draft-ietf-cdni-problem-statement-03.txt   draft-ietf-cdni-problem-statement-04.txt 
Network Working Group B. Niven-Jenkins Network Working Group B. Niven-Jenkins
Internet-Draft Velocix (Alcatel-Lucent) Internet-Draft Velocix (Alcatel-Lucent)
Intended status: Informational F. Le Faucheur Intended status: Informational F. Le Faucheur
Expires: July 24, 2012 Cisco Expires: September 11, 2012 Cisco
N. Bitar N. Bitar
Verizon Verizon
January 21, 2012 March 10, 2012
Content Distribution Network Interconnection (CDNI) Problem Statement Content Distribution Network Interconnection (CDNI) Problem Statement
draft-ietf-cdni-problem-statement-03 draft-ietf-cdni-problem-statement-04
Abstract Abstract
Content Delivery Networks (CDNs) provide numerous benefits: reduced Content Delivery Networks (CDNs) provide numerous benefits: reduced
delivery cost for cacheable content, improved quality of experience delivery cost for cacheable content, improved quality of experience
for End Users and increased robustness of delivery. For these for End Users and increased robustness of delivery. For these
reasons they are frequently used for large-scale content delivery. reasons they are frequently used for large-scale content delivery.
As a result, existing CDN Providers are scaling up their As a result, existing CDN Providers are scaling up their
infrastructure and many Network Service Providers (NSPs) are infrastructure and many Network Service Providers (NSPs) are
deploying their own CDNs. It is generally desirable that a given deploying their own CDNs. It is generally desirable that a given
content item can be delivered to an End User regardless of that End content item can be delivered to an End User regardless of that End
User's location or attachment network. This creates a requirement User's location or attachment network. This is the motivation for
for interconnecting standalone CDNs so they can interoperate as an interconnecting standalone CDNs so they can interoperate as an open
open content delivery infrastructure for the end-to-end delivery of content delivery infrastructure for the end-to-end delivery of
content from Content Service Providers (CSPs) to End Users. However, content from Content Service Providers (CSPs) to End Users. However,
no standards or open specifications currently exist to facilitate no standards or open specifications currently exist to facilitate
such CDN interconnection. such CDN interconnection.
The goal of this document is to outline the problem area of CDN The goal of this document is to outline the problem area of CDN
interconnection for the IETF CDNI (CDN Interconnection) working interconnection for the IETF CDNI (CDN Interconnection) working
group. group.
Status of this Memo Status of this Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 24, 2012. This Internet-Draft will expire on September 11, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 12 skipping to change at page 3, line 12
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. CDN Background . . . . . . . . . . . . . . . . . . . . . . 8 1.2. CDN Background . . . . . . . . . . . . . . . . . . . . . . 8
2. CDN Interconnection Use Cases . . . . . . . . . . . . . . . . 9 2. CDN Interconnection Use Cases . . . . . . . . . . . . . . . . 9
3. CDN Interconnection Model & Problem Area for IETF . . . . . . 10 3. CDN Interconnection Model & Problem Area for IETF . . . . . . 10
4. Design Approach for Realizing the CDNI Interfaces . . . . . . 14 4. Scoping the CDNI Problem . . . . . . . . . . . . . . . . . . . 14
4.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 15 4.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 14
4.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 17 4.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 15
4.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 18 4.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 16
4.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 19 4.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 16
5. Relevant work from other standardization activities . . . . . 19 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
5.1. Content Acquisition across CDNs and Delivery to End 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
User (Data plane) . . . . . . . . . . . . . . . . . . . . 20 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
5.2. CDNI Metadata . . . . . . . . . . . . . . . . . . . . . . 21 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6. Relationship to relevant IETF Working Groups . . . . . . . . . 22 8.1. Normative References . . . . . . . . . . . . . . . . . . . 17
6.1. ALTO . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8.2. Informative References . . . . . . . . . . . . . . . . . . 17
6.2. DECADE . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Appendix A. Design considerations for realizing the CDNI
6.3. PPSP . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Interfaces . . . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 A.1. CDNI Request Routing Interface . . . . . . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25 A.2. CDNI Metadata Interface . . . . . . . . . . . . . . . . . 21
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25 A.3. CDNI Logging Interface . . . . . . . . . . . . . . . . . . 22
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 A.4. CDNI Control Interface . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25 Appendix B. Additional Material . . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . . 25 B.1. Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 24
Appendix A. Additional Material . . . . . . . . . . . . . . . . . 28 B.2. Related standardization activites . . . . . . . . . . . . 25
A.1. Non-Goals for IETF . . . . . . . . . . . . . . . . . . . . 28 B.2.1. IETF CDI Working Group (Concluded) . . . . . . . . . . 26
A.2. Related standardization activities . . . . . . . . . . . . 29 B.2.2. 3GPP . . . . . . . . . . . . . . . . . . . . . . . . . 27
A.2.1. IETF CDI Working Group (Concluded) . . . . . . . . . . 29 B.2.3. ISO MPEG . . . . . . . . . . . . . . . . . . . . . . . 28
A.2.2. 3GPP . . . . . . . . . . . . . . . . . . . . . . . . . 30 B.2.4. ATIS IIF . . . . . . . . . . . . . . . . . . . . . . . 28
A.2.3. ISO MPEG . . . . . . . . . . . . . . . . . . . . . . . 31 B.2.5. CableLabs . . . . . . . . . . . . . . . . . . . . . . 29
A.2.4. ATIS IIF . . . . . . . . . . . . . . . . . . . . . . . 31 B.2.6. ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 29
A.2.5. CableLabs . . . . . . . . . . . . . . . . . . . . . . 31 B.2.7. ETSI TISPAN . . . . . . . . . . . . . . . . . . . . . 29
A.2.6. ETSI MCD . . . . . . . . . . . . . . . . . . . . . . . 32 B.2.8. ITU-T . . . . . . . . . . . . . . . . . . . . . . . . 29
A.2.7. ETSI TISPAN . . . . . . . . . . . . . . . . . . . . . 32 B.2.9. Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 30
A.2.8. ITU-T . . . . . . . . . . . . . . . . . . . . . . . . 32 B.2.10. TV-Anytime Forum . . . . . . . . . . . . . . . . . . . 30
A.2.9. Open IPTV Forum (OIPF) . . . . . . . . . . . . . . . . 33 B.2.11. SNIA . . . . . . . . . . . . . . . . . . . . . . . . . 30
A.2.10. TV-Anytime Forum . . . . . . . . . . . . . . . . . . . 33 B.2.12. Summary of existing stanardization work . . . . . . . 31
A.2.11. SNIA . . . . . . . . . . . . . . . . . . . . . . . . . 33 B.3. Related Research Projects . . . . . . . . . . . . . . . . 33
A.3. Related Research Projects . . . . . . . . . . . . . . . . 34 B.3.1. IRTF P2P Research Group . . . . . . . . . . . . . . . 33
A.3.1. IRTF P2P Research Group . . . . . . . . . . . . . . . 34 B.3.2. OCEAN . . . . . . . . . . . . . . . . . . . . . . . . 33
A.3.2. OCEAN . . . . . . . . . . . . . . . . . . . . . . . . 34 B.3.3. Eurescom P1955 . . . . . . . . . . . . . . . . . . . . 33
A.3.3. Eurescom P1955 . . . . . . . . . . . . . . . . . . . . 34 B.4. Relationship to relevant IETF Working Groups . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 B.4.1. ALTO . . . . . . . . . . . . . . . . . . . . . . . . . 33
B.4.2. DECADE . . . . . . . . . . . . . . . . . . . . . . . . 34
B.4.3. PPSP . . . . . . . . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
The volume of video and multimedia content delivered over the The volume of video and multimedia content delivered over the
Internet is rapidly increasing and expected to continue doing so in Internet is rapidly increasing and expected to continue doing so in
the future. In the face of this growth, Content Delivery Networks the future. In the face of this growth, Content Delivery Networks
(CDNs) provide numerous benefits: reduced delivery cost for cacheable (CDNs) provide numerous benefits: reduced delivery cost for cacheable
content, improved quality of experience for End Users and increased content, improved quality of experience for End Users and increased
robustness of delivery. For these reasons CDNs are frequently used robustness of delivery. For these reasons CDNs are frequently used
for large-scale content delivery. As a result, existing CDN for large-scale content delivery. As a result, existing CDN
Providers are scaling up their infrastructure and many Network Providers are scaling up their infrastructure and many Network
Service Providers (NSPs) are deploying their own CDNs. Service Providers (NSPs) are deploying their own CDNs.
