Subscriber basics

The system configuration process includes a critical step known as subscribing, which facilitates the connection of data from a sending IED to inputs of a receiving IED. This process is essential for the proper functioning of the tool. The sending data can be stored in a control block such as ReportControl, GSEControl, or SampledValueControl, or it can be referenced within the data model of the sending IED for polling purposes. The receiving IED's input is represented by the SCL element ExtRef. Subscribing essentially involves updating or creating an ExtRef element in the receiving IED. The connection between the sending data and receiving input is established through several attributes within the ExtRef element, including:

• iedName: Name of the sending IED.
• ldName: Name of the logical device where the sending data resides.
• prefix: Prefix of the logical node where the sending data is located.
• lnClass: Class of the logical node where the sending data resides.
• lnInst: Instance of the logical node where the sending data resides.
• doName: Path through the structure of data objects names where the data resides (e.g. Pos or A.phsA for a structured data object).
• daName: Path through the structure of the data attribute names where the data resides (e.g. stVal for simple types or cVal.mag.f for complex types).

For connections involving sending data with Report, GOOSE or SMV (Sampled Values), and for projects Ed2 and higher, additional attributes may be necessary:

• srcLDInst: Instance of the logical device where the sending control block resides.
• srcPrefix: Prefix of the logical node where the sending control block resides.
• srcLNClass: Class of the logical node where the sending control block resides.
• srcLNInst: Instance of the logical node where the sending control block resides.
• srcCBName: Name of the sending control block carrying the information.
• serviceType: Type of service sending the data GOOSE, Report or SMV.

NOTE: Reports are rarely connected to receiving IEDs using the subscription process. OpenSCD currently supports subscribing to GOOSE and SMV only.

OpenSCD offers three basic subscription plugins for GOOSE and three for SMV, each differing in how ExtRefs are created or updated.

Connecting Complete GOOSE/SMV

NOTE: See subscribe to GOOSE or subscribe to sampled value stream to see how to do this with OpenSCD

In this scenario, OpenSCD generates one ExtRef in the receiving IED for every data point transmitted via GOOSE/SMV. This allocation occurs within the first logical device of the logical node LN0. Let's delve into an example concerning GOOSE below. Here, two ExtRef instances are created, each corresponding to one of the FCDA elements within the DataSet linked to either the GOOSE control block or GSEControl. These FCDA elements share common attributes that define the reference to the data point in the data model: ldInst, prefix, lnClass, lnInst, doName, and daName. Furthermore, the name of the sending IED is included in the ExtRef. The remaining attributes serve to identify the control block to which the FCDA elements are connected or carried by.

NOTE: The decision to connect both FCDA elements is optional and not mandatory. Also, the allocation of ExtRef to the first logical node LN0 in the receiving IED distinguishes this connection method from others discussed below.

<IED name="sendingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="sendingLD">
                <LN0 prefix="" lnClass="LLN0" lnInst="">
                    <DataSet name="someDS">
                        <FCDA ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" fc="ST"/>
                        <FCDA ldInst="Meas" prefix="Meas" lnClass="MMXU" lnInst="1" doName="A.phsA" daName="cVal.mag.f" fc="ST"/>
                    </DataSet>
                    <GSEControl name="gooseCB" datSet="someDS">
                        ...
                    <GSEControl>
                </LN0>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>
...
<IED name="receivingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="receivingLD">
                <LN0 prefix="" lnClass="LLN0" lnInst="">
                    ...
                    <Inputs name="someDS">
                        <ExtRef iedName="sendingIED" ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" serviceType="GOOSE" srcLDInst="sendingLD" srcPrefix="" srcLNClass="LLN0" srcLNInst="" srcCBName="gooseCB"/>
                        <ExtRef iedName="sendingIED" ldInst="Meas" prefix="Meas" lnClass="MMXU" lnInst="1" doName="A.phsA" daName="cVal.mag.f" serviceType="GOOSE" srcLDInst="sendingLD" srcPrefix="" srcLNClass="LLN0" srcLNInst="" srcCBName="gooseCB" />
                    </Inputs>
                </LN0>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>

Connecting Single Data from GOOSE/SMV

NOTE: This feature is not yet implemented in OpenSCD.

