Re: [TICTOC] NSH Timestamp

Tal Mizrahi <talmi@marvell.com> Sun, 25 October 2015 12:49 UTC

From: Tal Mizrahi <talmi@marvell.com>
To: "Browne, Rory" <rory.browne@intel.com>, "sfc@ietf.org" <sfc@ietf.org>, "tictoc@ietf.org" <tictoc@ietf.org>
Thread-Topic: NSH Timestamp
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Date: Sun, 25 Oct 2015 12:49:13 +0000
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Subject: Re: [TICTOC] NSH Timestamp
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Hi Rory,

I believe that in-band timestamps can certainly be a useful feature in NSH.

Major comments:

1.       The draft currently does not clarify the use case. While the draft describes how the timestamp is inserted into the NSH, I could not find a description of how the timestamp is *used*, and what is the expected accuracy. It is hard to assess whether the solution is adequate without understanding the requirement.

2.       Why does the draft mandate specific synchronization protocols (NTP, Sync-E, PTP)? It seems that if you are defining an NSH timestamp TLV, you can avoid limiting the solution, and leave the synchronization protocol out of scope.

3.       The timestamp formats are not clearly defined. Specifically, the term "UTC format" is used throughout the document. I believe UTC defines a time reference, not a timestamp format. Did you mean NTP Timestamp format / PTP Timestamp format / RFC 3339 / other?


Other comments:


*         Section 3.1:

You require both Synchronous Ethernet (2), and IEEE 1588 for frequency distribution (3). These seem like two overlapping requirements. Why do you require both? Perhap you meant that IEEE 1588 should be used for *time* distribution?

*         Could you explain why you require very accurate frequency synchronization, but inaccurate time synchonization (section 3.1)?

*         The format of the fields "UTC Reference", "Ingress Timestamp", and "Egress Timestamp" is not clear.

*         Section 3: the terms SCL and FTSN are used before they are defined. SCL is not defined at all. I guess you mean Service Classifier, but this should be specified.

*         The terms "time stamp" and "timestamp" are used intermittently. I believe "timestamp" is the most common form in IETF documents.

*         "The FTSN also writes the UTC value into the header so the" - this sentence is not clear at this point.

*         The terms NTP and IEEE 1588 are used without a reference to the relevant standards.

*         Could you please clarify the following sentence:
     "the UTC stamp is merely being used as a reference inserted into
      the TSDB for performance monitoring. It is not a reference for the
      timestamp itself."

Regards,
Tal.


From: sfc [mailto:sfc-bounces@ietf.org] On Behalf Of Browne, Rory
Sent: Friday, October 23, 2015 7:45 PM
To: sfc@ietf.org
Subject: [sfc] NSH Timestamp

Please see below a link to a draft on performance monitoring of service chains using NSH

https://tools.ietf.org/html/draft-browne-ietf-sfc-nsh-timestamp-00

Comments welcome

BR Rory


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