IEC 60870-5-103 : Telegram structure

The LIAN 98 manual can and may not contain the complete IEC documentation, caused by legal position. Only all knowledge that is essential necessary for the LIAN 98 software operation is specified in parts in this manual.

Detailed information to the protocol you will find in the IEC-Standard-Documentation
<IEC 60870-5-103 : Telecontrol equipment and systems>
( English version EN 60870-5-103:1998 ).


Telegram format with variable length

The telegram with variable length is used for the data transmission of the user data between the controlling station and the controlled station and in the reversed direction.


Telegram format with fixed length

The telegram with fixed length is normally used for link layer services. In special cases this format with fixed length can also be used as an acknowledgement instead of a single character.


Single character

The single character is normally used in order to confirm data link services and user data.

E5H = ACK : Positive acknowledge
A2H = Not used !


Link control field :

You will find more information to the link control field in the standard documentation.
<IEC 60870-5-2 : Link transmission procedure>
( English version EN 60870-5-2:1993 ).



Unbalanced Transmission : Reserved

Balanced transmission : Physical transmission direction ( direction )
DIR = 1 : Data from controlling ( Master ) to controlled ( Slave ) station.
DIR = 0 : Data from controlled ( Slave ) to controlling ( Master ) station.


Primary message : Primary bit ( primary message )

0 = message from a secondary ( controlled ) station.
1 = message from a primary ( controlling ) station.


Primary message : frame count bit 

Alternating bit for consecutive  SEND/ CONFIRM or REQUEST/ RESPOND messages per station. The primary station alternates the FCB bit for each new SEND/ CONFIRM or REQUEST/ RESPOND transmission service directed to the same secondary station.

If an expected reply is timed out ( missing ), then the same SEND/ CONFIRM and REQUEST/ RESPOND service is repeated with the same frame count bit.
In case of a reset command the FCB bit is always zero, and upon receipt of these commands the secondary station expects always that the following primary message is set with FCV = valid ( FCV = 1 ) in order to have the opposite value of FCB ( i.e. FCB = 1 ).


Primary message : frame count bit valid )

0 = alternating function and FCB bit is invalid
1 = alternating function and FCB bit is valid

SEND/ NO REPLY services, broadcast messages and other transmission services that tolerate the duplication or the deletion of information output do not alternate the FCB bit and indicate this by a cleared FCV bit.


Balanced transmission : Reserved

Balanced transmission : Access demand
Secondary message :  Access demand 

There are two classes of message data provided, namely class 1 and class 2. Secondary stations indicate the primary station with it that data of class 1 are ready for transmission.

0 = no access demand on transmission of data class 1
1 = access demand on transmission of data class 1

The transmission of data class 1 is normally used for for events or for messages with high priority. Class 2 data transmission is normally used for cyclic transmission or for low priority.


Secondary message : data flow control

0 = more messages are accepted
1 =
further messages can cause a data overflow

Secondary ( responding ) stations indicate with this message to the initiating ( primary ) station that an immediate succession of a further message may cause a buffer overflow.


Funktion code ( FCT ) :

The function codes are described in the chapter <IEC 60870-5-103 : Simulation> later in this document.


Link address field :

Transmission procedures of the link layer are using the control field and an optional link address field.

The link address is a number for a communication interface that is used from a controlling station for the connection. It is only used as address in the communication network itself and shall not be part of the total address of a data point.

According to the standard this parameter can consist of  0, 1 or 2 octets. 0 is only valid for balanced transmission.


Type-identification ( TypeID ) :

The value ZERO is not used. The range of numbers 1 up to 127 is used for standard definitions from IEC 60870-5-101 standard. The range 128 up to 135 is reserved for routing of messages. The numbers 136 up to 255 are used for special use.

The range of numbers 128 to 255 is private and not defined in the standard, but it is recommended that the data unit identifier fields of private ASDUs have the same format as standard ASDUs.

The following table shows the definition of Type-identification numbers for process and system information in monitor and control direction.


Information in monitoring direction :


1 Time-tagged message  
2 Time-tagged message with relative time  
3 Measurands I  
4 Time-tagged measurands with relative time  
5 Identification  
6 Clock synchronization  
8 End of general interrogation  
9 Measurands II  
10 Generic data  
11 Generic identification  
23 List of recorded disturbances  
26 Ready for transmission of disturbance data  
27 Ready for transmission of a channel  
28 Ready for transmission of tags  
29 Transmission of tags  
30 Transmission of disturbance values  
31 End of transmission  


Information in control direction :


6 Clock synchronization  
7 General interrogation  
10 Generic data  
20 General command  
21 Generic command  
24 Order for disturbance data transmission  
25 Acknowledgement for disturbance data transmission  


LIAN 98 is able to process user-defined messages of non standard types up to 255, provided they have the same general telegram structure as IEC 60870-5-101 standard telegrams.


Variable structure qualifier :

The SQ bit specifies the method of addressing of the following information objects or elements.

SQ = 0

SQ = 1

Each single element or a combination of elements is addressed by the information object address. The ASDU may consist of one or more than one equal information object. The number of objects is binary coded ( number of objects ) and defines the number of the information objects.

number objects/

= 0 : ASDU contains no information object
> 0 : ASDU contains one or more ( number ) information objects or elements


Cause of transmission ( COT ) :

The cause of transmission directs the ASDU to a specific application task ( program ) for processing. ASDUs in control direction are confirmed application services and may be mirrored in monitor direction with different causes of transmission. The value ZERO is not used.


1 spontaneous  
2 cyclic  
3 Reset frame count bit ( FCB )  
4 Reset communication unit ( CU )  
5 Start/ restart  
6 Power ON  
7 Test mode  
8 Time synchronization  
9 General interrogation  
10 End of general interrogation  
11 Local control  
12 Distant control  
20 Command "ACK positive"  
21 Command "ACK negative"  
31 Transmission disturbance data  
40 Generic write command with ACK positive  
41 Generic write command with ACK negative  
42 Generic read command data valid  
43 Generic read command data invalid  
44 Generic write conformation  


Common address of ASDU :

The "Common address" ( station address ) is equal to the link address and is valid for all objects of an ASDU.

The global address is a broadcast address directed to all stations of a specific system ( broadcast address ). ASDUs with a broadcast address in control direction have to be answered in monitoring direction by the address that is the specific defined common address ( station address ).

According to the standard this parameter can consist of 1 octets.


Function type :

The first octet in the "information object identifier" indicates the function type in the protection equipment.


128 distance protection  
160 overcurrent protection  
176 transformer differential protection  
192 line differential protection  
254 generic function type  
255 global function type  


Information number :

The second octet in the "information object identifier" indicates the information number within a function type. The information number is used independently in control direction and monitoring direction.


Monitoring direction :


0... 15 System functions  
16... 31 State  
32... 47 Supervision  
48... 63 Accidental ground  
64... 127 Short circuit  
128... 143 Autoreclosure  
144... 159 Measurands  
240... 255 Generic Functions  


Control direction :


0... 15 System functions  
16... 31 General commands  
240... 255 Generic functions  


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Manual LIAN 98

LIAN 98 Protocol Router, Simulator and Analyzer
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