wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Industrial Internet 56-3
A systematic solution for this problem should develop specific application scenarios, clearly identify
technical requirements for the intended application functions, the features of the system component
where the function will be implemented, and the location where the component is implemented
inside the system. This may lead to different combinations. For all relevant combinations, the technical
details of the information flows have to be specified and the requirements for the technologies have to be
refined. This establishes a list of criteria by which the technologies have to be evaluated.
56.3 technologies
It is obvious that an evaluation process as the one mentioned above is not possible without knowing
communication paradigms and technologies in detail. The most common communication paradigm
used by Internet applications is client–server communication. The server provides the data, while the
client retrieves the data and displays it. Typically, confirmed services are used. The sequence can be
described by the well-known service primitives (see Figure 56.2). The client issues the request by invoking
the service at an appropriate service access point (SAP)—service primitive—. req—the server is
informed by an indication (.ind), executes the service, and prepares the answer. The server passes the
answer to the client as response (.rsp). Finally, the client gets the answer together with the confirmation
(.cnf) from the service, and can now use the data. Thus, from an architectural point of view, a client layer
and a server layer can be distinguished in Industrial Internet systems.
A further specialization of the functional components involved in the communication scenarios leads
to more sophisticated architectures. The separation of application and data leads to the well-known
three-tier-architecture (Figure 56.3), which can be further subdivided concerning application logic,
data source, and communication server component (Figure 56.4). All types of architectural examples
can be found in industrial applications. Thus, for the different functions the components of the architecture
have to provide, different technologies exist—all assembled within the term Internet Technologies.
Internet technologies can be grouped by function. The following functional clusters can be distinguished:
• Transport and communication related technologies
• Technologies for information description and presentation
• Technologies for server-side and client-side functions
Client
e.g., Web browser
.req
Request
Client layer
.cnf
Server
e.g., Web server
Documents
Server layer
Response
.ind
.rsp
Application
FIGURE 56.2
Basic architecture and communication paradigm of Industrial Internet applications.
© 2011 by Taylor and Francis Group, LLC