DECADE H. Song
Internet-Draft N. Zong
Intended status: Informational Huawei
Expires: April 14, 2012 Y. Yang
Yale University
R. Alimi
Google
October 12, 2011
DECoupled Application Data Enroute (DECADE) Problem Statement
draft-ietf-decade-problem-statement-04
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 (the download traffic may increase because the in-
network storage is likely much better connected). 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 refreshing mechanisms) and they do not have the feature to
allow users to manage access to content in the cache. For example,
Content Providers cannot easily control cache access and resource
usage policies to satisfy their own requirements. In this document,
a content provider is also the user of in-network storage. This
document discusses the introduction of in-network storage for P2P
applications, and shows the need for a standard protocol for
accessing this storage. It can also be used by other applications
with similar requirements.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Song, et al. Expires April 14, 2012 [Page 1]
Internet-Draft DECADE Problem Statement October 2011
This Internet-Draft will expire on April 14, 2012.
Copyright Notice
Copyright (c) 2011 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.
Song, et al. Expires April 14, 2012 [Page 2]
Internet-Draft DECADE Problem Statement October 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Concepts . . . . . . . . . . . . . . . . . . . 5
3. The Problems . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. P2P infrastructural stress and inefficiency . . . . . . . 6
3.2. P2P cache: a complex in-network storage . . . . . . . . . 6
3.3. Ineffective integration of P2P applications . . . . . . . 7
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. BitTorrent . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Content Publisher . . . . . . . . . . . . . . . . . . . . 9
5.3. CDN/P2P hybrid . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6.1. Denial of Service Attacks . . . . . . . . . . . . . . . . 11
6.2. Copyright and Legal Issues . . . . . . . . . . . . . . . . 11
6.3. Privacy issue . . . . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
9. Informative References . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Other Related Work in IETF . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Song, et al. Expires April 14, 2012 [Page 3]
Internet-Draft DECADE Problem Statement October 2011
1. Introduction
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 the networks.
Allowing P2P applications to store and retrieve data from inside
networks can reduce traffic on the last-mile uplink, as well as
backbone and transit links.
P2P caches provide in-network storage and have been deployed in some
networks. But 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 do not allow users to
implement control over the content that has been placed into the in-
network storage either.
Both of these challenges can be effectively addressed by using an
open, standard protocol to access in-network storage. 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.
This document introduces DECADE, a standard interface for various P2P
applications to access storage and data transport services in the
network to improve their efficiency and reduce load on the network
infrastructure.
With DECADE, P2P applications can still use their native protocols
for signaling and data transport. However, they may use a standard
protocol for data access incorporating in-network storage, and fall
back to their native data transport protocols if in-network storage
is not available or not used.
Song, et al. Expires April 14, 2012 [Page 4]
Internet-Draft DECADE Problem Statement October 2011
In essence, an open, standard protocol to access in-network storage
provides an alternative mechanism for P2P application data access
that is decoupled from P2P application control and signaling. This
decoupling leads to many advantages, which is explained further in
Section 4.
And further, either the existing P2P cache or any new type of in-
network storage should be deployed near the edge of the ISP's network
so as to gain better performance.
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.
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.
Content Publisher: An entity that originates content.
3. The Problems
The emergence of peer-to-peer (P2P) as a major network application
(esp. P2P file sharing and streaming apps) has led to substantial
opportunities. The P2P paradigm can be utilized in designing highly
scalable and robust applications at low cost, compared with
traditional client-server paradigms. For example, CNN reported that
P2P streaming by Octoshape played a major role in its distribution of
the historic inauguration address of President Obama[Octoshape].
PPLive, one of the largest P2P streaming vendors, is able to
distribute large-scale, live streaming programs to more than 2
million users with only a handful of servers[PPLive].
However, P2P applications also face substantial design challenges. A
particular problem facing P2P applications is the substantial stress
that they place on the network infrastructure. Also, lack of
infrastructure support can lead to unstable P2P application
performance during peer churns and flash crowd. Here flash crowds
Song, et al. Expires April 14, 2012 [Page 5]
Internet-Draft DECADE Problem Statement October 2011
means a large group of application users begin to access the same
service during a very short period of time, which is a challenge to
the system. Below we elaborate on the problems in more 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., [ipoque]) have shown
that P2P traffic has become a major type of traffic on some networks.
