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Versions: (draft-song-decade-survey) 00 01 02 03 04 05 06 RFC 6392

DECADE                                                     R. Alimi, Ed.
Internet-Draft                                                    Google
Intended status: Informational                            A. Rahman, Ed.
Expires: March 3, 2012                  InterDigital Communications, LLC
                                                            Y. Yang, Ed.
                                                         Yale University
                                                         August 31, 2011


                 A Survey of In-network Storage Systems
                      draft-ietf-decade-survey-06

Abstract

   This document surveys deployed and experimental in-network storage
   systems and describes their applicability for the DECADE (DECoupled
   Application Data Enroute) architecture.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 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
   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



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Survey Overview  . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Terminology and Concepts . . . . . . . . . . . . . . . . .  3
     2.2.  Historical Context . . . . . . . . . . . . . . . . . . . .  3
   3.  In-network Storage System Components . . . . . . . . . . . . .  5
     3.1.  Data Access Interface  . . . . . . . . . . . . . . . . . .  5
     3.2.  Data Management Operations . . . . . . . . . . . . . . . .  5
     3.3.  Data Search Capability . . . . . . . . . . . . . . . . . .  5
     3.4.  Access Control Authorization . . . . . . . . . . . . . . .  6
     3.5.  Resource Control Interface . . . . . . . . . . . . . . . .  6
     3.6.  Discovery Mechanism  . . . . . . . . . . . . . . . . . . .  6
     3.7.  Storage Mode . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  In-Network Storage Systems . . . . . . . . . . . . . . . . . .  7
     4.1.  Amazon S3  . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  BranchCache  . . . . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Cache-and-Forward Architecture . . . . . . . . . . . . . . 11
     4.4.  Cloud Data Management Interface  . . . . . . . . . . . . . 12
     4.5.  Content Delivery Network . . . . . . . . . . . . . . . . . 14
     4.6.  Delay-Tolerant Network . . . . . . . . . . . . . . . . . . 16
     4.7.  Named Data Networking  . . . . . . . . . . . . . . . . . . 17
     4.8.  Network of Information . . . . . . . . . . . . . . . . . . 19
     4.9.  Network Traffic Redundancy Elimination . . . . . . . . . . 21
     4.10. OceanStore . . . . . . . . . . . . . . . . . . . . . . . . 22
     4.11. Photo Sharing  . . . . . . . . . . . . . . . . . . . . . . 23
     4.12. P2P Cache  . . . . . . . . . . . . . . . . . . . . . . . . 25
     4.13. Usenet . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     4.14. Web Cache  . . . . . . . . . . . . . . . . . . . . . . . . 29
     4.15. Observations Regarding In-Network Storage Systems  . . . . 30
   5.  Storage And Other Related Protocols  . . . . . . . . . . . . . 31
     5.1.  HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
     5.2.  iSCSI  . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     5.3.  NFS  . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
     5.4.  OAuth  . . . . . . . . . . . . . . . . . . . . . . . . . . 35
     5.5.  WebDAV . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     5.6.  Observations Regarding Storage and Related Protocols . . . 38
   6.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 39
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 39
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 39
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 39
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 40
   11. Informative References . . . . . . . . . . . . . . . . . . . . 40
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43




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1.  Introduction

   DECADE (DECoupled Application Data Enroute) is an architecture that
   provides applications with access to provider based in-network
   storage for content distribution (hereafter referred to as only "in-
   network storage" in this document).  With access to in-network
   storage, content distribution applications can be designed to place
   less load on network infrastructure.  As a simple example, a peer of
   a P2P application may upload to other peers through its in-network
   storage, saving its usage of last-mile uplink bandwidth.  See [1] for
   further discussion.

   A major motivation for DECADE is the substantial increase of capacity
   and reduction in cost offered by storage systems.  For example, over
   the last two decades, there has been at least a 30-fold increase in
   the amount of storage that you can get for a given price (for flash
   memory and hard disk drives) [2], [3].

   High-capacity and low-cost in-network storage devices introduce
   substantial opportunities.  One example of in-network storage is
   content caches supporting Web and Peer-to-Peer (P2P) content.
   Different from existing content caches whose control fully reside at
   the owners of the caching devices, DECADE also allows applications to
   control access to their allocated in-network storage, as well as the
   resources consumed while accessing that storage (bandwidth,
   connections, storage space).  While designed in the context of P2P
   applications, it may be useful to other applications as well.  This
   document provides details on deployed and experimental in-network
   storage solutions, and evaluates their suitability for DECADE.

   We note that the survey presented in this document is only
   representative of the research in this area.  Rather than trying to
   enumerate an exhaustive list, we have chosen some typical techniques
   that lead to derivative works.


2.  Survey Overview

2.1.  Terminology and Concepts

   This document uses terms defined in [1].

2.2.  Historical Context

   In-network storage has been used previously in numerous scenarios to
   reduce network traffic and enable more efficient content
   distribution.  This section presents a brief history of content
   distribution techniques and illustrates how DECADE relates to past



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   approaches.  Systems have been developed with particular use cases in
   mind.  Thus, this survey is not meant to point out shortcomings of
   existing solutions, but rather to indicate where certain capabilities
   required in DECADE [4] are not provided by existing systems.

   In the early stage of Internet development, most Web content was
   stored at a central server and clients requested Web content from the
   central server.  In this architecture, the central server was
   required to provide a large amount of bandwidth.  Web browsing is
   still a primary activity on today's Internet.  As more and more users
   access Web content, a central server can become overloaded.  The use
   of web caches is one technique to reduce load on a central server.
   Web caches store frequently-requested content, and provide bandwidth
   for serving the content to clients.

   The ongoing growth of broadband technology in the worldwide market
   has been driven by the hunger of customers for new multimedia
   services as well as Web content.  In particular, the use of audio and
   video streaming formats has become common for delivery of rich
   information to the public, both residential and business.

   To overcome this challenge of massive multimedia consumption, just
   installing more Web cache will not be enough.  Moving content closer
   to the consumer results in greater network efficiency, improved QoS,
   and lower latency, while facilitating personalization of content
   through broadband content applications.  In these edge technologies,
   Content Delivery Networks (CDNs) is a representative technique.  CDNs
   are based on a large-scale distributed network of servers located
   closer to the edges of the Internet for efficient delivery of digital
   content including various forms of multimedia content.

   Although CDN is an effective means of information access and
   delivery, there are two barriers to making CDN a more common service:
   cost and replication integrity.  Deploying a CDN with its associated
   infrastructure is expensive.  A CDN also requires administrative
   control over nodes with large storage capacity at geographically
   dispersed locations with adequate connectivity.  CDN can be scalable,
   but due to this administrative and cost overhead, not rapidly
   deployable for the common user.

   The emergence and maturation of P2P has allowed improvements to many
   network applications.  P2P allows the use of client resources, such
   as CPU, memory, storage, and bandwidth, for serving content.  This
   can reduce the amount of resources required by a content provider.
   Multimedia content delivery using various P2P or peer-assisted
   frameworks has been shown to greatly reduce the dependence on CDN and
   central content servers.  However, the popularity of P2P applications
   has resulted in increased traffic on ISP networks.  P2P caches (both



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   transparent and non-transparent) have been introduced as a way to
   reduce the burden.  Though they can be effective in reducing traffic
   in certain areas of ISP networks, P2P caches have their shortcomings.
   In particular, they are application-dependent and thus difficult to
   keep up-to-date with new and evolving P2P application protocols.
   Second, applications may benefit from explicit control of in-network
   storage, which P2P caches do not provide.  See [1] for further
   discussion.

   DECADE aims to provide a standard protocol allowing P2P applications
   (including Content Providers) to make use of in-network storage to
   reduce the traffic burden on ISP networks, while enabling P2P
   applications to control access to content they have placed in in-
   network storage.


3.  In-network Storage System Components

   Before surveying individual technologies, we describe the basic
   components of in-network storage.  For consistency and for ease of
   comparison, we use the same model to evaluate each storage technology
   in this document.

   Note that the network protocol(s) used by a given storage system are
   also an important part of the design.  We omit details of particular
   protocol choices in this document.

3.1.  Data Access Interface

   A set of operations available to a client user for accessing data in
   the in-network storage.  Solutions typically allow both read and
   write, though the mechanisms for doing so can differ drastically.

