The DCS is the primary user interface to the overall facility process including the subsea system. Process data management is handled by the DCS as well as all process alarming, alarm management and event / data archiving. Although an MCS may have an alarm or event queue, the primary facility alarm management occurs at the DCS level. Access to the various subsea control functions are managed by the DCS user access level rather than in the subsea system. The DCS also serves as the master for time synchronisation (for addition details see section 10).
Normal control and monitoring of the subsea production system is conducted at the DCS HMI. There may be a separate maintenance or configuration workstation used by the SCV, but it is not within the scope of the MDIS interface.
OPC UA supports Subscription and polling (Read) manners of obtaining data. The Subscription based manner of obtaining data should be used by default. Subscription, which is exception reporting, typically provides improved performance over the polling interface.