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DECADE                                                          R. Alimi
Internet-Draft                                                    Google
Intended status: Informational                                   Y. Yang
Expires: May 3, 2012                                     Yale University
                                                               A. Rahman
                                        InterDigital Communications, LLC
                                                             D. Kutscher
                                                                     NEC
                                                                  H. Liu
                                                         Yale University
                                                        October 31, 2011


                          DECADE Architecture
                       draft-ietf-decade-arch-04

Abstract

   Content Distribution Applications (e.g., P2P applications) are widely
   used on the Internet and make up a large portion of the traffic in
   many networks.  One technique to improve the network efficiency of
   these applications is to introduce storage capabilities within the
   networks; this is the capability to be provided by DECADE (DECoupled
   Application Data Enroute).  This document presents an architecture
   for DECADE, discusses the underlying principles, and identifies core
   components and protocols for introducing in-network storage for these
   applications.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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."



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   The list of current Internet-Drafts can be accessed at
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   This Internet-Draft will expire on May 3, 2012.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   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.  Functional Entities  . . . . . . . . . . . . . . . . . . . . .  6
     2.1.  DECADE Server  . . . . . . . . . . . . . . . . . . . . . .  6
     2.2.  DECADE Client  . . . . . . . . . . . . . . . . . . . . . .  6
     2.3.  DECADE Storage Provider  . . . . . . . . . . . . . . . . .  6
     2.4.  Content Provider Using DECADE  . . . . . . . . . . . . . .  6
     2.5.  Content Consumer Using DECADE  . . . . . . . . . . . . . .  7
     2.6.  Content Distribution Application . . . . . . . . . . . . .  7
   3.  Protocol Flow  . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  An Example . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Architectural Principles . . . . . . . . . . . . . . . . . . .  9
     4.1.  Decoupled Control/Metadata and Data Planes . . . . . . . . 10
     4.2.  Immutable Data Objects . . . . . . . . . . . . . . . . . . 11
     4.3.  Data Object Identifiers  . . . . . . . . . . . . . . . . . 12
     4.4.  Explicit Control . . . . . . . . . . . . . . . . . . . . . 12
     4.5.  Resource and Data Access Control through User
           Delegation . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  System Components  . . . . . . . . . . . . . . . . . . . . . . 13
     5.1.  Content Distribution Application . . . . . . . . . . . . . 14
     5.2.  DECADE Server  . . . . . . . . . . . . . . . . . . . . . . 16
     5.3.  Data Sequencing and Naming . . . . . . . . . . . . . . . . 18
     5.4.  Token-based Authentication and Resource Control  . . . . . 21
     5.5.  Discovery  . . . . . . . . . . . . . . . . . . . . . . . . 22
   6.  DECADE Protocols . . . . . . . . . . . . . . . . . . . . . . . 23
     6.1.  DECADE Resource Protocol (DRP) . . . . . . . . . . . . . . 23
     6.2.  Standard Data Transport (SDT)  . . . . . . . . . . . . . . 26
   7.  Server-to-Server Protocols . . . . . . . . . . . . . . . . . . 29
     7.1.  Operational Overview . . . . . . . . . . . . . . . . . . . 29
   8.  Potential Optimizations  . . . . . . . . . . . . . . . . . . . 30
     8.1.  Pipelining to Avoid Store-and-Forward Delays . . . . . . . 30
     8.2.  Deduplication  . . . . . . . . . . . . . . . . . . . . . . 31
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 33
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 33
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 33
     12.2. Informative References . . . . . . . . . . . . . . . . . . 33
   Appendix A.  Appendix: Evaluation of Some Candidate Existing
                Protocols for DECADE DRP and SDT  . . . . . . . . . . 34
     A.1.  HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     A.2.  WEBDAV . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     A.3.  CDMI . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
   Appendix B.  In-Network Storage Components Mapped to DECADE
                Architecture  . . . . . . . . . . . . . . . . . . . . 42
     B.1.  Data Access Interface  . . . . . . . . . . . . . . . . . . 43



