


Network Working Group                                           I. Rimac
Internet-Draft                                                   V. Hilt
Intended status: Informational                                  M. Tomsu
Expires: December 30, 2010                                    V. Gurbani
                                               Bell Labs, Alcatel-Lucent
                                                              E. Marocco
                                                          Telecom Italia
                                                           June 28, 2010


   A Survey on Research on the Application-Layer Traffic Optimization
                             (ALTO) Problem
                    draft-irtf-p2prg-alto-survey-05

Abstract

   A significant part of the Internet traffic today is generated by
   Peer-to-peer (P2P) applications used traditionally for file-sharing,
   and more recently for real-time communications and live media
   streaming.  Such applications discover a route to each other through
   an overlay network with little knowledge of the underlying network
   topology.  As a result, they may choose peers based on information
   deduced from empirical measurements, which can lead to suboptimal
   choices.  This document, a product of the P2P Research Group,
   presents a survey of existing literature on discovering and using
   network topology information for application-layer traffic
   optimization.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 30, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the



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   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
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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Survey of Existing Literature  . . . . . . . . . . . . . . . .  4
     2.1.  Application-Level Topology Estimation  . . . . . . . . . .  5
     2.2.  Topology Estimation through Layer Cooperation  . . . . . .  8
       2.2.1.  P4P Architecture . . . . . . . . . . . . . . . . . . .  9
       2.2.2.  Oracle-based ISP-P2P Collaboration . . . . . . . . . .  9
       2.2.3.  ISP-Driven Informed Path Selection (IDIPS) Service . . 10
   3.  Application-Level Topology Estimation and the ALTO Problem . . 10
   4.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.1.  Coordinate estimation or path latencies? . . . . . . . . . 12
     4.2.  Malicious nodes  . . . . . . . . . . . . . . . . . . . . . 12
     4.3.  Information integrity  . . . . . . . . . . . . . . . . . . 12
     4.4.  Richness of topological information  . . . . . . . . . . . 13
     4.5.  Hybrid solutions . . . . . . . . . . . . . . . . . . . . . 13
     4.6.  Negative impact of over-localization . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 14
   8.  Informative References . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18















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1.  Introduction

   A significant part of today's Internet traffic is generated by Peer-
   to-peer (P2P) applications, used originally for file sharing, and
   more recently for realtime multimedia communications and live media
   streaming.  P2P applications are posing serious challenges to the
   Internet infrastructure; by some estimates, P2P systems are so
   popular that they make up anywhere between 40% to 85% of the entire
   Internet traffic [Meeker], [Karagiannis], [LightReading],
   [LinuxReviews], [Parker], [Glasner].

   P2P systems ensure that popular content is replicated at multiple
   instances in the overlay.  But perhaps ironically, a peer searching
   for that content may ignore the topology of the latent overlay
   network and instead select among available instances based on
   information it deduces from empirical measurements, which, in some
   particular situations may lead to suboptimal choices.  For example, a
   shorter round-trip time estimation is not indicative of the bandwidth
   and reliability of the underlying links, which have more of an
   influence than delay for large file transfer P2P applications.

   Most Distributed Hash Tables (DHT) -- the data structure that imposes
   a specific ordering for P2P overlays -- use greedy forwarding
   algorithms to reach their destination, making locally optimal
   decisions that may not turn out to be globally optimized [Gummadi].
   This naturally leads to the Application-Layer Traffic Optimization
   (ALTO) problem [RFC5693]: how to best provide the topology of the
   underlying network while at the same time allowing the requesting
   node to use such information to effectively reach the node on which
   the content resides.  Thus, it would appear that P2P networks with
   their application layer routing strategies based on overlay
   topologies are in direct competition against the Internet routing and
   topology.

   One way to solve the ALTO problem is to build distributed
   application-level services for location and path selection [Francis],
   [Ng], [Dabek], [Costa], [Wong], [Madhyastha], in order to enable
   peers to estimate their position in the network and to efficiently
   select their neighbors.  Similar solutions have been embedded into
   P2P applications such as Azureus [Azureus].  A slightly different
   approach is to have the Internet Service Provider (ISP) take a pro-
   active role in the routing of P2P application traffic; the means by
   which this can be achieved have been proposed [Aggarwal], [Xie],
   [Saucez].  There is an intrinsic struggle between the layers -- P2P
   overlay and network underlay -- when performing the same service
   (routing), however there are strategies to mitigate this dichotomy
   [Seetharaman].