3.2.  Data Management Operations

   Storage systems may provide users the ability to manage stored
   content.  For example, operations such as delete and move may be
   provided to users.  In this survey, we focus on data management
   operations that are provided to client users and omit those provided
   to system administrators.

3.3.  Data Search Capability

   Some storage systems may provide the capability to search or
   enumerate content that has been stored.  In this survey, we focus on
   search capabilities that are provided to client users and omit those
   provided to system administrators.  An example of a client search
   would be to find out the list of items stored by the given user over



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   a given period of time.

3.4.  Access Control Authorization

   Storage systems typically allow a client user, content owner or some
   other entity to define the access policies for the in-network
   storage.  The in-network storage system then checks the authorization
   of a user before it stores or retrieves content.  We define three
   types of access control authorization: public-unrestricted, public-
   restricted, and private.

   Public-unrestricted refers to content on an in-network storage system
   that is widely available to all clients (i.e., without restrictions).
   An example is accessing Wikipedia on the Web, or anonymous access to
   FTP sites.

   Public-restricted refers to content on an in-network storage system
   that is available to a restricted (though still potentially large)
   set of clients, but which do not require any confidential credentials
   from the client.  An example is some content (e.g., a TV show
   episode) on the Internet that can only be viewable in selected
   countries or networks (i.e., white/black lists or black-out areas).

   Private refers to content on an in-network storage system that is
   only made available to one or more clients presenting the required
   confidential credentials (e.g., password or key).  This content is
   not available to anyone without the proper confidential access
   credentials.

   Note that a combination of access control types may be applicable for
   a given scenario.  For example, the retrieval (read) of content from
   an in-network storage system may be public-unrestricted, but the
   storage (write) to the same system may be private.

3.5.  Resource Control Interface

   This is the interface through which users manage the resources on in-
   network storage that can be used by other peers, e.g., the bandwidth
   or connections.  The storage system may also allow users to indicate
   a time for which resources are granted.

3.6.  Discovery Mechanism

   Users use the discovery mechanism to find location of in-network
   storage, find access interface or resource control interface or other
   interfaces of in-network storage.





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3.7.  Storage Mode

   Storage systems may use the following modes of storage: file system,
   object-based, or block-based.

   A file system typically organizes files into a hierarchical tree
   structure.  Each level of the hierarchy normally contains one or more
   directories each with one or more files.  A file system may also be
   flat or use some other organizing principle.

   We define an object-based storage mode as one which stores discrete
   chunks of data (e.g., IP datagrams or another type of aggregation
   useful to an application) without a pre-defined hierarchy or meta
   structure.

   We define a block-based storage mode as one which stores a raw
   sequence of bytes, with a client being able to read and/or write data
   at offsets within that sequence.  Data is typically accessed in
   blocks for efficiency.  An common example for this storage mode is
   raw access to a hard disk.

   In this survey, we define Storage Mode to refer to how data is
   structured within the system, which may not be the same as how it is
   accessed by a client.  For example, a caching system may cache
   objects with hierarchical names, but may internally use an object-
   based Storage Mode.


4.  In-Network Storage Systems

   This section surveys in-network storage systems using the methodology
   defined above.  The survey includes some systems that are widely
   deployed today, some systems that are just being deployed, and some
   experimental/futuristic systems.  The survey covers both traditional
   client-server architectures and P2P architectures.  The surveyed
   systems are listed in alphabetical order.  Also, for each system, a
   brief explanation is given of the relevance to DECADE.

4.1.  Amazon S3

   Amazon S3 (Simple Storage Service) [5] provides an online storage
   service using web (HTTP) interfaces.  Users create buckets, and each
   bucket can contain stored objects.  Users are provided an interface
   through which they can manage their buckets.  Amazon S3 is a popular
   backend storage for other services.  Other related storage services
   is the Blob Service provided by Windows Azure [6], Google Storage for
   Developers [7], and Dropbox [8].




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4.1.1.  Applicability to DECADE

   Very widely used (deployed) example of in-network storage.  Amazon
   leases the storage to third party companies for disparate services.
   In particular, Amazon S3 has a rich model for authorization (using
   signed queries) to integrate with a wide variety of use cases.  A
   focus for Amazon S3 is scalability.  Particular simplifications that
   were made are the absence of a general, hierarchical namespace and
   the inability to update the contents of existing data.

4.1.2.  Data Access Interface

   Users can read, and write objects.

4.1.3.  Data Management Operations

   Users can delete previously-stored objects.

4.1.4.  Data Search Capability

   Users can list contents of buckets to find objects matching desired
   criteria.

4.1.5.  Access Control Authorization

   All methods of access control are supported for clients: public-
   unrestricted, public-restricted and private.

   For example, access to stored objects can be restricted by owner, a
   list of other Amazon Web Service users, all Amazon Web Service Users,
   or open to all users (anonymous access).  Another option is for the
   owner to generate and sign a query (e.g., a query to read an object)
   that can be used by any user until an owner-defined expiration time.

4.1.6.  Resource Control Interface

   Not provided.

4.1.7.  Discovery Mechanism

   Users are provided a well-known DNS name (either a default provided
   by Amazon, or one customized by a particular user).  Users accessing
   S3 storage use DNS to discover an IP address where S3 requests can be
   sent.







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4.1.8.  Storage Mode

   Object-based, with the extension that objects can be organized into
   user-defined buckets.

4.2.  BranchCache

   BranchCache [9] is a feature integrated into Windows (Windows 7 and
   Windows Server 2008R2) that aims to optimize enterprise branch office
   file access over the WAN links.  The main goals are to reduce WAN
   link utilization and improve application responsiveness by caching
   and sharing content within a branch while still maintaining end-to-
   end security.  BranchCache allows files retrieved from the web
   servers and file servers located in headquarters or datacenters to be
   cached in remote branch offices, and shared among users in the same
   branch accessing the same content.  BranchCache operates
   transparently by instrumenting the HTTP and SMB components of the
   networking stack.  It provides two modes of operation: Distributed
   Cache and Hosted Cache.

   In both modes, a client always contacts a BranchCache-enabled content
   server first to get the content identifiers for local search.  If the
   content is cached locally, the client then retrieves the content
   within the branch.  Otherwise, the client will go back to the
   original content server to request the content.  The two modes differ
   in how the content is shared.

   In the Hosted Cache mode, a locally provisioned server acts as a
   cache for files retrieved from the servers.  After getting the
   content identifiers, the client first consults the cache for the
   desired file.  If it is not present in the cache, the client
   retrieves it from the content server and sends it to the cache for
   storage.

   In the Distributed Cache mode, a client first queries other clients
   in the same network using the Web Services Discovery multicast
   protocol.  As in the Hosted Cache mode, the client retrieves the file
   from the content server if it is not available locally.  After
   retrieving the file (either from another client or the content
   server), the client stores the file locally.

   The original content server always authorizes requests from clients.
   Cached content is encrypted such that only clients can decrypt the
   data using keys derived from metadata returned by the content server.
   In addition to instrumenting the networking stack at clients, content
   servers must also support BranchCache.





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4.2.1.  Applicability to DECADE

   BranchCache is an example of an in-network storage system primarily
   targeted at enterprise networks.  It supports both a P2P like mode
   (Distributed Cache) as well as a client-server mode (Hosted Cache).
   Integration into the Microsoft OS will ensure wide distribution of
   this in-network storage technology.

4.2.2.  Data Access Interface

   Clients transparently retrieve (read) data from a cache (other
   clients or a Hosted Cache) since it operates by instrumenting the
   networking stack.  In Hosted Cache mode, clients write data to the
   Hosted Cache once it is retrieved from the content server.

4.2.3.  Data Management Operations

   Not provided.

4.2.4.  Data Search Capability

   Not provided.

4.2.5.  Access Control Authorization

   Access control method for clients is private.  For example,
   transferred content is encrypted, and can only be decrypted by keys
   derived from data received from the original content server.  Though
   data may be transferred to unauthorized clients, end-to-end security
   is maintained by only allowing authorized clients to decrypt the
   data.

4.2.6.  Resource Control Interface

   The storage capacity of caches on the clients and Hosted Caches are
   configurable by system administrators.  The Hosted Cache further
   allows configuration of the maximum number of simultaneous client
   accesses.  In the Distributed Caching mode, exponential back-off and
   throttling mechanisms are utilized to prevent reply storms of popular
   content requests.  The client will also spread data block access
   among multiple serving clients that have the content (complete or
   partial) to improve latency and provide some load balancing.