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     B.2.  Data Management Operations . . . . . . . . . . . . . . . . 43
     B.3.  Data Search Capability . . . . . . . . . . . . . . . . . . 43
     B.4.  Access Control Authorization . . . . . . . . . . . . . . . 43
     B.5.  Resource Control Interface . . . . . . . . . . . . . . . . 43
     B.6.  Discovery Mechanism  . . . . . . . . . . . . . . . . . . . 43
     B.7.  Storage Mode . . . . . . . . . . . . . . . . . . . . . . . 44
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 44












































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1.  Introduction

   Content Distribution Applications are widely used on the Internet
   today to distribute data, and they contribute a large portion of the
   traffic in many networks.  The DECADE architecture described in this
   document enables such applications to leverage in-network storage to
   achieve more efficient content distribution.  Specifically, in many
   subscriber networks, it can be 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 (Digital Subscriber Line Access Multiplexers) and CMTSs (Cable
   Modem Termination Systems) in remote locations.  Therefore, 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 an architecture for 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.  See [I-D.ietf-decade-reqs] for a
   definition of the target applications supported by 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.  Focusing on only core functionalities, DECADE
   may be simpler and easier to support by service providers.  If more
   complex functionalities are needed by a certain application or class
   of applications, it may be layered on top of DECADE.

   DECADE will leverage existing data transport and application-layer
   protocols.  The design is to work with a small set of alternative
   IETF protocols.  In this document, we use "data transport" to refer
   to a protocol that is used to read data from and write data into
   DECADE in-network storage.

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

   This document does not define any new protocol.  Instead, when
   identifying the need for a new protocol, it presents an abstract
   design including the necessary functions of that protocol (including



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   rationale) in order to guide future protocol development.


2.  Functional Entities

   This section defines the functional entities involved in a DECADE
   system.  Functional entities can be classified as follows:

   o  A physical or logical component in the DECADE architecture: DECADE
      Client, DECADE Server, Content Distribution Application and
      Application End Point;

   o  Operator of a physical or logical component in the DECADE
      architecture: DECADE Storage Provider; and

   o  Source or sink of content distributed via the DECADE architecture:
      DECADE Content Provider, and DECADE Content Consumer.

2.1.  DECADE Server

   A DECADE server stores DECADE data inside the network, and thereafter
   manages both the stored data and access to that data.  To reinforce
   that these servers are responsible for storage of raw data, this
   document also refers to them as storage servers.

2.2.  DECADE Client

   A DECADE client stores and retrieves data at DECADE Servers.

2.3.  DECADE Storage Provider

   A DECADE storage provider deploys and/or manages DECADE storage
   server(s) within a network.  A storage provider may also own or
   manage the network in which the DECADE servers are deployed, but this
   is not mandatory.

   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.

2.4.  Content Provider Using DECADE

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




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2.5.  Content Consumer Using DECADE

   A content consumer using DECADE accesses DECADE storage servers (by
   way of a DECADE client).  A content consumer can access one or more
   DECADE storage servers.  A content consumer may be a single process
   or a distributed application (e.g., in a P2P scenario), and may
   either be fixed or mobile.  An instance of a distributed application,
   such as a P2P application, may both provide content to and consume
   content from DECADE storage servers.

2.6.  Content Distribution Application

   A content distribution application (as a target application for
   DECADE as described in [I-D.ietf-decade-reqs]) is a distributed
   application designed for dissemination of a possibly-large data set
   to multiple consumers.  Content Distribution Applications typically
   divide content into smaller blocks for dissemination.

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

2.6.1.  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.  For example, an Application End-Point may
   be an instance of a video streaming client, or it may be the source
   providing the video to a set of clients.

   An Application End-Point need not be actively transferring data with
   other Application End-Points to interact with the DECADE storage
   system.  That is, an End-Point may interact with the DECADE storage
   servers as an offline activity.


