Internet DRAFT - draft-alimi-protocol
draft-alimi-protocol
APPSAWG R. Alimi
Internet-Draft Google
Intended status: Informational A. Rahman
Expires: December 12, 2013 InterDigital Communications, LLC
D. Kutscher
NEC
Y. Yang
Yale University
H. Song
K. Pentikousis
Huawei Technologies
June 10, 2013
DECADE: DECoupled Application Data Enroute
draft-alimi-protocol-01
Abstract
Content distribution applications, such as those those employing
peer-to-peer (P2P) technologies, are widely used on the Internet and
make up a large portion of the traffic in many networks. Often,
however, content distribution applications use network resources in a
counter-productive manner. One way to improve efficiency is to
introduce storage capabilities within the network and enable
cooperation between end-host and in-network content distribution
mechanisms. This is the capability provided by a DECADE-compatible
system, which is introduced in this document. DECADE enables
applications to take advantage of in-network storage when
distributing data objects as opposed to using solely end-to-end
resources. This document presents the underlying principles and key
functionalities of such a system and illustrates operation through a
set of examples.
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2013 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Architectural Principles . . . . . . . . . . . . . . . . . . 5
2.1. Data and Control/Metadata Plane Decoupling . . . . . . . 5
2.2. Immutable Data Objects . . . . . . . . . . . . . . . . . 6
2.3. Data Object Identifiers . . . . . . . . . . . . . . . . . 7
2.4. Explicit Control . . . . . . . . . . . . . . . . . . . . 8
2.5. Resource and Data Access Control through Delegation . . . 8
3. System Components . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Content Distribution Application . . . . . . . . . . . . 9
3.2. DECADE Client . . . . . . . . . . . . . . . . . . . . . . 10
3.3. DECADE Server . . . . . . . . . . . . . . . . . . . . . . 11
3.4. Data Sequencing and Naming . . . . . . . . . . . . . . . 12
3.5. Token-based Authorization and Resource Control . . . . . 13
3.6. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 14
4. DECADE Protocol Design . . . . . . . . . . . . . . . . . . . 15
4.1. Naming . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2. Resource Protocol . . . . . . . . . . . . . . . . . . . . 15
4.3. Data Transfer . . . . . . . . . . . . . . . . . . . . . . 19
4.4. Server-to-Server Protocols . . . . . . . . . . . . . . . 19
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5. In-Network Storage Components Mapping to DECADE . . . . . . . 20
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
6.1. Threat: System Denial of Service Attacks . . . . . . . . 21
6.2. Threat: Authorization Mechanisms Compromised . . . . . . 22
6.3. Threat: Data Object Spoofing . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
9. Informative References . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Content distribution applications, such as peer-to-peer (P2P)
applications, are widely used on the Internet to distribute data
objects, and comprise a large portion of the traffic in many
networks. Said applications can often introduce performance
bottlenecks in otherwise well-provisioned networks. In some cases,
operators are forced to invest substantially in infrastructure to
accommodate the use of such applications. For instance, in many
subscriber networks, it can be expensive to upgrade network equipment
in the "last-mile", because it can involve replacing equipment and
upgrading wiring and devices at individual homes, businesses,
DSLAMs(Digital Subscriber Line Access Multiplexers) and CMTSs (Cable
Modem Termination Systems) in remote locations. It may be more
practical and economical to upgrade the core infrastructure, instead
of the edge part of the network, as this involves fewer components
that are shared by many subscribers. See [RFC6646] and [RFC6392] for
a more complete discussion of the problem domain and general
discussions of the capabilities envisioned for a DECADE system.
This document presents mechanisms for providing in-network storage
that can be integrated into content distribution applications. The
primary focus is P2P-based content distribution, but DECADE may be
useful to other applications with similar characteristics and
requirements. The approach we adopt in this document is to define
the core functionalities and protocol functions that are needed to
support a DECADE system. This document provides illustrative
examples so that implementers can understand the main concepts in
DECADE, but it is generally assumed that readers are familiar with
the terms and concepts used in [RFC6646] and [RFC6392].
Figure 1 is a schematic of a simple DECADE system with two DECADE
clients and two DECADE servers. As illustrated, a client uses the
DECADE Resource Protocol (DRP) to convey to a server information
related to access control and resource scheduling policies. DRP can
also be used between servers for exchanging this type of information.
A DECADE system employs standard data transfer (SDT) protocol(s) to
transfer data objects to and from a server, as we will explain later.
