DECADE Y. Gu
Internet-Draft Huawei
Intended status: Informational D. Bryan
Expires: April 21, 2011 Cogent Force, LLC / Huawei
Y. Yang
Yale University
R. Alimi
Google
October 18, 2010
DECADE Requirements
draft-ietf-decade-reqs-00
Abstract
The target of DECoupled Application Data Enroute (DECADE) is to
provide an open and standard in-network storage system for
applications, primarily P2P applications, to store, retrieve and
manage their data. This draft enumerates and explains requirements,
not only for store and retrieve, but also for data management, access
control and resource control, that should be considered during the
design and implementation of a DECADE system. These are requirements
on the entire system; some of the requirements may eventually be
implemented by an existing protocol with/without some extensions
(e.g., the data transport level). A user of DECADE as a complete
architecture would be guaranteed complete functionality.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology and Concepts . . . . . . . . . . . . . . . . . . . 5
3. Requirements Structure . . . . . . . . . . . . . . . . . . . . 6
4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 7
4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Overall Protocol Requirements . . . . . . . . . . . . 7
4.1.1.1. Application-independent API . . . . . . . . . . . 7
4.1.1.2. Cross-platform Access . . . . . . . . . . . . . . 7
4.1.1.3. Connectivity Concerns . . . . . . . . . . . . . . 7
4.1.1.3.1. NATs and Firewalls . . . . . . . . . . . . . . 7
4.1.1.3.2. Connections to Clients . . . . . . . . . . . . 8
4.1.1.4. Error and Failure Conditions . . . . . . . . . . . 8
4.1.1.4.1. Overload Condition . . . . . . . . . . . . . . 8
4.1.1.4.2. Insufficient Resources . . . . . . . . . . . . 8
4.1.1.4.3. Unavailable and Deleted Data . . . . . . . . . 9
4.1.2. Transfer and Latency Requirements . . . . . . . . . . 9
4.1.2.1. Low-Latency Access . . . . . . . . . . . . . . . . 9
4.1.2.2. Indirect Transfer . . . . . . . . . . . . . . . . 9
4.1.2.3. Data Object Size . . . . . . . . . . . . . . . . . 10
4.1.2.4. Communication among In-network Storage Elements . 10
4.1.3. Data Access Requirements . . . . . . . . . . . . . . . 10
4.1.3.1. Reading/Writing Own Storage . . . . . . . . . . . 10
4.1.3.2. Access by Other Users . . . . . . . . . . . . . . 10
4.1.3.3. Negotiable Data Protocol . . . . . . . . . . . . . 11
4.1.3.4. Separation of Data Operations from Application
Control . . . . . . . . . . . . . . . . . . . . . 11
4.1.4. Data Management Requirements . . . . . . . . . . . . . 12
4.1.4.1. Agnostic of reliability . . . . . . . . . . . . . 12
4.1.4.2. Time-to-live for Stored Data . . . . . . . . . . . 12
4.1.4.3. Offline Usage . . . . . . . . . . . . . . . . . . 12
4.1.5. Resource Control . . . . . . . . . . . . . . . . . . . 12
4.1.5.1. Multiple Applications . . . . . . . . . . . . . . 12
4.1.5.2. Per-Peer, Per-Data Control . . . . . . . . . . . . 13
4.1.5.3. Server Involvement . . . . . . . . . . . . . . . . 13
4.1.6. Authorization . . . . . . . . . . . . . . . . . . . . 14
4.1.6.1. Per-Peer, Per-Data Read Access . . . . . . . . . . 14
4.1.6.2. Per-User Write Access . . . . . . . . . . . . . . 14
4.1.6.3. Authorization Checks . . . . . . . . . . . . . . . 15
4.1.6.4. Credentials Not IP-Based . . . . . . . . . . . . . 15
4.1.6.5. Server Involvement . . . . . . . . . . . . . . . . 15
5. Storage Requirements . . . . . . . . . . . . . . . . . . . . . 15
5.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Explicit Deletion of Stored Data . . . . . . . . . . . 15
5.1.2. Multiple writing . . . . . . . . . . . . . . . . . . . 16
5.1.3. Multiple reading . . . . . . . . . . . . . . . . . . . 16
5.1.4. Reading before completely written . . . . . . . . . . 16
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5.1.5. Writing model . . . . . . . . . . . . . . . . . . . . 16
5.1.6. Storage Status . . . . . . . . . . . . . . . . . . . . 17
5.2. Non-Requirements . . . . . . . . . . . . . . . . . . . . . 17
5.2.1. No ability to update . . . . . . . . . . . . . . . . . 17
6. Implementation Considerations . . . . . . . . . . . . . . . . 17
6.1. Resource Scheduling . . . . . . . . . . . . . . . . . . . 17
6.2. Removal of Duplicate Records . . . . . . . . . . . . . . . 18
7. Discussion and Open Issues . . . . . . . . . . . . . . . . . . 18
7.1. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 18
7.2. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . . 19
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The object of DECoupled Application Data Enroute (DECADE) is to
provide an open and standard in-network storage system for
applications, primarily applications that could be implemented using
a content distribution paradigm, where data is broken in to one or
more chunks and then distributed. This may already include many
types of applications including P2P applications, IPTV, and VoD.
