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Network Working Group                                       C. GriffithsRequest for Comments: 5632                                  J. LivingoodCategory: Informational                                          Comcast                                                               L. Popkin                                                                   Pando                                                               R. Woundy                                                                 Comcast                                                                 Y. Yang                                                                    Yale                                                          September 2009Comcast's ISP Experiences in a Proactive Network Provider Participation                     for P2P (P4P) Technical TrialAbstract   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, which is being   considered by the IETF as part of the Application Layer Transport   Optimization (ALTO) working group.Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.Griffiths, et al.            Informational                      [Page 1]

RFC 5632                Comcast P4P Experiences           September 2009Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .22.  High-Level Details . . . . . . . . . . . . . . . . . . . . . .33.  Differences between the P4P iTrackers Used . . . . . . . . . .43.1.  P4P Fine Grain . . . . . . . . . . . . . . . . . . . . . .43.2.  P4P Coarse Grain . . . . . . . . . . . . . . . . . . . . .53.3.  P4P Generic Weighted . . . . . . . . . . . . . . . . . . .54.  High-Level Trial Results . . . . . . . . . . . . . . . . . . .54.1.  Swarm Size . . . . . . . . . . . . . . . . . . . . . . . .64.2.  Impact on Download Speed . . . . . . . . . . . . . . . . .7     4.3.  General Impacts on Upstream and Downstream Traffic and           Other Interesting Data . . . . . . . . . . . . . . . . . .75.  Important Notes on Data Collected  . . . . . . . . . . . . . .86.  Next Steps . . . . . . . . . . . . . . . . . . . . . . . . . .97.  Security Considerations  . . . . . . . . . . . . . . . . . . .108.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .109.  Informative References . . . . . . . . . . . . . . . . . . . .101.  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 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 [RFC5594].  This work was discussed in greater detail   at the 72nd meeting of the IETF, in Dublin, Ireland, in the ALTO BoF   (Birds of a Feather meeting) 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.Griffiths, et al.            Informational                      [Page 2]

RFC 5632                Comcast P4P Experiences           September 2009   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 [DynamicSwarmMgmt], 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 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 inSection 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 that 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 asGriffiths, et al.            Informational                      [Page 3]

RFC 5632                Comcast P4P Experiences           September 2009   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.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 ongoing 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 (ASNs) 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 (OTNs) where all   Cable Modem Termination Systems (CMTS, as briefly defined inSection2.6 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 nodeGriffiths, et al.            Informational                      [Page 4]

RFC 5632                Comcast P4P Experiences           September 2009   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 ensured we would get similar data sets from the Fine Grain   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 wereGriffiths, et al.            Informational                      [Page 5]

RFC 5632                Comcast P4P Experiences           September 2009   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.                  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 RatesGriffiths, et al.            Informational                      [Page 6]

RFC 5632                Comcast P4P Experiences           September 20094.2.  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    |            |             |            |   +--------------+------------+------------+-------------+------------+           Table 2: Per-Swarm Global and Comcast Download Speeds4.3.  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 thatGriffiths, et al.            Informational                      [Page 7]

RFC 5632                Comcast P4P Experiences           September 2009   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   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 andGriffiths, et al.            Informational                      [Page 8]

RFC 5632                Comcast P4P Experiences           September 2009   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   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 a 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.).Griffiths, et al.            Informational                      [Page 9]

RFC 5632                Comcast P4P Experiences           September 20097.  Security Considerations   This document does not propose any kind of protocol, practice or   standard.   The experiment did show that an ISP can improve performance without   exposing fine-grained details about network structure, which might   otherwise be a security concern (seeSection 3.1 (P4P Fine Grain) andSection 3.2 (P4P Coarse Grain).Section 6 (Next Steps) mentions that   the opt-in architecture allows P2P users to maintain privacy.   Other security aspects were not considered in the experiment, which   focused on performance measurements.8.  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   results.9.  Informative References   [DynamicSwarmMgmt]              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/>.   [RFC3083]  Woundy, R., "Baseline Privacy Interface Management              Information Base for DOCSIS Compliant Cable Modems and              Cable Modem Termination Systems",RFC 3083, March 2001.   [RFC5594]  Peterson, J. and A. Cooper, "Report from the IETF Workshop              on Peer-to-Peer (P2P) Infrastructure, May 28, 2008",RFC 5594, July 2009.   [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>.Griffiths, et al.            Informational                     [Page 10]

RFC 5632                Comcast P4P Experiences           September 2009Authors' 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   Jason Livingood   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.comGriffiths, et al.            Informational                     [Page 11]

RFC 5632                Comcast P4P Experiences           September 2009   Richard Yang   Yale University   51 Prospect Street   New Haven, CT  06520   US   EMail: yry@cs.yale.edu   URI:http://www.cs.yale.eduGriffiths, et al.            Informational                     [Page 12]