DECADE Y. Gu
Internet-Draft Huawei
Intended status: Informational D. Bryan
Expires: September 15, 2011 Cogent Force, LLC / Huawei
Y. Yang
Yale University
R. Alimi
Google
March 14, 2011
DECADE Requirements
draft-ietf-decade-reqs-01
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. Cross-platform Access . . . . . . . . . . . . . . 7
4.1.1.2. Connectivity Concerns . . . . . . . . . . . . . . 7
4.1.1.2.1. NATs and Firewalls . . . . . . . . . . . . . . 7
4.1.1.2.2. Connections to Clients . . . . . . . . . . . . 7
4.1.1.3. Error and Failure Conditions . . . . . . . . . . . 8
4.1.1.3.1. Overload Condition . . . . . . . . . . . . . . 8
4.1.1.3.2. Insufficient Resources . . . . . . . . . . . . 8
4.1.1.3.3. Unavailable and Deleted Data . . . . . . . . . 8
4.1.1.3.4. Redirection . . . . . . . . . . . . . . . . . 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-Remote-Client, Per-Data Control . . . . . . . 13
4.1.5.3. Server Involvement . . . . . . . . . . . . . . . . 13
4.1.6. Authorization . . . . . . . . . . . . . . . . . . . . 14
4.1.6.1. Per-Remote-Client, 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. Hints concerning usage stored data . . . . . . . . . . 16
5.1.6. Writing model . . . . . . . . . . . . . . . . . . . . 17
5.1.7. Storage Status . . . . . . . . . . . . . . . . . . . . 17
5.2. Non-Requirements . . . . . . . . . . . . . . . . . . . . . 17
5.2.1. No ability to update . . . . . . . . . . . . . . . . . 18
6. Implementation Considerations . . . . . . . . . . . . . . . . 18
6.1. Resource Scheduling . . . . . . . . . . . . . . . . . . . 18
6.2. Removal of Duplicate Records . . . . . . . . . . . . . . . 18
7. Discussion and Open Issues . . . . . . . . . . . . . . . . . . 19
7.1. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 19
7.2. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
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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
client to a requesting client, the source/owner client can store and
manage its content on its in-network storage. The requesting client
can get the address of the in-network storage pertaining to the
source/owner client 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 for particular remote clients with which it is
sharing data and (2) controlling the resources used by remote clients
when they access data.
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.
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.
This includes scenarios where multiple applications or entities
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cooperate, such as with P2P/CDN hybrid architectures. 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 Target 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 Target
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 two categories:
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. These requirements may
be met by a new protocol to be defined within the DECADE Working
Group.
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. These requirements
should be met by the underling data transport used by DECADE.
It should also be made clear that the approach is to make DECADE a
simple protocol, while still enabling its usage within many Target
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
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.
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4. Protocol Requirements
4.1. Requirements
4.1.1. Overall Protocol Requirements
4.1.1.1. 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, object size, or access
control list), 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.
4.1.1.2. Connectivity Concerns
4.1.1.2.1. NATs and Firewalls
REQUIREMENT(S): DECADE SHOULD be usable across firewalls and NATs
without requiring additional network support (e.g., Application-
level Gateways).
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). Note that this requirement applies to both any
new protocol developed by the DECADE Working Group and any data
transport used with DECADE.
4.1.1.2.2. Connections to Clients
REQUIREMENT(S): DECADE SHOULD require that network connections be
made from DECADE clients to DECADE servers (i.e., not to the
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).
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4.1.1.3. Error and Failure Conditions
4.1.1.3.1. 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 and not be required to generate responses
to additional 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.
4.1.1.3.2. 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 remote clients, 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.
4.1.1.3.3. 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.
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4.1.1.3.4. Redirection
REQUIREMENT(S): DECADE SHOULD support the ability for a DECADE
server to redirect requests to another DECADE server. This may
be in response to either an error or failure condition, or to
support capabilities such as load balancing.
RATIONALE: A DECADE server may opt to redirect requests to another
server to support capabilities such as load balancing, or if the
implementation decides that another DECADE server is in a better
position to handle the request due to either its location in the
network, server status, or other consideration.
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 [PPLive]). The user experience may be
unsatisfactory if the use of in-network storage results in lower
performance than connecting directly to remote clients 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 remote client may get the
address of the storage pertaining to the source/owner client 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 Target 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 clients. 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 clients 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: Endpoints in Target Applications may be located across
multiple ISPs under multiple administrative domains. Thus, to be
useful by Target 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. DECADE MUST specify at least one mandatory protocol to
be supported by implementations; usage of a different protocol
may be selected via negotiation.
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 specified 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 remote
clients 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
(DECADE clients) 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-Remote-Client, Per-Data Control
REQUIREMENT(S): A DECADE client MUST be able to assign resource
quotas to individual remote clients 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: Target Applications can rely on control of resources on a
per-remote-client or per-data basis. For example, application
policy may indicate that certain remote clients have a higher
bandwidth share for receiving data [LLSB08]. Additionally,
certain data (e.g., chunks) may be distributed with a higher
priority. As another example, when allowing a remote client to
write data to a user's in-network storage, the remote client may
be restricted to write only a certain amount of data. Since the
client may need to manage multiple clients 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 to a DECADE
server, without itself contacting the server, resource control
policies for remote clients' 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 Target 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-Remote-Client, Per-Data Read Access
REQUIREMENT(S): A DECADE Client MUST be able to control which
individual remote clients are authorized to read particular data
stored on its in-network storage.
RATIONALE: A Target Application can control certain application-
level policies by sending particular data (e.g., chunks) to
certain remote clients. It is important that remote clients 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 control which
individual remote clients are authorized 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 clients to write data directly to a user's in-network
storage. Thus, a DECADE client should be able to grant only
certain remote clients this privilege.
Note that it is not (currently) a requirement to check that a
remote client stores a particular set of data (e.g., the check
that a remote client writes the expected chunk of a file).
Enforcing this as a requirement would require a client to know
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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 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 remote
clients' requests.
RATIONALE: See discussion in Section 4.1.5.3.
5. Storage Requirements
5.1. Requirements
5.1.1. Explicit Deletion of Stored Data
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REQUIREMENT(S): DECADE MUST support the ability for a DECADE client
to explicitly delete data from its own in-network storage.
DECADE MAY have an overwrite flag indicating that an object with
the same name should be replaced.
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
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 Target Applications is the ability
to upload an object to multiple clients. Thus, it is natural for
DECADE to allow multiple readers to read 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 Target Applications (in particular, P2P 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. Hints concerning usage stored data
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REQUIREMENT(S): DECADE MAY allow writers of new objects to indicate
specific hints concerning how the objects are expected to be used
(e.g., access frequency or time to live).
RATIONALE: Different Target Applications may have different usage
patterns for objects stored at in-network storage. For example,
a P2P live streaming application may indicate to a DECADE server
that the objects are expected to have a shore time-to-live, but
read frequently. The DECADE server may then opt to store the
objects in memory instead of in disk.
5.1.6. 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
Target 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
MUST NOT overwrite ranges of the object that have already been
stored).
5.1.7. Storage Status
REQUIREMENT(S): A DECADE client MUST be able to retrieve current
resource usage (including list of stored data), resource quotas,
and access permissions for its in-network storage. The returned
information MUST include resource usage resulting from the
client's own usage and usage by other clients that have been
authorized to read/write objects or open connections to that
client's 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 clients.
5.2. Non-Requirements
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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
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.
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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.
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.
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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
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.
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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
Richard Alimi
Google
Email: ralimi@google.com
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