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DECADE                                                          R. Alimi
Internet-Draft                                                    Google
Intended status: Informational                                   Y. Yang
Expires: November 22, 2011                               Yale University
                                                               A. Rahman
                                        InterDigital Communications, LLC
                                                             D. Kutscher
                                                                     NEC
                                                                  H. Liu
                                                         Yale University
                                                            May 21, 2011


                          DECADE Architecture
                       draft-ietf-decade-arch-01

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.  One technique to improve the network efficiency of P2P
   applications is to introduce storage capabilities within the
   networks.  The DECADE Working Group has been formed with the goal of
   developing an architecture to provide this capability.  This document
   presents an architecture, discusses the underlying principles, and
   identifies core components and protocols supporting the architecture.

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
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.




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   This Internet-Draft will expire on November 22, 2011.

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 BSD License.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Entities . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.1.  DECADE Storage Servers . . . . . . . . . . . . . . . . . .  6
     2.2.  DECADE Storage Provider  . . . . . . . . . . . . . . . . .  6
     2.3.  DECADE Content Providers . . . . . . . . . . . . . . . . .  6
     2.4.  DECADE Content Consumers . . . . . . . . . . . . . . . . .  6
     2.5.  Content Distribution Application . . . . . . . . . . . . .  6
     2.6.  Application End-Point  . . . . . . . . . . . . . . . . . .  7
   3.  Architectural Principles . . . . . . . . . . . . . . . . . . .  7
     3.1.  Decoupled Control/Metadata and Data Planes . . . . . . . .  7
     3.2.  Immutable Data Objects . . . . . . . . . . . . . . . . . .  8
     3.3.  Data Object Identifiers  . . . . . . . . . . . . . . . . .  9
     3.4.  Explicit Control . . . . . . . . . . . . . . . . . . . . . 10
     3.5.  Resource and Data Access Control through User
           Delegation . . . . . . . . . . . . . . . . . . . . . . . . 10
       3.5.1.  Resource Allocation  . . . . . . . . . . . . . . . . . 10
       3.5.2.  User Delegations . . . . . . . . . . . . . . . . . . . 10
   4.  System Components  . . . . . . . . . . . . . . . . . . . . . . 11
     4.1.  Content Distribution Application . . . . . . . . . . . . . 13
       4.1.1.  Data Assembly  . . . . . . . . . . . . . . . . . . . . 13
       4.1.2.  Native Protocols . . . . . . . . . . . . . . . . . . . 14
       4.1.3.  DECADE Client  . . . . . . . . . . . . . . . . . . . . 14
     4.2.  DECADE Server  . . . . . . . . . . . . . . . . . . . . . . 14
       4.2.1.  Access Control . . . . . . . . . . . . . . . . . . . . 14
       4.2.2.  Resource Scheduling  . . . . . . . . . . . . . . . . . 15
       4.2.3.  Data Store . . . . . . . . . . . . . . . . . . . . . . 15
     4.3.  Protocols  . . . . . . . . . . . . . . . . . . . . . . . . 15
       4.3.1.  DECADE Resource Protocol . . . . . . . . . . . . . . . 16
       4.3.2.  Standard Data Transports . . . . . . . . . . . . . . . 16
     4.4.  Data Sequencing and Naming . . . . . . . . . . . . . . . . 16
       4.4.1.  DECADE Data Object Naming Schame . . . . . . . . . . . 16
       4.4.2.  Application Usage  . . . . . . . . . . . . . . . . . . 17
       4.4.3.  Application Usage Example  . . . . . . . . . . . . . . 17
     4.5.  Token-based Authentication and Resource Control  . . . . . 19
     4.6.  In-Network Storage Components Mapped to DECADE
           Architecture . . . . . . . . . . . . . . . . . . . . . . . 20
       4.6.1.  Data Access Interface  . . . . . . . . . . . . . . . . 20
       4.6.2.  Data Management Operations . . . . . . . . . . . . . . 20
       4.6.3.  Data Search Capability . . . . . . . . . . . . . . . . 21
       4.6.4.  Access Control Authorization . . . . . . . . . . . . . 21
       4.6.5.  Resource Control Interface . . . . . . . . . . . . . . 21
       4.6.6.  Discovery Mechanism  . . . . . . . . . . . . . . . . . 21
       4.6.7.  Storage Mode . . . . . . . . . . . . . . . . . . . . . 21
   5.  DECADE Protocols . . . . . . . . . . . . . . . . . . . . . . . 21
     5.1.  DECADE Resource Protocol (DRP) . . . . . . . . . . . . . . 22
       5.1.1.  Controlled Resources . . . . . . . . . . . . . . . . . 22



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       5.1.2.  Token-based Authentication and Resource Control  . . . 22
       5.1.3.  Status Information . . . . . . . . . . . . . . . . . . 23
       5.1.4.  Object Properties  . . . . . . . . . . . . . . . . . . 24
     5.2.  Standard Data Transport (SDT)  . . . . . . . . . . . . . . 25
       5.2.1.  Writing/Uploading Objects  . . . . . . . . . . . . . . 25
       5.2.2.  Downloading Objects  . . . . . . . . . . . . . . . . . 26
   6.  Server-to-Server Protocols . . . . . . . . . . . . . . . . . . 27
     6.1.  Operational Overview . . . . . . . . . . . . . . . . . . . 27
   7.  Potential Optimizations  . . . . . . . . . . . . . . . . . . . 28
     7.1.  Pipelining to Avoid Store-and-Forward Delays . . . . . . . 28
     7.2.  Deduplication  . . . . . . . . . . . . . . . . . . . . . . 28
       7.2.1.  Traffic Deduplication  . . . . . . . . . . . . . . . . 29
       7.2.2.  Cross-Server Storage Deduplication . . . . . . . . . . 30
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 30
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 30
   10. Informative References . . . . . . . . . . . . . . . . . . . . 30
   Appendix A.  Appendix: Evaluation of Some Candidate Existing
                Protocols for DECADE DRP and SDT  . . . . . . . . . . 31
     A.1.  HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
       A.1.1.  HTTP Support for DECADE Resource Protocol
               Primitives . . . . . . . . . . . . . . . . . . . . . . 31
       A.1.2.  HTTP Support for DECADE Standard Transport
               Protocol Primitives  . . . . . . . . . . . . . . . . . 32
       A.1.3.  Traffic Deduplication Primitives . . . . . . . . . . . 33
       A.1.4.  Other Operations . . . . . . . . . . . . . . . . . . . 33
       A.1.5.  Conclusions  . . . . . . . . . . . . . . . . . . . . . 33
     A.2.  WEBDAV . . . . . . . . . . . . . . . . . . . . . . . . . . 33
       A.2.1.  WEBDAV Support for DECADE Resource Protocol
               Primitives . . . . . . . . . . . . . . . . . . . . . . 34
       A.2.2.  WebDAV Support for DECADE Standard Transport
               Protocol Primitives  . . . . . . . . . . . . . . . . . 35
       A.2.3.  Other Operations . . . . . . . . . . . . . . . . . . . 35
       A.2.4.  Conclusions  . . . . . . . . . . . . . . . . . . . . . 36
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37

















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1.  Introduction

   Peer-to-peer (P2P) applications have become widely used on the
   Internet today to distribute contents, and they contribute a large
   portion of the traffic in many networks.  The DECADE Working Group
   has been formed with the goal of developing an architecture to
   introduce in-network storage to be used by such applications, to
   achieve more efficient content distribution.  Specifically, in many
   subscriber networks, it is typically more expensive to upgrade
   network equipment in the "last-mile", because it can involve
   replacing equipment and upgrading wiring at individual homes,
   businesses, and devices such as DSLAMs and CMTSs.  On the other hand,
   it can be cheaper to upgrade the core infrastructure, which involves
   fewer components that are shared by many subscribers.  See
   [I-D.ietf-decade-problem-statement] for a more complete discussion of
   the problem domain and general discussions of the capabilities to be
   provided by DECADE.

