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Internet Engineering Task Force (IETF) J. Quittek, Ed. Request for Comments: 6988 NEC Europe Ltd. Category: Informational M. Chandramouli ISSN: 2070-1721 Cisco Systems, Inc.

                                                             R. Winter
                                                              T. Dietz
                                                       NEC Europe Ltd.
                                                             B. Claise
                                                   Cisco Systems, Inc.
                                                        September 2013
                 Requirements for Energy Management

Abstract

 This document defines requirements for standards specifications for
 Energy Management.  The requirements defined in this document are
 concerned with monitoring functions as well as control functions.
 Monitoring functions include identifying energy-managed devices and
 their components, as well as monitoring their Power States, Power
 Inlets, Power Outlets, actual power, Power Attributes, received
 energy, provided energy, and contained batteries.  Control functions
 include such functions as controlling power supply and Power State of
 energy-managed devices and their components.
 This document does not specify the features that must be implemented
 by compliant implementations but rather lists features that must be
 supported by standards for Energy Management.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6988.

Quittek, et al. Informational [Page 1] RFC 6988 Requirements for Energy Management September 2013

Copyright Notice

 Copyright (c) 2013 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
    1.1. Conventional Requirements for Energy Management ............3
    1.2. Specific Requirements for Energy Management ................4
 2. Terminology .....................................................5
 3. General Considerations Related to Energy Management .............6
    3.1. Power States ...............................................7
    3.2. Saving Energy versus Maintaining Service Level .............7
    3.3. Local versus Network-Wide Energy Management ................7
    3.4. Energy Monitoring versus Energy Saving .....................8
    3.5. Overview of Energy Management Requirements .................8
 4. Identification of Entities ......................................9
 5. Information on Entities ........................................10
    5.1. General Information on Entities ...........................10
    5.2. Power Interfaces ..........................................11
    5.3. Power .....................................................13
    5.4. Power State ...............................................15
    5.5. Energy ....................................................17
    5.6. Battery State .............................................18
    5.7. Time Series of Measured Values ............................19
 6. Control of Entities ............................................21
 7. Reporting on Other Entities ....................................21
 8. Controlling Other Entities .....................................22
    8.1. Controlling Power States of Other Entities ................22
    8.2. Controlling Power Supply ..................................23
 9. Security Considerations ........................................23
 10. Acknowledgments ...............................................25
 11. References ....................................................25
    11.1. Normative References .....................................25
    11.2. Informative References ...................................26

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1. Introduction

 With rising energy costs and an increasing awareness of the
 ecological impact of running information technology equipment, Energy
 Management (EMAN) functions and interfaces are becoming an additional
 basic requirement for network management systems and devices
 connected to a network.
 This document defines requirements for standards specifications for
 Energy Management, both monitoring functions and control functions.
 Energy Management functions focus mainly on devices and their
 components that receive and provide electrical energy.  Devices such
 as hosts, routers, and middleboxes may have an IP address or may be
 connected indirectly to the Internet via a proxy with an IP address
 providing a management interface for the device, for example, devices
 in a building infrastructure using non-IP protocols and a gateway to
 the Internet.
 These requirements are concerned with the standards specification
 process and not the implementation of specified standards.  All
 requirements in this document must be reflected by standards
 specifications to be developed.  However, which of the features
 specified by these standards will be mandatory, recommended, or
 optional for compliant implementations is to be defined by Standards
 Track document(s) and not in this document.
 Section 3 elaborates on a set of general needs for Energy Management.
 Requirements for an Energy Management standard are specified in
 Sections 4 through 8.
 Sections 4 through 6 contain conventional requirements specifying
 information on entities and control functions.
 Sections 7 and 8 contain requirements specific to Energy Management.
 Due to the nature of power supply, some monitoring and control
 functions are not conducted by interacting with the entity of
 interest but rather with other entities, for example, entities
 upstream in a power distribution tree.

1.1. Conventional Requirements for Energy Management

 The specification of requirements for an Energy Management standard
 starts with Section 4, which addresses the identification of entities
 and the granularity of reporting of energy-related information.  A
 standard must support the unique identification of entities,
 reporting per entire device, and reporting energy-related information
 on individual components of a device or attached devices.

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 Section 5 specifies requirements related to the monitoring of
 entities.  This includes general (type, context) information and
 specific information on Power States, Power Inlets, Power Outlets,
 power, energy, and batteries.  The control of Power State and power
 supply by entities is covered by requirements specified in Section 6.