Instead of always transferring data directly from a source-owner peer
to a requesting peer, the source-owner peer can store and manage its
content on its in-network storage. The requesting peer can get the
address of the in-network storage pertaining to the source-owner peer
and retrieve data from the storage.
This draft enumerates and explains the rationale behind SPECIFIC
requirements on the protocol design and on any data store
implementation that may be used to implement DECADE servers that
should be considered during the design and implementation of a DECADE
system. As such, it DOES NOT include general guiding principals.
General design considerations, explanation of the problem being
addressed, and enumeration of the types of applications to which
DECADE may be suited is not considered in this document. For general
information, please see the problem statement
[I-D.ietf-decade-problem-statement] and architecture drafts.
This document enumerates the requirements to enable target
applications to utilize in-network storage. In this context, using
storage resources includes not only basic capabilities such as
storing and retrieving data, and managing data, but also (1)
controlling access by peers with which it is sharing data and (2)
controlling the resources used by remote peers when accessing data.
This document will be updated to track revisions to the problem
statement.
Editors Note: Currently the Architecture document is a WG milestone,
but not yet a WG item. We have made the assumption that there will
be a WG item meeting this milestone going forward.
2. Terminology and Concepts
This document uses terms defined in
[I-D.ietf-decade-problem-statement]. In particular, IAP refers to
the In-network storage Access Protocol, which is the protocol used to
communicate between a DECADE client and DECADE server (in-network
storage) for access control and resource control.
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This document also defines additional terminology:
Target Application: An application (typically installed at end-hosts)
with the ability to explicitly control usage of network and/or
storage resources to deliver contents to a large number of users.
Such applications distribute large contents (e.g., a large file, or
video stream) by dividing the contents into smaller blocks for more
flexible distribution (e.g., multipath). The distributed content is
typically immutable (though it may be deleted). We use the term
Target Application to refer to the type of applications that are
explicitly (but not exclusively) supported by DECADE.
3. Requirements Structure
The DECADE protocol is intended to sit between P2P applications and a
back-end storage system. In the development of DECADE, it must be
made clear that the intention is to NOT develop yet another storage
system, but rather to create a protocol that enables P2P applications
to make use of storage within the network, leaving specific storage
system considerations to the implementation of the DECADE servers as
much as possible. For this reason, we have divided the requirements
into three categories:
o General Principles: Overall requirements that a DECADE system must
conform to.
o Protocol Requirements: Protocol requirements for Target
Applications to make use of in-network storage within their own
data dissemination schemes. Development of these requirements is
guided by a study of data access, search and management
capabilities used by Target Applications.
o Storage Requirements: Functional requirements necessary for the
back-end storage system employed by the DECADE server.
Development of these requirements is guided by a study of the data
access patterns used by Target Applications.
It should also be made clear that the approach is to make DECADE a
simple protocol, while still enabling its usage within many P2P
applications. For this reason, and to further reinforce the
distinction between DECADE and a storage system, in some cases we
also highlight the non-requirements of the protocol. These non-
requirements are intended to capture behaviors that will NOT be
assumed to be needed by DECADE's Target Applications and hence not
present in the DECADE protocol.
Finally, some implementation considerations are provided, which while
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strictly are not requirements, are intended to provide guidance and
highlight potential points of concern that need to be considered by
the protocol developers, and later by implementors.
