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A Framework for Energy Aware Control Planes
draft-retana-rtgwg-eacp-06

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Authors Alvaro Retana , Russ White , Manuel Paul
Last updated 2023-02-22
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draft-retana-rtgwg-eacp-06
Routing Area Working Group                                     A. Retana
Internet-Draft                              Futurewei Technologies, Inc.
Intended status: Informational                                  R. White
Expires: 26 August 2023                              Akamai Technologies
                                                                 M. Paul
                                                     Deutsche Telekom AG
                                                        22 February 2023

              A Framework for Energy Aware Control Planes
                       draft-retana-rtgwg-eacp-06

Abstract

   Energy is a primary constraint in large-scale network design,
   particularly in cloud-scale data center fabrics.  While compute and
   storage clearly consume the largest amounts of energy in large-scale
   networks, the optics and electronics used in transporting data also
   contribute to energy usage and heat generation.

   This document provides an overview of various areas of concern in the
   interaction between network performance and efforts at energy aware
   control planes, as a guide for those working on modifying current
   control planes or designing new ones to improve the energy efficiency
   of high density, highly complex, network deployments.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 26 August 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Business Drivers  . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Application Drivers . . . . . . . . . . . . . . . . . . .   4
   3.  Framework . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Example Network . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Modes of Reducing Energy Usage  . . . . . . . . . . . . .   6
     3.3.  Global Versus Local Decisions . . . . . . . . . . . . . .   7
   4.  Considerations  . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Energy Efficiency and Bandwidth Reduction . . . . . . . .   8
     4.2.  Energy Efficiency and Stretch . . . . . . . . . . . . . .   9
     4.3.  Energy Efficiency and Fast Recovery . . . . . . . . . . .  10
     4.4.  Energy Efficiency and Microsleeps . . . . . . . . . . . .  11
     4.5.  Other Operational Aspects . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The availability of low-cost energy sources, provisioning energy
   sources, and handling the heat generation from processing and
   transporting data are determining factors in the siting, development,
   and operation of large-scale data centers.  The rise of edge
   computing, 5G, and diversified compute is causing the importance of
   understanding and reducing energy usage in networks to become
   increasingly important.

   As with all network and protocol design, however, reducing energy use
   represents a tradeoff.  In the case of networks, increasing energy
   efficiency can result in a loss of optimization in network operations
   in other areas.  These kinds of tradeoffs can be described in terms
   of the state/optimization/surface triad; increasing local

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   optimization in one area, energy consumption, can result in global
   sub-optimization through increased state, more complex interaction
   surfaces, or even suboptimal global energy usage.

   This document provides background information and a framework for
   understanding the tradeoffs between modifications made to network
   control plane protocols to conserve energy and network performance.
   This document also makes suggestions to designers and implementers of
   modifications intended to enable energy conservation in networks.
   The intent of this document is to encourage work in the area of
   reducing network energy usage through protocol design, network
   design, and network operations.

   The document is organized as follows.  Section 2 provides material
   the reader needs to understand to appreciate the challenges inherent
   in balancing energy reduction with effective network performance.
   This section includes subsections considering the application and
   business requirements that are the basis of the reset of the
   document.  Section 3 provides a framework for understanding common
   mechanisms in energy management schemes.  Section 4 provides an
   analysis of the areas highlighted, including an explanation of how
   the specific area interacts with energy management, an example of the
   interaction, and, finally, a set of considerations for protocol
   designers when proposing either new protocols or modifications to
   existing protocols to reduce energy usage.

2.  Background

   This section describes the underlying business and application
   drivers for the considerations sections.

2.1.  Scope

   Radio based networks designed for rapid deployment for highly mobile
   users (often called Mobile Ad Hoc Networks [RFC2501]), and sensor
   networks designed using devices with limited power, memory, and
   processing resources [RFC7102], are not the target of this document.
   Readers should refer to the groups working within those areas for
   energy management requirements based on those specialized
   environments.  While protocol developers for those environments may
   draw useful information from this document, this work is not intended
   to address those specialized networks specifically.  Mobile cellular
   networks however are similarly affected by excess energy consumption
   as wireline networks and seek to save energy by methods such as the
   ones described in [SDO-3GPP.25.927].