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   This document, initially intended as a complement to RFC 5693
   [RFC5693] and discussed during the creation of the IETF ALTO Working
   Group, has been completed and refined in the IRTF P2P Research Group.
   Its goal is to summarize the contemporary research activities on the
   application layer traffic optimization problem as input to the ALTO
   working group protocol designers.

1.1.  Terminology

   Terminology adopted in this document includes terms such as "ring
   geometry", "tree structure", "butterfly network" borrowed from P2P
   scientific literature.  [RFC4981] provides an exaustive definition of
   such terminology.

   Certain security-related terms are to be understood in the sense
   defined in [RFC4949]; such terms include, but are not limited to,
   "attack", "authentication", "confidentiality", "encryption",
   "identity", "integrity".  Other security-related terms (for example,
   "denial of service") are to be understood in the sense defined in the
   referenced specifications.


2.  Survey of Existing Literature

   Gummadi et al.  [Gummadi] compare popular DHT algorithms and besides
   analyzing their resilience, provide an accurate evaluation of how
   well the logical overlay topology maps on the physical network layer.
   In their paper, relying only on measurements independently performed
   by overlay nodes without the support of additional location
   information provided by external entities, they demonstrate that the
   most efficient algorithms in terms of resilience and proximity
   performance are those based on the simplest geometric concept (i.e.
   the ring geometry, rather than tree structures, butterfly networks
   and hybrid geometries).

   Regardless of the geometrical properties of the distributed data
   structures involved, interactions between application-layer overlays
   and the underlying networks are a rich area of investigation.  The
   available literature in this field can be divided in two categories
   (Figure 1): using application-level techniques to estimate topology
   and through some kind of layer cooperation.










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     Application-layer traffic optimization
       |
       +--> Application-level topology estimation
       |      |
       |      +--> Coordinates-based systems
       |      |      |
       |      |      +--> GNP
       |      |      |
       |      |      +--> Vivaldi
       |      |      |
       |      |      +--> PIC
       |      |
       |      +--> Path selection services
       |      |      |
       |      |      +--> IDMaps
       |      |      |
       |      |      +--> Meridian
       |      |      |
       |      |      +--> Ono
       |      |
       |      +--> Link-layer Internet maps
       |             |
       |             +--> iPlane
       |
       +--> Topology estimation through layer cooperation
              |
              +--> P4P: Provider portal for applications
              |
              +--> Oracle-based ISPs and P2P cooperation
              |
              +--> ISP-driven informed path selection


   Taxonomy of solutions for the application-layer traffic optimization
   problem.

                                 Figure 1

2.1.  Application-Level Topology Estimation

   Estimating network topology information on the application layer has
   been an area of active research.  Early systems used triangulation
   techniques to bound the distance between two hosts using a common
   landmark host.  In such a technique, given a cost function C, a set
   of vertexes V and their corresponding edges, the triangle inequality
   holds if for any triple {a, b, c} in V, C(a, c) is always less than
   or equal to C(a, g) + C(b, c).  The cost function C could be
   expressed in terms of desirable metrics such as bandwidth or latency.



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   We note that the techniques presented in this section are only
   representative of the sizable research in this area.  Rather than
   trying to enumerate an exhaustive list, we have chosen certain
   techniques because they represent an advance in the area that further
   led to derivative works.

   Francis et al. proposed IDMaps [Francis], a system where one or more
   special hosts called tracers are deployed near an autonomous system.
   The distance measured in Round Trip Time (RTT) between hosts A and B
   is estimated as the cumulative distance between A and its nearest
   tracer Ta, plus the distance between B and its nearest tracer Tb,
   plus the shortest distance from Ta to Tb.  To aid in scalability
   beyond that provided by the client-server design of IDMaps, Ng et al.
   proposed a P2P-based Global Network Positioning (GNP) architecture
   [Ng].  GNP was a network coordinate system based on absolute
   coordinates computed from modeling the Internet as a geometric space.
   It proposed a two-part architecture: in the first part, a small set
   of finite distributed hosts called landmarks compute their own
   coordinates in a fixed geometric space.  In the second part, a host
   wishing to participate computes its own coordinates relative to those
   of the landmark hosts.  Thus, armed with the computed coordinates,
   hosts can then determine interhost distance as soon as they discover
   each other.

