The IEC 60870-5-104 standard requires an interoperability list to be filled in with the parameters each system uses. Some are mutually exclusive and must be equal across the whole system; others are sets from which each device picks a part. Comparing the server list with the client list avoids integration failures.
Short answer
The interoperability list of IEC 60870-5-104 is the form that the standard itself asks each system to fill in. It summarizes which options are used in the network, the link, the application and the functions. To integrate, the server list (the field device) and the client list (the control center) are compared, starting with the parameters that allow no differences. How to test a link with a server or client simulator is described in IEC 104: Testing a Link with Client and Server Simulators.
What it is and how it is ticked
The standard presents sets of parameters and alternatives, from which a subset must be chosen for each telecontrol system. There are two kinds:
- Mutually exclusive alternatives. Only one value per system is allowed. The standard’s example is structured or unstructured information object address.
- Sets from which a part is chosen. For example, the list of type identifications in monitor and control direction.
The list states expressly that, if the system is made of devices from several manufacturers, all of them must agree on the chosen parameters.
The marks in each box are:
| Mark | Meaning |
|---|---|
| Empty | The function or ASDU is not used |
| X | Used in the standard direction |
| R | Used in the reverse direction |
| B | Used in both directions |
| Black box | The standard does not allow it to be chosen |
The sections of the list
System or device
It declares whether the document describes a system, a controlling station (master, client) or a controlled station (slave, server). It is the first piece of data: the list of a server cannot be compared with that of another server.
Network configuration and physical layer
It states the network configurations used: point-to-point, multiple point-to-point, multipoint-party line or multipoint-star. In 104 transmission is over a network. The line speeds in the tables are inherited from 101. The useful item is the network interface of the device.
Link layer
104 inherits the frame format and link address from 101. For a network device, this section matters little.
Application layer: the parameters that do not forgive
These are the most critical, because they allow only one value per system:
| Parameter | Options | If it does not match |
|---|---|---|
| Common address of ASDU | One or two octets | The station is not recognized |
| Information object address | One, two or three octets; structured or not | Signals shift or disappear |
| Cause of transmission | One or two octets (with originator address) | Causes are misread |
| Maximum length of the APDU | 253 octets, fixed | The other end rejects or cuts long messages |
The size of the object address deserves special attention: with one octet only a few hundred signals fit, and with three, millions of addresses fit. To understand how these addresses are built, see the mapping of IEC 61850 to IEC 104.
ASDU selection
Four blocks, each with its types:
- Process information in monitor direction: single and double points, step position, 32-bit string, normalized, scaled and short floating point measured values, integrated totals and protection events.
- Process information in control direction: single, double and regulating step commands, setpoints and bitstring.
- System information: end of initialization, interrogation, counter interrogation, read, clock synchronization, test and reset.
- Parameters and files: parameter loading and activation, and file transfer.
Two rules specific to 104 avoid frequent misunderstandings:
- For information with a time tag only the set with the seven-octet time tag is allowed (types 30 to 40). The old types with a short time tag are not used.
- In control direction either the set without time tag (types 45 to 51) or the set with time tag (types 58 to 64) is used, but not both.
Type and cause of transmission
It is a matrix: for each type, the causes of transmission it is used with are marked. It shows, for example, that a measured value can travel cyclically, in background, spontaneously or by interrogation. A command, on the other hand, only allows activation, confirmation, termination and their variants.
Basic application functions
Initialization, data acquisition, interrogation, clock synchronization, commands, integrated totals, parameters, test and files. Each is marked with the same letter X, R or B.
Timers, windows and port
The list ends with the values of t0 to t3, of k and w, the port and the redundant connections. The defaults are t0 30 s, t1 15 s, t2 10 s, t3 20 s, k 12 and w 8, and all are configurable.
How to compare server and client
- Confirm the list type. One for the server and one for the client
- Match the exclusive alternatives. Common address, object address and cause of transmission
- Cross-check the data types. Those the server sends against those the client accepts
- Cross-check the cause matrix. Each type must travel with a known cause
- Cross-check functions and files. Interrogation, clock, commands, totals and files
- Cross-check timers and port. k, w and t0 to t3 must be compatible
Frequent mistakes
- Comparing different versions of the list of the same device.
- Overlooking that a function is marked in the reverse direction.
- Leaving the object address with a different number of octets from the client.
- Assuming a type with a short time tag will be accepted by the center.
How we can help
The list is the technical contract between your substation and the control center. At Tiza Group we cross-check it with that of your utility or control center, define the signal list and test the link end to end. See our SCADA and gateway integration or write to us to quote it.
Related guides
- IEC 60870-5-104: what it is, how it works and how it is tested
- IEC 60870-5-104 basic application functions
- IEC 60870-5-103 interoperability list: how to read it
- Type identifications in IEC 101 and 104: the TI list
- Substation signal list for the SCADA
- IEC 104: Testing a Link with Client and Server Simulators
- IEC 104: Timers t0 to t3 and the k and w Windows
References
- IEC 60870-5-104, Network access for IEC 60870-5-101 using standard transport profiles: interoperability list.
- IEC 60870-5-101, base interoperability list.
Frequently asked questions
Why do two IEC 104 devices not understand each other if both comply with the standard?
Because the standard leaves parameters to choose, such as address sizes or the set of data types. Both devices must choose the same in the mutually exclusive parameters, and match at least on the subset the project needs in the rest.
What do the letters X, R and B mean in the list?
X means the function is used in the standard direction, R that it is used in the reverse direction and B that it is used in both. An empty box means it is not used, and a black box means the standard does not allow it to be chosen.
Which part of the list is checked first?
The mutually exclusive parameters of the application layer: size of the common address, of the information object address and of the cause of transmission. If they do not match, not a single signal is interpreted correctly.