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   Inter-domain applications require more work in policy than in
   technical and business considerations, and therefore fall outside the
   scope of this document.  Intra-domain control planes are
   (intuitively) where most energy savings will be attained, at any
   rate.  Most high concentrations of routers, such as data centers and
   campus networks, are under a single administrative domain.
   Therefore, placing inter-domain control planes outside the scope of
   this document does not limit its usefulness in any meaningful way.

   Energy monitoring deals with the collection of information related to
   energy utilization and its characteristics, and energy control
   relates to directly influencing the optimization and/or efficiency of
   devices in the network [RFC7326].  The focus of this document is on
   understanding the tradeoffs between modifications made to network
   protocols to conserve energy and network performance metrics, rather
   than functions, steps or procedures required for energy monitoring or
   control.

2.2.  Business Drivers

   Networks are driven by organizational, application specific, and
   general connectivity requirements.  Organizational requirements
   include capital and operational expense, and the restrictions the
   network architecture places on the growth and operation of the
   organization.  The interaction between the network and organization
   is managed through change management, availability, and network
   agility (the ability to quickly support or shed application demands
   on the network).

   Modifying control planes to support energy awareness impacts capital
   and operational expenses primarily through tradeoffs against
   availability, and potentially through network agility.

2.3.  Application Drivers

   Applications drivers provide the background for each of the technical
   sections below.  While network operators and protocol designers need
   to pay attention to a wide array of factors when considering how best
   to support specific applications, this document focuses on factors
   with broad impact.  The first two questions involve bandwidth: how
   much bandwidth will the application consume, and is this bandwidth
   consumption fairly steady, or highly variable?  For instance,
   applications such as streaming video tend to have long lasting flows
   with high bandwidth requirements, file transfers tend to produce
   shorter flows requiring high bandwidth, and HTML traffic tends to be
   bursty, with much lower bandwidth requirements.

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   The next question a protocol or network designer might ask about a
   specific application is its tolerance to jitter.  Real time
   applications, such as voice and video conferencing, have a very low
   toleration for jitter.  File transfers and streaming video, on the
   other hand, can often handle large variations in packet arrival
   times.  If packets are delayed long enough, the application may
   actually time out, shutting down sessions.  Users will often "hang
   up" after a short period of time, as well, causing loss of revenue
   and productivity.

   Delay is another crucial factor in the performance of many
   applications.  Many server virtualization protocols, for instance,
   have very low tolerance for delay, having been written with
   connectivity through a short wire local broadcast segment in mind.
   Applications such as stock and commodity trading, remote medical, and
   collaborative video editing also exhibit very little tolerance for
   delay.  Applications built on a microservices model will often
   exhibit deep performance loss when running over a network with high
   or variable delay.

   Variable delay, or jitter, is another factor which broadly impacts
   application performance.  Networks with high jitter require longer
   flow and error control timeouts, reducing application performance.

   Control plane convergence events can cause jitter in traffic flows
   through the network.  Changing the number of hops through the network
   (an increase or reduction in stretch) will cause the delay through
   the network to vary, which is perceived by the application as jitter.
   The selection of a suboptimal route by the control plane, for
   instance through the introduction of aggregation or summarization of
   reachability information, or the selection of a more heavily loaded
   link over a more likely loaded one, can increase the number of hops
   traffic takes through the network, or select a path with more deeply
   filled queues.  Either of these can cause traffic to pass through the
   network more slowly, which is perceived by the application as delay.

   Jitter and delay can also be introduced directly into the packet
   stream by reducing the throughput of individual links, or putting
   devices and/or links into energy reduced modes for very short periods
   of time (microsleeps).  If a link is asleep when the first and third
   packets from a flow arrive at the head end of the link, and not when
   the second packet from that same flow arrives, each packet is going
   to be processed differently, and hence will have a different delay
   across the path.