   Both IDMaps and GNP require fixed network infrastructure support in
   the form of tracers or landmark hosts; this often introduces a single
   point of failure and inhibits scalability.  To combat this, new
   techniques were developed that embedded the network topology in a
   low-dimensional coordinate space to enable network distance
   estimation through vector analysis.  Costa et al. introduced
   Practical Internet Coordinates (PIC) [Costa].  While PIC used the
   notion of landmark hosts, it did not require explicit network support
   to designate specific landmark hosts.  Any node whose coordinates
   have been computed could act as a landmark host.  When a node joined
   the system, it probed the network distance to some landmark hosts.
   Then, it obtained the coordinates of each landmark host and computed
   its own coordinates relative to the landmark host, subject to the
   constraint of minimizing the error in the predicted distance and
   computed distance.

   Like PIC, Vivaldi [Dabek] proposed a fully distributed network
   coordinate systems without any distinguished hosts.  Whenever a node
   A communicates with another node B, it measures the RTT to that node
   and learns that node's current coordinates.  A subsequently adjusts
   its coordinates such that it is closer to, or further from B by
   computing new coordinates that minimize the squared error.  A Vivaldi
   node is thus constantly adjusting it's position based on a simulation
   of interconnected mass springs.  Vivaldi is now being used in the



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   popular P2P application Azureus and studies indicate that it scales
   well to very large networks [Ledlie].

   Network coordinate systems require the embedding of the Internet
   topology into a coordinate system.  This is not always possible
   without errors, which impacts the accuracy of distance estimations.
   In particular, it has proved to be difficult to embed the triangular
   inequalities found in Internet path distances [Ledlie].  Thus,
   Meridian [Wong] abandons the generality of network coordinate systems
   and provides specific distance evaluation services.  In Meridian,
   each node keeps track of small fixed number of neighbors and
   organizes them in concentric rings, ordered by distance from the
   node.  Meridian locates the closest node by performing a multi-hop
   search where each hop exponentially reduces the distance to the
   target.  Although less general than virtual coordinates, Meridian
   incurs significantly less error for closest node discovery.

   The Ono project [Ono] takes a different approach and uses network
   measurements from Content Distribution Network (CDN) like Akamai to
   find nearby peers.  Used as a plugin to the Azureus BitTorrent
   client, Ono provides 31% average download rate improvement [Su].

    Comparison of application-level topology estimation techniques, as
    reported in literature.  Results in terms of number of (D)imensions
             and (L)andmarks, 90th percentile relative error.

   +----------------+---------------+----------------+-----------------+
   | GNP vs.        | PIC(b) vs.    | Vivaldi vs.    | Meridian vs.    |
   | IDMaps(a) (7D, | GNP (8D, 16L) | GNP (2D, 32L)  | GNP (8D, 15L)   |
   | 15L)           |               |                |                 |
   +----------------+---------------+----------------+-----------------+
   | GNP: 0.50,     | PIC: 0.38,    | Vivaldi: 0.65, | Meridian: 0.78, |
   | IDMaps: 0.97   | GNP: 0.37     | GNP: 0.65      | GNP: 1.18       |
   +----------------+---------------+----------------+-----------------+

   (a) Does not use dimensions or landmarks. (b) Using results from the
                         hybrid strategy for PIC.

                                  Table 1

   Table 1 summarizes the application-level topology estimation
   techniques.  The salient performance metric is the relative error.
   While all approaches define this metric a bit differently, it can be
   generalized as how close a predicted distance comes to the
   corresponding measured distance.  A value of zero implies perfect
   prediction and a value of 1 implies that the predicted distance is in
   error by a factor of two.  PIC, Vivaldi, and Meridian compare their
   results with that of GNP, while GNP itself compares its results with



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   a precursor technique, IDMaps.  Because each of the techniques uses a
   different Internet topology and a varying number of landmarks and
   dimensions to interpret the data set, it is impossible to normalize
   the relative error across all techniques uniformly.  Thus we present
   the relative error data in pairs, as reported in the literature
   describing the specific technique.  Readers are urged to compare the
   relative error performance in each column on its own and not draw any
   conclusions by comparing the data across columns.

