactive relationship could relax
the problems encountered while the interactive approach is applied [25]. In this
case, the sessionless publisher-subscriber communication relationship is a typi-
cal pattern to implement the reactive interoperability paradigm. The sessionless
relationship is a message distribution scenario where senders of messages, called
publishers, do not send them directly to specific receivers, called subscribers, but
instead, categorize the published messages into topics without knowledge about
which subscribers, if any, there may be. Similarly, subscribers express interest in
one or more topics and only receive messages that are of interest, without knowl-
edge about which publishers, if any, there are. In this scenario, the publishers
and subscribers are loosely coupled, i.e. they are decoupled in time, space and
synchronization [6].
If the machine-centric Cyber-Physical System (CPS) - making up islands
of automation - must be monitored and/or controlled by a supervisory system,
the cloud computing concept may be recognized as a beneficial solution to re-
place or expand the above mentioned applications, i.e. HMI, SCADA, DCS, etc.
Cloud computing is a method to provide the requested functionality as a set
of services. There are many examples that cloud computing is useful to reduce
costs and increase robustness. It is also valuable in case the process data must be
exposed to many stakeholders. Following this idea and offering control systems
as a service, there is required a mechanism created on the service concept and
supporting abstraction and virtualization - two main pillars of the cloud com-
puting paradigm. In the cloud computing concept, virtualization is recognized
as the possibility of sharing the services by many users, and abstraction hides
implementation details.
This article addresses further research on the integration of the multi-vendor
machine-centric CPS designed atop of M2M communication and emerging
cloud computing as a human-centric front-end in the context of the Industry
4.0 (I4.0) and Industrial Internet of Things (IIoT) disciplines. For this integra-
tion, a new architecture is proposed to support the reactive relationship of com-
municating parties. To support the multi-vendor environment the OPC Unified
4 Mariusz Post´o l and Piotr Szymczak
Architecture [7,17, 18] interoperability standard has been selected. The propos-
als are backed by proof of concept reference implementations - the outcome has
been just published on GitHub as an open-source (MIT licensed) [24]. Prototyp-
ing addresses Microsoft Azure Cloud [4] as an example. The proposed solutions
have been harmonized with the more general concept called the Object-Oriented
Internet (OOI) [20, 23, 24].
The main goal of this article is to provide proof that:
reactive M2M interoperability based on the OPC UA standard can be im-
plemented as a powerful standalone library without dependency on the
Client/Server session-oriented archetype,
cloud interoperability can be implemented as an external part employing
out-of-band communication without dependency on the OPC UA imple-
mentation,
the proposed generic architecture allows that the gateway functionality is
implemented as a composable part at run-time - no programming required.
The remainder of this paper is structured as follows. Sect. 2 presents the
proposed open and reusable software model. It promotes a reactive interoper-
ability pattern and a generic approach to establishing interoperability-context.
A reference implementation of this archetype is described in Sect. 3. The most
important findings and future work are summarized in Sect. 4.
2 Sensors to Cloud Interconnection - Architecture
To follow the Industry 4.0 concept a hybrid environment integrating reactive
Machine to Machine interconnection and the interactive web-based user interface
is required (Sect. 1). The main challenge of the solution in concern is to design a
generic but reusable architecture that addresses interoperability of those diverse
interconnection scenarios ruled by different requirements, namely:
machine-centric machine to machine real-time mobile interoperability
human-centric cloud-based front-end
Interconnection of the reactive machine-centric and interactive human-
centric environments can be implemented by applying one of the following
scenarios:
direct interconnection (tightly coupled)-using a common protocol stack
gateway based interconnection (loosely coupled)-using an out-of-bound
protocol stack
By design, the direct interconnection approach requires that the cloud has
to be compliant with the interoperability standard the CPS uses. As a result, it
becomes a consistent communication node of the CPS. The decision to follow the
direct interconnection scenario must be derived from an analysis of the capa-
bilities of available services in concern. However, for the development strategy of
Object-Oriented Internet Cloud Interoperability 5
this type of solution, the analysis can be done partially taking into account the
following features that can be considered invariable. By design, the cloud-based
services must be virtual - they are used to handle many solutions at the same
time. Furthermore, M2M communication is usually constrained by real-time re-
quirements. The virtualization of cloud services means that they must be very
flexible to handle the attachment of new assets proactively (acting in advance)
at run time. As a result, the cloud services must be responsible to register and
authenticate devices by exposing endpoints in the public network to allow the
device to access a provisioning cloud service. It requires that a session over the
Internet has to be established by the data holding asset at a preparation step.
