wdiff draft-jenkins-cdni-problem-statement-00.txt draft-jenkins-cdni-problem-statement-01.txt

Network Working Group B. Niven-Jenkins
Internet-Draft Velocix (Alcatel-Lucent)
Intended status: Informational F. Le Faucheur
Expires: June 5, July 21, 2011 Cisco
N. Bitar
Verizon
December 2, 2010
January 17, 2011

Content Distribution Network Interconnection (CDNI) Problem Statement
draft-jenkins-cdni-problem-statement-00
draft-jenkins-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 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 for the IETF
with a view towards creating a working group. This working group
would work on interoperable and scalable solutions for CDN
interconnection.

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

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on June 5, July 21, 2011.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 5
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 5
1.2. CDN Background . . . . . . . . . . . . . . . . . . . . . . 6 8
2. CDN Interconnect Use Cases . . . . . . . . . . . . . . . . . . 6 9
3. CDN Interconnect Model & Problem Area for IETF . . . . . . . . 10
3.1. Candidate CDNI Problem Area for IETF . . . . . . . . . . . 12
3.2. Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 13
4. Design Approach for Realizing the CDNI APIs . . . . . . . . . 14
4.1. Relationship to the OSI network model . . . . . . . . . . 15
4.2. "Reuse Instead of Reinvent" Principle . . . . . . . . . . 15
4.3. CDNI Request Routing API . . . . . . . . . . . . . . . . . 15
4.4. CDNI Metadata API . . . . . . . . . . . . . . . . . . . . 17
4.5. CDNI Logging API . . . . . . . . . . . . . . . . . . . . . 18
4.6. CDNI Control API . . . . . . . . . . . . . . . . . . . . . 19
5. Prioritizing the CDNI Work . . . . . . . . . . . . . . . . . . 19
6. Gap Analysis of relevant Standardization and Research
Activities . . . . . 7
3.1. . . . . . . . . . . . . . . . . . . . . . 20
6.1. Related standardization activities . . . . . . . . . . . . 20
6.1.1. IETF Concluded CDI Working Group (Concluded) . . . . . . . . . . 20
6.1.2. 3GPP . . . 7
3.2. IRTF P2P Research Group . . . . . . . . . . . . . . . . . 8
3.3. ETSI . . . . . 21
6.1.3. ATIS IIF . . . . . . . . . . . . . . . . . . . . . . 9
3.3.1. TISPAN . . 21
6.1.4. Cable Labs . . . . . . . . . . . . . . . . . . . . . . 9
3.3.2. 22
6.1.5. ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 22
6.1.6. ETSI TISPAN . . . 9
3.4. ATIS IIF . . . . . . . . . . . . . . . . . . 22
6.1.7. ITU-T . . . . . . . 9
3.5. . . . . . . . . . . . . . . . . . 23
6.1.8. Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 23
6.1.9. TV-Anytime Forum . . 10
3.6. ITU-T . . . . . . . . . . . . . . . . . 23
6.1.10. SNIA . . . . . . . . . 10
3.7. . . . . . . . . . . . . . . . . 24
6.2. Related Research Projects . . . . . . . . . . . . . . . . 24
6.2.1. IRTF P2P Research Group . . . . . . . . . . . . . . . 24
6.2.2. OCEAN . . . . . . . . . . . . . . . . . . . . . . . . 24
6.2.3. Eurescom P1955 . . 10
3.8. CableLabs VoD Metadata . . . . . . . . . . . . . . . . . . 11
4. CDN Interconnect Problem Area for IETF 24
6.3. Gap Analysis . . . . . . . . . . . . 11
4.1. Candidate CDNI Goals for IETF . . . . . . . . . . . 25
6.3.1. Content Acquisition across CDNs and Delivery to
End User (Data plane) . . . 13
4.2. Non-Goals for IETF . . . . . . . . . . . . . 25
6.3.2. CDNI Metadata . . . . . . . 14
5. . . . . . . . . . . . . . 26
7. Relationship to relevant IETF Working Group Groups . . . . . . . . . 15
5.1. 27
7.1. ALTO . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6. 27
7.2. DECADE . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.3. PPSP . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. 29
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. 30
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
9. 30
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. 30
11.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. 30
11.2. Informative References . . . . . . . . . . . . . . . . . . 16 31

Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 32

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
End User regardless of that user's 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
they that their collective CDN footprint can interoperate as an open content delivery infrastructure be leveraged for the
end-to-end delivery of content from Content Service Providers (CSPs)
to end users. End Users. However, no standards or open specifications currently
exist to facilitate such CDN interconnection.

