Request/response Service procedures describe the processing of requests received by the Server, and the subsequent return of responses. The procedures begin with the requesting Client submitting a Service request Message to the Server.

Upon receipt of the request, the Server processes the Message in two steps. In the first step, it attempts to decode and locate the Service to execute. The error handling for this step is specific to the communication technology used and is described in OPC 10000-6.

If it succeeds, then it attempts to access each operation identified in the request and perform the requested operation. For each operation in the request, it generates a separate success/failure code that it includes in a positive response Message along with any data that is to be returned.

To perform these operations, both the Client and the Server may make use of the API of a Communication Stack to construct and interpret Messages and to access the requested operation.

The implementation of each service request or response handling shall check that each service parameter lies within the specified range for that parameter.