   Most of the work on estimating topology information focuses on
   predicting network distance in terms of latency and does not provide
   estimates for other metrics such as throughput or packet loss rate.
   However, for many P2P applications latency is not the most important
   performance metric and these applications could benefit from a richer
   information plane.  Sophisticated methods of active network probing
   and passive traffic monitoring are generally very powerful and can
   generate network statistics indirectly related to performance
   measures of interest, such as delay and loss rate on link-level
   granularity.  Extraction of these hidden attributes can be achieved
   by applying statistical inference techniques developed in the field
   of inferential network monitoring or network tomography subsequent to
   sampling of the network state.  Thus, network tomography enables the
   extraction of a richer set of topology information, but at the same
   time inherently increasing complexity of a potential information
   plane and introducing estimation errors.  For both active and passive
   methods statistical models for the measurement process need to be
   developed and the spatial and temporal dependence of the measurements
   should be assessed.  Moreover, measurement methodology and
   statistical inference strategy must be considered jointly.  For a
   deeper discussion of network tomography and recent developments in
   the field we refer the reader to [Coates].

   One system providing such a service is iPlane [Madhyastha], which
   aims at creating a annotated atlas of the Internet that contains
   information about latency, bandwidth, capacity and loss rate.  To
   determine features of the Internet topology, iPlane bridges and
   builds upon different ideas, such as active probing based on packet
   dispersion techniques to infer available bandwidth along path
   segments.  These ideas are drawn from different fields, including
   network measurement as described by Dovrolis et al. in [Dovrolis] and
   network tomography [Coates].

2.2.  Topology Estimation through Layer Cooperation

   Instead of estimating topology information on the application level
   through distributed measurements, this information could be provided
   by the entities running the physical networks -- usually ISPs or
   network operators.  In fact, they have full knowledge of the topology



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   of the networks they administer and, in order to avoid congestion on
   critical links, are interested in helping applications to optimize
   the traffic they generate.  The remainder of this section briefly
   describes three recently proposed solutions that follow such an
   approach to address the ALTO problem.

2.2.1.  P4P Architecture

   The architecture proposed by Xie et al.  [Xie] has been adopted by
   the DCIA P4P working group [P4P], an open group established by ISPs,
   P2P software distributors and technology researchers with the dual
   goal of defining mechanisms to accelerate content distribution and
   optimize utilization of network resources.

   The main role in the P4P architecture is played by servers called
   "iTrackers", deployed by network providers and accessed by P2P
   applications (or, in general, by elements of the P2P system) in order
   to make optimal decisions when selecting a peer to connect.  An
   iTracker may offer three interfaces:

   1.  Info: Allows P2P elements (e.g. peers or trackers) to get opaque
       information associated to an IP address.  Such information is
       kept opaque to hide the actual network topology, but can be used
       to compute the network distance between IP addresses.
   2.  Policy: Allows P2P elements to obtain policies and guidelines of
       the network, which specify how a network provider would like its
       networks to be utilized at a high level, regardless of P2P
       applications.
   3.  Capability: Allows P2P elements to request network providers'
       capabilities.

   The P4P architecture is under evaluation with simulations,
   experiments on the PlanetLab distributed testbed and in field tests
   with real users.  Initial simulations and PlanetLab experiments
   results [P4P] indicate that improvements in BitTorrent download
   completion time and link utilization in the range of 50-70% are
   possible.  Results observed on Comcast's network during a field test
   trial conducted with a modified version of the software used by the
   Pando content delivery network (documented in RFC 5632 [RFC5632])
   show average improvements in download rate in different scenarios
   varying between 57% and 85%, and a 34% to 80% drop in the cross-
   domain traffic generated by such an application.

2.2.2.  Oracle-based ISP-P2P Collaboration

   In the general solution proposed by Aggarwal et al.  [Aggarwal],
   network providers host servers, called "oracles", that help P2P users
   choose optimal neighbours.



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   The oracle concept uses the following mechanism: a P2P client sends
   the list of potential peers to the oracle hosted by its ISP and
   receives a re-arranged peer list, ordered according to the ISP's
   local routing policies and preferences.  For instance, to keep the
   traffic local, the ISP may prefer peers within its network, or it may
   pick links with higher bandwidth or peers that are geographically
   closer to improve application performance.  Once the client has
   obtained this ordered list, it has enough information to perform
   better-than-random initial peer selection.

   Such a solution has been evaluated with simulations and experiments
   run on the PlanetLab testbed and the results show both improvements
   in content download time and a reduction of overall P2P traffic, even
   when only a subset of the applications actually query the oracle to
   make their decisions.

