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Common Address vs Link Address

Link address belongs to the link layer. Common Address belongs to the ASDU. IOA identifies the information object inside the ASDU.

What it means

Link address belongs to the link layer. Common Address belongs to the ASDU. IOA identifies the information object inside the ASDU.

Link addressUsed by the link layer to reach the outstation on the serial line.

Common AddressUsed by the application layer to identify the ASDU station or group.

IOAIdentifies the information object such as a measured value, indication, or command point.

Profile sizesCOT, CA, and IOA length must match the target device profile.

What to check in ARIEC60870

Use the software to connect the explanation to the frame evidence.

1A device can answer link-layer frames while rejecting application data because CA is wrong.

2Wrong IOA often appears as no useful point change or unknown information object behavior.

3Use mapping profiles to translate raw addresses into project signal names.

TX10 49 01 4A 16request link status

RX10 0B 01 0C 16ACD=1, Class 1 waiting

TX10 7A 01 7B 16request Class 1 data

RX68 ... 16event or command confirmation

Protocol learning is easier when every concept is connected to a visible frame, counter, address, value, event, or report finding.