4.2.7.  Discovery Mechanism

   The Distributed Cache mode uses multicast for discovery of other
   clients and content within a local network.  Currently, the Hosted
   Cache mode uses policy provisioning or manual configuration of the



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   server used as the Hosted Cache.  In this mode, the address of the
   server may be found via DNS.

4.2.8.  Storage Mode

   Object-based.

4.3.  Cache-and-Forward Architecture

   Cache-and-Forward (CNF) [10] is an architecture for content delivery
   services for the future Internet.  In this architecture, storage can
   be exploited at nodes within the network, either directly at routers
   or deployed nearby the routers.  CNF is based on the concept of
   store-and-forward routers with large storage, providing for
   opportunistic delivery to occasionally disconnected mobile users and
   for in-network caching of content.  The proposed CNF protocol uses
   reliable hop-by-hop transfer of large data files between CNF routers
   in place of an end-to-end transport protocol like TCP.

4.3.1.  Applicability to DECADE

   An example of an experimental in-network storage system that would
   require storage space on (or near) a large number of routers in the
   Internet if it was deployed.  As the name of the system implies, it
   would provide short term caching and not long term network storage.

4.3.2.  Data Access Interface

   Users implicitly store content at Cache-and-forward routers by
   requesting files.  End hosts read content from in-network storage by
   submitting queries for content.

4.3.3.  Data Management Operations

   Not provided.

4.3.4.  Data Search Capability

   Not provided.

4.3.5.  Access Control Authorization

   Access control method is public-restricted (to any client which is
   part of the cache-and-forward network).







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4.3.6.  Resource Control Interface

   Not provided.

4.3.7.  Discovery Mechanism

   A query including a location-independent content ID is sent to the
   network and routed to a Cache-and-forward router, which handles
   retrieval of the data and forwarding to the end host.

4.3.8.  Storage Mode

   Object-based (with objects representing individual files).  The
   architecture proposes to cache large files in storage within the
   network, though objects could be made to represent smaller chunks of
   larger files.

4.4.  Cloud Data Management Interface

   The Cloud Data Management Interface (CDMI) is a specification to
   access and manage cloud storage.  CDMI is specified by the Storage
   Networking Industry Association (SNIA).

   CDMI is a functional interface that applications can use to create,
   retrieve, update and delete data elements from the cloud.  As part of
   this interface the client will be able to discover the capabilities
   of the cloud storage offering and use this interface to manage
   containers and the data that is placed in them.  In addition,
   metadata can be set on containers and their contained data elements
   through this interface [11].

   CDMI follows a traditional client server model, and operates over an
   HTTP interface using the Representational State Transfer (REST)
   model.  Similar to Amazon S3 buckets (see Section 4.1), users may
   create containers into which data objects may be stored.  Even though
   data objects may be accessed via a user-defined name within a
   container, it is also possible to access data objects by a storage-
   defined Object ID which is provided in the response upon creation of
   a Data Object.

4.4.1.  Applicability to DECADE

   CDMI is an important initiative to standardize storage interfaces for
   cloud services which are rapidly becoming an important storage
   service.  In particular, it specifies a set of operations for
   creating, reading, writing, and managing data objects at a remote
   server (or set of servers) via the HTTP protocol.




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4.4.2.  Data Access Interface

   Users can read and write data objects, and also update data in
   existing data objects.  CDMI data objects are sent on the wire
   embeded as a field in a JavaScript Object Notation (JSON) object.
   The protocol also defines interfaces in which the contents of data
   objects can be written via simple HTTP GET/PUT operations.

4.4.3.  Data Management Operations

   Users can delete already-existing data objects.  The create operation
   also supports modes in which the created object is copied or moved
   from an existing data object.

   Data System Metadata also allows users to configure policies
   regarding time-to-live after which a data object is automatically
   deleted, as well as the redundancy with which a data object is
   stored.

4.4.4.  Data Search Capability

   Users may list the contents of containers to locate data objects
   matching any desired criteria.

4.4.5.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.

   In particular CDMI allows access to data objects to be protected by
   ACLs which can allow or restrict access based on user, group,
   administrative status, or whether a user is authenticated or
   anonymous.

4.4.6.  Resource Control Interface

   CDMI supports attributes 'cdmi_max_latency' and 'cdmi_max_throughput'
   (set at either the level of containers, or a specific data object)
   which control the level of service offered to any users accessing a
   particular data object.

4.4.7.  Discovery Mechanism

   Users are provided a well-known DNS name.  The DNS name is resolved
   to determine the IP address to which requests may be sent.






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4.4.8.  Storage Mode

   Object-based, with the extension that objects can be organized into
   user-defined containers.

4.5.  Content Delivery Network

   A CDN provides services that improve performance by minimizing the
   amount of data transmitted through the network, improving
   accessibility and maintaining correctness through content
   replication.  CDNs offer fast and reliable applications and services
   by distributing content to cache or edge servers located close to
   users.  See [12] for an additional taxonomy and survey.

   A CDN has some combination of content-delivery, request-routing,
   distribution and accounting infrastructure.  The content-delivery
   infrastructure consists of a set of edge servers (also called
   surrogates) that deliver copies of content to end-users.  The
   request-routing infrastructure is responsible for directing client
   requests to appropriate edge servers.  It also interacts with the
   distribution infrastructure to keep an up-to-date view of the content
   stored in the CDN caches.  The distribution infrastructure moves
   content from the origin server to the CDN edge servers and ensures
   consistency of content in the caches.  The accounting infrastructure
   maintains logs of client accesses and records the usage of the CDN
   servers.  This information is used for traffic reporting and usage-
   based billing.

   In practice, a CDN typically hosts static content including images,
   video, media clips, advertisements, and other embedded objects for
   Web viewing.  A focus for CDNs is the ability to publish and deliver
   content to end-users in a reliable and timely manner.  A CDN focuses
   on building its network infrastructure to provide the following
   services and functionalities: storage and management of content;
   distribution of content among surrogates; cache management; delivery
   of static, dynamic and streaming content; backup and disaster
   recovery solutions; and monitoring, performance measurement and
   reporting.

   Examples of existing CDNs are Akamai, Limelight, and CloudFront.

   The following description uses the term "content provider" to refer
   to the entity purchasing a CDN service, and the term "client" to
   refer to the subscriber requesting content via the CDN from the
   content provider.






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4.5.1.  Applicability to DECADE

   Very widely used (deployed) example of in-network storage for
   multimedia content.  The existence and operation of the storage is
   totally transparent to the end user.  A CDN typically require a
   strong business relationship between the content providers and
   content distributors and often the business relationship extends to
   the ISPs.

4.5.2.  Data Access Interface

   A CDN is typically a closed system, and generally provides only read
   (retrieve) access interface to clients.  A CDN typically does not
   provide write (store) access interface to clients.  The content
   provider can access network edge servers and store content on them,
   or edge servers can retrieve content from content providers.  Client
   nodes can just retrieve content from edge servers.

4.5.3.  Data Management Operations

   A content provider can manage the data distributed in different cache
   nodes, such as moving popular data objects from one cache node to
   another cache node, or deleting rarely-accessed data objects in cache
   nodes.  Client user nodes, however, have no right to perform these
   operations.

4.5.4.  Data Search Capability

   A content provider can search or enumerate the data each cache node
   stores.  Client user nodes cannot perform search operations.

4.5.5.  Access Control Authorization

   All methods of access control (for reading) are supported for
   clients: public-unrestricted, public-restricted and private.  Some
   CDN edge servers will allow usage of HTTP basic authentication with
   the origin server, restrictions by IP address, or they can use a
   token-based technique to allow the origin server to apply its own
   authorization criteria.

   As mentioned previously, clients typically cannot write to the CDN.
   Writing is typically a private operation for the content providers.

4.5.6.  Resource Control Interface

   Not provided.





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4.5.7.  Discovery Mechanism

   Content providers can directly find internal CDN cache nodes to store
   content, since they typically have an explicit business relationship.
   Clients can locate CDN nodes through DNS or other redirection
   mechanisms.