Section 2 discusses the use cases for CDN interconnection. Section 3
presents the CDNI model and problem area to be considered by the
IETF. Section 4 discusses how existing protocols can be reused to
define the CDNI APIs while Section 5 proposes to focus the scope for
the initial charter of a CDNI Working Group to the minimum functional
elements necessary for basic CDN interconnection. Section 5 provides
a gap analysis of the work of other standards organization and
finally Section 5 discusses the relationship with 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
continuous media (i.e. where there is a timing relationship between
source and sink).

Metadata: Metadata in general is data about data.

Content Metata: this Metadata: This is metadata about content. It may vary in depth
from merely identifying Content. Content Metadata
comprises:

1. Metadata that is relevant to the distribution of the content (e.g. title or other information (and
therefore relevant to populate a program guide), CDN involved in the delivery of that
content). We refer to providing a complete index this type of
different scenes in a movie or providing business rules detailing how 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 be displayed, copied, or sold and it can include
policies
information pertaining to the Content's genre, cast, rating, etc
as well as information pertaining to control 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. 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 is the
subset of the with inter-CDN scope.
For example, CDNI Metadata pertaining may include geo-blocking information (i.e.
information defining geographical areas where the content is to rules that control how be
made available or blocked), availability windows (i.e. information
defining time windows during which the content is to be distributed made
available or blocked) and delivered by access control mechanisms to be enforced
(e.g. URI signature validation). CDNI Metadata may also include
information about desired distribution policy (e.g. prepositioning 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.

User:

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 the Content Service. The
User Agent will communicate with the CSP's 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 (STB), Dedicated content applications (e.g.

media players), etc.

Network Service Provider (NSP): Provides network-based connectivity/
services to Users.

Content Service Provider (CSP): Provides a Content Service to Users. End
Users (which they access via a User Agent). A CSP may own the content
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
CDN.

Content Distribution Network (CDN) / Content Delivery Network (CDN):
A type of network
Network infrastructure in which the content network elements are arranged cooperate at
layers 4 through layer 7 for more effective delivery of content Content to
User Agents. Typically a CDN consists of a Request Routing system, a
Distribution System and (that includes a set of Surrogates. 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 Interconnect (CDNI): The set of interfaces over which two or more
CDNs communicate with each other in order to achieve the delivery of
content to users User Agents by surrogates Surrogates in one CDN (the downstream CDN)
on behalf of another CDN (the upstream CDN).

Upstream CDN: For a given user request, the CDN (within a pair of
directly interconnected CDNs) that redirects the request to the other
CDN.

Downstream CDN: For a given 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 over the Internet
rather than by a particular NSP. 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
steering or directing
receiving a content request received directly from an end a user to agent, obtaining and
maintaining necessary information about a suitable Surrogate. set of candidate surrogates
or candidate CDNs, and for selecting and redirecting the user to the
appropriate surrogate or CDN. To enable CDN Interconnect, the
Request Routing System must also be capable of handling user agent
content requests passed to it by another CDN.

Distribution System: the function within a CDN responsible for
distributing Content Distribution Metadata as well as content inside
the CDN (e.g. down to the surrogates)

Delivery: the function within CDN surrogates responsible for
delivering a piece of content to the end user. 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
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 so that a given item
of content can be delivered by a CDN surrogate Surrogate (i.e. a cache) to
multiple end users User Agents (and their End Users) without transiting
multiple times through the network core (i.e from the content origin
to the cache). surrogate). This contributes to bandwidth cost reductions for
the NSP. NSP and to improved quality of experience for the end users.
CDNs also enable replication of popular content across many
surrogates, which enables content to be served to large numbers of users
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 IPTV television services to Set Top
Boxes, but are also used for delivery of content to other devices
including PCs, tablets, mobile phones etc.

Traditional CDNs have operated as over-the-top providers of digital
content distribution services, operating as an overlay on the
Internet. More recently, Network Service Providers have begun to
operate their own CDNs by deploying CDN devices within their network
infrastructure.

