draft-ietf-ippm-pam-07.txt		draft-ietf-ippm-pam-08.txt
	Network Working Group G. Mirsky		Network Working Group G. Mirsky
	Internet-Draft J. Halpern		Internet-Draft J. Halpern
	Intended status: Informational Ericsson		Intended status: Informational Ericsson
	Expires: 8 April 2024 X. Min		Expires: 20 April 2024 X. Min
	ZTE Corp.		ZTE Corp.
	A. Clemm		A. Clemm
	J. Strassner		J. Strassner
	Futurewei		Futurewei
	J. Francois		J. Francois
	Inria and University of Luxembourg		Inria and University of Luxembourg
	6 October 2023		18 October 2023
	Precision Availability Metrics for Services Governed by Service Level		Precision Availability Metrics for Services Governed by Service Level
	Objectives (SLOs)		Objectives (SLOs)
	draft-ietf-ippm-pam-07		draft-ietf-ippm-pam-08
	Abstract		Abstract
	This document defines a set of metrics for networking services with		This document defines a set of metrics for networking services with
	performance requirements expressed as Service Level Objectives (SLO).		performance requirements expressed as Service Level Objectives (SLO).
	These metrics, referred to as Precision Availability Metrics (PAM),		These metrics, referred to as Precision Availability Metrics (PAM),
	are useful for defining and monitoring SLOs. For example, PAM can be		are useful for defining and monitoring SLOs. For example, PAM can be
	used by providers and/or customers of an RFC XXXX Network Slice		used by providers and/or customers of an RFC XXXX Network Slice
	Service to assess whether the service is provided in compliance with		Service to assess whether the service is provided in compliance with
	its defined SLOs.		its defined SLOs.
	skipping to change at page 1, line 47 ¶		skipping to change at page 1, line 47 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 8 April 2024.		This Internet-Draft will expire on 20 April 2024.
	Copyright Notice		Copyright Notice
	Copyright (c) 2023 IETF Trust and the persons identified as the		Copyright (c) 2023 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 3, line 24 ¶		skipping to change at page 3, line 24 ¶
	Several metrics (often documented in the IANA Registry of Performance		Several metrics (often documented in the IANA Registry of Performance
	Metrics [IANA-PM-Registry] according to [RFC8911] and [RFC8912]), can		Metrics [IANA-PM-Registry] according to [RFC8911] and [RFC8912]), can
	be used to characterize the service quality, expressing the perceived		be used to characterize the service quality, expressing the perceived
	quality of delivered networking services versus their SLOs. Of		quality of delivered networking services versus their SLOs. Of
	concern is not so much the absolute service level (for example,		concern is not so much the absolute service level (for example,
	actual latency experienced) but whether the service is provided in		actual latency experienced) but whether the service is provided in
	compliance with the negotiated and eventually contracted service		compliance with the negotiated and eventually contracted service
	levels. For instance, this may include whether the experienced		levels. For instance, this may include whether the experienced
	packet delay falls within an acceptable range that has been		packet delay falls within an acceptable range that has been
	contracted for the service. The specific quality of service depends		contracted for the service. The specific quality of service depends
	on the SLO or a set of thereof for a given service that is in effect.		on the SLO or a set thereof for a given service that is in effect. A
	A non-compliance to an SLO might result in the degradation of the		non-compliance to an SLO might result in the degradation of the
	quality of experience for gamers or even jeopardize the safety of a		quality of experience for gamers or even jeopardize the safety of a
	large geographical area.		large geographical area.
	The same service level may be deemed acceptable for one application,		The same service level may be deemed acceptable for one application,
	while unacceptable for another, depending on the needs of the		while unacceptable for another, depending on the needs of the
	application. Hence it is not sufficient to measure service levels		application. Hence it is not sufficient to measure service levels
	per se over time, but to assess the quality of the service being		per se over time, but to assess the quality of the service being
	contextually provided (e.g., with the applicable SLO in mind).		contextually provided (e.g., with the applicable SLO in mind).