   This document presents a potential architecture of providing in-
   network storage that can be integrated into content distribution
   applications.  The primary focus is P2P-based content distribution,
   but the architecture may be useful to other applications with similar
   characteristics and requirements.  In particular, content
   distribution applications that may split data into smaller pieces for
   distribution may be able to utilize DECADE.

   The design philosophy of the DECADE architecture is to provide only
   the core functionalities that are needed for applications to make use
   of in-network storage.  With such core functionalities, the protocol
   may be simpler and easier to support by storage providers.  If more
   complex functionalities are needed by a certain application or class
   of applications, it may be layered on top of the DECADE protocol.

   The DECADE protocol will leverage existing transport and application
   layer protocols and will be designed to work with a small set of
   alternative IETF protocols.

   This document proceeds in two steps.  First, it details the core
   architectural principles that can guide the DECADE design.  Next,
   given these core principles, this document presents the core
   components of the DECADE architecture and identifies usage of
   existing protocols and where there is a need for new protocol
   development.

   This document will be updated to track the progress of the DECADE
   survey [I-D.ietf-decade-survey] and requirements
   [I-D.ietf-decade-reqs] drafts.




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2.  Entities

2.1.  DECADE Storage Servers

   DECADE storage servers are operated by DECADE storage providers and
   provide the DECADE functionality as specified in this document,
   including mechanisms to store, retrieve and manage data.  A storage
   provider may typically operate multiple storage servers.

2.2.  DECADE Storage Provider

   A DECADE in-network storage provider deploys and/or manages DECADE
   servers within a network.  A storage provider may also own or manage
   the network in which the DECADE servers are deployed.

   A DECADE storage provider, possibly in cooperation with one or more
   network providers, determines deployment locations for DECADE servers
   and determines the available resources for each.

2.3.  DECADE Content Providers

   DECADE content providers access DECADE storage servers (by way of a
   DECADE client) to upload and manage data.  A content provider can
   access one or more storage servers.  A content provider may be a
   single process or a distributed application (e.g., in a P2P
   scenario).

2.4.  DECADE Content Consumers

   DECADE content consumers access storage servers (by way of a DECADE
   client) to download data that has previously been stored by a content
   provider.  A content consumer can access one or more storage servers.
   A content consumer may be a single process or a distributed
   application (e.g., in a P2P scenario).  An instance of a distributed
   application, such as a P2P application, may both provide content to
   and consume content from DECADE storage servers.

2.5.  Content Distribution Application

   A content distribution application is a distributed application
   designed for dissemination of possibly-large data to multiple
   consumers.  Content Distribution Applications typically divide
   content into smaller immutable blocks for dissemination.

   The term Application Developer refers to the developer of a
   particular Content Distribution Application.





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2.6.  Application End-Point

   An Application End-Point is an instance of a Content Distribution
   Application that makes use of DECADE server(s).  A particular
   Application End-Point may be a DECADE Content Provider, a DECADE
   Content Consumer, or both.

   An Application End-Point need not be an active member of a "swarm" to
   interact with the DECADE storage system.  That is, an End-Point may
   interact with the DECADE storage servers as an offline activity.


3.  Architectural Principles

   We identify the following key principles.

3.1.  Decoupled Control/Metadata and Data Planes

   The DECADE infrastructure is intended to support multiple content
   distribution applications.  A complete content distribution
   application implements a set of control and management functions
   including content search, indexing and collection, access control, ad
   insertion, replication, request routing, and QoS scheduling.  A
   observation of DECADE is that different content distribution
   applications can have unique considerations designing the control and
   signaling functions:

   o  Metadata Management: Traditional file systems provide a standard
      metadata abstraction: a recursive structure of directories to
      offer namespace management; each file is an opaque byte stream.
      In content distribution, applications may use different metadata
      management schemes.  For example, one application may use a
      sequence of blocks (e.g., for file sharing), while another
      application may use a sequence of frames (with different sizes)
      indexed by time.  For example, Apple Live Streaming uses a dynamic
      playlist to allow switching of frames encoded at different
      encoding rates.

   o  Resource and Access Control: For example, a major competitive
      advantage of many successful P2P systems is their substantial
      expertise in achieving highly efficient utilization of peer and
      infrastructural resources.  For instance, many live P2P systems
      have their specific algorithms in constructing topologies to
      achieve low-latency, high-bandwidth streaming.  They continue to
      fine-tune such algorithms.

   Given the diversity of control-plane functions, in-network storage
   should export basic mechanisms and allow as much flexibility as



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   possible to the control planes to implement specific policies.  This
   conforms to the end-to-end systems principle and allows innovation
   and satisfaction of specific business goals.

   Specifically, in the DECADE architecture, the control plane focuses
   on the application-specific, complex, and/or processing intensive
   functions while the data plane provides storage and data transport
   functions.

   o  Control plane: Signals details of where the data is to be
      downloaded from.  The control signals may also include the time,
      quality of service, and receivers of the download.  It also
      provides higher layer meta-data management functions such as
      defining the sequence of data blocks forming a higher layer
      content object.  These are behaviors designed and implemented by
      the Application.  By Application, we mean the broad sense that
      includes other control plane protocols.

   o  Data plane: Stores and transfers basic data objects as instructed
      by the Application's Control Plane.

   Decoupling control plane and data plane is not new.  For example,
   OpenFlow is an implementation of this principle for Internet routing,
   where the computation of the forwarding table and the application of
   the forwarding table are separated.  Google File System applies the
   principle to file system design, by utilizing the Master to handle
   the meta-data management, and the Chunk Servers to handle the data
   plane functions (i.e., read and write of chunks of data).  NFS4 also
   implements this principle.

   Note that applications may have different Data Plane implementations
   in order to support particular requirements (e.g., low latency).  In
   order to provide interoperability, the DECADE architecture does not
   intend to enable arbitrary data transport protocols.  However, the
   architecture may allow for more-than-one data transport protocols to
   be used.

   Also note that although an application's existing control plane
   functions remain implemented within the application, the particular
   implementation may need to be adjusted to support DECADE.

3.2.  Immutable Data Objects

   A property of bulk contents to be broadly distributed is that they
   typically are immutable -- once a piece of content is generated, it
   is typically not modified.  It is not common that bulk contents such
   as video frames and images need to be modified after distribution.




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   Many content distribution applications divide content objects into
   blocks for two reasons: (1) multipath: different blocks may be
   fetched from different content sources in parallel, and (2) faster
   recovery and verification: individual blocks may be recovered and
   verified.  Typically, applications use a block size larger than a
   single packet in order to reduce control overhead.

   Common applications whose content matches this model include P2P
   streaming (live and video-on-demand) and P2P file-sharing content.
   However, other additional types of applications may match this model.

   DECADE adopts a design in which immutable data objects may be stored
   at a storage server.  Applications may consider existing blocks as
   DECADE data objects, or they may adjust block sizes before storing in
   a DECADE server.

   Focusing on immutable data blocks in the data plane can substantially
   simplify the data plane design, since consistency requirements can be
   relaxed.  It also allows effective reuse of data blocks and de-
   duplication of redundant data.

   Depending on its specific requirements, an application may store data
   in DECADE servers such that each data object is completely self-
   contained (e.g., a complete, independently decodable video segment).
   An application may also divide data into chunks that require
   application level assembly.  The DECADE architecture and protocols
   are agnostic to the nature of the data objects and do not specify a
   fixed size for them.

