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Versions: 00 01 02 03 04 05 06                                          
DECADE                                                           L. Chen
Internet-Draft                                                    H. Liu
Intended status: Informational                           Yale University
Expires: October 31, 2011                                 April 29, 2011


           Leveraging In-network Storage in P2P LiveStreaming
                draft-ietf-decade-integration-example-00

Abstract

   DECADE is an in-network storage infrastructure which is under
   discussions and constructions.  It can be integrated into Peer-to-
   Peer (P2P) applications to achieve more efficient content
   distributions.  This document represents a detailed example of how to
   integrate DECADE into P2P live streaming (a popular P2P application).
   Specifically, it describes mainly about: 1) a preliminary DECADE
   client API; 2) a P2P live streaming integration with DECADE; 3) a
   testing on our DECADE integrarion and 4) an application performance
   analysis from the test.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

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   This Internet-Draft will expire on October 31, 2011.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   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
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   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 BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  DECADE Server  . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  DECADE Module  . . . . . . . . . . . . . . . . . . . . . .  3
     2.3.  P2P LiveStreaming Client (P2PLS Client)  . . . . . . . . .  4
     2.4.  DECADE Client  . . . . . . . . . . . . . . . . . . . . . .  4
   3.  DECADE Client API  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  DECADE Integration of P2P LiveStreaming Client . . . . . . . .  5
     4.1.  DECADE Integration Architecture  . . . . . . . . . . . . .  5
       4.1.1.  Data Access  . . . . . . . . . . . . . . . . . . . . .  5
       4.1.2.  Message Control  . . . . . . . . . . . . . . . . . . .  6
     4.2.  Challenges in DECADE Integration . . . . . . . . . . . . .  6
       4.2.1.  Limited Connection Slot  . . . . . . . . . . . . . . .  6
       4.2.2.  Additional Control Latency . . . . . . . . . . . . . .  7
   5.  Test Environment and Settings  . . . . . . . . . . . . . . . .  7
     5.1.  Test Settings  . . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  Platforms and Components . . . . . . . . . . . . . . . . .  8
       5.2.1.  EC2 DECADE Server  . . . . . . . . . . . . . . . . . .  9
       5.2.2.  PlanetLab P2P Live Streaming Client  . . . . . . . . .  9
       5.2.3.  Tracker  . . . . . . . . . . . . . . . . . . . . . . .  9
       5.2.4.  Source Server  . . . . . . . . . . . . . . . . . . . .  9
       5.2.5.  Test Controller  . . . . . . . . . . . . . . . . . . .  9
   6.  Performance Analysis . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Performance Metrics  . . . . . . . . . . . . . . . . . . .  9
     6.2.  Result and Analysis  . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11









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1.  Introduction

   DECADE is an in-network storage infrastructure under discussions and
   constructions.  It can be integrated into Peer-to-Peer (P2P)
   applications to achieve more efficient content distributions.

   This draft introduces an instance of application integration with
   DECADE.  In our example system, the core component includes DECADE
   servers and DECADE-enabled P2P live streaming clients.  A DECADE
   server provides data storage and transport service with interactive
   control to DECADE clients.  We extended a P2P live streaming
   application, P2PLS (P2P LiveStreaming), to leverage DECADE service
   provided by the servers.  P2PLS clients are DECADE-enabled.  For our
   implementation, we used a preliminary API (Application Programming
   Interface) set, which is supposed to be provided by DECADE, to enable
   P2PLS clients to use DECADE in their data transmission.  In this
   draft, we introduce the design of the DECADE-P2PLS integration
   system, the main control flow for DECADE-enabled data transmission,
   and the testing performance with this system.

   Please note that P2PLS in this draft only represents the usage case
   of "live streaming" out of a large number of P2P applications, while
   DECADE itself can support other applications.  The API set used in
   this system is an experimental design and implementation.  It is not
   a standard and is still under development.  Currently, DECADE in this
   draft is only a preliminary framework of in-network storage for P2P.
   It is designed to test the pros and cons of in-network storage
   utilized by P2P applications rather than to reach a final solution.


2.  Concepts

2.1.  DECADE Server

   A DECADE server is implemented with DECADE protocols, management
   mechanism, and storage strategies.  It is a core element to provide
   DECADE service.  Each DECADE server manages a number of Data Lockers,
   each of which is a virtual account and corresponds to private storage
   space for clients.