	However, at this point, there are no standard metrics that can be		However, at this point, there are no standard metrics that can be
	used to account for the quality with which services are delivered		used to account for the quality with which services are delivered
	skipping to change at page 4, line 29 ¶		skipping to change at page 4, line 29 ¶
	governed by SLOs and must be delivered precisely according to the		governed by SLOs and must be delivered precisely according to the
	associated quality and performance requirements. It should be noted		associated quality and performance requirements. It should be noted
	that precision refers to what is being assessed, not the mechanism		that precision refers to what is being assessed, not the mechanism
	used to measure it. In other words, it does not refer to the		used to measure it. In other words, it does not refer to the
	precision of the mechanism with which actual service levels are		precision of the mechanism with which actual service levels are
	measured. Furthermore, the precision, with respect to the delivery		measured. Furthermore, the precision, with respect to the delivery
	of an SLO, particularly applies when a metric value approaches the		of an SLO, particularly applies when a metric value approaches the
	specified threshold levels in the SLO.		specified threshold levels in the SLO.
	The specification and implementation of methods that provide for		The specification and implementation of methods that provide for
	accurate measurements is a separate topic independent of the		accurate measurements are separate topics independent of the
	definition of the metrics in which the results of such measurements		definition of the metrics in which the results of such measurements
	would be expressed. Likewise, Service Level Expectations (SLEs), as		would be expressed. Likewise, Service Level Expectations (SLEs), as
	defined in Section 5.1 of [I-D.ietf-teas-ietf-network-slices], are		defined in Section 5.1 of [I-D.ietf-teas-ietf-network-slices], are
	outside the scope of this document.		outside the scope of this document.
	2. Conventions and Terminology		2. Conventions and Terminology
	2.1. Terminology		2.1. Terminology
	In this document, SLA and SLO are used as defined in [RFC3198]. The		In this document, SLA and SLO are used as defined in [RFC3198]. The
	skipping to change at page 5, line 32 ¶		skipping to change at page 5, line 32 ¶
	VFI Violation-Free Interval		VFI Violation-Free Interval
	3. Precision Availability Metrics		3. Precision Availability Metrics
	3.1. Introducing Violated Intervals		3.1. Introducing Violated Intervals
	When analyzing the availability metrics of a service between two		When analyzing the availability metrics of a service between two
	measurement points, a time interval as the unit of PAM needs to be		measurement points, a time interval as the unit of PAM needs to be
	selected. In [ITU.G.826], a time interval of one second is used.		selected. In [ITU.G.826], a time interval of one second is used.
	That is reasonable, but some services may require different		That is reasonable, but some services may require different
	granularity (e.g., second or decamillisecond). For that reason, the		granularity (e.g., decamillisecond). For that reason, the time
	time interval in PAM is viewed as a variable parameter though		interval in PAM is viewed as a variable parameter though constant for
	constant for a particular measurement session. Furthermore, for the		a particular measurement session. Furthermore, for the purpose of
	purpose of PAM, each time interval is classified either as Violated		PAM, each time interval is classified either as Violated Interval
	Interval (VI), Severely Violated Interval (SVI), or Violation-Free		(VI), Severely Violated Interval (SVI), or Violation-Free Interval
	Interval (VFI ). These are defined as follows:		(VFI). These are defined as follows:
	* VI is a time interval during which at least one of the performance		* VI is a time interval during which at least one of the performance
	parameters degraded below its pre-defined optimal level threshold.		parameters degraded below its pre-defined optimal level threshold.
	* SVI is a time interval during which at least one of the		* SVI is a time interval during which at least one of the
	performance parameters degraded below its pre-defined critical		performance parameters degraded below its pre-defined critical
	threshold.		threshold.
	* Consequently, VFI is a time interval during which all performance		* Consequently, VFI is a time interval during which all performance
	parameters are at or better than their respective pre-defined		parameters are at or better than their respective pre-defined
	optimal levels.		optimal levels.
	The monitoring performance parameters to determine the quality of an		The monitoring of performance parameters to determine the quality of
	interval is performed between the elements of the network that are		an interval is performed between the elements of the network that are
	referred to for the SLO corresponding to the performance parameter.		referred to for the SLO corresponding to the performance parameter.