It is generally desirable that a given content item can be delivered 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 to an End User regardless of that End User's location or attachment
network. However, a given CDN in charge of delivering a given network. However, a given CDN in charge of delivering a given
content may not have a footprint that expands close enough to the End content may not have a footprint that expands close enough to the End
User's current location or attachment network, or may not have the User's current location or attachment network, or may not have the
necessary resources, to realize the user experience and cost benefit necessary resources, to realize the user experience and cost benefit
that a more distributed CDN infrastructure would allow. This creates that a more distributed CDN infrastructure would allow. This is the
a requirement for interconnecting standalone CDNs so that their motivation for interconnecting standalone CDNs so that their
collective CDN footprint and resources can be leveraged for the end- collective CDN footprint and resources can be leveraged for the end-
to-end delivery of content from Content Service Providers (CSPs) to to-end delivery of content from Content Service Providers (CSPs) to
End Users. As an example, a CSP could contract with an End Users. As an example, a CSP could contract with an
"authoritative" CDN Provider for the delivery of content and that "authoritative" CDN Provider for the delivery of content and that
authoritative CDN Provider could contract with one or more downstream authoritative CDN Provider could contract with one or more downstream
CDN Provider(s) to distribute and deliver some or all of the content CDN Provider(s) to distribute and deliver some or all of the content
on behalf of the authoritative CDN Provider. The formation and on behalf of the authoritative CDN Provider. The formation and
details of any business relationships between a CSP and a CDN details of any business relationships between a CSP and a CDN
Provider and between one CDN Provider and another CDN Provider are Provider and between one CDN Provider and another CDN Provider are
out of scope of this document. However, no standards or open out of scope of this document. However, no standards or open
specifications currently exist to facilitate such CDN specifications currently exist to facilitate such CDN
interconnection. interconnection.
The goal of this document is to outline the problem area of CDN The goal of this document is to outline the problem area of CDN
interconnection for the IETF CDNI (CDN Interconnection) working interconnection. Section 2 discusses the use cases for CDN
group. Section 2 discusses the use cases for CDN interconnection. interconnection. Section 3 presents the CDNI model and problem area
Section 3 presents the CDNI model and problem area being considered being considered by the IETF. Section 4 describes each CDNI
by the IETF. Section 4 describes each CDNI interface individually interface individually and highlights example candidate protocols
and highlights example candidate protocols that could be considered that could be considered for reuse or leveraging to implement the
for reuse or leveraging to implement the CDNI interfaces. Section 5 CDNI interfaces. Appendix B.2 discusses the relevant work of other
discusses the relevant work of other standards organizations. standards organizations. Appendix B.4 describes the relationships
Section 6 describes the relationships between the CDNI problem space between the CDNI problem space and other relevant IETF Working
and other relevant IETF Working Groups. Groups.
1.1. Terminology 1.1. Terminology
This document uses the following terms: This document uses the following terms:
Content: Any form of digital data. One important form of Content Content: Any form of digital data. One important form of Content
with additional constraints on distribution and delivery is with additional constraints on distribution and delivery is
continuous media (i.e. where there is a timing relationship between continuous media (i.e. where there is a timing relationship between
source and sink). source and sink).
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CDN Provider: The service provider who operates a CDN and offers a CDN Provider: The service provider who operates a CDN and offers a
service of content delivery, typically used by a Content Service service of content delivery, typically used by a Content Service
Provider or another CDN Provider. Note that a given entity may Provider or another CDN Provider. Note that a given entity may
operate in more than one role. For example, a company may operate in more than one role. For example, a company may
simultaneously operate as a Content Service Provider, a Network simultaneously operate as a Content Service Provider, a Network
Service Provider and a CDN Provider. Service Provider and a CDN Provider.
CDN Interconnection (CDNI): A relationship between a pair of CDNs CDN Interconnection (CDNI): A relationship between a pair of CDNs
that enables one CDN to provide content delivery services on behalf that enables one CDN to provide content delivery services on behalf
of another CDN. A CDN Interconnection may be wholly or partially of another CDN. A CDN Interconnection may be wholly or partially
realised through a set of interfaces over which a pair of CDNs realized through a set of interfaces over which a pair of CDNs
communicate with each other in order to achieve the delivery of communicate with each other in order to achieve the delivery of
content to User Agents by Surrogates in one CDN (the downstream CDN) content to User Agents by Surrogates in one CDN (the downstream CDN)
on behalf of another CDN (the upstream CDN). on behalf of another CDN (the upstream CDN).
Authoritative CDN: A CDN which has a direct relationship with a CSP Authoritative CDN: A CDN which has a direct relationship with a CSP
for the distribution & delivery of that CSP's content by the for the distribution & delivery of that CSP's content by the
authoritative CDN or by downstream CDNs of the authoritative CDN. authoritative CDN or by downstream CDNs of the authoritative CDN.
Upstream CDN: For a given End User request, the CDN (within a pair of Upstream CDN: For a given End User request, the CDN (within a pair of
directly interconnected CDNs) that redirects the request to the other directly interconnected CDNs) that redirects the request to the other
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by the other CDN (the Upstream CDN). Note that in the case of 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. successive redirections (e.g. CDN1-->CDN2-->CDN3) a given CDN (e.g.
CDN2) may act as the Downstream CDN for a redirection (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 CDN1-->CDN2) and as the Upstream CDN for the subsequent redirection
of the same request (e.g. CDN2-->CDN3). of the same request (e.g. CDN2-->CDN3).
Over-the-top (OTT): A service, e.g. content delivery using a CDN, Over-the-top (OTT): A service, e.g. content delivery using a CDN,
operated by a different operator than the NSP to which the users of operated by a different operator than the NSP to which the users of
that service are attached. that service are attached.