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Native Application
.-------------. Protocol(s) .-------------.
| Application | <------------------> | Application |
| End-Point | | End-Point |
| | | |
| .--------. | | .--------. |
| | DECADE | | | | DECADE | |
| | Client | | | | Client | |
| `--------' | | `--------' |
`-------------' `-------------'
| ^ | ^
DECADE | | Standard | |
Resource | | Data DRP | | SDT
Protocol | | Transfer | |
(DRP) | | (SDT) | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
v V v V
.=============. DRP .=============.
| DECADE | <------------------> | DECADE |
| Server | <------------------> | Server |
`=============' SDT `============='
Figure 1: DECADE Overview
With Figure 1 at hand, assume that Application End-Point B requests a
data object from Application End-Point A. In this case, End-Point A
will act as the sender and End-Point B as the receiver for said data
object. Let S(A) denote the DECADE storage server to which A has
access. Figure 2 illustrates the four steps involved in the request,
starting with the initial contact between B and A during which the
former requests a data object using their native application protocol
(see Section 3.1). Next, A uses DRP to obtain a token corresponding
to the data object that was requested by B. There may be several ways
for A to obtain such a token, e.g., compute it locally or request one
from its DECADE storage server, S(A); see Section 4.2.1 for more
details. Once obtained, A then provides the token to B (again, using
their native application protocol). Finally, B provides the received
token to S(A) via DRP, and subsequently requests and downloads the
data object via SDT.
.----------.
2. Obtain --------> | S(A) | <------
Token / `----------' \ 4. Request and
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(DRP) / \ Download Data
Locally / \ Object
or From / \ (DRP + SDT)
S(A) v 1. App Request v
.-------------. <--------------------------- .-------------.
| Application | | Application |
| End-Point A | | End-Point B |
`-------------' ---------------------------> `-------------'
3. App Response (token)
Figure 2: Download from Storage Server
2. Architectural Principles
This section presents the key principles followed by any DECADE
system.
2.1. Data and Control/Metadata Plane Decoupling
A DECADE system aims to be application-independent and SHOULD support
multiple content distribution applications. Typically, a complete
content distribution application implements a set of control plane
functions including content search, indexing and collection, access
control, replication, request routing, and QoS scheduling.
Implementers of different content distribution applications may have
unique considerations when designing the control plane functions.
For example, with respect to the metadata management scheme,
traditional file systems provide a standard metadata abstraction: a
recursive structure of directories to offer namespace management
where each file is an opaque byte stream. Content distribution
applications may use different metadata management schemes. For
instance, one application might use a sequence of blocks (e.g., for
file sharing), while another application might use a sequence of
frames (with different sizes) indexed by time.
With respect to resource scheduling algorithms, a major advantage of
many successful P2P systems is their substantial expertise in
achieving efficient utilization of peer resources. For instance,
many streaming P2P systems include optimization algorithms for
constructing overlay topologies that can support low-latency, high-
bandwidth streaming. The research community as well as implementers
of such systems continuously fine-tune existing algorithms and invent
new ones. A DECADE system should be able to accommodate and benefit
from all new developments.
In short, given the diversity of control plane functions, a DECADE
system should allow for as much flexibility as possible to the
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control plane to implement specific policies. This conforms to the
end-to-end systems principle and allows innovation and satisfaction
of specific performance goals. Decoupling the control plane from the
data plane is not new, of course. For example, OpenFlow is an
implementation of this principle for Internet routing, where the
computation of the forwarding table and the application of the
forwarding table are separated. The Google File System
[GoogleFileSystem] applies the same principle to file system design
by utilizing a Master to handle meta-data management and several
Chunk servers to handle data plane functions (i.e., read and write of
chunks of data). Finally, NFSv4.1's pNFS extension [RFC5661] also
adheres to this principle.
2.2. Immutable Data Objects
A common property of bulk content to be broadly distributed is that
it is immutable -- once content is generated, it is typically not
modified. For example, once a movie has been edited and released for
distribution it is very uncommon that the corresponding video frames
and images need to be modified. The same applies to document
distribution, such as RFCs, audio files, such as podcasts, and
program patches. Focusing on immutable data can substantially
simplify data plane design, since consistency requirements can be
relaxed. It also simplifies data reuse and implementation of de-
duplication.
Depending on its specific requirements, an application may store
immutable data objects in DECADE servers such that each data object
is completely self-contained (e.g., a complete, independently
decodable video segment). An application may also divide data into
data objects that require application level assembly. Many content
distribution applications divide bulk content into data objects for
multiple reasons, including (a) fetching different data objects from
different sources in parallel; and (b) faster recovery and
verification as individual data objects might be recovered and
verified. Typically, applications use a data object size larger than
a single packet in order to reduce control overhead.
A DECADE system SHOULD be agnostic to the nature of the data objects
and SHOULD NOT specify a fixed size for them. A protocol
specification based on this architecture MAY prescribe requirements
on minimum and maximum sizes for compliant implementations.
Note that immutable data objects can still be deleted. Applications
can support modification of existing data stored at a DECADE server
through a combination of storing new data objects and deleting
existing data objects. For example, a meta-data management function
of the control plane might associate a name with a sequence of
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immutable data objects. If one of the data objects is modified, the
meta-data management function changes the mapping of the name to a
new sequence of immutable data objects.
Throughout this document, all data objects are assumed to be
immutable.
2.3. Data Object Identifiers
A data object stored in a DECADE server SHALL be accessed by content
consumers via a data object identifier. Each content consumer may be
able to access more than one storage server. A data object that is
replicated across different storage servers managed by a DECADE
Storage Provider MAY be accessed through a single identifier. Since
data objects are immutable, it SHALL be possible to support
persistent identifiers for data objects.