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) of) their content to very
large number of users 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. 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 otherwise, without
requiring the CSPs having to maintain direct business relationships with all
the CDNs involved in the delivery. Again, for this requirement, CDN
operators (NSPs or over-the-top) over-the-top CDN operators) are faced with a lack
of open specifications and best practices.

Finally,

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.

3. Gap Analysis of relevant Standardization Activities

3.1. IETF Concluded CDI Working Group

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 operational reasons (e.g. disaster, flash crowd) or commercial
reasons, an extract from the CDI WG charter
[CDI-Charter]:

o The goal of this working group is to define protocols over-the-top CDN may elect to allow the
interoperation make use of separately-administered content networks.
o A content network is another CDN
(e.g. 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.
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".

Although the market, design and requirements placed on CDNs has
changed since 2003, the RFCs above provide a reasonable starting
point and framework for discussing NSP CDN Interconnect.

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.

3.2. 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].

3.3. ETSI

ETSI is the European Telecommunications Standards Institute. ETSI
produces standards for Information and Communications Technologies
(ICT), including fixed, mobile, radio, converged, broadcast and
internet technologies.

3.3.1. TISPAN

TISPAN (Telecommunications and Internet converged Services and
Protocols on-net Surrogates for Advanced Networking) is an ETSI technical committee
creating Next Generation Networks (NGN) specifications.

TISPAN has published two IPTV specifications, one of which is based
on IMS. An extension of these specifications is being designed with a CDN architecture supporting VoD for delivery to TISPAN devices
(UEs) or regular PCs. The use cases allow given footprint) for hierarchically and
geographically distributed CDN scenarios, along with multi-CDN
cooperation. As
serving a result, the architecture contains reference points
to support interconnection of other TISPAN CDNs. There is no intent
to support heterogeneous interconnection at this point. Also, this
effort is focusing on managed IPTV services.

The protocols phase has not yet started, and thus no protocols have
yet been defined.

3.3.2. MCD

MCD (Media Content Distribution) is the ETSI technical committee "in
charge subset 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 user 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. However, no protocol level work has yet started in MCD for CDN
Interconnect.

3.4. ATIS IIF

ATIS ([ATIS]) is the Alliance for Telecommunications Industry
Solutions.

IIF is the IPTV Interoperability Forum (within ATIS) that develops
requirements, standards, and specifications for IPTV.

The IIF is developing the "IPTV Content on Demand (CoD) Service"
specification. This includes use of a CDN (referred (e.g. requests from users
attached to in ATIS IIF
CoD as the "Content Distribution and Delivery Functions") that NSP). Again, 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 requirement, CDN is administered by the IPTV
service provider) and does not cover the use, or interconnection, of
multiple CDNs.

The "IPTV Content on Demand (CoD) Service" specification 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 this protocol has not been explicitly
specified for content acquisition across CDNs, it could be a
candidate (in addition to others such as standard HTTP) for content
acquisition between CDNs in a operators
(over-the-top CDN Interconnect environment.

3.5. Open IPTV Forum (OIPF)

"The Open IPTV Forum has developed an end-to-end solution to allow
any consumer end-device, compliant to the Open IPTV Forum
specifications, to access enriched and personalised IPTV services
either in a managed or a non-managed network. To that end, the Open
IPTV Forum focuses on standardising the user-to-network interface
(UNI) both for a managed and a non-managed network" [OIPF-Overview].

OIPF has defined specifications for Content Metadata, however they
specify a definition for IPTV service related metadata and do not
include a metadata definition operators or interface that could be used between
CDNs.

3.6. ITU-T

Text to be added in a future version of this document.

3.7. OCEAN

OCEAN (http://www.ict-ocean.eu/) is an EU funded research project
that started in February 2010. Some of its objectives NSPs) are relevant
to CDNI, for example "design faced with a new content delivery framework" and
"foster multi-vendor solutions", however others are much more
implementation orientated, e.g. "self-learning caching algorithms" lack of open
specifications and "media-aware congestion control mechanisms".

OCEAN has not yet defined any protocols best practices.

Use cases for CDN Interconnection.

3.8. CableLabs VoD Metadata

"Founded Interconnection are further discussed in 1988 by cable operating companies, Cable Television
Laboratories, Inc. (CableLabs) is a non-profit research
[I-D.watson-cdni-use-cases] 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]

Cable Labs 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.