To meet the requirements of real-time distributed control the CPS may use pro-
tocols applicable only to local computer networks (e.g. multicast IP, Ethernet,
TSN 1, etc.). Because the cloud services support only protocols handling inter-
connection over the Internet the direct interconnection cannot be applied in
a general case.
To support also a local network attachment point, the interaction with the
cloud requires remote agents implemented by applying one of the following
archetypes:
edge device - a remote cloud agent acting as an intermediary for nodes of
the CPS
field level gateway - a dedicated custom agent acting as an intermediary
for nodes of the CPS
Embedded Gateway - a software part composed into a selected node of the
Cyber-physical network (Fig. 1)
Edge device connects directly to the cloud services but acts as an interme-
diary for other devices called leaf devices. Additionally, it allows the selection
of initial data and their processing using local resources. The edge device may
be located close to the leaf devices and attached to the Cyber-physical network
using protocols applicable only to local computer networks. In this scenario, it
is possible to use a custom protocol stack to get connected to the edge device
with the cloud and to help to save the bandwidth thanks to sending only the
results of local processing. In this approach, the edge device is part of cloud
vendor products and cannot be recognized as a generic solution that can be used
to connect to other clouds supporting a many-to-many relationship.
The field level gateway is also built atop of the middleware concept [27].
The only difference as compared with the edge device is a necessity to use ser-
vices officially supported by the cloud vendor to get connected. In this scenario,
the process data may be transferred to many clouds simultaneously.
Proposition 1. Unlike the above-described solutions, the Embedded Gateway
is not derived from the middleware concept. A generic domain model for this in-
terconnection is presented in the Fig. 1. Promoting separation of concerns design
principle, the gateway functionality should be implemented as a self-contained
1Time-Sensitive Networking (TSN) Task Group https://1.ieee802.org/tsn/
6 Mariusz Post´o l and Piotr Szymczak
software part embedded in the Networking service of the Cyber-physical node.
The main functionality of this component is to transfer selected data between
Cyber-physical network using Networking services of an existing Cyber-physical
node and Cloud-based front-end using interconnection services officially sup-
ported by the cloud vendor.
Fig. 1. Generic interconnection concept
The interconnection of assets
is not enough hence their inter-
operability is expected. In this
case, using the same commu-
nication stack must be recog-
nized as only a necessary con-
dition. To support interoperabil-
ity, common data understand-
ing is required. Additionally, to
meet this requirement, the cloud
and CPS have to establish di-
rectly the same semantic-context
and security-context. The possi-
bility of establishing a common
semantic-context in the multi-
vendor environment makes com-
munication standardization espe-
cially important. If that is the
case, it is required that the encoding of the payload exchanged over the net-
work (Data Transfer Object) is standardized so that the appropriate messages
can be factored on the data-gathering site and consumed on the ultimate des-
tination data processing sites. Security between the data origin and ultimate
data destination refers to the protection of messages (security-context) against
malicious users. It is required that communicating parties are using the same
cyber-security measures. To comply with the Industry 4.0 communication crite-
rion, it is required that any product must be addressable over the network via
TCP/UDP or IP and has to support the OPC UA Information Model [15,19,21].
As a result, any product being advertised as Industry 4.0 enabled must be OPC
UA-capable somehow.
The OPC Unified Architecture interoperability standard has been selected
to support the multi-vendor environment. OPC UA supports the following two
patterns to be used to transfer data between communicating parties:
– session-oriented: requires a session that must be established before any
data can be sent between sender and receiver
– sessionless-oriented: the sender may start sending messages (called pack-
ets or datagrams) to the destination without any preceding handshake pro-
cedure
Using the session-oriented communication pattern it is difficult or even im-
possible to gather and process mobile data (Sec. 1 ), which is one of the Internet
Object-Oriented Internet Cloud Interoperability 7
of Things paradigms. OPC UA Part 14 PubSub [2, 26] offers the sessionless
approach as an additional option to session-based client-server interoperability
relationship and is a consistent part of the OPC UA specifications suit. As a
result, it can be recognized as the IoT ready technology.
The proposals presented in the article are backed by proof of concept refer-
ence implementations [24]. For this study, prototyping addresses Microsoft Azure
cloud products. There are many reasons for selecting Azure to accomplish the
cloud-based front-end of a Cyber-Physical System (CPS). Azure offers Infras-
tructure as a Service (IaaS) and Platform as a Service (PaaS) capabilities. As
a result, the platform can be used not only as a cloud-based front-end for CPS.