Data object identifiers SHOULD be created by content providers when
uploading the corresponding objects to a DECADE server. The scheme
for the assignment/derivation of the data object identifier to a data
object depends as the data object naming scheme and is out of scope
of this document. One possibility is to name data objects using
hashes as described in [RFC6920]. Note that this document describes
naming schemes on a semantic level only but specific SDTs and DRPs
will use specific representations.
In particular, for some applications it is important that clients and
servers are able to validate the name-object binding, i.e., by
verifying that a received object really corresponds to the name
(identifier) that was used for requesting it (or that was provided by
a sender). Data object identifiers can support name-object binding
validation by providing message digests or so-called self-certifying
naming information -- if a specific application has this requirement.
Different name-object binding validation mechanisms MAY be supported
in a single DECADE system. Content distribution applications can
decide what mechanism to use, or to not provide name-object
validation (e.g., if authenticity and integrity can by ascertained by
alternative means). We expect that applications may be able to
construct unique names (with high probability) without requiring a
registry or other forms of coordination. Names may be self-
describing so that a receiving entity (i.e. the content consumer)
understands, for example, which hash function to use for validating
name-object binding.
Some content distribution applications will derive the name of a data
object from the hash over the data object, which is made possible by
the fact that DECADE objects are immutable. But there may be other
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applications such as live streaming where object names will not based
on hashes but rather on an enumeration scheme. The naming scheme
will also enable those applications to construct unique names.
In order to enable the uniqueness, flexibility and self-describing
properties, the naming scheme used in a DECADE system SHOULD provide
a "type" field that indicates the name-object validation function
type (for example, "sha-256") and the cryptographic data (such as an
object hash) that corresponds to the type information. Moreover, the
naming scheme MAY additionally provide application or publisher
information.
The specific format of the name (e.g., encoding, hash algorithms,
etc.) is out of scope of this document.
2.4. Explicit Control
To support the functions of an application's control plane,
applications SHOULD be able to keep track and coordinate which data
is stored at particular servers. Thus, in contrast with traditional
caches, applications are given explicit control over the placement
(selection of a DECADE server), deletion (or expiration policy), and
access control for stored data objects. Consider deletion/expiration
policy as a simple example. An application might require that a
DECADE server stores data objects for a relatively short period of
time (e.g., for live-streaming data). Another application might need
to store data objects for a longer duration (e.g., for video-on-
demand), and so on.
2.5. Resource and Data Access Control through Delegation
A DECADE system provides a shared infrastructure to be used by
multiple content consumers and content providers spanning multiple
content distribution applications. Thus, it needs to provide both
resource and data access control, as discussed in the following
subsections.
2.5.1. Resource Allocation
There are two primary interacting entities in a DECADE system.
First, in-network storage providers coordinate DECADE server
provisioning, including their total available resource; see
Section 4.2.1. Second, applications coordinate data transfers
amongst available DECADE servers and between servers and clients. A
form of isolation is required to enable concurrently-running
applications to each explicitly manage its own data objects and share
of resources at the available servers. Therefore, a storage provider
should delegate resource management on a DECADE server to content
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providers, enabling them to explicitly and independently manage their
own share of resources on a server.
2.5.2. User Delegation
In-network storage providers will have the ability to explicitly
manage the entities allowed to utilize the resources available on a
DECADE server. This is needed for reasons such as capacity-planning
and legal considerations in certain deployment scenarios. The DECADE
server SHOULD grant a share of the resources to the DECADE client of
a content provider or content consumer. The client can in turn share
the granted resources amongst its (possibly) multiple applications.
The share of resources granted by a server is called a User
Delegation. As a simple example, a DECADE server operated by an ISP
might be configured to grant each ISP subscriber 1.5 Mb/s of network
capacity. The ISP subscriber might in turn divide this share of
resources amongst a video streaming application and file-sharing
application which are running concurrently.
3. System Components
As noted earlier, the primary focus of this document is the
architectural principles and the system components that implement
them. While specific system components might differ between
implementations, this document details the major components and their
overall roles in the architecture. To keep the scope narrow, we only
discuss the primary components related to protocol development.
Particular deployments will require additional components (e.g.,
monitoring and accounting at a server), but they are intentionally
omitted from this document.
3.1. Content Distribution Application
Content distribution applications have many functional components.
For example, many P2P applications have components and algorithms to
manage overlay topology, rate allocation, piece selection, and so on.
In this document, we focus on the components directly engaged in a
DECADE system. Figure 3 illustrates the components discussed in this
section from the perspective of a single Application End-Point.
