[Cbor] Paywalled IEEE standards referenced in draft-bormann-cbor-time-tag

Emile Cormier <emile.cormier.jr@gmail.com> Fri, 02 April 2021 23:49 UTC

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From: Emile Cormier <emile.cormier.jr@gmail.com>
Date: Fri, 02 Apr 2021 20:49:05 -0300
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Subject: [Cbor] Paywalled IEEE standards referenced in draft-bormann-cbor-time-tag
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The IETF draft for cbor tags 1001 thru 1003 reference the IEEE1588-2008
standard for the clock quality keys.

Are there no other public domain or open-source standards that would serve
the same purpose as IEEE1588-2008 for the clock quality keys? I ask that
without any expertise on the subject, but merely as a C++ CBOR library
implementer who wants to support these CBOR tags (they are better for
transmitting std::chrono::time_point values losslessly).

At the very least, can the descriptions be more explicit about the data
types needed for the clock quality keys? ClockClass and ClockAccuracy
specify "one-byte integer", but it's not clear if it's signed or unsigned.
Also, "octet" would be a better word than "byte", since there are
architectures (such as DSPs) where a byte is 16 bits.

The OffsetScaledLogVariance key does not mention the value's data type(s)
or its physical units.

My motivation is to create an intermediate extended_time struct in my C++
library that contains all the possible fields of a CBOR extended time. If
an application wants to deserialize it into a std::chrono::time_point, my
library would discard the clock quality stuff. If some sort of scientific
application really wants the clock quality information, then they just
deserialize into an extended_time destination object and my library copies
all the available information.

It would be preferable if the numeric clock quality fields in my
extended_time struct were of a known static type, such as a double. But
since I don't have access to IEEE1588, I don't know if double is of
sufficient accuracy. I would appreciate it if an expert could illuminate me
on the required numeric precision, or point me in the right direction for
my own research on the subject.

Emile Cormier