4. Protocol Requirements
4.1. Requirements
4.1.1. Overall Protocol Requirements
4.1.1.1. Application-independent API
REQUIREMENT(S): The DECADE IAP MUST provide a simple, application-
independent API for P2P applications to access in-network
storage.
RATIONALE: Since the majority of existing P2P application APIs don't
support in-network storage management, new application-
independent API must be introduced. The API should be simple to
encourage adoption, as well as to ensure that a minimum set of
functions, and not an entire network storage system is
implemented.
4.1.1.2. Cross-platform Access
REQUIREMENT(S): If DECADE supports the ability to store metadata
associated with data objects, the DECADE protocol(s) MUST
transmit any metadata using an operating system-independent and
architecture-independent format.
RATIONALE: If DECADE supports the possibility for storing metadata
(e.g., a description, uploaded date, or object size), a possible
use for the metadata is to help a DECADE client locate a desired
data object. Data objects may be stored by DECADE clients
running on various platforms. To enable metadata to be readable
regardless of its source it must be transmitted to and from the
DECADE server in a standard format.
4.1.1.3. Connectivity Concerns
4.1.1.3.1. NATs and Firewalls
REQUIREMENT(S): DECADE SHOULD be usable across firewalls and NATs
without requiring additional network support (e.g., Application-
level Gateways).
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RATIONALE: Firewalls and NATs are widely used in the Internet today,
both in ISP networks and within households. Deployment of DECADE
must not require modifications to such devices (beyond, perhaps,
reconfiguration).
4.1.1.3.2. Connections to Clients
REQUIREMENT(S): DECADE SHOULD NOT require that network connections
be made to DECADE clients (e.g., from a server to a DECADE client
or from a DECADE client to another DECADE client).
RATIONALE: Many household networks and operating systems have
firewalls and NATs configured by default. To ease deployment by
avoiding configuration changes and help mitigate security risks,
DECADE should not require clients to listen for any incoming
network connections (beyond what is required by any other
already-deployed application).
4.1.1.4. Error and Failure Conditions
4.1.1.4.1. Overload Condition
REQUIREMENT(S): In-network storage, which is operating close to its
capacity limit (e.g., too busy servicing other requests), MUST be
able to reject requests.
RATIONALE: When in-network storage is operating at a limit where it
may not be able to process additional requests, it should not be
required to generate responses to such additional requests.
Forcing the in-network storage to do so can impair its ability to
service existing requests.
4.1.1.4.2. Insufficient Resources
REQUIREMENT(S): DECADE MUST support an error condition indicating to
a DECADE client that resources (e.g., storage space) were not
available to service a request (e.g., storage quota exceeded when
attempting to store data).
RATIONALE: The currently-used resource levels within the in-network
storage are not locally-discoverable, since the resources (disk,
network interfaces, etc) are not directly attached. In order to
allocate resources appropriately amongst peers, a client must be
able to determine when resource limits have been reached. The
client can then respond by explicitly freeing necessary resources
or waiting for such resources to be freed.
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4.1.1.4.3. Unavailable and Deleted Data
REQUIREMENT(S): DECADE MUST support error conditions indicating that
(1) data was rejected from being stored, (2) deleted, or (3)
marked unavailable by a storage provider.
RATIONALE: Storage providers may require the ability to (1) avoid
storing, (2) delete, or (3) quarantine certain data that has been
identified as illegal (or otherwise prohibited). DECADE does not
indicate how such data is identified, but applications using
DECADE should not break if a storage provider is obligated to
enforce such policies. Appropriate error conditions should be
indicated to applications.
4.1.2. Transfer and Latency Requirements
4.1.2.1. Low-Latency Access
REQUIREMENT(S): DECADE SHOULD provide "low-latency" access for
application clients. DECADE MUST allow clients to specify at
least two classes of services for service: lowest possible
latency and latency non-critical.
RATIONALE: Some applications may have requirements on delivery time
(e.g., live streaming). The user experience may be
unsatisfactory if the use of in-network storage results in lower
performance than connecting directly to peers over a low-speed,
possibly congested uplink. Additionally, the overhead required
for control-plane operations in DECADE must not cause the latency
to be higher than for a low-speed, possibly congested uplink.
While it is impossible to make a guarantee that a system using
in-network storage will always outperform a system that does not
for every transfer, the overall performance of the system should
be improved compared with direct connections, even considering
control overhead.