Native Protocol(s)
(with other Application End-Points)
.--------------------->
|
|
.----------------------------------------------------------------.
| Application End-Point |
| .-------------------. .-------------------. |
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| | Application-Layer | ... | App Data Assembly | |
| | Algorithms | | Sequencing | |
| `-------------------' `-------------------' |
| |
| .==========================================================. |
| | DECADE Client | |
| | .-------------------------. .--------------------------. | |
| | | Resource Controller | | Data Controller | | |
| | | .--------. .----------. | | .------------. .-------. | | |
| | | | Data | | Resource | | | | Data | | Data | | | |
| | | | Access | | Sharing | | | | Scheduling | | Index | | | |
| | | | Policy | | Policy | | | | | | | | | |
| | | '--------' `----------' | | `------------' `-------' | | |
| | `-------------------------' `--------------------------' | |
| | | ^ | |
| `== | ============================== | ====================' |
`----- | ------------------------------ | -----------------------'
| |
| DECADE Resource Protocol (DRP) | Standard Data Transfer
v V
Figure 3: Application and DECADE Client Components
A DECADE system is geared towards supporting applications that can
distribute content using data objects. To accomplish this,
applications can include a component responsible for creating the
individual data objects before distribution and then re-assembling
data objects at the content consumer. We call this component
Application Data Assembly. In producing and assembling data objects,
two important considerations are sequencing and naming. A DECADE
system assumes that applications implement this functionality
themselves. See Section 4.1 for further discussion. In addition to
DECADE DRP/SDT, applications will most likely also support other,
native application protocols (e.g., P2P control and data transfer
protocols).
3.2. DECADE Client
The DECADE client provides the local support to an application, and
can be implemented standalone, embedded into the application, or
integrated in other entities such as network devices themselves. In
general, applications may have different Resource Sharing Policies
and Data Access Policies to control their resource and data in DECADE
servers. These policies may be existing policies of applications or
custom policies. The specific implementation is decided by the
application.
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Recall that DECADE decouples the control and the data transfer of
applications. A Data Scheduling component schedules data transfers
according to network conditions, available servers, and/or available
server resources. The Data Index indicates data available at remote
servers. The Data Index (or a subset of it) can be advertised to
other clients. A common use case for this is to provide the ability
to locate data amongst distributed Application End-Points (i.e., a
data search mechanism such as a Distributed Hash Table).
3.3. DECADE Server
Figure 4 illustrates the primary components of a DECADE server. Note
that the description below does not assume a single-host or
centralized implementation: a DECADE server is not necessarily a
single physical machine but can also be implemented in a distributed
manner on a cluster of machines.
| DECADE Resource | Standard Data Transfer
| Protocol (DRP) |
| |
.= | ================= | ===========================.
| | v DECADE Server |
| | .----------------. |
| |----> | Access Control | <--------. |
| | `----------------' | |
| | ^ | |
| | | | |
| | v | |
| | .---------------------. | |
| `-> | Resource Scheduling | <------| |
| `---------------------' | |
| ^ | |
| | | |
| v .-----------------. |
| .-----------------. | User Delegation | |
| | Data Store | | Management | |
| `-----------------' `-----------------' |
`==================================================='
Figure 4: DECADE Server Components
Provided sufficient authorization, a client SHALL be able to access
its own data or other client's data in a DECADE server. Clients MAY
also authorize other clients to store data. If access is authorized
by a client, the server SHOULD provide access. Applications may
apply resource sharing policies or use a custom policy. DECADE
Servers will then perform resource scheduling according to the
resource sharing policies indicated by the client as well as any
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other previously configured User Delegations. Data from applications
will be stored at a DECADE server. Data may be deleted from storage
either explicitly or automatically (e.g., after a TTL expiration).
3.4. Data Sequencing and Naming
The DECADE naming scheme implies no sequencing or grouping of
objects, even if this is done at the application layer. To
illustrate these properties, this section presents several
illustrative examples of use.
3.4.1. Application with Fixed-Size Chunks
Similar to the example in Section 3.1, consider an application in
which each individual application-layer segment of data is called a
"chunk" and has a name of the form: "CONTENT_ID:SEQUENCE_NUMBER".
Furthermore, assume that the application's native protocol uses
chunks of size 16 KB. Now, assume that this application wishes to
store data in a DECADE server in data objects of size 64 KB. To
accomplish this, it can map a sequence of 4 chunks into a single data
object, as shown in Figure 5.
Application Chunks
.---------.---------.---------.---------.---------.---------.--------
| | | | | | |
| Chunk_0 | Chunk_1 | Chunk_2 | Chunk_3 | Chunk_4 | Chunk_5 | Chunk_6
| | | | | | |
`---------`---------`---------`---------`---------`---------`--------
DECADE Data Objects
.---------------------------------------.----------------------------
| |
| Object_0 | Object_1
| |
`---------------------------------------`----------------------------
Figure 5: Mapping Application Chunks to DECADE Data Objects
In this example, the application maintains a logical mapping that is
able to determine the name of a DECADE data object given the chunks
contained within that data object. The name may be conveyed from
either the original content provider, another End-Point with which
the application is communicating, etc. As long as the data contained
within each sequence of chunks is globally unique, the corresponding
data objects have globally unique names.
3.4.2. Application with Continuous Streaming Data
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Consider an application whose native protocol retrieves a continuous
data stream (e.g., an MPEG2 stream) instead of downloading and
redistributing chunks of data. Such an application could segment the
continuous data stream to produce either fixed-sized or variable-
sized data objects. Figure 6 depicts how a video streaming
application might produce variable-sized data objects such that each
data object contains 10 seconds of video data. Similarly with the
previous example, the application may maintain a mapping that is able
to determine the name of a data object given the time offset of the
video chunk.