2.2.3.  ISP-Driven Informed Path Selection (IDIPS) Service

   The solution proposed by Saucez et al.  [Saucez] is essentially a
   modified version of the oracle-based approach described in
   Section 2.2.2, intended to provide a network-layer service for
   finding best source and destination addresses when establishing a
   connection between two endpoints in multi-homed environments (which
   are common in IPv6 networking).  Peer selection optimization in P2P
   systems -- the ALTO problem in today's Internet -- can be addressed
   by the IDIPS solution as a specific sub-case where the options for
   the destination address consist of all the peers sharing a desired
   resource, while the choice of the source address is fixed.  An
   evaluation performed on IDIPS shows that costs for both providing and
   accessing the service are negligible.


3.  Application-Level Topology Estimation and the ALTO Problem

   The application-level techniques described in Section Section 2.1
   provide tools for peer-to-peer applications to estimate parameters of
   the underlying network topology.  Although these techniques can
   improve application performance, there are limitations of what can be
   achieved by operating only on the application level.

   Topology estimation techniques use abstractions of the network
   topology which often hide features that would be of interest to the
   application.  Network coordinate systems, for example, are unable to
   detect overlay paths shorter than the direct path in the Internet
   topology.  However, these paths frequently exist in the Internet
   [Wang].  Similarly, application-level techniques may not accurately
   estimate topologies with multipath routing.




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   When using network coordinates to estimate topology information the
   underlying assumption is that distance in terms of latency determines
   performance.  However, for file sharing and content distribution
   applications there is more to performance than just the network
   latency between nodes.  The utility of a long-lived data transfer is
   determined by the throughput of the underlying TCP protocol, which
   depends on the round-trip time as well as the loss rate experienced
   on the corresponding path [Padhye].  Hence, these applications
   benefit from a richer set of topology information that goes beyond
   latency including loss rate, capacity and available bandwidth.

   Some of the topology estimation techniques used by P2P applications
   need time to converge to a result.  For example, current BitTorrent
   clients implement local, passive traffic measurements and a tit-for-
   tat bandwidth reciprocity mechanism to optimize peer selection at a
   local level.  Peers eventually settle on a set of neighbors that
   maximizes their download rate but because peers cannot reason about
   the value of neighbors without actively exchanging data with them and
   the number of concurrent data transfers is limited (typically to
   5-7), convergence is delayed and easily can be sub-optimal.

   Skype's P2P Voice over IP (VoIP) application chooses a relay node in
   cases where two peers are behind NATs and cannot connect directly.
   Ren et al.  [Ren] measured that the relay selection mechanism of
   Skype is (1) not able to discover the best possible relay nodes in
   terms of minimum RTT, (2) requires a long setup and stabilization
   time which degrades the end user experience, and (3) is creating a
   non-negligible amount of overhead traffic due to probing a large
   number of nodes.  They further showed that the quality of the relay
   paths could be improved when the underlying network Autonomous System
   (AS) topology is considered.

   Some features of the network topology are hard to infer through
   application-level techniques and it may not be possible to infer them
   at all.  An example for such a feature are service provider policies
   and preferences such as the state and cost associated with
   interdomain peering and transit links.  Another example is the
   traffic engineering policy of a service provider, which may
   counteract the routing objective of the overlay network leading to a
   poor overall performance [Seetharaman].

   Finally, application-level techniques often require applications to
   perform measurements on the topology.  These measurements create
   traffic overhead, in particular, if measurements are performed
   individually by all applications interested in estimating topology.






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4.  Open Issues

   Beyond a significant amount of research work on the topic, we believe
   that there are sizable open issues to address in an infrastructure-
   based approach to traffic optimization.  The following is not an
   exhaustive list, but a representative sample of the pertinent issues.

4.1.  Coordinate estimation or path latencies?

   Despite the many solutions that have been proposed for providing
   applications with topology information in a fully distributed manner,
   there is currently an ongoing debate in the research community
   whether such solutions should focus on estimating nodes' coordinates
   or path latencies.  Such a debate has recently been fed by studies
   showing that the triangle inequality on which coordinate systems are
   based is often proved false in the Internet [Ledlie].  Proposed
   systems following both approaches -- in particular, Vivaldi [Dabek]
   and PIC [Costa] following the former, Meridian [Wong] and iPlane
   [Madhyastha] the latter -- have been simulated, implemented and
   studied in real-world trials, each one showing different points of
   strength and weaknesses.  Concentrated work will be needed to
   determine which of the two solutions will be conducive to the {ALTO}
   problem.

