DECADE R. Alimi, Ed.
Internet-Draft Google
Intended status: Informational A. Rahman, Ed.
Expires: September 3, 2011 InterDigital Communications, LLC
Y. Yang, Ed.
Yale University
March 2, 2011
A Survey of In-network Storage Systems
draft-ietf-decade-survey-04
Abstract
This document surveys deployed and experimental in-network storage
systems and describes their applicability for DECADE.
Status of this Memo
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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. Content Delivery Network . . . . . . . . . . . . . . . . . 12
4.5. Delay-Tolerant Network . . . . . . . . . . . . . . . . . . 14
4.6. Named Data Networking . . . . . . . . . . . . . . . . . . 16
4.7. Network of Information . . . . . . . . . . . . . . . . . . 17
4.8. Network Traffic Redundancy Elimination . . . . . . . . . . 19
4.9. OceanStore . . . . . . . . . . . . . . . . . . . . . . . . 21
4.10. Photo Sharing . . . . . . . . . . . . . . . . . . . . . . 22
4.11. P2P Cache . . . . . . . . . . . . . . . . . . . . . . . . 23
4.12. Usenet . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.13. Web Cache . . . . . . . . . . . . . . . . . . . . . . . . 27
4.14. Observations Regarding In-Network Storage Systems . . . . 28
5. Storage And Other Related Protocols . . . . . . . . . . . . . 29
5.1. HTTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2. iSCSI . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.3. NFS . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.4. OAuth . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.5. WebDAV . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.6. Observations Regarding Storage and Related Protocols . . . 36
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 37
7. Security Considerations . . . . . . . . . . . . . . . . . . . 37
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 37
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
11. Informative References . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
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1. Introduction
DECADE (DECoupled Application Data Enroute) is an architecture that
provides applications with access to in-network storage. With access
to in-network storage, content distribution applications can be
designed to place less load on network infrastructure, such as last-
mile links. 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 introduces
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
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.
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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,
CDN is a representative technique. Content Delivery Networks (CDN)
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 for publicly
available content is expensive. It 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
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.
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Second, applications may benefit from explicit control of in-network
storage, which P2P caches do not provided. 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
a given period of time.
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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], and the Google
Storage for Developers [7].
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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 [8] 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, and clients can only 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) [9] 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. Content Delivery Network
A Content Delivery Network (CDN) provides services that improve
network performance by maximizing bandwidth, improving accessibility
and maintaining correctness through content replication. They offer
fast and reliable applications and services by distributing content
to cache or edge servers located close to users. See [10] 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
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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.
4.4.1. 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.
4.4.2. 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.
4.4.3. 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.
4.4.4. Data Search Capability
A content provider can search or enumerate the data each cache node
stores. Client user nodes cannot perform search operations.
4.4.5. 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
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authorization criteria.
Also as mentioned previously, clients typically cannot write to the
CDN. Writing is typically a private operation for the content
providers.
4.4.6. Resource Control Interface
Not provided.
4.4.7. 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
mechanism.
4.4.8. Storage Mode
Though addressing objects uses URLs which typically refer to objects
in a hierarchical fashion, the storage mode is typically object-
based.
4.5. Delay-Tolerant Network
The Delay-Tolerant Network (DTN) [11] 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 [12]. 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
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(e.g., hard disk, flash memory, etc.) for DTN packets because of the
nature of the DTN environment.
4.5.1. Applicability to DECADE
An example of an experimental in-network storage system that would
require fundamental changes to the Internet protocols.
4.5.2. 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.
4.5.3. 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).
4.5.4. Data Search Capability
Not provided.
4.5.5. Access Control Authorization
Access control method is public-restricted (to any client which is
part of the DTN) or private.
4.5.6. Resource Control Interface
Not provided.
4.5.7. 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).
4.5.8. 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).
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4.6. Named Data Networking
Named Data Networking (NDN) [13] 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
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
[14].
A key aspect of NDN is that router 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.
4.6.1. 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.
4.6.2. 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.
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4.6.3. 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.
4.6.4. Data Search Capability
Not provided.
4.6.5. 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.
4.6.6. Resource Control Interface
Not provided.
4.6.7. 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.
4.6.8. 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.
4.7. Network of Information
Similar to NDN (see Section 4.6), Network of Information (NetInf)
[15] 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.,
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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
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 Content Distribution Networks (CDN) and
p2p distribution networks (e.g., BitTorrent) provide today.
