Internet Engineering Task Force                             C. Griffiths
(ALTO)                                                      J. Livingood
Internet-Draft                                                 R. Woundy
Intended status: Informational                                   Comcast
Expires: May 1, 2009                                    October 28, 2008

       Comcast's ISP Experiences In a Recent P4P Technical Trial

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   This document describes the experiences of Comcast, a large cable
   broadband Internet Service Provider (ISP) in the U.S., in a recent
   Proactive Network Provider Participation for P2P (P4P) technical
   trial.  This trial used iTracker technology being considered by the
   IETF, as part of what is currently known as the Application Layer
   Transport Optimization (ALTO) Birds of a Feather (BoF).

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Table of Contents

   1.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  High-Level Details . . . . . . . . . . . . . . . . . . . . . .  3
   4.  High-Level Trial Results . . . . . . . . . . . . . . . . . . .  4
     4.1.  Impact on Downloads, or Downstream Traffic . . . . . . . .  4
     4.2.  Other Impacts and Interesting Data . . . . . . . . . . . .  5
   5.  Differences Between the P4P iTrackers Used . . . . . . . . . .  6
     5.1.  P4P Fine Grain . . . . . . . . . . . . . . . . . . . . . .  6
     5.2.  P4P Coarse Grain . . . . . . . . . . . . . . . . . . . . .  6
     5.3.  P4P Generic Weighted . . . . . . . . . . . . . . . . . . .  7
   6.  Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   10. Normative References . . . . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  8
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

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1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Introduction

   Comcast is a large broadband ISP, based in the U.S., serving the
   majority of its customers via cable modem technology.  A trial was
   recently conducted with Pando Networks, Yale, and several ISP members
   of the P4P Working Group, which is part of the Distributed Computing
   Industry Association (DCIA).  Comcast is a member of the P4P Working
   Group, whose mission is to work with Internet service providers
   (ISPs), peer to peer (P2P) companies, and technology researchers to
   develop "P4P" mechanisms that accelerate distribution of content and
   optimize utilization of ISP network resources.  P4P theoretically
   allows P2P networks to optimize traffic within each ISP, reducing the
   volume of data traversing the ISP's infrastructure and creating a
   more manageable flow of data.  P4P can also accelerate P2P downloads
   for end users.

   P4P's so-called "iTracker" technology was conceptually discussed with
   the IETF at the Peer to Peer Infrastructure (P2Pi) Workshop held on
   May 22, 2008, at the Massachusetts Institute of Technology (MIT).
   This work was discussed in greater detail at the 72nd meeting of the
   IETF, in Dublin, Ireland, in the ALTO BoF on July 29, 2008.  Since
   that time, discussion of iTrackers has continued with participants of
   the ALTO BoF and P2Pi Workshop, as the IETF community plans for a
   second BoF at the 73rd meeting of the IETF in November, 2008.  At
   IETF 72, Comcast offered to share P4P trial data with the community,
   and to present this in some detail at the next ALTO BoF.

   The P4P trial was conducted, in cooperation with Pando, Yale, and
   three other P4P member ISPs, from July 2 to July 17, 2008.  This was
   the first P4P trial over a cable broadband network.  The trial used a
   Pando P2P client, and Pando distributed a special 21 MB licensed
   video file as in order to measure the effectiveness of P4P iTrackers.
   A primary objective of the trial was to measure the effects that
   increasing the localization of P2P swarms would have on P2P uploads,
   P2P downloads, and ISP networks, in comparison to normal P2P

3.  High-Level Details

   There were five different swarms for the content used in the trial.

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   The first was a random P2P swarm, as a control group.  The second,
   third, and fourth used different P4P iTrackers: Generic, Coarse
   Grained, and Fine Grained.  The fifth was a proprietary Pando
   mechanism.  (The results of the fifth swarm, while very good, are not
   included here since our focus is on open standards and a mechanism
   which may be leveraged for the benefit of the entire community of P2P
   clients.)  During the trial, there were 15,518 downloads to Comcast-
   based P2P clients.  Comcast deployed an iTracker server in our
   production network to support this trial, and configured multiple
   iTracker files to provide varying levels of localization to clients.

   In the trial itself, a P2P client begins a P2P session by querying a
   pTracker, which runs and manages the P2P network.  The pTracker
   occasionally queries the iTracker, which in this case was maintained
   by Comcast, the ISP.  Other ISPs either managed their own iTracker or
   used Pando or Yale to host their iTracker files.  The iTracker
   returns network topology information to the pTracker, which then
   communicates with P2P clients, in order to enable P2P clients to make
   network-aware decisions regarding peers.