4. [I-D.bertrand-cdni-use-cases].

3. CDN Interconnect Model & Problem Area for IETF

Interconnecting CDNs involves many interactions among multiple different
functions and components
being integrated to some degree. that form each CDN. Only some of those
require standardization. Out of those, only some fit within the expertise
and charter of the IETF. The CDNI model and problem area proposed
for IETF work is illustrated in Figure 1. The candidate goals problem area
(and respectively the non-goals) for IETF work on CDN Interconnection
are discussed in Section 4.1 3.1 (and respectively Section 4.2 3.2 ).

--------
/ \
| CSP |
\ /
--------
*
*
* /\
* / \
--------------------- |CDNI| ---------------------
/ Upstream CDN \ | | / Downstream CDN \
| +-------------+ | Control API | +-------------+ |
| |CDNI |CDN Control |<======|====|=======>| CDNI Control| CDN Control | |
| +------*-*-*--+ | | | | +-*-*-*-------+ |
| * * * | | | | * * * |
| +------*------+ | Logging API | +-----*-------+ |
| ****| Logging |<======|====|=======>| Logging |**** |
| * --------------+ | | | | +-------------+ * |
| * * * | | | | * * * |
| * +--------*----+ | Req-Routing API | +---*---------+ * |
| * **|Req-Routing |<======|====|=======>| Req-Routing |** * |
| * * +-------------+ | | | | +-------------+ * * |
| * * * | | | | * * * |
| * * +----------*--+ | CD |CDNI Metadata API | API| +-*-----------+ * * |
| * * |Distribution |<======|====|=======>| Distribution| * * |
| * * | | | \ / | | | * * |
| * * | | | \/ | | | * * |
| * ****+---------+ | | | | +---------+**** * |
| ******|Surrogate|*************************|Surrogate|****** |
| | +---------+ | | Acquisition | | +-----*---+ | |
| +-------------+ | | +-------*-----+ |
\ / \ * /
--------------------- ---------*-----------
*
* Delivery
*
+------+
| user User |
| Agent|
+------+

<==> interfaces inside the scope of CDNI

**** interfaces outside the scope of CDNI

Figure 1: CDNI Problem Area

4.1.

3.1. Candidate CDNI Goals Problem Area for IETF

Listed below are parts the four APIs required to interconnect a pair of
CDNs and that constitute the problem space that are is proposed to be
addressed by a potential CDNI working group in the IETF:
o Specification of a control plane architecture for CDN
Interconnect.
o Specification IETF. The use of
the APIs and protocols required term "API" is meant to Interconnect a
pair encompass the protocol over which CDNI
data representations (e.g. CDNI Metadata records) are exchanged as
well as the specification of CDNs (where the data representations themselves
(i.e. what properties/fields each record contains, its structure,
etc.). While "interface" would be a given CDN may support multiple interconnects
with different CDNs). This more accurate term, the term
"API" is expected to comprise (but possibly
grouped retained in a different manner):
* this document because of its common use.

o CDNI Control API: This API allows the "CDNI Control" system in
interconnected CDNs to communicate. This API may support the
following:
+ allows an upstream CDN and downstream CDN to establish,
update or terminate their CDNI relationship
+ allows
* Allow bootstrapping of the other CDNI APIs (e.g. API address
discovery and establishment of security
associations)
+ allows associations).
* Allow configuration of the other CDNI APIs (e.g. Upstream CDN
specifies information to be reported through the CDNI Logging
API)
+ allows
API).
* Allow the downstream CDN to communicate information about its
delivery capabilities, resources and policies
+ allows policies.
* Allow bootstrapping of the interface between CDNs for content
acquisition (even if that interface itself is outside the scope
of the CDNI work)
* Request-Routing work).
o CDNI Request Routing API: This API allows the Request-Routing Request Routing
system in interconnected CDNs to communicate to ensure that an end- 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 CDN).
* Content Distribution
o CDNI Metadata Signaling API: This API allows
the allows:
* The Distribution system in interconnected CDNs to communicate
to ensure content distribution metadata CDNI Metadata can be exchanged across CDNs. For example, the distribution metadata information may
include information about desired distribution policy (e.g.
prepositioning vs dynamic acquisition) See
Section 1.1 for definition and about examples of CDNI Metadata.
* Limited control management of a downstream CDN by an upstream
CDN, for example to allow an upstream CDN to request that
content access
policy (e.g. allowed/blocked time/geography, authorization
checks files and/or CDNI Metadata that it shared to be performed at delivery time). It may also contain
information about where/how to acquire the content. This may
also include purged
from a downstream CDN. Support for content management (e.g. deletion of Content from
caches) across interconnected CDNs. It a CDN
is expected that the
specification of this API will comprise (i) specification of a
schema key requirement for some Content Distribution Metadata as well as (ii)
specification/selection of a signaling protocol (quite possibly
an existing IETF protocol) Service Providers in
order, amongst other use cases for content deletion, to signal support
the actual Content
Distribution Metadata encoded as per content rights agreements they have negotiated. Today's
CDNs use proprietary control interfaces to enable CSPs to
remove content cached in the schema.
* CDN and therefore there is a need
to have a similar but standardised content deletion capability
between interconnected CDNs.