Surrogate: A device/function that interacts with other elements of Surrogate: A device/function (often called a cache) that interacts
the CDN for the control and distribution of Content within the CDN with other elements of the CDN for the control and distribution of
and interacts with User Agents for the delivery of the Content. 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 Request Routing System: The function within a CDN responsible for
receiving a content request from a User Agent, obtaining and receiving a content request from a User Agent, obtaining and
maintaining necessary information about a set of candidate surrogates maintaining necessary information about a set of candidate surrogates
or candidate CDNs, and for selecting and redirecting the user to the or candidate CDNs, and for selecting and redirecting the user to the
appropriate surrogate or CDN. To enable CDN Interconnection, the appropriate surrogate or CDN. To enable CDN Interconnection, the
Request Routing System must also be capable of handling User Agent Request Routing System must also be capable of handling User Agent
content requests passed to it by another CDN. content requests passed to it by another CDN.
Distribution System: The function within a CDN responsible for Distribution System: The function within a CDN responsible for
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Some service providers operate over multiple geographies and federate Some service providers operate over multiple geographies and federate
multiple affiliate NSPs. These NSPs typically operate independent multiple affiliate NSPs. These NSPs typically operate independent
CDNs. As they evolve their services (e.g. for seamless support of CDNs. As they evolve their services (e.g. for seamless support of
content services to nomadic users across affiliate NSPs) there is a content services to nomadic users across affiliate NSPs) there is a
need for interconnection of these CDNs, that represents a first use need for interconnection of these CDNs, that represents a first use
case for CDNI. However there are no open specifications, nor common case for CDNI. However there are no open specifications, nor common
best practices, defining how to achieve such CDN interconnection. best practices, defining how to achieve such CDN interconnection.
CSPs have a desire to be able to get (some of) their content to very 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 large numbers of End Users, who are often distributed across a number
with a high quality of experience, all without having to maintain of geographies, while maintaining a high quality of experience, all
direct business relationships with many different CDN Providers (or without having to maintain direct business relationships with many
having to extend their own CDN to a large number of locations). Some different CDN Providers (or having to extend their own CDN to a large
NSPs are considering interconnecting their respective CDNs (as well number of locations). Some NSPs are considering interconnecting
as possibly over-the-top CDNs) so that this collective infrastructure their respective CDNs (as well as possibly over-the-top CDNs) so that
can address the requirements of CSPs in a cost effective manner. this collective infrastructure can address the requirements of CSPs
This represents a second use case for CDNI. In particular, this in a cost effective manner. This represents a second use case for
would enable the CSPs to benefit from on-net delivery (i.e. within CDNI. In particular, this would enable the CSPs to benefit from on-
the Network Service Provider's own network/CDN footprint) whenever net delivery (i.e. within the Network Service Provider's own network/
possible and off-net delivery otherwise, without requiring the CSPs CDN footprint) whenever possible and off-net delivery otherwise,
to maintain direct business relationships with all the CDNs involved without requiring the CSPs to maintain direct business relationships
in the delivery. Again, for this requirement, CDN Providers (NSPs or with all the CDNs involved in the delivery. Again, CDN Providers
over-the-top CDN operators) are faced with a lack of open (NSPs or over-the-top CDN operators) are faced with a lack of open
specifications and best practices. specifications and best practices.
NSPs have often deployed CDNs as specialized cost-reduction projects NSPs have often deployed CDNs as specialized cost-reduction projects
within the context of a particular service or environment, some NSPs within the context of a particular service or environment. Some NSPs
operate separate CDNs for separate services. For example, there may operate separate CDNs for separate services. For example, there may
be a CDN for managed IPTV service delivery, a CDN for web-TV delivery 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 and a CDN for video delivery to Mobile terminals. As NSPs integrate
their service portfolio, there is a need for interconnecting these their service portfolio, there is a need for interconnecting these
CDNs, representing a third use case for CDNI. Again, NSPs face the CDNs, representing a third use case for CDNI. Again, NSPs face the
problem of lack of open interfaces for CDN interconnection. problem of lack of open interfaces for CDN interconnection.
For operational reasons (e.g. disaster, flash crowd) or commercial For operational reasons (e.g. disaster, flash crowd) or commercial
reasons, an over-the-top CDN may elect to make use of another CDN 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 (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 serving a subset of the user requests (e.g. requests from users
attached to that NSP), which results in a fourth use case for CDNI. attached to that NSP), which results in a fourth use case for CDNI
Again, for this requirement, CDN Providers (over-the-top CDN because CDN Providers (over-the-top CDN Providers or NSPs) are faced
Providers or NSPs) are faced with a lack of open specifications and with a lack of open specifications and best practices.
best practices.
Use cases for CDN Interconnection are further discussed in Use cases for CDN Interconnection are further discussed in
[I-D.ietf-cdni-use-cases]. [I-D.ietf-cdni-use-cases].
3. CDN Interconnection Model & Problem Area for IETF 3. CDN Interconnection Model & Problem Area for IETF
This section discusses the problem area for the IETF work on CDN
Interconnection.
Interconnecting CDNs involves interactions among multiple different Interconnecting CDNs involves interactions among multiple different
functions and components that form each CDN. Only some of those functions and components that form each CDN. Only some of those
require standardization. This section discusses the problem area for require standardization.
the IETF work on CDN Interconnection. The CDNI model and problem
area defined for IETF work is illustrated in Figure 1.
--------
/ \
| 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 Model 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
functionality can be achieved with existing CDN technology, the
current lack of any standardized CDNI interfaces with the necessary
level of functionality such as those discussed in this document is
preventing the deployment of CDN Interconnection.
Listed below are the four interfaces required to interconnect a pair Listed below are the four interfaces required to interconnect a pair
of CDNs and that constitute the problem space that is proposed to be of CDNs and that constitute the problem space of CDN Interconnection
addressed by the CDNI working group in the IETF. The use of the term along with the required functionality of each interface for which
"interface" is meant to encompass the protocol over which CDNI data standards do not currently exist. As part of the development of the
representations (e.g. CDNI Metadata objects) are exchanged as well CDNI interfaces it will also be necessary to agree on common
as the specification of the data representations themselves (i.e. mechanisms for how to identify and name the data objects that are to
what properties/fields each object contains, its structure, etc.). be interchanged between interconnected CDNs.
The use of the term "interface" is meant to encompass the protocol
over which CDNI data representations (e.g. CDNI Metadata objects)
are exchanged as well as the specification of the data
representations themselves (i.e. what properties/fields each object
contains, its structure, etc.).
o CDNI Control interface: This interface allows the "CDNI Control" o CDNI Control interface: This interface allows the "CDNI Control"
system in interconnected CDNs to communicate. This interface may system in interconnected CDNs to communicate. This interface may
support the following: support the following:
* Allow bootstrapping of the other CDNI interfaces (e.g. * Allow bootstrapping of the other CDNI interfaces (e.g.
interface address/URL discovery and establishment of security interface address/URL discovery and establishment of security
associations). associations).