   The following sections address bandwidth reduction, increasing
   stretch, network convergence, and introducing jitter through
   microsleeps, in more detail.

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3.  Framework

   This section contains a sample network which is used throughout the
   rest of this document, considers some ways in which energy usage can
   be reduced, and provides some examples.

3.1.  Example Network

   To illustrate the impacts of link and device removal throughout the
   rest of this document, the following network is used.

                            /--R2--R6--\  /---\
                          R1            R4     R5
                            \----R3----/  \---/

   This network is overly simplistic so the impact of removing various
   links and devices from the topology can be more clearly illustrated.
   More complex topologies will often exhibit these same effects in less
   obvious, and harder to understand, ways.

3.2.  Modes of Reducing Energy Usage

   There are four primary ways in which energy usage can be reduced:

   *  Removing redundant links from the network topology; for instance,
      one of the two parallel links between R4 and R5 may be removed

   *  Removing redundant network equipment from the network topology;
      for instance, R2 and R6, along with their associated links, may be
      removed

   *  Reducing the amount of time equipment or links are operational;
      for instance, one of the two parallel links between R4 and R5 may
      be shut down during time periods when the traffic flow through the
      network is not large enough to justify operating both links

   *  Reducing the link speed or processing rate of equipment; for
      instance, the speed of the two links between R4 and R5 may be
      reduced during time periods when the traffic through the network
      is not large enough to justify making some higher amount of
      bandwidth available

   Completely removing nodes or links from the network topology has
   several impacts on the control plane which must be considered.  In
   these cases, the control plane must:

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   *  Modify the network topology so removed links or devices are not
      used to forward traffic

   *  Remember that such links exist, possibly including the neighbors
      and destinations reachable through them

3.3.  Global Versus Local Decisions

   It is often tempting to optimize for local conditions while ignoring
   system-level results, or to optimize system-level conditions while
   ignoring local results.  Both of these, however, are often a mistake.
   The former extreme might be illustrated in a system where two nodes
   measure local link utilization, shutting down any interconnecting
   links when the utilization percentage drops below a certain level.
   In such a system, pairs of adjacent devices may decide to shut down a
   set of links which leaves no available path (or insufficient
   bandwidth) through the network as a system.  An example of the latter
   might be a system where every node in the network must agree to shut
   down a link before the link can be disabled for energy conservation.
   In this case, a false perception of overall system health caused by
   timing issues could cause a lack of local optimizations to take
   place.

   There are some considerations and tradeoffs which need to be outlined
   in considering the global versus local decisions in relation to
   energy efficiency.  System designers should take note of the
   difficulties with preventing pathological conditions when purely
   localized decisions are made.  For instance, in the example network,
   assume R1 determines to put the R1->R2 link into an energy saving
   mode, while R4 determines to put the R4->R3 link into an energy
   saving mode.  In this case, no path will remain available through the
   network.  It is also possible for the opposite to occur, that is for
   no links or devices to be placed into a reduced energy state because
   R1 and R4 don't agree through the control plane which links and
   devices should be removed from the topology.

   Protocol designers should consider these tradeoffs in proposals for
   energy aware control planes.

4.  Considerations

   Each subsection considers a single energy saving mechanism in detail.

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4.1.  Energy Efficiency and Bandwidth Reduction

   Bandwidth is an important consideration in high density networks;
   data center fabrics, for instance, are designed to provide a specific
   amount of bandwidth, often with relatively fixed delay and jitter,
   into and out of each server and to facilitate virtual server movement
   among physical devices.  In campus and core networks bandwidth is
   finely coupled with quality of service guarantees for applications
   and services.  It should be obvious that removing links or devices
   from a network topology will adversely affect the amount of available
   bandwidth, which could, in turn, cause well thought out quality of
   service mechanisms to degrade or fail.

   What might not be so obvious is the relationship between available
   bandwidth and jitter (or other network quality of service measures).
   If higher speed links are removed from the topology in order to
   continue using lower speed (and therefore presumably lower power)
   links, then serialization delays will have a larger impact on traffic
   flow.  Longer serialization delays can cause input queues to back up,
   which impacts not only delay but jitter, and possibly even traffic
   delivery.

