Network Working Group B. Niven-Jenkins
Internet-Draft Velocix (Alcatel-Lucent)
Intended status: Informational F. Le Faucheur
Expires: May 3, 2012 Cisco
N. Bitar
Verizon
October 31, 2011
Content Distribution Network Interconnection (CDNI) Problem Statement
draft-ietf-cdni-problem-statement-01
Abstract
Content Delivery Networks (CDNs) provide numerous benefits: reduced
delivery cost for cacheable content, improved quality of experience
for End Users and increased robustness of delivery. For these
reasons they are frequently used for large-scale content delivery.
As a result, existing CDN providers are scaling up their
infrastructure and many Network Service Providers (NSPs) are
deploying their own CDNs. It is generally desirable that a given
content item can be delivered to an End User regardless of that End
User's location or attachment network. This creates a requirement
for interconnecting standalone CDNs so they can interoperate as an
open content delivery infrastructure for the end-to-end delivery of
content from Content Service Providers (CSPs) to End Users. However,
no standards or open specifications currently exist to facilitate
such CDN interconnection.
The goal of this document is to outline the problem area of CDN
interconnection (CDNI) for the IETF.
Status of this Memo
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This Internet-Draft will expire on May 3, 2012.
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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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. CDN Background . . . . . . . . . . . . . . . . . . . . . . 8
2. CDN Interconnect Use Cases . . . . . . . . . . . . . . . . . . 8
3. CDN Interconnect Model & Problem Area for IETF . . . . . . . . 10
4. Design Approach for Realizing the CDNI APIs . . . . . . . . . 14
4.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 15
4.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 17
4.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 18
4.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 19
5. Gap Analysis of relevant Standardization Activities . . . . . 19
5.1. Content Acquisition across CDNs and Delivery to End
User (Data plane) . . . . . . . . . . . . . . . . . . . . 20
5.2. CDNI Metadata . . . . . . . . . . . . . . . . . . . . . . 21
6. Relationship to relevant IETF Working Groups . . . . . . . . . 22
6.1. ALTO . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.2. DECADE . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.3. PPSP . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8. Security Considerations . . . . . . . . . . . . . . . . . . . 24
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25
10.2. Informative References . . . . . . . . . . . . . . . . . . 25
Appendix A. Additional Material . . . . . . . . . . . . . . . . . 28
A.1. Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 28
A.2. Related standardization activities . . . . . . . . . . . . 29
A.2.1. IETF CDI Working Group (Concluded) . . . . . . . . . . 29
A.2.2. 3GPP . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.2.3. ISO MPEG . . . . . . . . . . . . . . . . . . . . . . . 30
A.2.4. ATIS IIF . . . . . . . . . . . . . . . . . . . . . . . 31
A.2.5. CableLabs . . . . . . . . . . . . . . . . . . . . . . 31
A.2.6. ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 32
A.2.7. ETSI TISPAN . . . . . . . . . . . . . . . . . . . . . 32
A.2.8. ITU-T . . . . . . . . . . . . . . . . . . . . . . . . 32
A.2.9. Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 33
A.2.10. TV-Anytime Forum . . . . . . . . . . . . . . . . . . . 33
A.2.11. SNIA . . . . . . . . . . . . . . . . . . . . . . . . . 33
A.3. Related Research Projects . . . . . . . . . . . . . . . . 33
A.3.1. IRTF P2P Research Group . . . . . . . . . . . . . . . 34
A.3.2. OCEAN . . . . . . . . . . . . . . . . . . . . . . . . 34
A.3.3. Eurescom P1955 . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34
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1. Introduction
The volume of video and multimedia content delivered over the
Internet is rapidly increasing and expected to continue doing so in
the future. In the face of this growth, Content Delivery Networks
(CDNs) provide numerous benefits: reduced delivery cost for cacheable
content, improved quality of experience for End Users and increased
robustness of delivery. For these reasons CDNs are frequently used
for large-scale content delivery. As a result, existing CDN
providers are scaling up their infrastructure and many Network
Service Providers (NSPs) are deploying their own CDNs.
It is generally desirable that a given content item can be delivered
to an End User regardless of that End User's location or attachment
network. However, the footprint of a given CDN in charge of
delivering a given content may not expand close enough to the End
User's current location or attachment network to realize the cost
benefit and user experience that a more distributed CDN would
provide. This creates a requirement for interconnecting standalone
CDNs so that their collective CDN footprint can be leveraged for the
end-to-end delivery of content from Content Service Providers (CSPs)
to End Users. For example, a CSP could contract with an
"authoritative" CDN for the delivery of content and that
authoritative CDN could contract with one or more downstream CDN(s)
to distribute and deliver some or all of the content on behalf of the
authoritative CDN. The formation and details of any business
relationships between a CSP and a CDN and between one CDN and another
CDN are out of scope of this document. However, no standards or open
specifications currently exist to facilitate such CDN
interconnection.
The goal of this document is to outline the problem area of CDN
interconnection (CDNI) for the IETF. Section 2 discusses the use
cases for CDN interconnection. Section 3 presents the CDNI model and
problem area being considered by the IETF. Section 4 describes each
CDNI interface individually and highlights example candidate
protocols that could considered for reuse or leveraging to implement
the CDNI interfaces. Section 5 provides a gap analysis against the
work of other standards organizations. Section 6 describes the
relationships between the CDNI problem space and other relevant IETF
Working Groups.
1.1. Terminology
This document uses the following terms:
Content: Any form of digital data. One important form of Content
with additional constraints on Distribution and Delivery is
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continuous media (i.e. where there is a timing relationship between
source and sink).
Metadata: Metadata in general is data about data.
Content Metadata: This is metadata about Content. Content Metadata
comprises:
1. Metadata that is relevant to the distribution of the content (and
therefore relevant to a CDN involved in the delivery of that
content). We refer to this type of metadata as "Content
Distribution Metadata". See also the definition of Content
Distribution Metadata.
2. Metadata that is associated with the actual Content (and not
directly relevant to the distribution of that Content) or content
representation. For example, such metadata may include
information pertaining to the Content's genre, cast, rating, etc
as well as information pertaining to the Content representation's
resolution, aspect ratio, etc.
Content Distribution Metadata: The subset of Content Metadata that is
relevant to the distribution of the content. This is the metadata
required by a CDN in order to enable and control content distribution
and delivery by the CDN. In a CDN Interconnection environment, some
of the Content Distribution Metadata may have an intra-CDN scope (and
therefore need not be communicated between CDNs), while some of the
Content Distribution Metadata have an inter-CDN scope (and therefore
needs to be communicated between CDNs).
CDNI Metadata: Content Distribution Metadata with inter-CDN scope.
For example, CDNI Metadata may include geo-blocking information (i.e.
information defining geographical areas where the content is to be
made available or blocked), availability windows (i.e. information
defining time windows during which the content is to be made
available or blocked) and access control mechanisms to be enforced
(e.g. URI signature validation). CDNI Metadata may also include
information about desired distribution policy (e.g. prepositioned vs
dynamic acquisition) and about where/how a CDN can acquire the
content. CDNI Metadata may also include content management
information (e.g. request for deletion of Content from Surrogates)
across interconnected CDNs.
Dynamic content acquisition: Dynamic content acquisition is where a
CDN acquires content from the content source in response to an End
User requesting that content from the CDN. In the context of CDN
Interconnection, dynamic acquisition means that a downstream CDN does
not acquire the content from content sources (including upstream
CDNs) until a request for that content has been delegated to the
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downstream CDN by an Upstream CDN.
Dynamic CDNI metadata acquisition: In the context of CDN
Interconnection, dynamic CDNI metadata acquisition means that a
downstream CDN does not acquire CDNI metadata for content from the
upstream CDN until a request for that content has been delegated to
the downstream CDN by an Upstream CDN.