4.2.  Malicious nodes

   Another open issue common in most distributed environments consisting
   of a large number of peers is the resistance against malicious nodes.
   Security mechanisms to identify misbehavior are based on triangle
   inequality checks [Costa], which however tend to fail and thus return
   false positives in presence of measurement inaccuracies induced, for
   example, by traffic fluctuations that occur quite often in large
   networks [Ledlie].  Beyond the issue of using triangle inequality
   checks, authoritatively authenticating the identity of an oracle, and
   preventing an oracle from attacks are also important.  Exploration of
   existing techniques -- such as Public Key Infrastructure (PKI)
   [RFC5280] or identity-based encryption [Boneh] for authenticating the
   identity and the use of secure multi-party computation techniques to
   prevent an oracle from collusion attacks -- need to be studied for
   judicious use in ALTO-type of solutions.

4.3.  Information integrity

   Similarly, even in controlled architectures deployed by network
   operators where system elements may be authenticated [Xie],
   [Aggarwal],[Saucez], it is still possible that the information
   returned to applications is deliberately altered, for example,
   assigning higher priority to financially inexpensive links instead of



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   neutrally applying proximity criteria.  What are the effects of such
   deliberate alterations if multiple peers collude to determine a
   different route to the target, one that is not provided by an oracle?
   Similarly, what are the consequences if an oracle targets a
   particular node in another AS by redirecting an inordinate number of
   querying peers to it causing, essentially, a Distributed Denial of
   Service (DDoS) [RFC4732] attack on the node?  Furthermore, does an
   oracle broadcast or multicast a response to a query?  If so,
   techniques to protect the confidentiality of the multi-cast stream
   will need to be investigated to thwart "free riding" peers.

4.4.  Richness of topological information

   Many systems already use RTT to account for delay when establishing
   connections with peers (e.g., CAN [Ratnasamy], Bamboo [Rhea]).  An
   operator can provide not only the delay metric but other metrics that
   the peer cannot figure out on its own.  These metrics may include the
   characteristics of the access links to other peers, bandwidth
   available to peers (based on operator's engineering of its network),
   network policies, and preferences such as state and cost associated
   with intradomain peering links, and so on.  Exactly what kinds of
   metrics can an operator provide to stabilize the network throughput
   will also need to be investigated.

4.5.  Hybrid solutions

   It is conceivable that P2P users may not be comfortable with operator
   intervention to provide topology information.  To eliminate this
   intervention, alternative schemes to estimate topological distance
   can be used.  For instance, Ono uses client redirections generated by
   Akamai CDN servers as an approximation for estimating distance to
   peers; Vivaldi, GNP and PIC use synthetic coordinate systems.  A
   neutral third-party can make available a hybrid layer cooperation
   service -- without the active participation of the ISP -- that uses
   alternative techniques discussed in Section 2.1 to create a
   topological map.  This map can be subsequently used by a subset of
   users who may not trust the ISP.

4.6.  Negative impact of over-localization

   The literature presented in Section 2 shows that a certain level of
   locality-awareness in the peer selection process of P2P algorithms is
   usually beneficial to the application performance.  However, an
   excessive localization of the traffic might cause partitioning in the
   overlay interconnecting peers, which will negatively affect the
   performance experienced by the peers themselves.

   Finding the right balance between localization and randomness in peer



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   selection is an open issue.  At the time of writing, it seems that
   different applications have different levels of tolerance and should
   be addressed separately.  Le Blond et al.  [LeBlond] have studied the
   specific case of BitTorrent, proposing a simple mechanism to prevent
   partitioning in the overlay, yet reaching a high level of cross-
   domain traffic reduction without adversely impacting peers.


5.  Security Considerations

   This draft is a survey of existing literature on topology estimation.
   As such, it does not introduce any new security considerations to be
   taken into account beyond what is already discussed in each paper
   surveyed.


6.  IANA Considerations

   None.


7.  Acknowledgments

   This document is a derivative work of a position paper submitted at
   the IETF RAI area/MIT workshop held on May 28th, 2008 on the topic of
   Peer-to-Peer Infrastructure (P2Pi) [RFC5594].  The article on a
   similar topic from the same authors published in IEEE Communications
   [Gurbani] was also partially derived from the same position paper.
   The authors thank profusely Arnaud Legout, Richard Yang, Richard
   Woundy, Stefano Previdi and the many people that have participated in
   discussions and provided insightful feedback at any stage of this
   work.