* Allow configuration of the other CDNI interfaces (e.g. * Allow configuration of the other CDNI interfaces (e.g.
Upstream CDN specifies information to be reported through the Upstream CDN specifies information to be reported through the
CDNI Logging interface). CDNI Logging interface).
* Allow the downstream CDN to communicate static (or fairly * Allow the downstream CDN to communicate static (or fairly
static) information about its delivery capabilities and static) information about its delivery capabilities and
policies. policies.
* Allow bootstrapping of the interface between CDNs for content * Allow bootstrapping of the interface between CDNs for content
acquisition (even if that interface itself is outside the scope acquisition (even if that interface itself is outside the scope
of the CDNI work). of the CDNI work).
* Allow upstream CDN to initiate or request specific actions to * Allow an upstream CDN to initiate or request specific actions
be undertaken in the downstream CDN. For example, this may to be undertaken in the downstream CDN. For example, to allow
include the following capabilities: an upstream CDN to initiate content or CDNI Metadata
+ Allow an upstream CDN to request that content files and/or acquisition (pre-positioning) or to request the invalidation or
CDNI Metadata that it previously shared, be purged from, or purging of content files and/or CDNI Metadata in a downstream
invalidated in, a downstream CDN. Support for content CDN.
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 o CDNI Request Routing interface: This interface allows the Request
Routing systems in interconnected CDNs to communicate to ensure Routing systems in interconnected CDNs to communicate to ensure
that an End User request can be (re)directed from an upstream CDN that an End User request can be (re)directed from an upstream CDN
to a surrogate in the downstream CDN, in particular where to a surrogate in the downstream CDN, in particular where
selection responsibilities may be split across CDNs (for example selection responsibilities may be split across CDNs (for example
the upstream CDN may be responsible for selecting the downstream the upstream CDN may be responsible for selecting the downstream
CDN while the downstream CDN may be responsible for selecting the CDN while the downstream CDN may be responsible for selecting the
actual surrogate within that downstream CDN). In particular, the actual surrogate within that downstream CDN). In particular, the
CDN Request Routing interface, may support the following: CDN Request Routing interface, may support the following:
* Allow the upstream CDN to query the downstream CDN at request * Allow the upstream CDN to query the downstream CDN at request
routing time before redirecting the request to the downstream routing time before redirecting the request to the downstream
CDN. CDN.
* Allow the downstream CDN to provide to the upstream CDN (static * Allow the downstream CDN to provide to the upstream CDN (static
or dynamic) information (e.g. resources, footprint, load) to or dynamic) information (e.g. resources, footprint, load) to
facilitate selection of the downstream CDN by the upstream CDN facilitate selection of the downstream CDN by the upstream CDN
request routing system when processing subsequent content request routing system when processing subsequent content
requests from User Agents. requests from User Agents.
o CDNI Metadata distribution interface: This interface allows the o CDNI Metadata distribution interface: This interface allows the
Distribution system in interconnected CDNs to communicate to Distribution system in interconnected CDNs to communicate to
skipping to change at page 13, line 37 skipping to change at page 12, line 29
Note that the actual grouping of functionalities under these four Note that the actual grouping of functionalities under these four
interfaces is considered tentative at this stage and may be changed interfaces is considered tentative at this stage and may be changed
after further study (e.g. some subset of functionality be moved from after further study (e.g. some subset of functionality be moved from
one interface into another). one interface into another).
The above list covers a significant potential problem space, in part The above list covers a significant potential problem space, in part
because in order to interconnect two CDNs there are several 'touch because in order to interconnect two CDNs there are several 'touch
points' that require standardization. However, it is expected that points' that require standardization. However, it is expected that
the CDNI interfaces need not be defined from scratch and instead can the CDNI interfaces need not be defined from scratch and instead can
very significantly reuse or leverage existing protocols: this is very significantly reuse or leverage existing protocols: this is
discussed further in Section 4. Also, it is expected that the items discussed further in Section 4.
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 The interfaces that form the CDNI problem area are illustrated in
will also be necessary to agree on common mechanisms for how to Figure 1.
identify and name the data objects that are to be interchanged
between interconnected CDNs.
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 | CSP |
[I-D.bertrand-cdni-experiments]. The conclusions of those \ /
experiments are that while some basic limited CDN Interconnection --------
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. ---------------------- |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: A Model for the CDNI Problem Area
As illustrated in Figure 1, the acquisition of content between As illustrated in Figure 1, the acquisition of content between
interconnected CDNs is out of scope for CDNI, which deserves some interconnected CDNs is out of scope for CDNI, which deserves some
additional explanation. The consequence of such a decision is that additional explanation. The consequence of such a decision is that
the CDNI working group is focussed on only defining the control plane the CDNI problem space described in this document is focussed on only
for CDNI; and the CDNI data plane (i.e. the acquisition & defining the control plane for CDNI; and the CDNI data plane (i.e.
distribution of the actual content objects) will not be addressed by the acquisition & distribution of the actual content objects) is out
the CDNI working group. The rationale for such a decision is that of scope. The rationale for such a decision is that CDNs today
CDNs today typically already use standardized protocols such as HTTP, typically already use standardized protocols such as HTTP, FTP,
FTP, rsync, etc. to acquire content from their CSP customers and it rsync, etc. to acquire content from their CSP customers and it is
is expected that the same protocols could be used for acquisition expected that the same protocols could be used for acquisition
between interconnected CDNs. Therefore the problem of content between interconnected CDNs. Therefore the problem of content
acquisition is considered already solved and all that is required acquisition is considered already solved and all that is required
from specifications developed by the CDNI working group is to from specifications developed by the CDNI working group is to
describe within the CDNI Metadata where to go and which protocol to describe within the CDNI Metadata where to go and which protocol to
use to retrieve the content. use to retrieve the content.
4. Design Approach for Realizing the CDNI Interfaces 4. Scoping the CDNI Problem
This section expands on how CDNI interfaces can reuse and leverage This section outlines how the scope of work addressing the CDNI
existing protocols before describing each CDNI interface individually problem space can be constrained through reuse or leveraging of
and highlighting example candidate protocols that could be considered existing protocols to implement the CDNI interfaces. This discussion
for reuse or leveraging to implement the CDNI interfaces. This is not intended to pre-empt any working group decision as to the most
discussion is not intended to pre-empt any working group decision as appropriate protocols, technologies and solutions to select to
to the most appropriate protocols, technologies and solutions to realize the CDNI interfaces but is intended as an illustration of the
select to realize the CDNI interfaces but is intended as an fact that the CDNI interfaces need not be created in a vacuum and
illustration of the fact that the CDNI interfaces need not be created that reuse or leverage of existing protocols is likely possible.
in a vacuum and that reuse or leverage of existing protocols is
likely possible.