4.1.1.  An Example of Lowering Bandwidth by Removing Parallel Links

   In the network illustrated above, one of the two links between R4 and
   R5 could be an obvious candidate for removal from the network,
   especially if the network load can easily be transferred to the
   remaining link without failure.  There can be multiple negative
   impacts from the perspective of optimal traffic flow, among which
   could be the mixing of different kinds of flows with multiple quality
   of service requirements.

   If, for instance, a flow carrying voice data is mixed with a large
   file transfer, the mixed queueing of traffic with two different
   classes of service could cause variable delay (jitter), reducing
   application performance.

4.1.2.  Considerations

   Modifications to control plane protocols to achieve network energy
   efficiency should provide the ability to set the minimal bandwidth,
   jitter, and delay through the network, and not shut down links or
   devices that would violate those minimal requirements.

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4.2.  Energy Efficiency and Stretch

   In any given network, there is a shortest path between any source and
   any destination.  Network protocols discover these paths from the
   destination's perspective --routing draws traffic along a path,
   rather than driving along a path.  Along with the shortest path,
   there are a number of paths that can also carry traffic from a given
   source to a given destination without the packets passing along the
   same logical link, or through the same logical device, more than
   once.  These are considered loop-free alternate [RFC5714] paths.

   The primary difference between the shortest path and the loop-free
   alternate paths is the total cost of using the path.  In simple
   terms, this difference can be calculated as the number of links and
   devices a packet must pass through when being carried from the source
   to the destination, or the hop count.  While most networks use much
   more sophisticated metrics based on bandwidth, congestion, and other
   factors, the hop count of the path a flow takes through the network
   is a convenient measure of path efficiency.

   When the control plane causes traffic to pass from the source to the
   destination along a path which is longer than the shortest path, the
   network is said to have stretch (see [Krioukov] for a more in depth
   explanation of network stretch).  To measure stretch, simply subtract
   the metric of the shortest path from the metric of the longer path.
   For example, in hop count terms, if the best path is three hops, and
   the current path is four hops, the network exhibits a stretch of 1.

4.2.1.  An Example of Stretch

   In the network illustrated above, if a modification is made to the
   control plane to remove the link between R1 and R3 in order to save
   energy, all the destinations shown in the diagram remain reachable.
   However, from the perspective of R1, the best path available to reach
   R2 has increased in length by one hop.  The original path is
   R1->R3->R4->R5, the new path is R1->R2->R6->R4->R5.  This represents
   a stretch of 1.

   Along with this increased stretch will most likely also come
   increased delay through the network; each hop in the network
   represents a measurable amount of delay.  This increased stretch
   might also represent an increased amount of jitter, as there are more
   queues and more serialization events in the path of each packet
   carried.  There will also be the modifications in jitter as the
   network switches between the optimal performance configuration and an
   energy efficient configuration.

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4.2.2.  Considerations

   Designers who propose modifications to control plane protocols to
   achieve network energy efficiency should analyze the impact of their
   mechanisms on the stretch in typical network topologies, and should
   include such analysis when explaining the applicability of their
   proposals.  This analysis may include an examination of the absolute,
   or maximum, stretch caused by the modifications to the control plane
   as well as analysis at the 95th percentile, the average stretch
   increase in a given set of topologies, and/or the mean increase in
   stretch.

   Mechanisms that could impact the stretch of a network should provide
   the ability for the network administrator to limit the amount of
   stretch the network will encounter when moving into a more energy
   efficient mode.

4.3.  Energy Efficiency and Fast Recovery

   A final area where modifications to the control plane for energy
   efficiency is fast convergence or fast recovery.  Many networks are
   now designed to recover from failures quickly enough to only reult in
   a handful of traffic lost; recovery on the order of half a second is
   not an uncommon goal.  It should be obvious that removing redundant
   links and devices from the network to reduce energy consumption could
   adversely affect these goals.