4.7.1. 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.
4.7.2. 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.
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4.7.3. 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.
4.7.4. Data Search Capability
Not provided.
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 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.
4.7.6. Resource Control Interface
Not provided.
4.7.7. 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.
4.7.8. 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.
4.8. Network Traffic Redundancy Elimination
Redundancy Elimination (RE) (e.g., [16]) 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
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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.
4.8.1. 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.
4.8.2. 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.
4.8.3. Data Management Operations
Not provided.
4.8.4. Data Search Capability
Not provided.
4.8.5. 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.
4.8.6. 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.
4.8.7. Discovery Mechanism
No discovery mechanism is necessary. Routers can use redundancy-
elimination without the users' knowledge.
4.8.8. Storage Mode
Object-based, with "objects" being data from packets transmitted
within the network.
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4.9. OceanStore
OceanStore [17] 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
utilizing Byzantine agreement and erasure codes to store data at
primary replicas.
4.9.1. Applicability to DECADE
An example of an experimental in-network storage system that provides
a high degree of network resilience to failure scenarios.
4.9.2. Data Access Interface
Users may read and write objects
4.9.3. Data Management Operations
Objects may be replaced by newer versions, and multiple versions of
an object may be maintained.
4.9.4. Data Search Capability
Not provided.
4.9.5. Access Control Authorization
Provided, but specifics for clients are unclear from the available
references.
4.9.6. Resource Control Interface
Not provided.
4.9.7. 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.
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4.9.8. Storage Mode
Object-based.
4.10. Photo Sharing
There are a growing number of popular on line Photo Sharing (storing)
systems. For example, the Kodak Gallery system [18] serves over 60
million users and stores billions of images [19]. Other well known
examples of Photo Sharing systems include Flickr [20] and ImageShack
[21]. Also there are a number of popular blogging services, such as
Tumblr [22], which specialize in also sharing large numbers of photos
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.
4.10.1. 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.
4.10.2. Data Access Interface
Users can read (view) and write (store) photos.
4.10.3. Data Management Operations
Users can delete previously stored photos.
4.10.4. 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.
4.10.5. 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
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read photos to allow sharing with a limited set of friends.
4.10.6. Resource Control Interface
Not provided.
4.10.7. 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.
4.10.8. 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.
4.11. 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
do not require changes to P2P protocols and can be deployed
transparently from clients.
P2P caches operate similarly to web caches, 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.
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4.11.1. 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.
4.11.2. Transparent P2P Caches
4.11.2.1. 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.
4.11.2.2. Data Management Operations
Not provided.
4.11.2.3. Data Search Capability
Not provided.
4.11.2.4. Access Control Authorization
Access control method is typically public-restricted (to any client
which is part of the P2P channel or swarm).
4.11.2.5. Resource Control Interface
Not provided.
4.11.2.6. Discovery Mechanism
Use of Deep Packet Inspection (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.
4.11.2.7. Storage Mode
Object-based. Chunks (typically, the unit of transfer amongst P2P
clients) of content are stored in the cache.
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4.11.3. Non-transparent P2P Caches
4.11.3.1. 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.
4.11.3.2. Data Management Operations
Not provided.
4.11.3.3. Data Search Capability
Not provided.
4.11.3.4. Access Control Authorization
Access control method is typically public-restricted (to any client
which is part of the P2P channel or swarm)
4.11.3.5. Resource Control Interface
Not provided.
4.11.3.6. 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.
4.11.3.7. Storage Mode
Object-based. Chunks (typically, the unit of transfer amongst P2P
clients) of content are stored in the cache.
4.12. 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
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eventually reaches every server in the network [23].
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
newsgroups and client access is via a standard HTTP based web browser
[24].
4.12.1. 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.
4.12.2. Data Access Interface
Users can read and post (store) messages.
4.12.3. Data Management Operations
Users sometimes have limited ability to delete messages that they
previously posted.
4.12.4. 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.
4.12.5. Access Control Authorization
Access control method is either public-unrestricted or private (to
client members of that newsgroup).
4.12.6. Resource Control Interface
Not provided.
4.12.7. Discovery Mechanism
Usually by manually logging on to the Usenet account. DNS may be
used to resolve hostnames to their corresponding addresses.
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4.12.8. Storage Mode
File system. Messages are usually stored as files which are then
organized hierarchically by subject into newsgroups.
