What is OPC?
OPC is a specification for the transport and use of industrial data. It is published and maintained by the OPC Foundation, an organization comprised of hundreds of member companies that strives to ensure interoperability on the plant floor and beyond.
The OPC-UA specification is the latest specification in a line spanning back to the mid '90s. The original OPC specifications used Microsoft DCOM technology to provide a uniform way for industrial applications to share data. There were several separate specifications that provided functions such as Data Access (OPC-DA), Alarms and Events (A&E), Historical data (HDA) and more.
DCOM always proved difficult to work with, and by 2004 it was clear that a more modern solution was needed. Therefore, a new specification was developed that used common networking principals instead of DCOM, was platform independent, and combined the various separate specifications into one: OPC-UA.
Clients and Servers
When discussing OPC (as the specifications are often called collectively), it is common to hear about "OPC servers" and "OPC clients". An OPC Server is a piece of software that implements the OPC interface and provides data. An OPC Client is an application which connects to an OPC Server and uses the specification to retrieve and work with data.
The Ignition platform inherently offers OPC-UA client functionality. That is, even with no modules installed, the gateway can connect to any compliant OPC-UA server and work with data. With the addition of the OPC-UA Module, Ignition becomes an OPC server as well, hosting device drivers that read and publish data.
The OPC-COM module is available to provide client access to older, DCOM based, OPC-DA servers.
The OPC-UA specification offers a wide range of flexibility in choosing technologies, from the transport mechanism, to the way data is encoded, to the encryption used to secure the data.
Ignition supports the UA/TCP transport with the UA/Binary encoding scheme for maximum performance. Additionally, Ignition supports all of the common encryption schemes.
This means that Ignition connects to OPC-UA servers (and allows connections from clients) over TCP/IP, using encryption, and sends data by first encoding it into an efficient format defined by the OPC-UA specification. This is in contrast to other schemes outlined in the specification, which can use web services and XML encoding, and are not as efficient.