8.  Informative References

   [Aggarwal]
              Aggarwal, V., Feldmann, A., and C. Scheidler, "Can ISPs
              and P2P systems co-operate for improved performance?",
              in ACM SIGCOMM Computer Communications Review, vol. 37,
              no. 3.

   [Azureus]  "Azureus BitTorrent Client", <http://www.azureus.com/>.

   [Boneh]    Boneh, D. and M. Franklin, "Identity-Based Encryption from
              the Weil Pairing", in proceedings of the 21st Annual
              International Cryptology Conference on Advances in
              Cryptology, August 2001.



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   [Coates]   Coates, M., Hero, A., Nowak, R., and B. Yu, "Internet
              Tomography", in IEEE Signal Processing Magazine, vol. 19,
              no. 3.

   [Costa]    Costa, M., Castro, M., Rowstron, A., and P. Key, "PIC:
              Practical Internet coordinates for distance estimation",
              in proceedings of International Conference on Distributed
              Systems 2003.

   [Dabek]    Dabek, F., Cox, R., Kaashoek, F., and R. Morris, "Vivaldi:
              A Decentralized Network Coordinate System", in ACM
              SIGCOMM: Proceedings of the 2004 conference on
              Applications, technologies, architectures, and protocols
              for computer communications, vol. 34, no. 4.

   [Dovrolis]
              Dovrolis, C., Ramanathan, P., and D. Moore, "What do
              packet dispersion techniques measure?", in proceedings of
              IEEE INFOCOM 2001.

   [Francis]  Francis, P., Jamin, S., Jin, C., Jin, Y., Raz, D.,
              Shavitt, Y., and L. Zhang, "IDMaps: A global Internet host
              distance estimation service", in proceedings of IEEE
              INFOCOM 2001.

   [Glasner]  Glasner, J., "P2P fuels global bandwidth binge", available
              from http://www.wired.com/.

   [Gummadi]  Gummadi, K., Gummadi, R., Gribble, S., Ratnasamy, S.,
              Shenker, S., and I. Stoica, "The impact of DHT routing
              geometry on resilience and proximity", in ACM SIGCOMM:
              Proceedings of the 2003 conference on Applications,
              technologies, architectures, and protocols for computer
              communications.

   [Gurbani]  Gurbani, V., Hilt, V., Rimac, I., Tomsu, M., and E.
              Marocco, "A Survey of Research on the Application-Layer
              Traffic Optimization Problem and the Need for Layer
              Cooperation", in IEEE Communications, vol. 47, no. 8.

   [Karagiannis]
              Karagiannis, T., Broido, A., Brownlee, N., Claffy, K., and
              M. Faloutsos, "Is P2P dying or just hiding?",
              in proceedings of IEEE GLOBECOM 2004 Conference.

   [LeBlond]  Le Blond, S., Legout, A., and W. Dabbous, "Pushing
              BitTorrent Locality to the Limit", available
              at http://hal.inria.fr/.



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   [Ledlie]   Ledlie, J., Gardner, P., and M. Seltzer, "Network
              Coordinates in the Wild", in USENIX: Proceedings of NSDI
              2007.

   [LightReading]
              LightReading, "Controlling P2P traffic", available
              from http://www.lightreading.com/.

   [LinuxReviews]
              linuxReviews.org, "Peer to peer network traffic may
              account for up to 85% of Interneta??s bandwidth usage",
              available from http://linuxreviews.org/.

   [Madhyastha]
              Madhyastha, H., Isdal, T., Piatek, M., Dixon, C.,
              Anderson, T., Krishnamurthy, A., and A. Venkataramani.,
              "iPlane: an information plane for distributed services",
              in USENIX: Proceedings of the 7th symposium on Operating
              systems design and implementation.

   [Meeker]   Meeker, M. and D. Joseph, "The State of the Internet, Part
              3", available from http://www.morganstanley.com/.

   [Ng]       Ng, T. and H. Zhang, "Predicting internet network distance
              with coordinates-based approaches", in proceedings of
              INFOCOM 2002.

   [Ono]      "Northwestern University Ono Project",
              <http://www.aqualab.cs.northwestern.edu/projects/
              Ono.html>.

