Comparison of Methods to Transfer Point Data Between ClearSCADA Systems

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When required to transfer data values between two ClearSCADA systems there are a number of options available, each with their own advantages and disadvantages. The table below acts as a guide to assist the design process when deciding the best option to choose.

	DNP3	EcoStruxture Web Services (EWS)	OPC-DA	OPC-XML-DA
Environment Description	DNP3 slave running at one end, DNP3 master at the other; both components of the DNP3 driver	EWS server enabled at one end, Advanced EWS client driver at the other	OPC-DA client driver at one end, DBServer is inherently an OPC-DA server. Recommended to use the Advanced OPC driver in ClearSCADA if possible	OPC-XML-DA client driver at one end, DBServer is inherently an OPC-XML-DA server
Available Target for Data	Main server only	Any Main or Standby server	Any Main or Standby server	Any Main or Standby server
Data Addressing Method	DNP3 point address as defined in the valuemap at the slave	Database object's fullname and property	Database object's fullname and property	Database object's fullname and property
Data Read Classes	Current value, historical data and trends	Current value, historical data and forecasts	Current value only	Current value only
Data Read Efficiency	Great, class 0, 1, 2, 3 polls and unsolicited	Poor, only synchronous supported	Great, asynchronous and synchronous supported	Poor, only synchronous supported
Bandwidth Requirements	Low, binary protocol	High, XML based data transfer	Medium, binary protocol with transfer overhead	High, XML based data transfer
Low Latency Dependency	Low, able to handle high latency, e.g. satellite, when configured with suitable timeouts	Medium, http based	High	Medium, http based
Controls Supported	Yes	Yes	Yes	Yes
Method Calls	Yes	No	No	No
File Transfer	Yes	No	No	No
ClearSCADA Licence Requirements	DNP3 driver included by default in the core licence	No additional licence required. See footnote 1	OPC licence required	OPC licence required
Protocol Encryption	None, could use external IPSec tunnels	Use of https if configured	AES tunnel when using DBClient to tunnel, when using DCOM dependent on DCOM configuration	Use of https if configured
Database Authentication	Device based, DNP3Secure v2 supported	Connection based, defined at the server for all connecting clients	Defined at the client, using private security only	None (not supported by OPC standard)
Ease of Configuration and Maintenance	Poor, lots of options to tweak, valuemaps to maintain	Great, simple configuration options	Good, simple configuration options, connectivity options when using DCOM can be problematic	Great, simple configuration options
Network Security	Statically configured TCP or UDP connection	Statically configured TCP connection	Uses DCOM for dynamic port assignments, requires DCOM aware firewalls to secure better than any-any between IPs	Statically configured TCP connection
Network Analysis Support (e.g. DPI/NIDS/NIPS)	Limited protocol support on specialist devices	XML based protocol, able to be processed by most IT appliances	Limited processing possible by specialist devices	XML based protocol, able to be processed by most IT appliances

Footnote ¹ - In ClearSCADA 2017 R3, ClearSCADA 2017 R2 and ClearSCADA 2017 from build version 7013 (~15th March 2019) onwards ensures no WebX licence is consumed. Previous versions of ClearSCADA may consume a WebX licence under certain circumstances which may stop users successfully connecting.

The information provided above is for connecting two ClearSCADA 2017 R2 versions together. For earlier versions of ClearSCADA the information above should still be accurate should the required drivers be available. For connecting to non-ClearSCADA systems the information will depend on what protocols and functions are supported by the remote device and as such this table should not be used for that decision making

The use of terms such as 'Low', 'Medium', 'High', 'Poor', 'Good' and 'Great' are subjective and should act as a guide only. Additional research, such as review of the protocol and specific system testing should occur to identify and quantify any metrics for your system design

From a general point of guidance:

• DNP3 is great for situations where connectivity between the systems is unreliable or poor, or where bandwidth cost is a significant consideration

• OPC-DA is great for quick setups where connectivity availability is extremely high or where the current value is all that is required

• EWS is a great general purpose option to transfer data in an easy to manage way and where security requirements may require third-party systems the ability to inspect the data

• OPC-XML-DA has limited use in this scenario

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