Furthermore, network-agnostic peering (P2P transmission level) leads
to unnecessary traversal across network domains or spanning the
backbone of a network, leading to network inefficiency [RFC5693].
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 pure 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% at the down-links and
60-90% at the uplinks ([DCIA], [ICNP], [ipoque.P2P_survey.],
[P2P_file_sharing]). 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.
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.
Song, et al. Expires April 14, 2012 [Page 6]
Internet-Draft DECADE Problem Statement October 2011
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 be evolving
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, high cost, and low
reliability.
Third, many P2P applications use proprietary protocols or support
end-to-end encryption. This can render P2P caches ineffective.
3.3. Ineffective integration of P2P applications
As P2P applications evolve, it is becoming increasingly clear that
they will need in-network resources to provide positive user
experiences. 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.
A requirement by some P2P applications in using in-network
infrastructural resources, however, is 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. They continue to
fine-tune such algorithms. In other words, in-network storage should
expose basic mechanisms and allow as much flexibility as possible to
P2P applications to implement specific policies. 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.
Song, et al. Expires April 14, 2012 [Page 7]
Internet-Draft DECADE Problem Statement October 2011
4. Motivation
DECADE aims to provide access to storage and data transport services
in the network to P2P applications to improve their efficiency and
reduce the stress on the network infrastructure. Unlike the existing
P2P caching architecture, DECADE aims to provide a standard interface
for various P2P applications (both content publishers and end users)
to access in-network storage. This decoupling of P2P data access
from P2P application control and signaling reduces the complexity of
in-network storage services. Furthermore, DECADE is aimed to provide
basic access mechanisms and allows P2P applications to implement
flexible policies to create an ecosystem for application innovation
and various business goals. Besides that, it also improves the
availability of P2P contents because the in-network storage is
always-on.
-----------+
| DECADE |
| v
+--------------------+
| In-network Storage |
+--------------------+
DECADE ^ DECADE ^
| |
+-------------v-+ +-v-------------+
| P2P | | Content |
| application | | publishers |
| clients | +---------------+
+---------------+
| ^
| |
+-------------+
P2P application
native protocol
Figure 1 Overview
5. Usage Scenarios
Usage scenarios are presented to illustrate how DECADE in-network
storage may be used in both CDN and P2P scenarios. Interactions with
in-network storage are described at an abstract level so as not to
constrain future protocol development.
Song, et al. Expires April 14, 2012 [Page 8]
Internet-Draft DECADE Problem Statement October 2011
5.1. BitTorrent
BitTorrent may be integrated with DECADE to be more network efficient
and reduce the bandwidth consumed on ISP networks. When a BitTorrent
client uploads a block to peers, the block traverses the last-mile
uplink once for each peer. With DECADE, 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.
We now describe in more detail how BitTorrent can utilize DECADE.
For illustration, we assume that both the BitTorrent client (A) and
its peer (B) utilize in-network storage. When A requests a block,
peer B replies with a 'redirect' message indicating that the content
should be retrieved from in-network storage. If the peer B had not
previously stored the content in in-network storage, it uploads the
block before A retrieves it. If there is support, A may first copy
the block to in-network storage that is nearer to it before
retrieving it.
Note that this requires extensions to the BitTorrent protocol. While
there are multiple ways to do so, this example assumes the native
BitTorrent 'request' message is extended to carry additional
information and that a new 'redirect' message is added. Upload and
download to/from in-network storage uses a standard protocol.
This example has illustrated how utilizing DECADE can increase
BitTorrent's network efficiency. First, notice that peer B does not
utilize any uplink bandwidth if the block was already present in its
in-network storage. Second, notice that the block may be copied to
in-network storage nearer to A. When A wishes to share the block with
another peer (say, peer C) that supports DECADE, it may upload
directly from its in-network storage, again avoiding usage of the
last-mile uplink.
This technique can be applied to other P2P applications as well.
Since P2P applications use a standard for communicating with in-
network storage, they no longer require in-network storage to
explicitly support their protocol. P2P applications retain the
ability to explicitly manage which content is placed in in-network
storage, as well as access and resource control polices.
5.2. 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
Song, et al. Expires April 14, 2012 [Page 9]
Internet-Draft DECADE Problem Statement October 2011
peers.
