Internet Engineering Task Force                                 B. Zhang
Internet-Draft                                                    J. Shi
Intended status: Informational                          Univ. of Arizona
Expires: April 18, 2014                                          J. Dong
                                                                M. Zhang
                                                            M. Boucadair
                                                          France Telecom
                                                        October 15, 2013

            Power-Aware Networks (PANET): Problem Statement


   Energy consumption of network infrastructures is growing fast due to
   exponential growth of data traffic and the deployment of increasingly
   powerful equipment.  There are emerging needs for power-aware routing
   and traffic engineering, which adapt routing paths to traffic load in
   order to reduce energy consumption network-wide.  This document
   outlines the design space and problem areas for potential IETF work.

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   This Internet-Draft will expire on August 29, 2013.

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   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Motivation and Problem Scope . . . . . . . . . . . . . . . . .  3
   3.  Potential Solution Approaches  . . . . . . . . . . . . . . . .  4
   4.  Problem Areas for IETF . . . . . . . . . . . . . . . . . . . .  6
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   6.  Informative References . . . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  9

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1.  Introduction

   Driven by exponential growth of Internet traffic, networks worldwide
   are expanding their infrastructures at a fast pace by deploying more
   high-capacity, power-hungry routers, which also leads to increasing
   energy consumption.  For example, in the US, the energy bill for
   powering the wired network reaches up to 2.4 billion dollars per year
   [Doverspike10].  Telecom Italia, the largest ISP in Italy, is now the
   second largest consumer of electricity after the National Railway
   system [Pileri07].  As one of the biggest energy consumers in the
   United Kingdom, British Telecom consumed about 0.7% of the entire
   nation's electricity in 2007 [Bolla11].  In Japan, predictions say
   that routers will consume 9% of the total electricity by 2015
   [Nakamura07].  Besides operational costs and environmental impacts,
   the ever-increasing energy consumption has become a limiting factor
   to long-term growth of network infrastructure due to challenges in
   power delivery and heat removal for both router components and
   hosting facilities [Gupta03] [Epps06].

   Traditionally energy efficiency is improved at the device level or
   the link level.  For example, energy management techniques can be
   applied to adjust router CPU's power status or CPU frequency in
   response to different CPU workload; Links can be put to sleep mode
   when it has been idle for a while.  More recently, there have been a
   number of research work that look beyond a single router or linecard
   for network-wide solutions towards energy proportionality.

   The purpose of this document is to discuss the problem scope, outline
   potential approaches, and problem areas for IETF work on power-aware

2.  Motivation and Problem Scope

   Today's ISP networks have redundant routers and links, over-
   provisioned link capacity, and load-balancing traffic engineering. As
   a result, routers and links operate at full capacity all the time
   with low average usage, typically less than 40% of link utilization.
   This practice makes networks resilient to traffic spikes and
   component failures, but also makes networks far from energy-

   Power-aware routing and traffic engineering have been proposed to
   improve network's energy efficiency, for example, by aggregating
   traffic onto a subset of links and putting other links with no
   traffic into sleep.  Data from various sources (e.g., [Heddeghem12]
   [Chabarek08]) have shown that line cards are a significant source of
   router's power consumption, accounting for 40% - 70% of total power
   consumption.  Most of the energy is consumed even in standby state,

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   and forwarding packets at full speed only increases the energy
   consumption by a small percentage.  This implies that being able to
   put links into sleep mode can potentially save a lot of energy.  In
   face, this has been demonstrated in several research works such as
   [GreenTE] [Nedevschi08] [Chabarek08].