The four CDNI interfaces (CDNI Control interface, CDNI Request The four CDNI interfaces (CDNI Control interface, CDNI Request
Routing interface, CDNI Metadata interface, CDNI Logging interface) Routing interface, CDNI Metadata interface, CDNI Logging interface)
described in Section 3 within the CDNI problem area are all control described in Section 3 within the CDNI problem area are all control
plane interfaces operating at the application layer (Layer 7 in the plane interfaces operating at the application layer (Layer 7 in the
OSI network model). Firstly, since it is not expected that these OSI network model). Firstly, since it is not expected that these
interfaces would exhibit unique session, transport or network interfaces would exhibit unique session, transport or network
requirements as compared to the many other existing applications in requirements as compared to the many other existing applications in
the Internet, it is expected that the CDNI interfaces will be defined the Internet, it is expected that the CDNI interfaces will be defined
on top of existing session, transport and network protocols. on top of existing session, transport and network protocols.
skipping to change at page 15, line 16 skipping to change at page 15, line 8
4.1. CDNI Request Routing Interface 4.1. CDNI Request Routing Interface
The CDNI Request Routing interface enables a Request Routing function The CDNI Request Routing interface enables a Request Routing function
in an upstream CDN to query a Request Routing function in a in an upstream CDN to query a Request Routing function in a
downstream CDN to determine if the downstream CDN is able (and downstream CDN to determine if the downstream CDN is able (and
willing) to accept the delegated content request and to allow the willing) to accept the delegated content request and to allow the
downstream CDN to control what the upstream Request Routing function downstream CDN to control what the upstream Request Routing function
should return to the User Agent in the redirection message. should return to the User Agent in the redirection message.
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 working group to define a new protocol
for the request/response element of the CDNI Request Routing
interface.
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 working group 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 leveraging ALTO).
4.2. CDNI Metadata Interface
The CDNI Metadata interface enables the Distribution System in a
downstream CDN to request CDNI Metadata from an upstream CDN so that
the downstream CDN can properly process and respond to redirection
requests received over the CDNI Request Routing interface and Content
Requests received directly from User Agents.
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 working group to define a new
protocol for the request/response element of the CDNI Metadata
interface.
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 for
example log lines related to the delivery of content (similar to the
log lines recorded in a web server's access log) as well as real-time
or near-real time events before, during or after content delivery and
operations and diagnostic messages.
Several protocols already exist that could potentially be used to
exchange CDNI logs between interconnected CDNs including SNMP,
syslog, ftp, HTTP POST, etc.
4.4. CDNI Control Interface
The CDNI Control interface allows the 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.
It is expected that for the Control interface, as for the other CDNI
Interfaces, existing protocols can be reused or leveraged.
5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
Distribution of content by a 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 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
interconnections.
7. 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, Mahesh Viveganandhan and Richard Woundy for their review
comments and contributions to the text.
8. References
8.1. Normative References
8.2. Informative References
[3GP-DASH]
"Transparent end-to-end Packet-switched Streaming Service
(PSS); Progressive Download and Dynamic Adaptive Streaming
over HTTP (3GP-DASH)
http://www.3gpp.org/ftp/Specs/html-info/26247.htm".
[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]
"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]
Faucheur, F. and L. Peterson, "Content Distribution
Network Interconnection (CDNI) Experiments",
draft-bertrand-cdni-experiments-02 (work in progress),
February 2012.
[I-D.ietf-cdni-use-cases]
Gilles, B., Watson, G., Ma, K., Eardley, P., Emile, S.,
and T. Burbridge, "Use Cases for Content Delivery Network
Interconnection", draft-ietf-cdni-use-cases-03 (work in
progress), January 2012.
[I-D.jenkins-alto-cdn-use-cases]
Previdi, S., Watson, G., Medved, J., Bitar, N., and B.
Niven-Jenkins, "Use Cases for ALTO within CDNs",
draft-jenkins-alto-cdn-use-cases-02 (work in progress),
December 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)",
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.
Appendix A. Design considerations for realizing the CDNI Interfaces
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 be considered
for reuse or leveraging to implement the CDNI interfaces.
A.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.
Therefore, the CDNI Request Routing interface needs to offer a Therefore, the CDNI Request Routing interface needs to offer a
mechanism for an upstream CDN to issue a "Redirection Request" to a mechanism for an upstream CDN to issue a "Redirection Request" to a
downstream CDN. The Request Routing interface needs to be able to downstream CDN. The Request Routing interface needs to be able to
support scenarios where the initial User Agent request to the support scenarios where the initial User Agent request to the
upstream CDN is received over DNS as well as over a content specific upstream CDN is received over DNS as well as over a content specific
application protocol (e.g. HTTP, RTSP, RTMP, etc.). application protocol (e.g. HTTP, RTSP, RTMP, etc.).
Therefore a Redirection Request is expected to contain information Therefore a Redirection Request is expected to contain information
such as: such as:
skipping to change at page 17, line 8 skipping to change at page 21, line 49
footprint, load) to facilitate selection of the downstream CDN by the footprint, load) to facilitate selection of the downstream CDN by the
upstream CDN request routing system when processing subsequent upstream CDN request routing system when processing subsequent
content requests from User Agents. It is expected that such content requests from User Agents. It is expected that such
functionality of the CDNI request Routing could be specified by the functionality of the CDNI request Routing could be specified by the
CDNI working group with significant leveraging of existing IETF CDNI working group with significant leveraging of existing IETF
protocols supporting the dynamic distribution of reachability protocols supporting the dynamic distribution of reachability
information (for example by leveraging existing routing protocols) or information (for example by leveraging existing routing protocols) or
supporting application level queries for topological information (for supporting application level queries for topological information (for
example by leveraging ALTO). example by leveraging ALTO).
4.2. CDNI Metadata Interface A.2. CDNI Metadata Interface
The CDNI Metadata interface enables the Distribution System in a The CDNI Metadata interface enables the Distribution System in a
downstream CDN to obtain CDNI Metadata from an upstream CDN so that downstream CDN to obtain CDNI Metadata from an upstream CDN so that
the downstream CDN can properly process and respond to: the downstream CDN can properly process and respond to:
o Redirection Requests received over the CDNI Request Routing o Redirection Requests received over the CDNI Request Routing
interface. interface.
o Content Requests received directly from User Agents. o Content Requests received directly from User Agents.
The CDNI Metadata interface needs to offer a mechanism for an The CDNI Metadata interface needs to offer a mechanism for an
skipping to change at page 18, line 4 skipping to change at page 22, line 42
interface. interface.
Thus, the CDNI working group would be left only with the task of Thus, the CDNI working group would be left only with the task of
specifying: specifying:
o The recommended request/response protocol to use along with any o The recommended request/response protocol to use along with any
additional semantics that are specific to the CDNI Metadata additional semantics that are specific to the CDNI Metadata
interface (e.g. handling of malformed requests/responses). interface (e.g. handling of malformed requests/responses).
o The syntax (i.e representation/encoding) of the CDNI Metadata o The syntax (i.e representation/encoding) of the CDNI Metadata
objects that will be exchanged over the interface. objects that will be exchanged over the interface.
o The semantics (i.e. meaning and expected contents) of the o The semantics (i.e. meaning and expected contents) of the
individual properties of a Metadata object. individual properties of a Metadata object.
o How the relationships between different CDNI Metadata objects are o How the relationships between different CDNI Metadata objects are
represented. represented.
