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Keywords: In-network storage, P2P
Internet Engineering Task Force (IETF) H. Song
Request for Comments: 6646 N. Zong
Category: Informational Huawei
ISSN: 2070-1721 Y. Yang
Yale University
R. Alimi
Google
July 2012
DECoupled Application Data Enroute (DECADE) Problem Statement
Abstract
Peer-to-peer (P2P) applications have become widely used on the
Internet today and make up a large portion of the traffic in many
networks. In P2P applications, one technique for reducing the
transit and uplink P2P traffic is to introduce storage capabilities
within the network. Traditional caches (e.g., P2P and Web caches)
provide such storage, but they can be complex (e.g., P2P caches need
to explicitly support individual P2P application protocols), and do
not allow users to manage resource usage policies for content in the
cache. This document discusses the introduction of in-network
storage for P2P applications and shows the need for a standard
protocol for accessing this storage.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6646.
Song, et al. Informational [Page 1]
RFC 6646 DECADE Problem Statement July 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
2. Terminology and Concepts ........................................3
3. The Problems ....................................................4
3.1. P2P Infrastructural Stress and Inefficiency ................4
3.2. P2P Cache: A Complex Type of In-Network Storage ............5
3.3. Ineffective Integration of P2P Applications ................6
4. Usage Scenarios .................................................6
4.1. BitTorrent .................................................6
4.2. Content Publisher ..........................................7
5. Security Considerations .........................................8
5.1. Denial-of-Service Attacks ..................................8
5.2. Copyright and Legal Issues .................................8
5.3. Traffic Analysis ...........................................8
5.4. Modification of Information ................................8
5.5. Masquerade .................................................9
5.6. Disclosure .................................................9
5.7. Message Stream Modification ................................9
6. Acknowledgments .................................................9
7. Informative References .........................................10
1. Introduction
Peer-to-peer (P2P) applications, including both P2P streaming and P2P
file-sharing applications, make up a large fraction of the traffic in
many Internet Service Provider (ISP) networks today. One way to
reduce bandwidth usage by P2P applications is to introduce storage
capabilities in networks. Allowing P2P applications to store and
retrieve data from inside networks can reduce traffic on the last-
mile uplink, as well as on backbone and transit links.
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RFC 6646 DECADE Problem Statement July 2012
Existing P2P caches provide in-network storage and have been deployed
in some networks. However, the current P2P caching architecture
poses challenges to both P2P cache vendors and P2P application
developers. For P2P cache vendors, it is challenging to support a
number of continuously evolving P2P application protocols, due to
lack of documentation, ongoing protocol changes, and rapid
introduction of new features by P2P applications. For P2P
application developers, closed P2P caching systems limit P2P
applications from effectively utilizing in-network storage. In
particular, P2P caches typically do not allow users to explicitly
store content into in-network storage. They also do not allow
applications to specific resource and access control policies over
the usage of in-network storage. The challenges, if not addressed,
may lead to reduced efficiency for P2P applications, and increased
load on the network infrastructure.
The challenges can be effectively addressed by using a standard, open
protocol to access in-network storage [Data_Lockers]. P2P
applications can store and retrieve content in the in-network
storage, as well as control resources (e.g., bandwidth, connections)
consumed by peers in a P2P application. As a simple example, a peer
of a P2P application may upload to other peers through its in-network
storage, saving its usage of last-mile uplink bandwidth.
In this document, we distinguish between two functional components of
the native P2P application protocol: signaling and data access.
Signaling includes operations such as handshaking and discovering
peer and content availability. The data access component transfers
content from one peer to another.
In essence, coupling of the signaling and data access makes
in-network storage complex to support various application services.
However, these applications have common requirements for data access,
making it possible to develop a standard protocol.
2. Terminology and Concepts
The following terms have special meaning in the definition of the
in-network storage system.
In-network storage: A service inside a network that provides storage
and bandwidth to network applications. In-network storage may
reduce upload/transit/backbone traffic and improve network
application performance. The position of in-network storage is in
the core of a network -- for example, co-located with the border
router (network attached storage) or inside a data center.
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P2P cache (peer-to-peer cache): A kind of in-network storage that
understands the signaling and transport of specific P2P
application protocols. It caches the content for those specific
P2P applications in order to serve peers and reduce traffic on
certain links.