2.2.  DECADE Module

   DECADE module is a functional component for application clients to
   utilize DECADE.  This component serves as an application-specific
   interface between a particular application and DECADE servers.  It
   can be a simple implementation of basic DECADE access APIs, or a more
   intelligent integration, e.g. consider application-specific control
   strategies when using DECADE APIs.



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2.3.  P2P LiveStreaming Client (P2PLS Client)

   P2P LiveStreaming Client (P2PLS Client) is our self-maintained
   version of a native P2P live streaming application.  It is one
   example out of a large number of P2P applications.

2.4.  DECADE Client

   DECADE client is an integration of a native P2PLS Client and a DECADE
   module.  It is not required to embed DECADE module into native P2P
   clients, since it can also be an independent component running at a
   remote server.


3.  DECADE Client API

   In order to simplify the DECADE integration with P2P clients, we
   provide an API set which covers the communications with DECADE
   servers and token-generation.  On top of this API, a P2P client can
   develop its own application-specific control and data distribution
   policies.

   There are five basic interfaces:

   o  Get_Object: to get an object from a DECADE server with an
      authorized token.  The get operation can be classified into two
      categories: Local Get and Remote Get. Local Get is to get an
      object from a local DECADE server.  Remote Get is to use a
      client's local DECADE server to indirectly get an object from a
      remote DECADE server.  The object will be firstly passed to the
      local DECADE server, then returned to the application client

   o  Put_Object: to store an object into a DECADE server with an
      authorized token.  A client can either store an object into its
      local DECADE server or into other clients' DECADE servers, if it
      has an authorized token.  Both of the operations are direct, for
      we don't provide indirectly storing (i.e. remote put).

   o  Delete_Object: to delete an object in a DECADE server explicitly
      with an authorized token.  Note that an object can also be deleted
      implicitly by setting an expired time or a specific TTL.

   o  Status_Query: to query current status of an application itself,
      including listing stored objects, resource usage, etc..  Such
      information is private.

   o  Generate_Token: to generate an authorized token.  The token can be
      used to access an application client's local DECADE server, or



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      passed to other clients to allow them to access the client's local
      DECADE server.


4.  DECADE Integration of P2P LiveStreaming Client

   We integrate a DECADE module into a P2P live streaming application--
   P2PLS, in order that clients of this application can easily leverage
   DECADE in their data distributions.

4.1.  DECADE Integration Architecture

   The architecture of the P2PLS application and DECADE integration is
   shown in Figure 1:

               +---------------+                       +---------------+
               |    DECADE     |                       |    DECADE     |
               |     Peer      |                       |     Peer      |
               |+-------------+|   +---------------+   |+-------------+|
               ||DECADE Module||---| DECADE Server |---||DECADE Module||
               |+------^------+|   +---------------+   |+------^------+|
               |   API |       |                       |   API |       |
               |+------v------+|   +---------------+   |+------v------+|
               ||Native Client||---|    Tracker    |---||Native Client||
               |+-------------+|   +---------------+   |+-------------+|
               +---------------+                       +---------------+

                                 Figure 1

   A DECADE-integrated P2PLS client uses DECADE client to communicate
   with its DECADE server and transmit data between itself and its
   DECADE server.  It is compatible with its original P2P protocol,
   while it also uses a DECADE protocol to exchange DECADE related
   messages with other peers.

4.1.1.  Data Access

   DECADE module is called whenever a client wants to get data objects
   from (or put data objects into) its DECADE server.  Each data object
   transferred between a client and its DECADE server should go through
   DECADE module.  Neither the DECADE server and the original client
   knows each other.  A data object is a data transfer unit between
   DECADE servers and application clients.  Its size can be application-
   customized, according to variable requirements of performance or
   sensitive factors (e.g. low latency, high bandwidth utilization).






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4.1.2.  Message Control

   Control and data plane decoupling is a design principle of DECADE.
   Control messages are propagated in an original P2P way.  DECADE only
   introduces an additional control message between DECADE module which
   carries DECADE authorized token.  By exchanging DECADE authorized
   tokens, P2P live streaming clients can retrieve or store data objects
   into or from others' DECADE servers.