Azure aids Internet protocols and open standards such as JSON, XML, SOAP,
REST, MQTT [5], AMQP [8], and HTTP. Software development kits for C#,
Java, PHP, and Ruby are available for custom applications.
Based on the sessionless and session-oriented communication patterns ex-
amination against the IoT requirements [25] it could be concluded that the
connectionless pattern better suites issues related to assets mobility and traffic
asymmetry that is characteristic for the application domains in concern. Ad-
ditionally, to promote interoperability and address the demands of the M2M
communication in the context of a multi-vendor environment, the prototyping
should use a framework that must be compliant with the OPC UA Part 14
PubSub specification. According to proposed generic architecture (Fig. 1) to
implement the Embedded Gateway as a composable part of the Cyber-physical
node a library implementing Networking functionality in compliance with above
mentioned specification is a starting point for further development. Additionally,
it must be assumed that the library used to deploy Embedded Gateway supports
dependency injection and is capable of composing an external part supporting
cloud/PubSub gateway functionality. The composition process must be available
without modification of the core code of an existing library. As a result, the pro-
totyping is to be limited to implementation of the Embedded Gateway software
part only.
To promote interoperability and address the demands of the M2M communi-
cation in the context of a multi-vendor environment the prototyping should use
a framework that must be compliant with the OPC UA Part 14 PubSub and
support the Reactive Interoperability (Sect. 1) concept. A framework compliant
with these requirements has been implemented as an open-source library2named
UAOOI.Networking (Networking for short) under an umbrella of the Object-
Oriented Internet project [24]. The library is designed to be a foundation for
developing application programs that are taking part in a message-centric com-
munication pattern and interconnected using the reactive networking concept.
The diagram in Fig. 2 shows the relationship between the library (SDK ) and
external parts composing any reactive networking application (Reactive Appli-
cation). The Reactive Application is an aggregation of parts implementing the
Producer and Consumer roles. By design, they support access to real-time pro-
cess data, hence they are recognized as an extension of DataRepository class. To
2https://github.com/mpostol/OPC-UA-OOI
8 Mariusz Post´o l and Piotr Szymczak
implement the DataRepository dedicated implementation of the IBindingFactory
interface should be provided to create a bridge between CPS and an external
raw data represented by the LocalResources class. A more in-depth description
of the OOI Reactive Application library enabling data exchange over a network
using the reactive networking pattern is covered in [25].
Fig. 2. Reactive interoperability architecture
To promote the polymorphic
approach, the library has a fac-
tory class called DataManage-
mentSetup that is a placeholder
to gather all injection points used
to compose external parts. To
be injected, the part support-
ing data exchange with the un-
derlying process must be compli-
ant with the IBindingFactory in-
terfaces. It is expected that the
functionality implementation ex-
pressed by this interface is pro-
vided as an independent exter-
nal composable part. The com-
position is accomplished at run
time, and the effective applica-
tion functionality depends essen-
tially on reusable loosely coupled
parts composed applying the de-
pendency injection software engineering concept.
The DataRepository represents data holding assets in the Reactive Appli-
cation implementing the IBindingFactory interface. It captures functionality
responsible for accessing the external process data from LocalResources. The
LocalResources represents an external part that has a very broad usage purpose.
For example, it may be any kind of the process data source/destination, i.e. raw
data (e.g. PLC internal registers), OPC UA Address Space Management [25],
cloud, file, database, graphical user interface, to name only a few.
Depending on the expected network role the library supports the implemen-
tation of:
Consumer - entities processing data from incoming messages,
Producer - entities gathering process data and populating outgoing messages.
The Consumer and Producer classes are derived from the DataRepository
(Fig. 2). The Consumer uses the IBindingFactory to gather the data recovered
from the Message instances pulled from a network. The received data may be
processed or driven to any data destination, e.g. cloud-based front-end. The
Producer mirrors the Consumer functionality and, after reading data from an
associated source, populates the Message using the gathered data. By design,
the DataRepository and associated entities, i.e. Local Resources,Consumer,Pro-
ducer are embedded in external parts, and, consequently, the application scope
Object-Oriented Internet Cloud Interoperability 9
may cover practically any concern that can be separated from the core Reactive
Application implementation.