4.5.8.  Storage Mode

   Though addressing objects uses URLs which typically refer to objects
   in a hierarchical fashion, the storage mode is typically object-
   based.

4.6.  Delay-Tolerant Network

   The Delay-Tolerant Network (DTN) [13] is an evolution of an
   architecture originally designed for the Interplanetary Internet.
   The Interplanetary Internet is a communication system envisioned to
   provide Internet-like services across interplanetary distances in
   support of deep space exploration.  The DTN architecture can be
   utilized in various operational environments characterized by severe
   communication disruptions, disconnections and high-delays (e.g., a
   month long loss of connectivity between two planetary networks
   because of high solar radiation due to sun spots).  The DTN
   architecture is thus suitable for environments including deep space
   networks, sensor-based networks, certain satellite networks and
   underwater acoustic networks.

   A key aspect of the DTN is a store and forward overlay layer called
   the "Bundle Protocol" or "Bundle Layer" that exists between the
   transport and application layers [14].  The Bundle Layer forms a
   logical overlay that employs persistent storage to help combat long
   term network interruptions by providing a store and forwarding
   service.  While traditional IP networks are also based on store and
   forward principles, the amount of time of a packet being kept in
   "storage" at a traditional IP router is typically in the order of
   milli-seconds (or less).  In contrast, the DTN architecture assumes
   that most Bundle Layer nodes will use some form of persistent storage
   (e.g., hard disk, flash memory, etc.) for DTN packets because of the
   nature of the DTN environment.

4.6.1.  Applicability to DECADE

   An example of an experimental in-network storage system that would
   require fundamental changes to the Internet protocols.






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4.6.2.  Data Access Interface

   Users implicitly cause content to be stored (until successfully
   forwarded) at Bundle Layer nodes by initiating/terminating any
   transaction that traverses the DTN.

4.6.3.  Data Management Operations

   Users can implicitly cause deletion of content stored at Bundle Layer
   nodes via a "Time To Live" type parameter that the user can control
   (for transactions originating from the user).

4.6.4.  Data Search Capability

   Not provided.

4.6.5.  Access Control Authorization

   Access control method is public-restricted (to any client which is
   part of the DTN) or private.

4.6.6.  Resource Control Interface

   Not provided.

4.6.7.  Discovery Mechanism

   A Uniform Resource Identifier (URI) approach is used as the basis of
   the addressing scheme for DTN transactions (and subsequent store and
   forward routing through the DTN network).

4.6.8.  Storage Mode

   Object-based.  DTN applications send data to the Bundle Layer which
   then breaks the data into segments.  These segments are then routed
   through the DTN network, and stored in Bundle Layer nodes as required
   (before being forwarded).

4.7.  Named Data Networking

   Named Data Networking (NDN) [15] is a research initiative which
   proposes to move to a new model of addressing and routing for the
   Internet.  NDN uses "named data" based routing and forwarding, to
   replace the current IP address based model.  NDN also uses name-based
   data caching in the routers.

   Each NDN Data packet will be assigned a content name and will be
   cryptographically signed.  Data delivery is driven by the requesting



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   end.  Routers disseminate name-based prefix announcements by using
   routing protocols like Intermediate System to Intermediate System
   (IS-IS) or Border Gateway Protocol (BGP).  The requester will send
   out an "Interest" packet which identifies the name of the data that
   it wants.  Routers that receive this Interest packet will remember
   the interface it came from and will then forward it on a named-based
   routing protocol.  Once an Interest packet reaches a node that has
   the desired data, a named Data packet is sent back, which carries
   both the name and content of the data, along with a digital signature
   of the producer.  This named Data packet is then forwarded back to
   the original requester on the reverse path of the Interest packet
   [16].

   A key aspect of NDN is that routers have the capability to cache the
   named data.  If a request for the same data (i.e., same name) comes
   to the router, then the NDN router will forward the named data stored
   locally to fulfill the request.  The proponents of NDN believe that
   the network can be designed naturally matching data delivery
   characteristics instead of communication between endpoints because
   data delivery has become the primary use of the network.

4.7.1.  Applicability to DECADE

   An example of an experimental in-network storage system that would
   require storage space on a large number of routers in the Internet.
   Named Data packets would be kept in storage in the NDN routers and
   provided to new requesters of the same data.

4.7.2.  Data Access Interface

   Users implicitly store content at NDN routers by requesting content
   (named Data packets) from the network.  Subsequent requests by
   different users for the same content will cause the named Data
   packets to be read from the NDN routers in-network storage.

4.7.3.  Data Management Operations

   Users do not have the direct ability to delete content stored in the
   NDN routers.  However, there will be some type of "Time To Live"
   parameter associated with the named Data packets though this has not
   yet been specified.

4.7.4.  Data Search Capability

   Not provided.






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4.7.5.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.

   The basic security mechanism in NDN is for the sender to digitally
   sign the content (named Data packet) that it sends.  It is envisioned
   that a complete access control system can be built on top of this
   though this has not yet been specified.

4.7.6.  Resource Control Interface

   Not provided.

4.7.7.  Discovery Mechanism

   Names are used as the basis of the addressing and discovery scheme
   for NDN (and subsequent store and forward routing through the NDN
   network).  NDN names are assumed to be hierarchical and to be able to
   be deterministically constructed.  This is still an active area of
   research.

4.7.8.  Storage Mode

   Object-based.  NDN sends named Data packets through the network.
   These Data packets are routed through the NDN network, and stored in
   NDN routers.

4.8.  Network of Information

   Similar to NDN (see Section 4.7), Network of Information (NetInf)
   [17] is another information centric approach in which the named data
   objects are the basic component of the networking architecture.
   NetInf is thus moving away from today's host centric networking
   architecture where the nodes in the network are the primary objects.
   In today's network the information objects are named relative to the
   hosts they are stored on (e.g.,
   http://www.example.com/information-object.txt).

   The NetInf naming and security framework builds the foundation for an
   information centric security model that integrates security deeply
   into the architecture.  In this model, trust is based on the
   information itself.  Information Objects (IOs) are given a unique
   name with cryptographic properties.  Together with additional
   metadata, the name can be used to verify the data integrity as well
   as several other security properties, like self-certification, name
   persistency, and owner authentication and identification.  The
   approach also gives some benefits over the security model in today's



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   host centric networks, as it minimizes the need for trust in the
   infrastructure, including the hosts providing the data, the channel,
   or the resolution service.

   In NetInf the information objects are published into the network.
   They are registered with a Name Resolution Service (NRS).  The NRS is
   also used to register network locators that can be used to retrieve
   data objects that represent the published IOs.  When a receiver wants
   to retrieve an IO, the request for the IO is resolved by the NRS into
   a set of locators.  These locators are then used to retrieve a copy
   of the data object from the "best" available source(s).  NetInf is
   open to use any type of underlying transport networks.  The locators
   can thus be a heterogeneous set, e.g., IPv4, IPv6, MAC, etc.

   NetInf will make extensive use of caching of information objects in
   the network and will provide network functionality that is similar to
   what overlay solutions like CDNs and P2P distribution networks (e.g.,
   BitTorrent) provide today.

4.8.1.  Applicability to DECADE

   An example of an experimental information centric network
   architecture that will require storage space for storage and caching
   of information objects on a large number of NetInf nodes in the
   Internet.

4.8.2.  Data Access Interface

   Users will publish IOs with specific IDs into the network.  This is
   done by the client sending a register message to the NRS stating that
   the IO with the specific ID is available.  When another user wishes
   to retrieve the IO they will use the given ID to make a request for
   the IO.  The ID is then resolved by the NRS and the IO is delivered
   from a nearby in-network storage location.

4.8.3.  Data Management Operations

   Users do not have the direct ability to delete content stored in the
   NetInf nodes.  However, there can be some type of "Time To Live"
   parameter associated with the information objects though this has not
   yet been specified.

4.8.4.  Data Search Capability

   Not provided.






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4.8.5.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.  The basic security
   mechanism in NetInf is for the publisher to digitally sign the
   content of the information object that it publish.  It is envisioned
   that a complete access control system can be built on top of this
   though this has not yet been specified.

4.8.6.  Resource Control Interface

   Not provided.

4.8.7.  Discovery Mechanism

   NetInf IDs are used for naming and accessing information objects.
   The IDs are resolved by the NRS into locators that are used for
   routing and transport of data through the transport networks.  This
   is still an active area of research.

