Internet DRAFT - draft-ietf-decade-problem-statement
draft-ietf-decade-problem-statement
DECADE H. Song
Internet-Draft N. Zong
Intended status: Informational Huawei
Expires: November 8, 2012 Y. Yang
Yale University
R. Alimi
Google
May 7, 2012
DECoupled Application Data Enroute (DECADE) Problem Statement
draft-ietf-decade-problem-statement-06
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 are complex (due to explicitly
supporting individual P2P application protocols and cache refresh
mechanisms) and they do not allow users to manage access to content
in the cache. For example, content providers wishing to use in-
network storage cannot easily control cache access and resource usage
policies to satisfy their own requirements. 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 Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on November 8, 2012.
Copyright Notice
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Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Concepts . . . . . . . . . . . . . . . . . . . 4
3. The Problems . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. P2P infrastructural stress and inefficiency . . . . . . . 4
3.2. P2P cache: a complex 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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. Informative References . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Other Related Work in IETF . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Peer-to-peer (P2P) applications, including both P2P streaming and P2P
filesharing applications, make up a large fraction of the traffic in
many 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.
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 applications, 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 users to implement control over the content that has
been placed into the in-network storage.
P2P applications suffer decreased efficiency, and the network
infrastructure suffers increased load because there is no
standardized interface for accessing storage and data transport
services in the Internet.
Both of these challenges can be effectively addressed by using an
open, standard 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 very complex to support various application services.
However, these applications have common requirements for data access,
making it possible to develop a standard protocol.
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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.
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 peer-to-peer (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 problem facing P2P applications is the additional stress
that they place on the network infrastructure. Furthermore, lack of
infrastructure support can lead to unstable P2P application
performance during peer churns and flash crowds, when a large group
of users begin to retrieve the content during a short period of time.
A potential way to solve it would be to make it possible for peers
that were on bandwidth constrained access to put things in a place
that is both not bandwidth constrained and 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 Internet service
providers (ISPs). Multiple measurements (e.g.,
[Internet_Study_2008-2009]) 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].
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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.
The inefficiency is also represented 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 in-network storage
An effective technique to reduce P2P infrastructural stress and
inefficiency is to introduce in-network storage. The 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.
Furthermore, a specific P2P application protocol may evolve
continuously, to add new features or fix bugs. This forces a P2P
cache vendor to continuously update to track the changes of the P2P
application, 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. So
these three problems make the P2P cache as a network middle-box, hard
to support these P2P application distribution in their own ways.
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Finally, a P2P cache is likely to be much better connected to end
hosts than remote peers that connected to end hosts. 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.
3.3. Ineffective integration of P2P applications
As P2P applications evolve, it has become increasingly clear that
usage of in-network resources can improve user 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 chose 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
P2P application in-network storage 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. And after
that, the peer B who 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
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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.
As previously discussed, BitTorrent or other P2P applications
currently cannot explicitly manage which content is placed in the
existing P2P caches, nor access and resource control polices.
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 the 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 endhosts 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 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 publisher's
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 the content publisher to retain control
over content placed in their own in-network storage, and grant access
and resources only to the desired endhosts and peers.
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In the hybrid CDN/P2P scenario, if only the endhosts 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 a 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.
5. Security Considerations
There are several security considerations to the 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 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
solving.
5.3. Traffic Analysis
If the content is stored in the provider-based in-network storage,
there may be a privacy risk that the provider can correlate the
people who are accessing the same data object using the same object
identity. This correlation can be used to presume that they have the
same interest, so as to use it as a basis for a phishing attack.
5.4. Modification of Information
The modification threat is the danger 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
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either through the data on a legitimate store being modified, or
through a bogus store being introduced into the network.
5.5. Masquerade
A type of threat action whereby 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 spec, when accessing
in-network storage, one malicious end host can try to act as another
authorized end host or application server to access a protected
resource in the in-network storage.
5.6. Disclosure
The disclosure threat is the danger of eavesdropping on the 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
The message stream modification threat is the danger that messages
may be maliciously re-ordered, delayed or replayed to an extent which
is greater than can occur through natural network system, in order to
effect unauthorized management operations to in-network storage. If
the middle box, such like NAT (network address translator) or proxy
between an end host and in-network storage is compromised, it is easy
to do the stream modification attack.
6. IANA Considerations
There are no IANA considerations in this document.
7. Acknowledgments
We would like to thank the following people for contributing to this
document:
David Bryan
Ronald Bonica
Kar Ann Chew
Roni Even
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Lars Eggert
Francois Le Faucheur
Adrian Farrel
Yingjie Gu
David Harrington
Leif Johansson
Hongqiang Liu
Tao Ma
Borje Ohlman
Akbar Rahman
Robert Sparks
Peter Saint-Andre
Sean Turner
Yu-shun Wang
Richard Woundy
Yunfei Zhang
8. Informative References
[Internet_Study_2008-2009]
"Internet Study 2008/2009", <http://www.ipoque.com/
resources/internet-studies/internet-study-2008_2009>.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC6392] Alimi, R., Rahman, A., and Y. Yang, "A Survey of In-
Network Storage Systems", RFC 6392, October 2011.
[Data_Lockers]
Yang, Y., "Open Content Distribution using Data Lockers",
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<http://cs-www.cs.yale.edu/homes/yry/projects/p4p/
open-data-lockers-nov-2010-coxnet.pdf>.