3.  Protocol Flow

3.1.  Overview

   The DECADE Architecture uses two protocols, as shown in Figure 1.
   First, the DECADE Resource Protocol is responsible for communication
   of access control and resource scheduling policies from DECADE Client
   to DECADE Server, as well as between DECADE Servers.  The DECADE
   Architecture includes exactly one DRP for interoperability and a
   common format through which these policies can be communicated.





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                         Native Application
         .-------------.      Protocol(s)     .-------------.
         | Application | <------------------> | Application |
         |  End-Point  |                      |  End-Point  |
         |             |                      |             |
         | .--------.  |                      | .--------.  |
         | | DECADE |  |                      | | DECADE |  |
         | | Client |  |                      | | Client |  |
         | `--------'  |                      | `--------'  |
         `-------------'                      `-------------'
             |     ^                              |     ^
     DECADE  |     | Standard                     |     |
    Resource |     |   Data                   DRP |     | SDT
    Protocol |     | Transport                    |     |
     (DRP)   |     |   (SDT)                      |     |
             |     |                              |     |
             |     |                              |     |
             |     |                              |     |
             |     |                              |     |
             |     |                              |     |
             |     |                              |     |
             v     V                              v     V
         .=============.         DRP          .=============.
         |   DECADE    | <------------------> |   DECADE    |
         |   Server    | <------------------> |   Server    |
         `============='         SDT          `============='

                      Figure 1: Generic Protocol Flow

   Second, Standard Data Transport protocols (e.g., HTTP, WebDAV, or
   CDMI) are used to transfer data objects to and from a DECADE Server.
   The DECADE architecture may be used with multiple standard data
   transports.

   Decoupling the protocols in this way allows DECADE to directly
   utilize existing standard data transports, as well as allowing both
   DECADE and DRP to evolve independently from data transports.

   It is also important to note that the two protocols do not need to be
   separate on the wire.  For example, DRP messages may be piggybacked
   within some extension fields provided by certain data transport
   protocols.  In such a scenario, DRP is technically a data structure
   (transported by other protocols), but it can still be considered as a
   logical protocol that provides the services of configuring DECADE
   resource usage.  Hence, this document considers SDT and DRP as two
   separate, logical functional components for clarity.





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3.2.  An Example

   Before discussing details of the architecture, this section provides
   an example data transfer scenario to illustrate how the DECADE
   Architecture can be applied.

   In this example, we assume that Application End-Point B (the
   receiver) is requesting a data object from Application End-Point A
   (the sender).  Let S(A) denote A's DECADE storage server.  There are
   multiple usage scenarios (by choice of the Content Distribution
   Application).  For simplicity of introduction, we design the example
   to use only a single DECADE Server; Section 7 details a case when
   both A and B wish to employ DECADE Servers.

   When an Application End-Point wishes to use its DECADE storage
   server, it provides a token (see Section 6.1.2 for details) to the
   other Application End-Point.  The token is sent using the Content
   Distribution Application's native protocol.

   The steps of the example are illustrated in Figure 2.  First, B
   requests a data object from A using their native protocol.  Next, A
   uses the DECADE Resource Protocol (DRP) to obtain a token from its
   DECADE storage server, S(A).  A then provides the token to B (again,
   using their native protocol).  Finally, B provides the token to S(A)
   via DRP, and requests and downloads the data object via a Standard
   Data Transport (SDT).

                               .----------.
                   ----------> |   S(A)   | <------
     2. Obtain    /            `----------'        \   4. Request and
        Token    /                                  \    Download Object
        (DRP)   /                                    \    (DRP + SDT)
               v            1. App request            v
      .-------------. <--------------------------- .-------------.
      | End-Point A |                              | End-Point B |
      `-------------' ---------------------------> `-------------'
                         3. App response (token)


                  Figure 2: Download from Storage Server


4.  Architectural Principles

   We identify the following key principles.






