© University of Fribourg, Switzerland1 Chapter 18: Energy-efficient Peer-to-Peer Networking and...

© University of Fribourg, Switzerland 1

Chapter 18: Energy-efficient Peer-to-Peer

Networking and Overlays

1Apostolos Malatras, 1Fei Peng, and 1Béat Hirsbrunner

1University of Fribourg, Switzerland

HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS

The work presented here was conducted in the context of SNF-funded BioMPE project, grant number 200021_130132


Outline

Introduction Motivation

P2P Systems Energy profile of P2P Systems Taxonomy of energy-efficient P2P approaches

Proxying Sleep-and-Wake Task allocation optimization Message reduction Overlay structure optimization Location-based

Conclusions


Introduction

Peer-to-peer paradigm has gained wide acceptance over the last years Allows for more manageable networks due to its

nature as networking abstraction layer

Information Technology is a large consumer of energy resources Recent surveys indicate it’s responsible for up to 3%

of global energy consumption Rapidly increasing due to wide deployment of IT

devices and exponential growth of networks (wired and wireless)

P2P network traffic has been measured to be from 40% to 73% of the overall Internet traffic


Introduction

Motivation Growing need for energy proportional computing

approaches• Energy consumption proportional to operation and Energy consumption proportional to operation and

performanceperformance

A lot of potential in overall IT energy savings from energy-efficient P2P approaches

Challenges• Distributed nature of P2PDistributed nature of P2P• Need to address end hosts (peers), overlay networks and Need to address end hosts (peers), overlay networks and

communication protocolscommunication protocols


Terminology & Focus

Terms used interchangeably P2P systems P2P overlays P2P networks

Focus of study Work with experimental or testbed validation Not dealing with MANETs

• Similar concept, but different OSI layerSimilar concept, but different OSI layer

Energy-efficient research work and P2P systems that are targeted at extending lifetime of mobile devices


What is a P2P Overlay?

A logical, virtual network that is built upon a real, physical network The peers, i.e. nodes in the physical network, are

organized in a distributed manner Peer organization adheres to specific criteria/rules All peers are operating as both clients and servers

Its goal is to support a variety of services and applications Hide complexity, heterogeneity and dynamicity of

underlying networking infrastructures Promote scalability


Structured vs. Unstructured P2P

Structured P2P Topology is tightly controlled Rules about placement of resources on specific peers

• Usually exploit Distributed Hash TablesUsually exploit Distributed Hash Tables

Quick discovery of resources High maintenance and management overhead costs

Unstructured P2P No rules to control topology Flexible membership and resource positioning Flooding used to locate resources More flexible and resilient to failures More effort/time required to locate resources


Examples of P2P Overlays

Structured Unstructured

Chord Freenet

Tapestry Gnutella

Pastry FastTrack/Kazaa

Kademlia BitTorrent

Viceroy UMM

CAN Newscast

Cycloid Phenix

SkipNet BlatAnt

P-Grid


Energy profile of P2P systems

Important to know how much energy P2P systems consume and on what operations Accurate measurements can validate the potential

reductions in energy consumption Selection of strategy to follow, e.g. promoting

modifications in energy consuming operations Energy models can be a good alternative

• Give a quick indication of energy behaviorsGive a quick indication of energy behaviors• Allow for early validation experiments/analysisAllow for early validation experiments/analysis• Shorter rollout times for new, green P2PShorter rollout times for new, green P2P

Standard metrics are lacking, hence no reliable comparisons between different P2P can be drawn



Energy model described in [Nedevschi et al., 2008] Comparison of P2P with centralized solutions End-to-end analysis of energy behaviors P2P are greener when considering only end-hosts Centralized are greener in the end-to-end case

Energy model by [Hlavacs et al., 2010, 2011] Focus on BitTorrent and peer participation Relation between optimal time to actively participate in

the BitTorrent P2P and the optimal energy efficiency

Energy model by [Zhang & Helvik, 2010] Models amount of time peers stay actively in the P2P

network vs. consumed energy



Viability of mobile devices participating in a P2P network studied in [Zhuang et al., 2010] Possible but at a high battery cost as shown in

