IEC 60870-5-101 Protocol
IEC 60870-5-101 is an international standard for power system monitoring, control and associated communications for telecontrol, teleprotection, and associated telecommunications for electric power systems.
The protocol is used between an RTU (Remote Terminal Unit) in a substation and a control center.
Protocol Layers
| ISO/OSI Layer | IEC 101 Layer |
|---|---|
| 7. Application layer | Application layer |
| 6. Presentation layer | |
| 5. Session layer | |
| 4. Transport layer | Link layer |
| 3. Network layer | |
| 2. Data link layer | |
| 1. Physical layer | Physical layer |
Physical Layer
Usually:
- 1 start bit
- 8 data bits
- 1 parity bit (even)
- 1 stop bit
Link Layer
Usually:
- 1 start bit
- 8 data bits
- 1 parity bit (even)
- 1 stop bit
Frame Format
| Field | Size (bytes) | Description |
|---|---|---|
| Start | 1 | Start character (0x68) |
| Length | 1 | Length of user data |
| Length (repeat) | 1 | Repeated length field |
| Start (repeat) | 1 | Repeated start character (0x68) |
| Control | 1 | Control field |
| Address | 1-2 | Link address |
| ASDU | Variable | Application Service Data Unit |
| Checksum | 1 | Frame check sequence |
| End | 1 | End character (0x16) |
Control Field
| Bit | Function | Description |
|---|---|---|
| 0 | DIR | Direction (0=from primary, 1=from secondary) |
| 1 | PRM | Primary message (0=secondary, 1=primary) |
| 2 | FCB | Frame count bit |
| 3 | FCV | Frame count valid |
| 4-7 | Function Code | Function code (see function codes table) |
Function Codes
| Code | Name | Description |
|---|---|---|
| 0 | RESET_REMOTE_LINK | Reset of remote link |
| 1 | RESET_USER_PROCESS | Reset of user process |
| 2 | TEST_FUNCTION_LINK | Test function for link |
| 3 | USER_DATA | User data |
| 4 | USER_DATA_NO_REPLY | User data, no reply expected |
| 9 | REQUEST_LINK_STATUS | Request link status |
| 10 | REQUEST_CLASS_1_DATA | Request class 1 data |
| 11 | REQUEST_CLASS_2_DATA | Request class 2 data |
Application Layer
To be documented...
SerialMon Support
Enhanced in SerialMon v3.0 with full Master and Slave support
Operating Modes
| Mode | Description |
|---|---|
| Monitor | Passive sniffing of IEC 101 communication between RTU and control center |
| Master | Simulate a control center polling RTUs/IEDs |
| Slave/IED | Simulate an RTU or IED responding to master polls |
Supported Features
- Real-time frame decoding and display
- Protocol validation and error detection with warnings
- Traffic analysis and statistics
- Historical data logging and replay
- Signal acceptance marking for FAT/SAT testing
- Quick command sending from tracking window
- Balanced and unbalanced mode support