4.3. CDNI Logging Interface A.3. CDNI Logging Interface
The CDNI Logging interface enables details of logs or events to be The CDNI Logging interface enables details of logs or events to be
exchanged between interconnected CDNs, where events could be: exchanged between interconnected CDNs, where events could be:
o Log lines related to the delivery of content (similar to the log o Log lines related to the delivery of content (similar to the log
lines recorded in a web server's access log). lines recorded in a web server's access log).
o Real-time or near-real time events before, during or after content o Real-time or near-real time events before, during or after content
delivery, e.g. content delivery interruption delivery, e.g. content delivery interruption
o Operations and diagnostic messages. o Operations and diagnostic messages.
skipping to change at page 19, line 4 skipping to change at page 23, line 42
Although it is not necessary to define a new protocol for exchanging Although it is not necessary to define a new protocol for exchanging
logs across the CDNI Logging interface, the CDNI working group would logs across the CDNI Logging interface, the CDNI working group would
still need to specify: still need to specify:
o The recommended protocol to use. o The recommended protocol to use.
o A default set of log fields and their syntax & semantics. Today o A default set of log fields and their syntax & semantics. Today
there is no standard set of common log fields across different there is no standard set of common log fields across different
content delivery protocols and in some cases there is not even a content delivery protocols and in some cases there is not even a
standard set of log field names and values for different standard set of log field names and values for different
implementations of the same delivery protocol. implementations of the same delivery protocol.
o A default set of events that trigger logs to be generated. o A default set of events that trigger logs to be generated.
4.4. CDNI Control Interface A.4. CDNI Control Interface
The CDNI Control interface allows the Control System in The CDNI Control interface allows the Control System in
interconnected CDNs to communicate. The exact inter-CDN control interconnected CDNs to communicate. The exact inter-CDN control
functionality required to be supported by the CDNI Control interface functionality required to be supported by the CDNI Control interface
is less well defined than the other three CDNI interfaces at this is less well defined than the other three CDNI interfaces at this
time. time.
However, as discussed in Section 3, the CDNI Control interface may be However, as discussed in Section 3, the CDNI Control interface may be
required to support functionality similar to the following: required to support functionality similar to the following:
o Allow an upstream CDN and downstream CDN to establish, update or o Allow an upstream CDN and downstream CDN to establish, update or
skipping to change at page 19, line 33 skipping to change at page 24, line 21
interface). interface).
o Allow the downstream CDN to communicate static information about o Allow the downstream CDN to communicate static information about
its delivery capabilities, resources and policies. its delivery capabilities, resources and policies.
o Allow bootstrapping of the interface between CDNs for content o Allow bootstrapping of the interface between CDNs for content
acquisition (even if that interface itself is outside the scope of acquisition (even if that interface itself is outside the scope of
the CDNI work). the CDNI work).
It is expected that for the Control interface also, existing It is expected that for the Control interface also, existing
protocols can be reused or leveraged. Those will be considered once protocols can be reused or leveraged. Those will be considered once
the requirements for the Control interface have been refined. the requirements for the Control interface have been refined.
5. Relevant work from other standardization activities Appendix B. Additional Material
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 working group and any component that could potentially be
reused to realize the CDNI interfaces.
A number of standards bodies have produced specifications related to
CDNs, for example:
o ETSI TISPAN (Telecommunications and Internet converged Services
and Protocols for Advanced Networking) has a series of
specifications focusing on CDNs.
o The Open IPTV Forum (OIPF) and ATIS IPTV Interoperability Forum
(IIF) 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 and do not cover interconnection of
CDNs.
o ATIS Cloud Services Forum (CSF) has started investigating
interconnection of CDNs. The ATIS CSF focuses on defining use
cases and requirements for such CDN interconnection, which are
expected to be considered as input into the work of the CDNI
working group. At the time of writing this document, ATIS CSF is
not specifying the corresponding protocols or interfaces and is
expected to leverage the work of the IETF CDNI working group for
those.
o CableLabs, SNIA and ITU have developed (or are working on)
definitions for content related metadata and specifications for
its distribution. However, they do not include metadata specific
to the distribution of content within a CDN or between
interconnected CDNs.
o IETF CDI working group (now concluded) touched on the same problem
space as the present document. However, in accordance with its
initial charter, the CDI working group 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 working group
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 Content on Demand
(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 IIF 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
working group 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. 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 the CDNI working group. The CDNI working group
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
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 working group 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 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 current 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 working
group. 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.
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.
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 working
group 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
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
interconnections.
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
[3GP-DASH]
"Transparent end-to-end Packet-switched Streaming Service
(PSS); Progressive Download and Dynamic Adaptive Streaming
over HTTP (3GP-DASH)
http://www.3gpp.org/ftp/Specs/html-info/26247.htm".
[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]
"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]
Gilles, B., Emile, S., Watson, G., Burbridge, T., Eardley,
P., and K. Ma, "Use Cases for Content Delivery Network
Interconnection", draft-ietf-cdni-use-cases-02 (work in
progress), January 2012.
[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.
[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)",
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.
Appendix A. Additional Material
Note to RFC Editor: This appendix is to be removed on publication as Note to RFC Editor: This appendix is to be removed on publication as
an RFC. an RFC.
A.1. Non-Goals for IETF B.1. Non-Goals for IETF
Listed below are aspects of content delivery that the authors propose Listed below are aspects of content delivery that the authors propose
be kept outside of the scope of a potential CDNI working group: be kept outside of the scope of a potential CDNI working group:
o The interface between Content Service Provider and the o The interface between Content Service Provider and the
Authoritative CDN (i.e. the upstream CDN contracted by the CSP for Authoritative CDN (i.e. the upstream CDN contracted by the CSP for
delivery by this CDN or by its downstream CDNs). delivery by this CDN or by its downstream CDNs).
o The delivery interface between the delivering CDN surrogate and o The delivery interface between the delivering CDN surrogate and
the User Agent, such as streaming protocols. the User Agent, such as streaming protocols.
o The request interface between the User Agent and the request- o The request interface between the User Agent and the request-
routing system of a given CDN. Existing IETF protocols (e.g. routing system of a given CDN. Existing IETF protocols (e.g.
skipping to change at page 28, line 40 skipping to change at page 24, line 49
the User Agent requests. The CDNI working group need not define the User Agent requests. The CDNI working group need not define
new protocols for this purpose. Note however, that the CDNI new protocols for this purpose. Note however, that the CDNI
control plane interface may indirectly affect some of the control plane interface may indirectly affect some of the
information exchanged through the request interface (e.g. URI). information exchanged through the request interface (e.g. URI).
o The content acquisition interface between CDNs (i.e. the data o The content acquisition interface between CDNs (i.e. the data
plane interface for actual delivery of a piece of content from one plane interface for actual delivery of a piece of content from one
CDN to the other). This is expected to use existing protocols CDN to the other). This is expected to use existing protocols
such as HTTP or protocols defined in other forums for content such as HTTP or protocols defined in other forums for content
acquisition between an origin server and a CDN (e.g. HTTP-based acquisition between an origin server and a CDN (e.g. HTTP-based
C2 reference point of ATIS IIF CoD). The CDN Interconnection C2 reference point of ATIS IIF CoD). The CDN Interconnection
solution may only concern itself with the agreement/negotiation problem space described in this document may therefore only
aspects of which content acquisition protocol is to be used concern itself with the agreement/negotiation aspects of which
between two interconnected CDNs in view of facilitating content acquisition protocol is to be used between two
interoperability. interconnected CDNs in view of facilitating interoperability.