Pre-positioned content acquisition: Content Pre-positioning is where
a CDN acquires content from the content source prior to or
independent of any End User requesting that content from the CDN. In
the context of CDN interconnection the Upstream CDN instructs the
Downstream CDN to acquire the content from content sources (including
upstream CDNs) in advance of or independent of any End User
requesting it.
Pre-positioned CDNI Metadata acquisition: In the context of CDN
Interconnection, CDNI Metadata pre-positioning is where the
Downstream CDN acquires CDNI metadata for content prior to or
independent of any End User requesting that content from the
Downstream CDN.
End User (EU): The 'real' user of the system, typically a human but
maybe some combination of hardware and/or software emulating a human
(e.g. for automated quality monitoring etc.)
User Agent (UA): Software (or a combination of hardware and software)
through which the End User interacts with a Content Service. The
User Agent will communicate with a Content Service for the selection
of content and one or more CDNs for the delivery of the Content.
Such communication is not restricted to HTTP and may be via a variety
of protocols. Examples of User Agents (non-exhaustive) are:
Browsers, Set Top Boxes (STBs), dedicated content applications (e.g.
media players), etc.
Network Service Provider (NSP): Provides network-based connectivity/
services to End Users.
Content Service Provider (CSP): Provides a Content Service to End
Users (which they access via a User Agent). A CSP may own the
Content made available as part of the Content Service, or may license
content rights from another party.
Content Service: The service offered by a Content Service Provider.
The Content Service encompasses the complete service which may be
wider than just the delivery of items of Content, e.g. the Content
Service also includes any middleware, key distribution, program
guide, etc. which may not require any direct interaction with the
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CDN.
Content Distribution Network (CDN) / Content Delivery Network (CDN):
Network infrastructure in which the network elements cooperate at
layers 4 through layer 7 for more effective delivery of Content to
User Agents. Typically a CDN consists of a Request Routing system, a
Distribution System (that includes a set of Surrogates), a Logging
System and a CDN control system.
CDN Provider: The service provider who operates a CDN. Note that a
given entity may operate in more than one role. For example, a
company may simultaneously operate as a Content Service Provider, a
Network Service Provider and a CDN Provider.
CDN Interconnection (CDNI): The set of interfaces over which two or
more CDNs communicate with each other in order to achieve the
delivery of content to User Agents by Surrogates in one CDN (the
downstream CDN) on behalf of another CDN (the upstream CDN).
Authoritative CDN: A CDN which has a direct relationship with a CSP
for the distribution & delivery of that CSP's content.
Upstream CDN: For a given End User request, the CDN (within a pair of
directly interconnected CDNs) that redirects the request to the other
CDN.
Downstream CDN: For a given End User request, the CDN (within a pair
of directly interconnected CDNs) to which the request is redirected
by the other CDN (the Upstream CDN). Note that in the case of
successive redirections (e.g. CDN1-->CDN2-->CDN3) a given CDN (e.g.
CDN2) may act as the Downstream CDN for a redirection (e.g.
CDN1-->CDN2) and as the Upstream CDN for the subsequent redirection
of the same request (e.g. CDN2-->CDN3).
Over-the-top (OTT): A service, e.g. a CDN, operated by a different
operator than the NSP to which the users of that service are
attached.
Surrogate: A device/function that interacts with other elements of
the CDN for the control and distribution of Content within the CDN
and interacts with User Agents for the delivery of the Content.
Request Routing System: The function within a CDN responsible for
receiving a content request from a User Agent, obtaining and
maintaining necessary information about a set of candidate surrogates
or candidate CDNs, and for selecting and redirecting the user to the
appropriate surrogate or CDN. To enable CDN Interconnection, the
Request Routing System must also be capable of handling User Agent
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content requests passed to it by another CDN.
Distribution System: The function within a CDN responsible for
distributing Content Distribution Metadata as well as the Content
itself inside the CDN (e.g. down to the surrogates).
Delivery: The function within CDN surrogates responsible for
delivering a piece of content to the User Agent. For example,
delivery may be based on HTTP progressive download or HTTP adaptive
streaming.
Logging System: The function within a CDN responsible for collecting
the measurement and recording of distribution and delivery
activities. The information recorded by the logging system may be
used for various purposes including charging (e.g. of the CSP),
analytics and monitoring.
1.2. CDN Background
Readers are assumed to be familiar with the architecture, features
and operation of CDNs. For readers less familiar with the operation
of CDNs, the following resources may be useful:
o RFC 3040 [RFC3040] describes many of the component technologies
that are used in the construction of a CDN.
o Taxonomy [TAXONOMY] compares the architecture of a number of CDNs.
o RFC 3466 [RFC3466] and RFC 3570 [RFC3570] are the output of the
IETF Content Delivery Internetworking (CDI) working group which
was closed in 2003.
Note: Some of the terms used in this document are similar to terms
used the above referenced documents. When reading this document
terms should be interpreted as having the definitions provided in
Section 1.1.
2. CDN Interconnect Use Cases
An increasing number of NSPs are deploying CDNs in order to deal
cost-effectively with the growing usage of on-demand video services
and other content delivery applications.
CDNs allow caching of content closer to the edge of a network so that
a given item of content can be delivered by a CDN Surrogate (i.e. a
cache) to multiple User Agents (and their End Users) without
transiting multiple times through the network core (i.e from the
content origin to the surrogate). This contributes to bandwidth cost
reductions for the NSP and to improved quality of experience for the
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End Users. CDNs also enable replication of popular content across
many surrogates, which enables content to be served to large numbers
of User Agents concurrently. This also helps dealing with situations
such as flash crowds and denial of service attacks.
The CDNs deployed by NSPs are not just restricted to the delivery of
content to support the Network Service Provider's own 'walled garden'
services, such as IP delivery of television services to Set Top
Boxes, but are also used for delivery of content to other devices
including PCs, tablets, mobile phones etc.
Some service providers operate over multiple geographies and federate
multiple affiliate NSPs. These NSPs typically operate independent
CDNs. As they evolve their services (e.g. for seamless support of
content services to nomadic users across affiliate NSPs) there is a
need for interconnection of these CDNs. However there are no open
specifications, nor common best practices, defining how to achieve
such CDN interconnection.
CSPs have a desire to be able to get (some of) their content to very
large number of End Users and/or over many/all geographies and/or
with a high quality of experience, all without having to maintain
direct business relationships with many different CDN providers (or
having to extend their own CDN to a large number of locations). Some
NSPs are considering interconnecting their respective CDNs (as well
as possibly over-the-top CDNs) so that this collective infrastructure
can address the requirements of CSPs in a cost effective manner. In
particular, this would enable the CSPs to benefit from on-net
delivery (i.e. within the Network Service Provider's own network/CDN
footprint) whenever possible and off-net delivery otherwise, without
requiring the CSPs to maintain direct business relationships with all
the CDNs involved in the delivery. Again, for this requirement, CDN
providers (NSPs or over-the-top CDN operators) are faced with a lack
of open specifications and best practices.
NSPs have often deployed CDNs as specialized cost-reduction projects
within the context of a particular service or environment, some NSPs
operate separate CDNs for separate services. For example, there may
be a CDN for managed IPTV service delivery, a CDN for web-TV delivery
and a CDN for video delivery to Mobile terminals. As NSPs integrate
their service portfolio, there is a need for interconnecting these
CDNs. Again, NSPs face the problem of lack of open interfaces for
CDN interconnection.
For operational reasons (e.g. disaster, flash crowd) or commercial
reasons, an over-the-top CDN may elect to make use of another CDN
(e.g. an NSP CDN with on-net Surrogates for a given footprint) for
serving a subset of the user requests (e.g. requests from users
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attached to that NSP). Again, for this requirement, CDN providers
(over-the-top CDN providers or NSPs) are faced with a lack of open
specifications and best practices.