4.2.  Challenges in DECADE Integration

   One essential objective of DECADE integration is to improve (or at
   least not to hurt) the application performance.  However, as a brand
   new architecture, DECADE has some inherit challenges which will
   potentially be harmful to application performance.  In our P2P live
   streaming case, we met mainly two such limitations of DECADE:

4.2.1.  Limited Connection Slot

   Limited Connection Slot: In native P2P systems, a peer can establish
   tens or hunderds of concurrent connections with other peers.
   However, this situation can hardly be ture when the application is
   integrated with DECADE, because it is too expensive for a DECADE
   server to maintain so many connections for each peer.  Typically,
   each DECADE peer only have m connection slots, which means it can
   only at most have m active connections with its DECADE server
   simultaneously.  A potential "side effect" of limited connection slot
   is that the content availability and downloading rate might be
   impacted negatively by fewwer connections carrying data traffic.
   This requests us to adjust the peer's behavior in resource
   allocation, downloading/uploading scheduling, etc. to fully utilize
   the connection slots to archieve a satisfying and robust data
   downloading.

   In our integration, we mainly employed two technical strategies:

   o  Batch Request: In order to fully utilize the connection bandwidth
      of a DECADE server and reduce overhead, a P2PLS client may combine
      multiple requests in a single request to DECADE server.  Note that
      for the sake of improving data transfer efficiency in P2P live
      streaming, we may combine multiple data requests into a batch
      request.  Generally, a batch may consist of different kinds of
      access requests.

   o  Larger Data Object Size: In typical P2P live streaming
      application, the size of a data block is relatively small,
      considering to reduce end-to-end transport latency.  However,
      existing data size may incur large control overhead and low



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      transport utilization.  A larger data object size may be needed to
      utilize DECADE more efficiently.

4.2.2.  Additional Control Latency

   Addtional Control Latency: In native P2P systems, when an uploader
   decides to reply a request for a piece, it sends the piece out
   directly.  Nevertheless, in DECADE-aware P2P systems, the uploader
   typically only replies with a token of the piece.  And then the
   downloader will leverage this token to fetch the piece from the
   uploader's DECADE server.  This process obviously introduces
   additional control latency compared with native P2P systems.  It is
   even more serious in latency sensitive applications such as P2P live
   streaming.  We need to consider how to reduce such additional delay
   or how to compensate the lose with other inherit advantages of
   DECADE.

   In our integration, we addressed this challenge by multiplexing
   pieces into one token:

   o  Range Token: One way to reduce request latency is to use range
      token.  A P2PLS client may piggyback a range token when it
      propagates its bitmap to its neighbors, to indicate that all
      available pieces in the bitmap are accassable by this range token.
      Then instead of requesting specific pieces from this client and
      waiting for response, the neighbors can directly use this range
      token to access data in DECADE servers.  Note that this method not
      only reduce request latency, but also reduce message overhead.

   With these adjustments and strategies (it is not necessary to use
   "Batch Request" and "Larger Object Size" both), DECADE clients'
   performance was not impacted by the liminations of DECADE and was
   even better than native clients' as we will see in following
   sections.


5.  Test Environment and Settings

   In order to demonstrate the performance of our DECADE implementation
   and DECADE-integrated P2P live streaming application, we conduct some
   experimental tests in Amazon EC2 and PlanetLab.  We perform a pair of
   comparative experiments: DECADE integrated P2P live streaming v.s.
   native P2P live streaming, in the same environment using the same
   settings.







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5.1.  Test Settings

   Our tests ran on a wide-spread area and diverse platforms, including
   a famous commercial cloud platform, Amazon EC2 and a well-known test
   bed, PlanetLab.  The environment settings are as following:

   o  EC2 Regions: we setup DECADE servers in Amazon EC2 cloud,
      including all four regions around the world, US east, US west,
      Europe and Asia.

   o  PlanetLab: we run our P2P live streaming clients (both DECADE
      integrated and native clients) on PlanetLab of a wild-spread area.

   o  Arrival pattern: we made all the clients join into the system
      within a short duration to simulate a flash crowd scenario.

   o  Total Bandwidth: for a fair comparison, we set the system's total
      supply bandwidth to be exact the same in both test.