o End User/User Agent Authentication. End User/User Agent o End User/User Agent Authentication. End User/User Agent
authentication and authorization are the responsibility of the authentication and authorization are the responsibility of the
Content Service Provider. Content Service Provider.
o Content preparation, including encoding and transcoding. The CDNI o Content preparation, including encoding and transcoding. The CDNI
architecture aims at allowing distribution across interconnected architecture aims at allowing distribution across interconnected
CDNs of content treated as opaque objects. Interpretation and CDNs of content treated as opaque objects. Interpretation and
processing of the objects, as well as optimized delivery of these processing of the objects, as well as optimized delivery of these
objects by the surrogate to the End User are outside the scope of objects by the surrogate to the End User are outside the scope of
CDNI. CDNI.
o Digital Rights Management (DRM). DRM is an end-to-end issue o Digital Rights Management (DRM). DRM is an end-to-end issue
skipping to change at page 29, line 30 skipping to change at page 25, line 39
acquisition methods are outside the scope of the CDNI work. acquisition methods are outside the scope of the CDNI work.
Content management (e.g. Content Deletion) as it relates to CDNI Content management (e.g. Content Deletion) as it relates to CDNI
content management policies, is in scope but the internal content management policies, is in scope but the internal
algorithms used by a cache to determine when to no longer cache an 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 item of Content (in the absence of any specific metadata to the
contrary) is out of scope. contrary) is out of scope.
o Element management interfaces. o Element management interfaces.
o Commercial, business and legal aspects related to the o Commercial, business and legal aspects related to the
interconnections of CDNs. interconnections of CDNs.
A.2. Related standardization activities B.2. Related standardization activites
A.2.1. IETF CDI Working Group (Concluded) 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 working group and any component that could potentially be
reused to realize the CDNI interfaces.
A number of standards bodies have produced specifications related to
CDNs, for example:
o ETSI TISPAN (Telecommunications and Internet converged Services
and Protocols for Advanced Networking) has a series of
specifications focusing on CDNs.
o The Open IPTV Forum (OIPF) and ATIS IPTV Interoperability Forum
(IIF) 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 and do not cover interconnection of
CDNs.
o ATIS Cloud Services Forum (CSF) has started investigating
interconnection of CDNs. The ATIS CSF focuses on defining use
cases and requirements for such CDN interconnection, which are
expected to be considered as input into the work of the CDNI
working group. At the time of writing this document, ATIS CSF is
not specifying the corresponding protocols or interfaces and is
expected to leverage the work of the IETF CDNI working group for
those.
o CableLabs, SNIA and ITU have developed (or are working on)
definitions for content related metadata and specifications for
its distribution. However, they do not include metadata specific
to the distribution of content within a CDN or between
interconnected CDNs.
o IETF CDI working group (now concluded) touched on the same problem
space as the present document. However, in accordance with its
initial charter, the CDI working group 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 working group
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.
B.2.1. IETF CDI Working Group (Concluded)
The Content Distribution Internetworking (CDI) Working Group was The Content Distribution Internetworking (CDI) Working Group was
formed in the IETF following a BoF in December 2000 and closed in mid formed in the IETF following a BoF in December 2000 and closed in mid
2003. 2003.
For convenience, here is an extract from the CDI working group For convenience, here is an extract from the CDI working group
charter [CDI-Charter]: charter [CDI-Charter]:
" "
o The goal of this working group is to define protocols to allow the o The goal of this working group is to define protocols to allow the
interoperation of separately-administered content networks. interoperation of separately-administered content networks.
o A content network is an architecture of network elements, arranged o A content network is an architecture of network elements, arranged
for efficient delivery of digital content. Such content includes, for efficient delivery of digital content. Such content includes,
but is not limited to, web pages and images delivered via HTTP, but is not limited to, web pages and images delivered via HTTP,
and streaming or continuous media which are controlled by RTSP. and streaming or continuous media which are controlled by RTSP.
o The working group will first define requirements for three modes o The working group will first define requirements for three modes
of content internetworking: interoperation of request-routing of content internetworking: interoperation of request-routing
systems, interoperation of distribution systems, and systems, interoperation of distribution systems, and
interoperation of accounting systems. These requirements are interoperation of accounting systems. These requirements are
skipping to change at page 30, line 22 skipping to change at page 27, line 31
Thus, the CDI working group touched on the same problem space as the Thus, the CDI working group touched on the same problem space as the
present document. present document.
The CDI working group published 3 Informational RFCs: The CDI working group published 3 Informational RFCs:
o RFC 3466 [RFC3466] - "A Model for Content Internetworking (CDI)". o RFC 3466 [RFC3466] - "A Model for Content Internetworking (CDI)".
o RFC 3568 [RFC3568] - "Known Content Network (CN) Request-Routing o RFC 3568 [RFC3568] - "Known Content Network (CN) Request-Routing
Mechanisms". Mechanisms".
o RFC 3570 [RFC3570] - "Content Internetworking (CDI) Scenarios". o RFC 3570 [RFC3570] - "Content Internetworking (CDI) Scenarios".
A.2.2. 3GPP B.2.2. 3GPP
3GPP was the first organization that released a specification related 3GPP was the first organization that released a specification related
to adaptive streaming over HTTP. 3GPP Release 9 specification on to adaptive streaming over HTTP. 3GPP Release 9 specification on
adaptive HTTP streaming was published in March 2010, and there have adaptive HTTP streaming was published in March 2010, and there have
been some bug fixes on this specification since the publication. In been some bug fixes on this specification since the publication. In
addition, 3GPP is preparing an extended version for Release 10, which addition, 3GPP has produced an extended version for Release 10, which
is scheduled to be published later in 2011. This release will was published in 2011. This release will include a number of
include a number of clarifications, improvements and new features. clarifications, improvements and new features.
[3GP-DASH] is defined as a general framework independent of the data [3GP-DASH] is defined as a general framework independent of the data
encapsulation format. It has support for fast initial startup and encapsulation format. It has support for fast initial startup and
seeking, adaptive bitrate switching, re-use of HTTP origin and cache seeking, adaptive bitrate switching, re-use of HTTP origin and cache
servers, re-use of existing media playout engines, on-demand, live servers, re-use of existing media playout engines, on-demand, live
and time-shifted delivery. It specifies syntax and semantics of and time-shifted delivery. It specifies syntax and semantics of
Media Presentation Description (MPD), format of segments and delivery Media Presentation Description (MPD), format of segments and delivery
protocol for segments. It does not specify content provisioning, protocol for segments. It does not specify content provisioning,
client behavior or transport of MPD. client behavior or transport of MPD.