Use cases for CDN Interconnection are further discussed in
[I-D.ietf-cdni-use-cases].
3. CDN Interconnect Model & Problem Area for IETF
Interconnecting CDNs involves interactions among multiple different
functions and components that form each CDN. Only some of those
require standardization. This section discusses the problem area for
the IETF work on CDN Interconnection. The CDNI model and problem
area defined for IETF work is illustrated in Figure 1.
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--------
/ \
| CSP |
\ /
--------
*
*
* /\
* / \
---------------------- |CDNI| ----------------------
/ Upstream CDN \ | | / Downstream CDN \
| +-------------+ | Control Interface| +-------------+ |
|******* Control |<======|====|========>| Control *******|
|* +------*----*-+ | | | | +-*----*------+ *|
|* * * | | | | * * *|
|* +------*------+ | Logging Interface| +------*------+ *|
|* ***** Logging |<======|====|========>| Logging ***** *|
|* * +-*-----------+ | | | | +-----------*-+ * *|
|* * * * | Request Routing | * * * *|
.....*...+-*---------*-+ | Interface | +-*---------*-+...*.*...
. |* * *** Req-Routing |<======|====|========>| Req-Routing *** * *| .
. |* * * +-------------+.| | | | +-------------+ * * *| .
. |* * * . CDNI Metadata | * * *| .
. |* * * +-------------+ |. Interface | +-------------+ * * *| .
. |* * * | Distribution|<==.===|====|========>| Distribution| * * *| .
. |* * * | | | . \ / | | | * * *| .
. |* * * |+---------+ | | . \/ | | +---------+| * * *| .
. |* * ***| +---------+| | ....Request......+---------+ |*** * *| .
. |* *****+-|Surrogate|************************|Surrogate|-+***** *| .
. |******* +---------+| | Acquisition | |+----------+ *******| .
. | +-------------+ | | +-------*-----+ | .
. \ / \ * / .
. ---------------------- ---------*------------ .
. * .
. * Delivery .
. * .
. +--*---+ .
...............Request.............................| User |..Request..
| Agent|
+------+
<==> interfaces inside the scope of CDNI
**** interfaces outside the scope of CDNI
.... interfaces outside the scope of CDNI
Figure 1: CDNI Problem Area
Listed below are the four interfaces required to interconnect a pair
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of CDNs and that constitute the problem space that is proposed to be
addressed by a potential CDNI working group in the IETF. The use of
the term "interface" is meant to encompass the protocol over which
CDNI data representations (e.g. CDNI Metadata records) are exchanged
as well as the specification of the data representations themselves
(i.e. what properties/fields each record contains, its structure,
etc.).
o CDNI Control interface: This interface allows the "CDNI Control"
system in interconnected CDNs to communicate. This interface may
support the following:
* Allow bootstrapping of the other CDNI interfaces (e.g.
interface address/URL discovery and establishment of security
associations).
* Allow configuration of the other CDNI interfaces (e.g.
Upstream CDN specifies information to be reported through the
CDNI Logging interface).
* Allow the downstream CDN to communicate static (or fairly
static) information about its delivery capabilities and
policies.
* Allow bootstrapping of the interface between CDNs for content
acquisition (even if that interface itself is outside the scope
of the CDNI work).
* Allow upstream CDN to initiate or request specific actions to
be undertaken in the downstream CDN. For example, this may
include the following capabilities:
+ Allow an upstream CDN to request that content files and/or
CDNI Metadata that it previously shared, be purged from, or
invalidated in, a downstream CDN. Support for content
deletion or invalidation from a CDN is a key requirement for
some Content Service Providers in order, amongst other use
cases for content deletion, to support the content rights
agreements they have negotiated. Today's CDNs use
proprietary control interfaces to enable CSPs to remove
content cached in the CDN and therefore there is a need to
have a similar but standardized content deletion capability
between interconnected CDNs.
+ Allow an upstream CDN to initiate Pre-positioned content
acquisition and/or Pre-positioned CDNI Metadata acquisition
in a downstream CDN.
o CDNI Request Routing interface: This interface allows the Request
Routing systems in interconnected CDNs to communicate to ensure
that an End User request can be (re)directed from an upstream CDN
to a surrogate in the downstream CDN, in particular where
selection responsibilities may be split across CDNs (for example
the upstream CDN may be responsible for selecting the downstream
CDN while the downstream CDN may be responsible for selecting the
actual surrogate within that downstream CDN). In particular, the
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CDN Request Routing interface, may support the following:
* Allow the upstream CDN to query the downstream CDN at request
routing time before redirecting the request to the downstream
CDN.
* Allow the downstream CDN to provide to the upstream CDN (static
or dynamic) information (e.g. resources, footprint, load) to
facilitate selection of the downstream CDN by the upstream CDN
request routing system when processing subsequent content
requests from User Agents.
o CDNI Metadata distribution interface: This interface allows the
Distribution system in interconnected CDNs to communicate to
ensure CDNI Metadata can be exchanged across CDNs. See
Section 1.1 for definition and examples of CDNI Metadata.
o CDNI Logging interface: This interface allows the Logging system
in interconnected CDNs to communicate the relevant activity logs
in order to allow log consuming applications to operate in a
multi-CDN environments. For example, an upstream CDN may collect
delivery logs from a downstream CDN in order to perform
consolidated charging of the CSP or for settlement purposes across
CDNs. Similarly, an upstream CDN may collect delivery logs from a
downstream CDN in order to provide consolidated reporting and
monitoring to the CSP.
Note that the actual grouping of functionalities under these four
interfaces is considered tentative at this stage and may be changed
after further study (e.g. some subset of functionality be moved from
one interface into another).
The above list covers a significant potential problem space, in part
because in order to interconnect two CDNs there are several 'touch
points' that require standardization. However, it is expected that
the CDNI interfaces need not be defined from scratch and instead can
very significantly reuse or leverage existing protocols: this is
discussed further in Section 4. Also, it is expected that the items
above will be prioritized so that the CDNI Working Group can focus
(at least initially) on the most essential and urgent work.
As part of the development of the CDNI interfaces and solutions it
will also be necessary to agree on common mechanisms for how to
identify and name the data objects that are to be interchanged
between interconnected CDNs, as well as how to describe which policy
should be used when doing so.
Some NSPs have started to perform experiments to explore whether
their CDN use cases can already be addressed with existing CDN
implementations. One set of such experiments is documented in
[I-D.bertrand-cdni-experiments]. The conclusions of those
experiments are that while some basic limited CDN Interconnection
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functionality can be achieved with existing CDN technology, the
current lack of any standardized CDNI interfaces/protocols such as
those discussed in this document is preventing the deployment of
production CDN Interconnection solutions with the necessary level of
functionality.
The acquisition of content between interconnected CDNs is out of
scope for CDNI and deserves some additional explanation. The
consequence of such a decision is that the CDNI WG is focussed on
only defining the control plane for CDNI; and the CDNI data plane
(i.e. the acquisition & distribution of the actual content objects)
will not be addressed by the CDNI WG. The rationale for such a
decision is that CDNs today typically already use standardized
protocols such as HTTP, FTP, rsync, etc. to acquire content from
their CSP customers and it is expected that the same protocols could
be used for acquisition between interconnected CDNs. Therefore the
problem of content acquisition is considered already solved and all
that is required from specifications developed by the CDNI WG is to
describe within the CDNI Metadata where to go and which protocol to
use to retrieve the content.
