Subject: [mpls] Spencer Dawkins' No Objection on draft-ietf-mpls-residence-time-14: (with COMMENT)

From: Spencer Dawkins <[email-masked]>
Date: Sun, 26 Feb 2017 13:54:23 -0800

Spencer Dawkins has entered the following ballot position for
draft-ietf-mpls-residence-time-14: No Objection

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COMMENT:
----------------------------------------------------------------------

I'm a bit confused on one point. There's one reference to NTP in the
Introduction, everything else is about PTP, but the specification never
actually says if this mechanism is intended to be usable for NTP as well.
Could that be clearer?

---

From: Greg Mirsky <[email-masked]>
Date: Mon, 27 Feb 2017 07:55:47 -0800

Hi Spencer,
thank you for your thorough review and the question.
NTP yet doesn't use transparent clock paradigm but in section 3 G-ACh for
Residence Time Measurement we've noted that NTP may be one type of TLV and
have requested appropriate allocation by IANA in the new sub-registry MPLS
RTM TLV Registry (section 7.2). Thus, if NTP will be enhanced to use
transparent clock, the RTM over MPLS will be capable to support it.
We're open to your suggestions to make it clearer.

Kind regards,
Greg

---

From: Spencer Dawkins at IETF <[email-masked]>
Date: Mon, 27 Feb 2017 11:06:18 -0600

Hi, Greg,

On Feb 27, 2017 09:55, "Greg Mirsky" <[email-masked]> wrote:

Hi Spencer,

So, is it correct to say that PTP is the only time protocol that uses the
transparent clock paradigm today?

Spencer

Kind regards,
Greg

---

From: Greg Mirsky <[email-masked]>
Date: Mon, 27 Feb 2017 09:13:23 -0800

Hi Spencer,
yes, only PTP has defined operation of the transparent clock and how to use
the residence time to improve accuracy of distributed time.

Regards,
Greg

---

From: Spencer Dawkins at IETF <[email-masked]>
Date: Mon, 27 Feb 2017 11:46:32 -0600

Hi, Greg,

On Feb 27, 2017 11:13, "Greg Mirsky" <[email-masked]> wrote:

Hi Spencer,

(Remembering that this is a no-blocking comment)

I'd suggest removing the text reference to NTP in the Introduction, and
mentioning that you're allocating the value for NTP in Section 7.2, but
that NTP can't make use of this mechanism unless it adds support for
transparent clock.

Does that make sense?

Spencer

Regards,
Greg

---

From: Greg Mirsky <[email-masked]>
Date: Mon, 27 Feb 2017 09:58:27 -0800

Hi Spencer,
thank you for your consideration.
I think that reference to NTP as one of protocols, and it is broadly used
protocol, to synchronize clocks in the Introduction may be justified. I
propose to add a note, as you've suggested, in section 3 that allocation of
the value for NTP payload is forward looking as use of the transparent
clock not yet been defined for NTP.

Regards,
Greg

On Mon, Feb 27, 2017 at 9:46 AM, Spencer Dawkins at IETF <
[email-masked]> wrote:

> yes, only PTP has defined operation of the transparent clock and how to
> use the residence time to improve accuracy of distributed time.
>
>
>> NTP yet doesn't use transparent clock paradigm but in section 3 G-ACh
>> for Residence Time Measurement we've noted that NTP may be one type of TLV
>> and have requested appropriate allocation by IANA in the new sub-registry MPLS

---

From: Eric Gray <[email-masked]>
Date: Mon, 27 Feb 2017 19:41:45 +0000

Spencer,

                While the reference to NTP is forward looking (as Greg suggested) – there is no strong reason to suspect that additional work relative to this specification will _necessarily_ be required.

Transparent Clock (again as Greg mentioned) has not yet been defined for NTP.

                The essential element of transparent clock is that there needs to be a way to determine the amount of time a message spends at each hop (this is the variable component of delay for any given path) so that this delay can be corrected for.  The more hops for which you have this information, the more accurate the corrected time values will be.

                If you can determine the variable delay experienced by a time message, you can combine this information with the measurable fixed delay (associated mostly with light-speed delays) to provide a very precise corrected time value.

                Transparent Clock is quite elegant in that sense, as long as it can be done without layer-violations.  ☺

--
Eric

From: Spencer Dawkins at IETF [mailto:[email-masked]]
Sent: Monday, February 27, 2017 12:47 PM
To: Greg Mirsky <[email-masked]>
Cc: [email-masked]; [email-masked]; Loa Andersson <[email-masked]>; [email-masked]; [email-masked]
Subject: Re: Spencer Dawkins' No Objection on draft-ietf-mpls-residence-time-14: (with COMMENT)

Hi, Greg,

On Feb 27, 2017 11:13, "Greg Mirsky" <[email-masked]<mailto:[email-masked]>> wrote:
Hi Spencer,
yes, only PTP has defined operation of the transparent clock and how to use the residence time to improve accuracy of distributed time.

