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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 5632

Internet Engineering Task Force                             C. Griffiths
Internet-Draft                                         J. Livingood, Ed.
Intended status: Informational                                   Comcast
Expires: December 14, 2009                                     L. Popkin
                                                                   Pando
                                                               R. Woundy
                                                                 Comcast
                                                                 Y. Yang
                                                                    Yale
                                                           June 12, 2009


           Comcast's ISP Experiences In a P4P Technical Trial
               draft-livingood-woundy-p4p-experiences-10

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Abstract

   This document describes the experiences of Comcast, a large cable
   broadband Internet Service Provider (ISP) in the U.S., in a Proactive
   Network Provider Participation for P2P (P4P) technical trial in July
   2008.  This trial used P4P iTracker technology being considered by
   the IETF, as part of the Application Layer Transport Optimization
   (ALTO) working group.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  High-Level Details . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Differences Between the P4P iTrackers Used . . . . . . . . . .  5
     3.1.  P4P Fine Grain . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  P4P Coarse Grain . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  P4P Generic Weighted . . . . . . . . . . . . . . . . . . .  6
   4.  High-Level Trial Results . . . . . . . . . . . . . . . . . . .  6
     4.1.  Swarm Size . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Impact on Download Speed . . . . . . . . . . . . . . . . .  7
     4.3.  General Impacts on Upstream and Downstream Traffic and
           Other Interesting Data . . . . . . . . . . . . . . . . . .  8
   5.  Important Notes on Data Collected  . . . . . . . . . . . . . .  8
   6.  Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Informative References . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11





















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1.  Introduction

   Comcast is a large broadband Internet Service Provider (ISP), based
   in the U.S., serving the majority of its customers via cable modem
   technology.  A trial was conducted in July 2008 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 DCIA's 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, such as so-
   called "iTrackers" (hereafter P4P iTrackers), that accelerate
   distribution of content and optimize utilization of ISP network
   resources.  P4P iTrackers theoretically allow 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 iTrackers can also accelerate P2P downloads for
   end users.

   P4P's so-called "iTracker" technology [SIGCOMM] was conceptually
   discussed with the IETF at the Peer-to-Peer Infrastructure (P2Pi)
   Workshop held on May 28, 2008, at the Massachusetts Institute of
   Technology (MIT), as documented in [I-D.p2pi-cooper-workshop-report].
   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.  Due to
   interest from the community, Comcast shared P4P iTracker trial data
   at the 73rd meeting of the IETF, in Minneapolis, Minnesota, in the
   ALTO BoF on November 18, 2008.  Since that time, discussion of P4P
   iTrackers and alternative technologies has continued among
   participants of the ALTO working group.

   The P4P iTracker 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 iTracker trial over a cable broadband network.
   The trial used a Pando P2P client, and Pando distributed a special 21
   MB licensed video file 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 activity.


2.  High-Level Details

   As noted in Section 1 of [Dynamic Swarm Management], a swarm is
   defined in the following way: "The content and the set of peers
   distributing it [a file] is usually called a torrent.  A peer that
   only uploads content is called a seed, while a peer that uploads and
   downloads at the same time is called a leecher.  The connected set of



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   peers participating in the piece exchanges of a torrent is referred
   to as a swarm."

   There were five different swarms for the content used in the trial.
   The second, third, and fourth used different P4P iTrackers: Generic,
   Coarse Grained, and Fine Grained, all of which are described in
   Section 3.  The fifth was a proprietary Pando mechanism.  (The
   results of the fifth swarm, while satisfactory, 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.)
   Comcast deployed a P4P iTracker server in its 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 P4P iTracker, which in this case was
   maintained by Comcast, the ISP.  Other ISPs either managed their own
   P4P iTracker or used Pando or Yale to host their P4P iTracker files.
   The P4P 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.

   The Pando client was enabled to capture extended logging, when the
   version of the client included support for it.  The extended logging
   included the source and destination IP address of all P2P transfers,
   the number of bytes transferred, and the start and end timestamps.
   This information gives a precise measurement of the data flow in the
   network, allowing computation of data transfer volumes as well as
   data flow rates at each point in time.  With standard logging, Pando
   captured the start and completion times of every download, as well as
   the average transfer rate observed by the client for the download.

   Pando served the data from an origin server external to Comcast's
   network.  This server served about 10 copies of the file, after which
   all transfers (about 1 million downloads across all ISPs) were
   performed purely via P2P.

   The P2P clients in the trial start with tracker-provided peers, then
   use peer exchange to discover additional peers.  Thus, the initial
   peers were provided according to P4P iTracker guidance (90% guidance
   based on P4P iTracker topology, and 10% random guidance), then later
   peers discover the entire swarm via either additional announces or
   peer exchange.