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4.1.  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.  An
   observation of DECADE is that different content distribution
   applications can have unique considerations designing the control and
   signaling functions:

   o  Metadata Management Scheme: 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.

   o  Resource Scheduling Algorithms: 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
   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.

   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
   [GoogleFileSystem] 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).  NFSv4.1's pNFS extension [RFC5661] 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



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   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.

4.2.  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.

   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 using the aforementioned data model include P2P
   streaming (live and video-on-demand) and P2P file-sharing.  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



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   mapping of the name to a new sequence of immutable blocks.

   Throughout this document, all the data objects/blocks are referred as
   immutable data objects/blocks.

4.3.  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
   persistent identifiers for data objects.

4.4.  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).

4.5.  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.

4.5.1.  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



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   explicitly manage its 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.

4.5.2.  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
   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.

   As a simple example, a DECADE Server operated by an ISP may be
   configured to grant each ISP Subscriber 1.5 Mbps of bandwidth.  The
   ISP Subscriber may in turn divide this share of resources amongst a
   video streaming application and file-sharing application which are
   running concurrently.

   In general, 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.


5.  System Components

   The primary focus of this document is the architectural principals
   and the system components that implement them.  While certain system
   components might differ amongst implementations, the document details
   the major components and their overall roles in the architecture.




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   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 this document.

5.1.  Content Distribution Application

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

   Figure 3 illustrates the components discussed in this section from
   the perspective of a single Application End-Point and their relation
   to DECADE.

































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                                    Native Protocol(s)
                            (with other Application End-Points)
                                    .--------------------->
                                    |
                                    |
   .----------------------------------------------------------.
   | Application End-Point                                    |
   | .------------.                 .-------------------.     |
   | | App-Layer  |   ...           | App Data Assembly |     |
   | | Algorithms |                 |    Sequencing     |     |
   | `------------'                 `-------------------'     |
   |                                                          |
   | .------------------------------------------------------. |
   | | DECADE Client                                        | |
   | |                                                      | |
   | | .-------------------------. .----------------------. | |
   | | | Resource Controller     | | Data Controller      | | |
   | | | .--------. .----------. | | .--------. .-------. | | |
   | | | |  Data  | | Resource | | | |  Data  | | Data  | | | |
   | | | | Access | | Sharing  | | | | Sched. | | Index | | | |
   | | | | Policy | |  Policy  | | | |        | |       | | | |
   | | | '--------' `----------' | | `--------' `-------' | | |
   | | `-------------------------' `----------------------' | |
   | |             |                   ^                    | |
   | `------------ | ----------------- | -------------------' |
   `-------------- | ----------------- | ---------------------'
                   |                   |
                   |  DECADE           | Standard
                   | Resource          |   Data
                   | Protocol          | Transport
                   |   (DRP)           |   (SDT)
                   v                   V

                     Figure 3: Application Components

5.1.1.  Data Assembly

   DECADE is primarily designed to support applications that can divide
   distributed contents into 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.



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   See Section 5.3 for further discussion.

5.1.2.  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).

5.1.3.  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.

5.1.3.1.  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.

5.1.3.2.  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.  A Data Scheduling component
   schedules data transfers according to network conditions, available
   DECADE Servers, and/or available DECADE Server resources.  The Data
   Index indicates data available at remote DECADE servers.  The Data
   Index (or a subset of it) may be advertised to other Application End-
   Points.  A common use case for this is to provide the ability to
   locate data amongst a distributed set of Application End-Points
   (i.e., a data search mechanism).

5.2.  DECADE Server

   A DECADE Server 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.