3. The Problems
The emergence of P2P as a major network application (especially P2P
file sharing and streaming) has led to substantial opportunities.
The P2P paradigm can be utilized to design highly scalable and robust
applications at low cost, compared to the traditional client-server
paradigm.
However, P2P applications also face substantial design challenges. A
particular challenge facing P2P applications is the additional stress
that they place on the network infrastructure. At the same time,
lack of infrastructure support can lead to unstable P2P application
performance, in particular during peer churns and flash crowds, when
a large group of users begin to retrieve the content during a short
period of time, leading to stress on bandwidth-constrained access
uplinks. A potential way to reduce network stress and improve P2P
application performance would be to make it possible for peers that
are on bandwidth-constrained access to put data in a place that is
free of bandwidth constraints and also accessible by other peers.
These problems are now discussed in further detail.
3.1. P2P Infrastructural Stress and Inefficiency
A particular problem of the P2P paradigm is the stress that P2P
application traffic places on the infrastructure of ISPs. Multiple
measurements (e.g., [ipoque_Internet_Study]) have shown that P2P
traffic has become a major type of traffic on some networks.
Furthermore, the inefficiency of network-agnostic peering (at the P2P
transmission level) leads to unnecessary traversal across network
domains or spanning the backbone of a network [RFC5693].
Using network information alone to construct more efficient P2P
swarms is not sufficient to reduce P2P traffic in access networks, as
the total access upload traffic is equal to the total access download
traffic in a traditional P2P system. On the other hand, it is
reported that P2P traffic is becoming the dominant traffic on the
access networks of some networks, reaching as high as 50-60% on the
downlinks and 60-90% on the uplinks [DCIA] [ICNP] [ipoque_P2P_Survey]
[P2P_File_Sharing]. Consequently, it becomes increasingly important
to reduce upload access traffic, in addition to cross-domain and
backbone traffic.
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RFC 6646 DECADE Problem Statement July 2012
The inefficiency of P2P is also observed when traffic is sent
upstream as many times as there are remote peers interested in
getting the corresponding information. For example, the P2P
application transfer completion times remain affected by potentially
(relatively) slow upstream transmission. Similarly, the performance
of real-time P2P applications may be affected by potentially
(relatively) higher upstream latencies.
3.2. P2P Cache: A Complex Type of In-Network Storage
An effective technique to reduce P2P infrastructural stress and
inefficiency is to introduce in-network storage. A survey of
existing in-network storage systems can be found in [RFC6392].
In the current Internet, in-network storage is introduced as P2P
caches, either transparently or explicitly as a P2P peer. To provide
service to a specific P2P application, the P2P cache server must
support the specific signaling and transport protocols of the
specific P2P application. This can lead to substantial complexity
for the P2P cache vendor.
First, there are many P2P applications on the Internet (e.g.,
BitTorrent, eMule, Flashget, and Thunder for file sharing; Abacast,
Kontiki, Octoshape, PPLive, PPStream, and UUSee for P2P streaming).
Consequently, a P2P cache vendor faces the challenge of supporting a
large number of P2P application protocols, leading to product
complexity and increased development cost.
Second, a specific P2P application protocol may evolve continuously
to add new features or fix bugs. This in turn forces a P2P cache
vendor to continuously monitor application updates to track such
changes, leading to product complexity and increased costs.
Third, many P2P applications use proprietary protocols or support
end-to-end encryption. This can render P2P caches ineffective.
Therefore, these three problems make it difficult to use the P2P
cache as a network middlebox to support P2P application distribution.
Finally, an end host has better connectivity and connection quality
to a P2P cache than to a remote peer. Without the ability to manage
bandwidth usage, the P2P cache may increase the volume of download
traffic, which runs counter to the reduction of upload access
traffic.
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3.3. Ineffective Integration of P2P Applications
As P2P applications evolve, it has become increasingly clear that
usage of in-network resources can improve the user's experience. For
example, multiple P2P streaming systems seek additional in-network
resources during a flash crowd, such as just before a major live
streaming event. In asymmetric networks, when the aggregated upload
bandwidth of a channel cannot meet the download demand, a P2P
application may seek additional in-network resources to maintain a
stable system.