4.1.2.2. Indirect Transfer
REQUIREMENT(S): DECADE MUST allow a user's in-network storage to
directly fetch from other user's in-network storage.
RATIONALE: As an example, a requesting peer may get the address of
the storage pertaining to the source-owner peer and then tell its
own in-network storage to fetch the content from the source-
owner's in-network storage. This helps to avoid extra transfers
across ISP network links where possible.
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4.1.2.3. Data Object Size
REQUIREMENT(S): DECADE MUST allow for efficient data transfer of
small objects (e.g., 16KB) between a DECADE client and in-network
storage with minimal additional latency required by the protocol.
RATIONALE: Though P2P applications are frequently used to share
large amounts of data (e.g., continuous streams or large files),
the data itself is typically subdivided into smaller chunks that
are transferred between peers. Additionally, the small chunks
may have requirements on delivery time (e.g., in a live-streaming
application). DECADE must enable data to be efficiently
transferred amongst peers at this granularity.
4.1.2.4. Communication among In-network Storage Elements
REQUIREMENT(S): DECADE SHOULD support the ability for two in-network
storage elements in different administrative domains to store
and/or retrieve data directly between each other. If such a
capability is supported, this MAY be the same (or a subset or
extension of) as the IAP used by clients to access data.
RATIONALE: Allowing server-to-server communication can reduce
latency in some common scenarios. Consider a scenario when a
DECADE client is downloading data into its own storage from
another client's in-network storage. One possibility is for the
client to first download the data itself, and then upload it to
its own storage. However, this causes unnecessary latency and
network traffic. Allowing the data to be downloaded from the
remote in-network storage into the client's own in-network
storage can alleviate both.
4.1.3. Data Access Requirements
4.1.3.1. Reading/Writing Own Storage
REQUIREMENT(S): DECADE MUST support the ability for a DECADE client
to read data from and write data to its own in-network storage.
RATIONALE: Two basic capabilities for any storage system are reading
and writing data. A DECADE client can read data from and write
data to in-network storage space that it owns.
4.1.3.2. Access by Other Users
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REQUIREMENT(S): DECADE MUST support the ability for a user to apply
access control policies to users other than itself for its
storage. The users with whom access is being shared can be under
a different administrative domain than the user who owns the in-
network storage. The authorized users may read from or write to
the user's storage.
RATIONALE: Peers in a P2P application may be located across multiple
ISPs under multiple administrative domains. Thus, to be useful
by P2P applications, DECADE allows a user to specify access
control policies for users that may or may not be known to the
user's storage provider.
4.1.3.3. Negotiable Data Protocol
REQUIREMENT(S): DECADE MUST support the ability for a DECADE client
to negotiate with its In-network storage about which protocol it
can use to read data from and write data to its In-network
storage.
RATIONALE: Since typical data transport protocols (e.g., NFS and
WebDAV) already provide read and write operations for network
storage, it may not be necessary for DECADE to define such
operations in a new protocol. However, because of the particular
application requirements and deployment considerations, different
applications may support different protocols. Thus, a DECADE
client must be able to select an appropriate protocol also
supported by the in-network storage. This requirement also
follows as a result of the requirement of Separation of Control
and Data Operations (Section 4.1.3.4).
4.1.3.4. Separation of Data Operations from Application Control
REQUIREMENT(S): The DECADE IAP MUST only provide a minimal set of
core operations to support diverse policies implemented and
desired by Target Applications.
RATIONALE: Target Applications support many complex behaviors and
diverse policies to control and distribute data, such as (e.g.,
search, index, setting permissions/passing authorization tokens).
Thus, to support such Target Applications, these behaviors must
be logically separated from the data transfer operations (e.g.,
retrieve, store). Some minimal overlap (for example obtaining
credentials needed to encrypt or authorize data transfer using
control operations) may be required to be directly supported by
DECADE.
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4.1.4. Data Management Requirements
4.1.4.1. Agnostic of reliability
REQUIREMENT(S): DECADE SHOULD remain agnostic of reliability/
fault-tolerance level offered by storage provider.
RATIONALE: Providers of a DECADE service may wish to offer varying
levels of service for different applications/users. However, a
single compliant DECADE client should be able to use multiple
DECADE services with differing levels of service.
