Encoding of SV message shall be according to ASN.1 and BER rules. BER rules allow for three length field encoding formats: short definite (1 byte), long definite (minimum 2 bytes) and indefinite format.
SV messages needs to have determinable size, based on (SCL) settings, to enable efficient parsing.
In order for SV message to have deterministic size, encoding of Length field must be well defined. As it is now, any Length field encoding is allowed, leading to indeterministic message size. For example, length of 4 can be coded as 04 (short definite) or 81 04 (long definite).
Length of some fields depends on settings (e.g. svID or ASDU depending on number of U/I element in it) and some are fixed (e.g. smpCnt always 2 bytes), but still Length field encoding of all of them needs to be minimum size.
Proposal
The size for encoding the Length field (TLV) of the variable size elements shall always use minimum length encoding.
This will make SV encoding to be in line with fix-length GOOSE encoding, part 8-1 annex A-3.
Discussion
Created
Status
Ballot period expired without comment.
Move to solution accepted.
20 Mar 24
Solution Accepted
Starting ballot period
15 Feb 24
Ballot Period
Test case sSvp7 already states the encoding shall use the minimum length TLV encoding.
No change needed.
25 Jul 23
Conformance Test Verification
Next state: Conformance Test Preparation.
The test procedure for SV publisher shall verify that all BER TLV Length fields of published SV messages are definite form, and encoded using the minimum size BER encoding possible.
09 Dec 22
Conformance Test Preparation
Go to status "Analysis of compatibility":
I'm not aware of any implementation of SV publishers not already complying with the proposal.
As well, I don't expect any SV subscribers not accepting SV complying with the proposal.
07 Nov 22
Analysis Of Compatibility
Proposed change:
adding a sentence to the beginning of the "8.5.2 Presentation Layer Functionality" clause:
[... the sampled value buffer is encoded as specified in Table 14.] All BER TLV Length fields shall be definite form, and encoded using the minimum size BER encoding possible.