However, some P2P applications using in-network infrastructural
resources require flexibility in implementing resource allocation
policies. A major competitive advantage of many successful P2P
systems is their substantial expertise in how to most efficiently
utilize peer and infrastructural resources. For example, many live
P2P systems have specific algorithms to select those peers that
behave as stable, higher-bandwidth sources. Similarly, the higher-
bandwidth sources frequently use algorithms to choose to which peers
the source should send content. Developers of these systems continue
to fine-tune these algorithms over time.
To permit developers to evolve and fine-tune their algorithms and
policies, the in-network storage should expose basic mechanisms and
allow as much flexibility as possible to P2P applications. This
conforms to the end-to-end systems principle and allows innovation
and satisfaction of specific business goals. Existing techniques for
in-network storage in P2P applications lack these capabilities.
4. Usage Scenarios
Usage scenarios are presented to illustrate the problems in both
Content Distribution Network (CDN) and P2P scenarios.
4.1. BitTorrent
When a BitTorrent client A uploads a block to multiple peers, the
block traverses the last-mile uplink once for each peer. After that,
the peer B that just received the block from A also needs to upload
through its own last-mile uplink to others when sharing this block.
This is not an efficient use of the last-mile uplink. With an
in-network storage server, however, the BitTorrent client may upload
the block to its in-network storage. Peers may retrieve the block
from the in-network storage, reducing the amount of data on the
last-mile uplink. If supported by the in-network storage, a peer can
also save the block in its own in-network storage while it is being
retrieved; the block can then be uploaded from the in-network storage
to other peers.
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As previously discussed, BitTorrent or other P2P applications
currently cannot explicitly manage which content is placed in the
existing P2P caches, nor can they manage access and resource control
policies. Applications need to retain flexibility to control the
content distribution policies and topology among peers.
4.2. Content Publisher
Content publishers may also utilize in-network storage. For example,
consider a P2P live streaming application. A Content Publisher
typically maintains a small number of sources, each of which
distributes blocks in the current play buffer to a set of P2P peers.
Some content publishers use another hybrid content distribution
approach incorporating both P2P and CDN modes. As an example,
Internet TV may be implemented as a hybrid CDN/P2P application by
distributing content from central servers via a CDN, and also
incorporating a P2P mode amongst end hosts and set-top boxes.
In-network storage may be beneficial to hybrid CDN/P2P applications
as well to support P2P distribution and to enable content publisher
standard interfaces and controls.
However, there is no standard interface for different content
publishers to access in-network storage. One streaming content
publisher may need the existing in-network storage to support
streaming signaling or another such capability, such as transcoding
capability, bitmap information, intelligent retransmission, etc.,
while a different content publisher may only need the in-network
storage to distribute files. However, it is reasonable that the
application services are only supported by content publishers'
original servers and clients, and intelligent data plane transport
for those content publishers are supported by in-network storage.
A content publisher also benefits from a standard interface to access
in-network storage servers provided by different providers. The
standard interface must allow content publishers to retain control
over content placed in their own in-network storage and to grant
access and resources only to the desired end hosts and peers.
In the hybrid CDN/P2P scenario, if only the end hosts can store
content in the in-network storage server, the content must be
downloaded and then uploaded over the last-mile access link before
another peer may retrieve it from an in-network storage server.
Thus, in this deployment scenario, it may be advantageous for a
content publisher or CDN provider to store content in in-network
storage servers.
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5. Security Considerations
There are several security considerations related to in-network
storage.
5.1. Denial-of-Service Attacks
An attacker can try to consume a large portion of the in-network
storage, or exhaust the connections of the in-network storage through
a denial-of-service (DoS) attack. Authentication, authorization, and
accounting mechanisms should be considered in the cross-domain
environment. Limitation of access from an administrative domain sets
up barriers for content distribution.
5.2. Copyright and Legal Issues
Copyright and other laws may prevent the distribution of certain
content in various localities. In-network storage operators may
adopt system-wide ingress or egress filters to implement necessary
policies for storing or retrieving content, and applications may
apply Digital Rights Management (DRM) to the data stored in the
network storage. However, the specification and implementation of
such policies (e.g., filtering and DRM) is not in scope for the
problem this document proposes to solve.