4.1.4.2. Time-to-live for Stored Data
REQUIREMENT(S): DECADE MUST support the ability for a DECADE client
to indicate a time-to-live value (or expiration time) indicating
a length of time until particular data can be deleted by the in-
network storage element.
RATIONALE: Some data stored by a DECADE client may be usable only
within a certain window of time, such as in live-streaming P2P
applications. Providing a time-to-live value for stored data
(e.g., at the time it is stored) can reduce management overhead
by avoiding many 'delete' commands sent to in-network storage.
The in-network storage may still keep the data in cache for
bandwidth optimization. But this is guided by the privacy policy
of the DECADE provider.
4.1.4.3. Offline Usage
REQUIREMENT(S): DECADE MAY support the ability for a user to provide
authorized access to its in-network storage even if the user has
no DECADE applications actively running or connected to the
network.
RATIONALE: If an application desires, it can authorize peers to
access its storage even after the application exits or network
connectivity is lost. An example use case is mobile scenarios,
where a client can lose and regain network connectivity very
often.
4.1.5. Resource Control
4.1.5.1. Multiple Applications
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REQUIREMENT(S): DECADE SHOULD support the ability for users to
define resource sharing policies for multiple applications being
run/managed by the user.
RATIONALE: A user may own in-network storage and share the in-
network storage resources amongst multiple applications. For
example, the user may run a video-on-demand application and a
live-streaming (or even two different live-streaming
applications) application which both make use of the user's in-
network storage. The applications may be running on different
machines and may not directly communicate. Thus, DECADE should
enable the user to determine resource sharing policies between
the applications.
One possibility is for a user to indicate the particular resource
sharing policies between applications out-of-band (not using a
standard protocol), but this requirement may manifest itself in
passing values over IAP to identify individual applications.
Such identifiers can be either user-generated or server-generated
and do not need to be registered by IANA.
4.1.5.2. Per-Peer, Per-Data Control
REQUIREMENT(S): A DECADE client MUST be able to assign resource
quotas to individual peers for reading from and writing
particular data to its in-network storage within a particular
range of time. The DECADE server MUST enforce these constraints.
RATIONALE: P2P applications can rely on control of resources on a
per-peer or per-data basis. For example, application policy may
indicate that certain peers have a higher bandwidth share for
receiving data. Additionally, certain data (e.g., chunks) may be
distributed with a higher priority. As another example, when
allowing a remote peer to write data to a user's in-network
storage, the remote peer may be restricted to write only a
certain amount of data. Since the client may need to manage
multiple peers accessing its data, it should be able to indicate
the time over which the granted resources are usable. For
example, an expiration time for the access could be indicated to
the server after which no resources are granted (e.g., indicate
error as access denied).
4.1.5.3. Server Involvement
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REQUIREMENT(S): A DECADE client MUST be able to indicate, without
contacting the server itself, resource control policies for
peers' requests.
RATIONALE: One important consideration for in-network storage
elements is scalability, since a single storage element may be
used to support many users. Many P2P applications use small
chunk sizes and frequent data exchanges. If such an application
employed resource control and contacted the in-network storage
element for each data exchange, this could present a scalability
challenge for the server as well as additional latency for
clients.
An alternative is to let requesting users get the resource
control policies and users can then present the policy to the
storage directly. This can result in reduced messaging handled
by the in-network storage.
4.1.6. Authorization
4.1.6.1. Per-Peer, Per-Data Read Access
REQUIREMENT(S): A DECADE Client MUST be able to authorize individual
peers to read particular data stored on its in-network storage.
RATIONALE: A P2P application can control certain application-level
policies by sending particular data (e.g., chunks) to certain
peers. It is important that peers not be able to circumvent such
decisions by arbitrarily reading any currently-stored data in in-
network storage.
4.1.6.2. Per-User Write Access
REQUIREMENT(S): A DECADE Client MUST be able to authorize individual
peers to store data into its in-network storage.
RATIONALE: The space managed by a user in in-network storage can be
a limited resource. At the same time, it can be useful to allow
remote peers to write data directly to a user's in-network
storage. Thus, a DECADE client should be able to grant only
certain peers this privilege.
Note that it is not (currently) a requirement to check that a
peer stores a particular set of data (e.g., the check that a
remote peer writes the expected chunk of a file). Enforcing this
as a requirement would require a client to know which data is
expected (e.g., the full chunk itself or a hash of the chunk)
which may not be available in all applications. Checking for a
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particular hash could be considered as a requirement in the
future that could optionally be employed by applications.
