DECADE Y. Gu
Internet-Draft Huawei
Intended status: Informational D. Bryan
Expires: May 3, 2012 Polycom, Inc.
Y. Yang
Yale University
R. Alimi
Google
October 31, 2011
DECADE Requirements
draft-ietf-decade-reqs-05
Abstract
The target of DECoupled Application Data Enroute (DECADE) is to
provide an open and standard in-network storage system for
applications, primarily P2P (peer-to-peer) applications, to store,
retrieve and manage their data. This draft enumerates and explains
requirements, not only for storage and retrieval, 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., a protocol used to read and write data from
the storage system). The requirements in this document are intended
to ensure that the DECADE architecture includes all of the desired
functionality for intended applications.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [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
Gu, et al. Expires May 3, 2012 [Page 1]
Internet-Draft DECADE Requirements October 2011
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 3, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Gu, et al. Expires May 3, 2012 [Page 2]
Internet-Draft DECADE Requirements October 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology and Concepts . . . . . . . . . . . . . . . . . . . 6
3. Requirements Structure . . . . . . . . . . . . . . . . . . . . 6
4. Protocol Requirements . . . . . . . . . . . . . . . . . . . . 7
4.1. Overall Protocol Requirements . . . . . . . . . . . . . . 7
4.1.1. Connectivity Concerns . . . . . . . . . . . . . . . . 7
4.1.1.1. NATs and Firewalls . . . . . . . . . . . . . . . . 7
4.1.1.2. Connections to Clients . . . . . . . . . . . . . . 7
4.1.2. Security . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.2.1. Secure Transport . . . . . . . . . . . . . . . . . 8
4.1.3. Error and Failure Conditions . . . . . . . . . . . . . 8
4.1.3.1. Overload Condition . . . . . . . . . . . . . . . . 8
4.1.3.2. Insufficient Resources . . . . . . . . . . . . . . 8
4.1.3.3. Unavailable and Deleted Data . . . . . . . . . . . 9
4.1.3.4. Insufficient Permissions . . . . . . . . . . . . . 9
4.1.3.5. Redirection . . . . . . . . . . . . . . . . . . . 9
4.2. Transfer and Latency Requirements . . . . . . . . . . . . 9
4.2.1. Low-Latency Access . . . . . . . . . . . . . . . . . . 9
4.2.2. Data Object Size . . . . . . . . . . . . . . . . . . . 10
4.2.3. Communication among DECADE Servers . . . . . . . . . . 10
4.3. Data Access Requirements . . . . . . . . . . . . . . . . . 11
4.3.1. Reading/Writing Own Storage . . . . . . . . . . . . . 11
4.3.2. Access by Other Users . . . . . . . . . . . . . . . . 11
4.3.3. Negotiable Data Transport Protocol . . . . . . . . . . 11
4.3.4. Separation of Data and Control Policies . . . . . . . 12
4.4. Data Management Requirements . . . . . . . . . . . . . . . 12
4.4.1. Agnostic of reliability . . . . . . . . . . . . . . . 12
4.4.2. Data Object Attributes . . . . . . . . . . . . . . . . 12
4.4.3. Time-to-live for Written Data Objects . . . . . . . . 13
4.4.4. Offline Usage . . . . . . . . . . . . . . . . . . . . 13
4.5. Data Naming Requirements . . . . . . . . . . . . . . . . . 13
4.5.1. Unique Names . . . . . . . . . . . . . . . . . . . . . 13
4.6. Resource Control . . . . . . . . . . . . . . . . . . . . . 14
4.6.1. Multiple Applications . . . . . . . . . . . . . . . . 14
4.6.2. Per-Remote-Client, Per-Data Control . . . . . . . . . 14
4.6.3. Server Involvement . . . . . . . . . . . . . . . . . . 15
4.7. Authorization . . . . . . . . . . . . . . . . . . . . . . 15
4.7.1. Per-Remote-Client, Per-Data Read Access . . . . . . . 15
4.7.2. Per-User Write Access . . . . . . . . . . . . . . . . 15
4.7.3. Default Access Permissions . . . . . . . . . . . . . . 16
4.7.4. Authorization Checks . . . . . . . . . . . . . . . . . 16
4.7.5. Cryptographic Credentials . . . . . . . . . . . . . . 16
4.7.6. Server Involvement . . . . . . . . . . . . . . . . . . 16
4.7.7. Protocol Reuse . . . . . . . . . . . . . . . . . . . . 17
4.8. Non-Requirements . . . . . . . . . . . . . . . . . . . . . 17
4.8.1. Application-defined Properties and Metadata . . . . . 17
Gu, et al. Expires May 3, 2012 [Page 3]
Internet-Draft DECADE Requirements October 2011
5. Storage Requirements . . . . . . . . . . . . . . . . . . . . . 17
5.1. Immutable Data . . . . . . . . . . . . . . . . . . . . . . 17
5.2. Explicit Deletion of Data . . . . . . . . . . . . . . . . 18
5.3. Multiple writing . . . . . . . . . . . . . . . . . . . . . 18