5.2.  Platforms and Components

   In the tests, we have different functional components running in
   different platforms, including DECADE servers, P2P live streaming
   clients(DECADE integrated or Native), Tracker, Source server and Test
   Controller, as shown in Figure 2.


                +----------+    +------------+    +------------+
                |  P2PLS   |   /|   DECADE   |----|   DECADE   |
                |  Manager |  / |   Server   |    |   Server   |
                +--------^\+ /  +-----|------+    +------|-----+ EC2
                ___________\/_________|__________________|_______
                           /\         |                  |
                +---------/+ \  +-----|------+    +------|-----+
                |  P2PLS   ^  \ |   P2PLS    ^    ^   P2PLS    |
                |  Source  |\  \|   Client   |\  /|   Client   |
                +-----|----+ \  \------^-----+ \/ +------^-----+ PlanetLab
                ______|_______\__\_____|_______/\________|_______
                      |        \  \    |      /  \       |
                +-----|----+    v--v---v-----v    v------v-----+
                | Streaming|    |   P2PLS    |    |    Test    |
                |   Files  |    |   Tracker  |    | Controller |
                +----------+    +------------+    +------------+ Yale Lab

   P2PLS represents to P2P Live Streaming.

                                 Figure 2




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5.2.1.  EC2 DECADE Server

   DECADE Servers ran on Amazon EC2 small instances, with bandwidth
   constraint.

5.2.2.  PlanetLab P2P Live Streaming Client

   Both DECADE integrated and Native P2P live streaming clients ran on
   PlanetLab which spreads in various locations around the world.  The
   DECADE integrated P2P live streaming clients connect to the closest
   DECADE server according to its Geo-location distance to the servers.
   DECADE integrated P2P live streaming clients use their DECADE servers
   to upload to neighbors, instead of their own "last-mile" bandwidth.

5.2.3.  Tracker

   A native P2P live streaming tracker ran at Yale's laboratory and
   served both DECADE integrated clients and native clients during the
   test.

5.2.4.  Source Server

   A native P2P live streaming source server ran at Yale's laboratory
   and serve both DECADE integrated clients and native clients during
   the test.  The capacity of source is equivalently constrain for both
   cases.

5.2.5.  Test Controller

   Test Controller is a manager to control all machines' behaviors in
   both EC2 and PlanetLab during the test.


6.  Performance Analysis

   During the test, DECADE integrated P2P live streaming clients
   achieved an impressively better performance than native clients.

6.1.  Performance Metrics

   To measure the performance of a P2P live streaming client, we employ
   mainly four metrics:

   o  Startup Delay: the duration from a peer joins the channel to the
      moment it starts to play.

   o  Piece Missed Rate: the number of pieces a peer loses when playing
      over the total number of pieces.



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   o  Freeze Times: the number of times a peer re-buffers during
      playing.

   o  Average Peer Uploading Rate: Average uploading bandwidth of a
      peer.

6.2.  Result and Analysis

   o  Startup Delay: In the test, DECADE integrated P2P live streaming
      clients startup around 35~40 seconds. some of them startup at
      about 10 seconds.  Native P2P live streaming clients startup
      around 110~120 seconds. less than 20% of them startup within 100
      seconds.

   o  Piece Missed Rate: In the test, both DECADE integrated P2P live
      streaming clients and native P2P live streaming clients achieved a
      good performance in pieces missed rate.  Only about 0.02% of total
      pieces missed in both cases.

   o  Freeze Times: In the test, native P2P live streaming clients
      suffered from more freezing than DECADE Integrated P2P live
      streaming clients by 40%.

   o  Average Peer Uploading Rate: In the test, according to our
      settings, DECADE integrated P2P live streaming clients had no
      upload in their "last-mile" access network.  While in the native
      P2P live streaming system, more than 70% of peers uploaded in a
      rate that is much more than streaming rate.  In another word,
      DECADE can shift uploading traffic from clients' "last-mile" to
      in-network devices, which saves a lot of expensive bandwidth on
      access links..


7.  Security Considerations

   This document does not contain any security considerations.


8.  IANA Considerations

   This document does not have any IANA considerations.


9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.




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Authors' Addresses

   Lijiang Chen
   Yale University

   Email: lijiang.chen@yale.edu


   Hongqiang Liu
   Yale University

   Email: hongqiang.liu@yale.edu







































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