4.3.1.  An Example of Impact on Fast Recovery

   In the network shown, assume R2 and its associated links are shut
   down in order to save energy.  The result is a one-connected network
   with no redundant link, impacting the resilience of the network to
   node and link failures.  It is possible to craft a mechanism that
   will bring devices and links which have been powered down or taken
   into a low-energy mode back into service, but these will necessarily
   require some startup time, which will impact the Mean Time to Repair
   (MTTR) enabled through the control plane.  This impact will appear to
   applications running over the network as extended jitter, and
   potentially the loss of packets.

   For these reasons, it may be that only links and devices which are a
   "third point of failure" may be acceptable as removal candidates in
   order to conserve energy.

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4.3.2.  Considerations

   Modifications to the control plane in order to remove links or nodes
   to conserve energy should entail the ability to choose the level of
   redundancy available after the network topology has been trimmed.
   For instance, it might be acceptable in some situations to move to
   single points of failure throughout the network, or in specific
   sections of the network, for certain periods of time.  In other
   situations, it may only be acceptable to reduce the network to a
   double point of failure, and never to a single point of failure.

4.4.  Energy Efficiency and Microsleeps

   Another mechanism to reduce energy usage in a network is to sleep
   links or devices for very short periods of time, called microsleeps.
   For instance, if a particular link is only used at 50% of the actual
   available bandwidth, it should be possible to place the link in some
   lower power state for 50% of the time, thus reducing energy usage by
   some percentage.  An example of one such mechanism is Energy-
   Efficient Ethernet [IEEE_802.3az_2010].

   Such schemes can introduce delay and jitter into the network path
   directly; if a packet arrives while the link is in a reduced energy
   state, it must wait until the link enters a normal operational mode
   before it can be forwarded.  Most of the time the proposed sleep
   states are so small as to be presumably inconsequential on overall
   packet delay, but multiple packets crossing a series of links, each
   encountering different links in different states, could take very
   different amounts of time to pass along the path.

   One possible way to resolve this somewhat random accrual of delays on
   a per packet basis is to coordinate these sleep states such that
   packets accepted at the entry of the network are consistently passed
   through the network when all links and devices are in a normal
   operating mode, and simply delaying all packets at the entry point
   into the network while the devices in the network are in an energy
   reduced state.  This solution still introduces some amount of jitter;
   some packets will be delayed by the sleep state at the edge of the
   network, while others will not.  This solution also requires
   coordinated timers at the speed of forwarding itself to effectively
   control the sleep and wake cycles of the network.

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4.4.1.  An Example of Microsleeps to Reduce Energy Usage

   In the example network, assume the bandwidth utilization along the
   path R1->R3->R4->R5 is 50% of the actual available bandwidth.  It is
   possible to consider a scheme where the R1->R3, R3->R4, and R4->R5
   links are all put into an energy reduced operational mode 50% of the
   time, since packets are only available to send 50% of the time.  A
   packet entering at R1 may encounter a short delay at the R1->R3,
   R3->R4, and R4->R5 links, or it might not.  Even if these delays are
   small, say 200ms at each hop, the accumulated delay through the
   network due to sleep states may be 0ms (all links and devices awake)
   or 600ms (all links and devices asleep) as the packet passes through
   the network.

   As network paths lengthen to more realistic path lengths in real
   deployments, the jitter introduced varies more widely, which could
   cause problems for the operation of a number of applications.

4.4.2.  Considerations

   Protocol designers should analyze the impact of accumulated jitter
   when proposing mechanisms that rely on microsleeps in either
   equipment or links.  This analysis should include both worst case and
   best case scenarios, as well as an analysis of how coordinated clocks
   are to be handled in the case of coordinated sleep states.

4.5.  Other Operational Aspects

   Modification of the network topology in order to save energy needs to
   consider the operational needs of the network as well as application
   requirements.  Change management, operational downtime, and business
   usage of the network need to be considered when determining which
   links and nodes should be placed into a low energy state.  Energy
   provisions have to be assigned and changed for nodes and links,
   optimally according to network usage profiles over the time of day.