   Designing practical protocols, however, has been challenging, because
   making routing protocols power-aware brings significant changes to
   the routing system and the entire network, thus it involves hardware
   support, protocol design, network monitoring, and operational
   practices.  These issues often depend on the specific network
   environments under discussion.  In order to focus on protocol-related
   issues, we suggest that as the first step we limit the scope of the
   discussion to intra-domain routing within one administrative domain,
   to avoid inter-domain policy issues.  This includes transit networks
   as well as edge networks.  We leave data center networks out of this
   draft since that usually requires concerted efforts beyond network

3.  Potential Solution Approaches

   The high-level idea of power-aware networks is to adjust routing
   paths based on traffic level.  When traffic level is high, use more
   links to carry the traffic; when traffic level is low, merge traffic
   onto a subset of all links so that other links can be put to sleep or
   reduce rate in order to save power.  This needs to be done without
   significantly impacting network QoS, network resiliency, and
   interoperation with other protocols.

   In the last few years a number of power-aware network designs have
   emerged.  Instead of listing them individually, here we categorize
   the solutions along three different dimensions.

   Link Sleep vs. Rate Adaptation

   Sleeping and rate adaptation are two major ways to save energy in
   computer systems.  Many hardware, including line cards and chassises,
   consumes a significant amount of power when they stand by without
   doing any actual work.  When put into sleep mode, they will consume
   only a little power.  Thus putting an idle component to sleep is a
   common way to save energy.  If there is a need to use this component,
   it can be waken up and become usable after a transition time.  The
   longer a component is in sleep mode, the more power saved.  A power-
   aware protocol adjusts routing paths to increase the sleep time for
   certain links in the network.

   A network interface often supports multiple data rates.  Operating at
   a lower data rate usually consumes less energy, though the actual

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   rate-power curve varies from device to device.  Rate-adaptation-based
   approaches operate interfaces at lower data rates when the traffic
   demand is low and increase the data rate when traffic demand is high.
   Thus the routers can save power during low utilization period.

   These two approaches are also related in the case of "bundled links"
   [Fisher10].  A bundled link is a virtual link comprised of multiple
   physical links.  A sleep-based approach can put some physical links
   into sleep to save power, which is same as conducting rate adaptation
   on the virtual link with adjustment unit of a physical link.

   Configured vs. Adaptive

   The key in power-aware routing and traffic engineering is to adjust
   routing paths in response to traffic changes, so that the power state
   of routers (or router components) will also change accordingly to
   achieve energy saving.  Different approaches differ at the
   granularity of the adjustment.

   Some approaches take the long-term traffic average as input, and
   output a routing configuration that is applied to the network
   regardless of short-term traffic variation.  This is mostly useful
   when network traffic exhibits a stable, clear pattern, e.g., diurnal
   pattern where traffic is high during work hours and low during off
   hours.  It can only exploit the target traffic pattern; it cannot
   react dynamically to short-term traffic changes to either save energy
   (by putting links to sleep) or avoid congestion (by waking links up),
   but the design and implementation should be simple.

   Another type of approach is to adapt to traffic changes dynamically
   on much smaller time granularity.  This approach may be able to save
   more energy and have better performance because it is more
   responsive, but the design and implementation usually are more
   complicated.  This approach needs to continuously collect traffic
   data in order to adjust routing dynamically.  The adjustment may be
   done periodically or whenever significant traffic changes are

   Distributed vs. Centralized

   In distributed solutions, routers make power-aware adjustment
   decisions, such as link sleep/wake-up and rate increase/decrease,
   locally without a central controller.  These routers need to exchange
   information in order to achieve consistent network states.
   Distributed approach fits the Internet operation model well but its
   design is the most challenging.  Traditional routing does not respond
   to traffic variation while power-aware routing does, and it needs to
   do so without causing loops or congestions.

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   In centralized solutions, a controller computes the routing paths
   considering the network topology and traffic demand, and informs
   routers how to adjust their routing paths.  A centralized server
   usually has more complete information, more computation power, and
   more memory and storage than routers, thus it may make better
   decisions than distributed approach.  The server locates in the
   network NOC and can be backed up by server replicas.  Nevertheless,
   this approach requires high reliability of the server.