1.2. Specific Requirements for Energy Management

 While the conventional requirements summarized above seem to be all
 that would be needed for Energy Management, there are significant
 differences between Energy Management and most well-known network
 management functions.  The most significant difference is the need
 for some devices to report on other entities.  There are three major
 reasons for this.
 o  For monitoring a particular entity, it is not always sufficient to
    communicate only with that entity.  When the entity has no
    instrumentation for determining power, it might still be possible
    to obtain power values for the entity via communication with other
    entities in its power distribution tree.  A simple example of this
    would be the retrieval of power values from a power meter at the
    power line into the entity.  A Power Distribution Unit (PDU) and a
    Power over Ethernet (PoE) switch are common examples.  Both supply
    power to other entities at sockets or ports, respectively, and are
    often instrumented to measure power per socket or port.
 o  Similar considerations apply to controlling the power supply of an
    entity that often needs direct or indirect communications with
    another entity upstream in the power distribution tree.  Again, a
    PDU and a PoE switch are common examples, if they have the
    capability to switch power on or off at their sockets or ports,
    respectively.
 o  Energy Management often extends beyond entities with IP network
    interfaces to non-IP building systems accessed via a gateway
    (sometimes called an Energy Management System or controller).
    Requirements in this document do not cover the details of these
    networks and energy devices but specify means for opening IP
    network management towards them.
 These specific issues of Energy Management, as well as other issues,
 are covered by requirements specified in Sections 7 and 8.
 The requirements in these sections need a new Energy Management
 framework that deals with the specific nature of Energy Management.
 The actual standards documents, such as MIB module specifications,
 address conformance by specifying which features must, should, or may
 be implemented by compliant implementations.

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2. Terminology

 The terms specified in the terminology section are capitalized
 throughout the document; the exceptions are the well-known terms
 "energy" and "power".  These terms are generic and are used in
 generated terms such as "energy-saving", "low-power", etc.
 Energy
    Energy is the capacity of a system to do work.  As used by
    electric utilities, it is generally a reference to electrical
    energy and is measured in kilowatt-hours (kWh) [IEEE-100].
 Power
    Power is the time rate at which energy is emitted, transferred, or
    received; power is usually expressed in watts (or in joules per
    second) [IEEE-100].  (The term "power" does not refer to the
    concept of demand, which is an averaged power value.)
 Power Attributes
    Power Attributes are measurements of electric current, voltage,
    phase, and frequencies at a given point in an electrical power
    system (adapted from [IEC.60050]).
    NOTE: Power Attributes are not intended to be "judgmental" with
    respect to a reference or technical value and are independent of
    any usage context.
 Energy Management
    Energy Management is a set of functions for measuring, modeling,
    planning, and optimizing networks to ensure that the network
    elements and attached devices use energy efficiently and in a
    manner appropriate to the nature of the application and the cost
    constraints of the organization [ITU-M.3400].
 Energy Management System
    An Energy Management System is a combination of hardware and
    software used to administer a network with the primary purpose
    being Energy Management.

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 Energy Monitoring
    Energy Monitoring is a part of Energy Management that deals with
    collecting or reading information from network elements and
    attached devices and their components to aid in Energy Management.
 Energy Control
    Energy Control is a part of Energy Management that deals with
    controlling energy supply and Power State of network elements, as
    well as attached devices and their components.
 Power Interface
    A Power Interface is an interface at which a device is connected
    to a power transmission medium, at which it can in turn receive
    power, provide power, or both.
 Power Inlet
    A Power Inlet is a Power Interface at which a device can receive
    power from other devices.
 Power Outlet
    A Power Outlet is a Power Interface at which a device can provide
    power to other devices.
 Power State
    A Power State is a condition or mode of a device that broadly
    characterizes its capabilities, power consumption, and
    responsiveness to input [IEEE-1621].

3. General Considerations Related to Energy Management

 The basic objective of Energy Management is to operate sets of
 devices using minimal energy, while maintaining a certain level of
 service.  [EMAN-STATEMENT] presents the applicability of the EMAN
 framework to a variety of scenarios and also lists use cases and
 target devices.

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3.1. Power States

 Entities can be set to an operational state that results in the
 lowest power level that still meets the service-level performance
 objectives.  In principle, there are three basic types of Power
 States for an entity or for a whole system:
 o  full Power State
 o  sleep state (not functional but immediately available)
 o  off state (may require significant time to become operational)
 In specific devices, the number of Power States and their properties
 vary considerably.  Simple entities may only have the extreme states:
 full Power State and off state.  Many devices have three basic Power
 States: on, off, and sleep.  However, more finely grained Power
 States can be implemented.  Examples are various operational low
 Power States in which a device requires less energy than in the full
 power "on" state, but -- compared to the sleep state -- is still
 operational with reduced performance or functionality.

3.2. Saving Energy versus Maintaining Service Level

 One of the objectives of Energy Management is to reduce energy
 consumption.  While this objective is clear, attaining that goal is
 often difficult.  In many cases, there is no way to reduce power
 without the consequence of a potential service (performance or
 capacity) degradation.  In this case, a trade-off needs to be made
 between service-level objectives and energy minimization.  In other
 cases, a reduction of power can easily be achieved while still
 maintaining sufficient service-level performance, for example, by
 switching entities to lower Power States when higher performance is
 not needed.

3.3. Local versus Network-Wide Energy Management

 Many energy-saving functions are executed locally by an entity; it
 monitors its usage and dynamically adapts its power according to the
 required performance.  It may, for example, switch to a sleep state
 when it is not in use, or outside of scheduled business hours.  An
 Energy Management System may observe an entity's Power State and
 configure its power-saving policies.
 Energy savings can also be achieved with policies implemented by a
 network management system that controls Power States of managed
 entities.  Information about the power received and provided by

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 entities in different Power States may be required in order to set
 such policies.  Often, this information is best acquired through
 monitoring.
 Network-wide and local Energy Management methods both have advantages
 and disadvantages, and it is often desirable to combine them.
 Central management is often favorable for setting Power States of a
 large number of entities at the same time, for example, at the
 beginning and end of business hours in a building.  Local management
 is often preferable for power-saving measures based on local
 observations, such as the high or low functional load of an entity.