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          |                   |
          |  DECADE           | Standard
          | Resource          |   Data
          | Protocol          | Transport
          |   (DRP)           |   (SDT)
          |                   |
       .= | ================= | ======================.
       |  |                   v                       |
       |  |      .----------------.                   |
       |  |----> | Access Control | <--------.        |
       |  |      `----------------'          |        |
       |  |                   ^              |        |
       |  |                   |              |        |
       |  |                   v              |        |
       |  |   .---------------------.        |        |
       |  `-> | Resource Scheduling | <------|        |
       |      `---------------------'        |        |
       |                      ^              |        |
       |                      |              |        |
       |                      v        .------------. |
       |        .-----------------.    |    User    | |
       |        |    Data Store   |    | Delegation | |
       |        `-----------------'    | Management | |
       | DECADE Server                 `------------' |
       `=============================================='

                    Figure 4: DECADE Server Components

5.2.1.  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
   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, the providing Application End-Point, or the
   DECADE Server itself.

5.2.2.  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.




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5.2.3.  Data Store

   Data from applications may be stored at a DECADE Server.  Data can be
   deleted from storage either explicitly or automatically (e.g., after
   a TTL expiration).  It may be possible to perform optimizations in
   certain cases, such as avoiding writing temporary data (e.g., live
   streaming) to persistent storage, if appropriate storage hints are
   supported by the SDT.

5.3.  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.

5.3.1.  DECADE Data Object Naming Scheme

   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
   DECADE to evolve by either changing the hashing algorithm (e.g., if
   security vulnerabilities with an existing hashing algorithm are
   discovered), or moving 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
   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



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   supported by the DECADE server, client B may begin downloading the
   object before A is finished storing the object.

   In certain scenarios (e.g., where a DECADE client has limited
   computational power), it may be advantageous to offload the
   computation of a data object's name to the DECADE Server.  This
   possibility is not considered in the current architecture, but may be
   a topic for future extensions.

5.3.2.  Application Usage

   Recall from Section 5.1.1 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.

5.3.3.  Application Usage Example

   To illustrate these properties, this section presents multiple
   examples.

5.3.3.1.  Application with Fixed-Size Chunks

   Similar to the example in Section 5.1.1, 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 5.



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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 5: 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.

5.3.3.2.  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 6 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 6: 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.

5.4.  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 6.1.2
   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 6.1.2 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 for
   DECADE, but in such a case, a DECADE Client may be denied access even
   though it possess a valid token.

5.5.  Discovery

   DECADE includes a discovery mechanism through which DECADE clients
   locate an appropriate DECADE Server.  [I-D.ietf-decade-reqs] details
   specific requirements of the discovery mechanism; this section
   discusses how they relate to other principles outlined in this
   document.

   A discovery mechanism allows a DECADE client to determine an IP
   address or some other identifier that can be resolved to locate the
   server for which the client will be authorized to generate tokens
   (via DRP).  (Note that the discovery mechanism may also result in an
   error if no such DECADE servers can be located.)  After discovering
   one or more DECADE servers, a DECADE client may distribute load and
   requests across them (subject to resource limitations and policies of
   the DECADE servers themselves) according to the policies of the
   Application End-Point in which it is embedded.

   The particular protocol used for discovery is out of scope of this
   document, but any specification will re-use standard protocols
   wherever possible.

   It is important to note that the discovery mechanism outlined here



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   does not provide the ability to locate arbitrary DECADE servers to
   which a DECADE client might obtain tokens from others.  To do so
   requires application-level knowledge, and it is assumed that this
   functionality is implemented in the Content Distribution Application,
   or if desired and needed, as an extension to this DECADE
   architecture.


6.  DECADE Protocols

   This section presents 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
   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).

6.1.  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 apply access control and resource sharing policies on
   each of them.

6.1.1.  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.







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6.1.2.  Access and Resource Control Token

   A 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 (e.g., a
      weight used in a weighted bandwidth sharing scheme)

      Amount of data that may be read or written

   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 identifier to allow a
   DECADE Server to detect when a token is used multiple times.







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6.1.3.  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 4.5.  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)

      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 4.5.  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.





