GOOSE vs MMS in IEC 61850: differences and uses

Two mappings of the same standard

IEC 61850 defines an abstract data model and a set of services; IEC 61850-8-1 says how those services travel over a real network. It does so with two different mappings that coexist on the station bus:

• MMS (Manufacturing Message Specification, ISO 9506), for client-server services.
• GOOSE (Generic Object Oriented Substation Event), for fast messages between IEDs.

A third mapping, the sampled values of IEC 61850-9-2, carries digitized currents and voltages on the process bus. Here the first two are compared; the comparison of IEC 61850 with telecontrol protocols is in IEC 61850, IEC 104, DNP3 and Modbus. Each one has its own detailed guide: IEC 61850 MMS and IEC 61850 GOOSE.

The underlying difference: who talks to whom

MMS is client-server. The HMI, the gateway or an engineering tool (clients) open a connection with each IED (server) and keep it open. Through it they read data, receive reports when something changes, send commands and download files. It is a conversation between two devices, with acknowledgments.

GOOSE is publisher-subscriber. An IED publishes a dataset in a multicast frame; every IED configured as a subscriber receives it at the same time. There is no connection and no acknowledgment: the publisher repeats the frame continuously, and when a data item changes it sends it immediately with a new state number and repeats it at short intervals that grow until it returns to the steady-state rate. The subscriber knows the publisher is still alive because every frame carries a time allowed to live.

Side-by-side comparison

The transfer time classes come from IEC 61850-5: from TT0 (over 1 s, files) to TT6 (3 ms, trips and blocking). What each link of the chain adds is detailed in IEC 61850 transfer time.

When each one is used

Typical GOOSE uses:

• breaker failure (50BF) trip to the adjacent breakers;
• blocking signals in logic selectivity schemes;
• disconnector positions for station interlocking;
• starting reclosing or recorders.

Typical MMS uses:

• the station HMI and the gateway receiving status, measurements, alarms and events;
• operator commands with select-before-operate (SBO);
• downloading fault records in COMTRADE;
• reading the configuration and diagnostics from a tool.

How they coexist on the network

GOOSE and MMS share the same cable and the same switch, but they do not behave the same. GOOSE floods the ports of the VLAN where it is published, so the network is designed by separating traffic with VLANs and priority and filtering multicast where it is not needed. MMS is ordinary unicast traffic and its load depends on how many clients reserve reports in each IED.

A practical consequence: a poorly segmented network hits GOOSE first, because it has no retransmission or acknowledgment. A slow MMS is a nuisance; a late GOOSE is a late trip.

Configuration: two different control blocks

Both messages come from the same data model and the same datasets, but each one has its own control block in the IED, and both are defined in the SCD file with the system configurator:

• For MMS, the report control block says which dataset to watch, which changes trigger the report and whether events are kept during a loss of communication (buffered report) or not. Each client reserves its own block, so the number of available blocks limits how many clients receive reports from the same IED.
• For GOOSE, the control block defines the message identifier, the dataset, the configuration revision, the multicast address, the VLAN, the priority and the APPID. The subscriber, in turn, declares which message it subscribes to and which input of its logic each data item connects to.

That is why a change to a dataset can affect both services at once: the report received by the HMI changes and so does the GOOSE revision expected by other IEDs. When publisher and subscriber come from different brands, additional points appear, described in GOOSE between relays of different brands.

What fails in each one

Diagnosing a failing GOOSE is covered in GOOSE not arriving or arriving late. A traffic capture shows what is really happening; the analyzers, MMS clients and simulators used are in IEC 61850 test tools.

How they are tested

During commissioning, GOOSE is tested end to end: the publisher changes the data and the subscriber is verified to act, on the real network. Loss of the message is tested too, to verify that the subscriber detects it and that the logic takes the safe value. MMS is tested signal by signal up to the HMI and the gateway, including rejected commands. The addresses and APPID of each GOOSE stream can be planned with our free GOOSE and SV addresses tool.

We help you with your IEC 61850 configuration

At Tiza Group we configure GOOSE and MMS in relays and bay controllers of the main brands, for substations and industry. If the problem is in one or a few relays, remote relay configuration solves it remotely. For engineering of the complete system and on-site testing, see IEC 61850 configuration, in Colombia, or elsewhere on request.

Related guides

• IEC 61850 GOOSE: how it works, stNum, sqNum and testing
• IEC 61850 MMS: reports, SBO commands and files
• IEC 61850 Sampled Values
• IEC 61850 transfer time
• GOOSE between substations (R-GOOSE)
• Station bus
• Substation automation system (SAS): functions and levels
• IEC 61850 system configurator: what it is and which exist
• IED not communicating over IEC 61850 MMS: diagnosis
• IEC 61850 traffic in Wireshark: what a capture reveals
• GOOSE interlocking with CILO and CSWI (IEC 61850)

References

• IEC 61850-5, communication requirements, transfer time classes.
• IEC 61850-7-2, abstract communication service interface (ACSI).
• IEC 61850-8-1, mapping to MMS (ISO 9506-1 and ISO 9506-2) and to ISO/IEC 8802-3.
• IEC TR 61850-90-5, use of IEC 61850 to transmit synchrophasor information (includes routable GOOSE).
• ISO 9506, Manufacturing Message Specification.
• RFC 1006, ISO transport over TCP.

Frequently asked questions