In clause A.4 is stated, that the implementation of fixed-length GOOSE is optional and shall be stated in the PICS.
This is in contradiction with clause A.3 which somehow states fixed-length GOOSE should be supported by subscribers as long as they do not check if the shortest-length strategy has been respected in the BER encoding.
As discussed in the UCA Testing Group telephone conference 2017-03-07 the Ed.2 compliant implemenation of a GOOSE subscriber shall support fixed-length GOOSE encoding anyhow.
This needs to be clarified for Edition 2 because in Ed.2.1 there is this solution already defined.
The GOOSE subscriber should not check if the publisher consequently used the BER encoding rules for the shortest length. So the GOOSE subscriber should support fixed-length GOOSE by default.
Clients/Subscribers generally speaking allways have to support variance that are allowed in servers / publishers - example: Control Model.
In the current case: clause A.4 states:
"The support for the Fixed-length ENCODING shall be declared in the implementation's PICs and is therefore optional".
-> The support of the Fixed-length DECODING is mentioned in A.3
"The fixed-lgth propoerty for GOOSE is however backward compatible, as long as the subscriber implemetnation does not check if the shortest-length strategy has been respected in the BER encoding of the
This means: Ed1 subscriber (backward compatibility) will support the fixed length implementation as long as they do not check the shortest length strategy. Ed2 subscriber as mentioned above have no options.
10 Mar 17
I agree that no change is needed. Subscribers / clients always have the burden to accept any allowable interpretation of the standard. Refusing to parse other than minimum length BER would be a bad implementation choice.
09 Mar 17
“clause A.3 which somehow states fixed-length GOOSE should be supported by subscribers”. My opinion is that this means that subscribers which ignore the fixed-GOOSE BER rules will accept fixed-length GOOSE and it is suggested that subscribers ignore those BER rules (at least for GOOSE).
A.3 text is a recommendation and not a requirement. This TISSUE recommends converting the recommendation (“local issue”) to a requirement.
Clause A.4 states that the decision whether or not to accept fixed-length GOOSE be documented and is therefore consistent with Clause A.4
There is no inconsistency which need to be "fixed" by a TISSUE.