3.4. Energy Monitoring versus Energy Saving

 Monitoring energy, power, and Power States alone does not reduce the
 energy needed to run an entity.  In fact, it may even increase it
 slightly due to monitoring instrumentation that needs energy.
 Reporting measured quantities over the network may also increase
 energy use, though the acquired information may be an essential input
 to control loops that save energy.
 Monitoring energy and Power States can also be required for other
 purposes, including:
 o  investigating energy-saving potential
 o  evaluating the effectiveness of energy-saving policies and
    measures
 o  deriving, implementing, and testing power management strategies
 o  accounting for the total power received and provided by an entity,
    a network, or a service
 o  predicting an entity's reliability based on power usage
 o  choosing the time of the next maintenance cycle for an entity

3.5. Overview of Energy Management Requirements

 The following basic management functions are required:
 o  monitoring Power States
 o  monitoring power (energy conversion rate)
 o  monitoring (accumulated) received and provided energy

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 o  monitoring Power Attributes
 o  setting Power States
 Power control is complementary to other energy-saving measures, such
 as low-power electronics, energy-saving protocols, energy-efficient
 device design (for example, low-power modes for components), and
 energy-efficient network architectures.  Measurement of received and
 provided energy can provide useful data for developing these
 technologies.

4. Identification of Entities

 Entities must be capable of being uniquely identified within the
 context of the management system.  This includes entities that are
 components of managed devices as well as entire devices.
 Entities that report on or control other entities must identify the
 entities they report on or control: see Section 7 or Section 8,
 respectively, for the detailed requirements.
 An entity may be an entire device or a component of it.  Examples of
 components of interest are a hard drive, a battery, or a line card.
 The ability to control individual components to save energy may be
 required.  For example, server blades can be switched off when the
 overall load is low, or line cards at switches may be powered down at
 night.
 Identifiers for devices and components are already defined in
 standard MIB modules, such as the Link Layer Discovery Protocol
 (LLDP) MIB module [IEEE-802.1AB] and the Link Layer Discovery
 Protocol -- Media Endpoint Discovery (LLDP-MED) MIB module
 [ANSI-TIA-1057] for devices, and the Entity MIB module [RFC6933] and
 the power Ethernet MIB [RFC3621] for components of devices.  Energy
 Management needs a means to link energy-related information to such
 identifiers.
 Instrumentation for measuring the received and provided energy of a
 device is typically more expensive than instrumentation for
 retrieving its Power State.  Many devices may provide Power State
 information for all individual components separately, while reporting
 the received and provided energy only for the entire device.

4.1. Identifying Entities

 The standard must provide means for uniquely identifying entities.
 Uniqueness must be preserved such that collisions of identities are
 avoided at potential receivers of monitored information.

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4.2. Persistence of Identifiers

 The standard must provide means for indicating whether identifiers of
 entities are persistent across a restart of the entity.

4.3. Change of Identifiers

 The standard must provide means to indicate any change of entity
 identifiers.

4.4. Using Entity Identifiers of Existing MIB Modules

 The standard must provide means for reusing entity identifiers from
 existing standards, including at least the following:
 o  the entPhysicalIndex in the Entity MIB module [RFC6933]
 o  the LldpPortNumber in the LLDP MIB module [IEEE-802.1AB] and in
    the LLDP-MED MIB module [ANSI-TIA-1057]
 o  the pethPsePortIndex and the pethPsePortGroupIndex in the Power
    Ethernet MIB [RFC3621]
 Generic means for reusing other entity identifiers must be provided.

5. Information on Entities

 This section describes information on entities for which the standard
 must provide means for retrieving and reporting.
 Required information can be structured into seven groups.
 Section 5.1 specifies requirements for general information on
 entities, such as type of entity or context information.
 Requirements for information on Power Inlets and Power Outlets of
 entities are specified in Section 5.2.  The monitoring of power and
 energy is covered by Sections 5.3 and 5.5, respectively.  Section 5.4
 covers requirements related to entities' Power States.  Section 5.6
 specifies requirements for monitoring batteries.  Finally, the
 reporting of time series of values is covered by Section 5.7.

5.1. General Information on Entities

 For Energy Management, understanding the role and context of an
 entity may be required.  An Energy Management System may aggregate
 values of received and provided energy according to a defined
 grouping of entities.  When controlling and setting Power States, it
 may be helpful to understand the grouping of the entity and role of

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 an entity in a network.  For example, it may be important to exclude
 some mission-critical network devices from being switched to lower
 power or even from being switched off.

5.1.1. Type of Entity

 The standard must provide means to configure, retrieve, and report a
 textual name or a description of an entity.

5.1.2. Context of an Entity

 The standard must provide means for retrieving and reporting context
 information on entities, for example, tags associated with an entity
 that indicate the entity's role.

5.1.3. Significance of Entities

 The standard must provide means for retrieving and reporting the
 significance of entities within its context, for example, how
 important the entity is.