   Control plane protocol operation, in terms of operational efficiency
   on the wire, also needs to be considered when modifying protocol
   parameters.  Any changes that negatively impact the operation of the
   protocol, in terms of the amount of traffic, the size of routing
   information transmitted over the network, and interaction with
   network management operations need to be carefully analyzed for
   scaling and operational implications.

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4.5.1.  An Example of Operational Impact

   Time of day is an important consideration in business operations.
   During normal operational hours, the network needs to be fully
   available, including all available redundancy and bandwidth.  During
   holidays, night hours, and other times when a campus might not be
   used, or when there are lower traffic and resiliency demands on the
   network, network elements can be removed to reduce energy usage.

4.5.2.  Considerations

   Protocol designers should analyze operational requirements, such as
   time of day and network traffic load considerations, and explain how
   proposed protocols or modifications to protocols will interact with
   them.  Protocols designers should analyze increases in network
   traffic and the operational efficiency impact of proposed changes or
   protocols.

5.  Security Considerations

   This document provides an overview of various areas of concern in the
   interaction between network performance and the use of energy
   efficient control planes to improve the energy efficiency of a
   network.  As such, it doesn't introduce any new security risk.

   However, providing an API or other mechanism to dynamically modify
   available bandwidth, put devices in reduced energy states, and
   otherwise modify network behavior introduces surfaces along which
   attackers can use to deny effective service to critical applications.
   By reducing the amount of available bandwidth along a link by
   invoking energy saving mechanisms, for instance, an attacker could
   reduce the performance of an application, harming the interests of
   organizations relying on the network.

   Protocol designers should carefully consider the introduction of any
   potential vulverabilities as a result of the implementation of an
   energy aware control plane.

6.  IANA Considerations

   This document has no IANA actions.

7.  Acknowledgements

   The authors of this document would like to acknowledge the
   suggestions and ideas provided by Sujata Banerjee, Puneet Sharma,
   Dirk Von Hugo, and John Scudder.

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8.  References

8.1.  Informative References

   [IEEE_802.3az_2010]
              IEEE, "IEEE Standard for Information technology-- Local
              and metropolitan area networks-- Specific requirements--
              Part 3: CSMA/CD Access Method and Physical Layer
              Specifications Amendment 5: Media Access Control
              Parameters, Physical Layers, and Management Parameters for
              Energy-Efficient Ethernet", IEEE 802-3az-2010,
              DOI 10.1109/IEEESTD.2010.5621025, 11 July 2013,
              <https://ieeexplore.ieee.org/document/5621025>.

   [Krioukov] Krioukov, D., "On Compact Routing for the Internet", 2007,
              <http://www.caida.org/publications/papers/2007/
              compact_routing/>.

   [RFC2501]  Corson, S. and J. Macker, "Mobile Ad hoc Networking
              (MANET): Routing Protocol Performance Issues and
              Evaluation Considerations", RFC 2501,
              DOI 10.17487/RFC2501, January 1999,
              <https://www.rfc-editor.org/info/rfc2501>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <https://www.rfc-editor.org/info/rfc5714>.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <https://www.rfc-editor.org/info/rfc7102>.

   [RFC7326]  Parello, J., Claise, B., Schoening, B., and J. Quittek,
              "Energy Management Framework", RFC 7326,
              DOI 10.17487/RFC7326, September 2014,
              <https://www.rfc-editor.org/info/rfc7326>.

   [SDO-3GPP.25.927]
              3GPP and B. Prakash, "Solutions for energy saving within
              UTRA Node B", 3GPP TR 25.927 14.0.0, 25 March 2017,
              <http://www.3gpp.org/ftp/Specs/
              archive/25_series/25.927/25927-e00.zip>.

Authors' Addresses

   Alvaro Retana
   Futurewei Technologies, Inc.
   Email: aretana@futurewei.com

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   Russ White
   Akamai Technologies
   Email: russw@riw.us

   Manuel Paul
   Deutsche Telekom AG
   Email: Manuel.Paul@telekom.de

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