   Both distributed and centralized solutions may find their places in
   ISP networks.  For example, centralized solution can be integrated
   into the Path Computation Element (PCE) framework [PCE-WG].  There
   can also be hybrid designs, e.g., using a centralized solution based
   on long-term traffic pattern, and distributed mechanisms to handle
   short-term traffic variations.

4.  Problem Areas for IETF

   Power-aware networks have great potentials to improve network energy
   efficiency while maintaining network services at desired levels.  Its
   effectiveness, however, depends on various supports from hardware and
   software, especially protocol designs that address operational
   issues.  In this section we list a few problem areas that will
   benefit from additional input from the IETF community, or have the
   potential to become work items in related IETF working groups.

   Motivation and Problem Scope

   o  What are the motivations for Power-Aware Networking (PANET)?

   o  To what extent power consumption is a key factor for Internet

   o  To what extent power-aware system at router level and link level
      are not sufficient to reduce the overall energy consumption of

   Technical Development

   o  What are the technical requirements for an efficient PANET

   o  What are the technical tracks to reduce the overall power
      consumption at the level of an IP network?

   o  How protocols can be designed to be power-aware and still maintain
      enough network resiliency?

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   o  What are the technical challenges for deploying efficient PANET

   o  How routing protocols (e.g., OSPF) can be extended to disseminate
      power-related information?

   o  How PCE architecture can be used to compute power-aware paths?

   o  How PANET can be deployed in centralized or in distributed model?

   Operation Practice

   o  What will be the impacts of PANET to network operations?

   o  What will be the guidelines for deploying PANET systems?

5.  Security Considerations

   This draft is a discussion on the Internet's necessity to follow an
   evolutionary path towards the future.  There is no direct impact on
   the Internet security.

6.  Informative References

   [Bolla11] Bolla, R. and et al. , "Energy Efficiency in the Future
      Internet: A Survey of Existing Approaches and Trends in Energy-
      Aware Fixed Network Infrastructures", IEEE Communications Surveys
      and Tutorials, 2011.

   [Chabarek08] Chabarek, J. and et al. , "Power Awareness in Network
      Design and Routing", IEEE INFOCOM 2008.

   [Doverspike10] Doverspike, R., Ramakrishnan, K., and C. Chas,
      "Structural overview of ISP networks", Guide to Reliable Internet
      Services and Applications, Springer, 2010.

   [EMAN-WG] "IETF Energy Management Working Group", 2012,

   [Epps06] Epps, G. and et al. , "System Power Challenges", 2006,
      < routing research/ seminar
      august 29/1562106>.

   [Fisher10] Fisher, W. and et al. , "Greening Backbone Networks:
      Reducing Energy Consumption by Shutting Off Cables in Bundled
      Links", Green Networking 2010.

   [GreenTE] Zhang, M. and et al. , "GreenTE: Power-Aware Traffic

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      Engineering", ICNP 2010.

   [Gupta03] Gupta, M. and S. Singh, "Greening the Internet", ACM
      SIGCOMM 2003.

   [Heddeghem12] Van Heddeghem, W. and F. Idzikowski, "Equipment power
      consumption in optical multilayer networks - source data", IBCN
      Technical Report 2012.
   [Nakamura07] Nakamura, M., "Advanced photonic technologies for the
      information era", Nature Photonics Technology conference, 2007.

   [Nedevschi08] Nedevschi, S. and et al. , "Reducing Network Energy
      Consumption via Sleeping and Rate- Adaptation", USENIX NSDI 2008.
   [PCE-WG] "IETF Path Computation Element Working Group", 2012,

   [Pileri07] Pileri, S., "Energy and communication: engine of the human
      progress", 2007.

   [TM] Roughan, M., Thorup, M., and Y. Zhang, "Traffic Engineering with
      Estimated Traffic Matrices", IMC 2003.

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Authors' Addresses

   Beichuan Zhang
   Univ. of Arizona


   Junxiao Shi
   Univ. of Arizona


   Jie Dong


   Mingui Zhang


   Mohamed Boucadair
   France Telecom


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