5.1.4. Power Priority

 The standard must provide means for retrieving and reporting power
 priorities of entities.  Power priorities indicate an order in which
 Power States of entities are changed, for example, to lower Power
 States for saving power.

5.1.5. Grouping of Entities

 The standard must provide means for grouping entities.  This can be
 achieved in multiple ways, for example, by providing means to tag
 entities, assign them to domains, or assign device types to them.

5.2. Power Interfaces

 A Power Interface is an interface at which a device is connected to a
 power transmission medium, at which it can in turn receive power,
 provide power, or both.
 A Power Interface is either an inlet or an outlet.  Some Power
 Interfaces change over time from being an inlet to being an outlet
 and vice versa.  However, most Power Interfaces never change.
 Devices have Power Inlets at which they are supplied with electric
 power.  Most devices have a single Power Inlet, while some have
 multiple inlets.  Different Power Inlets on a device are often
 connected to separate power distribution trees.  For Energy

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 Monitoring, it is useful to retrieve information on the number of
 inlets of a device, the availability of power at inlets, and which
 inlets are actually in use.
 Devices can have one or more Power Outlets for supplying other
 devices with electric power.
 For identifying and potentially controlling the source of power
 received at an inlet, identifying the Power Outlet of another device
 at which the received power is provided may be required.
 Analogously, for each outlet, it is of interest to identify the Power
 Inlets that receive the power provided at a certain outlet.  Such
 information is also required for constructing the wiring topology of
 electrical power distribution to devices.
 Static properties of each Power Interface are required information
 for Energy Management.  Static properties include the kind of
 electric current (AC or DC), the nominal voltage, the nominal AC
 frequency, and the number of AC phases.  Note that the nominal
 voltage is often not a single value but a voltage range, such as, for
 example, (100V-120V), (100V-240V), (100V-120V,220V-240V).

5.2.1. List of Power Interfaces

 The standard must provide means for monitoring the list of Power
 Interfaces of a device.

5.2.2. Operational Mode of Power Interfaces

 The standard must provide means for monitoring the operational mode
 of a Power Interface, which is either "Power Inlet" or "Power
 Outlet".

5.2.3. Corresponding Power Outlet

 The standard must provide means for identifying the Power Outlet that
 provides the power received at a Power Inlet.

5.2.4. Corresponding Power Inlets

 The standard must provide means for identifying the list of Power
 Inlets that receive the power provided at a Power Outlet.

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5.2.5. Availability of Power

 If the Power States allow it, the standard must provide means for
 monitoring the availability of power at each Power Interface.  This
 includes indicating whether a power supply at a Power Interface is
 switched on or off.

5.2.6. Use of Power

 The standard must provide means for monitoring each Power Interface
 if it is actually in use.  For inlets, this means that the device
 actually receives power at the inlet.  For outlets, this means that
 power is actually provided from the outlet to one or more devices.

5.2.7. Type of Current

 The standard must provide means for reporting the type of current (AC
 or DC) for each Power Interface as well as for a device.

5.2.8. Nominal Voltage Range

 The standard must provide means for reporting the nominal voltage
 range for each Power Interface.

5.2.9. Nominal AC Frequency

 The standard must provide means for reporting the nominal AC
 frequency for each Power Interface.

5.2.10. Number of AC Phases

 The standard must provide means for reporting the number of AC phases
 for each Power Interface.

5.3. Power

 Power is measured as an instantaneous value or as the average over a
 time interval.
 Obtaining highly accurate values for power and energy may be costly
 if dedicated metering hardware is required.  Entities without the
 ability to measure with high accuracy their power, received energy,
 and provided energy may just report estimated values, for example,
 based on load monitoring, Power State, or even just the entity type.
 Depending on how power and energy values are obtained, the confidence
 in a reported value and its accuracy will vary.  Entities reporting
 such values should qualify the confidence in the reported values and

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 quantify the accuracy of measurements.  For reporting accuracy, the
 accuracy classes specified in IEC 62053-21 [IEC.62053-21] and
 IEC 62053-22 [IEC.62053-22] should be considered.
 Further properties of the power supplied to a device are also of
 interest.  For AC power supply in particular, several Power
 Attributes beyond the real power are of potential interest to Energy
 Management Systems.  The set of these properties includes the complex
 Power Attributes (apparent power, reactive power, and phase angle of
 the current or power factor) as well as the actual voltage, the
 actual AC frequency, the Total Harmonic Distortion (THD) of voltage
 and current, and the impedance of an AC phase or of the DC supply.  A
 new standard for monitoring these Power Attributes should be in line
 with already-existing standards, such as [IEC.61850-7-4].
 For some network management tasks, it is desirable to receive
 notifications from entities when their power value exceeds or falls
 below given thresholds.

5.3.1. Real Power / Power Factor

 The standard must provide means for reporting the real power for each
 Power Interface as well as for an entity.  Reporting power includes
 reporting the direction of power flow.

5.3.2. Power Measurement Interval

 The standard must provide means for reporting the corresponding time
 or time interval for which a power value is reported.  The power
 value can be measured at the corresponding time or averaged over the
 corresponding time interval.

5.3.3. Power Measurement Method

 The standard must provide means to indicate the method used to obtain
 these values.  Based on how the measurement was conducted, it is
 possible to associate a certain degree of confidence with the
 reported power value.  For example, there are methods of measurement
 such as direct power measurement, estimation based on performance
 values, or hard-coding average power values for an entity.