5.4. Multiple reading . . . . . . . . . . . . . . . . . . . . . 18
5.5. Reading before completely written . . . . . . . . . . . . 18
5.6. Hints concerning usage of written data . . . . . . . . . . 19
5.7. Writing model . . . . . . . . . . . . . . . . . . . . . . 19
5.8. Storage Status . . . . . . . . . . . . . . . . . . . . . . 19
6. Discovery Requirements . . . . . . . . . . . . . . . . . . . . 20
6.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 20
6.1.1. Locating DECADE Servers . . . . . . . . . . . . . . . 20
6.1.2. Support for Clients Behind NATs and Firewalls . . . . 20
6.1.3. Prefer Existing Protocols . . . . . . . . . . . . . . 20
7. Future Considerations . . . . . . . . . . . . . . . . . . . . 21
7.1. Fairness . . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2. Removal of Duplicate Data Objects . . . . . . . . . . . . 21
7.3. Gaming of the Resource Control Mechanism . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8.1. Authentication and Authorization . . . . . . . . . . . . . 22
8.2. Encrypted Data . . . . . . . . . . . . . . . . . . . . . . 22
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
Gu, et al. Expires May 3, 2012 [Page 4]
Internet-Draft DECADE Requirements October 2011
1. Introduction
The object of DECoupled Application Data Enroute (DECADE) is to
provide an open and standard in-network storage system for content
distribution applications, where data is typically broken into one or
more chunks and then distributed. This may already include many
types of applications including P2P applications, IPTV (Internet
Protocol Television), and VoD (Video on Demand). (For a precise
definition of the applications targeted in DECADE, see the definition
for Target Application in Section 2.) Instead of always transferring
data directly from a source/owner client to a requesting client, the
source/owner client can write to 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 read
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 principles.
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
[I-D.ietf-decade-arch] 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
writing, reading, and managing data, but also controlling access for
particular remote clients with which it is sharing data.
Additionally, we also consider controlling the resources used by
remote clients when they access data as an integral part of utilizing
the network storage.
This document discusses requirements pertaining to DECADE
protocol(s). In certain deployments, several logical in-network
storage systems could be deployed (e.g., within the same
administrative domain). These in-network storage systems can
communicate and transfer data through internal or non-standard
communication messages that are outside of the scope of these
requirements, but they SHOULD use DECADE protocol(s) when
communicating with other DECADE-capable in-network storage systems.
Gu, et al. Expires May 3, 2012 [Page 5]
Internet-Draft DECADE Requirements October 2011
2. Terminology and Concepts
This document uses terms defined in
[I-D.ietf-decade-problem-statement].
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 content to a large number of users.
This includes scenarios where multiple applications or entities
cooperate, such as with P2P, CDN, and hybrid P2P/CDN architectures.
Such applications distribute large amounts of content (e.g., a large
file, or video stream) by dividing the content into smaller blocks
for more flexible distribution (e.g., over multiple application-level
paths). 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. DECADE does not intend to 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 primary 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 combination of existing protocols and new protocols.
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 underlying data transport used by DECADE. In
this document, we use "data transport" to refer to a protocol used
to read and write data from DECADE in-network storage.
Note that a third category also enumerates requirements on the
protocol used to discover DECADE Servers.
Gu, et al. Expires May 3, 2012 [Page 6]
Internet-Draft DECADE Requirements October 2011
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
not strictly requirements, are intended to provide guidance and
highlight potential points that need to be considered by the protocol
developers, and later by implementors.
4. Protocol Requirements
This section details the requirements of DECADE protocol(s).