Application's Video Stream
.--------------------------------------------------------------------
|
|
|
`--------------------------------------------------------------------
^ ^ ^ ^ ^
| | | | |
0 Seconds 10 Seconds 20 Seconds 30 Seconds 40 Seconds
0 B 400 KB 900 KB 1200 KB 1500 KB
DECADE Data Objects
.--------------.--------------.--------------.--------------.--------
| | | | |
| Object_0 | Object_1 | Object_2 | Object_3 |
| (400 KB) | (500 KB) | (300 KB) | (300 KB) |
`--------------`--------------`--------------`--------------`--------
Figure 6: Mapping a Continuous Data Stream to DECADE Data Objects
3.5. Token-based Authorization and Resource Control
A key feature of a DECADE system is that an application endpoint can
authorize other application endpoints to store or retrieve data
objects from in-network storage. This is accomplished using an OAuth
[RFC6749] based authorization scheme. A separate OAuth flow can be
used for this purpose: a client authenticates with the application
server or the P2P application peer, and requests the trusted by the
client, and the token contains particular self-contained properties
(see Section 4.2.1 for details). The client then uses the token when
sending requests to the DECADE server. Upon receiving a token, the
server validates the signature and the operation being performed.
This is a simple scheme, but has some important advantages over an
alternative approach, for example, in which a client explicitly
manipulates an Access Control List (ACL) associated with each data
object. In particular, it has the following advantages when applied
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to DECADE target applications. First, authorization policies are
implemented within the application, thus it explicitly controls when
tokens are generated and to whom they are distributed and for how
long they will be valid. Second, fine-grained access and resource
control can be applied to data objects; see Section 4.2.1 for the
list of restrictions that can be enforced with a token. Third, there
is no messaging between a client and server to manipulate data object
permissions. This can simplify, in particular, applications which
share data objects with many dynamic peers and need to frequently
adjust access control policies attached to data objects. Finally,
tokens can provide anonymous access, in which a server does not need
to know the identity of each client that accesses it. This enables a
client to send tokens to clients belonging to other storage
providers, and allow them to read or write data objects from the
storage of its own storage provider. In addition to clients applying
access control policies to data objects, the server MAY be configured
to apply additional policies based on user, object properties,
geographic location, etc. A client might thus be denied access even
though it possesses a valid token.
There are existing protocols (e.g., OAuth [RFC6749]) that implement
similar referral mechanisms using tokens. A protocol specification
for a DECADE system SHOULD endeavor to use existing mechanisms
wherever possible.
3.6. Discovery
A DECADE system SHOULD include a discovery mechanism through which
clients locate an appropriate server. A discovery mechanism SHOULD
allow a client to determine an IP address or some other identifier
that can be resolved to locate the server for which the client will
be authorized to generate tokens (via DRP). (The discovery mechanism
might also result in an error if no such servers can be located.)
After discovering one or more servers, a client can distribute load
and requests across them (subject to resource limitations and
policies of the servers themselves) according to the policies of the
Application End-Point in which it is embedded. The discovery
mechanism outlined here does not provide the ability to locate
arbitrary DECADE servers to which a client might obtain tokens from
others. To do so will require application-level knowledge, and it is
assumed that this functionality is implemented in the content
distribution application.
The particular protocol used for discovery is out of scope of this
document, but any specification SHOULD re-use standard protocols
wherever possible.
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4. DECADE Protocol Design
This section presents the DRP and the SDT protocol in terms of
abstract protocol interactions that are intended to be mapped to
specific protocols in an implementation. In general, the DRP/SDT
functionality between a DECADE client-server are very similar to the
DRP/SDT functionality between server-server. Any differences are
highlighted below. DRP is used by a DECADE client to configure the
resources and authorization used to satisfy requests (reading,
writing, and management operations concerning data objects) at a
server. SDT will be used to transport data between a client and a
server, as illustrated in Figure 1.
4.1. Naming
A DECADE system SHOULD use [RFC6920] as the recommended and default
naming scheme. Other naming schemes that meet the guidelines in
Section 2.3 may alternatively be used. In order to provide a simple
and generic interface, the DECADE server will be responsible only for
storing and retrieving individual data objects.
The DECADE naming format SHOULD NOT attempt to replace any naming or
sequencing of data objects already performed by an Application.
Instead, naming is intended to apply only to data objects referenced
by DECADE-specific purposes. An application using a DECADE client
may use a naming and sequencing scheme independent of DECADE names.
The DECADE client SHOULD maintain a mapping from its own data objects
and their names to the DECADE-specific data objects and names.
Furthermore, the DECADE naming scheme implies no sequencing or
grouping of objects, even if this is done at the application layer.
4.2. Resource Protocol
DRP will provide configuration of access control and resource sharing
policies on DECADE servers. A content distribution application,
e.g., a live P2P streaming session, can have permission to manage
data at several servers, for instance, servers belonging to different
storage providers. DRP allows one instance of such an application,
i.e., an Application End-Point, to apply access control and resource
sharing policies on each of them.