o CDNI Logging API: This API 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 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. 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.
o Scalability

Note that the actual grouping of functionalities under these four
APIs is considered tentative at this stage and may be changed after
further study (e.g. some subset of functionality be moved from one
API 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 protocols & approach.

4.2. APIs 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 esssential and urgent work: this is discussed
further in Section 5.

3.2. 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 enduser, User Agent, such as streaming protocols.
o The content acquisition interface between CDNs (i.e. the dataplane 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 User End User/User Agent Authentication. User 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 optimised optimized delivery of these
objects by the surrogate to the enduser end user are outside the scope of
CDNI.
o Digital Right Rights Management (DRM). DRM is an end-to-end issue
between Origin a content protection system and User-Agent. the User Agent.
o applications Applications consuming CDNI logs (e.g. charging, analytics,
reporting,...)
reporting,...).
o Internal CDN Protocols. i.e. protocols within one CDN.
o Scalability of individual CDNs. While scalability of the CDNI
protocols/approach is in scope, how an individual CDN scales is
out of scope.
o actual criteria and Actual algorithms for selection of CDN CDNs or Surrogate Surrogates by Request-Routing systems. 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 - e.g. how to acquire and content or cache
replacement algorithms.
acquistion 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 interfaces.
o commercial, Commercial, business and legal aspects related to the
interconnections of CDNs.

The third bullet in the list above places the acquisition of content
between interconnected CDNs as out of scope for CDNI and deserves
some additional explanation. The consequence of such a decision is
that a CDNI WG would be focussed on only defining the control plane
for CDNI; and the CDNI data plane (i.e. the acquisition &
distribution of the actual content objects) would not be addressed by
a 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 a CDNI WG is describing 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 APIs can reuse and leverage existing
protocols. First the "reuse instead of reinvent" design principle is
restated, then each API is discussed individually with example
candidate protocols that can be considered for reuse or leverage.
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 these
APIs need not be created in a vacuum and that reuse or leverage of
existing protocols is likely possible.

4.1. Relationship to the OSI network model

The four CDNI APIs (CDNI Control API, CDNI Request Routing API, CDNI
Metadata API, CDNI Logging API) described in Section 3.1 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 APIs 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 APIs will
be defined on top of existing session, transport and network
protocols.

4.2. "Reuse Instead of Reinvent" Principle

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 [RFC3920], for
example) to realize the CDNI APIs.

4.3. CDNI Request Routing API

The CDNI Request Routing API 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 API needs to offer a mechanism for an
upstream CDN to issue a "Redirection Request" to a downstream CDN.
The Request Routing API 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 API 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 protocols), e.g. configured.

On receiving a Redirection Request, the downstream CDN will use the
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 API is therefore a fairly straightforward
request/response protocol 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 a
CDNI WG to define a new protocol for the request/response element of
the Request Routing API. Thus, a 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 API (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.

4.4. CDNI Metadata API

The CDNI Metadata API 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 API.
o Content Requests received directly from User Agents.

The CDNI Metadata API 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 API is therefore similar to the CDNI Request
Routing API because it is a request/response protocol 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 API, the CDNI Metadata API
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 [RFC3920].
This removes the need for a CDNI WG to define a new protocol for the
request/response element of the Metadata API.

Thus, a 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 API
(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 API.
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.

