rfc9581v5.txt		rfc9581.txt
	skipping to change at line 145 ¶		skipping to change at line 145 ¶
	2. Objectives		2. Objectives
	For the time tag, the present specification addresses the following		For the time tag, the present specification addresses the following
	objectives that go beyond the original tags 0 and 1 (defined in		objectives that go beyond the original tags 0 and 1 (defined in
	Sections 3.4.1 and 3.4.2 of [RFC8949]):		Sections 3.4.1 and 3.4.2 of [RFC8949]):
	* Additional resolution for epoch-based time (as in tag 1). CBOR		* Additional resolution for epoch-based time (as in tag 1). CBOR
	tag 1 only provides for representation of time as an integer and		tag 1 only provides for representation of time as an integer and
	as up to a binary64 floating-point value [IEEE754], which limits		as up to a binary64 floating-point value [IEEE754], which limits
	the resolution to approximately microseconds at the time of		the resolution to approximately microseconds at the time of
	writing (and progressively becoming worse over time).		writing (progressively becoming worse over time).
	* Indication of timescale. Tags 0 and 1 are defined for UTC;		* Indication of timescale. Tags 0 and 1 are defined for UTC;
	however, some interchanges are better performed on TAI. Other		however, some interchanges are better performed on TAI. Other
	timescales may be registered once they become relevant (e.g., one		timescales may be registered once they become relevant (e.g., one
	of the proposed successors to UTC that might no longer use leap		of the proposed successors to UTC that might no longer use leap
	seconds or a scale based on smeared leap seconds).		seconds or a scale based on smeared leap seconds).
	By incorporating a way to transport [RFC9557] suffix information (see		By incorporating a way to transport [RFC9557] suffix information (see
	Sections 3.6 and 3.7), additional indications of intents about the		Sections 3.6 and 3.7), additional indications of intents about the
	interpretation of the time given can be provided; in particular, for		interpretation of the time given can be provided; in particular, for
	skipping to change at line 313 ¶		skipping to change at line 313 ¶
	instance in C timespec (Section 7.27.1 of [C]). When ingesting a		instance in C timespec (Section 7.27.1 of [C]). When ingesting a
	timestamp with one of these keys into a type provided by the target		timestamp with one of these keys into a type provided by the target
	platform, care has to be taken to meet its invariants. For example,		platform, care has to be taken to meet its invariants. For example,
	for C timespec, the fractional part tv_nsec needs to be between 0		for C timespec, the fractional part tv_nsec needs to be between 0
	inclusive and 10^9 exclusive, which can be achieved by also adjusting		inclusive and 10^9 exclusive, which can be achieved by also adjusting
	the base time appropriately.		the base time appropriately.
	3.4. Keys -1, -13, and 13: Timescale		3.4. Keys -1, -13, and 13: Timescale
	Keys -1, -13, and 13 are used to indicate a timescale, where key 13		Keys -1, -13, and 13 are used to indicate a timescale, where key 13
	is critical. Keys -1 and -13 have identical semantics (they are both		is critical. Keys -1 and -13 have identical semantics (both are
	assigned because key -1 was chosen first and then, when key 13 was		assigned because key -1 was chosen first and then, when key 13 was
	added, it appeared desirable to have a negative equivalent). Each		added, it appeared desirable to have a negative equivalent). Each
	extended time data item MUST NOT contain more than one of these keys.		extended time data item MUST NOT contain more than one of these keys.
	The value 0 indicates UTC, with the POSIX epoch [TIME_T]; the value 1		The value 0 indicates UTC, with the POSIX epoch [TIME_T]; the value 1
	indicates TAI, with the Precision Time Protocol (PTP) epoch (1		indicates TAI, with the Precision Time Protocol (PTP) epoch (1
	January 1970 00:00:00 TAI, see [IEEE1588-2019] or [IEEE1588-2008]).		January 1970 00:00:00 TAI, see [IEEE1588-2019] or [IEEE1588-2008]).
	$$ETIME-ELECTIVE //= (-1 => $ETIME-TIMESCALE)		$$ETIME-ELECTIVE //= (-1 => $ETIME-TIMESCALE)
	$$ETIME-ELECTIVE //= (-13 => $ETIME-TIMESCALE)		$$ETIME-ELECTIVE //= (-13 => $ETIME-TIMESCALE)
	skipping to change at line 362 ¶		skipping to change at line 362 ¶
	| earth-referenced timescales (such as UT1 and TT), as well as		| earth-referenced timescales (such as UT1 and TT), as well as
	| possibly for specific realizations of abstract timescales (such		| possibly for specific realizations of abstract timescales (such
	| as TAI(USNO), the specific realization obtained at the United		| as TAI(USNO), the specific realization obtained at the United
	| States Naval Observatory, which is more accurate as a constant		| States Naval Observatory, which is more accurate as a constant
	| offset basis for GPS times). While the registration process		| offset basis for GPS times). While the registration process
	| itself is trivial, these registrations need to be made based on		| itself is trivial, these registrations need to be made based on
	| a solid specification of their actual definition.		| a solid specification of their actual definition.
	3.5. Clock Quality		3.5. Clock Quality
	A number of keys are defined to indicate the quality of clock that		A number of keys are defined to indicate the quality of the clock
	was used to determine the point in time.		that was used to determine the point in time.
	The first three are analogous to clock-quality-grouping in [RFC8575],		The first three are analogous to clock-quality-grouping in [RFC8575],
	which is in turn based on the definitions in [IEEE1588-2008]; the		which is in turn based on the definitions in [IEEE1588-2008]; the
	last two are specific to this document.		last two are specific to this document.
	ClockQuality-group = (		ClockQuality-group = (
	? &(ClockClass: -2) => uint .size 1 ; PTP/RFC8575		? &(ClockClass: -2) => uint .size 1 ; PTP/RFC8575
	? &(ClockAccuracy: -4) => uint .size 1 ; PTP/RFC8575		? &(ClockAccuracy: -4) => uint .size 1 ; PTP/RFC8575
	? &(OffsetScaledLogVariance: -5) => uint .size 2 ; PTP/RFC8575		? &(OffsetScaledLogVariance: -5) => uint .size 2 ; PTP/RFC8575
	? &(Uncertainty: -7) => ~time/~duration		? &(Uncertainty: -7) => ~time/~duration
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