4. Design Approach for Realizing the CDNI APIs
This section expands on how CDNI interfaces can reuse and leverage
existing protocols before describing each CDNI interface individually
and highlighting example candidate protocols that could considered
for reuse or leveraging to implement the CDNI interfaces. This
discussion is not intended to pre-empt any WG decision as to the most
appropriate protocols, technologies and solutions to select to solve
CDNI but is intended as an illustration of the fact that the CDNI
interfaces need not be created in a vacuum and that reuse or leverage
of existing protocols is likely possible.
The four CDNI interfaces (CDNI Control interface, CDNI Request
Routing interface, CDNI Metadata interface, CDNI Logging interface)
described in Section 3 within the CDNI problem area are all control
plane interfaces operating at the application layer (Layer 7 in the
OSI network model). Since it is not expected that these interfaces
would exhibit unique session, transport or network requirements as
compared to the many other existing applications in the Internet, it
is expected that the CDNI interfaces will be defined on top of
existing session, transport and network protocols.
Although a new application protocol could be designed specifically
for CDNI we assume that this is unnecessary and it is recommended
that existing application protocols be reused or leveraged (HTTP
[RFC2616], Atom Publishing Protocol [RFC5023], XMPP [RFC6120], for
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example) to realize the CDNI interfaces.
4.1. CDNI Request Routing Interface
The CDNI Request Routing interface enables a Request Routing function
in an upstream CDN to query a Request Routing function in a
downstream CDN to determine if the downstream CDN is able (and
willing) to accept the delegated content request and to allow the
downstream CDN to control what the upstream Request Routing function
should return to the User Agent in the redirection message.
The CDNI Request Routing interface needs to offer a mechanism for an
upstream CDN to issue a "Redirection Request" to a downstream CDN.
The Request Routing interface needs to be able to support scenarios
where the initial User Agent request to the upstream CDN is received
over DNS as well as over a content specific application protocol
(e.g. HTTP, RTSP, RTMP, etc.).
Therefore a Redirection Request needs to contain information such as:
o The protocol (e.g. DNS, HTTP) over which the upstream CDN
received the initial User Agent request.
o Additional details of the User Agent request that are required to
perform effective Request Routing by the Downstream CDN. For DNS
this would typically be the IP address of the DNS resolver making
the request on behalf of the User Agent. For requests received
over content specific application protocols the Redirection
Request could contain significantly more information related to
the original User Agent request but at a minimum would need to
contain the User Agent's IP address, the equivalent of the HTTP
Host header and the equivalent of the HTTP abs_path defined in
[RFC2616].
It should be noted that, the CDNI architecture needs to consider that
a downstream CDN may receive requests from User Agents without first
receiving a Redirection Request from an upstream CDN, for example
because:
o User Agents (or DNS resolvers) may cache DNS or application
responses from Request Routers.
o Responses to Redirection Requests over the Request Routing
interface may be cacheable.
o Some CDNs may want broader policies, e.g. CDN B agrees to always
take CDN A's delegated redirection requests, in which case the
necessary redirection details are exchanged out of band (of the
CDNI interfaces), e.g. configured.
On receiving a Redirection Request, the downstream CDN will use the
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information provided in the request to determine if it is able (and
willing) to accept the delegated content request and needs to return
the result of its decision to the upstream CDN.
Thus, a Redirection Response from the downstream CDN needs to contain
information such as:
o Status code indicating acceptance or rejection (possibly with
accompanying reasons).
o Information to allow redirection by the Upstream CDN. In the case
of DNS-based request routing, this is expected to include the
equivalent of a DNS record(s) (e.g. a CNAME) that the upstream CDN
should return to the requesting DNS resolver. In the case of
application based request routing, this is expected to include the
application specific redirection response(s) to return to the
requesting User Agent. For HTTP requests from User Agents this
could be in the form of a URI that the upstream CDN could return
in a HTTP 302 response.
The CDNI Request Routing interface is therefore a fairly
straightforward request/response interface and could be implemented
over any number of request/response protocols. For example, it may
be implemented as a WebService using one of the common WebServices
methodologies (XML-RPC, HTTP query to a known URI, etc.). This
removes the need for the CDNI WG to define a new protocol for the
request/response element of the CDNI Request Routing interface.
Thus, the CDNI WG would be left only with the task of specifying:
o The recommended request/response protocol to use along with any
additional semantics and procedures that are specific to the CDNI
Request Routing interface (e.g. handling of malformed requests/
responses).
o The syntax (i.e representation/encoding) of the redirection
requests and responses.
o The semantics (i.e. meaning and expected contents) of the
redirection requests and responses.
Additionally, as discussed in Section 3, the CDNI Request Routing
interface is also expected to enable a downstream CDN to provide to
the upstream CDN (static or dynamic) information (e.g. resources,
footprint, load) to facilitate selection of the downstream CDN by the
upstream CDN request routing system when processing subsequent
content requests from User Agents. It is expected that such
functionality of the CDNI request Routing could be specified by the
CDNI WG with significant leveraging of existing IETF protocols
supporting the dynamic distribution of reachability information (for
example by leveraging existing routing protocols) or supporting
application level queries for topological information (for example by
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leveraging ALTO).
4.2. CDNI Metadata Interface
The CDNI Metadata interface enables the Metadata function in a
downstream CDN to obtain CDNI Metadata from an upstream CDN so that
the downstream CDN can properly process and respond to:
o Redirection Requests received over the CDNI Request Routing
interface.
o Content Requests received directly from User Agents.
The CDNI Metadata interface needs to offer a mechanism for an
Upstream CDN to:
o Distribute/update/remove CDNI Metadata to a Downstream CDN.
and/or to allow a downstream CDN to:
o Make direct requests for CDNI Metadata records where the
downstream CDN knows the identity of the Metadata record(s) it
requires.
o Search for CDNI Metadata records where the downstream CDN does not
know the specific Metadata record(s) it requires but does know
some property of the record it is searching for. For example, it
may know the value of the HTTP Host header received in a HTTP
request and it wants to obtain the CDNI Metadata for that host so
that it can determine how to further process the received HTTP
request.
The CDNI Metadata interface is therefore similar to the CDNI Request
Routing interface because it is a request/response interface with the
potential addition that CDNI Metadata search may have more complex
semantics than a straightforward Request Routing redirection request.
Therefore, like the CDNI Request Routing interface, the CDNI Metadata
interface may be implemented as a WebService using one of the common
WebServices methodologies (XML-RPC, HTTP query to a known URI, etc.)
or possibly using other existing protocols such as XMPP [RFC6120].
This removes the need for the CDNI WG to define a new protocol for
the request/response element of the CDNI Metadata interface.
Thus, the CDNI WG would be left only with the task of specifying:
o The recommended request/response protocol to use along with any
additional semantics that are specific to the CDNI Metadata
interface (e.g. handling of malformed requests/responses).
o The syntax (i.e representation/encoding) of the CDNI Metadata
records that will be exchanged over the interface.
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o The semantics (i.e. meaning and expected contents) of the
individual properties of a Metadata record.
o How the relationships between different CDNI Metadata records are
represented.
4.3. CDNI Logging Interface
The CDNI Logging interface enables details of logs or events to be
exchanged between interconnected CDNs, where events could be:
o Log lines related to the delivery of content (similar to the log
lines recorded in a web server's access log).
o Real-time or near-real time events before, during or after content
delivery, e.g. content Start/Pause/Stop events, etc.
o Operations and diagnostic messages.
Within CDNs today, logs and events are used for a variety of purposes
in addition to real-time and non real-time diagnostics and auditing
by the CDN Provider and its customers. Specifically CDNs use logs to
generate Call Data Records (CDRs) for passing to billing and payment
systems and to real-time (and near real-time) analytics systems.
