1968   PICS mandates SNTP even when PTP is required

Created: 27 Feb 2025

Status: Drafting Implementation

Part: Part 8-1 (2020; Edition 2.1)

Links:

Page: 143

Clause: PICS

Paragraph: Table 122

Issue

The PICS states SNTP is mandatory for a server device. In case a device offers functionality that requires accurate (PTP) timesynch, like for example SV publish, it does not make sense that that device also shall support SNTP.

For example: relay test sets with SV publisher, merging units, phasor merging units.

Proposal

Proposal is to change the SNTP condition from mandatory to conditional. Something like: "in case a device supports functionality that requires more accurate timesynch, SNTP is optional, otherwise mandatory".

Discussion Created Status
Proposed change for Table 10 - Time sync A-Profile: replace presence condition SNTP m/ 9-3 o to atLeastOne in order to respect the application requirement for example for SV Publisher or Sync Phasor application. 17 Jun 25 Drafting Implementation
The time synchronization issue can be solved by replacing in an existing system the SNTP server with a 9-3 PTP clock offering SNTP Server capabilities.

Proposed change for Table 10 - Time sync A-Profile: replace presence condition SNTP m/ 9-3 o to atLeastOne in order to respect the application requirement for example for SV Publisher or Sync Phasor application. 		13 May 25 Accepted
A "time synchronization issue" is the same as an "interoperability issue". The server will have no idea of absolute time and will be forced to transmit all data with "time unknown" which will confuse (or as least cause error logging) of clients. 03 Apr 25 Accepted
As PTP is becoming more common, it would be forward looking not to keep SNTP as mandatory anymore.
This does not forbid to implement and offer SNTP anyway if a vendor finds it beneficial for the intended application of its product.
Not supporting SNTP will not create an interoperability issue, maybe a time synchronization issue.
And forcing a MU to support SNTP just because it contains a server makes no sense.
My suggestion: if a device supports PTP, SNTP should become optional. The vendor shall decide what implications it will have for the applicability of the product if SNTP is no longer supported. 		03 Apr 25 Accepted
Agree to keep SNTP mandatory for the reasons stated in the previous comment.
I prefer counter-suggestion #1, to make it clearer and provide an explicit answer for the Tissue; but going for counter-suggestion #2 would be ok as well. 		01 Apr 25 Accepted
This may create system interoperability problems if specific (non-SV) device ONLY allows PTP but system ONLY provides SNTP. This is similar to the existing problem of server only allowing unbuffered-report but client only supporting buffered-report.

Counter-suggestion #1: Keep SNTP mandatory and make PTP conditional on SV (i.e. if SV then PTP is required, otherwise optional)

Counter-suggestion #2: No change to existing standard. It should be obvious that PTP is needed for SV use cases. It is important to keep SNTP as the last-choice time sync option because time sync is so important to every 61850 operation. 		01 Apr 25 Accepted
SNTP does not provide enough precision for SV publisher or sync phasor application.
9-2 Ed2.1.
Proposed change for Table 10 - Time sync A-Profile: replace presence condition SNTP m/ 9-3 o to atLeastOne in order to respect the application requirement for example for SV Publisher or Sync Phasor application. 		01 Apr 25 Accepted
I disagree with proposal.

61850-8-1 has nothing to do with SV, that is for 61850-9-2.
I believe that any device supporting MMS or GOOSE (those parts specified in part 8-1) only need the accuracy which is supported by SNTP.
For devices using PTP, the SNTP is a backstop for when PTP is not functioning adequately (for example, local GNSS becomes unavailable); then NTP can be used with external servers such as those hosted by substation owners.

There might a case for devices only using 61850-9-2 to make SNTP optional, but that would be a different TISSUE. 		27 Feb 25 Triage
Agree.

Also, when a device is capable to time synchronize via other means (e.g., PTP), the requirement to support SNTP is superfluous.

If the wording is really "for a server device" it might be worthwhile to clarify if this applies to devices which have just GOOSE and SV publisher and subscriber features, but no C/S (MMS) communication interface. 		27 Feb 25 Triage

 

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