[I-D.ietf-p2psip-base]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-21 (work in
progress), March 2012.
[DCIA] http://www.dcia.info, "Distributed Computing Industry
Association".
[ipoque.P2P_survey.]
"Emerging Technologies Conference at MIT", Sept. 2007.
[P2P_file_sharing]
Parker, A., "The true picture of peer-to-peer
filesharing", July 2004.
[Octoshape]
"http://www.octoshape.com/?page=company/about".
[PPLive] "http://www.synacast.com/products/".
[ICNP] Wu, H., "Challenges and opportunities of Internet
developments in China, ICNP 2007 Keynote", Oct. 2007.
Appendix A. Other Related Work in IETF
(To the RFC editor: Please remove this section and the related
references in this section upon publication. The purpose of this
section is to give the IESG and RFC editor a better understanding of
the current P2P related work in IETF and the relationship with DECADE
WG.)
Note that DECADE WG's work is independent of current IETF work on
P2P. The ALTO work is aimed for better peer selection and the RELOAD
[I-D.ietf-p2psip-base] protocol is used for P2P overlay maintenance
and resource discovery.
The Peer to Peer Streaming Protocol effort in the IETF is
investigating the specification of signaling protocols (called the
PPSP tracker protocol and peer protocol) for multiple entities (e.g.,
intelligent endpoints, caches, content distribution network nodes,
and/or other edge devices) to participate in P2P streaming systems in
both fixed and mobile Internet. As discussed in the PPSP problem
statement, one important PPSP use case is the support of an in-
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network edge cache for P2P Streaming. However, this approach to
providing in-network cache has different applicability, different
objectives and different implications for the in-network cache
operator. The goal of DECADE WG is to provide in-network storage
service that can be used for any application transparently to the in-
network storage operator: it can be used for any P2P Streaming
application (whether it supports PPSP protocols or not), for any
other P2P application, and for non P2P applications that simply want
to benefit from in-network storage. With DECADE, the operator is
providing a generic in-network storage service that can be used by
any application without application involvement or awareness by the
operator; in the PPSP cache use case, the cache operator is
participating in the specific P2P streaming service.
DECADE and PPSP can both contribute independently, and (where
appropriate) simultaneously, to making content available closer to
peers. Here are a number of example scenarios:
A given network supports DECADE in-network storage, and its CDN
nodes do not participate as PPSP Peers for a given "stream" (e.g.,
because no CDN arrangement has been put in place between the
content provider and the particular network provider). In that
case, PPSP Peers will all be "off-net" but will be able to use
DECADE in-network storage to exchange chunks.
A given network does not support DECADE in-network storage, and
(some of) its CDN nodes participate as PPSP Peers for a given
"stream" (e.g., say because an arrangement has been put in place
between the content provider and the particular network provider).
In that case, the CDN nodes will participate as in-network PPSP
Peers. The off-net PPSP Peers (i.e., end users) will be able to
get chunks from the in-network CDN nodes (using PPSP protocols
with the CDN nodes).
A given network supports DECADE in-network storage, and (some of)
its CDN nodes participate as PPSP Peers for a given "stream"
(e.g., because an arrangement has been put in place between the
content provider and the particular network provider). In that
case, the CDN nodes will participate as in-network PPSP Peers.
The off-net PPSP Peers (i.e., end users) will be able to get
chunks from the in-network CDN nodes (using PPSP protocols with
the CDN nodes) as well as be able to get chunks / share chunks
using DECADE in-network storage populated by PPSP Peers (both off-
net end-users and in-network CDN Nodes).
PPSP and DECADE jointly provide P2P streaming service for
heterogeneous networks including both fixed and mobile connections
and enables the mobile nodes to use DECADE. In this case there
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may be some solutions that require more information in PPSP
tracker protocol, e.g., the mobile node can indicate its DECADE
in-network proxy to the PPSP tracker and the following requesting
peer can finish data transfer with the DECADE proxy.
An ALTO (Application Layer Traffic Optimization) server provides P2P
applications with network information so that they can perform
better-than-random initial peer selection [RFC5693]. However, there
are limitations on what ALTO can achieve alone. For example, network
information alone cannot 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. Consequently, it becomes
increasingly important to complement the ALTO effort and reduce
upload access traffic, in addition to cross-domain and backbone
traffic.
The IETF Low Extra Delay Background Transport (LEDBAT) Working Group
is focusing on techniques that allow large amounts of data to be
consistently transmitted without substantially affecting the delays
experienced by other users and applications. It is expected that
some P2P applications would start using such techniques, thereby
somewhat alleviating the perceivable impact (at least on other
applications) of their high volume traffic. However, such techniques
may not be adopted by all P2P applications. Also, when adopted,
these techniques do not remove all inefficiencies, such as those
associated with traffic being 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.
Authors' Addresses
Haibin Song
Huawei
101 Software Avenue, Yuhua District,
Nanjing, Jiangsu Province 210012
China
Phone: +86-25-56624792
Email: haibin.song@huawei.com
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Ning Zong
Huawei
101 Software Avenue, Yuhua District,
Nanjing, Jiangsu Province 210012
China
Phone: +86-25-56624760
Email: zongning@huawei.com
Y. Richard Yang
Yale University
Email: yry@cs.yale.edu
Richard Alimi
Google
Email: ralimi@google.com
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