Such use cases place requirements on the CDNI Logging interface to
support guaranteed and timely delivery of log messages between
interconnected CDNs. It may also be necessary to be able to prove
the integrity of received log messages.
Several protocols already exist that could potentially be used to
exchange CDNI logs between interconnected CDNs including SNMP Traps,
syslog, ftp, HTTP POST, etc. although it is likely that some of the
candidate protocols may not be well suited to meet all the
requirements of CDNI. For example SNMP traps pose scalability
concerns and SNMP does not support guaranteed delivery of Traps and
therefore could result in log records being lost and the consequent
CDRs and billing records for that content delivery not being produced
as well as that content delivery being invisible to any analytics
platforms.
Although it is not necessary to define a new protocol for exchanging
logs across the CDNI Logging interface, the CDNI WG would still need
to specify:
o The recommended protocol to use.
o A default set of log fields and their syntax & semantics. Today
there is no standard set of common log fields across different
content delivery protocols and in some cases there is not even a
standard set of log field names and values for different
implementations of the same delivery protocol.
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o A default set of events that trigger logs to be generated.
4.4. CDNI Control Interface
The CDNI Control interface allows the "CDNI Control" system in
interconnected CDNs to communicate. The exact inter-CDN control
functionality required to be supported by the CDNI Control interface
is less well defined than the other three CDNI interfaces at this
time.
However, as discussed in Section 3, the CDNI Control interface may be
required to support functionality similar to the following:
o Allow an upstream CDN and downstream CDN to establish, update or
terminate their CDNI interconnection.
o Allow bootstrapping of the other CDNI interfaces (e.g. protocol
address discovery and establishment of security associations).
o Allow configuration of the other CDNI interfaces (e.g. Upstream
CDN specifies information to be reported through the CDNI Logging
interface).
o Allow the downstream CDN to communicate static information about
its delivery capabilities, resources and policies.
o Allow bootstrapping of the interface between CDNs for content
acquisition (even if that interface itself is outside the scope of
the CDNI work).
It is expected that for the Control interface also, existing
protocols can be reused or leveraged. Those will be considered once
the requirements for the Control interface have been refined.
5. Gap Analysis of relevant Standardization Activities
There are a number of other standards bodies and industry forums that
are working in areas related to CDNs, and in some cases related to
CDNI. This section outlines any potential overlap with the work of
the CDNI WG and any component that could potentially be reused by
CDNI.
A number of standards bodies have produced specifications related to
CDNs, for example:
o TISPAN has a dedicated specification for CDN.
o OIPF and ATIS specify the architecture and the protocols of an
IPTV solution. Although OIPF and ATIS specifications include the
interaction with a CDN, the CDN specifications are coupled with
their IPTV specifications.
o CableLabs, SNIA and ITU have defined (or are working on)
definitions for content related metadata definitions and
specification for its distribution. However, they do not include
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metadata specific to the distribution of content within a CDN or
between interconnected CDNs.
o IETF CDI WG (now concluded) touched on the same problem space as
the present document. However, in accordance with its initial
charter, the CDI WG did not define any protocols or interfaces to
actually enable CDN Interconnection and at that time (2003) there
was not enough industry interest and real life requirements to
justify rechartering the WG to conduct the corresponding protocol
work.
Although some of the specifications describe multi-CDN cooperation or
include reference points for interconnecting CDNs, none of them
specify in sufficient detail all the CDNI interfaces and CDNI
Metadata representations required to enable even a base level of CDN
Interconnection functionality to be implemented.
The following sections will summarize the existing work of the
standard bodies listed earlier against the CDNI problem space.
Section 5.1 summarises existing interfaces that could be leveraged
for content acquisition between CDNs and Section 5.2 summarises
existing metadata specifications that may be applicable to CDNI. To
date we are not aware of any standardisation activities in the areas
of the remaining CDNI interfaces (CDNI Request Routing, CDNI Control
and CDNI Logging).
5.1. Content Acquisition across CDNs and Delivery to End User (Data
plane)
A number of standards bodies have completed work in the areas of
content acquisition interface between a CSP and a CDN, as well as as
on the delivery interface between the surrogate and the User Agent.
Some of this work is summarized below.
TISPAN, OIPF and ATIS have specified IPTV and/or CoD services,
including the data plane aspects (typically different flavors of RTP/
RTCP and HTTP) to obtain content and deliver it to User Agents. For
example, :
o The OIPF data plane includes both RTP and HTTP flavors (HTTP
progressive download, HTTP Adaptive streaming [_3GP-DASH]).
o The ATIS specification "IPTV Content on Demand (CoD) Service"
[ATIS-COD] defines a reference point (C2) and the corresponding
HTTP-based data plane protocol for content acquisition between an
authoritative origin server and the CDN.
While these protocols have not been explicitly specified for content
acquisition across CDNs, they are suitable (in addition to others
such as standard HTTP) for content acquisition between CDNs in a CDN
Interconnection environment. Therefore for the purpose of the CDNI
WG there are already multiple existing data plane protocols that can
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be used for content acquisition across CDNs.
Similarly, there are multiple existing standards (e.g. the OIPF data
plane mentioned above, HTTP adaptive streaming [_3GP-DASH]) or public
specifications (e.g. vendor specific HTTP Adaptive streaming
specifications) so that content delivery can be considered already
solved (or at least sufficiently addressed in other forums
Thus, specification of the content acquisition interface between CDNs
and the delivery interface between the surrogate and the User Agent
are out of scope for CDNI. CDNI may only concern itself with the
negotiation/selection aspects of the acquisition protocol to be used
in a CDN interonnect scenario.
5.2. CDNI Metadata
CableLabs, ITU, OIPF and TV-Anytime have work items dedicated to the
specification of content metadata:
o CableLabs has defined specifications for CoD Content Metadata as
part of its VOD Metadata project. "The VOD Metadata project is a
cable television industry and cross-industry-wide effort to
specify the metadata and interfaces for distribution of video-on-
demand (VOD) material from multiple content providers to cable
operators." [CableLabs-Metadata]. However, while the CableLabs
work specifies an interface between a content provider and a
service provider running a CDN, it does not include an interface
that could be used between CDNs.
o ITU Study Group 16 has started work on a number of draft
Recommendations (H.IPTV-CPMD, H.IPTV-CPMD, HSTP.IPTV-CMA,
HSTP.IPTV-UMCI) specifying metadata for content distribution in
IPTV services.
o An Open IPTV Terminal receives the technical description of the
content distribution from the OIPF IPTV platform before receiving
any content. The Content distribution metadata is sent in the
format of a TV-Anytime XSD including tags to describes the
location and program type (on demand or Live) as well as
describing the time availability of the on demand and live
content.
However the specifications outlined above do not include metadata
specific to the distribution of content within a CDN or between
interconnected CDNs, for example geo-blocking information,
availability windows, access control mechanisms to be enforced by the
surrogate, how to map an incoming content request to a file on the
origin server or acquire it from the upstream CDN etc.
The CDMI standard ([SNIA-CDMI]) from SNIA defines metadata that can
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be associated with data that is stored by a cloud storage provider.
While the metadata currently defined do not match the need of a CDN
Interconnection solution, it is worth considering CDMI as one of the
existing pieces of work that may potentially be leveraged for the
CDNI Metadata interface (e.g by extending the CDMI metadata to
address more specific CDNI needs).
6. Relationship to relevant IETF Working Groups
6.1. ALTO
As stated in the ALTO Working Group charter [ALTO-Charter]:
"The Working Group will design and specify an Application-Layer
Traffic Optimization (ALTO) service that will provide applications
with information to perform better-than-random initial peer
selection. ALTO services may take different approaches at balancing
factors such as maximum bandwidth, minimum cross-domain traffic,
lowest cost to the user, etc. The WG will consider the needs of
BitTorrent, tracker-less P2P, and other applications, such as content
delivery networks (CDN) and mirror selection."