3 Cloud - OOI Interoperability Implementation
Proposition 2. A generic domain model presenting interconnection architec-
ture between the Cloud-based Front-end and Cyber-physical node attached to
the Cyber-physical network is presented in Fig. 1. It is proposed to implement
the Cyber-physical node by adopting the Reactive Application archetype compli-
ant with the reactive interoperability concept (Fig. 2). Merging selected entities
of this archetype into the proposed domain model (Fig. 1) leads to a model ex-
pressed as the diagram presented in Fig. 3. In the proposed approach the Embed-
ded Gateway is derived from the Consumer role implemented as a composable
part aggregated by the Reactive Application.
Fig. 3. Architecture Domain Model
In the final deployment ar-
chitecture (Fig. 4) the Consumer
role has been realized by the
PartDataManagementSetup that
is derived from DataManage-
mentSetup provided by the li-
brary. Networking (SDK) was re-
moved from this diagram for the
sake of simplicity. Instantiating
PartDataManagementSetup is the
first step for bootstrapping pro-
cess of the Consumer role func-
tionality. This class provides an
entry point to initialize all prop-
erties, which are injection points
of all parts composing this role.
It extends the functionality of the
DataManagementSetup based on
the following associated classes:
PartBindingFactory and Commu-
nicationContext.
The PartBindingFactory im-
plements the IBindingFactory to gather the data recovered from the Message
instances pulled from a network. The received data is driven to Communication-
Context for further encoding and finally pushing it to the cloud services using
the configured out-of-band protocol.
The cloud interconnection is realized using the CommunicationContext. It
implements a message encoder and establishes the out-of-band communication
stack.
10 Mariusz Post´o l and Piotr Szymczak
Fig. 4. Implementation Architecture
The data recovered from the Mes-
sage is obtained from the PartBind-
ingFactory using the IDTOProvider
that defines a contract used to pull the
Data Transfer Object created from
a subscription by the PartBinding-
Factory. The transfer process requires
data conversion from source to des-
tination encoding, i.e. replacing bit-
streams used by the CPS with equiva-
lent ones for the cloud-based services.
The Azure offers a vast variety of
built-in types ready to be used in com-
mon cases, but not necessarily there
are equivalent counterparts in use by
the CPS. The Azure uses JSON based
Data Transfer Object encoding and schema defined based on the solution meta-
data. The PubSub uses JSON and binary Data Transfer Object encodings. In
any case, the data recovered from the Message pulled from a subscription is
stored locally using the object model based on standard .NET types. PartBind-
ingFactory maps selected object graph onto the JSON message required by the
cloud services.
The encoded JSON messages must be transferred to cloud over the net-
work using the selected protocol stack. The Azure supports HTTP, AMQP, and
MQTT protocol stacks, which are all standard ones. Consequently, it is possible
to apply any available implementation compliant with an appropriate specifica-
tion to achieve connectivity. In this case, all parameters required to establish
semantic and security contexts are up to the gateway responsibility. Alterna-
tively, the API offered by the dedicated frameworks (libraries) may be used.
Using a framework, the configuration process may be reduced significantly, and
the communication protocol selection has only an indirect impact on the inter-
operability features. In the proposed implementation, the Azure interconnection
has been obtained using the above mentioned frameworks.
Azure and PubSub use different security mechanisms so in the proposed solu-
tion establishing security-context is realized independently. The Communication-
Context is responsible for establishing this context as an embedded negotiation
phase tightly coupled with establishing interconnection.
4 Conclusion
Nowadays, the macro optimization of the industrial processes requires an in-
tegration of a vast variety of distributed applications provided by Information
and Communication Technology. It requires further research on the integration
of machine - centric Cyber-Physical Systems (CPS) with human - centric
Object-Oriented Internet Cloud Interoperability 11
front-end in the context of new emerging disciplines, i.e. Industry 4.0 and the
Industrial Internet of Things (Sect. 1).
CPS is composed using the multi-vendor components (data holding assets)
interconnected atop of the Machine To Machine (M2M) communication. In many
applications, the dynamic nature of the CPS must be considered. Dynamic na-
ture means that interconnected assets may be added/removed from the network
at any time. By design, CPS must typically fulfill the real-time and mobility of
the assets requirements.