Consider a case where the Content Publisher owns an in-network
storage account within ISP A. If there are multiple P2P peers within
ISP A, the Content Publisher may utilize DECADE to distribute content
to the peers.
First, the Content Publisher stores a block in the in-network
storage, configures necessary access control, and notifies peers in
ISP A. Second, each peer may then download from the Content
Publisher's in-network storage.
In this example, the block is distributed in a more network efficient
way (the content only traverses the ISP's interdomain link once),
while the Content Publisher retains explicit control over access to
the content placed in its own storage. The Content Publisher can
remove content from its in-network storage when it is stale or needs
to be replaced, and grant access and resources to only the desired
peers.
Note that Content Publishers and individual peers can each use in-
network storage. For example, after downloading content from the
Content Publisher's in-network storage, peers may each utilize their
own in-networks storage similar to the usage scenario in Section 5.1.
This can have the benefit of increased network efficiency, while
Content Publishers and peers still retain control over content placed
in their own in-network storage.
If it desires, a content publisher may still apply DRM to the
payload. This is independent of any authentication or authorization
provided by DECADE.
5.3. CDN/P2P hybrid
Some applications use a 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.
DECADE may be beneficial to hybrid CDN/P2P applications as well.
However, if only the endhost can store content in the DECADE server,
the content must be downloaded and then uploaded over the last-mile
access link before another peer may retrieve it from a DECADE server.
Thus, in this deployment scenario, it may be advantageous for a
Content Publisher or CDN provider to store content to DECADE servers.
Song, et al. Expires April 14, 2012 [Page 10]
Internet-Draft DECADE Problem Statement October 2011
6. Security Considerations
There are multiple security considerations. We can not enumerate all
of them but focus on three main concerns in this section.
6.1. 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.
6.2. Copyright and Legal Issues
Copyright and other laws may prevent the distribution of certain
content in various localities. While in-network storage operators
may adopt system-wide ingress or egress filters to implement
necessary policies for storing or retrieving content, and
applications may still apply DRM to the data stored in the network
storage, the specification and implementation of such policies (e.g.,
filtering and DRM) is outside of the scope of this working group.
6.3. Privacy issue
If the content 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.
7. IANA Considerations
There are no IANA considerations in this document.
8. Acknowledgments
We would like to thank the following people for contributing to this
document:
David Bryan
Kar Ann Chew
Roni Even
Lars Eggert
Yingjie Gu
Song, et al. Expires April 14, 2012 [Page 11]
Internet-Draft DECADE Problem Statement October 2011
Francois Le Faucheur
Hongqiang Liu
Tao Ma
Borje Ohlman
Akbar Rahman
Yu-shun Wang
Richard Woundy
Yunfei Zhang
9. Informative References
[ipoque.com]
"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.
[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-18 (work in
progress), August 2011.
[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/".
Song, et al. Expires April 14, 2012 [Page 12]
Internet-Draft DECADE Problem Statement October 2011
[ICNP] Wu, H., "Challenges and opportunities of Internet
developments in China, ICNP 2007 Keynote", Oct. 2007.
Appendix A. Other Related Work in IETF
Note that DECADE is independent of current IETF work on P2P. The ALTO
work as described above 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-
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. A DECADE service can be used for any application
transparently to the DECADE 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. So
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
Song, et al. Expires April 14, 2012 [Page 13]
Internet-Draft DECADE Problem Statement October 2011
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.
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) 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 to 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
may be some solutions to require more information in PPSP tracker
protocol, e.g., the mobile node can indicate its DECADE in-network
proxy to PPSP tracker and the following requesting peer can finish
data transfer with the DECADE proxy.
Authors' Addresses
Haibin Song
Huawei
101 Software Avenue, Yuhua District,
Nanjing, Jiangsu Province 210012
China
Phone: +86-25-56624792
Email: haibin.song@huawei.com
Ning Zong
Huawei
101 Software Avenue, Yuhua District,
Nanjing, Jiangsu Province 210012
China
Phone: +86-25-56624760
Email: zongning@huawei.com
Song, et al. Expires April 14, 2012 [Page 14]
Internet-Draft DECADE Problem Statement October 2011
Y. Richard Yang
Yale University
Email: yry@cs.yale.edu
Richard Alimi
Google
Email: ralimi@google.com
Song, et al. Expires April 14, 2012 [Page 15]
