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The clock specifications (e.g., as per ITU-T G.8262 or G.8273.2) are defined at the interfaces of a network element. This means that in general the timing performance of a clock not only depends on the oscillator characteristics, but also on the system design specific configuration (e.g., PLL, line card, internal clock distribution, etc.) at the time of testing.

However some of the requirements such as frequency accuracy and holdover are mostly related to the , the timing performance in freerun and holdover clock modes is primarily dominated by the system oscillator characteristics; in this case an oscillator the system may be tested against the clock requirements irrespectively of the reference design that is used for the test activity with less importance given to the specific system configuration at the time of testing.

The Table below summarizes the applicability of clock requirements to the oscillator characteristics for the main clock specifications.

Option reference Depends on specifc Reference system design ; ;

Specification	Clause / Osc. Characteristic	Sufficiently independent from	system	configuration	Specific to system configuration (PLL	, Line card	, etc.)	Notes
SyncPHY clocks: *G.812, G.8262, G.8262.1** *G.812 includes ANSI Stratum 3 (Type IV) Stratum 3E (Type III) Stratum 2 (Type II)	Frequency Accuracy	X		Sync PHY clocks
	Pull-in , Hold-In, Pull-out		X	depends Depends on PLL design
	Noise Gen		X
	Noise Tolerance		X
	Noise Transfer		X
	Short-Term phase transient response		X
	Long-Term phase transient response (Holdover)	X (see Notes)	X (see Notes)	Temperature characteristics depends depend on system design
	Phase response to input signal interruptions		X
	Phase discontinuity		X
	Interfaces		X
Packet Clocks (Full timing Support): G.8273.2, G.8273.3	SyncE clock		See Notes	See G.8262/G.8262.1
	Time Error Noise Gen		X
	Noise Transfer		X
	Noise Tolerance		X
	Transient Response due to PTP and SyncE		See Notes	For further study
	Transient Response due to SyncE		X	Strongly related to system design For further study for G.8273.3
	Transient/ PTP Holdover (loss of SyncE)		See Notes	For class C it practically assumes a G.8262.1 clock. N/A to G.8273.3
	Holdover (loss of SyncE and PTP)	See Notes		For further study N/A to G.8273.3
	Holdover based on physical layer assistance (loss of PTP)		X
	Interfaces		X
Packet Clocks (Partial timing Support): G. 8273.4	Frequency Accuracy	X
	SyncE clock (optional)	See Notes	See Notes	See G.8262/G.8262.1
	Time Error Noise Gen		X
	Noise Transfer		X
	Noise Tolerance		X
	Transient Response (from GNSS to PTP)		X	Strongly related to system design
	Holdover based on oscillator	X
	Holdover based on physical layer assistance (loss of PTP) (T-BC-P)		X	Same as per G.8273.2
	Interfaces		X

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