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3.  Differences Between the P4P iTrackers Used

   Given the size of the Comcast network, it was felt that in order to
   truly evaluate the P4P iTracker application we would need to test
   various network topologies that reflected its 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, P4P
   iTrackers were configured with automation in mind, so that any
   successful P4P iTracker configuration would be automatically
   updating, rather than manually configured on an on-going basis.  All
   P4P iTrackers were hosted on the same small server, and it appeared
   to be relatively easy and inexpensive to scale up a P4P iTracker
   infrastructure should P4P iTracker-like mechanisms become
   standardized and widely adopted.

3.1.  P4P Fine Grain

   The Fine Grain topology was the first and most complex P4P 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 the Comcast 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 Optical Transport Nodes (OTN) where all Cable
   Modem Termination Systems (CMTS, as briefly defined in Section 2.6 of
   [RFC3083]) reside .  This design gave a highly localized and detailed
   description of the Comcast network for the iTracker to disseminate.
   This design defined 1,182 P4P iTracker node identifiers, and resulted
   in a 107,357-line configuration file.

   This P4P 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.

3.2.  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 the Comcast 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 insured we would get similar data sets from the Fine Grain



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   design, but without the more detailed localization of each of the
   networks attached to the Comcast backbone.  This design defined 22
   P4P iTracker node identifiers, and resulted in a 998-line
   configuration file.

   From an overall cost, complexity, risk, and effectiveness standpoint,
   this was judged to be the optimal P4P 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.

3.3.  P4P Generic Weighted

   The Generic Weighted design was a copy of the Coarse Grained design
   but instead of using 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.  Gathering and providing the information necessary to support
   the Generic Weighted iTracker was roughly the same level of effort as
   for Coarse Grain.


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 iTracker 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.  Swarm Size

   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
   swarms.

   For each swarm, Table 1 below gives the number of downloads per swarm
   from Comcast that finished downloading, and the number of downloads
   from Comcast that canceled downloading before finishing.




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                  Characteristics of P4P iTracker Swarms:

   +-----------+-----------+---------------+------------+--------------+
   |   Swarm   | Completed | Cancellations |    Total   | Cancellation |
   |           | Downloads |               |  Attempts  |     Rate     |
   +-----------+-----------+---------------+------------+--------------+
   |   Random  |   2,719   |       89      |    2,808   |     3.17%    |
   | (Control) |           |               |            |              |
   | --------- | --------- |  -----------  | ---------- |  ----------- |
   |  P4P Fine |   2,846   |       64      |    2,910   |     2.20%    |
   |  Grained  |           |               |            |              |
   | --------- | --------- |  -----------  | ---------- |  ----------- |
   |    P4P    |   2,775   |       63      |    2,838   |     2.22%    |
   |  Generic  |           |               |            |              |
   |   Weight  |           |               |            |              |
   | --------- | --------- |  -----------  | ---------- |  ----------- |
   |    P4P    |   2,886   |       52      |    2,938   |     1.77%    |
   |   Coarse  |           |               |            |              |
   |  Grained  |           |               |            |              |
   +-----------+-----------+---------------+------------+--------------+

              Table 1: Per-Swarm Size and Cancellation Rates

4.2.  Impact on Download Speed

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

                   Impact of P4P iTrackers 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    |            |             |            |
   +--------------+------------+------------+-------------+------------+




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           Table 2: Per-Swarm Global and Comcast Download Speeds

4.3.  General Impacts on Upstream and Downstream Traffic and Other
      Interesting Data

   An analysis of the effects of P4P iTracker use on upstream
   utilization and Internet transit was also interesting.  It did not
   appear that P4P iTrackers significantly increased upstream
   utilization in the Comcast access network; in essence uploading was
   already occurring no matter what and a P4P iTracker in and of itself
   did not appear to materially increase uploading for this specific,
   licensed content.  (A P4P iTracker 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 using a P4P iTracker 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 the use of a P4P
   iTracker reduced incoming Internet traffic by an average of 80% at
   peering points.  Random was 47,013 MB, P4P Generic Weight was 8,610
   MB, and P4P Coarse Grained was 7,764 MB.  However, we did notice that
   download activity in the Comcast 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.  Note that for each swarm, the
   number of downloaded bytes according to logging reports is very close
   to the number of downloads multiplied by file size.  But they do not
   exactly match due to log report errors and duplicated chunks.  One
   factor contributing to the differences in access network download
   activity is that different swarms have different numbers of
   downloaders, due to random variations during uniform random
   assignment of downloaders to swarms (see Table 1).  One interesting
   observation is that Random has higher cancellation rate (3.17%) than
   that of the guided swarms (1.77%-2.22%).  Whether guided swarms
   achieve lower cancellation rate is an interesting issue for future
   research.


5.  Important Notes on Data Collected

   Raw data is presented in this document.  We did not normalize traffic
   volume data (e.g. upload and download) by the number of downloads in
   order to preserve this underlying raw data.