   Note that immutable content may still be deleted.  Also note that
   immutable data blocks do not imply that contents cannot be modified.
   For example, a meta-data management function of the control plane may
   associate a name with a sequence of immutable blocks.  If one of the
   blocks is modified, the meta-data management function changes the
   mapping of the name to a new sequence of immutable blocks.

3.3.  Data Object Identifiers

   Objects that are stored in a DECADE storage server can be accessed by
   DECADE content consumers by a resource identifier that has been
   assigned within a certain application context.

   Because a DECADE content consumer can access more than one storage
   server within a single application context, a data object that is
   replicated across different storage servers managed by a DECADE
   storage provider, can be accessed by a single identifier.

   Note that since data objects are immutable, it is possible to support



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   persistent identifiers for data objects.

3.4.  Explicit Control

   To support the functions of an application's control plane,
   applications must be able to know and control which data is stored at
   particular locations.  Thus, in contrast with content caches,
   applications are given explicit control over the placement (selection
   of a DECADE server), deletion (or expiration policy), and access
   control for stored data.

   Consider deletion/expiration policy as a simple example.  An
   application may require that a DECADE server store content for a
   relatively short period of time (e.g., for live-streaming data).
   Another application may need to store content for a longer duration
   (e.g., for video-on-demand).

3.5.  Resource and Data Access Control through User Delegation

   DECADE provides a shared infrastructure to be used by multiple
   tenants of multiple content distribution applications.  Thus, it
   needs to provide both resource and data access control.

3.5.1.  Resource Allocation

   There are two primary interacting entities in the DECADE
   architecture.  First, Storage Providers control where DECADE storage
   servers are provisioned and their total available resources.  Second,
   Applications control data transfers amongst available DECADE servers
   and between DECADE servers and end-points.  A form of isolation is
   required to enable concurrently-running Applications to each
   explicitly manage their own content and share of resources at the
   available servers.

   The Storage Provider delegates the management of the resources at a
   DECADE server to one or more applications.  Applications are able to
   explicitly and independently manage their own shares of resources.

3.5.2.  User Delegations

   Storage providers have the ability to explicitly manage the entities
   allowed to utilize the resources at a DECADE server.  This capability
   is needed for reasons such as capacity-planning and legal
   considerations in certain deployment scenarios.

   To provide a scalable way to manage applications granted resources at
   a DECADE server, we consider an architecture that adds a layer of
   indirection.  Instead of granting resources to an application, the



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   DECADE server grants a share of the resources to a user.  The user
   may in turn share the granted resources amongst multiple
   applications.  The share of resources granted by a storage provider
   is called a User Delegation.

   A User Delegation may be granted to an end-user (e.g., an ISP
   subscriber), a Content Provider, or an Application Provider.  A
   particular instance of an application may make use of the storage
   resources:

   o  granted to the end-user (with the end-user's permission),

   o  granted to the Content Provider (with the Content Provider's
      permission), and/or

   o  granted to the Application Provider.


4.  System Components

   The primary focus of the current version of this document is on the
   architectural principles.  The detailed system components will be
   discussed in the next document revision.

   This section presents an overview of the components in the DECADE
   architecture.

























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           .--------------------------------------------------------------.
           | Application End-Point                                        |
           | .------------.                 .-------------------.         |
           | | App-Layer  |   ...           | App Data Assembly |         |
           | | Algorithms |                 |    Sequencing     |         |
           | `------------'                 `-------------------'         |
           |                                                              |
           | .----------------------------------------------------------. |
           | | DECADE Client                                            | |
           | |                                                          | |
           | | .-------------------------. .--------------------------. | |
           | | | Resource Controller     | | Data Controller          | | |
           | | | .--------. .----------. | | .------------. .-------. | | |
 Native    | | | |  Data  | | Resource | | | |    Data    | | Data  | | | |
  App      | | | | Access | | Sharing  | | | | Scheduling | | Index | | | |
Protocol(s)| | | | Policy | |  Policy  | | | |            | |       | | | |
      .--> | | | '--------' `----------' | | `------------' `-------' | | |
      |    | | `-------------------------' `--------------------------' | |
      |    | |             |                   ^                        | |
      |    | `------------ | ----------------- | -----------------------' |
      |    `-------------- | ----------------- | -------------------------'
      |                    |                   |
      v                    | DECADE            | Standard
.-------------.            | Resource          | Data
| Application |            | Protocol (DRP)    | Transport (SDT)
|  End-Point  |            |                   |
`-------------'            |                   |      Content Distribution
  ^       ^                |                   |          Application
= | ===== | ============== | ================= | ==========================
  |       |                |                   |        DECADE Server(s)
  |       |                |                   |
  |       |             .- | ----------------- | ----------------------.
  |       |             |  |                   v                       |
  |       |             |  |      .----------------.                   |
  |       |             |  |----> | Access Control | <--------.        |
  | DRP   | SDT         |  |      `----------------'          |        |
  |       |             |  |                   ^              |        |
  |       |             |  |                   v              |        |
  |       |             |  |   .---------------------.        |        |
  |       |             |  `-> | Resource Scheduling | <------|        |
  v       v      DRP    |      `---------------------'        |        |
.------------. <------> |                      ^              |        |
|   DECADE   |          |                      v        .------------. |
|   Server   |   SDT    |        .-----------------.    |    User    | |
`------------' <------> |        |    Data Store   |    | Delegation | |
                        |        `-----------------'    | Management | |
                        | DECADE Server                 `------------' |
                        `----------------------------------------------'



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                 Figure 1: DECADE Architecture Components

   A component diagram of the DECADE architecture is displayed in
   Figure 1.  The diagram illustrates the major components of a Content
   Distribution Application related to DECADE, as well as the functional
   components of a DECADE Server.

   To keep the scope narrow, we only discuss the primary components
   related to protocol development.  Particular deployments may require
   additional components (e.g., monitoring and accounting at a DECADE
   server), but they are intentionally omitted from the current version
   of this document.

4.1.  Content Distribution Application

   Content Distribution Applications have many functional components.
   For example, many P2P applications have components to manage overlay
   topology management, piece selection, etc.  In supporting DECADE, it
   may be advantageous to consider DECADE within some of these
   components.  However, in this architecture document, we focus on the
   components directly employed to support DECADE.

4.1.1.  Data Assembly

   DECADE is primarily designed to support applications that can divide
   distributed contents into immutable data objects.  To accomplish
   this, applications include a component responsible for creating the
   individual data objects before distribution and then re-assembling
   data objects at the Content Consumer.  We call this component
   Application Data Assembly.  The specific implementation is entirely
   decided by the application.

   In producing and assembling the data objects, two important
   considerations are sequencing and naming.  The DECADE architecture
   assumes that applications implement this functionality themselves.

   For example, a Content Distribution Application might divide a single
   content (e.g., a finite-length file or a live stream) into multiple
   data objects with names of the form "CONTENT_ID:SEQUENCE_NUMBER"
   where CONTENT_ID identifies the particular content (e.g., a
   particular movie or TV channel distributed by the application), and
   SEQUENCE_NUMBER both identifies an individual data object and
   determines its order when a client reconstructs individual data
   objects into the full content.







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4.1.2.  Native Protocols

   Applications may still use existing protocols.  In particular, an
   application may reuse existing protocols primarily for control/
   signaling.  However, an application may still retain its existing
   data transport protocols, in addition to DECADE as the data transport
   protocol.  This can be important for applications that are designed
   to be highly robust (e.g., if DECADE servers are unavailable).

4.1.3.  DECADE Client

   An application may be modified to support DECADE.  We call the layer
   providing the DECADE support to an application the DECADE Client.  It
   is important to note that a DECADE Client need not be embedded into
   an application.  It could be implemented alone, or could be
   integrated in other entities such as network devices themselves.