I'd suggest removing the text reference to NTP in the Introduction, and mentioning that you're allocating the value for NTP in Section 7.2, but that NTP can't make use of this mechanism unless it adds support for transparent clock.

Does that make sense?

Spencer

Regards,
Greg

On Mon, Feb 27, 2017 at 9:06 AM, Spencer Dawkins at IETF <[email-masked]<mailto:[email-masked]>> wrote:
Hi, Greg,

On Feb 27, 2017 09:55, "Greg Mirsky" <[email-masked]<mailto:[email-masked]>> wrote:
Hi Spencer,
thank you for your thorough review and the question.
NTP yet doesn't use transparent clock paradigm but in section 3 G-ACh for Residence Time Measurement we've noted that NTP may be one type of TLV and have requested appropriate allocation by IANA in the new sub-registry MPLS RTM TLV Registry (section 7.2). Thus, if NTP will be enhanced to use transparent clock, the RTM over MPLS will be capable to support it.
We're open to your suggestions to make it clearer.

So, is it correct to say that PTP is the only time protocol that uses the transparent clock paradigm today?

Spencer

Kind regards,
Greg

On Sun, Feb 26, 2017 at 1:54 PM, Spencer Dawkins <[email-masked]<mailto:[email-masked]>> wrote:
Spencer Dawkins has entered the following ballot position for
draft-ietf-mpls-residence-time-14: No Objection

---

From: Alexander Vainshtein <[email-masked]>
Date: Mon, 27 Feb 2017 22:53:22 +0200

Spencer and all,
I concur with Eric.

The RTM mechanism defined in this spec does not depend on the protocol -
NPT, PTP or something else - that is carried over an LSP.

However, PTP by design can use the information about accummulated on-path
delay (the Correction field in its PDUs has been defined for just this
purpose), while NTP, in its present form, cannot do that.

If/when the NTP spec is updated so that it can use measured on-path delay,
it would be able to benefit from RTM as well - as I see it, without any
substantial changes to this spec.

Hopefully this helps.

My 2c,
Sasha

On Feb 27, 2017 21:41, "Eric Gray" <[email-masked]> wrote:

Spencer,

                While the reference to NTP is forward looking (as Greg
suggested) – there is no strong reason to suspect that additional work
relative to this specification will _*necessarily*_ be required.

Transparent Clock (again as Greg mentioned) has not yet been defined for
NTP.

                The essential element of transparent clock is that there
needs to be a way to determine the amount of time a message spends at each
hop (this is the variable component of delay for any given path) so that
this delay can be corrected for.  The more hops for which you have this
information, the more accurate the corrected time values will be.

                If you can determine the variable delay experienced by a
time message, you can combine this information with the measurable fixed
delay (associated mostly with light-speed delays) to provide a very precise
corrected time value.

                Transparent Clock is quite elegant in that sense, as long
as it can be done without layer-violations.  J

--

Eric

*From:* Spencer Dawkins at IETF [mailto:[email-masked]]
*Sent:* Monday, February 27, 2017 12:47 PM
*To:* Greg Mirsky <[email-masked]>
*Cc:* [email-masked]; [email-masked]; Loa Andersson
<[email-masked]>; [email-masked]; [email-masked]
*Subject:* Re: Spencer Dawkins' No Objection on
draft-ietf-mpls-residence-time-14:
(with COMMENT)

Hi, Greg,

Hi Spencer,

Does that make sense?

Spencer

Regards,

Greg

Hi, Greg,

Hi Spencer,

Spencer

Kind regards,

Greg

---

From: Spencer Dawkins at IETF <[email-masked]>
Date: Mon, 27 Feb 2017 15:36:12 -0600

Keeping in mind that these are non-blocking comments (so, do the right
thing) ...

On Feb 27, 2017 14:53, "Alexander Vainshtein" <[email-masked]>
wrote:

Spencer and all,
I concur with Eric.

Right, and the Introduction starts out that way, but the Abstract calls out
PTP specifically, and a quick string search turns up 4 "NTP" strings and 70
"PTP" strings in the document (counting the table of contents but you get
the idea). That's probably what misled me.

But the good news is that I'm not likely to be your typical reader ;-)

Thanks,

Spencer

Hopefully this helps.

My 2c,
Sasha

Spencer,

--

Eric

draft-ietf-mpls-residence-time-14: (with COMMENT)

Hi, Greg,

Hi Spencer,

Does that make sense?

Spencer

Regards,

Greg

Hi, Greg,

Hi Spencer,

Spencer

Kind regards,

Greg