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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.

{note}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{note}

{warning}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{warning}

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