4.1.3.1.  Resource Controller

   Applications may have different Resource sharing policies and Data
   access policies to control their resource and data in DECADE servers.
   These policies can be existing policies of applications (e.g., tit-
   for-tat) or custom policies adapted for DECADE.  The specific
   implementation is decided by the application.

4.1.3.2.  Data Controller

   DECADE is designed to decouple the control and the data transport of
   applications.  Data transport between applications and DECADE servers
   uses standard data transport protocols.  It may need to schedule the
   data being transferred according to network conditions, available
   DECADE Servers, and/or available DECADE Server resources.  An index
   indicates data available at remote DECADE servers.  The index (or a
   subset of it) may be advertised to other Application End-Points.

4.2.  DECADE Server

   DECADE server is an important functional component of DECADE.  It
   stores data from Application End-Points, and provides control and
   access of those data to Application End-Points.  Note that a DECADE
   server is not necessarily a single physical machine, it could also be
   implemented as a cluster of machines.

4.2.1.  Access Control

   An Application End-Point can access its own data or other Application
   End-Point's data (provided sufficient authorization) in DECADE
   servers.  Application End-Points may also authorize other End-Points



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   to store data.  If an access is authorized by an Application End-
   Point, the DECADE Server will provide access.

   Note that even if a request is authorized, it may still fail to
   complete due to insufficient resources by either the requesting
   Application End-Point or the providing Application End-Point.

4.2.2.  Resource Scheduling

   Applications may apply their existing resource sharing policies or
   use a custom policy for DECADE.  DECADE servers perform resource
   scheduling according to the resource sharing policies indicated by
   Application End-Points as well as configured User Delegations.

   Access control and resource control are separated in DECADE server.
   It is possible that an Application End-Point provides only access to
   its data without any resources.  In order to access this data,
   another Application End-Point may use the granted access along with
   its own available resources to store or retrieve data from a DECADE
   Server.

4.2.3.  Data Store

   Data from applications may be stored into disks.  Data can be deleted
   from disks either explicitly or automatically (e.g., after a TTL).
   It may be possible to perform optimizations in certain cases, such as
   avoiding writing temporary data (e.g., live streaming) to a disk.

4.3.  Protocols

   The DECADE Architecture uses two protocols.  First, the DECADE
   Resource Protocol is responsible for communicating access control and
   resource scheduling policies to the DECADE Server.  Second, standard
   data transport protocols (e.g., WebDAV or NFS) are used to transfer
   data objects to and from a DECADE Server.  The DECADE architecture
   will specify a small number of Standard Data Transport instances.

   Decoupling the protocols in this way allows DECADE to both directly
   utilize existing standard data transports and to evolve
   independently.

   It is also important to note that the two protocols do not need to be
   separate on the wire.  For example, the DECADE Resource Protocol
   messages may be piggybacked within the extension fields provided by
   certain data transport protocols.  However, this document considers
   them as two separate, logical functional components for clarity.





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4.3.1.  DECADE Resource Protocol

   The DECADE Resource Protocol is responsible for communicating both
   access control and resource sharing policies to DECADE Servers used
   for data transport.

   The DECADE architecture specification will provide exactly one DECADE
   Resource Protocol.

4.3.2.  Standard Data Transports

   Existing data transport protocols are used to read and write data
   from a DECADE Server.  Protocols under consideration are WebDAV and
   NFS.

4.4.  Data Sequencing and Naming

   In order to provide a simple and generic interface, the DECADE Server
   is only responsible for storing and retrieving individual data
   objects.  Furthermore, DECADE uses its own simple naming scheme that
   provides uniqueness (with high probability) between data objects,
   even across multiple applications.

4.4.1.  DECADE Data Object Naming Schame

   The name of a data object is derived from the hash over the data
   object's content (the raw bytes), which is made possible by the fact
   that DECADE objects are immutable.  This scheme multiple appealing
   properties:

   o  Simple integrity verification

   o  Unique names (with high probability)

   o  Application independent, without a new IANA-maintained registry

   The DECADE naming scheme also includes a "type" field, the "type"
   identifier indicates that the name is the hash of the data object's
   content and the particular hashing algorithm used.  This allows the
   DECADE protocol to evolve by either changing the hashing algorithm
   (e.g., if security vulernabilities with an existing hashing algorithm
   are discovered), or move to a different naming scheme altogether.

   The specific format of the name (e.g., encoding, hash algorithms,
   etc) is out of scope of this document, and left for protocol
   specification.

   Another advantage of this scheme is that a DECADE client knows the



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   name of a data object before it is completely stored at the DECADE
   server.  This allows for particular optimizations, such as
   advertising data object while the data object is being stored,
   removing store-and-forward delays.  For example, a DECADE client A
   may simultaneously begin storing an object to a DECADE server, and
   advertise that the object is available to DECADE client B. If it is
   supported by the DECADE server, client B may begin downloading the
   object before A is finished storing the object.

4.4.2.  Application Usage

   Recall from Section 4.1.1 that an Application typically includes its
   own naming and sequencing scheme.  It is important to note that the
   DECADE naming format does not attempt to replace any naming or
   sequencing of data objects already performed by an Application;
   instead, the DECADE naming is intended to apply only to data objects
   referenced at the DECADE layer.

   DECADE names are not necessarily correlated with the naming or
   sequencing used by the Application using a DECADE client.  The DECADE
   client is expected to maintain a mapping from its own data objects
   and their names to the DECADE data objects and names.  Furthermore,
   the DECADE naming scheme implies no sequencing or grouping of
   objects, even if this is done at the application layer.

   Not only does an Application retain its own naming scheme, it may
   also decide the sizes of data objects to be distributed via DECADE.
   This is desirable since sizes of data objects may impact Application
   performance (e.g., overhead vs. data distribution delay), and the
   particular tradeoff is application-dependent.

4.4.3.  Application Usage Example

   To illustrate these properties, this section presents multiple
   examples.

4.4.3.1.  Application with Fixed-Size Chunks

   Similar to the example in Section 4.1.1, consider an Application in
   which each individual application-layer segment of data is called a
   "chunk" and has a name of the form: "CONTENT_ID:SEQUENCE_NUMBER".
   Furthermore, assume that the application's native protocol uses
   chunks of size 16KB.

   Now, assume that this application wishes to make use of DECADE, and
   assume that it wishes to store data to DECADE servers in data objects
   of size 64KB.  To accomplish this, it can map a sequence of 4 chunks
   into a single DECADE object, as shown in Figure 2.



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  Application Chunks
.---------.---------.---------.---------.---------.---------.---------.--
|         |         |         |         |         |         |         |
| Chunk_0 | Chunk_1 | Chunk_2 | Chunk_3 | Chunk_4 | Chunk_5 | Chunk_6 |
|         |         |         |         |         |         |         |
`---------`---------`---------`---------`---------`---------`---------`--


  DECADE Data Objects
.---------------------------------------.--------------------------------
|                                       |
|               Object_0                |               Object_1
|                                       |
`---------------------------------------`--------------------------------

        Figure 2: Mapping Application Chunks to DECADE Data Objects

   In this example, the Application might maintain a logical mapping
   that is able to determine the name of a DECADE data object given the
   chunks contained within that data object.  The name might be learned
   from either the original source, another endpoint with which the it
   is communicating, a tracker, etc.

   It is important to note that as long as the data contained within
   each sequence of chunks is unique, the corresponding DECADE data
   objects have unique names.  This is desired, and happens
   automatically if particular Application segments the same stream of
   data in a different way, including different chunk size sizes or
   different padding schemes.

4.4.3.2.  Application with Continuous Streaming Data

   Next, consider an Application whose native protocol retrieves a
   continuous data stream (e.g., an MPEG2 stream) instead of downloading
   and redistributing chunks of data.  Such an application could segment
   the continuous data stream to produce either fixed-sized or variable-
   sized DECADE data objects.

