To maximise efficient use of bandwidth and performance, communication should be subscription based, by default.

The OPC UA interface is exception driven and a publishing interval of 2 seconds or less should be used between the SPCS and the DCS. Update rates from subsea to the SPCS is outside the scope of MDIS and can be much longer than 2 seconds. Maximum allowable update rates for individual controllers should be determined and based on system architecture and hardware capabilities.

It is expected that update rates will vary according to general categories of data. Critical data will have update rates that could be under 1 second while housekeeping data might have update rates in the 1-minute time range. These data rates shall be constant for the supported counts of Objects. i.e. if a device supports 3 wells (say 3000 critical values and 10,000 housekeeping values), the 1 second and 1 minute data rates will be support, not just for 1 well, but for the advertised 3 wells.

Conformance units provided general ranges of performance numbers that a product can be tested against. It is understood that performance will vary according to the hardware provided and the other loading on the hardware. The ConformanceUnits do not guarantee any performance, but they will point out performance issues earlier. i.e. a device that can support 5000 objects as part of a test is may not support 5000 when it is fully loaded with non-MDIS functionality, but it is likely that it would still be able to support 3000 objects. These conformance units are included to provide some general bench marks for performance.

Systems can be architected to include multiple server/devices to offset load. These number are targeted to allow better choice of configuration. For example, if 10,000 objects are desired and the software can only pass 5000 objects, the system should be architected to have at least 2 devices, but to allow for other factor, it might be a good idea to target 3 devices.

Requirements should be developed on a project basis to provide sufficient bandwidth between the SPCS and DCS to ensure all commands, issued both during normal operation and shutdowns, are passed across the interface effectively.

Evaluation of communication performance and testing requirements should take into account any latency or communication limitations due to physical system architecture constraints between SPCS and the DCS. (i.e. radio communication).