4   ASDU segmentation and MAC calculation

Created: 14 Jan 2025

Status: Approval (Editoral)

Part: Part 5-7 (2013, Edition 1)

Links:

Page: 12

Clause: 7.2.6

Paragraph: Whole clause

Issue

In IEC 62351-5 the MAC or Wrapped Key Data (WKD) is calculated including the entire ASDUs transmitted and/or previously received.

The IEC 60870-5-7 introduces the ASC (ASDU Segmentation Control) field in all the S_XX_NA_1 ASDUs, except for S_KR_NA_1.
In IEC 60870-5-7 the statement indicating if the ASC field shall or shall not be included in the MAC/WKD calculation is missed.
This approach requires to take each individual segment of the ASDUs received or transmitted, including ASC, to calculate the MAC.

Proposal

ASDU segmentation control field (ASC) introduced in IEC 60870-5-7 is a message transport information, not an application information. The ASC shall not be included in the MAC calculation.

Discussion Created Status
The proposed tissue resolution provides a clarification of specifications in the Clause 7.2.6 of the IEC 62351-5:2013.

This resolution is already considered in IEC TS 60870-5-7 Ed.2 (expected to be published in March 2025) 		21 Feb 25 Approval (Editoral)
Accepted for discussion 21 Feb 25 Discussion (red)
See attache proposal for the tissue resolution 21 Feb 25 Accepted
Accepted 21 Feb 25 Accepted

 

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