In particular, the ALTO service can be used by a CDN Request Routing
system to improve its selection of a CDN surrogate to serve a
particular User Agent request (or to serve a request from another
surrogate). [I-D.jenkins-alto-cdn-use-cases] describes a number of
use cases for a CDN to be able to obtain network topology and cost
information from an ALTO server(s) and [I-D.penno-alto-cdn] discusses
how CDN Request Routing could be used as an integration point of ALTO
into CDNs. It is possible that the ALTO service could be used in the
same manner in a multi-CDN environment based on CDN Interconnection.
For example, an upstream CDN may take advantage of the ALTO service
in its decision for selecting a downstream CDN to which a user
request should be delegated.
However, the work of ALTO is complementary to and does not overlap
with the work described in this document because the integration
between ALTO and a CDN is an internal decision for a specific CDN and
is therefore out of scope for the CDNI WG. One area for further
study is whether additional information should be provided by an ALTO
service to facilitate CDNI CDN selection.
6.2. DECADE
The DECADE Working Group [DECADE-Charter] is addressing the problem
of reducing traffic on the last-mile uplink, as well as backbone and
transit links caused by P2P streaming and file sharing applications.
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It addresses the problem by enabling an application endpoint to make
content available from an in-network storage service and by enabling
other application endpoints to retrieve the content from there.
Exchanging data through the in-network storage service in this
manner, instead of through direct communication, provides significant
gain where:
o The network capacity/bandwidth from in-network storage service to
application endpoint significantly exceeds the capacity/bandwidth
from application endpoint to application endpoint (e.g. because of
an end-user uplink bottleneck); and
o Where the content is to be accessed by multiple instances of
application endpoints (e.g. as is typically the case for P2P
applications).
While, as is the case for any other data distribution application,
the DECADE architecture and mechanisms could potentially be used for
exchange of CDNI control plane information via an in-network-storage
service (as opposed to directly between the entities terminating the
CDNI interfaces in the neighbor CDNs), we observe that:
o CDNI would operate as a "Content Distribution Application" from
the DECADE viewpoint (i.e. would operate on top of DECADE).
o There does not seem to be obvious benefits in integrating the
DECADE control plane responsible for signaling information
relating to control of the in-network storage service itself, and
the CDNI control plane responsible for application-specific CDNI
interactions (such as exchange of CDNI metadata, CDNI request
redirection, transfer of CDNI logging information).
o There would typically be limited benefits in making use of a
DECADE in-network storage service because the CDNI interfaces are
expected to be terminated by a very small number of CDNI clients
(if not one) in each CDN, and the CDNI clients are expected to
benefit from high bandwidth/capacity when communicating directly
to each other (at least as high as if they were communicating via
an in-network storage server).
The DECADE in-network storage architecture and mechanisms may
theoretically be used for the acquisition of the content objects
themselves between interconnected CDNs. It is not expected that this
would have obvious benefits in typical situations where a content
object is acquired only once from an Upstream CDN to a Downstream CDN
(and then distributed as needed inside the Downstream CDN). But it
might have benefits in some particular situations. Since the
acquisition protocol between CDNs is outside the scope of the CDNI
work, this question is left for further study.
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The DECADE in-network storage architecture and mechanisms may
potentially also be used within a given CDN for the distribution of
the content objects themselves among surrogates of that CDN. Since
the CDNI work does not concern itself with operation within a CDN,
this question is left for further study.
Therefore, the work of DECADE may be complementary to but does not
overlap with the CDNI work described in this document.
6.3. PPSP
As stated in the PPSP Working Group charter [PPSP-Charter]:
"The Peer-to-Peer Streaming Protocol (PPSP) working group develops
two signaling and control protocols for a peer-to-peer (P2P)
streaming system for transmitting live and time-shifted media content
with near real-time delivery requirements." and "The PPSP WG designs
a protocol for signaling and control between trackers and peers (the
PPSP "tracker protocol") and a signaling and control protocol for
communication among the peers (the PPSP "peer protocol"). The two
protocols enable peers to receive streaming data within the time
constraints required by specific content items."
Therefore PPSP is concerned with the distribution of the streamed
content itself along with the necessary signaling and control
required to distribute the content. As such, it could potentially be
used for the acquisition of streamed content across interconnected
CDNs. But since the acquisition protocol is outside the scope of the
work proposed for CDNI, we leave this for further study. Also,
because of its streaming nature, PPSP is not seen as applicable to
the distribution and control of the CDNI control plane and CDNI data
representations.
Therefore, the work of PPSP may be complementary to but does not
overlap with the work described in this document for CDNI.
7. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
Distribution of content by a CDN comes with a range of security
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considerations such as how to enforce control of access to the
content by users in line with the CSP policy. These security aspects
are already dealt with by CDN Providers and CSPs today in the context
of standalone CDNs. However, interconnection of CDNs introduces a
new set of security considerations by extending the trust model (i.e.
the CSP "trusts" a CDN that "trusts" another CDN).
Maintaining the security of the content itself, its associated
metadata (including distribution and delivery policies) and the CDNs
distributing and delivering it, are critical requirements for both
CDN Providers and CSPs and any work on CDN Interconnection must
provide sufficient mechanisms to maintain the security of the overall
system of interconnected CDNs as well as the information (content,
metadata, logs, etc) distributed and delivered through any CDN
interconnects.
9. Acknowledgements
The authors would like to thank Andre Beck, Gilles Bertrand, Mark
Carlson, Bruce Davie, David Ferguson, Yiu Lee, Kent Leung, Will Li,
Kevin Ma, Julien Maisonneuve, Guy Meador, Emile Stephan, Oskar van
Deventer and Mahesh Viveganandhan for their review comments and
contributions to the text.
10. References
10.1. Normative References
10.2. Informative References
[ALTO-Charter]
"IETF ALTO WG Charter
(http://datatracker.ietf.org/wg/alto/charter/)".
[ATIS] "ATIS (http://www.atis.org/)".
[ATIS-COD]
"ATIS IIF: IPTV Content on Demand Service, January 2011 (h
ttp://www.atis.org/iif/_Com/Docs/Task_Forces/ARCH/
ATIS-0800042.pdf)".
[CDI-Charter]
"IETF CDI WG Charter
(http://www.ietf.org/wg/concluded/cdi)".
[CableLabs]
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Internet-Draft CDN Interconnection Problem Statement October 2011
"CableLabs (http://www.cablelabs.com/about/)".
[CableLabs-Metadata]
"CableLabs VoD Metadata Project Primer
(http://www.cablelabs.com/projects/metadata/primer/)".
[DECADE-Charter]
"IETF DECADE WG Charter
(http://datatracker.ietf.org/wg/decade/charter/)".
[I-D.bertrand-cdni-experiments]
Bertrand, G., Faucheur, F., and L. Peterson, "Content
Distribution Network Interconnection (CDNI) Experiments",
draft-bertrand-cdni-experiments-01 (work in progress),
August 2011.
[I-D.ietf-cdni-use-cases]
Bertrand, G., Emile, S., Watson, G., Burbridge, T.,
Eardley, P., and K. Ma, "Use Cases for Content Delivery
Network Interconnection", draft-ietf-cdni-use-cases-00
(work in progress), September 2011.
[I-D.jenkins-alto-cdn-use-cases]
Niven-Jenkins, B., Watson, G., Bitar, N., Medved, J., and
S. Previdi, "Use Cases for ALTO within CDNs",
draft-jenkins-alto-cdn-use-cases-01 (work in progress),
June 2011.
[I-D.penno-alto-cdn]
Penno, R., Medved, J., Alimi, R., Yang, R., and S.