4.1.6.3. Authorization Checks
REQUIREMENT(S): In-network storage MUST check the authorization of a
client before it executes a supplied request. The in-network
storage MAY use optimizations to avoid such authorization checks
as long as the enforced permissions are the the same.
RATIONALE: Authorization granted by a DECADE client are meaningless
unless unauthorized requests are denied access. Thus, the in-
network storage element must verify the authorization of a
particular request before it is executed.
4.1.6.4. Credentials Not IP-Based
REQUIREMENT(S): Access MUST be able to be granted on other
credentials than the IP address
RATIONALE: DECADE clients may be operating on hosts without constant
network connectivity or without a permanent attachment address
(e.g., mobile devices). To support access control with such
hosts, DECADE servers must support access control policies that
use information other than IP addresses.
4.1.6.5. Server Involvement
REQUIREMENT(S): A DECADE client MUST be able to indicate, without
contacting the server itself, access control policies for peers'
requests.
RATIONALE: See discussion in Section 4.1.5.3.
5. Storage Requirements
5.1. Requirements
5.1.1. Explicit Deletion of Stored Data
REQUIREMENT(S): DECADE MUST support the ability for a DECADE client
to explicitly delete data from its own in-network storage.
RATIONALE: A DECADE client may continually be writing data to its
in-network storage. Since there may be a limit (e.g., imposed by
the storage provider) to how much total storage can be used, some
data may need to be removed to make room for additional data. A
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DECADE client should be able to explicitly remove particular
data. This may be implemented using existing protocols.
5.1.2. Multiple writing
REQUIREMENT(S): DECADE MUST NOT allow multiple writers for the same
object. Implementations raise an error to one of the writers.
RATIONALE: This avoids data corruption in a simple way while
remaining efficient.
5.1.3. Multiple reading
REQUIREMENT(S): DECADE MUST allow for multiple readers for an
object..
RATIONALE: One characteristic of P2P applications is the ability to
upload an object to multiple peers. Thus, it is natural for
DECADE to allow multiple readers to access the content
concurrently.
5.1.4. Reading before completely written
REQUIREMENT(S): DECADE MAY allow readers to read from objects before
they have been completely written.
RATIONALE: Some P2P systems (in particular, streaming) can be
sensitive to latency. A technique to reduce latency is to remove
store-and-forward delays for data objects (e.g., make the object
available before it is completely stored). Appropriate handling
for error conditions (e.g., a disappearing writer) needs to be
specified.
5.1.5. Writing model
REQUIREMENT(S): DECADE MUST provide at least a writing model (while
storing an object) that appends data to data already stored.
RATIONALE: Depending on the object size (e.g., chunk size) used by a
P2P application, the application may need to send data to the
DECADE server in multiple packets. To keep implementation
simple, the DECADE must at least support the ability to write the
data sequentially in the order received. Implementations MAY
allow application to write data in an object out-of-order (but
MAY NOT overwrite ranges of the object that have already been
stored).
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5.1.6. Storage Status
REQUIREMENT(S): A DECADE client MUST be able to retrieve current
resource usage (including list of stored data) and resource
quotas on its in-network storage.
RATIONALE: The resources used by a client are not directly-attached
(e.g., disk, network interface, etc). Thus, the client cannot
locally determine how such resources are being used. Before
storing and retrieving data, a client should be able to determine
which data is available (e.g., after an application restart).
Additionally, a client should be able to determine resource
availability to better allocate them to remote peers.
5.2. Non-Requirements
5.2.1. No ability to update
REQUIREMENT(S): DECADE SHOULD NOT provide ability to update existing
objects. That is, objects are immutable once they are stored.
RATIONALE: Reasonable consistency models for updating existing
objects would significantly complicate implementation (especially
if implementation chooses to replicate data across multiple
servers). If a user needs to update a resource, it can store a
new resource and then distribute the new resource instead of the
old one.
6. Implementation Considerations
The intent of this section is to collect discussion items and
implementation considerations that have been discovered as this
requirements document has been produced. The content of this section
will be migrated to an appropriate place as the document and the
Working Group progress.