[Gurun et al., 2006], [Rollins et al., 2011]

P2P energy efficiency in wired vs. wireless networks has been studied Different behavior due to wireless medium

characteristics was observed in [Gerla et al., 2005] Feasible operation, works better when high data

transfer rates can be ensured • Studies in [Ou et al., 2009, 2010], [Kassinen et al., 2008, Studies in [Ou et al., 2009, 2010], [Kassinen et al., 2008,

2009], 2009],


Taxonomy of energy-efficient P2P approaches

Category Examples

Proxying [Agarwal et al., 2009], [Kelenyi et al., 2009] , [Kelenyi et al., 2010] , [Anastasi et al., 2010], [Purushothaman at al., 2006]

Sleep-and-Wake [Sucevic et al., 2009], [Gurun et al., 2006], [Blackburn & Christensen, 2009]

Task allocation optimization [Aikebaier et al., 2009], [Enokido et al., 2010], [Li et al., 2009]

Message reduction [Kelenyi et al., 2008], [da Hora et al., 2007], [Kelenyi et al., 2010]

Overlay structure optimization [Leung & Kwok, 2008], [Han et al., 2008], [Choi &Woo, 2006], [Rollins et al., 2011], [Mawji et al., 2011], [Macedo et al., 2011]

Location-based [Park & Valduriez, 2011], [Tung & Lin, 2011], [Joseph et al. 2005], [Feng et al., 2007]


Proxying

Use of proxies by P2P hosts to delegate P2P-related activities and operations and thus allow to have more idle time. Peers can then go on sleep mode, consuming less

energy Overall P2P system energy consumption is reduced

Challenges Which P2P operations to offload to the proxy? When to wake up the P2P host? Where should the proxy be located? Since participation to the P2P has to be active, e.g. file

sharing, how can this be accommodated with a proxy?


Proxying Solutions proposed in the literature

1 proxy for many peers• Proxy consumes energy as wellProxy consumes energy as well

Offloaded P2P operations• AllAll• SelectiveSelective

Proxy location• Wireless gatewaysWireless gateways• NIC of hostNIC of host• Dedicated machinesDedicated machines

Host wake up• Completion of file downloadCompletion of file download• Threshold for number of downloaded pieces (e.g. BitTorrent)Threshold for number of downloaded pieces (e.g. BitTorrent)

P2P operation• Proxy acts as full delegate for the P2P hosts it servesProxy acts as full delegate for the P2P hosts it serves• Peers are still part of the P2P network, but passive membersPeers are still part of the P2P network, but passive members


Sleep-and-Wake

P2P hosts adopt and adaptive operational behavior by selectively switching between on and off state in order to save energy Motivation lies in the energy requirements of wireless

interfaces• Has been measured to be up to 64% of overall energy Has been measured to be up to 64% of overall energy

consumptionconsumption

Random switching on and off is harmful for P2P operation

Specially designed scheduling is required• As soon as downloads have been completedAs soon as downloads have been completed• Be active only when high data rates can be guaranteedBe active only when high data rates can be guaranteed• Buffer all requests and handled them when going onlineBuffer all requests and handled them when going online


Sleep-and-Wake

Challenges Proper operation of the P2P network is hindered

because of high peer churn When buffering requests, efficiency of the P2P

network is diminished, e.g. longer delays Connectivity of the P2P overlay cannot be

guaranteed due to peer churn Most proposed solutions require global network

information to properly schedule sleeping and waking times

• Unviable assumption that cannot be applied in real settingsUnviable assumption that cannot be applied in real settings


Task allocation optimization

Scheduling of tasks across P2P hosts in a manner that limits overall energy consumption by utilizing host availability more efficiently Considers the P2P overlay similarly to a grid system Not all hosts have the same energy capacity/capability The more processing a peer does and the more

information it transfers/receives, the more energy it consumes

Scheduling ensures a fair consumption of energy among participating peers

• Additionally, ensures proper operation of the P2P overlay Additionally, ensures proper operation of the P2P overlay because energy depletion implies the node will go because energy depletion implies the node will go permanently offlinepermanently offline


Task allocation optimization

Challenges Task allocation optimization requires global knowledge

about the status of peers in the P2P network All related work is modeled as multi-constraint

optimization problem• Constraints include battery lifetime, processing load, data Constraints include battery lifetime, processing load, data

transfer rates, etc.transfer rates, etc.