4.1. Overall Protocol Requirements
4.1.1. Connectivity Concerns
4.1.1.1. NATs and Firewalls
REQUIREMENT(S): DECADE client to server protocols SHOULD be usable
across firewalls and NAT (Network Address Translation) devices
without requiring additional network support (e.g., Application-
level Gateways).
RATIONALE: Firewalls and NATs are widely used in the Internet today,
both in ISP (Internet Service Provider) and Enterprise networks
and by consumers. 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. Connections to Clients
REQUIREMENT(S): DECADE SHOULD require that network connections be
made from DECADE clients to DECADE servers (i.e., not from the
server to the DECADE client).
RATIONALE: Many household networks and operating systems have
firewalls and NATs configured by default to block incoming
connections. To ease deployment by avoiding configuration
changes and help mitigate security risks, DECADE should not
Gu, et al. Expires May 3, 2012 [Page 7]
Internet-Draft DECADE Requirements October 2011
require clients to listen for any incoming network connections
(beyond what is required by any other already-deployed
application).
4.1.2. Security
4.1.2.1. Secure Transport
REQUIREMENT(S): DECADE MUST contain a mode in which all
communication between a DECADE client and server is over a secure
transport that provides confidentiality, integrity, and
authentication.
RATIONALE: Target Applications may wish to write sensitive data. To
satisfy this use case, DECADE must provide a mode in which all
communication between a DECADE client and server occurs over a
secure transport protocol (e.g., SSL/TLS).
4.1.3. Error and Failure Conditions
4.1.3.1. Overload Condition
REQUIREMENT(S): In-network storage, which is operating close to its
capacity limit (e.g., too busy servicing other requests), MUST be
permitted to reject requests and not be required to generate
responses to additional requests. In-network storage MUST also
be permitted to redirect requests (see Section 4.1.3.5) as a
load-shedding technique.
RATIONALE: Forcing the in-network storage to respond to requests
when operating close to its capacity can impair its ability to
service existing requests, and thus is permitted to avoid
generating responses to additional requests.
4.1.3.2. 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 write 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.
Gu, et al. Expires May 3, 2012 [Page 8]
Internet-Draft DECADE Requirements October 2011
4.1.3.3. Unavailable and Deleted Data
REQUIREMENT(S): DECADE MUST support error conditions indicating that
(1) data was rejected from being written, (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.
4.1.3.4. Insufficient Permissions
REQUIREMENT(S): DECADE MUST support error conditions indicating that
the requesting client does not have sufficient permissions to
access requested data objects.
RATIONALE: DECADE clients may request objects to which they do not
have sufficent access permissions, and DECADE servers must be
able to signal that this has occurred. Note that access
permissions may be insufficient due to a combination of the
credentials presented by a client as well as additional policies
defined by the storage provider.
4.1.3.5. Redirection
REQUIREMENT(S): DECADE SHOULD support the ability for a DECADE
server to redirect requests to another DECADE server. This may
either be in response to an error, failure, or overload
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.
4.2. Transfer and Latency Requirements
4.2.1. Low-Latency Access
Gu, et al. Expires May 3, 2012 [Page 9]
Internet-Draft DECADE Requirements October 2011
REQUIREMENT(S): DECADE SHOULD provide "low-latency" access for
application clients. DECADE MUST allow clients to specify at
least two classes of services: 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 low-speed uplink
connections, even considering control overhead.
4.2.2. 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 imposed 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. It is important
to note that DECADE may be used to store and retrieve larger
objects, but protocol(s) should not be designed such that usage
with smaller data objects cannot meet the requirements of Target
Applications.
4.2.3. Communication among DECADE Servers
REQUIREMENT(S): DECADE SHOULD support the ability for two in-network
storage elements in different administrative domains to write
and/or read data directly between each other (if authorized as
described in Section 4.7). If such a capability is supported,
this MAY be the same (or a subset or extension of) as the DECADE
protocol(s) used by clients to access data.
Gu, et al. Expires May 3, 2012 [Page 10]
Internet-Draft DECADE Requirements October 2011
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 uploading 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.
4.3. Data Access Requirements
4.3.1. 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.
4.3.2. Access by Other Users
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 implement
access control policies for users that may or may not be known to
the user's storage provider.
4.3.3. Negotiable Data Transport 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.
Gu, et al. Expires May 3, 2012 [Page 11]
Internet-Draft DECADE Requirements October 2011
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 4.3.4).