   Figure 3 shows how a video streaming application might produce
   variable-sized DECADE data objects such that each DECADE data object
   contains 10 seconds of video data.










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  Application's Video Stream
.------------------------------------------------------------------------
|
|
|
`------------------------------------------------------------------------
^              ^              ^              ^              ^
|              |              |              |              |
0 Seconds     10 Seconds     20 Seconds     30 Seconds     40 Seconds
0 B           400 KB         900 KB         1200 KB        1500 KB



  DECADE Data Objects
.--------------.--------------.--------------.--------------.------------
|              |              |              |              |
|   Object_0   |   Object_1   |   Object_2   |   Object_3   |
|   (400 KB)   |   (500 KB)   |   (300 KB)   |   (300 KB)   |
`--------------`--------------`--------------`--------------`------------

     Figure 3: Mapping a Continuous Data Stream to DECADE Data Objects

   Similar to the previous example, the Application might maintain a
   mapping that is able to determine the name of a DECADE data object
   given the time offset of the video chunk.

4.5.  Token-based Authentication and Resource Control

   A primary use case for DECADE is a DECADE Client authorizing other
   DECADE Clients to store or retrieve data objects from its DECADE
   storage.  To support this, DECADE uses a token-based authentication
   scheme.

   In particular, an entity trusted by a DECADE Client generates a
   digitally-signed token with particular properties (see Section 5.1.2
   for details).  The DECADE Client distributes this token to other
   DECADE Clients which then use the token when sending requests to the
   DECADE Server.  Upon receiving a token, the DECADE Server validates
   the signature and the operation being performed.

   This is a simple scheme, but has multiple important advantages over
   an alternate approach in which a DECADE Client explicitly manipulates
   an Access Control List (ACL) associated with each DECADE data object.
   In particular, it has the following advantages when applied to
   DECADE's target applications:

   o  Authorization policies are implemented within the Application; an
      Application explicitly controls when tokens are generated and to



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      whom they are distributed.

   o  Fine-grained access and resource control can be applied to data
      objects; see Section 5.1.2 for the list of restrictions that can
      be enforced with a token.

   o  There is no messaging between a DECADE Client and DECADE Server to
      manipulate data object permissions.  This can simplify, in
      particular, Applications which share data objects with many
      dynamic peers and need to frequently adjust access control
      policies attached to DECADE data objects.

   o  Tokens can provide anonymous access, in which a DECADE Server does
      not need to know the identity of each DECADE Client that accesses
      it.  This enables a DECADE Client to send tokens to DECADE Clients
      in other administrative or security domains, and allow them to
      read or write data objects from its DECADE storage.

   It is important to note that, in addition to DECADE Clients applying
   access control policies to DECADE data objects, the DECADE Server may
   be configured to apply additional policies based on user, object,
   geographic location, etc.  Defining such policies is out of scope of
   the DECADE Working Group, but in such a case, a DECADE Client may be
   denied access even though it possess a valid token.

4.6.  In-Network Storage Components Mapped to DECADE Architecture

   In this section we evaluate how the basic components of an in-network
   storage system identified in Section 3 of [I-D.ietf-decade-survey]
   map into the DECADE architecture.

   It is important to note that complex and/or application-specific
   behavior is delegated to applications instead of tuning the storage
   system wherever possible.

4.6.1.  Data Access Interface

   Users can read and write objects of arbitrary size through the DECADE
   Client's Data Controller, making use of a standard data transport.

4.6.2.  Data Management Operations

   Users can move or delete previously stored objects via the DECADE
   Client's Data Controller, making use of a standard data transport.







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4.6.3.  Data Search Capability

   Users can enumerate or search contents of DECADE servers to find
   objects matching desired criteria through services provided by the
   Content Distribution Application (e.g., buffer-map exchanges, a DHT,
   or peer-exchange).  In doing so, End-Points may consult their local
   data index in the DECADE Client's Data Controller.

4.6.4.  Access Control Authorization

   All methods of access control are supported: public-unrestricted,
   public-restricted and private.  Access Control Policies are generated
   by a Content Distribution Application and provided to the DECADE
   Client's Resource Controller.  The DECADE Server is responsible for
   implementing the access control checks.

4.6.5.  Resource Control Interface

   Users can manage the resources (e.g. bandwidth) on the DECADE server
   that can be used by other Application End-Points.  Resource Sharing
   Policies are generated by a Content Distribution Application and
   provided to the DECADE Client's Resource Controller.  The DECADE
   Server is responsible for implementing the resource sharing policies.

4.6.6.  Discovery Mechanism

   This is outside the scope of the DECADE architecture.  However, it is
   expected that DNS or some other well known protocol will be used for
   the users to discover the DECADE servers.

4.6.7.  Storage Mode

   DECADE Servers provide an object-based storage mode.  Immutable data
   objects may be stored at a DECADE server.  Applications may consider
   existing blocks as DECADE data objects, or they may adjust block
   sizes before storing in a DECADE server.


5.  DECADE Protocols

   This section specifies the DECADE Resource Protocol (DRP) and the
   Standard Data Transport (SDT) in terms of abstract protocol
   interactions that are intended to mapped to specific protocols.  Note
   that while the protocols are logically separate, DRP is specified as
   being carried through extension fields within an SDT (e.g., HTTP
   headers).

   The DRP is the protocol used by a DECADE client to configure the



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   resources and authorization used to satisfy requests (reading,
   writing, and management operations concerning DECADE objects) at a
   DECADE server.  The SDT is used to send the operations to the DECADE
   server.  Necessary DRP metadata is supplied using mechanisms in the
   SDT that are provided for extensibility (e.g., additional request
   parameters or extension headers).

5.1.  DECADE Resource Protocol (DRP)

   DRP provides configuration of access control and resource sharing
   policies on DECADE servers.  A content distribution application,
   e.g., a live P2P streaming session, MAY employ several DECADE
   servers, for instance, servers in different operator domains, and DRP
   allows one instance of such an application, e.g., an application
   endpoint, to configure access control and resource sharing policies
   on a set of servers.

5.1.1.  Controlled Resources

   On a single DECADE server, the following resources may be managed:

   communication resources:  DECADE servers have limited communication
      resources in terms of bandwidth (upload/download) but also in
      terms of number of connected clients (connections) at a time.

   storage resources:  DECADE servers have limited storage resources.

5.1.2.  Token-based Authentication and Resource Control

   DECADE uses a token-based scheme that allows a DECADE Client to
   authorize other DECADE Clients to perform certain actions (e.g., read
   or write data objects) on the client's DECADE Server.  The token
   includes the following fields:

      Permitted operations (e.g., read, write)

      Permitted objects (e.g., names of data objects that may be read or
      written)

      Permitted clients (e.g., as indicated by IP address or other
      identifier) that may use the token

      Expiration time

      Priority for bandwidth given to requested operation

      Amount of data that may be read or written




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   The particular format for the token is out of scope of this document.

   The tokens are generated by a trusted entity at the request of a
   DECADE Client.  It is out of scope of this document to identify which
   entity serves this purpose, but examples include the DECADE Client
   itself, a DECADE Server trusted by the DECADE Client, or another
   server managed by a Storage Provider trusted by the DECADE Client.

   Upon generating a token, a DECADE Client may distribute it to another
   DECADE Client (e.g., via their native Application protocol).  The
   receiving DECADE Client may then connect to the sending DECADE
   Client's DECADE Server and perform any operation permitted by the
   token.  The token must be sent along with the operation.  The DECADE
   Server validates the token to identify the DECADE Client that issued
   it and whether the requested operation is permitted by the contents
   of the token.  If the token is successfully validated, the DECADE
   Server applies the resource control policies indicated in the token
   while performing the operation.