How to model energy consumption is a difficult problem

• Task allocation requires some level of prediction regarding the Task allocation requires some level of prediction regarding the expected energy consumption to decide whether re-allocation expected energy consumption to decide whether re-allocation of a task makes sense or notof a task makes sense or not

Selfish behavior of peers• Selfless behavior has been shown to extend the overall P2P Selfless behavior has been shown to extend the overall P2P

overlay lifetimeoverlay lifetime


Message reduction

Technique used to reduce number of messages. By minimizing the number of sent messages, processing and transmission times are reduced and thus energy is conserved Both for wired and wireless networks

• Wired: less processingWired: less processing• Wireless: less transmissions/receptionsWireless: less transmissions/receptions

Studies validated that peers that act only as clients have less power consumption that full-fledged ones [Kelenyi et al., 1008]

• This selfish behavior can have adverse effect on the proper This selfish behavior can have adverse effect on the proper operation of the P2P overlay [Feldman & Chuang, 2005]operation of the P2P overlay [Feldman & Chuang, 2005]


Message reduction

Benefits In [Kelenyi et al., 2008] it was shown that with a 50%

drop probability the consumed energy was reduced by 55%

Challenges Dropping of messages

• Selective, e.g. not management messagesSelective, e.g. not management messages• RandomRandom

Ensuring proper operation of the P2P overlay• Replication of messagesReplication of messages• Replication of resourcesReplication of resources• Not all peers dropping messagesNot all peers dropping messages


Overlay structure optimization

New topology designs for energy efficient P2P overlays or modifications to existing ones to satisfy energy requirements Existing popular P2P systems do not take into

account energy resources for construction and maintenance

Main reason was the abundance of mains power in wired devices

Nowadays, wireless devices are the norm and designs need to be reconsidered

Such omission can quickly deplete energy-constrained devices and thus compromise the viability of the P2P overlay as a whole


Overlay structure optimization

Solution proposed by [Leung & Kwok, 2008] Peers decide on who their neighbors will be based on

their remaining battery levels Nodes who don’t have a lot of battery will be leaf

nodes, while relay nodes have high energy capacity Promotes P2P overlay longevity

Super peer approaches Building maximal independent set of most energy-

powerful peers Information relaying happens through this set of

super peers Adaptive approaches needed to ensure super peer

energy does not get drained quickly


Location-based

Location-information is used to make P2P overlays more closely matching their physical underlay counterparts, thus reducing multi-hop transmissions Mostly useful for wireless networks One overlay hop can be multiple physical layer hops,

so many retransmissions might be needed for a single message

When overlay and underlay match each other closely, less retransmissions are likely to occur and thus less energy is to be consumed

Some overlay structure optimization approaches can be classified in this category


Location-based

Location-based resource discovery greatly benefits from such approaches When location is taken into account to construct the

P2P overlay, this information is always available Resource queries for spatial data can then be satisfied

much quicker and in a more energy efficient manner• Queries are quickly directed to the nodes who can satisfy Queries are quickly directed to the nodes who can satisfy

themthem

Similar concept as geographic routing

Challenges Acquiring location information Sharing location information in distributed settings Privacy issues


Conclusions

Survey of green P2P Scholar overview of existing solutions Highlight pitfalls and challenges Promote novel solutions by cross-examination

Future directions to engage in green P2P Need for standard metrics that will lead to

comparable measurements Accurate and reliable models of energy efficiency of

P2P systems End-to-end solutions, i.e. not only considering end

hosts but also the energy footprint of the core and that of communications


Thanks for your attention!

© University of Fribourg, Switzerland1 Chapter 18: Energy-efficient Peer-to-Peer Networking and...

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