4.3.4. Separation of Data and Control Policies
REQUIREMENT(S): DECADE Protocol(s) 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.,
read, write). 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.
4.4. Data Management Requirements
4.4.1. 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.
4.4.2. Data Object Attributes
REQUIREMENT(S): DECADE MUST support the ability to associate
attributes with data objects with a scope local to a DECADE
server, and for DECADE clients to query these attributes. DECADE
protocol(s) MUST transmit any attributes using an operating
system-independent and architecture-independent standard format.
DECADE protocol(s) MUST be designed such that new attributes can
be added by later protocol revisions or extensions.
Gu, et al. Expires May 3, 2012 [Page 12]
Internet-Draft DECADE Requirements October 2011
RATIONALE: DECADE supports associating attributes (e.g., a time-to-
live, creation timestamp, or object size) with a data object.
These attributes are local to a data object stored by a
particular DECADE server, and are thus not applied to any DECADE
server or client to which the data object is copied. These
attributes may be used as hints to the storage system, internal
optimizations, or as additional information queryable by DECADE
clients.
4.4.3. Time-to-live for Written Data Objects
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 objects written 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
data objects (e.g., at the time they are written) 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.
4.4.4. 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.
4.5. Data Naming Requirements
4.5.1. Unique Names
REQUIREMENT(S): DECADE MUST support a naming scheme that ensures a
high probability of uniqueness and supports the operation of
DECADE servers under diverse administrative domains with no
coordination. DECADE SHOULD provide a mechanism (minimally
rejection) to handle the improbable case of a collision.
Gu, et al. Expires May 3, 2012 [Page 13]
Internet-Draft DECADE Requirements October 2011
RATIONALE: When writing a data object, a DECADE Client should be
able to write it without being concerned over whether an object
of the same name already exists, unless the existing object
contains the exact same data. Note that it may be reasonable for
DECADE to satisfy this requirement probabilistically (e.g., using
a hashing mechanism). As a result, it is wise to provide a
collision handling mechanism, even if the probability of
collisions is extremely low.
4.6. Resource Control
4.6.1. Multiple Applications
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 one or more video-on-demand
application(s) and a live-streaming application(s) 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 within DECADE protocol(s) to identify individual
applications. Such identifiers can be either user-generated or
server-generated and do not need to be registered by IANA.
4.6.2. Per-Remote-Client, Per-Data Control
REQUIREMENT(S): A DECADE client MUST be able to assign resource
policies (bandwidth share, storage quota, and network connection
quota) 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
Gu, et al. Expires May 3, 2012 [Page 14]
Internet-Draft DECADE Requirements October 2011
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).
4.6.3. Server Involvement
REQUIREMENT(S): A DECADE client SHOULD 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.
Our preferred alternative is to let requesting users obtain
signed resource control policies (in the form of a token) from
the owning user, and then users can then present the policy to
the storage directly. This can result in reduced messaging
handled by the in-network storage.
4.7. Authorization
4.7.1. 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
from 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
data in in-network storage.
4.7.2. Per-User Write Access
Gu, et al. Expires May 3, 2012 [Page 15]
Internet-Draft DECADE Requirements October 2011
REQUIREMENT(S): A DECADE Client MUST be able to control which
individual remote clients are authorized to write 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.
4.7.3. Default Access Permissions
REQUIREMENT(S): Unless read or write access is granted by a DECADE
Client to a remote client, the default access MUST be no access.
RATIONALE: The current leading proposal for an access control model
in DECADE is via token passing, resulting in a system with little
state on the server side.
4.7.4. 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 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.
4.7.5. Cryptographic Credentials
REQUIREMENT(S): Access MUST be able to be granted using
cryptographic credentials.
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 cryptographic credentials, not simply by tying access to IP
addresses.
4.7.6. Server Involvement
Gu, et al. Expires May 3, 2012 [Page 16]
Internet-Draft DECADE Requirements October 2011
REQUIREMENT(S): A DECADE client SHOULD be able to indicate, without
contacting the server itself, access control policies for remote
clients' requests.
RATIONALE: See discussion in Section 4.6.3.
4.7.7. Protocol Reuse
REQUIREMENT(S): If possible, DECADE SHOULD reuse existing protocol
and mechanisms for Authentication, Access, and Authorization
(AAA).