Previdi, "ALTO and Content Delivery Networks",
draft-penno-alto-cdn-03 (work in progress), March 2011.
[MPEG-DASH]
"Information technology - MPEG systems technologies - Part
6: Dynamic adaptive streaming over HTTP (DASH), (DIS
version), February 2011
http://mpeg.chiariglione.org/
working_documents.htm#MPEG-B".
[OIPF-Overview]
"OIPF Release 2 Specification Volume 1 - Overview",
September 2010.
[P2PRG-CDNI]
Davie, B. and F. Le Faucheur, "Interconnecting CDNs aka
"Peering Peer-to-Peer"
(http://www.ietf.org/proceedings/77/slides/P2PRG-2.pdf)",
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Internet-Draft CDN Interconnection Problem Statement October 2011
March 2010.
[PPSP-Charter]
"IETF PPSP WG Charter
(http://datatracker.ietf.org/wg/ppsp/charter/)".
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web
Replication and Caching Taxonomy", RFC 3040, January 2001.
[RFC3466] Day, M., Cain, B., Tomlinson, G., and P. Rzewski, "A Model
for Content Internetworking (CDI)", RFC 3466,
February 2003.
[RFC3568] Barbir, A., Cain, B., Nair, R., and O. Spatscheck, "Known
Content Network (CN) Request-Routing Mechanisms",
RFC 3568, July 2003.
[RFC3570] Rzewski, P., Day, M., and D. Gilletti, "Content
Internetworking (CDI) Scenarios", RFC 3570, July 2003.
[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
Protocol", RFC 5023, October 2007.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[SNIA-CDMI]
"SNIA CDMI (http://www.snia.org/tech_activities/standards/
curr_standards/cdmi)".
[TAXONOMY]
Pathan, A., "A Taxonomy and Survey of Content Delivery
Networks
(http://www.gridbus.org/reports/CDN-Taxonomy.pdf)", 2007.
[Y.1910] "ITU-T Recomendation Y.1910 "IPTV functional
architecture"", September 2008.
[Y.2019] "ITU-T Recomendation Y.2019 "Content delivery functional
architecture in NGN"", September 2010.
[_3GP-DASH]
"Transparent end-to-end Packet-switched Streaming Service
(PSS); Progressive Download and Dynamic Adaptive Streaming
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over HTTP (3GP-DASH)
http://www.3gpp.org/ftp/Specs/html-info/26247.htm".
Appendix A. Additional Material
Note to RFC Editor: This appendix is to be removed on publication as
an RFC.
A.1. Non-Goals for IETF
Listed below are aspects of content delivery that the authors propose
be kept outside of the scope of a potential CDNI working group:
o The interface between Content Service Provider and the
Authoritative CDN (i.e. the upstream CDN contracted by the CSP for
delivery by this CDN or by its downstream CDNs).
o The delivery interface between the delivering CDN surrogate and
the User Agent, such as streaming protocols.
o The request interface between the User Agent and the request-
routing system of a given CDN. Existing IETF protocols (e.g.
HTTP, RTSP, DNS) are commonly used by User Agents to request
content from a CDN and by CDN request routing systems to redirect
the User Agent requests. The CDNI working group need not define
new protocols for this purpose. Note however, that the CDNI
control plane interface may indirectly affect some of the
information exchanged through the request interface (e.g. URI).
o The content acquisition interface between CDNs (i.e. the data
plane interface for actual delivery of a piece of content from one
CDN to the other). This is expected to use existing protocols
such as HTTP or protocols defined in other forums for content
acquisition between an origin server and a CDN (e.g. HTTP-based
C2 reference point of ATIS IIF CoD). The CDN Interconnection
solution may only concern itself with the agreement/negotiation
aspects of which content acquisition protocol is to be used
between two interconnected CDNs in view of facilitating
interoperability.
o End User/User Agent Authentication. End User/User Agent
authentication and authorization are the responsibility of the
Content Service Provider.
o Content preparation, including encoding and transcoding. The CDNI
architecture aims at allowing distribution across interconnected
CDNs of content treated as opaque objects. Interpretation and
processing of the objects, as well as optimized delivery of these
objects by the surrogate to the End User are outside the scope of
CDNI.
o Digital Rights Management (DRM). DRM is an end-to-end issue
between a content protection system and the User Agent.
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o Applications consuming CDNI logs (e.g. charging, analytics,
reporting,...).
o Internal CDN interfaces & protocols (i.e. interfaces & protocols
within one CDN).
o Scalability of individual CDNs. While scalability of the CDNI
interfaces/approach is in scope, how an individual CDN scales is
out of scope.
o Actual algorithms for selection of CDNs or Surrogates by Request
Routing systems (however, some specific parameters required as
input to these algorithms may be in scope when they need to be
communicated across CDNs).
o Surrogate algorithms. For example caching algorithms and content
acquisition methods are outside the scope of the CDNI work.
Content management (e.g. Content Deletion) as it relates to CDNI
content management policies, is in scope but the internal
algorithms used by a cache to determine when to no longer cache an
item of Content (in the absence of any specific metadata to the
contrary) is out of scope.
o Element management interfaces.
o Commercial, business and legal aspects related to the
interconnections of CDNs.
A.2. Related standardization activities
A.2.1. IETF CDI Working Group (Concluded)
The Content Distribution Internetworking (CDI) Working Group was
formed in the IETF following a BoF in December 2000 and closed in mid
2003.
For convenience, here is an extract from the CDI WG charter
[CDI-Charter]:
"
o The goal of this working group is to define protocols to allow the
interoperation of separately-administered content networks.
o A content network is an architecture of network elements, arranged
for efficient delivery of digital content. Such content includes,
but is not limited to, web pages and images delivered via HTTP,
and streaming or continuous media which are controlled by RTSP.
o The working group will first define requirements for three modes
of content internetworking: interoperation of request-routing
systems, interoperation of distribution systems, and
interoperation of accounting systems. These requirements are
intended to lead to a follow-on effort to define protocols for
interoperation of these systems.
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o In its initial form, the working group is not chartered to deliver
those protocols [...]
"
Thus, the CDI WG touched on the same problem space as the present
document.
The CDI WG published 3 Informational RFCs:
o RFC 3466 [RFC3466] - "A Model for Content Internetworking (CDI)".
o RFC 3568 [RFC3568] - "Known Content Network (CN) Request-Routing
Mechanisms".
o RFC 3570 [RFC3570] - "Content Internetworking (CDI) Scenarios".
A.2.2. 3GPP
3GPP was the first organization that released a specification related
to adaptive streaming over HTTP. 3GPP Release 9 specification on
adaptive HTTP streaming was published in March 2010, and there have
been some bug fixes on this specification since the publication. In
addition, 3GPP is preparing an extended version for Release 10, which
is scheduled to be published later in 2011. This release will
include a number of clarifications, improvements and new features.
[_3GP-DASH] is defined as a general framework independent of the data
encapsulation format. It has support for fast initial startup and
seeking, adaptive bitrate switching, re-use of HTTP origin and cache
servers, re-use of existing media playout engines, on-demand, live
and time-shifted delivery. It specifies syntax and semantics of
Media Presentation Description (MPD), format of segments and delivery
protocol for segments. It does not specify content provisioning,
client behavior or transport of MPD.
The content retrieved by a client using [_3GP-DASH] adaptive
streaming could be obtained from a CDN but this is not discussed or
specified in the 3GPP specifications as it is transparent to
[_3GP-DASH] operations. Similarly, it is expected that [_3GP-DASH]
can be used transparently from the CDNs as a delivery protocol
(between the delivering CDN surrogate and the User Agent) in a CDN
Interconnection environment. [_3GP-DASH] could also be a candidate
for content acquisition between CDNs in a CDN Interconnection
environment.
