719   ConfDataSet - maxAttributes definition is confusing

Created: 01 Apr 2011

Status: In Force (green)

Part: Part 6 (2009-12; Edition 2)

Links:

Page: 63

Clause: table 11

Paragraph: 9.3.1

Category: Issue may impact interoperability of implementations of Edition 2

Issue

The definition of ConfDataSet - maxAttributes is confusing especially the part in brackets (an FCDA can contain several attributes).
2 interpretations seem possible :
- maxAttributes = max nb of members in the dataset
- maxAttributes = max sum of attributes of all dataset member

Second interpretation is maybe more in line with definition but is quite complex to manage. What is also the interest as this does not give any indication about the overall size allowed ?

Proposal

Change text to clearly indicate that maxAttributes = max number of members allowed in the dataset (whatever members are DO, SDO, DA, SDA as defined in 7-2 §13.1).

Discussion Created Status
Although this is true, mostly this number is used to estimate the memory size of the data set definition, and not that of the message related to the data set, as that size does not just depend on the number of attributes but also on how they are structured inside the message. 19 Mar 13 In Force (green)
maxAttributes is related to the memory allocation capabilities of an IED.

With the approach of maxAttributes = maximun number of basicTypes, the memory needed to allocate this can be estimated.

If maxAttributes definition is the maximum fcda number, the amount of memory can not be estimated easily. Some FCDAs can be only a BOOLEAN LD/MMXU1.PPV.phsa.cVal.mag.f other can be a complex structure as LD/MMXU1.PPV[MX]

If a vendor declares that they can hold 100 FCDA in their dataset they should accept 100 structures as LD/MMXU1.PPV[MX].

The approach of counting the basictypes gives a better control of the real size of a dataset, although it is more complex to count through the templates to know the exact number of basicTypes in a fcda, of course.


19 Mar 13 In Force (green)
09 Jun 11 In Force (green)
Accepted. ConfDataSet.maxAttributes shall define the maximum number of members in a data set - in SCL terms the maximum number of FCDA elements it might contain. Observe that for GOOSE and SV telegrams additional restrictions come from the maximum size of an Ethernet packet. 11 Apr 11 Discussion (red)

 

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