4.  High-Level Trial Results

   Trial data was collected by Pando Networks and Yale University, and
   raw trial results were shared with Comcast and all of the other ISPs
   involved in the trial.  Analysis of the raw results was performed by
   Pando and Yale, and these organizations delivered an analysis of the
   P4P trial.  Using the raw data, Comcast also analyzed the trial
   results.  Furthermore, the raw trial results for Comcast were shared
   with Net Forecast, Inc., which performed an independent analysis of
   the trial for Comcast.

4.1.  Impact on Downloads, or Downstream Traffic

   The results of the trial indicated that P4P can improve the speed of
   downloads to P2P clients.  In addition, P4P was effective in
   localizing P2P traffic within the Comcast network.

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                        Impact of P4P on Downloads:

   |     Swarm    | Global Avg |   Change   | Comcast Avg |   Change   |
   |              |     bps    |            |     bps     |            |
   |    Random    |   144,045  |     n/a    | 254,671 bps |     n/a    |
   |   (Control)  |     bps    |            |             |            |
   |  ----------  | ---------- | ---------- |  ---------- | ---------- |
   |   P4P Fine   |   162,344  |    +13%    | 402,043 bps |    +57%    |
   |    Grained   |     bps    |            |             |            |
   |  ----------  | ---------- | ---------- |  ---------- | ---------- |
   |  P4P Generic |   163,205  |    +13%    | 463,782 bps |    +82%    |
   |    Weight    |     bps    |            |             |            |
   |  ----------  | ---------- | ---------- |  ---------- | ---------- |
   |  P4P Coarse  |   166,273  |    +15%    | 471,218 bps |    +85%    |
   |    Grained   |     bps    |            |             |            |

      Table 1: Data Collected with Pando Networks and Yale University

4.2.  Other Impacts and Interesting Data

   An analysis of the effects of P4P on upstream utilization and
   Internet transit was also interesting.  It did not appear that P4P
   significantly increased upstream utilization in our access network;
   in essence uploading was already occurring no matter what and P4P in
   and of itself did not appear to materially increase uploading for
   this specific, licensed content.  (P4P is not intended as a solution
   for the potential of network congestion to occur.)  Random was
   143,236 MB and P4P Generic Weight was 143,143 MB, while P4P Coarse
   Grained was 139,669 MB.  We also observed that P4P reduced outgoing
   Internet traffic by an average of 34% at peering points.  Random was
   134,219 MB and P4P Generic Weight was 91,979 MB, while P4P Coarse
   Grained was 86,652 MB.

   In terms of downstream utilization, we observed that P4P reduced
   incoming Internet traffic by an average of 80% at peering points.
   Random was 47,013 MB and P4P Generic Weight was 8,610 MB, while P4P
   Coarse Grained was 7,764 MB.  However, we did notice that download
   activity in our access network increased somewhat, from 56,030 MB for
   Random, to 59,765 MB for P4P Generic Weight, and 60,781 MB for P4P
   Coarse Grained.

   During the trial, downloads peaked at 24,728 per day, per swarm, or
   nearly 124,000 per day for all five swarms.  The swarm size peaked at
   11,703 peers per swarm, or nearly 57,000 peers for all five swarms.
   We observed a comparable number of downloads in each of the five

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5.  Differences Between the P4P iTrackers Used

   Given the size of the Comcast network, it was felt that in order to
   truly evaluate the iTracker application we would need to test various
   network topologies that reflected our network and would help gauge
   the level of effort and design requirements necessary to get correct
   statistical data out of the trial.  In all cases, iTrackers were
   configured with automation in mind, so that any successful iTracker
   configuration would be automatically updating, rather than manually
   configured on an on-going basis.  All iTrackers were hosted on the
   same small server, and it appeared to be relatively easy and
   inexpensive to scale up an iTracker infrastructure should P4P-like
   mechanisms become standardized and widely adopted.

5.1.  P4P Fine Grain

   The Fine Grain topology was the first and most complex iTracker that
   we built for this trial.  It was a detailed mapping of Comcast
   backbone-connected network Autonomous System Numbers (ASN) to IP
   Aggregates which were weighted based on priority and distance from
   each other.  Included in this design was a prioritization of all Peer
   and Internet transit connected ASNs to our backbone to ensure that
   P4P traffic would prefer settlement free and lower cost networks
   first, and then more expensive transit links.  This attempted to
   optimize and lower transit costs associated with this traffic.  We
   then took the additional step of detailing each ASN and IP aggregate
   into IP subnets down to our Optical Transport Nodes (OTN) where all
   Cable Modem Termination Systems (CMTS) reside.  This design gave a
   highly localized and detailed description of our network for the
   iTracker to disseminate.  This design defined 1,182 iTracker node
   identifiers, and resulted in a 210,727 line configuration file.

