Generic Object Oriented Substation Event (GOOSE)

GOOSE operates on a publisher-subscriber model, fundamentally different from client-server protocols like MMS. A single IED publishes a GOOSE message onto the network, and multiple subscribing IEDs simultaneously receive and process it.

• Multicast transmission: Uses Layer 2 Ethernet multicast (01:0C:CD:01:00:00 to 01:0C:CD:01:01:FF range) to ensure one-to-many communication
• No acknowledgment required: Subscribers do not send confirmation back to the publisher, reducing network overhead
• VLAN tagging: IEEE 802.1Q priority tagging (typically priority 4-7) ensures GOOSE frames bypass standard queuing in switches
• Logical separation: Virtual LANs isolate protection traffic from other substation data streams, preventing congestion from affecting critical signals

GOOSE achieves reliability not through TCP acknowledgments but through rapid, repetitive retransmission. After an initial state change, the message is sent at exponentially increasing intervals until a steady-state background cycle is reached.

• Event-driven burst: First transmission occurs within 4 ms of a detected state change
• Exponential backoff: Retransmission intervals follow a pattern like 2 ms, 4 ms, 8 ms, 16 ms, doubling until reaching a maximum (typically 1-2 seconds)
• Steady-state heartbeat: Continuous background retransmission at a configurable interval (e.g., 1 second) allows subscribers to detect communication loss
• Time-allowed-to-live (TAL): Each message carries a TAL parameter; if a subscriber does not receive a new message within this window, it assumes communication failure and sets data to a predefined default quality state

GOOSE is designed for protection-class applications requiring total transmission times under 3 ms for the most critical use cases, as defined by IEC 61850-5 performance classes.

• Type 1A performance class: Total transmission time ≤ 3 ms for tripping and interlocking (P1 class)
• Type 1B performance class: Total transmission time ≤ 20 ms for less critical interlocking (P2/P3 class)
• Direct Layer 2 mapping: GOOSE bypasses TCP/IP and UDP stacks, mapping directly to the Ethernet data link layer for minimal protocol overhead
• ASN.1 BER encoding: Abstract Syntax Notation One with Basic Encoding Rules provides compact, deterministic message encoding that can be parsed with minimal CPU cycles
• Hardware acceleration: Modern IEDs use FPGA-based network processors to achieve sub-millisecond encoding and decoding of GOOSE frames

The data published in a GOOSE message is defined by a dataset—a ordered collection of data attributes from one or more Logical Nodes. The transmission behavior is configured through a GOOSE Control Block (GoCB).

• Dataset definition: Specifies exactly which data attributes are included (e.g., XCBR1.Pos.stVal, PTRC1.Tr.general), their order, and encoding
• GoCB parameters: Configure the multicast MAC address, APPID (Application Identifier), VLAN priority, and retransmission intervals
• Configuration revision (ConfRev): A counter incremented whenever the dataset or GoCB configuration changes, allowing subscribers to detect mismatches
• State number (StNum): Incremented on each actual state change event, allowing subscribers to identify new data versus retransmissions
• Sequence number (SqNum): Incremented on every transmission, resetting to zero on each StNum increment, providing a sequential counter for message loss detection

Every data attribute published via GOOSE carries associated quality flags that allow subscribers to evaluate the trustworthiness of the received information before acting on it.

• Validity: Indicates if the value is good, invalid, questionable, or overflow
• Source: Distinguishes between process (real measurement) and substituted (manually entered value for testing)
• Test bit: When set to TRUE, indicates the data is generated in test mode; subscribers must be configured to either process or ignore test data
• OperatorBlocked: Indicates that an operator has manually blocked further commands to this object
• DetailQual: Provides granular failure codes including old-data, failure, oscillatory, and inconsistent, enabling precise diagnostic responses by subscribing protection functions

GOOSE fundamentally replaces hardwired binary signal circuits between substation devices. A single fiber-optic Ethernet connection carries hundreds of virtual signals that previously required individual copper conductors.

• Cost reduction: Eliminates thousands of meters of copper control cable, associated trenching, and termination labor
• Signal multiplication: A single GOOSE message can carry dozens of boolean statuses (e.g., breaker position, protection pickup, trip commands) simultaneously
• Flexibility: Adding a new interlocking signal between two IEDs requires only a configuration change in the SCL file, not physical rewiring
• Continuous monitoring: Unlike hardwired circuits that fail silently (open circuit), the GOOSE heartbeat provides constant supervision of the communication path, immediately alarming on failure
• Testing efficiency: Virtual signals can be simulated via software without disconnecting physical wiring, dramatically reducing commissioning and maintenance testing time