4.8.8.  Storage Mode

   Object-based.  From an application perspective NetInf can be used for
   publishing entire files or chunks of files.  NetInf is agnostic to
   the application perspective and treats everything as information
   objects.

4.9.  Network Traffic Redundancy Elimination

   Redundancy Elimination (RE) (e.g., [18]) is used for identifying and
   removing repeated content from network transfers.  This technique has
   been proposed to improve network performance in many types of
   networks, such as ISP backbones and enterprise access links.  One
   example of redundancy elimination proposal is SmartRE, proposed by
   Anand et al., which focuses on network-wide redundancy elimination.
   In packet-level redundancy elimination, forwarding elements are
   equipped with additional storage which can be used to cache data from
   forwarded packets.  Upstream routers may replace packet data with a
   fingerprint that tells a downstream router how to decode and
   reconstruct the packet based on cached data.

4.9.1.  Applicability to DECADE

   An example of an experimental in-network storage system that would
   require a large amount of associated packet processing at routers if
   it was ever deployed.





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4.9.2.  Data Access Interface

   Redundancy-elimination are typically transparent to the user.
   Writing into the storage is done by transferring data that has not
   already been cached.  Storage is read when users transmit data
   identical to previously-transmitted data.

4.9.3.  Data Management Operations

   Not provided.

4.9.4.  Data Search Capability

   Not provided.

4.9.5.  Access Control Authorization

   Access control method is public-restricted (to any client which is
   part of the RE network).  Note that the content provider still
   retains control over which peers receive the requested data.  The
   returned data is "compressed" as it is transferred within the
   network.

4.9.6.  Resource Control Interface

   Not provided.  The content provider still retains control over the
   rate at which packets are sent to a peer.  The packet size within the
   network may be reduced.

4.9.7.  Discovery Mechanism

   No discovery mechanism is necessary.  Routers can use redundancy-
   elimination without the users' knowledge.

4.9.8.  Storage Mode

   Object-based, with "objects" being data from packets transmitted
   within the network.

4.10.  OceanStore

   OceanStore [19] is a storage platform developed at University of
   California, Berkeley, that provides globally-distributed storage.
   OceanStore implements a model where multiple storage providers can
   pool resources together.  Thus, a major focus is on resiliency and
   self-organization and self-maintenance.

   The protocol is resilient to some storage nodes being compromised by



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   utilizing Byzantine agreement and erasure codes to store data at
   primary replicas.

4.10.1.  Applicability to DECADE

   An example of an experimental in-network storage system that provides
   a high degree of network resilience to failure scenarios.

4.10.2.  Data Access Interface

   Users may read and write objects

4.10.3.  Data Management Operations

   Objects may be replaced by newer versions, and multiple versions of
   an object may be maintained.

4.10.4.  Data Search Capability

   Not provided.

4.10.5.  Access Control Authorization

   Provided, but specifics for clients are unclear from the available
   references.

4.10.6.  Resource Control Interface

   Not provided.

4.10.7.  Discovery Mechanism

   Users require an entry-point into the system in the form of one
   storage node that is part of OceanStore.  If a hostname is provided,
   the address of a storage node may be determined via DNS.

4.10.8.  Storage Mode

   Object-based.

4.11.  Photo Sharing

   There are a growing number of popular on line Photo Sharing (storing)
   systems.  For example, the Kodak Gallery system [20] serves over 60
   million users and stores billions of images [21].  Other well known
   examples of Photo Sharing systems include Flickr [22] and ImageShack
   [23].  Also there are a number of popular blogging services, such as
   Tumblr [24], which specialize in also sharing large numbers of photos



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   and other multimedia content (e.g., video, text, audio, etc.) as part
   of their service.  All these in-network storage systems utilize both
   free and paid subscription models.

   Most Photo Sharing systems are traditional client-server
   architecture.  However, a minority of systems also offer a P2P mode
   of operation.  The client-server architecture is typically based on
   HTTP with a browser client and a web server.

4.11.1.  Applicability to DECADE

   Very widely used (deployed) example of in-network storage where the
   end user has direct visibility and extensive control of the system.
   Typical end user interface is through a HTTP based web browser.

4.11.2.  Data Access Interface

   Users can read (view) and write (store) photos.

4.11.3.  Data Management Operations

   Users can delete previously stored photos.

4.11.4.  Data Search Capability

   Users can tag photos and/or organize them using sophisticated web
   photo album generators.  Users can then search for objects (photos)
   matching desired criteria.

4.11.5.  Access Control Authorization

   Access control method for clients is typically either private or
   public-unrestricted.  For example, writing (storing) to a Photo blog
   is typically private to the owner of the account.  However, all other
   clients can view (read) the contents of the blog (i.e., public-
   unrestricted).  Some photo sharing websites provide private access to
   read photos to allow sharing with a limited set of friends.

4.11.6.  Resource Control Interface

   Not provided.

4.11.7.  Discovery Mechanism

   Usually by manually logging on to a central web page for the service
   and entering the appropriate information to access the desired
   information.  The address to which the client connects is usually
   determined by DNS using the hostname from the provided URL.



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4.11.8.  Storage Mode

   File-based.  Photos are usually stored as files.  They can then be
   organized into meta-structures (e.g., albums, galleries, etc.) using
   sophisticated web photo album generators.

4.12.  P2P Cache

   Caching of P2P traffic is a useful approach to reduce P2P network
   traffic, because objects in P2P systems are mostly immutable and the
   traffic is highly repetitive.  In addition, making use of P2P caches
   does not require changes to P2P protocols and can be deployed
   transparently from clients.

   P2P caches operate similarly to web caches (Section 4.14) in that
   they temporarily store frequently-requested content.  Requests for
   content already stored in the cache can be served from local storage
   instead of requiring the data to be transmitted over expensive
   network links.

   Two types of P2P caches exist: non-transparent P2P caches and
   transparent P2P caches.  A non-transparent cache appears as a super
   peer; it explicitly peers with other P2P clients.  For a transparent
   cache, once a P2P cache is established, the network will
   transparently redirect P2P traffic to the cache, which either serves
   the file directly or passes the request on to a remote P2P user and
   simultaneously caches that data.  Transparency is typically
   implemented using Deep Packet Inspection (DPI).  DPI products
   identify and pass P2P packets to the P2P caching system so it can
   cache the traffic and accelerate it.

   To enable operation with existing P2P software, P2P caches directly
   support P2P application protocols.  A large number of P2P protocols
   are used by P2P software, and hence are supported by caches, leading
   to higher complexity.  Additionally, these protocols evolve over
   time, and new protocols are introduced.

4.12.1.  Applicability to DECADE

   An example of in-network storage for P2P systems.  However, unlike
   DECADE, the existence and operation of the storage is totally
   transparent to the end user.

4.12.2.  Transparent P2P Caches







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4.12.2.1.  Data Access Interface

   Data Access Interface allows P2P content to be cached (stored) and
   supplied (retrieved) locally such that network traffic is reduced,
   but it is transparent to P2P users, and P2P users implicitly use the
   data-access interface (in the form of their native P2P application
   protocol) to store or retrieve content.

4.12.2.2.  Data Management Operations

   Not provided.

4.12.2.3.  Data Search Capability

   Not provided.

4.12.2.4.  Access Control Authorization

   Access control method is typically public-restricted (to any client
   which is part of the P2P channel or swarm).

4.12.2.5.  Resource Control Interface

   Not provided.

4.12.2.6.  Discovery Mechanism

   Use of DPI means no discovery mechanism is provided to P2P users, it
   is transparent to P2P users.  Since DPI is used to recognize P2P
   applications' private protocols, P2P Cache implementations must be
   updated as new applications are added and existing protocols evolve.

4.12.2.7.  Storage Mode

   Object-based.  Chunks (typically, the unit of transfer amongst P2P
   clients) of content are stored in the cache.

4.12.3.  Non-transparent P2P Caches

4.12.3.1.  Data Access Interface

   Data Access Interface allows P2P content to be cached (stored) and
   supplied (retrieved) locally such that network traffic is reduced.
   P2P users implicitly store and retrieve from the cache using the P2P
   application's native protocol.






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4.12.3.2.  Data Management Operations

   Not provided.

4.12.3.3.  Data Search Capability

   Not provided.

