I have been selected as the General Area Review Team (Gen-ART) reviewer for
this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html). Please resolve
these comments along with any other Last Call comments you may receive.
Document: draft-livingood-woundy-p4p-experiences-07
Reviewer: Spencer Dawkins
Review Date: 2009-05-27
IETF LC End Date: 2009-06-16
IESG Telechat date: (not known)
Summary: This document is nearly ready for publication as an Informational
RFC. I did identify some minor issues (listed below) that should be
considered as this document moves forward in the approval process.
I also identified some nits, which aren't actually part of the Gen-ART
review but are included for the convenience of the editor.
Thanks,
Spencer
1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Spencer (nit): idnits says no 2119 keywords in the document, so this section
can be deleted (along with the [rfc2119] reference.
2. Introduction
Comcast is a large broadband ISP, based in the U.S., serving the
Spencer (nit):
http://www.rfc-editor.org/rfc-style-guide/abbrev.expansion.txt doesn't list
"ISP" as an abbreviation that isn't expanded ("please expand on first use").
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.
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
Spencer (nit): suggest s/21 MB/21-MB/ for clarity
iTrackers. A primary objective of the trial was to measure the
effects that increasing the localization of P2P swarms would have on
Spencer (minor): it would be helpful to add a definition for "swarm" -
everyone kind of knows what you're talking about, but it's not even defined
in Wikipedia :-) (per
http://en.wikipedia.org/wiki/Swarm_(disambiguation))...
P2P uploads, P2P downloads, and ISP networks, in comparison to normal
P2P activity.
3. High-Level Details
There were five different swarms for the content used in the trial.
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, all of which are described in Section 4.
The fifth was a proprietary Pando mechanism. (The results of the
fifth swarm, while very good, are not included here since our focus
Spencer (minor): "while very good" is slightly more marketing-speak than I
was comfortable with... the ADs can ignore this comment, of course.
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.
4.1. 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) reside. This design gave a highly
Spencer (minor): you're referring to components of cable networking that
probably aren't familiar to many IETF participants - is there a generic
reference you could include here, for people who see a bunch of terms they
aren't familiar with, and want to investigate further? If not, you could
probably end the sentence at "into IP subnets".
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.
4.2. 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
design, but without the more detailed localization of each of the
networks off of the Comcast backbone. This design defined 22 P4P
Spencer (nit): "off of" wasn't clear to me - could you rephrase? is this
"attached to"? "adjacent to"?
iTracker node identifiers, and resulted in a 998 line configuration
file.
4.3. 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. Providing the information necessary to support the Generic
Weighted iTracker was roughly the same as for Coarse Grain.
Spencer (minor): is this "the level of effort was roughly the same"? not
quite sure what you're saying here...
5.2. 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.
Spencer (minor): I'm not sure I understand how the table below shows
localization (speedup which could be attributed to localization, maybe?)...
is the table supposed to show this?
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 Speeds
6. Important Notes on Data Collected
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.
Spencer (minor): it would be great if there was a table that showed these
ratios explicitly, if we're supposed to focus on them... :-) 5.1 and 5.2
with tables are a lot easier to grok than 5.3 without ...
7. Next Steps
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 what
P2P clients were downloading what content.
Spencer (nit): s/what/which/ seemed more natural to me in this sentence (but
do the right thing)
9. IANA Considerations
Spencer (nit): we often include "Note to RFC Editor: please delete this
section before publication" for null IANA sections, as Russ commented on one
of my drafts earlier today :-)
There are no IANA considerations in this document.
10. 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.
11.1. Normative References
Spencer (nit): as above, you can delete this reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2. Informative References
Spencer (nit): idnits says [SIGCOMM] isn't used as a reference in the
document, so it can go away, too.
[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>.
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