5.3.4. Accuracy of Power and Energy Values

 The standard must provide means for reporting the accuracy of
 reported power and energy values.

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5.3.5. Actual Voltage and Current

 The standard must provide means for reporting the actual voltage and
 actual current for each Power Interface as well as for a device.  For
 AC power supply, means must be provided for reporting the actual
 voltage and actual current per phase.

5.3.6. High-Power/Low-Power Notifications

 The standard must provide means for creating notifications if power
 values of an entity rise above or fall below given thresholds.

5.3.7. Complex Power / Power Factor

 The standard must provide means for reporting the complex power for
 each Power Interface and for each phase at a Power Interface.  In
 addition to the real power, at least two of the following three
 quantities need to be reported: apparent power, reactive power, and
 phase angle.  The phase angle can be substituted by the power factor.

5.3.8. Actual AC Frequency

 The standard must provide means for reporting the actual AC frequency
 for each Power Interface.

5.3.9. Total Harmonic Distortion

 The standard must provide means for reporting the Total Harmonic
 Distortion (THD) of voltage and current for each Power Interface.
 For AC power supply, means must be provided for reporting the THD per
 phase.

5.3.10. Power Supply Impedance

 The standard must provide means for reporting the impedance of a
 power supply for each Power Interface.  For AC power supply, means
 must be provided for reporting the impedance per phase.

5.4. Power State

 Many entities have a limited number of discrete Power States.
 There is a need to report the actual Power State of an entity and to
 provide the means for retrieving the list of all supported Power
 States.

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 Different standards bodies have already defined sets of Power States
 for some entities, and others are creating new Power State sets.  In
 this context, it is desirable that the standard support many of these
 Power State standards.  In order to support multiple management
 systems that possibly use different Power State sets while
 simultaneously interfacing with a particular entity, the Energy
 Management System must provide means for supporting multiple Power
 State sets used simultaneously at an entity.
 Power States have parameters that describe their properties.  It is
 required to have a standardized means for reporting some key
 properties, such as the typical power of an entity in a certain
 state.
 There is also a need to report statistics on Power States, including
 the time spent as well as the received and provided energy in a Power
 State.

5.4.1. Actual Power State

 The standard must provide means for reporting the actual Power State
 of an entity.

5.4.2. List of Supported Power States

 The standard must provide means for retrieving the list of all
 potential Power States of an entity.

5.4.3. Multiple Power State Sets

 The standard must provide means for supporting multiple Power State
 sets simultaneously at an entity.

5.4.4. List of Supported Power State Sets

 The standard must provide means for retrieving the list of all Power
 State sets supported by an entity.

5.4.5. List of Supported Power States within a Set

 The standard must provide means for retrieving the list of all
 potential Power States of an entity for each supported Power State
 set.

5.4.6. Typical Power Per Power State

 The standard must provide means for retrieving the typical power for
 each supported Power State.

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5.4.7. Power State Statistics

 The standard must provide means for monitoring statistics per Power
 State, including the total time spent in a Power State, the number of
 times each state was entered, and the last time each state was
 entered.  More Power State statistics are addressed by the
 requirements in Section 5.5.3.

5.4.8. Power State Changes

 The standard must provide means for generating a notification when
 the actual Power State of an entity changes.

5.5. Energy

 The monitoring of electrical energy received or provided by an entity
 is a core function of Energy Management.  Since energy is an
 accumulated quantity, it is always reported for a certain interval of
 time.  This can be, for example, the time from the last restart of
 the entity to the reporting time, the time from another past event to
 the reporting time, the last given amount of time before the
 reporting time, or a certain interval specified by two timestamps in
 the past.
 It is useful for entities to record their received and provided
 energy per Power State and report these quantities.

5.5.1. Energy Measurement

 The standard must provide means for reporting measured values of
 energy and the direction of the energy flow received or provided by
 an entity.  The standard must also provide the means to report the
 energy passing through each Power Interface.

5.5.2. Time Intervals

 The standard must provide means for reporting the time interval for
 which an energy value is reported.

5.5.3. Energy Per Power State

 The standard must provide means for reporting the received and
 provided energy for each individual Power State.  This extends the
 requirements on Power State statistics described in Section 5.4.7.

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5.6. Battery State

 Batteries are special entities that supply power.  The status of
 these batteries is typically controlled by automatic functions that
 act locally on the entity, and manually by users of the entity.
 There is a need to monitor the battery status of these entities by
 network management systems.
 Devices containing batteries can be modeled in two ways.  The entire
 device can be modeled as a single entity on which energy-related
 information is reported, or the battery can be modeled as an
 individual entity for which energy-related information is monitored
 individually according to requirements in Sections 5.1 through 5.5.
 Further information on batteries is of interest for Energy
 Management, such as the current charge of the battery, the number of
 completed charging cycles, the charging state of the battery, its
 temperature, and additional static and dynamic battery properties.
 It is desirable to receive notifications if the charge of a battery
 becomes very low or if a battery needs to be replaced.

5.6.1. Battery Charge

 The standard must provide means for reporting the current charge of a
 battery, in units of milliampere-hours (mAh).

