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Re: [Cbor] Robert Wilton's Discuss on draft-ietf-cbor-time-tag-11: (with DISCUSS and COMMENT)

Carsten Bormann <cabo@tzi.org> Wed, 25 October 2023 20:36 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Wed, 25 Oct 2023 22:35:44 +0200
Cc: Robert Wilton <rwilton@cisco.com>, The IESG <iesg@ietf.org>, "draft-ietf-cbor-time-tag@ietf.org" <draft-ietf-cbor-time-tag@ietf.org>, "cbor-chairs@ietf.org" <cbor-chairs@ietf.org>, "cbor@ietf.org" <cbor@ietf.org>, Barry Leiba <barryleiba@computer.org>
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To: "lgl island-resort.com" <lgl@island-resort.com>
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Subject: Re: [Cbor] Robert Wilton's Discuss on draft-ietf-cbor-time-tag-11: (with DISCUSS and COMMENT)
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On 25. Oct 2023, at 21:01, lgl island-resort.com <lgl@island-resort.com> wrote:
> 
> Also, here’s a time tag implementation FAQ I wrote some time ago: https://github.com/laurencelundblade/QCBOR/blob/master/doc/TimeTag1FAQ.md

This may need some debugging.

Preferred encoding for floating point values means that you will get (and, if deterministic, send) binary32 (what you call “single”) occasionally.  Binary64 has 53 bits of resolution, not 52.  Binary64 (“double”) only gets microsecond resolution until next century, not beyond the end of solar system.  If you are "transmitting thousands of time stamps and space is a problem”, don’t use Tag 1 but a representation that is appropriate for your needs (e.g., custom epoch, custom resolution).

Anyway, draft-ietf-cbor-time-tag is not a document about tag 1 (which indeed stays available for use where it is sufficient), but about tags 1001..1003.

Grüße, Carsten

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