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

OPC UA 57-3
Enterprise network
Operations network
Plant floor
network
UA
server
UA
server
UA
client
UA
client
UA
client
UA
client
UA
server
UA
server
UA
client
UA
server
UA
client
Enterprise
semantics
Process
semantics
Device
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.
FIGURE 57.3
Chaining of UA servers and UA clients.
• 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 software 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. This is a very important domain of applications that
OPC UA is aimed at, bridging the industrial information systems with the enterprise one.
The 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:
UA server
UA Binary TCP
or
SOAP XML over HTTP
Server
interface
Client
interface
IP network
Client
interface
Server
interface
UA server
FIGURE 57.4
Peer-to-peer interactions between UA servers.
© 2011 by Taylor and Francis Group, LLC