5.6.2. Battery Charging State

 The standard must provide means for reporting the charging state
 (charging, discharging, etc.) of a battery.

5.6.3. Battery Charging Cycles

 The standard must provide means for reporting the number of completed
 charging cycles of a battery.

5.6.4. Actual Battery Capacity

 The standard must provide means for reporting the actual capacity of
 a battery.

5.6.5. Actual Battery Temperature

 The standard must provide means for reporting the actual temperature
 of a battery.

Quittek, et al. Informational [Page 18] RFC 6988 Requirements for Energy Management September 2013

5.6.6. Static Battery Properties

 The standard must provide means for reporting static properties of a
 battery, including the nominal capacity, the number of cells, the
 nominal voltage, and the battery technology.

5.6.7. Low Battery Charge Notification

 The standard must provide means for generating a notification when
 the charge of a battery decreases below a given threshold.  Note that
 the threshold may depend on the battery technology.

5.6.8. Battery Replacement Notification

 The standard must provide means for generating a notification when
 the number of charging cycles of a battery exceeds a given threshold.

5.6.9. Multiple Batteries

 If the battery technology allows, the standard must provide means for
 meeting requirements in Sections 5.6.1 through 5.6.8 for each
 individual battery contained in a single entity.

5.7. Time Series of Measured Values

 For some network management tasks, obtaining time series of measured
 values from entities, such as power, energy, battery charge, etc., is
 required.
 In general, time series measurements could be obtained in many
 different ways.  Means should be provided to either push such values
 from the location where they are available to the management system
 or to have them stored locally for a sufficiently long period of time
 such that a management system can retrieve the full time series.
 The following issues are to be considered when designing time series
 measurement and reporting functions:
 1.  Which quantities should be reported?
 2.  Which time interval type should be used (total, delta, sliding
     window)?
 3.  Which measurement method should be used (sampled, continuous)?
 4.  Which reporting model should be used (push or pull)?

Quittek, et al. Informational [Page 19] RFC 6988 Requirements for Energy Management September 2013

 The most discussed and probably most needed quantity is energy.  But
 a need for others, such as power and battery charge, can be
 identified as well.
 There are three time interval types under discussion for accumulated
 quantities such as energy.  They can be reported as total values,
 accumulated between the last restart of the measurement and a certain
 timestamp.  Alternatively, energy can be reported as delta values
 between two consecutive timestamps.  Another alternative is reporting
 values for sliding windows as specified in [IEC.61850-7-4].
 For non-accumulative quantities, such as power, different measurement
 methods are considered.  Such quantities can be reported using values
 sampled at certain timestamps or, alternatively, by mean values for
 these quantities averaged between two (consecutive) timestamps or
 over a sliding window.
 Finally, time series can be reported using different reporting
 models, particularly push-based or pull-based.  Push-based reporting
 can, for example, be realized by reporting power or energy values
 using the IP Flow Information Export (IPFIX) protocol [RFC7011]
 [RFC7012].  The Simple Network Management Protocol (SNMP) [RFC3411]
 is an example of a protocol that can be used for realizing pull-based
 reporting of time series.
 For reporting time series of measured values, the following
 requirements have been identified.  Further decisions concerning
 issues discussed above need to be made when developing concrete
 Energy Management standards.

5.7.1. Time Series of Energy Values

 The standard must provide means for reporting time series of energy
 values.  If the comparison of time series between multiple entities
 is required, then time synchronization between those entities must be
 provided (for example, with the Network Time Protocol [RFC5905]).

5.7.2. Time Series Interval Types

 The standard must provide means for supporting alternative interval
 types.  The requirement in Section 5.5.2 applies to every reported
 time value.

5.7.3. Time Series Storage Capacity

 The standard should provide means for reporting the number of values
 of a time series that can be stored for later reporting.

Quittek, et al. Informational [Page 20] RFC 6988 Requirements for Energy Management September 2013

6. Control of Entities

 Many entities control their Power State locally.  Other entities need
 interfaces for an Energy Management System to control their Power
 State.
 A power supply is typically not self-managed by devices, and control
 of a power supply is typically not conducted as an interaction
 between an Energy Management System and the device itself.  It is
 rather an interaction between the management system and a device
 providing power at its Power Outlets.  Similar to Power State
 control, power supply control may be policy driven.  Note that
 shutting down the power supply abruptly may have severe consequences
 for the device.

6.1. Controlling Power States

 The standard must provide means for setting Power States of entities.

6.2. Controlling Power Supply

 The standard must provide means for switching a power supply off or
 turning a power supply on at Power Interfaces providing power to one
 or more devices.

7. Reporting on Other Entities

 As discussed in Section 5, not all energy-related information may be
 available at the entity in question.  Such information may be
 provided by other entities.  This section covers only the reporting
 of information.  See Section 8 for requirements on controlling other
 entities.
 There are cases where a power supply unit switches power for several
 entities by turning power on or off at a single Power Outlet or where
 a power meter measures the accumulated power of several entities at a
 single power line.  Consequently, it should be possible to report
 that a monitored value does not relate to just a single entity but is
 an accumulated value for a set of entities.  All of the entities
 belonging to that set need to be identified.