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6.1.4.  Object Attributes

   Objects that are stored on a DECADE server may have associated
   attributes (in addition to the object identifier and the actual
   content) that relate to the data storage and its management.  These
   attributes may be used by the DECADE server (and possibly the
   underlying storage system) to perform specialized processing or
   handling for the data object, or to attach related DECADE server or
   storage-layer properties to the data object.  These attributes have a
   scope local to a DECADE server.  In particular, these attributes are
   not applied to a DECADE server or client to which a data object is
   copied.

   Depending on authorization, DECADE clients may get or set such
   attributes.  This authorization (and the mapping to application
   contexts) is based on the user delegation concept as described in
   Section 4.5.  The DECADE architecture does not limit the set of
   permissible attributes, but rather specifies a set of baseline
   attributes that SHOULD be supported by implementations.

   Suggested attributes are the following:

   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)

   It is important to note that the Object Attributes defined here are
   distinct from application metadata (see Section 4.1).  Application
   metadata is custom information that an application may wish to
   associate with a data object to understand its semantic meaning
   (e.g., whether it is video and/or audio, its playback length in time,
   or its index in a stream).  If an application wishes to store such
   metadata persistently within DECADE, it can be stored within data
   objects themselves.

6.2.  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.

   An SDT used in DECADE SHOULD offer a transport mode that provides



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   confidentiality and integrity.

6.2.1.  Writing/Uploading Objects

   To write an object, a client first generates the object's name (see
   Section 5.3), and then uploads the object to a DECADE server and
   supplies the generated name.  The 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 MAY 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 5.3.
   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 5.3

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

   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:






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

      ERRORs:

         VALIDATION_FAILED:  The contents of the data object received by
            the DECADE server did not match the provided name (i.e.,
            hash validation failed).

         PERMISSION_DENIED:  The DECADE client lacked sufficient
            permission to store the object.

         Specifics regarding error handling, including additional error
         conditions, precedence for returned errors and its relation
         with server policy, are deferred to eventual protocol
         specification.

6.2.2.  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 Appendix A.1 for an example
   how this could be mapped to HTTP.

   Method  GET:

   Parameters:

      NAME:  The naming of the object according to Section 5.3.

   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:

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

         PERMISSION_DENIED:  The DECADE client lacked sufficient
            permission to read the object.





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         NOT_AVAILABLE:  The data object exists but is currently
            unavailable for download (e.g., due to server policy).

         Specifics regarding error handling, including additional error
         conditions (e.g. overload), precedence for returned errors and
         its relation with server policy, are defered to eventual
         protocol specification.


7.  Server-to-Server Protocols

   An important feature of DECADE is the capability for one DECADE
   server to directly download 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.

   To support this functionality, DECADE uses the DRP and SDT 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.
   Note, however, that the objects being processed do not necessarily
   have to originate or terminate at the DECADE client (i.e. the object
   may be limited to being exchanged between DECADE servers even if the
   instruction is triggered by the client).  DECADE clients thus 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 (e.g.  PUT, GET); and

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

   In this way, a DECADE server acts as a proxy for a DECADE client, and
   a DECADE client may instantiate requests via that proxy.  The
   operations are performed as if the original requester had its own
   DECADE client co-located with the DECADE server.  It is this mode of
   operation that provides substantial savings in uplink capacity.  Note
   that this mode of operation may also be triggered by an
   administrative/management application outside the DECADE
   architecture.

7.1.  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



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   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
   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.
   Note that object attributes (see Section 6.1.4) may also be specified
   in the request to the remote server.

   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 (proxy) 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 optionally return
   the object to a client.  In the case of a PUT operation, the DECADE
   server is to store the object to the remote server using the
   specified credentials (via a PUT request to the remote server).  The
   object may optionally be uploaded from the client or may already
   exist at the proxying server.


8.  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.