RATIONALE: If possible, reusing an existing AAA protocol/mechanism
will minimize the development required by applications, and will
maximize interoperability of the DECADE protocol with existing
infrastructure.
4.8. Non-Requirements
4.8.1. Application-defined Properties and Metadata
REQUIREMENT(S): DECADE MUST NOT provide a mechanism for associating
Application-defined properties (metadata) with data objects
beyond what is provided by Section 4.4.2.
RATIONALE: Associating key-value pairs that are defined by Target
Applications with data objects introduces substantial complexity
to the DECADE protocol. If Target Applications wish to associate
additional metadata with a data object, possible alternatives
include (1) managing such metadata within the Target Application
itself, (2) storing metadata inside of the data object, or (3)
storing metadata in a different data object at the DECADE server.
5. Storage Requirements
This section details the requirements of the underlying storage used
to support the DECADE protocol(s).
5.1. Immutable Data
REQUIREMENT(S): DECADE MUST only store and manage data objects that
are immutable once they are written to storage.
RATIONALE: Immutable data objects are an important simplification in
DECADE. Reasonable consistency models for updating existing
objects would significantly complicate implementation (especially
if implementation chooses to replicate data across multiple
Gu, et al. Expires May 3, 2012 [Page 17]
Internet-Draft DECADE Requirements October 2011
servers). If a user needs to update a resource, it can write a
new resource and then distribute the new resource instead of the
old one.
5.2. Explicit Deletion of 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
DECADE client should be able to explicitly remove particular
data. This may be implemented using existing protocols.
5.3. Multiple writing
REQUIREMENT(S): DECADE MUST NOT allow multiple simultaneous writers
for the same object. Implementations MUST raise an error to one
of the writers.
RATIONALE: This avoids data corruption in a simple way while
remaining efficient. Alternately, the DECADE server would need
to either manage locking, handle write collisions, or merge data,
all of which reduce efficiency and increase complexity.
5.4. Multiple reading
REQUIREMENT(S): DECADE MUST allow for multiple simultaneous 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.
5.5. 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 written). Appropriate
handling for error conditions (e.g., a disappearing writer) needs
to be specified.
Gu, et al. Expires May 3, 2012 [Page 18]
Internet-Draft DECADE Requirements October 2011
5.6. Hints concerning usage of written data
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 written to in-network storage. For example,
a P2P live streaming application may indicate to a DECADE server
that the objects are expected to have a short time-to-live, but
read frequently. The DECADE server may then opt to persist the
objects in memory instead of in disk.
5.7. Writing model
REQUIREMENT(S): DECADE storage MUST provide at least a writing model
(while writing an object) that appends data to data already
written.
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
written).
5.8. Storage Status
REQUIREMENT(S): A DECADE client MUST be able to read current
resource usage (including list of written data objects), 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. DECADE protocol(s) MUST support the ability
for a DECADE client to read aggregated resource usage information
(across all other clients to which it has authorized access), and
MAY support the ability to request this information for each
other authorized client.
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
Gu, et al. Expires May 3, 2012 [Page 19]
Internet-Draft DECADE Requirements October 2011
availability to better allocate them to remote clients. Due to
scalability issues, it is not required that DECADE support
returning usage information broken down by each remote client
which has been authorized access, but this feature may be useful
in certain deployment scenarios.
6. Discovery Requirements
6.1. Requirements
6.1.1. Locating DECADE Servers
REQUIREMENT(S): The DECADE Discovery mechanism MUST allow a DECADE
Client to identify one or more DECADE Servers to which it is
authorized to read/write data and to which it may authorize other
DECADE Clients to read/write data, or fail if no such DECADE
Servers are available.
RATIONALE: A basic goal of DECADE is to allow DECADE Clients to
read/write data for access by other DECADE Clients or itself.
Executing the Discovery process should result in a DECADE Client
finding a DECADE Server that it can use for these purposes. It
is possible that no such DECADE Servers are available. Note that
even if a DECADE Client may not successfully locate a DECADE
Server that fits these criteria, it may still read/write data
from/to a DECADE Server if authorized by another DECADE Client.
6.1.2. Support for Clients Behind NATs and Firewalls
REQUIREMENT(S): The Discovery mechanism MUST support DECADE Clients
operating behind NATs and Firewalls without requiring additional
network support (e.g., Application-level Gateways).