On a single DECADE server, the following resources SHOULD be managed:
a) communication resources in terms of bandwidth (upload/download)
and also in terms of number of active clients (simultaneous
connections); and b) storage resources.
4.2.1. Access and Resource Control Token
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As in DECADE system, the resource owner agent is always the same
entity or co-located with the authorization server, so we use a
separate OAuth 2.0 request and response flow for the access and
resource control token.
An OAuth request to access the data objects MUST include the
following fields:
response_type: REQUIRED. Value MUST be set to "token".
client_id: the client_id indicates either the application that is
using the DECADE service or the end user who is using the DECADE
service from a DECADE storage service provider. DECADE storage
service providers MUST provide the ID distribution and management
function, which is out of the scope of this document.
scope: data object names that are requested.
An OAuth response includes the following information:
token_type: "Bearer"?
expires_in: The lifetime in seconds of the access token.
access_token: a token denotes the following information.
service URI: the server address or URI which is providing the
service;
Permitted operations (e.g., read, write) and objects (e.g., names
of data objects that might be read or written);
Priority: optional. If it is presented, value MUST be set to be
either "Urgent", "High", "Normal" or "Low".
Bandwidth: given to requested operation, a weight value used in a
weighted bandwidth sharing scheme, or a integer in number of bps;
Amount: data size in number of bytes that might be read or
written.
token_signature: the signature of the access token.
The tokens SHOULD be generated by an entity trusted by both the
DECADE client and the server at the request of a DECADE client. For
example, this entity could be the client, a server trusted by the
client, or another server managed by a storage provider and trusted
by the client. It is important for a server to trust the entity
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generating the tokens since each token may incur a resource cost on
the server when used. Likewise, it is important for a client to
trust the entity generating the tokens since the tokens grant access
to the data stored at the server.
Upon generating a token, a client can distribute it to another client
(e.g., via their native application protocol). The receiving client
can then connect to the server specified in the token and perform any
operation permitted by the token. The token SHOULD be sent along
with the operation. The server SHOULD validate the token to identify
the client that issued it and whether the requested operation is
permitted by the contents of the token. If the token is successfully
validated, the server SHOULD apply the resource control policies
indicated in the token while performing the operation.
Tokens SHOULD include a unique identifier to allow a server to detect
when a token is used multiple times and reject the additional usage
attempts. Since usage of a token incurs resource costs to a server
(e.g., bandwidth and storage) and a Content Provider may have a
limited budget (see Section 2.5), the Content Provider should be able
to indicate if a token may be used multiple times.
It SHOULD be possible to revoke tokens after they are generated.
This could be accomplished by supplying the server the unique
identifiers of the tokens which are to be revoked.
4.2.2. Status Information
DRP SHOULD provide a status request service that clients can use to
request status information of a server. Access to such status
information SHOULD require client authorization; that is, clients
need to be authorized to access the requested status information.
This authorization is based on the user delegation concept as
described in Section 2.5. The following status information elements
SHOULD be obtained: a) list of associated data objects (with
properties); and b) resources used/available. In addition, the
following information elements MAY be available: c) list of servers
to which data objects have been distributed (in a certain time-
frame); and d) list of clients to which data objects have been
distributed (in a certain time-frame).
For the list of servers/clients to which data objects have been
distributed to, the server SHOULD be able to decide on time bounds
for which this information is stored and specify the corresponding
time frame in the response to such requests. Some of this
information may be used for accounting purposes, e.g., the list of
clients to which data objects have been distributed.
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Access information MAY be provided for accounting purposes, for
example, when content providers are interested in access statistics
for resources and/or to perform accounting per user. Again, access
to such information requires client authorization and SHOULD based on
the delegation concept as described in Section 2.5. The following
type of access information elements MAY be requested: a) what data
objects have been accessed by whom and for how many times; and b)
access tokens that a server as seen for a given data object.
The server SHOULD decide on time bounds for which this information is
stored and specify the corresponding time frame in the response to
such requests.
4.2.3. Data Object Attributes
Data Objects that are stored on a DECADE server SHOULD have
associated attributes (in addition to the object identifier and data
object) that relate to the data storage and its management. These
attributes may be used by the server (and possibly the underlying
storage system) to perform specialized processing or handling for the
data object, or to attach related server or storage-layer properties
to the data object. These attributes have a scope local to a server.
In particular, these attributes SHOULD NOT be applied to a server or
client to which a data object is copied.
Depending on authorization, clients SHOULD be permitted to get or set
such attributes. This authorization is based on the delegation as
per Section 2.5. DECADE does not limit the set of permissible
attributes, but rather specifies a set of baseline attributes that
SHOULD be supported:
Expiration Time: Time at which the data object can be deleted;
Data Object size: In bytes;
Media type Labelling of type as per [RFC6838];
Access statistics: How often the data object has been accessed (and
what tokens have been used).
The data object attributes defined here are distinct from application
metadata (see Section 2.1). Application metadata is custom
information that an application might wish to associate with a data
object to understand its semantic meaning (e.g., whether it is video
and/or audio, its playback length in time, or its index in a stream).