   It is possible for DRP to allow tokens to apply to a batch of
   operations to reduce communication overhead required between DECADE
   Clients.

   DRP may also define tokens to include a unique identifer to allow a
   DECADE Server to detect when a token is used multiple times.

5.1.3.  Status Information

   DRP provides a request service for status information that DECADE
   clients can use to request information from a DECADE server.

   status information per application context on a specific server:
      Access to such status information requires client authorization,
      i.e., DECADE clients need to be authorized to access status
      information for a specific application context.  This
      authorization (and the mapping to application contexts) is based
      on the user delegation concept as described in Section 3.5.  The
      following status information elements can be obtained:

      *  list of associated objects (with properties)

      *  resources used/available

      *  list of servers to which objects have been distributed (in a
         certain time-frame)

      *  list of clients to which objects have been distributed (in a
         certain time-frame)



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      For the list of servers/clients to which objects have been
      distributed to, the DECADE server can decide on time bounds for
      which this information is stored and specify the corresponding
      time frame in the response to such requests.  Some of this
      information can be used for accounting purposes, e.g., the list of
      clients to which objects have been distributed.

   access information per application context on a specific server:
      Access information can be provided for accounting purposes, for
      example, when application service providers are interested to
      maintain access statistics for resources and/or to perform
      accounting per user.  Again, access to such information requires
      client authorization based on the user delegation concept as
      described in Section 3.5.  The following access information
      elements can be requested:

      *  what objects have been accessed how many times

      *  access tokens that a server as seen for a given object

      The DECADE server can decide on time bounds for which this
      information is stored and specify the corresponding time frame in
      the response to such requests.

5.1.4.  Object Properties

   Objects that are stored on a DECADE server can provide properties (in
   addition to the object identifier and the actual content).  Depending
   on authorization, DECADE clients may get or set such properties.
   This authorization (and the mapping to application contexts) is based
   on the user delegation concept as described in Section 3.5.  The
   DECADE architecture does not limit the set of permissible properties,
   but rather specifies a set of baseline properties that SHOULD be
   supported by implementations.

   TTL:  TTL of the object as an absolute time value

   object size:  in bytes

   MIME type

   access statistics:  how often the object has been accessed (and what
      tokens have been used)








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5.2.  Standard Data Transport (SDT)

   A DECADE server provide a data access interface, and SDT is used to
   write objects to a server and to read (download) objects from a
   server.  Semantically, SDT is a client-server protocol, i.e., the
   DECADE server always responds to client requests.

5.2.1.  Writing/Uploading Objects

   For writing objects, a client uploads an object to a DECADE server.
   The object on the server will be named (associated to an identifier),
   and this name can be used to access (download) the object later,
   e.g., the client can pass the name as a reference to other client
   that can then refer to the object.

   DECADE objects can be self-contained objects such as multimedia
   resources, files etc., but also chunks, such as chunks of a P2P
   distribution protocol that can be part of a containing object or a
   stream.

   A server MUST accept download requests for an object that is still
   being uploaded.

   The application that originates the objects MUST generate DECADE
   object names according to the naming specification in Section 4.4.
   The naming scheme provides that the name is unique.  DECADE clients
   (as parts of application entities) upload a named object to a server,
   and a DECADE server MUST not change the name.  It MUST be possible
   for downloading clients, to access the object using the original
   name.  A DECADE server MAY verify the integrity and other security
   properties of uploaded objects.

   In the following we provide an abstract specification of the upload
   operation that we name 'PUT METHOD'.  See Appendix A.1 for an example
   how this could be mapped to HTTP.

   Method  PUT:

   Parameters:

      NAME:  The naming of the object according to Section 4.4

      OBJECT:  The object itself.  The protocol MUST provide transparent
         binary object transport.







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   Description:  The PUT method is used by a DECADE client to upload an
      object with an associated name 'NAME' to a DECADE server.

   RESPONSES:  The DECADE server MUST respond with one the following
      response messages:

      OK:  The object has been uploaded successfully and has replaced an
         existing object with the same name.

      CREATED:  The object has been uploaded successfully and is now
         available under the specified name.

      ERRORs:  possible error codes later will be specified in a later
         version of this document

5.2.2.  Downloading Objects

   A DECADE client can request named objects from a DECADE server.  In
   the following, we provide an abstract specification of the download
   operation that we name 'GET METHOD'.  See Section 4.4 for an example
   how this could be mapped to HTTP.

   Method  GET:

   Parameters:

      NAME:  The naming of the object according to Section 4.4.

   Description:  The GET method is used by a DECADE client to download
      an object with an associated name 'NAME' from a DECADE server.

   RESPONSES:  The DECADE server MUST respond with one the following
      response messages:

      OK:  The request has succeeded, and an entity corresponding to the
         requested resource is sent in the response.

      ERRORs:

         NOTFOUND:  The DECADE server has not found anything matching
            the request object name.

         Other Errors:  TBD in a future version of this document








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6.  Server-to-Server Protocols

   An important feature of DECADE is the capability for one DECADE
   server to directly download data objects from another DECADE server.
   This capability allows Applications to directly replicate data
   objects between servers without requiring end-hosts to use uplink
   capacity to upload data objects to a different DECADE server.
   Similar to other operations in DRP and SDT, replicating data objects
   between DECADE servers is an explicit operation.

   To support this functionality, DECADE re-uses the already-specified
   protocols to support operations directly between servers.  DECADE
   servers are not assumed to trust each other nor are configured to do
   so.  All data operations are performed on behalf of DECADE clients
   via explicit instruction, so additional capabilities are needed in
   the DECADE client-server protocols DECADE clients must be able to
   indicate to a DECADE server the following additional parameters:

   o  which remote DECADE server(s) to access;

   o  the operation to be performed (PUT or GET); and

   o  Credentials indicating permission to perform the operation at the
      remote DECADE server.

   In this way, a DECADE server is also a DECADE client, and requests
   may instantiate requests via that client.  The operations are
   performed as if the original requestor had its own DECADE client co-
   located with the DECADE server.  It is this mode of operation that
   provides substantial savings in uplink capacity.

6.1.  Operational Overview

   DECADE's server-to-server support is focused on reading and writing
   data objects between DECADE servers.  A DECADE GET or PUT request MAY
   supply the following additional parameters:

   REMOTE_SERVER:  Address of the remote DECADE server.  The format of
      the address is out-of-scope of this document.

   REMOTE_USER:  The account at the remote server from which to retrieve
      the object (for a GET), or in which the object is to be stored
      (for a PUT).

   TOKEN:  Credentials to be used at the remote server.

   These parameters are used by the DECADE server to instantiate a
   request to the specified remote server.  It is assumed that the data



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   object referred to at the remote server is the same as the original
   request.  It is also assumed that the operation performed at the
   remote server is the same as the operation in the original request.
   Though explicitly supplying these may provide additional freedom, it
   is not clear what benefit they might provide.

   Note that when a DECADE client invokes a request a DECADE server with
   these additional parameters, it is giving the DECADE server
   permission to act on its behalf.  Thus, it would be wise for the
   supplied token to have narrow privileges (e.g., limited to only the
   necessary data objects) or validity time (e.g., a small expiration
   time).

   In the case of a GET operation, the DECADE server is to retrieve the
   data object from the remote server using the specified credentials
   (via a GET request to the remote server), and then return the object
   to the client.  In the case of a PUT operation, the DECADE server is
   to store the object from the client, and then store the object to the
   remote server using the specified credentials (via a PUT request to
   the remote server).


7.  Potential Optimizations

   As suggestions for the protocol design and eventual implementations,
   we discuss particular optimizations that are enabled by the DECADE
   Architecture discussed in this document.