   [P4P]      "DCIA P4P Working group",
              <http://www.dcia.info/activities/#P4P.>.

   [Padhye]   Padhye, J., Firoiu, V., Towsley, D., and J. Kurose,
              "Modeling TCP throughput: A simple model and its empirical
              validation", in Technical Report UM-CS-1998-008,
              University of Massachusetts 1998.

   [Parker]   Parker, A., "The true picture of peer-to-peer
              filesharing", available from http://www.cachelogic.com/.

   [RFC4732]  Handley, M., Rescorla, E., and IAB, "Internet Denial-of-
              Service Considerations", RFC 4732, December 2006.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.




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   [RFC4981]  Risson, J. and T. Moors, "Survey of Research towards
              Robust Peer-to-Peer Networks: Search Methods", RFC 4981,
              September 2007.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5594]  Peterson, J. and A. Cooper, "Report from the IETF Workshop
              on Peer-to-Peer (P2P) Infrastructure, May 28, 2008",
              RFC 5594, July 2009.

   [RFC5632]  Griffiths, C., Livingood, J., Popkin, L., Woundy, R., and
              Y. Yang, "Comcast's ISP Experiences in a Proactive Network
              Provider Participation for P2P (P4P) Technical Trial",
              RFC 5632, September 2009.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [Ratnasamy]
              Ratnasamy, S., Francis, P., Handley, M., Karp, R., and S.
              Shenker, "A Scalable Content-Addressable Network", in ACM
              SIGCOMM: Proceedings of the 2001 conference on
              Applications, technologies, architectures, and protocols
              for computer communications, January 2001.

   [Ren]      Ren, S., Guo, L., and X. Zhang, "ASAP: An AS-aware peer-
              relay protocol for high quality VoIP", in proceedings of
              IEEE ICDCS 2006.

   [Rhea]     Rhea, S., Godfrey, B., Karp, B., Kubiatowicz, J.,
              Ratnasamy, S., Shenker, S., Stoica, I., and H. Yu,
              "OpenDHT: a public DHT service and its uses", in ACM
              SIGCOMM: Proceedings of the 2005 conference on
              Applications, technologies, architectures, and protocols
              for computer communications, August 2005.

   [Saucez]   Saucez, D., Donnet, B., and O. Bonaventure,
              "Implementation and Preliminary Evaluation of an ISP-
              Driven Informed Path Selection", in proceedings of ACM
              CoNEXT 2007.

   [Seetharaman]
              Seetharaman, S., Hilt, V., Hofmann, M., and M. Ammar,
              "Preemptive Strategies to Improve Routing Performance of



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              Native and Overlay Layers", in proceedings of IEEE INFOCOM
              2007.

   [Su]       Su, A., Choffnes, D., Kuzmanovic, A., and F. Bustamante,
              "Drafting behind Akamai (travelocity-based detouring)",
              in ACM SIGCOMM: Proceedings of the 2006 conference on
              Applications, technologies, architectures, and protocols
              for computer communications.

   [Wang]     Wang, G., Zhang, B., and T. Ng, "Towards Network Triangle
              Inequality Violation Aware Distributed Systems", in ACM
              SIGCOMM: Proceedings of the 7th conference on Internet
              measurement.

   [Wong]     Wong, B., Slivkins, A., and E. Sirer, "Meridian: A
              lightweight network location service without virtual
              coordinates", in ACM SIGCOMM: Proceedings of the 2005
              conference on Applications, technologies, architectures,
              and protocols for computer communications.

   [Xie]      Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A.
              Silberschatz, "P4P: Explicit Communications for
              Cooperative Control Between P2P and Network Providers",
              in ACM SIGCOMM Computer Communication Review, vol. 38, no.
              4.


Authors' Addresses

   Ivica Rimac
   Bell Labs, Alcatel-Lucent

   Email: rimac@bell-labs.com


   Volker Hilt
   Bell Labs, Alcatel-Lucent

   Email: volkerh@bell-labs.com


   Marco Tomsu
   Bell Labs, Alcatel-Lucent

   Email: marco.tomsu@alcatel-lucent.com






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   Vijay K. Gurbani
   Bell Labs, Alcatel-Lucent

   Email: vkg@bell-labs.com


   Enrico Marocco
   Telecom Italia

   Email: enrico.marocco@telecomitalia.it









































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