Transfer time t = ta + tb + tc for a 184-byte trip GOOSE through three store-and-forward switches, with worst-case queuing behind full-size frames. Every term worked by hand and compared with SCL NetStudio.
| Message | P132_Q01 trip GOOSE, 184-byte frame, priority 6 |
| Requirement | Type 1A trip, performance class P2/P3: TT6, t ≤ 3 ms |
| Path | 3 store-and-forward switches: 2 device links at 100 Mb/s, 2 backbone links at 1 Gb/s, 5 µs switch latency each, 300 m of cable |
| Devices | Sender processing ta = 1 ms, receiver processing tc = 1 ms |
| Queuing | A 1 522-byte frame already being sent at each egress port, plus 2 frames of the same priority ahead |
At each egress port a maximum-size frame may have just started; priority cannot interrupt it. The two backbone egress ports run at 1 Gb/s, the last one to the receiver at 100 Mb/s.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Network part tb | Small share of 3 ms | 0.233 ms | ✓ PASS |
| Total transfer time | ≤ 3 ms (TT6) | 2.233 ms | ✓ PASS |
Key insight: With 100 Mb/s device ports the worst case is set by queuing behind one full-size frame at the last egress port (123 µs). Gigabit links and strict priority keep the network part well below 1 ms even through many switches.
Every input in this example is editable in the live calculator — no signup needed.
Open SCL NetStudio (IEC 61850 network design) calculator →The largest tagged Ethernet frame (1 518 bytes plus the 4-byte VLAN tag). Strict priority cannot pre-empt a frame that has started; it only chooses the next frame.
IEC 61850-10 describes performance tests; in practice a test set publishes a GOOSE and measures the round trip to the subscriber's reply, which includes ta and tc of both devices.