1295 Port modelling has redundant information which can lead to inconsistencies
Created: 04 Aug 2014
Part: Part 90-4 (2013; Edition 1)
Category: Issue for edition 2 of this part
The Switch IEC61850 DATA model contains portNam ("Label of the terminal on the device", optional) and portNum ("Number of the terminal on the device") as well as the instance number LNInst of LPCPx.
The communication section has a <P type="Port">xxx</P> element which can contain a string as value. There must be a way to match such a port with an LPCP (e.g. needed to relate an IP address to a physical port; however, currently there is no specified way to match those two items.
Additionally, SNMP has an ifIndex for which it specifies: “It is recommended that values are assigned contiguously starting from 1”.
The above-mentioned information items are redundant; therefore certain rules must be introduced, otherwise confusion will result.
1) Make it mandatory that PortNum is identical to LPCP index (LNInst). Otherwise, an identification of the port information becomes unnecessarily complicated (e.g. if I want to find the Port which matches Port 1 as labelled on the switch front plate, I need to parse all LPCPs to find the one with PortNum 1).
2) Make it mandatory that LPCP index and portNum match ifIndex of referenced port for all devices that understand SNMP. This is to avoid confusion if a switch can be queried via IEC61850 *and* SNMP. Typically ifIndex matches the Label on the switch front plate for switches who label their ports with sequential numbers.
3) define what is used to be as a reference to match an LPCP with its port definition on a ConnectedAP.
Best solution: extend tPredefinedPTypePhysConnEnum with another element "PortNum" which can have an unsigned integer as value and which must match PortNum and LPCP index (<P type="PortNum">1</P>).
To use <P type="Port">xxx</P> is not recommended for legacy reasons as it can contain a string and cannot be forced to match PortNum without potentially changing an existing configuration.
4) Make it mandatory that PortNam and <P type="Port">xxx</P> are either identical or that <P type="Port">xxx</P> is only used if PortNam is not available. This, however, requires 3) above.
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