If an application wishes to store such metadata persistently, it can
be stored within data objects themselves.
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4.3. Data Transfer
A DECADE server will provide a data access interface, and SDT will be
used to write data objects to a server and to read (download) data
objects from a server. Semantically, SDT is a client-server
protocol; that is, the server always responds to client requests.
To write a data object, a client first generates the object's name
(see Section 4.1), and then uploads the object to a server and
supplies the generated name. The name can be used to access
(download) the object later; for example, the client can pass the
name as a reference to other clients that can then refer to the
object. Data objects can be self-contained objects such as
multimedia resources, files etc., but also chunks, such as chunks of
a P2P distribution protocol that can be part of a containing object
or a stream. If supported, a server can verify the integrity and
other security properties of uploaded objects.
A client can request named data objects from a server. In a
corresponding request message, a client specifies the object name and
a suitable access and resource control token. The server checks the
validity of the received token and its associated resource usage-
related properties. If the named data object exists on the server
and the token can be validated, the server delivers the requested
object in a response message. If the data object cannot be delivered
the server provides a corresponding status/reason information in a
response message. Specifics regarding error handling, including
additional error conditions (e.g., overload), precedence for returned
errors and its relation with server policy, are deferred to eventual
protocol specification.
4.4. Server-to-Server Protocols
An important feature of a DECADE system is the capability for one
server to directly download data objects from another server. This
capability allows applications to directly replicate data objects
between servers without requiring end-hosts to use uplink capacity to
upload data objects to a different server.
DRP and SDT SHOULD support operations directly between servers.
Servers are not assumed to trust each other nor are configured to do
so. All data operations are performed on behalf of clients via
explicit instruction. However, the objects being processed do not
necessarily have to originate or terminate at the client (i.e., the
data object might be limited to being exchanged between servers even
if the instruction is triggered by the client). Clients thus will be
able to indicate to a server which remote server(s) to access, what
operation is to be performed, the content provider at the remote
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server from which to retrieve the data object, or in which the object
is to be stored, and the credentials indicating access and resource
control to perform the operation at the remote server.
Server-to-server support is focused on reading and writing data
objects between servers. The data object referred to at the remote
server is the same as the original data object requested by the
client. Object attributes (see Section 4.2.3) might also be
specified in the request to the remote server. In this way, a server
acts as a proxy for a client, and a client can instantiate requests
via that proxy. The operations will be performed as if the original
requester had its own client co-located with the server. When a
client sends a request to a server with these additional parameters,
it is giving the server permission to act (proxy) on its behalf.
Thus, it would be prudent for the supplied token to have narrow
privileges (e.g., limited to only the necessary data objects) or
validity time (e.g., a small expiration time).
In the case of a retrieval operation, the server is to retrieve the
data object from the remote server using the specified credentials,
and then optionally return the object to a client. In the case of a
storage operation, the server is to store the object to the remote
server using the specified credentials. The object might optionally
be uploaded from the client or might already exist at the server.
5. In-Network Storage Components Mapping to DECADE
This section evaluates how the basic components of an in-network
storage system (see Section 3 of [RFC6392]) map into a DECADE system.
With respect to Data Access Interface, DECADE clients can read and
write objects of arbitrary size through the client's Data Controller,
making use of standard data transfer (SDT). With respect to Data
Management Operations, clients can move or delete previously stored
objects via the client's Data Controller, making use of SDT. Clients
can enumerate or search contents of servers to find objects matching
desired criteria through services provided by the Content
Distribution Application (e.g., buffer-map exchanges, a DHT, or peer-
exchange). In doing so, Application End-Points might consult their
local Data Index in the client's Data Controller (Data Search
Capability).
With respect to Access Control Authorization, all methods of access
control are supported: public-unrestricted, public-restricted and
private. Access Control Policies are generated by a content
distribution application and provided to the client's Resource
Controller. The server is responsible for implementing the access
control checks. Clients can manage the resources (e.g., bandwidth)
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on the DECADE server that can be used by other Application End-Points
(Resource Control Interface). Resource Sharing Policies are
generated by a content distribution application and provided to the
client's Resource Controller. The server is responsible for
implementing the resource sharing policies.
Although the particular protocol used for discovery is outside the
scope of this document, different options and considerations have
been discussed in Section 3.6. Finally with respect to the storage
mode, DECADE servers provide an object-based storage mode. Immutable
data objects might be stored at a server. Applications might
consider existing blocks as data objects, or they might adjust block
sizes before storing in a server.
6. Security Considerations
In general, the security considerations mentioned in [RFC6646] apply
to this document as well. A DECADE system provides a distributed
storage service for content distribution and similar applications.
The system consists of servers and clients that use these servers to
upload data objects, to request distribution of data objects, and to
download data objects. Such a system is employed in an overall
application context -- for example in a P2P application, and it is
expected that DECADE clients take part in application-specific
communication sessions. The security considerations here focus on
threats related to the DECADE system and its communication services,
i.e., the DRP/SDT protocols that have been described in an abstract
fashion in this document.