4.5. CDNI Logging API

The CDNI Logging API 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 Operator 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 API 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 API, a 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.
o A default set of events that trigger logs to be generated.

4.6. CDNI Control API

The CDNI Control API allows the "CDNI Control" system in
interconnected CDNs to communicate. The exact inter-CDN control
functionality required to be supported by the CDNI Control API is
less well defined than the other three CDNI interfaces at this time.

However, as discussed in Section 3.1, the CDNI Control API 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 APIs (e.g. API address
discovery and establishment of security associations).
o Allow configuration of the other CDNI APIs (e.g. Upstream CDN
specifies information to be reported through the CDNI Logging
API).
o Allow the downstream CDN to communicate 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 API also, existing protocols can
be reused or leveraged. Those will be considered once the
requirements for the Control API have been refined.

5. Prioritizing the CDNI Work

In order to manage the potential workload of a CDNI WG, it is
recommended that the work be prioritized in a "walk before you run"
approach.

The CDNI problem area can be categorized into different solution
scopes as follows:

o "Base CDNI" Scope: This solution scope comprises the solution
elements that can be considered as the 'minimum' needed to
actually deliver any content using interconnected CDNs. For
example, a base CDNI Request Routing API and a base CDNI Metadata
API belong to this scope because without them the upstream CDN is
unable to redirect User Agents to the downstream CDN and the
downstream CDN is unable to obtain the delivery policies and other
CDNI Metadata required to ingest and deliver the content.
o "Operationalized CDNI" Scope: This solution scope comprises the
solution elements that can be considered as the 'minimum' needed
to 'operationalize' CDN Interconnects. For example, the CDNI
Logging API and the base capabilities of the CDNI Control API
(e.g. content file/metadata deletion) belong to this scope because
without them CDN operators are required to substitute for them
either with manual processes or proprietary interfaces.
o "Enhanced CDNI" Scope: This solution scope comprises the solution
elements that can be classed as 'enhanced features'. For example,
the aspects of the CDNI Control API related to automatic
bootstrapping and configuration belong to this scope.

It is proposed that these solution scopes be addressed primarily
sequentially by a CDNI WG and that the initial charter be centered
around the "Base CDNI" scope. However there is obvious benefit from
having a solution for the "Base CDNI" scope that is amenable to
extension for support of the "Operational" scope and "Enhanced"
scope. Therefore it is proposed that the initial CDNI WG charter
also includes definition of (at least) the main requirements for the
"Operationalized CDNI" scope and "Enhanced CDNI" Scope, so those can
be kept in mind when defining the solution for the "Base CDNI" scope.

6. Gap Analysis of relevant Standardization and Research Activities

There are a number of other standards bodies and industry forums that
are working in areas related to CDN, and in some cases related to
CDNI. This section will first outline the key standardization
organizations undertaking related work, some related research
projects, and will then outline any potential overlap with the
proposed CDNI WG and any component that could potentially be reused
by CDNI .

6.1. Related standardization activities

6.1.1. IETF CDI Working Group

5.1. (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.
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:

6.1.2. 3GPP

3GPP has specified a Progressive Download and Dynamic Adaptive
Streaming over HTTP [3GPP-DASH] based on a Media Presentation
Description (MPD) and Media Segmentation Format. The 3GPP DASH work
is focussed on the information required by a User Agent to obtain and
present (e.g. play) content to an end user. Such content could be
obtained from a CDN but that is independent of the DASH
specifications. 3GPP DASH could be a candidate for content
acquisition between CDNs in a CDN Interconnect environment.

6.1.3. 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.

6.1.4. Cable Labs

"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]

Cable Labs has defined specifications for CoD Content Metadata as
part of its VOD Metadata project.

6.1.5. 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 Interconnect.

6.1.6. 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.

6.1.7. 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.

6.1.8. 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

6.1.9. 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.

6.1.10. 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."

6.2. Related Research Projects

6.2.1. 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].

6.2.2. 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 [IETF RFC3466], which
encompasses CDNs).

OCEAN has not yet published any open specifications, nor common best
practices, defining how to achieve such CDN interconnection.

6.2.3. 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 made publically available as a deliverable of this project.

6.3. Gap Analysis

A number of standards bodies have produced specifications related to
CDNs, namely:

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 <TODO: Add a sentence on ITU>
o IETF CDN 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 protocols/APIs and CDNI
Metadata representations required to enable even a base level of CDN
Interconnect functionality to be implemented.