7.1.  Pipelining to Avoid Store-and-Forward Delays

   DECADE server may choose to not fully store an object before
   beginning to serve it.  For example, in the case of a GET request, a
   DECADE server may begin to receive a data object from a remote server
   or DECADE Client, and immediately begin returning it to the DECADE
   client.  This pipelining mode avoids store-and-forward delays, which
   could be substantial for large objects.  A similar behavior could be
   used for PUT.

7.2.  Deduplication

   A common concern amongst Storage Providers is the total volume of
   data that needs to be stored.  An optimization frequently applied in
   existing storage systems is de-duplication techniques which attempt
   to avoid storing identical data multiple times.  DECADE Server
   implementations may internally perform de-duplication of data on
   disk, but the DECADE architecture enables other forms of de-
   duplication.




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   Note that these techniques may impact protocol design.  Discussion of
   whether or not they should be adopted is out of scope of this
   document.

7.2.1.  Traffic Deduplication

7.2.1.1.  Rationale

   When a DECADE client (A) indicates its DECADE account on a DECADE
   server (S) to fetch an object from a remote entity (R) (a DECADE
   server or DECADE client) and if the object is already stored locally
   in S, S may perform Traffic Deduplication.  This means that S does
   not download the object from R, which saves network traffic.
   Instead, it performs a challenge to make sure that the remote entity
   R actually has the object and then replies with its local object copy
   directly.

7.2.1.2.  Example

   As shown in Figure 4 , without Traffic Deduplication, redundant
   traffic flows between S and R will be issued if the server already
   has the object requested by A. If Traffic Deduplication is enabled, S
   only needs to challenge R to verify that it does have the data to
   avoid data-stealing attacks.

              A                       S                      R
         +----------+ obj req  +------------+ obj req   +----------+
         |  DECADE  |=========>|     A's    |==========>|  Remote  |
         |  CLIENT  |<=========|   Account  |<==========|  Entity  |
         +----------+ obj rsp  +------------+ obj rsp   +----------+

                         (a) Without Traffic Deduplication

              A                       S                       R
         +----------+ obj req  +------------+ challenge +----------+
         |  DECADE  |=========>|     A's    |---------->|  Remote  |
         |  CLIENT  |<=========|   Account  |<----------|  Entity  |
         +----------+ obj rsp  +------------+ obj hash  +----------+

                         (b) With Traffic Deduplication

                                 Figure 4

7.2.1.3.  HTTP Compatibility of Challenge

   How to integrate traffic deduplication with HTTP is shown in
   Appendix A.1.3.




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7.2.2.  Cross-Server Storage Deduplication

   The same object might be uploaded for multiple times to different
   DECADE servers.  For storage efficiency, storage providers may desire
   a single object to be stored on one or a few servers.  They might
   design internal system architecture to achieve that, or simply
   redirect the requests to proper servers.  DECADE protocol support
   redirections of DECADE client request to support further cross-server
   storage deduplication.


8.  Security Considerations

   This document currently does not contain any security considerations
   beyond those mentioned in [I-D.ietf-decade-problem-statement].


9.  IANA Considerations

   This document does not have any IANA considerations.


10.  Informative References

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3744]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
              Distributed Authoring and Versioning (WebDAV)
              Access Control Protocol", RFC 3744, May 2004.

   [RFC4331]  Korver, B. and L. Dusseault, "Quota and Size Properties fo
              r Distributed Authoring and Versioning (DAV) Collections",
              RFC 4331, February 2006.

   [RFC4709]  Reschke, J., "Mounting Web Distributed Authoring and
              Versioning (WebDAV) Servers", RFC 4709, October 2006.

   [RFC4918]  Dusseault, L., "HTTP Extensions for Web Distributed
              Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

   [I-D.ietf-decade-problem-statement]
              Song, H., Zong, N., Yang, Y., and R. Alimi, "DECoupled
              Application Data Enroute (DECADE) Problem Statement",
              draft-ietf-decade-problem-statement-03 (work in progress),
              March 2011.




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   [I-D.ietf-decade-survey]
              Alimi, R., Rahman, A., and Y. Yang, "A Survey of In-
              network Storage Systems", draft-ietf-decade-survey-04
              (work in progress), March 2011.

   [I-D.ietf-decade-reqs]
              Yingjie, G., Bryan, D., Yang, Y., and R. Alimi, "DECADE
              Requirements", draft-ietf-decade-reqs-02 (work in
              progress), May 2011.

   [GoogleStorageDevGuide]
              "Google Storage Developer Guide", <http://code.google.com/
              apis/storage/docs/developer-guide.html>.


Appendix A.  Appendix: Evaluation of Some Candidate Existing Protocols
             for DECADE DRP and SDT

   In this section we evaluate how well the abstract protocol
   interactions specified in Section 5 for DECADE DRP and SDT can be
   fulfilled by existing protocols such as HTTP and WEBDAV.

A.1.  HTTP

   HTTP [RFC2616] is a key protocol for the Internet in general and
   especially for the World Wide Web. HTTP is a request-response
   protocol.  A typical transaction involves a client (e.g. web browser)
   requesting content (resources) from a web server.  Another example is
   when a client stores or deletes content from a server.

A.1.1.  HTTP Support for DECADE Resource Protocol Primitives

   DRP provides configuration of access control and resource sharing
   policies on DECADE servers.

A.1.1.1.  Access Control Primitives

   Access control requires mechanisms for defining the access policies
   for the server, and then checking the authorization of a user before
   it stores or retrieves content.  HTTP supports a rudimentary access
   control via "HTTP Secure" (HTTPS).  HTTPS is a combination of HTTP
   with SSL/TLS.  The main use of HTTPS is to authenticate the server
   and encrypt all traffic between the client and the server.  There is
   also a mode to support client authentication though this is less
   frequently used.






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A.1.1.2.  Communication Resource Controls Primitives

   Communications resources include bandwidth (upload/download) and
   number of simultaneous connected clients (connections).  HTTP
   supports bandwidth control indirectly through "persistent" HTTP
   connections.  Persistent HTTP connections allows a client to keep
   open the underlying TCP connection to the server to allow streaming
   and pipelining (multiple simultaneous requests for a given client).

   HTTP does not define protocol operation to allow limiting the
   communciation resources to a client.  However servers typically
   perform this function via implementation algorithms.

A.1.1.3.  Storage Resource Control Primitives

   Storage resources include amount of memory and lifetime of storage.
   HTTP does not allow direct control of storage at the server end
   point.  However HTTP supports caching at intermediate points such as
   a web proxy.  For this purpose, HTTP defines cache control mechanisms
   that define how long and in what situations the intermediate point
   may store and use the content.

A.1.2.  HTTP Support for DECADE Standard Transport Protocol Primitives

   SDT is used to write objects and read (download) objects from a
   DECADE server.  The object can be either a self-contained object such
   as a multimedia file or a chunk from a P2P system.

A.1.2.1.  Writing Primitives

   Writing involves uploading objects to the server.  HTTP supports two
   methods of writing called PUT and POST.  In HTTP the object is called
   a resource and is identified by a URI.  PUT uploads a resource to a
   specific location on the server.  POST, on the other hand, submits
   the object to the server and the server decides whether to update an
   existing resource or to create a new resource.

   For DECADE, the choice of whether to use PUT or POST will be
   influenced by which entity is responsible for the naming.  If the
   client performs the naming, then PUT is appropriate.  If the server
   performs the naming, then POST should be used (to allow the server to
   define the URI).

A.1.2.2.  Downloading Primitives

   Downloading involves fetching of an object from the server.  HTTP
   supports downloading through the GET and HEAD methods.  GET fetches a
   specific resource as identified by the URL.  HEAD is similiar but



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   only fetches the metadata ("header") associated with the resource but
   not the resource itself.