5.3. Traffic Analysis
If the content is stored in the provider-based in-network storage,
there may be a risk to privacy: a malicious service provider could
use some link that a victim user is interested in, estimate that
another user accessing the same data may have the same interest, and
use this information as a basis to perform a phishing attack on the
other user.
5.4. Modification of Information
This type of threat means that some unauthorized entity may alter
in-transit in-network storage access messages generated on behalf of
an authorized principal in such a way as to effect unauthorized
management operations, including falsifying the value of an object.
This threat may result in false data being supplied either because
the data on a legitimate store is modified or because a bogus store
is introduced into the network.
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5.5. Masquerade
This type of threat means that an unauthorized entity gains access to
a system or performs a malicious act by illegitimately posing as an
authorized entity. In the context of this specification, when
accessing in-network storage, one malicious end host can masquerade
as another authorized end host or application server to access a
protected resource in the in-network storage.
5.6. Disclosure
This type of threat involves the danger of someone eavesdropping on
exchanges between in-network storage and application clients.
Protecting against this threat may be required as a matter of
application policy.
5.7. Message Stream Modification
This type of threat means that messages may be maliciously
re-ordered, delayed, or replayed to an extent greater than what would
occur in a natural network system, in order to effect unauthorized
management operations on in-network storage. If the middlebox (such
as a Network Address Translator (NAT)) or proxy between an end host
and in-network storage is compromised, it is easy to do a stream
modification attack.
6. Acknowledgments
We would like to thank the following people for contributing to this
document:
Ronald Bonica
David Bryan
Kar Ann Chew
Lars Eggert
Roni Even
Adrian Farrel
Yingjie Gu
David Harrington
Leif Johansson
Song, et al. Informational [Page 9]
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Francois Le Faucheur
Hongqiang Liu
Tao Ma
Borje Ohlman
Akbar Rahman
Peter Saint-Andre
Robert Sparks
Sean Turner
Yu-shun Wang
Richard Woundy
Yunfei Zhang
7. Informative References
[DCIA] Parker, A., "P2P Media Summit presentation", Distributed
Computing Industry Association, October 2006,
<http://www.dcia.info/activities/p2pmsla2006/
CacheLogic.ppt>.
[Data_Lockers]
Yang, Y., "Open Content Distribution using Data Lockers",
CoXNet Workshop, Beijing, China, November 2010,
<http:// cs-www.cs.yale.edu/homes/yry/projects/p4p/
open-data-lockers-nov-2010-coxnet.pdf>.
[ICNP] Wu, H., "Challenges and Opportunities of Internet
Developments in China", ICNP 2007 Keynote Speech,
October 2007,
<http://www.ieee-icnp.org/2007/keynote_D.html>.
[P2P_File_Sharing]
Casadesus-Masanell, R. and A. Hervas-Drane, "Peer-to-Peer
File Sharing and the Market for Digital Information
Goods", Journal of Economics & Management Strategy,
Vol. 19, No. 2, pp. 333-373, Summer 2010.
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RFC 6646 DECADE Problem Statement July 2012
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC6392] Alimi, R., Ed., Rahman, A., Ed., and Y. Yang, Ed., "A
Survey of In-Network Storage Systems", RFC 6392,
October 2011.
[ipoque_Internet_Study]
Schulze, H. and K. Mochalski, "Internet Study 2008/2009",
2009, <http://www.ipoque.com/resources/internet-studies>.
[ipoque_P2P_Survey]
"ipoque's 2007 P2P Survey to be presented at Technology
Review's Emerging Technologies Conference at MIT",
August 2007, <http://www.ipoque.com/en/news-events/
press-center/press-releases/2007/
ipoque%C2%B4s-2007-p2p-survey-to-be-presented-at-
technology>.
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Authors' Addresses
Haibin Song
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu Province 210012
China
EMail: haibin.song@huawei.com
Ning Zong
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu Province 210012
China
EMail: zongning@huawei.com
Y. Richard Yang
Yale University
EMail: yry@cs.yale.edu
Richard Alimi
Google
EMail: ralimi@google.com
Song, et al. Informational [Page 12]