OPC Foundation Adds Express Interface (OPC Xi) to
Technology Portfolio
The OPC Foundation Board of Directors voted to add Express Interface (OPC Xi) to the OPC Foundation
technology portfolio, complementing OPC UA and COM-based OPC
Classic technologies.
OPC
Xi is an interface specification based on
Microsoft .NET Windows Communication Foundation (WCF)
technology. It is specifically designed for secure reliable
access to real-time, historical and alarm and event based
information.
The OPC Xi specification and
server reference base code are
available under the Express Interface
public license.
Visit News and
www.opcfoundation.org/xi
for more information. |
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Xi Feature Overview
Express Interface (OPC Xi) is a new Microsoft .NET interface designed
for secure and reliable access to automation systems. Xi provides an
integrated set of methods for accessing both run-time and historical
data, events, and alarms. It has been designed for fast and secure
communication through firewalls and for simple implementation and
use.
OPC
Xi defines a Service Oriented Architecture (SOA) that is based on
MMS (Manufacturing Messaging Service) and WCF (Windows Communication
Foundation).
The main design goals were:
- Security – for secure communications including access through
firewalls
- Simplicity - to make servers and clients easy to implement,
configure, and deploy
- Robustness – for reliable communications with error recovery
- Plug-and-Play – for automatic discovery of servers and their
communications capabilities
- Backward compatibility - for accessing OPC DA, AE and HDA servers
using a single .NET interface
- Protocol transparency – for efficient client/server communications
when both the client and server are on the same platform or within
the same local area network, and when the client is located on
external networks, including the Internet (see Figure below).
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OPC Xi Communication
OPC
Xi is designed to be a native interface for communication between
Microsoft based clients and servers. It is based on .NET3.5 WCF and
allows the use of any WCF binding such as:
- Named Pipes for fast local communication
- TCP with or without security
- HTTP in different forms (including industry standard Web Services)
Supplementing traditional security mechanisms, including those
available through .NET, OPC Xi uses an innovative, patent pending
security mechanism that gives plant administrators the ability to
restrict access to servers based on, but not limited to, the
location of the client.
Additionally, separate server communication endpoints are used for
different types of server access:
- Management services are handled with high security because the
communicated data could easily be interpreted. Top performance isn’t
required for these services and the security overhead is acceptable.
- Read/Write/Subscribe services use endpoints designed for high
performance. Encryption may optionally be used on these endpoints;
however values transmitted by these endpoints are not accompanied by
identifiers to make interpretation more difficult.
OPC Xi Use
OPC
Xi has been designed to provide new .NET client applications a
simple .NET interface for easy access to OPC DA (Data Access), OPC
HDA (Historical Data), OPC A&E (Alarms & Events), and to proprietary
Alarm and Event historians.
OPC
Xi was designed to be backwards compatible with OPC servers and may
be used in the same system as OPC clients and servers. Xi and
classic OPC
DCOM communications are compatible on the same network.
OPC
Xi has been designed for plug-and-play. Plug-and-play allows clients
to automatically discover and connect to Xi servers. Clients no
longer need to be configured with information required to address
and connect to servers. Further, servers can be kept up-to-date with
the latest communications available knowing that clients will be
able to automatically adapt and connect to the server.
Xi has been designed as a secure and robust .NET interface that
supports a native interface for .NET clients and web service
interface for non-Microsoft based clients. In addition, because it
has been designed as a native interface, additional protocols, such
as OPC UA can be easily layered on top to extend the types of
clients that can connect.
Summary
OPC
Xi is a secure, robust .NET interface that has been designed for
ease of implementation and use. It has also been designed to ensure
that future communications can be easily integrated and used without
having to make changes to clients or servers.
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