6.1. Resource Scheduling
The particular resource scheduling policy may have important
ramifications on the performance of applications. This document has
explicitly mentioned simultaneous support for both low-latency
applications and latency-tolerant applications.
Denial of Service attacks may be another risk. For example,
rejecting new requests due to overload conditions may introduce the
ability to perform a denial of service attack depending on a
particular DECADE server's scheduling implementation and resource
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allocation policies.
6.2. Removal of Duplicate Records
There are actually two possible scenarios here. The first is the
case of removing duplicates within one particular DECADE server (or
logical server). While not a requirement, as it does not impact the
protocol and is technically not noticeable on message across the
wire, a DECADE server may implement internal mechanisms to monitor
for duplicate records and use internal mechanisms to prevent
duplication of internal storage.
The second scenario is removing duplicates across a distributed set
of DECADE servers. This is a more difficult problem, and if the
group decides to support this capability, it may require protocol
support. See Section 7.2 for more details.
7. Discussion and Open Issues
7.1. Discussion
Sometimes, several logical in-network storages could be deployed on
the same physical network device. In this case, in-network storages
on the same physical network device can communicate and transfer data
through internal communication messages. However in-network storages
deployed on different physical network devices SHOULD communicate
with in-network storage Access Protocol (IAP).
To provide fairness among users, the in-network storage provider
should assign resource (e.g., storage, bandwidth, connections) quota
for users. This can prevent a small number of clients from occupying
large amounts of resources on the in-network storage, while others
starve.
7.2. Open Issues
Gaming of the Resource Control Mechanism: There has been some
discussion of how applications may be able game the scheduling
system by manipulating the resource control mechanism, for
example by specifying many small peers to increase total
throughput. This is a serious concern, and we need to identify
specific requirements on the protocol (hopefully independent of
particular scheduling/resource control schemes) to help address
this.
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Discovery: There needs to be some mechanism for a user to discover
that there is a DECADE service available for their use, and to
locate that server. This is particularly important in the case
of mobile applications, since the actual servers that are
available at any given time may differ. However, the specifics
of what mechanisms (DHCP, HTTP page, etc.) have not been
discussed, or even if the protocol should specify one or leave it
as an implementation detail. This needs to be defined, and
specific requirements formulated if needed.
Removal of Duplicate Records Across Servers: If the group wishes to
allow for automated mechanisms to remove duplicates across a
number of separate servers, some protocol support may need to be
added. In the case of removing duplicates within a single
(logical) DECADE server, this is simply an implementation
concern. See Section 6 for more details.
8. Security Considerations
Authorization for access to in-network storage is an important part
of the requirements listed in this document. Authorization for
access to storage resources and the data itself is important for
users to be able to manage and limit distribution of content. For
example, a user may only wish to share particular content with
certain peers.
If the authorization technique implemented in DECADE passes any
private information (e.g., user passwords) over the wire, it MUST be
passed in a secure way.
9. IANA Considerations
There are no IANA considerations with this document.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[I-D.ietf-decade-problem-statement]
Yongchao, S., Zong, N., Yang, Y., and R. Alimi, "DECoupled
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Application Data Enroute (DECADE) Problem Statement",
draft-ietf-decade-problem-statement-00 (work in progress),
August 2010.
[LLSB08] Dave Levin, Katrina LaCurts, Neil Spring, Bobby
Bhattacharjee., "BitTorrent is an Auction: Analyzing and
Improving BitTorrent's Incentives", In SIGCOMM 2008.
[PPLive] "PPLive", http://www.pplive.com.
Appendix A. Acknowledgments
We would also like to thank Haibin Song for substantial contributions
to earlier versions of this document. We would also like to thank
Reinaldo Penno, Alexey Melnikov, Rich Woundy, Ning Zong, Roni Even,
David McDysan, Boerje Ohlman and Dirk Kutscher for contributions
(including some text used verbatim) and general feedback.
Authors' Addresses
Yingjie Gu
Huawei
No. 101 Software Avenue
Nanjing, Jiangsu Province 210012
P.R.China
Phone: +86-25-56624760
Email: guyingjie@huawei.com
David A. Bryan
Cogent Force, LLC / Huawei
Email: dbryan@ethernot.org
Yang Richard Yang
Yale University
Email: yry@cs.yale.edu
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Richard Alimi
Google
Email: ralimi@google.com
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