4.12.3.4.  Access Control Authorization

   Access control method is typically public-restricted (to any client
   which is part of the P2P channel or swarm)

4.12.3.5.  Resource Control Interface

   Not provided.

4.12.3.6.  Discovery Mechanism

   A cache pretends to be normal peers to join the P2P overlay network.
   Other P2P users can find these cache nodes through overlay routing
   mechanism, just looking to them as normal neighbor nodes.

4.12.3.7.  Storage Mode

   Object-based.  Chunks (typically, the unit of transfer amongst P2P
   clients) of content are stored in the cache.

4.13.  Usenet

   Usenet is a distributed Internet based discussion (message) system.
   The Usenet messages are arranged as a set of "newsgroups" that are
   classified hierarchically by subject.  Usenet information is
   distributed and stored among a large conglomeration of servers that
   store and forward messages to one another in so called news feeds.
   Individual users may read messages from and post messages to a local
   news server typically operated by an ISP.  This local server
   communicates with other servers and exchanges articles with them.  In
   this fashion, the message is copied from server to server and
   eventually reaches every server in the network [25].

   Traditional Usenet as described above operates as a P2P network
   between the servers, and in a client-server architecture between the
   user and their local news server.  The user requires a Usenet client
   to be installed on their computer and a Usenet server account
   (through their ISP).  However, with the rise of web browsers the
   Usenet architecture is evolving to be web based.  The most popular
   example of this is Google Groups where Google hosts all the



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   newsgroups and client access is via a standard HTTP based web browser
   [26].

4.13.1.  Applicability to DECADE

   A historically very important and widely used (deployed) example of
   in-network storage in the Internet.  The use of this system is
   rapidly declining but efforts have been made to preserve the stored
   content for historical purposes.

4.13.2.  Data Access Interface

   Users can read and post (store) messages.

4.13.3.  Data Management Operations

   Users sometimes have limited ability to delete messages that they
   previously posted.

4.13.4.  Data Search Capability

   Traditionally, users could manually search through the newsgroups as
   they are classified hierarchically by subject.  In the newer web
   based systems there is also automatic search capability based on key
   word matches.

4.13.5.  Access Control Authorization

   Access control method is either public-unrestricted or private (to
   client members of that newsgroup).

4.13.6.  Resource Control Interface

   Not provided.

4.13.7.  Discovery Mechanism

   Usually by manually logging on to the Usenet account.  DNS may be
   used to resolve hostnames to their corresponding addresses.

4.13.8.  Storage Mode

   File system.  Messages are usually stored as files which are then
   organized hierarchically by subject into newsgroups.







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4.14.  Web Cache

   Web cache [27] has been widely deployed by many ISPs to reduce
   bandwidth consumption and web access latency since the late 1990s.  A
   web cache can cache the web documents (e.g., HTML pages, images)
   between server and client to reduce bandwidth usage, server load, and
   perceived lag.  A web cache server is typically shared by many
   clients, and stores copies of documents passing through it;
   subsequent requests may be satisfied from the cache if certain
   conditions are met.

   Another form of cache is a client-side cache, typically implemented
   in web browsers.  A client side cache can keep a local copy of all
   pages recently displayed by browser, and when the user returns to one
   of these web pages, the local cached copy is reused.

   A related protocol for P2P applications to use web cache is HPTP
   (HTTP based Peer to Peer) [28].  It proposes to share chunks of P2P
   files/streams using HTTP protocol with cache-control headers.

4.14.1.  Applicability to DECADE

   Very widely used (deployed) example of in-network storage for the key
   Internet application of Web browsing.  The existence and operation of
   the storage is transparent to the end user in most cases.  The
   content caching time is controlled by Time To Live parameters
   associated with the original content.  The principle of web caching
   is to speed up web page reading by using (the same) content
   previously requested by a preceding user to service a new user.

4.14.2.  Data Access Interface

   Users explicitly read from a web cache by making requests, but they
   cannot explicitly write data into it.  Data is implicitly stored into
   the web cache by requesting content that is not already cached and
   meets policy restrictions of the cache provider.

4.14.3.  Data Management Operations

   Not provided.

4.14.4.  Data Search Capability

   Not provided.







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4.14.5.  Access Control Authorization

   Access control method for clients is public-unrestricted.  It is
   important to note that if content is authenticated or encrypted
   (e.g., HTTPS, SSL) it will not be cached.  Also if the content is
   flagged as private (vs public) at the HTTP level by the origin server
   it will not be cached.

4.14.6.  Resource Control Interface

   Not provided.

4.14.7.  Discovery Mechanism

   Web Caches can be transparently deployed between Web Server and Web
   Clients, employing DPI for discovery.  Alternatively, web caches
   could be explicitly discovered by clients using techniques such as
   DNS or manual configuration.

4.14.8.  Storage Mode

   Object based.  Web content is keyed within the cache by HTTP Request
   fields, such as Method, URI, and Headers.

4.15.  Observations Regarding In-Network Storage Systems

   This following observations about the surveyed In-Network storage
   systems are made in the context of DECADE as defined by [1].

   The majority of the surveyed systems were designed for client-server
   architectures and do not support P2P. However, there are some
   important exceptions, especially for some of the newer technologies
   such as BranchCache and P2P Cache which do support a P2P mode.

   The P2P cache systems are interesting since they do not require
   changes to P2P applications themselves.  However, this is also a
   limitation in that they are required to support each application
   protocol.

   Many of the surveyed systems were designed for caching as opposed to
   long term network storage.  Thus during DECADE protocol design it
   should be carefully considered if a caching mode should be supported
   in addition to a long term network storage mode.  There is typically
   a trade-off between providing a caching mode and long-term (and
   usually also reliable) storage with regards to some performance
   metrics.  Note that [1] identifies issues with classical caching from
   a DECADE perspective such as the fact that P2P caches typically do
   not allow users to explicitly control content stored in the cache.



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   Certain components of the surveyed systems are outside of the scope
   of DECADE.  For example, a protocol used for searching across
   multiple DECADE servers is out of scope.  However, applications may
   still be able to implement such functionality if DECADE exposes the
   appropriate primitives.  This has the benefit of keeping the core in-
   network storage systems simple, while permitting diverse applications
   to design mechanisms that meet their own requirements.

   Today, most in-network storage systems follow some variant of the
   authorization model of public-unrestricted, public-restricted, and
   private.  For DECADE, we may need to evolve the authorization model
   to support a resource owner (e.g., end user) authorization, in
   addition to the network authorization.


5.  Storage And Other Related Protocols

   This section surveys existing storage and other related protocols, as
   well as comments on the usage of these protocols to satisfy DECADE's
   use cases.  The surveyed protocols are listed alphabetically.

5.1.  HTTP

   HTTP [29] is a key protocol for the World Wide Web. It is a stateless
   client-server protocol that allows applications to be designed using
   the REST model.  HTTP is often associated with downloading (reading)
   content from web servers to web browsers, but it also has support for
   uploading (writing) of content to web servers.  It has been used as
   the underlying protocol for other protocols such as WebDAV.

   HTTP is used in some of the most popular in-network storage systems
   surveyed previously including CDNs, Photo Sharing, and Web Cache.
   Usage of HTTP by a storage protocol implies that no extra SW is
   required in the client (i.e., web based client) as all standard Web
   browsers are based on HTTP.

5.1.1.  Data Access Interface

   Basic read and write operations are supported (using HTTP GET, PUT
   and POST methods).

5.1.2.  Data Management Operations

   Not provided.







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5.1.3.  Data Search Capability

   Not provided

5.1.4.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.

   The majority of web pages are public-unrestricted in terms of reading
   but do not allow any uploading of content.  In-network storage
   systems range from private or public-unrestricted for Photo Sharing
   described in Section 4.11.5 to public-unrestricted for Web Caching
   described in Section 4.14.5.

5.1.5.  Resource Control Interface

   Not provided.

5.1.6.  Discovery Mechanism

   Manual configuration is typically used.  Clients typically address
   HTTP servers by providing a hostname, which is resolved to an address
   using DNS.

5.1.7.  Storage Mode

   HTTP is a protocol, it thus does not define a Storage Mode.  However,
   a non-collection resource can typically be thought of as a "file").
   These files may be organized into collections, which typically map on
   to the HTTP Path hierarchy, creating the illusion of a file system.