7.1. Reports on Other Entities

 The standard must provide means for an entity to report information
 on another entity.

Quittek, et al. Informational [Page 21] RFC 6988 Requirements for Energy Management September 2013

7.2. Identity of Other Entities on Which Information Is Reported

 For entities that report on one or more other entities, the standard
 must provide means for reporting the identity of other entities on
 which information is reported.  Note that, in some situations, a
 manual configuration might be required to populate this information.

7.3. Reporting Quantities Accumulated over Multiple Entities

 The standard must provide means for reporting the list of all
 entities from which contributions are included in an accumulated
 value.

7.4. List of All Entities on Which Information Is Reported

 For entities that report on one or more other entities, the standard
 must provide means for reporting the complete list of all those
 entities on which energy-related information can be reported.

7.5. Content of Reports on Other Entities

 For entities that report on one or more other entities, the standard
 must provide means for indicating what type or types of energy-
 related information can be reported, and for which entities.

8. Controlling Other Entities

 This section specifies requirements for controlling Power States and
 power supply of entities by communicating with other entities that
 have the means for doing that control.

8.1. Controlling Power States of Other Entities

 Some entities have control over Power States of other entities.  For
 example, a gateway to a building system may have the means to control
 the Power State of entities in the building that do not have an IP
 interface.  For this scenario and other similar cases, a way to make
 this control accessible to the Energy Management System is needed.
 In addition, it is required that an entity that has its state
 controlled by other entities has the means to report the list of
 these other entities.

Quittek, et al. Informational [Page 22] RFC 6988 Requirements for Energy Management September 2013

8.1.1. Control of Power States of Other Entities

 The standard must provide means for an Energy Management System to
 send Power State control commands to an entity that controls the
 Power States of entities other than the entity to which the command
 was sent.

8.1.2. Identity of Other Power State Controlled Entities

 The standard must provide means for reporting the identities of the
 entities for which the reporting entity has the means to control
 their Power States.  Note that, in some situations, a manual
 configuration might be required to populate this information.

8.1.3. List of All Power State Controlled Entities

 The standard must provide means for an entity to report the list of
 all entities for which it can control the Power State.

8.1.4. List of All Power State Controllers

 The standard must provide means for an entity that receives commands
 controlling its Power State from other entities to report the list of
 all those entities.

8.2. Controlling Power Supply

 Some entities may have control of the power supply of other entities,
 for example, because the other entity is supplied via a Power Outlet
 of the entity.  For this and similar cases, means are needed to make
 this control accessible to the Energy Management System.  This need
 is already addressed by the requirement in Section 6.2.
 In addition, it is required that an entity that has its supply
 controlled by other entities has the means to report the list of
 these other entities.  This need is already addressed by requirements
 in Sections 5.2.3 and 5.2.4.

9. Security Considerations

 Controlling Power State and power supply of entities are considered
 highly sensitive actions, since they can significantly affect the
 operation of directly and indirectly connected devices.  Therefore,
 all control actions addressed in Sections 6 and 8 must be
 sufficiently protected through authentication, authorization, and
 integrity protection mechanisms.

Quittek, et al. Informational [Page 23] RFC 6988 Requirements for Energy Management September 2013

 Entities that are not sufficiently secure to operate directly on the
 public Internet do exist and can be a significant cause of risk, for
 example, if the remote control functions described in Sections 6 and
 8 can be exercised on those devices from anywhere on the Internet.
 The standard needs to provide means for dealing with such cases.  One
 solution is providing means that allow the isolation of such devices,
 e.g., behind a sufficiently secured gateway.  Another solution is to
 allow compliant implementations to disable sensitive functions, or to
 not implement such functions at all.
 The monitoring of energy-related quantities of an entity as addressed
 in Sections 5 through 8 can be used to derive more information than
 just the received and provided energy; therefore, monitored data
 requires protection.  This protection includes authentication and
 authorization of entities requesting access to monitored data as well
 as confidentiality protection during transmission of monitored data.
 Privacy of stored data in an entity must be taken into account.
 Monitored data may be used as input to control, accounting, and other
 actions, so integrity of transmitted information and authentication
 of the origin may be needed.

9.1. Secure Energy Management

 The standard must provide privacy, integrity, and authentication
 mechanisms for all actions addressed in Sections 5 through 8.  The
 security mechanisms must meet the security requirements detailed in
 Section 1.4 of [RFC3411].

9.2. Isolation of Insufficiently Secure Entities

 The standard must provide means to allow the isolation of entities
 that are not sufficiently secure to operate on the public Internet,
 e.g., behind a gateway that implements sufficient security that the
 vulnerable entities are not directly exposed to the Internet.

9.3. Optional Restriction of Functions

 The standard must allow compliant implementations to disable
 sensitive functions, or to not implement such functions at all, when
 operating in environments that are not sufficiently secured.  This
 applies particularly to the control functions described in Sections 6
 and 8.