   We also recommend that readers not focus too much on the absolute
   numbers, such as bytes downloaded from internal sources and bytes
   downloaded from external sources.  Instead, we recommend readers



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   focus on ratios such as the percentage of bytes downloaded that came
   from internal sources in each swarm.  As a result, the small random
   variation between number of downloads of each swarm does not distract
   readers from important metrics like shifting traffic from external to
   internal sources, among other things.

   We also wish to note that the data was collected from a sample of the
   total swarm.  Specifically, there were some peers running older
   versions of the Pando client that did not implement the extended
   transfer logging.  For those nodes, which participated in the swarms
   but did not report their data transfers, we have download counts.
   The result of this is that, for example, the download counts
   generated from the standard logging are a bit higher than the
   download counts generated by the extended logging.  That being said,
   over 90% of downloads were by peers running the newer software, which
   we believe shows that the transfer records are highly representative
   of the total data flow.

   In terms of which analysis was performed from the standard logging
   compared to extended logging, all of the data flow analysis was
   performed using the extended logging.  Pando's download counts and
   performance numbers were generated via standard logging (i.e. all
   peers report download complete/cancel, data volumes, and measured
   download speed on the client).  Yale's download counts and
   performance numbers were derived via extended logging (e.g. by
   summing the transfer records, counting IP addresses reported, etc.).

   One benefit of having two data sources is that we can compare the
   two.  In this case, the two approaches both reported comparable
   impacts.


6.  Next Steps

   One objective of this document is to share with the IETF community
   the results of one P4P iTracker trial in a large broadband network,
   given skepticism regarding the benefits to P2P users as well as to
   ISPs.  From the perspective of P2P users, P4P iTrackers potentially
   deliver 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 P4P iTracker adoption by ISPs leads us to believe that,
   while P4P iTracker-type mechanisms are valuable on a single ISP
   basis, the value of P4P iTrackers increases dramatically as many ISPs
   choose to deploy it.

   We believe these results can inform the technical discussion in the



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   IETF over how to use P4P iTracker mechanisms.  Should such a
   mechanism be standardized, the use of ISP-provided P4P 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 P4P iTracker to improve
   performance, which benefits both the user and the ISP at the same
   time.  Importantly in terms of privacy, the P4P iTracker makes
   available only network topology information, and would not in its
   current form enable an ISP, via the P4P iTracker, to determine which
   P2P clients were downloading any specific content, whether to
   determine for example if content was a song or a movie or even the
   title.

   It is also possible that a P4P 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 iTrackers 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 in this document.

   NOTE TO RFC EDITOR: PLEASE REMOVE THIS NULL SECTION PRIOR TO
   PUBLICATION.


8.  IANA Considerations

   There are no IANA considerations in this document.

   NOTE TO RFC EDITOR: PLEASE REMOVE THIS NULL SECTION PRIOR TO
   PUBLICATION.


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



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   NetForecast, Inc., for their valued independent analysis of the trial
   results.


10.  Informative References

   [Dynamic Swarm Management]
              Carlsson, N. and G. Dan, "Dynamic Swarm Management for
              Improved BitTorrent Performance", USENIX 8th International
              Workshop on Peer-to-Peer Systems, March 2009, <http://
              www.usenix.org/events/iptps09/tech/full_papers/dan/
              dan_html/>.

   [I-D.p2pi-cooper-workshop-report]
              Peterson, J. and A. Cooper, "Report from the IETF workshop
              on P2P Infrastructure, May 28, 2008",
              draft-p2pi-cooper-workshop-report-01 (work in progress),
              February 2009.

   [RFC3083]  Woundy, R., "Baseline Privacy Interface Management
              Information Base for DOCSIS Compliant Cable Modems and
              Cable Modem Termination Systems", RFC 3083, March 2001.

   [SIGCOMM]  Xie, H., Yang, Y., Krishnamurthy, A., Liu, Y., and A.
              Silberschatz, "ACM SIGCOMM 2008 - P4P: Provider Portal for
              Applications", Association for Computing Machinery SIGCOMM
              2008 Proceedings, August 2008,
              <http://ccr.sigcomm.org/online/files/p351-xieA.pdf>.


Authors' Addresses

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

   Email: chris_griffiths@cable.comcast.com
   URI:   http://www.comcast.com










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

   Email: jason_livingood@cable.comcast.com
   URI:   http://www.comcast.com


   Laird Popkin
   Pando Networks
   520 Broadway Street
   10th Floor
   New York, NY  10012
   US

   Email: laird@pando.com
   URI:   http://www.pando.com


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

   Email: richard_woundy@cable.comcast.com
   URI:   http://www.comcast.com


   Richard Yang
   Yale University
   51 Prospect Street
   New Haven, CT  06520
   US

   Email: yry@cs.yale.edu
   URI:   http://www.cs.yale.edu











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