   This iTracker was obviously the most time-consuming to create and the
   most complex to maintain.  Trial results indicated that this level of
   localization was too high, and was less effective compared to lower
   levels of localization.

5.2.  P4P Coarse Grain

   Given the level of detail in the Fine Grain design, it was important
   that we also enable a high-level design which still used priority and
   weighting mechanisms for our backbone and transit links.  The Coarse
   Grain design was a limited or summarized version of the Fine Grain
   design, which used the ASN to IP Aggregate and weighted data for
   transit links, but removed all additional localization data.  This

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   insured we would get similar data sets from the Fine Grain design,
   but without the more detailed localization of each of our networks
   off of our backbone.  This design defined 22 iTracker node
   identifiers, and resulted in a 1,461 line configuration file.

   From an overall cost, complexity, risk, and effectiveness standpoint,
   this was judged to be the optimal iTracker for Comcast.  Importantly,
   this did not require revealing the complex, internal network topology
   that the Fine Grain did.  Updates to this iTracker were also far
   simpler to automate, which will better ensure that it is accurate
   over time, and keeps administrative overhead relatively low.
   However, the differences, costs, and benefits of Coarse Grain and
   Generic Weighted (see below) likely merit further study.

5.3.  P4P Generic Weighted

   The Generic Weighted design was a copy of the Coarse Grained design
   but instead of using our ISP-designated priority and weights, all
   weights were defaulted to pre-determined parameters that the Yale
   team had designed.  All other data was replicated from the Coarse
   Grain design.  Providing the information necessary to support the
   Generic Weighted iTracker was roughly the same as for Coarse Grain.

6.  Next Steps

   One objective of this document is to share with the IETF community
   the results of one P4P trial in a large broadband network, given
   skepticism regarding both the benefits to P2P users and to ISPs.
   From the perspective of P2P users, P4P potentially delivers faster
   P2P downloads.  At the same time, ISPs can increase the localization
   of swarms, enabling them to reduce bytes flowing over transit points,
   while also delivering an optimized P2P experience to customers.
   However, an internal analysis of varying levels of iTracker adoption
   by ISPs leads us to believe that, while P4P-type mechanisms are
   valuable on a single ISP basis, the value of P4P increases
   dramatically as many ISPs choose to deploy it.

   We believe these results can inform the technical discussion in the
   IETF over how to use iTracker mechanisms.  Should such a mechanism be
   standardized, the use of ISP-provided iTrackers should probably be an
   opt-in feature for P2P users, or at least a feature of which they are
   explicitly aware of and which has been enabled by default in a
   particular P2P client.  In this way, P2P users could choose to opt-in
   either explicitly or by their choice of P2P client in order to choose
   to use the iTracker to improve performance, which benefits both the
   user and the ISP at the same time.  Importantly in terms of privacy,
   the iTracker makes available only network topology information, and

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   would not in its current form enable an ISP, via the iTracker, to
   determine what P2P clients were downloading what content.

   It is also possible that an iTracker type of mechanism, in
   combination with a P2P cache, could further improve P2P download
   performance, which merits further study.  In addition, this was a
   limited trial that, while very promising, indicates a need for
   additional technical investigation and trial work.  Such follow-up
   study should explore the effects of P4P when more P2P client software
   variants are involved, with larger swarms, and with additional and
   more technically diverse content (file size, file type, duration of
   content, etc.).

7.  Security Considerations

   There are no security considerations to include at this time.

8.  IANA Considerations

   There are no IANA considerations in this document.

9.  Acknowledgements

   The authors wish to acknowledge the hard work of all of the P4P
   working group members, and specifically the focused efforts of the
   teams at both Pando and Yale for the trial itself.  Finally, the
   authors recognize and appreciate Peter Sevcik and John Bartlett, of
   NetForecast, Inc., for their valued independent analysis of the trial

10.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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Authors' Addresses

   Chris Griffiths
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103


   Jason Livingood
   Comcast Cable Communications
   One Comcast Center
   1701 John F. Kennedy Boulevard
   Philadelphia, PA  19103


   Richard Woundy
   Comcast Cable Communications
   27 Industrial Avenue
   Chelmsford, MA  01824


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