What is the difference between Unbalance and Balance Transmission in IEC 60870-5-101 Protocol?

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Issue:
What is the difference between Unbalance and Balance Transmission in IEC 60870-5-101 Protocol?

Product Line:
Modicon M580 Controller, M340, BMXNOR0200H,BMENOR2200H.

Environment:
All

Resolution:

IEC 101 allows two alternative transmission procedures:

Unbalanced transmission – the controlling station controls the data traffic by polling the controlled outstations sequentially. It initiates all the message transfers while the controlled outstations only respond to these messages. The following services are supported:
- SEND/NO REPLY – for global messages and for cyclic set-point commands
- SEND/CONFIRM – for control commands and set-point commands
- REQUEST/RESPOND – for polling data from the controlled outstations

Balanced transmission – in this mode, each station can initiate message transfer. The stations can act simultaneously as controlling stations and controlled stations (they are called combined stations). The balanced transmission is restricted to point-to-point and multiple point-to-point configurations. Supported services are:
- SEND/CONFIRM
- SEND/NO REPLY – this can be initiated only by a controlling station with a broadcast address in multiple point-to-point configurations

Note:
By defaults, the Unbalance transmission is selected. Check the snapshot below for reference.
Controlling Station: Refers to the Scada/Master Station or RTU configured as a (Master/Client)
Controller Station: Refers to the RTU configured as a (Slave/Server).