OPC is built on Microsoft technology called COM, which stands for Component Object Model. It is
a framework that defines how applications communicate with each other and share data. When
OPC applications are installed on the same computer they use COM to exchange data. However,
when installed on 2 separate PCs, then the COM messages are wrapped in a Microsoft security
layer called DCOM (Distributed COM).
Most OPC configurations involve the use of DCOM. There are circumstances where DCOM can
experience timeouts that can lead to unreliable data delivery and even data loss. Such
circumstances can include:
- Hardware problems, such as a faulty network card, router or switch
- System issues, such as an overloaded network
- Inherently unstable network architectures that use satellite links, WAN, radio
communication, etc.
It should be noted that most networks, even reliable ones, suffer from these problems from time
to time.
OPC Tunnelling provides an alternative approach that eliminates the DCOM risk altogether. This
technology uses standards-based TCP/IP communications instead of DCOM for carrying OPC
messages. It provides users with configurable timeouts that are appropriate for the specific
installation.