5.1.8.  Comments

   HTTP is based on a client-server architecture and thus is not
   directly applicable for the DECADE focus on P2P. Also, HTTP offers
   only a rudimentary toolset for storage operations compared to some of
   the other storage protocols.

5.2.  iSCSI

   Small Computer System Interface (SCSI) is a set of protocols enabling
   communication with storage devices such as disk drives and tapes;
   internet SCSI (iSCSI) [30] is a protocol enabling SCSI commands to be
   sent over TCP.  As in SCSI, iSCSI allows an Initiator to send
   commands to a Target.  These commands operate on the device level as
   opposed to individual data objects stored on the device.




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5.2.1.  Data Access Interface

   Read and write commands indicate which data is to be read or written
   by specifying the offset (using Logical Block Addressing) into the
   storage device.  The size of data to be read or written is an
   additional parameter in the command.

5.2.2.  Data Management Operations

   Since commands operate at the device level, management operations are
   different than with traditional file systems.  Management commands
   for SCSI/iSCSI including explicit device control such as starting and
   stopping the device and formatting the device.

5.2.3.  Data Search Capability

   SCSI/iSCSI does not provide the ability to search for particular data
   within a device.  Note that such capabilities can be implemented
   outside of iSCSI.

5.2.4.  Access Control Authorization

   With respect to access to devices, the access control method is
   private. iSCSI uses CHAP [31] to authenticate initiators and targets
   when accessing storage devices.  However, since SCSI/iSCSI operates
   at the device level, neither authentication nor authorization are
   provided for individual data objects.  Note that such capabilities
   can be implemented outside of iSCSI.

5.2.5.  Resource Control Interface

   Not provided.

5.2.6.  Discovery Mechanism

   Manual configuration may be used.  An alternative is the internet
   Storage Name Service (iSNS) [32] provides the ability to discover
   available storage resources.

5.2.7.  Storage Mode

   As a protocol, iSCSI does not explicitly have a storage mode.
   However, it provides block-based access to clients.  SCSI/iSCSI
   provides an Initiator block-level access to the storage device.







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5.3.  NFS

   The Network File System is designed to allow users to access files
   over a network in a manner similar to how local storage is accessed.
   NFS is typically used in local area network or enterprise settings,
   though changes made in later versions of NFS make it easier to
   operate over the Internet.

5.3.1.  Data Access Interface

   Traditional file-system operations such as read, write, and update
   (overwrite) are provided.  Locking is provided to support concurrent
   access by multiple clients.

5.3.2.  Data Management Operations

   Traditional file-system operations such as move and delete are
   provided.

5.3.3.  Data Search Capability

   User has the ability to list contents of directories to find
   filenames matching desired criteria.

5.3.4.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.  For example, files and
   directories can be protected using read, write, and execute
   permissions for the files owner, group, and the public (others).
   Also, NFSv4.1 has a rich ACL model allowing a list of Access Control
   Entries (ACEs) to be configured for each file or directory.  The ACEs
   can specify per-user read/write access to file data, file/directory
   attributes, creation/deletion of files in a directory, etc.

5.3.5.  Resource Control Interface

   While disk space quotas can be configured, it typically limits the
   total amount of storage allocated to a particular user.  User control
   of bandwidth and connections used by remote peers is not provided.

5.3.6.  Discovery Mechanism

   Manual configuration is typically used.  Clients address NFS servers
   by providing a hostname and a directory that should be mounted.  DNS
   may be used lookup an address for the provided hostname.





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5.3.7.  Storage Mode

   As a protocol, there is no defined internal storage mode.  However,
   implementations typically use the underlying filesystem storage.
   Note that extensions have been defined for alternate storage modes
   (e.g., block-based [34] and object-based [35]).

5.3.8.  Comments

   The efficiency and scalability of the NFS access control method is a
   concern in the context of DECADE.  In particular, Section 6.2.1 of
   [33] states that:

       Only ACEs that have a "who" that matches the requester
       are considered.

   Thus, in the context of DECADE, to specify per-peer access control
   policies for an object, a client would need to explicitly configure
   the ACL for the object for each individual peer.  A concern with this
   approach is scalability when a client's peers may change frequently
   and ACLs for many small objects need to be updated constantly during
   participation in a swarm.

   Note that NFS v4.1's usage of RPCSEC_GSS provides support for
   multiple security mechanisms.  Kerberos V5 is required, but others
   such as X.509 certificates are also supported by way of GSS-API.
   Note, however, that NFSv4.1's usage of such security mechanisms is
   limited to linking a requesting user to a particular account
   maintained by the NFS server.

5.4.  OAuth

   OAuth [36] is a protocol that enriches the traditional client-server
   authentication model for web resources.  In particular, OAuth
   distinguishes the "client" from the "resource owner", thus enabling a
   resource owner to authorize a particular client for access (e.g., for
   a particular lifetime) to private resources.

   We include OAuth in this survey so that its authentication model can
   be evaluated in the context of DECADE.  OAuth itself, however, is not
   a network storage protocol.

5.4.1.  Data Access Interface

   Not provided.






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5.4.2.  Data Management Operations

   Not provided.

5.4.3.  Data Search Capability

   Not provided.

5.4.4.  Access Control Authorization

   Not provided.  While similar in spirit to the WebDAV ticketing
   extensions [37], OAuth instead uses the following process: (1) a
   client constructs a delegation request, (2) the client forwards the
   request to the resource owner for authorization, (3) the resource
   owner authorizes the request, and finally (4) a callback is made to
   the client indicating that its request has been authorized.

   Once the process is complete, the client has a set of token
   credentials that grant it access to the protected resource.  The
   token credentials may have an expiration time, and they can also be
   revoked by the resource owner at any time.

5.4.5.  Resource Control Interface

   Not provided.

5.4.6.  Discovery Mechanism

   Not provided.

5.4.7.  Storage Mode

   Not provided.

5.4.8.  Comments

   The ticketing mechanism requires server involvement and the
   discussion relating to WebDAV's proposed ticketing mechanism (see
   Section 5.5.8) applies here as well.

5.5.  WebDAV

   WebDAV [38] is a protocol designed for Web content authoring.  It is
   developed as an extension to HTTP described in Section 5.1, meaning
   it can be simpler to integrate into existing software.  WebDAV
   supports traditional operations for reading/writing from storage, as
   well as other constructs such as locking and collections which are
   important when multiple users collaborate to author or edit a set of



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   documents.

5.5.1.  Data Access Interface

   Traditional read and write operations are supported (using HTTP GET
   and PUT methods, respectively).  Locking is provided to ease
   concurrent access by multiple clients.

5.5.2.  Data Management Operations

   WebDAV supports traditional file-system operations such as move,
   delete and copy.  Objects are organized into collections, and these
   operations can also be performed on collections.  WebDAV also allows
   objects to have user-defined properties.

5.5.3.  Data Search Capability

   User has the ability to list contents of collections to find objects
   matching desired criteria.  A SEARCH extension [39] has also been
   specified allowing listing of objects matching client-defined
   criteria.

5.5.4.  Access Control Authorization

   All methods of access control for clients are supported: public-
   unrestricted, public-restricted and private.

   For example, an ACL extension [40] is provided for WebDAV.  ACLs
   allow both user- and group-based access control policies (relating to
   reading, writing, properties, locking, etc) to be defined for objects
   and collections.

   A ticketing extension [37] has also been proposed, but has not
   progressed beyond an Internet Draft.  This extension allows a client
   to request the WebDAV server to create a "ticket" (e.g., for reading
   an object) that can be distributed to other clients.  Tickets may be
   given expiration times, or may only allow for a fixed number of uses.
   The proposed extension requires the server to generate tickets and
   maintain state for outstanding tickets.

5.5.5.  Resource Control Interface

   An extension [41] allows disk space quotas to be configured for
   Collections.  The extension also allows WebDAV clients to query
   current disk space usage.  User control of bandwidth and connections
   used by remote peers is not provided.





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5.5.6.  Discovery Mechanism

   Manual configuration is typically used.  Clients address WebDAV
   servers by providing a hostname, which can be resolved to an address
   using DNS.

5.5.7.  Storage Mode

   Though no storage mode is explicitly defined, WebDAV can be thought
   of as providing file-based storage to a client.  A non-collection
   resource can typically be thought of as a "file".  Files may be
   organized into collections, which typically map on to the HTTP Path
   hierarchy.