4.13. Web Cache
Web cache [25] 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) [26]. It proposes to share chunks of P2P
files/streams using HTTP protocol with cache-control headers.
4.13.1. 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.
4.13.2. 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.
4.13.3. Data Management Operations
Not provided.
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4.13.4. Data Search Capability
Not provided.
4.13.5. 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.
4.13.6. Resource Control Interface
Not provided.
4.13.7. 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.
4.13.8. Storage Mode
Object based. Web content is keyed within the cache by HTTP Request
fields, such as Method, URI, and Headers.
4.14. 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
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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.
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 [27] is a key protocol for the World Wide Web. It is a stateless
client-server protocol that allows applications to be designed using
the Representational State Transfer (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).
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5.1.2. Data Management Operations
Not provided.
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 4.10.5 to public-unrestricted for Web Caching
described in Section 4.13.5.
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) [28] is a protocol enabling SCSI commands to be
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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.
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 [29] 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) [30] 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 [32] and object-based [33]).
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
[31] 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 [34] 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 [35], 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 [36] 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 [37] 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 [38] 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 [35] 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 [39] 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-02 (work in progress),
January 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-00 (work in progress),
October 2010.
[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] Microsoft Corporation, "BranchCache",
http://technet.microsoft.com/en-us/network/dd425028.aspx.
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[9] 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.
[10] 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.
[11] 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.
[12] Scott, K. and S. Burleigh, "Bundle Protocol Specification",
RFC 5050, November 2007.
[13] Named Data Networking, "Named Data Networking Home Page",
http://www.named-data.net/.
[14] Named Data Networking, "Named Data Networking Project
Proposal", http://www.named-data.net/ndn-proj.pdf.
[15] Network of Information., "Network of Information Overview",
http://www.netinf.org/home/overview/.
[16] A. Anand, V. Sekar, A. Akella., "SmartRE: An Architecture for
Coordinated Network-wide Redundancy Elimination", In SIGCOMM
2009.
[17] S. Rhea, P. Eaton, D. Geels, H. Weatherspoon, B. Zhao, and J.
Kubiatowicz., "Pond: the OceanStore Prototype", In FAST 2003.
[18] Kodak, "Kodak Gallery Home Page",
http://www.kodakgallery.com/gallery/welcome.jsp.
[19] Wikipedia, "Kodak Gallery",
http://en.wikipedia.org/wiki/Kodak_Gallery.
[20] Flickr, "Flickr Home Page", http://www.flickr.com.
[21] ImageShack, "ImageShack Home Page", http://imageshack.us.
[22] Tumblr, "Tumblr Home Page", http://www.tumblr.com.
[23] Wikipedia, "Usenet", http://en.wikipedia.org/wiki/Usenet.
[24] Google, "Google Groups", http://groups.google.com.
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[25] Geoff Huston, Telstra., "Web Caching", In The Internet Protocol
Journal Volume 2, No. 3.
[26] 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).
[27] 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.
[28] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.
Zeidner, "Internet Small Computer Systems Interface (iSCSI)",
RFC 3720, April 2004.
[29] Simpson, W., "PPP Challenge Handshake Authentication Protocol
(CHAP)", RFC 1994, August 1996.
[30] Tseng, J., Gibbons, K., Travostino, F., Du Laney, C., and J.
Souza, "Internet Storage Name Service (iSNS)", RFC 4171,
September 2005.
[31] Shepler, S., Eisler, M., and D. Noveck, "Network File System
(NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
January 2010.
[32] Black, D., Fridella, S., and J. Glasgow, "Parallel NFS (pNFS)
Block/Volume Layout", RFC 5663, January 2010.
[33] Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
NFS (pNFS) Operations", RFC 5664, January 2010.
[34] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.
[35] Ito, K., "Ticket-Based Access Control Extension to WebDAV",
draft-ito-dav-ticket-00 (work in progress), October 2001.
[36] Dusseault, L., "HTTP Extensions for Web Distributed Authoring
and Versioning (WebDAV)", RFC 4918, June 2007.
[37] Reschke, J., Reddy, S., Davis, J., and A. Babich, "Web
Distributed Authoring and Versioning (WebDAV) SEARCH",
RFC 5323, November 2008.
[38] Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
Distributed Authoring and Versioning (WebDAV)
Access Control Protocol", RFC 3744, May 2004.
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[39] 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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