The following sections will summarize the existing work described in
Section 6.1 against the CDNI problem space.

6.3.1. 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 [3GPP-DASH],...).

o ATIS specification "IPTV Content on Demand (CoD) Service" [REF]
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
Interconnect environment. Therefore for the purpose of a CDNI WG
there are already multiple existing data plane protocols that can be
used for content acquisition across CDNs.

Similarly, there are multiple existing standards (e.g. OIPTF data
plane mentioned above, HTTP adaptive streaming [3GPP-DASH]) or public
specifications (e.g. vendor specific HTTP Adaptive streaming
specification) so that content delivery is considered already solved
(or at least sufficiently addressed in other forums).

Thus, specificatio 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.

6.3.2. CDNI Metadata

Cable Labs, ITU, OIPF and TV-Anytime have work items dedicated to the
specification of content metadata:

o Cable Labs 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
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
Interconnect solution, it is worth considering CDMI as one of the
existing pieces of work that may potentially be leveraged for the
CDNI Metadata API (e.g by extending the CDMI metadata to address more
specific CDNI needs).

7. Relationship to relevant IETF Working Groups

7.1. 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 could can be used by a CDN Request Routing
system to improve its selection of a CDN surrogate to serve a
particular user request. User Agent request (or to serve a request from another
surrogate). See [I-D.penno-alto-cdn] for a detailed discussion on
how CDN Request Routing can 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 Interconnect.
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 proposed in this document because the integration
between ALTO and a CDN would fall under "algorithms for selection of
CDN or Surrogate by Request-Routing systems" in Section 4.2

6. 3.2 and is
therefore out of scope for a CDNI WG. One area for further study is
whether additional information should be provided by an ALTO service
to facilitate CDNI CDN selection.

7.2. 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.
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 APIs 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 APIs 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 API between CDNs is outside the scope of the CDNI work,
this question is left for further study.

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 proposed in this document.

7.3. 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 API 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 proposed in this document for CDNI.

8. IANA Considerations

This document makes no request of IANA.

Note to RFC Editor: this section may be removed on publication as an
RFC.

9. Security Considerations

This document describes

Distribution of content by a problem faced CDN comes with a range of security
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 does not
itself introduce any CSPs today in the context
of standalone CDNs. However, interconnection of CDNs introduces a
new set of security considerations.

However, maintaining 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 it, are critical requirements for both
CDN Providers and their customers 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.

10. Acknowledgements

The authors would like to thank Andre Beck, Mark Carlson, Bruce
Davie, David Ferguson, Yiu Lee, Julien Maisonneuve, Emile Stephan and
Mahesh Viveganandhan and Bruce Davie for their early review comments and contributions to
the text.

11. References

9.1.

11.1. Normative References

[I-D.bertrand-cdni-use-cases]
Bertrand, G. and E. Stephan, "Use Cases for Content
Distribution Network Interconnection",
draft-bertrand-cdni-use-cases-00 (work in progress),
January 2011.

[I-D.watson-cdni-use-cases]
Watson, G., "CDN Interconnect Use Cases",
draft-watson-cdni-use-cases-00 (work in progress),
January 2011.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2.

11.2. Informative References

[3GPP-DASH]
""Progressive Download and Dynamic Adaptive Streaming over
HTTP" http://www.3gpp.org/ftp/Specs/html-info/26.234.htm".

[ALTO-Charter]
"IETF ALTO WG Charter
(http://datatracker.ietf.org/wg/alto/charter/)".

[ATIS] "ATIS (http://www.atis.org/)".

[CDI-Charter]
"IETF CDI WG Charter
(http://www.ietf.org/wg/concluded/cdi)".

[CableLabs]
"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.penno-alto-cdn]
Penno, R., Raghunath, S., Medved, J., Alimi, R., Yang, R.,
and S. Previdi, "ALTO and Content Delivery Networks",
draft-penno-alto-cdn-02 (work in progress), October 2010.

[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)",
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.

[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.

[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
Protocol", RFC 5023, October 2007.

[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.

Authors' Addresses

Ben Niven-Jenkins
Velocix (Alcatel-Lucent)
326 Cambridge Science Park
Milton Road, Cambridge CB4 0WG
UK

Email: ben@velocix.com

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