6.1. Threat: System Denial of Service Attacks
A DECADE network might be used to distribute data objects from one
client to a set of servers using the server-to-server communication
feature that a client can request when uploading an object; see
Section 4.4. Multiple clients uploading many objects at different
servers at the same time and requesting server-to-server distribution
for them could thus mount massive distributed denial of service
(DDOS) attacks, overloading a network of servers. This threat is
addressed by the server's access control and resource control
framework. Servers can require Application End-Points to be
authorized to store and to download objects, and Application End-
Points can delegate authorization to other Application End-Points
using the token mechanism. Of course the effective security of this
approach depends on the strength of the token mechanism. See below
for a discussion of this and related communication security threats.
Denial of Service Attacks against a single server (directing many
requests to that server) might still lead to considerable load for
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processing requests and invalidating tokens. SDT therefore MUST
provide a redirection mechanism.
6.2. Threat: Authorization Mechanisms Compromised
A DECADE system does not require Application End-Points to
authenticate in order to access a server for downloading objects,
since authorization is not based on End-Point or user identities but
on a delegation-based authorization mechanism. Hence, most protocol
security threats are related to the authorization scheme. The
security of the token mechanism depends on the strength of the token
mechanism and on the secrecy of the tokens. A token can represent
authorization to store a certain amount of data, to download certain
objects, to download a certain amount of data per time etc. If it is
possible for an attacker to guess, construct or simply obtain tokens,
the integrity of the data maintained by the servers is compromised.
This is a general security threat that applies to authorization
delegation schemes. Specifications of existing delegation schemes
such as [RFC6749] discuss these general threats in detail. We can
say that the DRP has to specify appropriate algorithms for token
generation. Moreover, authorization tokens should have a limited
validity period that should be specified by the application. Token
confidentiality should be provided by application protocols that
carry tokens, and the SDT and DRP should provide secure
(confidential) communication modes.
6.3. Threat: Data Object Spoofing
In a DECADE system, an Application End-Point is referring other
Application End-Points to servers to download a specified data
objects. An attacker could "inject" a faked version of the object
into this process, so that the downloading End-Point effectively
receives a different object (compared to what the uploading End-Point
provided). As result, the downloading End-Point believes that is has
received an object that corresponds to the name it was provided
earlier, whereas in fact it is a faked object. Corresponding attacks
could be mounted against the application protocol (that is used for
referring other End-Points to servers), servers themselves (and their
storage sub-systems), and the SDT by which the object is uploaded,
distributed and downloaded.
A DECADE systems fundamental mechanism against object spoofing is
name-object binding validation, i.e., the ability of a receiver to
check whether the name he was provided and that he used to request an
object, actually corresponds to the bits he received. As described
above, this allows for different forms of name-object binding, for
example using hashes of data objects, with different hash functions
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(different algorithms, different digest lengths). For those
application scenarios where hashes of data objects are not applicable
(for example live-streaming) other forms of name-object binding can
be used (see Section 4.1). This flexibility also addresses
cryptographic algorithm evolution: hash functions might get
deprecated, better alternatives might be invented etc., so that
applications can choose appropriate mechanisms meeting their security
requirements.
DECADE servers MAY perform name-object binding validation on stored
objects, but Application End-Points MUST NOT rely on that. In other
words, Application End-Points SHOULD perform name-object binding
validation on received objects.
7. IANA Considerations
This document does not have any IANA considerations.
8. Acknowledgments
We thank the following people for their contributions to and/or
detailed reviews of this or earlier versions of this document:
Carsten Bormann, David Bryan, Dave Crocker, Yingjie Gu, David
Harrington, Hongqiang (Harry) Liu, David McDysan, Borje Ohlman,
Martin Stiemerling, Richard Woundy, and Ning Zong.
9. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File
System (NFS) Version 4 Minor Version 1 Protocol", RFC
5661, January 2010.
[RFC6392] Alimi, R., Rahman, A., and Y. Yang, "A Survey of In-
Network Storage Systems", RFC 6392, October 2011.
[RFC6646] Song, H., Zong, N., Yang, Y., and R. Alimi, "DECoupled
Application Data Enroute (DECADE) Problem Statement", RFC
6646, July 2012.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
6749, October 2012.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, RFC
6838, January 2013.
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[RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
Keranen, A., and P. Hallam-Baker, "Naming Things with
Hashes", RFC 6920, April 2013.
[GoogleFileSystem]
Ghemawat, S., Gobioff, H., and S. Leung, "The Google File
System", SOSP 2003, October 2003.
Authors' Addresses
Richard Alimi
Google
Email: ralimi@google.com
Akbar Rahman
InterDigital Communications, LLC
Email: akbar.rahman@interdigital.com
Dirk Kutscher
NEC
Email: dirk.kutscher@neclab.eu
Y. Richard Yang
Yale University
Email: yry@cs.yale.edu
Haibin Song
Huawei Technologies
Email: haibin.song@huawei.com
Kostas Pentikousis
Huawei Technologies
Email: k.pentikousis@huawei.com
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