OPC FAQ

DCOM provides a versatile and secure platform for OPC communication. It is also freely available with Windows. However, there are instances where DCOM does not or cannot provide an acceptable solution, and Integrators prefer to pay money to install an OPC tunneling product from a vendor. The following lists the scenarios in which DCOM OPC tunneling technology is preferred over DCOM:

• Integrators don’t know how to configure DCOM. (This is the most common reason people use OPC Tunneling.)
• Integrators don’t know how to configure the firewall. (This is the second most common reason people use OPC Tunneling.)
• There is a requirement to use only a single port for OPC communication. (DCOM typically uses 4 ports.)
• Communication timeouts must be closely controlled. (Note that DCOM recovers very quickly in most cases, but there are reported circumstances where timeouts take longer.)
• Communication has strict bandwidth restrictions that can only be overcome with OPC Tunneling. (This is sometimes the case when bandwidth is restricted such as in off-shore communication, or wireless telemetry communication.)

• Does the Tunneling product provide Encryption services, or does it send data "in the clear?" If Encryption is available, does it provide an acceptable level of encryption? DCOM provides encryption services that enable it to keep communication secret on a network.
• Does the Tunneling product provide Authentication services, or does it allow anyone to connect? Authentication prevents unauthorized users from connecting to a data source.
• Does the Tunneling product provide centralized administration of security aspects, or must security be handled at each PC? When using a Domain, DCOM enables users to have a single point for all aspects of security.

Whether you decide to use OPC Tunneling or DCOM, the OPC Training Institute hopes that you endeavor to learn DCOM before you make your decision. Most people find DCOM to be surprisingly logical once they understand how it works.