A.1.3.  Traffic Deduplication Primitives

   To challenge a remote entity for an object, the DECADE server should
   provide a seed number, which is generated by the server randomly, and
   ask the remote entity to return a hash calculated from the seed
   number and the content of the object.  The server MAY also specify
   the hash function which the remote entity should use.  HTTP supports
   the challenge message through the GET methods.  The message type
   ("challenge"), the seed number and the hash funtion name are put in
   URL.  In the reply, the hash is sent in an ETAG header.

A.1.4.  Other Operations

   HTTP supports deleting of content on the server through the DELETE
   method.

A.1.5.  Conclusions

   HTTP can provide a rudimentary DRP and SDT for some aspects of
   DECADE, but will not be able to satisfy all the DECADE requirements.
   For example, HTTP does not provide a complete access control
   mechanism, nor does it support storage resource controls at the end
   point server.

   It is possible, however, to envision combining HTTP with a custom
   suite of other protocols to fulfill most of the DECADE requirements
   for DRP and SDT.  For example, Google Storage for Developers is built
   using HTTP (with extensive proprietary extensions such as custom HTTP
   headers).  Google Storage also uses OAUTH 2.0 (for access control) in
   combination with HTTP [GoogleStorageDevGuide].

A.2.  WEBDAV

   WebDAV [RFC4918] is a protocol for enhanced Web content creation and
   management.  It was developed as an extension to HTTP Appendix A.1.
   WebDAV supports traditional operations for reading/writing from
   storage, as well as more advanced features such as locking and
   namespace management which are important when multiple users
   collaborate to author or edit a set of documents.  HTTP is a subset
   of WebDAV functionality.  Therefore, all the points noted above in
   Appendix A.1 apply implicitly to WebDAV as well.







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A.2.1.  WEBDAV Support for DECADE Resource Protocol Primitives

   DRP provides configuration of access control and resource sharing
   policies on DECADE servers.

A.2.1.1.  Access Control Primitives

   Access control requires mechanisms for defining the access policies
   for the server, and then checking the authorization of a user before
   it stores or retrieves content.  WebDAV has an Access Control
   Protocol defined in [RFC3744].

   The goal of WebDAV access control is to provide an interoperable
   mechanism for handling discretionary access control for content and
   metadata managed by WebDAV servers.  WebDAV defines an Access Control
   List (ACL) per resource.  An ACL contains a set of Access Control
   Entries (ACEs), where each ACE specifies a principal (i.e. user or
   group of users) and a set of privileges that are granted to that
   principal.  When a principal tries to perform an operation on that
   resource, the server evaluates the ACEs in the ACL to determine if
   the principal has permission for that operation.

   WebDAV also requires that an authentication mechanism be available
   for the server to validate the identity of a principal.  As a
   minimum, all WebDAV compliant implementations are required to support
   HTTP Digest Authentication.

A.2.1.2.  Communication Resource Controls Primitives

   Communications resources include bandwidth (upload/download) and
   number of simultaneous connected clients (connections).  WebDAV
   supports communication resource control as described in
   Appendix A.1.1.2.

A.2.1.3.  Storage Resource Control Primitives

   Storage resources include amount of memory and lifetime of storage.
   WebDAV supports the concept of properties (which are metadata for a
   resource).  A property is either "live" or "dead".  Live properties
   include cases where a) the value of a property is protected and
   maintained by the server, and b) the value of the property is
   maintained by the client, but the server performs syntax checking on
   submitted values.  A dead property has its syntax and semantics
   enforced by the client; the server merely records the value of the
   property.

   WebDAV supports a list of standardized properties [RFC4918] that are
   useful for storage resource control.  These include the self-



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   explanatory "creationdate", and "getcontentlength" properties.  There
   is also an operation called PROPFIND to retrieve all the properties
   defined for the requested URI.

   WebDAV also has a Quota and Size Properties mechanism defined in
   [RFC4331] that can be used for storage control.  Specifically, two
   key properties are defined per resource: "quota-available-bytes" and
   "quota-used-bytes".

   WebDAV does not define protocol operation for storage resource
   control.  However servers typically perform this function via
   implementation algorithms in conjunction with the storage related
   properties discussed above.

A.2.2.  WebDAV Support for DECADE Standard Transport Protocol Primitives

   SDT is used to write objects and read (download) objects from a
   DECADE server.  The object can be either a self-contained object such
   as a multimedia file or a chunk from a P2P system.

A.2.2.1.  Writing Primitives

   Writing involves uploading objects to the server.  WebDAV supports
   PUT and POST as described in Appendix A.1.2.1.  WebDAV LOCK/UNLOCK
   functionality is not needed as DECADE assumes immutable data objects.
   Therefore, resources cannot be edited and so do not need to be
   locked.  This approach should help to greatly simplify DECADE
   implementations as the LOCK/UNLOCK functionality is quite complex.

A.2.2.2.  Downloading Primitives

   Downloading involves fetching of an object from the server.  WebDAV
   supports GET and HEAD as described in Appendix A.1.2.2.  WebDAV LOCK/
   UNLOCK functionality is not needed as DECADE assumes immutable data
   objects.

A.2.3.  Other Operations

   WebDAV supports DELETE as described in Appendix A.1.4.  In addition
   WebDAV supports COPY and MOVE methods.  The COPY operation creates a
   duplicate of the source resource identified by the Request-URI, in
   the destination resource identified by the URI in the Destination
   header.

   The MOVE operation on a resource is the logical equivalent of a COPY,
   followed by consistency maintenance processing, followed by a delete
   of the source, where all three actions are performed in a single
   operation.  The consistency maintenance step allows the server to



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   perform updates caused by the move, such as updating all URLs, other
   than the Request-URI that identifiesthe source resource, to point to
   the new destination resource.

   WebDAV also supports the concept of "collections" of resources to
   support joint operations on related objects (e.g. file system
   directories) within a server's namespace.  For example, GET and HEAD
   may be done on a single resource (as in HTTP) or on a collection.
   The MKCOL operation is used to create a new collection.  DECADE may
   find the concept of collections to be useful if there is a need to
   support directory like structures in DECADE.

   WebDAV servers can be interfaced from an HTML-based user interface in
   a web browser.  However, it is frequently desirable to be able to
   switch from an HTML-based view to a persentation provided by a native
   WebDAV client, directly supporting WebDAV features.  The method to
   perform this in a platform-neutral mechanism is specified in the
   WebDAV protocol for "mounting WebDAV servers" [RFC4709].  This type
   of feature may also be attractive for DECADE clients.

A.2.4.  Conclusions

   WebDAV has a rich array of features that can provide a good base for
   DRP and SDT for DECADE.  An initial analysis finds that the following
   WebDAV features will be useful for DECADE:

      -  access control

      -  properties (and PROPFIND operation)

      -  COPY/MOVE operations

      -  collections

      -  mounting WebDAV servers

   It is recommended that the following WebDAV features NOT be used for
   DECADE:

      -  LOCK/UNLOCK

   Finally, some extensions to WebDAV may still be required to meet all
   DECADE requirements.  For example, defining a new WebDAV "time-to-
   live" property may be useful for DECADE.  Further analysis is
   required to fully define the potential extensions to WebDAV to meet
   all DECADE requirements.





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Authors' Addresses

   Richard Alimi
   Google

   Email: ralimi@google.com


   Y. Richard Yang
   Yale University

   Email: yry@cs.yale.edu


   Akbar Rahman
   InterDigital Communications, LLC

   Email: akbar.rahman@interdigital.com


   Dirk Kutscher
   NEC

   Email: dirk.kutscher@neclab.eu


   Hongqiang Liu
   Yale University

   Email: hongqiang.liu@yale.edu





















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