Quittek, et al. Informational [Page 24] RFC 6988 Requirements for Energy Management September 2013

10. Acknowledgments

 The authors would like to thank Ralf Wolter for his first essay on
 this document.  Many thanks to William Mielke, John Parello,
 JinHyeock Choi, Georgios Karagiannis, and Michael Suchoff for their
 helpful comments on the document.  Many thanks to Stephen Farrell,
 Robert Sparks, Adrian Farrel, Barry Leiba, Brian Haberman, Peter
 Resnick, Sean Turner, Stewart Bryant, and Ralph Droms for their IESG
 reviews.  Finally, special thanks to the document shepherd, Nevil
 Brownlee, and to the EMAN working group chairs: Nevil Brownlee and
 Bruce Nordman.

11. References

11.1. Normative References

 [ANSI-TIA-1057]
            Telecommunications Industry Association, ANSI-
            TIA-1057-2006, "TIA Standard -- Telecommunications -- IP
            Telephony Infrastructure -- Link Layer Discovery Protocol
            for Media Endpoint Devices", April 2006.
 [IEC.61850-7-4]
            International Electrotechnical Commission, "Communication
            networks and systems for power utility automation --
            Part 7-4: Basic communication structure -- Compatible
            logical node classes and data object classes", March 2010.
 [IEC.62053-21]
            International Electrotechnical Commission, "Electricity
            metering equipment (a.c.) -- Particular requirements --
            Part 21: Static meters for active energy (classes 1
            and 2)", January 2003.
 [IEC.62053-22]
            International Electrotechnical Commission, "Electricity
            metering equipment (a.c.) -- Particular requirements --
            Part 22: Static meters for active energy (classes 0,2 S
            and 0,5 S)", January 2003.
 [IEEE-100] IEEE, "The Authoritative Dictionary of IEEE Standards
            Terms, IEEE 100, Seventh Edition", December 2000.
 [IEEE-1621]
            Institute of Electrical and Electronics Engineers,
            "IEEE 1621-2004 - IEEE Standard for User Interface
            Elements in Power Control of Electronic Devices Employed
            in Office/Consumer Environments", 2004.

Quittek, et al. Informational [Page 25] RFC 6988 Requirements for Energy Management September 2013

 [IEEE-802.1AB]
            IEEE Computer Society, "IEEE Std 802.1AB-2009 -- IEEE
            Standard for Local and Metropolitan Area Networks --
            Station and Media Access Control Discovery",
            September 2009.
 [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
            Architecture for Describing Simple Network Management
            Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
            December 2002.
 [RFC3621]  Berger, A. and D. Romascanu, "Power Ethernet MIB",
            RFC 3621, December 2003.
 [RFC6933]  Bierman, A., Romascanu, D., Quittek, J., and M.
            Chandramouli, "Entity MIB (Version 4)", RFC 6933,
            May 2013.

11.2. Informative References

 [EMAN-STATEMENT]
            Schoening, B., Chandramouli, M., and B. Nordman, "Energy
            Management (EMAN) Applicability Statement", Work in
            Progress, April 2013.
 [IEC.60050]
            International Electrotechnical Commission, "Electropedia:
            The World's Online Electrotechnical Vocabulary", 2013,
            <http://www.electropedia.org/iev/iev.nsf/
            welcome?openform>.
 [ITU-M.3400]
            International Telecommunication Union, "ITU-T
            Recommendation M.3400 -- Series M: TMN and Network
            Maintenance: International Transmission Systems, Telephone
            Circuits, Telegraphy, Facsimile and Leased Circuits --
            Telecommunications Management Network - TMN management
            functions", February 2000.
 [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
            "Specification of the IP Flow Information Export (IPFIX)
            Protocol for the Exchange of Flow Information", STD 77,
            RFC 7011, September 2013.
 [RFC7012]  Claise, B., Ed., and B. Trammell, Ed., "Information Model
            for IP Flow Information Export (IPFIX)", RFC 7012,
            September 2013.

Quittek, et al. Informational [Page 26] RFC 6988 Requirements for Energy Management September 2013

 [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
            Time Protocol Version 4: Protocol and Algorithms
            Specification", RFC 5905, June 2010.

Authors' Addresses

 Juergen Quittek (editor)
 NEC Europe Ltd.
 NEC Laboratories Europe
 Network Research Division
 Kurfuersten-Anlage 36
 Heidelberg  69115
 Germany
 Phone: +49 6221 4342-115
 EMail: quittek@neclab.eu
 Mouli Chandramouli
 Cisco Systems, Inc.
 Sarjapur Outer Ring Road
 Bangalore
 India
 Phone: +91 80 4426 3947
 EMail: moulchan@cisco.com
 Rolf Winter
 NEC Europe Ltd.
 NEC Laboratories Europe
 Network Research Division
 Kurfuersten-Anlage 36
 Heidelberg  69115
 Germany
 Phone: +49 6221 4342-121
 EMail: Rolf.Winter@neclab.eu

Quittek, et al. Informational [Page 27] RFC 6988 Requirements for Energy Management September 2013

 Thomas Dietz
 NEC Europe Ltd.
 NEC Laboratories Europe
 Network Research Division
 Kurfuersten-Anlage 36
 Heidelberg  69115
 Germany
 Phone: +49 6221 4342-128
 EMail: Thomas.Dietz@neclab.eu
 Benoit Claise
 Cisco Systems, Inc.
 De Kleetlaan 6a b1
 Diegem  1831
 Belgium
 Phone: +32 2 704 5622
 EMail: bclaise@cisco.com

Quittek, et al. Informational [Page 28]

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