	Mechanisms of setting levels of a threshold of an SLO are outside the		Mechanisms of setting levels of a threshold of an SLO are outside the
	scope of this document.		scope of this document.
	From these definitions, a set of basic metrics can be defined that		From these definitions, a set of basic metrics can be defined that
	count the numbers of time intervals that fall into each category:		count the numbers of time intervals that fall into each category:
	* VI count.		* VI count.
	* SVI count.		* SVI count.
	* VFI count.		* VFI count.
	These count metrics are essential in calculating respective ratios		These count metrics are essential in calculating respective ratios
	(see Section 3.2) that can be used to assess the instability of a		(see Section 3.2) that can be used to assess the instability of a
	service.		service.
	Beyond accounting for violated intervals, it is sometimes beneficial		Beyond accounting for violated intervals, it is sometimes beneficial
	to maintain counts of packets for which a performance threshold is		to maintain counts of packets for which a performance threshold is
	violated. For example, this allows to distinguish between cases in		violated. For example, this allows distinguishing between cases in
	which violated intervals are caused by isolated violation occurrences		which violated intervals are caused by isolated violation occurrences
	(such as, a sporadic issue that may be caused by a temporary spike in		(such as, a sporadic issue that may be caused by a temporary spike in
	a queue depth along the packet's path) or by broad violations across		a queue depth along the packet's path) or by broad violations across
	multiple packets (such as a problem with slow route convergence		multiple packets (such as a problem with slow route convergence
	across the network or more foundational issues such as insufficient		across the network or more foundational issues such as insufficient
	network resources). Maintaining such counts and comparing them with		network resources). Maintaining such counts and comparing them with
	the overall amount of traffic also facilitates assessing compliance		the overall amount of traffic also facilitates assessing compliance
	with statistical SLOs (see Section 4). For these reasons, the		with statistical SLOs (see Section 4). For these reasons, the
	following additional metrics are defined:		following additional metrics are defined:
	skipping to change at page 7, line 41 ¶		skipping to change at page 7, line 41 ¶
	* Mean packets between SVIs is the arithmetic mean of the number of		* Mean packets between SVIs is the arithmetic mean of the number of
	SLO-compliant packets between consecutive SVIs. (Another		SLO-compliant packets between consecutive SVIs. (Another
	variation of "MTBF" in a service setting.)		variation of "MTBF" in a service setting.)
	To indicate a historic degree of precision availability, additional		To indicate a historic degree of precision availability, additional
	derived PAMs can be defined as follows:		derived PAMs can be defined as follows:
	* Violated Interval Ratio (VIR) is the ratio of the summed numbers		* Violated Interval Ratio (VIR) is the ratio of the summed numbers
	of VIs and SVIs to the total number of time unit intervals in a		of VIs and SVIs to the total number of time unit intervals in a
	time of the availability periods during a fixed measurement		time of the availability periods during a fixed measurement
	interval.		session.
	* Severely Violated Interval Ratio (SVIR) is the ratio of SVIs to		* Severely Violated Interval Ratio (SVIR) is the ratio of SVIs to
	the total number of time unit intervals in a time of the		the total number of time unit intervals in a time of the
	availability periods during a fixed measurement interval.		availability periods during a fixed measurement session.
	3.3. PAM Configuration Settings and Service Availability		3.3. PAM Configuration Settings and Service Availability
	It might be useful for a service provider to determine the current		It might be useful for a service provider to determine the current
	condition of the service for which PAMs are maintained. To		condition of the service for which PAMs are maintained. To
	facilitate this, it is conceivable to complement PAM with a state		facilitate this, it is conceivable to complement PAM with a state
	model. Such a state model can be used to indicate whether a service		model. Such a state model can be used to indicate whether a service
	is currently considered as available or unavailable depending on the		is currently considered as available or unavailable depending on the
	network's recent ability to provide service without incurring		network's recent ability to provide service without incurring
	intervals during which violations occur. It is conceivable to define		intervals during which violations occur. It is conceivable to define
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