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DNP3 Outstation Addressing
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DNP3 in ClearSCADA uses a system-wide unique address policy. This means that every outstation must use a unique address to communicate via a channel. Even outstations that communicate via completely separate channels must use unique addresses between 1 and 65519 (addresses 65520 - 65535 are reserved). Address 0 is typically used as an RTU default address and while it is valid, it is not recommended in a live system.
System-wide unique address policies are regarded as good practice as they eliminate the problem of messages being sent to incorrect outstations.
Each outstation uses an address for communicating via a channel. ClearSCADA uses the address to identify the outstation during communications, both direct and PSTN. For direct communications, it is possible - in theory - to have the same address used more than once but for different COM ports. However, ClearSCADA does not allow this and enforces a unique address policy. The reason for this is that DNP3 direct outstations also support PSTN fallback, and for PSTN communications the only way ClearSCADA can identify an outstation is by the address being used. Therefore, the address has to be unique on the system.
If the DNP3 outstation addresses were not unique system-wide, communications could be established with the wrong outstation. For example:
DNP3 PSTN Comms 1.JPG
In the diagram above, the DNP3 outstation named OS1 communicates with ClearSCADA via a direct channel connected to COM 1. It uses Address 1. The DNP3 outstation named OS 2 uses a direct channel connected to COM 2 which also uses Address 1. In theory, this would work correctly as ClearSCADA can differentiate between the outstations as they use different COM ports. However, as the outstations support PSTN fallback, there is a problem if the direct channels fail and the outstations communicate via PSTN - both outstations use Address 1 and so ClearSCADA cannot differentiate between the two outstations.
By using a unique address policy, ClearSCADA ensures all messages are received from and sent to the correct outstation.
DNP3 PSTN Comms 2.JPG
As every single outstation in the system uses a unique address, ClearSCADA can identify every outstation irrespective of the port or type of communications.
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DNP3 in ClearSCADA uses a system-wide unique address policy. This means that every outstation must use a unique address to communicate via a channel. Even outstations that communicate via completely separate channels must use unique addresses between 1 and 65519 (addresses 65520 - 65535 are reserved). Address 0 is typically used as an RTU default address and while it is valid, it is not recommended in a live system.
System-wide unique address policies are regarded as good practice as they eliminate the problem of messages being sent to incorrect outstations.
Each outstation uses an address for communicating via a channel. ClearSCADA uses the address to identify the outstation during communications, both direct and PSTN. For direct communications, it is possible - in theory - to have the same address used more than once but for different COM ports. However, ClearSCADA does not allow this and enforces a unique address policy. The reason for this is that DNP3 direct outstations also support PSTN fallback, and for PSTN communications the only way ClearSCADA can identify an outstation is by the address being used. Therefore, the address has to be unique on the system.
If the DNP3 outstation addresses were not unique system-wide, communications could be established with the wrong outstation. For example:
DNP3 PSTN Comms 1.JPG
In the diagram above, the DNP3 outstation named OS1 communicates with ClearSCADA via a direct channel connected to COM 1. It uses Address 1. The DNP3 outstation named OS 2 uses a direct channel connected to COM 2 which also uses Address 1. In theory, this would work correctly as ClearSCADA can differentiate between the outstations as they use different COM ports. However, as the outstations support PSTN fallback, there is a problem if the direct channels fail and the outstations communicate via PSTN - both outstations use Address 1 and so ClearSCADA cannot differentiate between the two outstations.
By using a unique address policy, ClearSCADA ensures all messages are received from and sent to the correct outstation.
DNP3 PSTN Comms 2.JPG
As every single outstation in the system uses a unique address, ClearSCADA can identify every outstation irrespective of the port or type of communications.
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