8.1.  Pipelining to Avoid Store-and-Forward Delays

   A DECADE server may choose to not fully store an object before
   beginning to serve it.  For example, when serving a GET request,
   instead of waiting for the complete data to arrive from a remote
   server or DECADE client, a DECADE server may forward received data



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   bytes as they come in.  This pipelining mode reduces store-and-
   forward delays, which could be substantial for large objects.  A
   similar behavior could be used for PUT.

8.2.  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, which attempts to avoid
   storing identical data multiple times.  A DECADE Server
   implementation may internally perform de-duplication of data on disk.
   The DECADE architecture enables additional forms of de-duplication.

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

8.2.1.  Traffic De-duplication

8.2.1.1.  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 De-duplication.  This means that S does
   not download the object from R, in order to save network traffic.  In
   particular, S performs a challenge to make sure that the remote
   entity R actually has the object and then replies with its local
   object copy directly.

8.2.1.2.  An Example

   As shown in Figure 7, without Traffic De-duplication, unnecessary
   transfer of an object from R to S may happen, if the server S already
   has the object requested by A. If Traffic De-duplication is enabled,
   S only needs to challenge R to verify that it does have the data to
   avoid data-stealing attacks.














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

                         (a) Without Traffic De-duplication

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

                         (b) With Traffic De-duplication

                                 Figure 7

8.2.1.3.  HTTP Compatibility of Challenge

   How to integrate traffic de-duplication with HTTP is shown in
   Appendix A.1.3.

8.2.2.  Cross-Server Storage De-duplication

   The same object might be uploaded multiple times to different DECADE
   servers.  For storage efficiency, storage providers may desire that a
   single object be stored on one or a few servers.  They might
   implement an internal mechanism to achieve the goal, for example, by
   redirecting requests to proper servers.  DECADE supports the
   redirection of DECADE client requests to support further cross-server
   storage de-duplication.


9.  Security Considerations

   In general, the security considerations mentioned in
   [I-D.ietf-decade-problem-statement] apply to this document as well.

   In addition, it should be noted that the token-based approach
   Section 5.4 provides authorization through token delegation.  The
   strength of this authorization depends on several factors:

   1.  the uniqueness of tokens: tokens should be constructed in a way
       that minimize the possibilities for collisions;

   2.  validity of tokens: applications/users should not re-use tokens;
       and



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   3.  secrecy of tokens: if tokens are compromised to unauthorized
       entities, access control for the associated resources cannot be
       provided.

   Depending on the specific application, DECADE can be used to access
   confidential information.  Hence DECADE implementations SHOULD
   provide a secure transport mode that allows for encryption.


10.  IANA Considerations

   This document does not have any IANA considerations.


11.  Acknowledgments

   We thank the following people for their contributions to this
   document:

   David Bryan

   Yingjie Gu

   David McDysan

   Borje Ohlman

   Haibin Song

   Martin Stiemerling

   Richard Woundy

   Ning Zong


12.  References

12.1.  Normative References

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

12.2.  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.



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   [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.

   [RFC5661]  Shepler, S., Eisler, M., and D. Noveck, "Network File
              System (NFS) Version 4 Minor Version 1 Protocol",
              RFC 5661, January 2010.

   [RFC6392]  Alimi, R., Rahman, A., and Y. Yang, "A Survey of In-
              Network Storage Systems", RFC 6392, October 2011.

   [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-04 (work in progress),
              October 2011.

   [I-D.ietf-decade-reqs]
              Yingjie, G., Bryan, D., Yang, Y., and R. Alimi, "DECADE
              Requirements", draft-ietf-decade-reqs-04 (work in
              progress), September 2011.

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

   [GoogleFileSystem]
              Ghemawat, S., Gobioff, H., and S. Leung, "The Google File
              System", SOSP 2003, October 2003.

   [CDMI]     "CDMI", <http://www.snia.org/cdmi>.


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 6 for DECADE DRP and SDT can be



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   fulfilled by existing protocols such as HTTP, WEBDAV, and CDMI.

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.

A.1.1.2.  Communication Resource Controls Primitives

   Communication 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
   communication 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.