A.2.3. ISO MPEG
Within ISO MPEG, the Dynamic Adaptive Streaming over HTTP (DASH) ad-
hoc group adopted the 3GPP Release 9 [_3GP-DASH] specification as a
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starting point and has made some improvements and extensions.
Similar to 3GPP SA4, the MPEG DASH ad-hoc group has been working on
standardizing the manifest file and the delivery format.
Additionally, the MPEG DASH ad-hoc group has also been working on the
use of MPEG-2 Transport Streams as a media format, conversion from/to
existing file formats, common encryption, and so on. The MPEG DASH
specification could also be a candidate for delivery to the User
Agent and for content acquisition between CDNs in a CDN
Interconnection environment. The Draft International Standard (DIS)
version [MPEG-DASH] is currently publicly available since early
February 2011.
In the 95th MPEG meeting in January 2011, the DASH ad-hoc group
decided to start a new evaluation experiment called "CDN-EE". The
goals are to understand the requirements for MPEG DASH to better
support CDN-based delivery, and to provide a guidelines document for
CDN operators to better support MPEG DASH streaming services. The
ongoing work is still very preliminary and does not currently target
looking into CDN Interconnection use cases.
A.2.4. ATIS IIF
ATIS ([ATIS]) IIF is the IPTV Interoperability Forum (within ATIS)
that develops requirements, standards, and specifications for IPTV.
ATIS IIF is developing the "IPTV Content on Demand (CoD) Service"
specification. This includes use of a CDN (referred to in ATIS IIF
CoD as the "Content Distribution and Delivery Functions") for support
of a Content on Demand (CoD) Service as part of a broader IPTV
service. However, this only covers the case of a managed IPTV
service (in particular where the CDN is administered by the service
provider) and does not cover the use, or interconnection, of multiple
CDNs.
A.2.5. CableLabs
"Founded in 1988 by cable operating companies, Cable Television
Laboratories, Inc. (CableLabs) is a non-profit research and
development consortium that is dedicated to pursuing new cable
telecommunications technologies and to helping its cable operator
members integrate those technical advancements into their business
objectives." [CableLabs]
CableLabs has defined specifications for CoD Content Metadata as part
of its VOD Metadata project.
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A.2.6. ETSI MCD
ETSI MCD (Media Content Distribution) is the ETSI technical committee
"in charge of guiding and coordinating standardization work aiming at
the successful overall development of multimedia systems (television
and communication) responding to the present and future market
requests on media content distribution".
MCD created a specific work item on interconnection of heterogeneous
CDNs ("CDN Interconnection, use cases and requirements") in March
2010. MCD very recently created a working group to progress this
work item. However, no protocol level work has yet started in MCD
for CDN Interconnection.
A.2.7. ETSI TISPAN
ETSI TISPAN has published two sets of IPTV specifications, one of
which is based on IMS. In addition, TISPAN is about to complete the
specifications of a CDN architecture supporting delivery of various
content services such as time-shifted TV and VoD to TISPAN devices
(UEs) or regular PCs. The use cases allow for hierarchically and
geographically distributed CDN scenarios, along with multi-CDN
cooperation. As a result, the architecture contains reference points
to support interconnection of other TISPAN CDNs. The protocol
definition phase for the corresponding CDN architecture was kicked-
off at the end of 2010. In line with its long history of leveraging
IETF protocols, ETSI could potentially leverage CDNI interfaces
developed in the IETF for their related protocol level work on
interconnections of CDNs.
A.2.8. ITU-T
SG13 is developing standards related to the support of IPTV services
(i.e.. multimedia services such as television/VoD/audio/text/
graphics/data delivered over IP-based managed networks).
ITU-T Recommendation Y.1910 [Y.1910] provides the description of the
IPTV functional architecture. This architecture includes functions
and interfaces for the distribution and delivery of content. This
architecture is aligned with the ATIS IIF architecture.
Based upon ITU-T Rec. Y.1910, ITU-T Rec. Y.2019 [Y.2019] describes in
more detail the content delivery functional architecture. This
architecture allows CDN Interconnection: some interfaces (such as D3,
D4) at the control level allow relationships between different CDNs,
in the same domain or in different domains. Generic procedures are
described, but the choice of the protocols is open.
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A.2.9. Open IPTV Forum (OIPF)
The Open IPTV Forum has developed an end-to-end solution to allow any
OIPF terminal to access enriched and personalized IPTV services
either in a managed or a non-managed network[OIPF-Overview]. Some
OIPF services (such as Network PVR) may be hosted in a CDN.
To that end, the Open IPTV Forum specification is made of 5 parts:
o Media Formats including HTTP Adaptive Streaming
o Content Metadata
o Protocols
o Terminal (Declarative or Procedural Application Environment)
o Authentication, Content Protection and Service Protection
A.2.10. TV-Anytime Forum
Version 1 of the TV-Anytime Forum specifications were published as
ETSI TS 102 822-1 through ETSI TS 102 822-7 "Broadcast and On-line
Services: Search, select, and rightful use of content on personal
storage systems ("TV-Anytime")". It includes the specification of
content metadata in XML schemas (ETSI TS 102 822-3) which define
technical parameters for the description of CoD and Live contents.
The specification is referenced by DVB and OIPF.
The TV-anytime Forum was closed in 2005.
A.2.11. SNIA
The Storage Networking Industry Association (SNIA) is an association
of producers and consumers of storage networking products whose goal
is to further storage networking technology and applications.
SNIA has published the Cloud Data Management Interface (CDMI)
standard ([SNIA-CDMI]).
"The Cloud Data Management Interface defines the functional interface
that applications will use to create, retrieve, update and delete
data elements from the Cloud. As part of this interface the client
will be able to discover the capabilities of the cloud storage
offering and use this interface to manage containers and the data
that is placed in them. In addition, metadata can be set on
containers and their contained data elements through this interface."
A.3. Related Research Projects
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A.3.1. IRTF P2P Research Group
Some information on CDN interconnection motivations and technical
issues were presented in the P2P RG at IETF 77. The presentation can
be found in [P2PRG-CDNI].
A.3.2. OCEAN
OCEAN (http://www.ict-ocean.eu/) is an EU funded research project
that started in February 2010 for 3 years. Some of its objectives
are relevant to CDNI. It aims, among other things, at designing a
new architectural framework for audiovisual content delivery over the
Internet, defining public interfaces between its major building
blocks in order to foster multi-vendor solutions and interconnection
between Content Networks (the term "Content Networks" corresponds
here to the definition introduced in [RFC3466], which encompasses
CDNs).
OCEAN has not yet published any open specifications, nor common best
practices, defining how to achieve such CDN interconnection.
A.3.3. Eurescom P1955
Eurescom P1955 was a 2010 research project involving a four European
Network operators, which studied the interests and feasibility of
interconnecting CDNs by firstly elaborating the main service models
around CDN interconnection, as well as analyzing an adequate CDN
interconnection technical architecture and framework, and finally by
providing recommendations for telcos to implement CDN
interconnection. The Eurescom P1955 project ended in July 2010.
The authors are not aware of material discussing CDN interconnection
protocols or interfaces made publically available as a deliverable of
this project.
Authors' Addresses
Ben Niven-Jenkins
Velocix (Alcatel-Lucent)
326 Cambridge Science Park
Milton Road, Cambridge CB4 0WG
UK
Email: ben@velocix.com
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Francois Le Faucheur
Cisco Systems
Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410
France
Phone: +33 4 97 23 26 19
Email: flefauch@cisco.com
Nabil Bitar
Verizon
40 Sylvan Road
Waltham, MA 02145
USA
Email: nabil.bitar@verizon.com
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