RATIONALE: NATs and Firewalls are prevalent in network deployments,
and it is common for Target Applications that include a DECADE
Client to be deployed behind these devices.
6.1.3. Prefer Existing Protocols
REQUIREMENT(S): The DECADE Server discovery mechanism SHOULD
leverage existing mechanisms and protocols wherever possible.
RATIONALE: Existing protocols such as DNS and DHCP are widespread.
Using existing protocols, or combinations of the protocols that
have been specified in other contexts, is strictly preferred over
developing a new discovery protocol for DECADE.
Gu, et al. Expires May 3, 2012 [Page 20]
Internet-Draft DECADE Requirements October 2011
7. Future Considerations
This section enumerates considerations that should be taken into
account during the DECADE design and implementation. They have been
intentionally omitted as requirements since they are either out of
scope or implementation-dependent. Nevertheless, enumerating them
may help to guide future application of the requirements included in
this document.
7.1. Fairness
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. Removal of Duplicate Data Objects
There are actually two possible scenarios. 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, a DECADE server may implement internal mechanisms to
monitor for duplicate objects and use internal mechanisms to prevent
duplication in internal storage.
The second scenario is removing duplicates across a distributed set
of DECADE servers. DECADE does not explicitly design for this, but
does offer a redirection mechanism (Section 4.1.3.5) that is one
primitive that may be used to support this feature in certain
deployment scenarios.
7.3. Gaming of the Resource Control Mechanism
The particular resource control policy communicated by a DECADE
protocol and enforced by the scheduling system of a DECADE
implementation may be open to certain gaming by clients. for example
by specifying many small peers to increase total throughput or
inciting overload conditions at a DECADE server. Identifying and
protecting against all such opportunities for gaming is outside the
scope of this document, but DECADE protocol(s) and implementations
SHOULD be aware that opportunities to game the system may be
attempted.
8. Security Considerations
The security model is an important component of DECADE. It is
Gu, et al. Expires May 3, 2012 [Page 21]
Internet-Draft DECADE Requirements October 2011
crucial for users to be able to manage and limit distribution of
content to only authorized parties, and the mechanism needs to work
on the general Internet which spans multiple administrative and
security domains. Previous sections have enumerated detailed
requirements, but this section discusses the overall approach and
other considerations that do not merit requirements.
8.1. Authentication and Authorization
DECADE only uses authentication when allowing a particular client to
access its own storage at a server. DECADE servers themselves do not
authenticate other clients which are reading/writing a client's own
storage. Instead, DECADE relies on clients to authenticate others to
access its storage, and then communicate the result of that
authentication to the DECADE server so that the DECADE server may
implement the necessary authorization checks.
8.2. Encrypted Data
DECADE Servers provide the ability to write raw data objects (subject
to any policies instituted by the owner/administrator of the DECADE
server, which are outside of the scope of this document). Thus,
DECADE clients may opt to encrypt data before it is written to the
DECADE Server. However, DECADE itself does not provide encryption of
data objects other than is provided by Section 4.1.2.1.
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]
Song, H., Zong, N., Yang, Y., and R. Alimi, "DECoupled
Application Data Enroute (DECADE) Problem Statement",
draft-ietf-decade-problem-statement-03 (work in progress),
March 2011.
[I-D.ietf-decade-arch]
Gu, et al. Expires May 3, 2012 [Page 22]
Internet-Draft DECADE Requirements October 2011
Alimi, R., Yang, Y., Rahman, A., Kutscher, D., and H. Liu,
"DECADE Architecture", draft-ietf-decade-arch-02 (work in
progress), July 2011.
[LLSB08] Levin, D., LaCurts, K., Spring, N., and B. Bhattacharjee,
"BitTorrent is an Auction: Analyzing and Improving
BitTorrent's Incentives", SIGCOMM 2008, August 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, Borje Ohlman, Dirk Kutscher, Akbar Rahman, Xiao Zhu,
Yunfei Zhang, and Jin Peng for contributions 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
Polycom, Inc.
Email: dbryan@ethernot.org
Yang Richard Yang
Yale University
Email: yry@cs.yale.edu
Gu, et al. Expires May 3, 2012 [Page 23]
Internet-Draft DECADE Requirements October 2011
Richard Alimi
Google
Email: ralimi@google.com
Gu, et al. Expires May 3, 2012 [Page 24]