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A.1.2.  HTTP Support for DECADE Standard Data 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 similar but only
   fetches the metadata ("header") associated with the resource but not
   the resource itself.

A.1.3.  Traffic De-duplication 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 function 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.






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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.

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.




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   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-
   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.






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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
   perform updates caused by the move, such as updating all URLs, other
   than the Request-URI that identifies the 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 presentation 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.




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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.

A.3.  CDMI

   The Cloud Data Management Interface (CDMI) specification defines a
   functional interface through which applications can store and manage
   data objects in a cloud storage environment.  The CDMI interface for
   reading/writing data is based on standard HTTP requests, with CDMI-
   specific encodings using JavaScript Object Notation (JSON).  CDMI is
   specified by the Storage Networking Industry Association (SNIA)
   [CDMI].

A.3.1.  CDMI Support for DECADE Resource Protocol Primitives

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

A.3.1.1.  Access Control Primitives

   Access control includes mechanisms for defining the access policies
   for the server, and then checking the authorization of a user before
   it stores or retrieves content.  CDMI defines an Access Control List
   (ACL) per data object, and thus supports access control (read and/or



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   write) at the data object granularity.  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.

   CDMI requires that an HTTP authentication mechanism be available for
   the server to validate the identity of a principal (client).
   Specifically, CDMI requires that either HTTP Basic Authentication or
   HTTP Digest Authentication be supported.  CDMI recommends that HTTP
   over TLS (HTTPS) is supported to encrypt the data sent over the
   network.

A.3.1.2.  Communication Resource Controls Primitives

   Communication resources include bandwidth (upload/download) and
   number of simultaneous connected clients (connections).  CDMI
   supports two key data attributes which provide control over the
   communication resources to a client: "cdmi_max_throughput" and
   "cdmi_max_latency".  These attributes are defined in the metadata for
   data objects and indicate the desired bandwidth or delay for
   transmission of the data object from the cloud server to the client.

A.3.1.3.  Storage Resource Control Primitives

   Storage resources include amount of quantity and lifetime of storage.
   CDMI defines metadata for individual data objects and general storage
   system configuration which can be used for storage resource control.
   In particular, CDMI defines the following metadata fields:

      -  cdmi_data_redundancy: desired number of copies to be
      maintained,

      -  cdmi_geographic_placement: region where object is permitted to
      be stored,

      -  cdmi_retention_period: time interval object is to be retained,
      and

      -  cdmi_retention_autodelete: whether object should be auto
      deleted after retention period.

A.3.2.  CDMI 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.





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A.3.2.1.  Writing Primitives

   Writing involves uploading objects to the server.  CDMI supports
   standard HTTP methods for PUT and POST as described in
   Appendix A.1.2.1.

A.3.2.2.  Downloading Primitives

   Downloading involves fetching of an object from the server.  CDMI
   supports the standard HTTP GET method as described in
   Appendix A.1.2.2.

A.3.3.  Other Operations

   CDMI supports DELETE as described in Appendix A.1.4.  CDMI also
   supports COPY and MOVE operations.

   CDMI supports the concept of containers of data objects to support
   joint operations on related objects.  For example, GET may be done on
   a single data object or on an entire container.

   CDMI supports a global naming scheme.  Every object stored within a
   CDMI system will have a globally unique object string identifier
   (ObjectID) assigned at creation time.

A.3.4.  Conclusions

   CDMI 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
   CDMI features may be useful for DECADE:

      -  access control

      -  storage resource control

      -  communication resource control

      -  COPY/MOVE operations

      -  data containers

      -  naming scheme


Appendix B.  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 [RFC6392] map into the



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   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.

B.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.

B.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.

B.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.

B.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.

B.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.

B.6.  Discovery Mechanism

   The particular protocol used for discovery is outside the scope of
   this document.  However, options and considerations have been
   discussed in Section 5.5.






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B.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.


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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