5.5.8.  Comments

   The efficiency and scalability of the WebDAV access control method is
   a concern in the context of DECADE, for similar reasons as stated in
   Section 5.3.8 for NFS.  The proposed WebDAV ticketing extension
   partially alleviates this concern, but the particular technique may
   need further evaluation before being applied to DECADE.  In
   particular, since DECADE clients may continuously upload/download a
   large number of small-size objects, and a single DECADE server may
   need to scale to many concurrent DECADE clients, requiring the server
   to maintain ticket state and generate tickets may not be the best
   design choice.  Server-generated tickets can also increase latency
   for data transport operations depending on the message flow used by
   DECADE.

5.6.  Observations Regarding Storage and Related Protocols

   This following observations about the surveyed storage and related
   protocols are made in the context of DECADE as defined by [1].

   All of the surveyed protocols were primarily designed for client-
   server architectures and not for P2P. However, it is conceivable that
   some of the protocols could be adapted to work in a P2P architecture.

   Several popular in-network storage systems today use HTTP as their
   key protocol even though it is not classically considered as a
   storage protocol.  HTTP is a stateless protocol that is used to
   design RESTful applications.  HTTP is a well supported and widely
   implemented protocol which can provide important insights for DECADE.

   The majority of the surveyed protocols do not support low latency
   access for applications such as live streaming.  This was one of the
   key general requirements for DECADE.




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   The majority of the surveyed protocols do not support any form of
   resource control interface.  Resource control is required for users
   to manage the resources on in-network storage that can be used by
   other peers, e.g., the bandwidth or connections.  Resource control is
   a key capability required for DECADE.

   Nearly all surveyed protocols did however support the following
   capabilities which are required for DECADE: user ability to read/
   write content; some form of access control; some form of error
   indication; and ability to traverse firewalls and NATs.


6.  Conclusions

   Though there have been many successful in-network storage systems,
   they have been designed for use cases different from those defined in
   DECADE.  For example, many of the surveyed in-network storage systems
   and protocols were designed for client-server architectures and not
   P2P. No surveyed system or protocol has the functionality and
   features to fully meet the set of requirements defined for DECADE.
   DECADE aims to provide a standard protocol for P2P applications and
   content provider to access and control in-network storage, resulting
   in increased network efficiency while retaining control over content
   shared with peers.  Additionally, defining a standard protocol can
   reduce complexity of in-network storage since multiple P2P
   application protocols no longer need to be implemented by in-network
   storage systems.


7.  Security Considerations

   This draft is a survey of existing in-network storage systems, and
   does not introduce any security considerations beyond those of the
   surveyed systems.

   For more information on security considerations of DECADE, see [1].


8.  IANA Considerations

   This document does not have any IANA Considerations.


9.  Contributors

   The editors would like to thank the following people for contributing
   to the development of this document:




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   - ZhiHui Lu

   - Borje Ohlman

   - Pang Tao

   - Lucy Yong

   - Juan Carlos Zuniga


10.  Acknowledgments

   The editors would like to thank the following people for providing
   valuable comments to various versions of this document: David Bryan,
   Tao Mao, Haibin Song, Ove Strandberg, Yu-Shun Wang, Richard Woundy,
   Yunfei Zhang, and Ning Zong.


11.  Informative References

   [1]   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.

   [2]   Storage Search, "Flash Memory vs. Hard Disk Drives - Which Will
         Win?", http://www.storagesearch.com/semico-art1.html.

   [3]   Matt's Computer Trends, "Flash and Disk Trends",
         http://www.mattscomputertrends.com/flashdiskcomparo.html.

   [4]   Yingjie, G., Bryan, D., Yang, Y., and R. Alimi, "DECADE
         Requirements", draft-ietf-decade-reqs-03 (work in progress),
         July 2011.

   [5]   Amazon, "Amazon Simple Storage Service (Amazon S3)",
         http://aws.amazon.com/s3/.

   [6]   Microsoft Corporation, "Windows Azure Blob - Programming Blob
         Storage".

   [7]   Google, "Google Storage for Developers",
         http://code.google.com/apis/storage.

   [8]   Dropbox, "Dropbox Features", http://www.dropbox.com/features.

   [9]   Microsoft Corporation, "BranchCache",



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         http://technet.microsoft.com/en-us/network/dd425028.aspx.

   [10]  S. Paul, R. Yates, D. Raychaudhuri, J. Kurose., "The Cache-and-
         Forward Network Architecture for Efficient Mobile Content
         Delivery Services in the Future Internet", In Innovations in
         NGN: Future Network and Services, 2008.

   [11]  SNIA, "Cloud Data Management Interface",
         http://www.snia.org/cdmi.

   [12]  Pathan, A.K., Buyya, R., "A Taxonomy and Survey of Content
         Delivery Networks", In Grid Computing and Distributed Systems
         Laboratory in University of Melbourne, Technology Report, Feb.
         2007.

   [13]  Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, R.,
         Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant Networking
         Architecture", RFC 4838, April 2007.

   [14]  Scott, K. and S. Burleigh, "Bundle Protocol Specification",
         RFC 5050, November 2007.

   [15]  Named Data Networking, "Named Data Networking Home Page",
         http://www.named-data.net/.

   [16]  Named Data Networking, "Named Data Networking Project
         Proposal", http://www.named-data.net/ndn-proj.pdf.

   [17]  Network of Information., "Network of Information Overview",
         http://www.netinf.org/home/overview/.

   [18]  A. Anand, V. Sekar, A. Akella., "SmartRE: An Architecture for
         Coordinated Network-wide Redundancy Elimination", In SIGCOMM
         2009.

   [19]  S. Rhea, P. Eaton, D. Geels, H. Weatherspoon, B. Zhao, and J.
         Kubiatowicz., "Pond: the OceanStore Prototype", In FAST 2003.

   [20]  Kodak, "Kodak Gallery Home Page",
         http://www.kodakgallery.com/gallery/welcome.jsp.

   [21]  Wikipedia, "Kodak Gallery",
         http://en.wikipedia.org/wiki/Kodak_Gallery.

   [22]  Flickr, "Flickr Home Page", http://www.flickr.com.

   [23]  ImageShack, "ImageShack Home Page", http://imageshack.us.




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   [24]  Tumblr, "Tumblr Home Page", http://www.tumblr.com.

   [25]  Wikipedia, "Usenet", http://en.wikipedia.org/wiki/Usenet.

   [26]  Google, "Google Groups", http://groups.google.com.

   [27]  Geoff Huston, Telstra., "Web Caching", In The Internet Protocol
         Journal Volume 2, No. 3.

   [28]  G. Shen, Y. Wang, Y. Xiong, B.Y. Zhao, Z.-L. Zhang, "HPTP:
         Relieving the tension between isps and p2p", In 6th
         International workshop on Peer-To-Peer Systems (IPTPS2007).

   [29]  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.

   [30]  Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.
         Zeidner, "Internet Small Computer Systems Interface (iSCSI)",
         RFC 3720, April 2004.

   [31]  Simpson, W., "PPP Challenge Handshake Authentication Protocol
         (CHAP)", RFC 1994, August 1996.

   [32]  Tseng, J., Gibbons, K., Travostino, F., Du Laney, C., and J.
         Souza, "Internet Storage Name Service (iSNS)", RFC 4171,
         September 2005.

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

   [34]  Black, D., Fridella, S., and J. Glasgow, "Parallel NFS (pNFS)
         Block/Volume Layout", RFC 5663, January 2010.

   [35]  Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
         NFS (pNFS) Operations", RFC 5664, January 2010.

   [36]  Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
         April 2010.

   [37]  Ito, K., "Ticket-Based Access Control Extension to WebDAV",
         draft-ito-dav-ticket-00 (work in progress), October 2001.

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

   [39]  Reschke, J., Reddy, S., Davis, J., and A. Babich, "Web



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         Distributed Authoring and Versioning (WebDAV) SEARCH",
         RFC 5323, November 2008.

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

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


Authors' Addresses

   Richard Alimi (editor)
   Google

   Email: ralimi@google.com


   Akbar Rahman (editor)
   InterDigital Communications, LLC

   Email: Akbar.Rahman@InterDigital.com


   Yang Richard Yang (editor)
   Yale University

   Email: yry@cs.yale.edu





















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