In this scenario, OpenSCD creates one ExtRef in the receiving IED for the selected data point within a GOOSE/SMV control block. The user has the flexibility to choose the location of the ExtRef, allowing placement within any logical node in the server. Further details are illustrated in the example below, focusing on GOOSE.

There is only one ExtRef representing the connection to the selected FCDA element within the DataSet associated with the GOOSE control block or GSEControl. FCDA elements share common attributes defining the reference to the data point in the data model: ldInst, prefix, lnClass, lnInst, doName, and daName. User-directed allocation to the logical node enhances project organization.

NOTE: This method's uniqueness lies in the connection of a single FCDA element and the freedom granted to the user for allocating the ExtRef within the receiving IED.

<IED name="sendingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="sendingLD">
                <LN0 prefix="" lnClass="LLN0" lnInst="">
                    <DataSet name="someDS">
                        <FCDA ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" fc="ST"/>
                        <FCDA ldInst="Meas" prefix="Meas" lnClass="MMXU" lnInst="1" doName="A.phsA" daName="cVal.mag.f" fc="ST"/>
                    </DataSet>
                    <GSEControl name="gooseCB" datSet="someDS">
                        ...
                    <GSEControl>
                </LN0>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>
...
<IED name="receivingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="receivingLD">
                ...
                <LN prefix="someLN" lnClass="CILO" lnInst="1">
                    ...
                    <Inputs name="someDS">
                        <ExtRef iedName="sendingIED" ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" serviceType="GOOSE" srcLDInst="sendingLD" srcPrefix="" srcLNClass="LLN0" srcLNInst="" srcCBName="gooseCB"/>
                    </Inputs>
                </LN>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>

Connecting on later binding type inputs

NOTE: This feature is not yet implemented in OpenSCD!

Later binding is a concept that enables the predefinition of ExtRef elements in the IED configuration Tool (ICT) before system configuration. You can identify a predefined ExtRef by the attribute intAddr. This attribute is a string set by the ICT to identify which internal function utilizes a specific input. Consequently, OpenSCD does not create new ExtRef elements but updates existing ones.

Below, we provide an example related to GOOSE. There is only one ExtRef representing the connection to the selected FCDA element within the DataSet associated with the GOOSE control block or GSEControl. These FCDA elements share common attributes that define the reference to the data point in the data model: ldInst, prefix, lnClass, lnInst, doName, daName. The intAddr attribute is already predefined and must not be altered, nor can OpenSCD delete such an ExtRef.

NOTE: The unique aspect of this plugin lies in its ability to connect a single FCDA element to an existing ExtRef with a set instAddr, distinguishing it from the other methods.

<IED name="sendingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="sendingLD">
                <LN0 prefix="" lnClass="LLN0" lnInst="">
                    <DataSet name="someDS">
                        <FCDA ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" fc="ST"/>
                        <FCDA ldInst="Meas" prefix="Meas" lnClass="MMXU" lnInst="1" doName="A.phsA" daName="cVal.mag.f" fc="ST"/>
                    </DataSet>
                    <GSEControl name="gooseCB" datSet="someDS">
                        ...
                    <GSEControl>
                </LN0>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>
...
<IED name="receivingIED" ...>
    <AccessPoint ...>
        <Server>
            <LDevice inst="receivingLD">
                ...
                <LN prefix="someLN" lnClass="CILO" lnInst="1">
                    ...
                    <Inputs name="someDS">
                        <ExtRef intAddr="someIntAddr" iedName="sendingIED" ldInst="CircuitBreaker" prefix="CB" lnClass="XCBR" lnInst="1" doName="Pos" daName="stVal" serviceType="GOOSE" srcLDInst="sendingLD" srcPrefix="" srcLNClass="LLN0" srcLNInst="" srcCBName="gooseCB"/>
                    </Inputs>
                </LN>
                ...
            </LDevice>
        </Server>
    </AccessPoint>
</IED>