Subject: Re: [Ntp] I-D Action: draft-ietf-ntp-packet-timestamps-08.txt

From: Doug Arnold <[email-masked]>
Date: Tue, 25 Feb 2020 21:03:12 +0000

This is a useful informative document.

One comment:  In the discussion of PTP timestamps, it might be worth talking about the correctionField.  This field is intended to be used to make various types of corrections to the PTP timestamps, including the ability to add sub ns resolution to the timestamps.

Doug

________________________________
From: ntp <[email-masked]> on behalf of [email-masked] <[email-masked]>
Sent: Monday, February 24, 2020 5:39 AM
To: [email-masked] <[email-masked]>
Cc: [email-masked] <[email-masked]>
Subject: [Ntp] I-D Action: draft-ietf-ntp-packet-timestamps-08.txt

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Network Time Protocol WG of the IETF.

        Title           : Guidelines for Defining Packet Timestamps
        Authors         : Tal Mizrahi
                          Joachim Fabini
                          Al Morton
        Filename        : draft-ietf-ntp-packet-timestamps-08.txt
        Pages           : 21
        Date            : 2020-02-24

Abstract:
   Various network protocols make use of binary-encoded timestamps that
   are incorporated in the protocol packet format, referred to as packet
   timestamps for short.  This document specifies guidelines for
   defining packet timestamp formats in networking protocols at various
   layers.  It also presents three recommended timestamp formats.  The
   target audience of this document includes network protocol designers.
   It is expected that a new network protocol that requires a packet
   timestamp will, in most cases, use one of the recommended timestamp
   formats.  If none of the recommended formats fits the protocol
   requirements, the new protocol specification should specify the
   format of the packet timestamp according to the guidelines in this
   document.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-ntp-packet-timestamps/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-ntp-packet-timestamps-08
https://datatracker.ietf.org/doc/html/draft-ietf-ntp-packet-timestamps-08

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-ntp-packet-timestamps-08

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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From: Joachim Fabini <[email-masked]>
Date: Wed, 26 Feb 2020 08:48:10 +0100

Valid comment. Imo the correctionField - like other features we left out
- fits well into the planned controlField draft. Section 7 of the
timestamp draft mentions briefly requirements on the control field but
we decided to split the two documents (timestamp and control field) to
keep the timestamp draft concise.

Whereas the timestamp draft focuses on the basic timestamp (data)
formats, the control field draft will tackle timestamp semantics and
attributes. Examples include assertions on timestamp accuracy, time
source details, and more information on timestamp quality. Corrections,
resolutions, and interpretations that differ from (or extend) the basic
timestamp definition imo fit into the control field.

thanks,
Joachim

On 25/02/2020 22:03, Doug Arnold wrote:
> One comment:  In the discussion of PTP timestamps, it might be worth
> talking about the correctionField.  This field is intended to be used to
> make various types of corrections to the PTP timestamps, including the
> ability to add sub ns resolution to the timestamps.  
> 
> Doug
> 
> ------------------------------------------------------------------------
> *From:* ntp <[email-masked]> on behalf of [email-masked]
> <[email-masked]>
> *Sent:* Monday, February 24, 2020 5:39 AM
> *To:* [email-masked] <[email-masked]>
> *Cc:* [email-masked] <[email-masked]>
> *Subject:* [Ntp] I-D Action: draft-ietf-ntp-packet-timestamps-08.txt
>  
> 

-- 
---------------------------------------
Dr. Joachim Fabini
Senior Scientist
Institute of Telecommunications
TU Wien
Gusshausstrasse 25/E389
A-1040 Vienna, Austria
Tel: +43 1 58801-38813
mailto: [email-masked]
---------------------------------------

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From: Doug Arnold <[email-masked]>
Date: Wed, 26 Feb 2020 16:09:49 +0000

Separating timestamps and correction fields seems like a sensible approach.

But just to be clear, PTP allows a device to partition a timestamp between the timestamp field and the correctionField any way it likes as long as the combined fields yield the right value.  So the correction field may include some of the original time stamp and not just added corrections.  I'm not sure that this is a good thing, but that is what 1588-2019 says.   It might be worth adding a cautionary statement when talking about PTP.

Doug

________________________________
From: Joachim Fabini <[email-masked]>
Sent: Tuesday, February 25, 2020 11:48 PM
To: Doug Arnold <[email-masked]>; [email-masked] <[email-masked]>; [email-masked] <[email-masked]>
Subject: Re: [Ntp] I-D Action: draft-ietf-ntp-packet-timestamps-08.txt

thanks,
Joachim