Highly-distributed solutions used to control/monitor a set of geographically
dispersed islands of automation (e.g. virtual power plants producing renewable
energy) must additionally leverage public communication infrastructure, namely
the Internet. If islands of automation must be controlled over the Internet, the
cloud computing concept may be recognized as a reasonable answer. Following
this concept, the cloud-based supervisory control functionality is applied as a
set of services employing abstraction and virtualization - two main pillars of the
cloud computing paradigm. In the cloud computing concept, virtualization is rec-
ognized as the possibility of sharing the services by many users, and abstraction
hides implementation details.
The main goal of this research is working out a new generic architecture and
deployment scenario applicable for the integration of the machine-centric CPS
and emerging cloud computing as a human-centric front-end.
If we must bother with the network traffic propagation asymmetry or mobil-
ity of the asset network attachment points the reactive relationship [25] could
alleviate the challenges posed by the interactive approach. The real-time multi-
vendor environment makes communication standardization especially important.
To support this environment, the OPC Unified Architecture [11] interoperability
standard has been selected. As it was pointed out in Sect. 2 using OPC UA Pub-
Sub [2] the aggregation of nodes by the network is loosely coupled, i.e. nodes can
be added and removed from the network dynamically, and nodes may represent
mobile data holding assets.
From the analysis covered by Sect. 2 it is concluded that the Embedded Gate-
way archetype best suits all requirements described above. It relaxes most of
the issues related to direct interconnection and solutions inferred from the
middleware concept, i.e. edge device - a remote cloud agent and field level
gateway - a dedicated custom agent. Additionally, it could be used to connect
to many independent clouds at the same time. The generic domain model for
the proposed interconnection archetype is presented in Fig. 1. We have high-
lighted that to promote the separation of concerns design principle, the gate-
way functionality should be implemented as a self-contained dedicated software
part embedded in the core Networking service of the Cyber-physical node. The
main functionality of this component is to transfer process data between Cyber-
physical network using Networking services of an existing Cyber-physical node
and Cloud-based front-end using interconnection services officially supported by
the cloud vendor.
12 Mariusz Post´o l and Piotr Szymczak
To promote interoperability and address the demands of the M2M communi-
cation in the context of a multi-vendor environment the prototyping should use
a framework that must be compliant with the OPC UA Part 14 PubSub (Sect.
2) and support the Reactive Interoperability (Sect. 1) concept. We proposed to
use an open-source library named UAOOI.Networking (Networking for short)
(Fig. 2) for this purpose. It is worth stressing that based on this approach only
dedicated functionality related to the communication with the cloud must be
implemented.
We derived the final model presented in Fig. 4 by merging selected entities
from the Networking library (Fig. 2) into the generic interconnection domain
model (Fig. 1). In the proposed approach the Embedded Gateway is derived
from the Consumer role implemented as a composable part aggregated by the
Reactive Application.
The proposals are backed by proof of concept reference implementations.
Prototyping addresses Microsoft Azure cloud as an example. The outcome has
been just published on GitHub as the open-source (MIT licensed) repository.
The proposed solutions have been harmonized with the more general concept
called the Object-Oriented Internet.
The described results prove that the Embedded Gateway archetype imple-
mentation is possible based on the existing standalone framework supporting
reactive interoperability atop the M2M communication compliant with the OPC
UA PubSub standard. It is worth stressing that there is no dependency on the
Client/Server session-oriented relationship. This relationship is in contrast to
the architecture described in the OPC UA Part 1 [14] specification where the
publisher role is tightly coupled with the Address Space [1] embedded com-
ponent of the OPC UA Server. The real challenge of the future work is to prove
that the proposed solution is flexible enough to be used as an archetype to inject
the Embedded Gateway part into the OPC UA Client/Server to get connected
with the cloud addressing the interactive relationship.
In the proposed approach the cloud interoperability is obtained by imple-
menting a dedicated part employing out-of-band communication only without
dependency on the OPC UA functionality at all. It is worth stressing that the
gateway functionality is implemented as a part composable to the whole with-
out programming skills. Because the part is composed at the runtime it makes
it possible to modify its functionality later after releasing the library or even
deploying the application program in the production environment.
Concluding, the paper describes a proof of concept that applying the pro-
posed architecture and deployment scenario it is possible to integrate cloud ser-
vices (e.g. Azure IoT Central) with the Cyber-physical network interconnected
as one whole atop of the OPC UA PubSub. It is in contrast to interconnecting
cloud-based front-end services with the Address Space instance exposed by a
selected OPC UA server limiting the PubSub role to data exporter transferring
the data out of the OPC UA ecosystem.
Object-Oriented Internet Cloud Interoperability 13
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