The content retrieved by a client using [3GP-DASH] adaptive streaming The content retrieved by a client using [3GP-DASH] adaptive streaming
could be obtained from a CDN but this is not discussed or specified could be obtained from a CDN but this is not discussed or specified
in the 3GPP specifications as it is transparent to [3GP-DASH] in the 3GPP specifications as it is transparent to [3GP-DASH]
operations. Similarly, it is expected that [3GP-DASH] can be used operations. Similarly, it is expected that [3GP-DASH] can be used
transparently from the CDNs as a delivery protocol (between the transparently from the CDNs as a delivery protocol (between the
delivering CDN surrogate and the User Agent) in a CDN Interconnection delivering CDN surrogate and the User Agent) in a CDN Interconnection
environment. [3GP-DASH] could also be a candidate for content environment. [3GP-DASH] could also be a candidate for content
acquisition between CDNs in a CDN Interconnection environment. acquisition between CDNs in a CDN Interconnection environment.
A.2.3. ISO MPEG B.2.3. ISO MPEG
Within ISO MPEG, the Dynamic Adaptive Streaming over HTTP (DASH) ad- Within ISO MPEG, the Dynamic Adaptive Streaming over HTTP (DASH) ad-
hoc group adopted the 3GPP Release 9 [3GP-DASH] specification as a hoc group adopted the 3GPP Release 9 [3GP-DASH] specification as a
starting point and has made some improvements and extensions. starting point and has made some improvements and extensions.
Similar to 3GPP SA4, the MPEG DASH ad-hoc group has been working on Similar to 3GPP SA4, the MPEG DASH ad-hoc group has been working on
standardizing the manifest file and the delivery format. standardizing the manifest file and the delivery format.
Additionally, the MPEG DASH ad-hoc group has also been working on the 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 use of MPEG-2 Transport Streams as a media format, conversion from/to
existing file formats, common encryption, and so on. The MPEG DASH existing file formats, common encryption, and so on. The MPEG DASH
specification could also be a candidate for delivery to the User specification could also be a candidate for delivery to the User
skipping to change at page 31, line 29 skipping to change at page 28, line 35
February 2011. February 2011.
In the 95th MPEG meeting in January 2011, the DASH ad-hoc group In the 95th MPEG meeting in January 2011, the DASH ad-hoc group
decided to start a new evaluation experiment called "CDN-EE". The decided to start a new evaluation experiment called "CDN-EE". The
goals are to understand the requirements for MPEG DASH to better goals are to understand the requirements for MPEG DASH to better
support CDN-based delivery, and to provide a guidelines document for support CDN-based delivery, and to provide a guidelines document for
CDN operators to better support MPEG DASH streaming services. The CDN operators to better support MPEG DASH streaming services. The
ongoing work is still very preliminary and does not currently target ongoing work is still very preliminary and does not currently target
looking into CDN Interconnection use cases. looking into CDN Interconnection use cases.
A.2.4. ATIS IIF B.2.4. ATIS IIF
ATIS ([ATIS]) IIF is the IPTV Interoperability Forum (within ATIS) ATIS ([ATIS]) IIF is the IPTV Interoperability Forum (within ATIS)
that develops requirements, standards, and specifications for IPTV. that develops requirements, standards, and specifications for IPTV.
ATIS IIF is developing the "IPTV Content on Demand (CoD) Service" ATIS IIF is developing the "IPTV Content on Demand (CoD) Service"
specification. This includes use of a CDN (referred to in ATIS IIF specification. This includes use of a CDN (referred to in ATIS IIF
CoD as the "Content Distribution and Delivery Functions") for support CoD as the "Content Distribution and Delivery Functions") for support
of a Content on Demand (CoD) Service as part of a broader IPTV 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. However, this only covers the case of a managed IPTV
service (in particular where the CDN is administered by the service service (in particular where the CDN is administered by the service
provider) and does not cover the use, or interconnection, of multiple provider) and does not cover the use, or interconnection, of multiple
CDNs. CDNs.
A.2.5. CableLabs B.2.5. CableLabs
"Founded in 1988 by cable operating companies, Cable Television "Founded in 1988 by cable operating companies, Cable Television
Laboratories, Inc. (CableLabs) is a non-profit research and Laboratories, Inc. (CableLabs) is a non-profit research and
development consortium that is dedicated to pursuing new cable development consortium that is dedicated to pursuing new cable
telecommunications technologies and to helping its cable operator telecommunications technologies and to helping its cable operator
members integrate those technical advancements into their business members integrate those technical advancements into their business
objectives." [CableLabs] objectives." [CableLabs]
CableLabs has defined specifications for CoD Content Metadata as part CableLabs has defined specifications for CoD Content Metadata as part
of its VOD Metadata project. of its VOD Metadata project.
A.2.6. ETSI MCD B.2.6. ETSI MCD
ETSI MCD (Media Content Distribution) is the ETSI technical committee ETSI MCD (Media Content Distribution) is the ETSI technical committee
"in charge of guiding and coordinating standardization work aiming at "in charge of guiding and coordinating standardization work aiming at
the successful overall development of multimedia systems (television the successful overall development of multimedia systems (television
and communication) responding to the present and future market and communication) responding to the present and future market
requests on media content distribution". requests on media content distribution".
MCD created a specific work item on interconnection of heterogeneous MCD created a specific work item on interconnection of heterogeneous
CDNs ("CDN Interconnection, use cases and requirements") in March CDNs ("CDN Interconnection, use cases and requirements") in March
2010. MCD very recently created a working group to progress this 2010. MCD very recently created a working group to progress this
work item. However, no protocol level work has yet started in MCD work item. However, no protocol level work has yet started in MCD
for CDN Interconnection. for CDN Interconnection.
A.2.7. ETSI TISPAN B.2.7. ETSI TISPAN
ETSI TISPAN has published two sets of IPTV specifications, one of ETSI TISPAN has published two sets of IPTV specifications, one of
which is based on IMS. In addition, TISPAN is about to complete the which is based on IMS. In addition, TISPAN has published a CDN
specifications of a CDN architecture supporting delivery of various architecture supporting delivery of various content services such as
content services such as time-shifted TV and VoD to TISPAN devices time-shifted TV and VoD to TISPAN devices (UEs) or regular PCs. The
(UEs) or regular PCs. The use cases allow for hierarchically and use cases allow for hierarchically and geographically distributed CDN
geographically distributed CDN scenarios, along with multi-CDN scenarios, along with multi-CDN cooperation. As a result, the
cooperation. As a result, the architecture contains reference points architecture contains reference points to support interconnection of
to support interconnection of other TISPAN CDNs. The protocol other TISPAN CDNs. The protocol definition phase for the
definition phase for the corresponding CDN architecture was kicked- corresponding CDN architecture was kicked-off at the end of 2010 as
off at the end of 2010. In line with its long history of leveraging is still in progress. In line with its long history of leveraging
IETF protocols, ETSI could potentially leverage CDNI interfaces IETF protocols, ETSI could potentially leverage CDNI interfaces
developed in the IETF for their related protocol level work on developed in the IETF for their related protocol level work on
interconnections of CDNs. interconnections of CDNs.
A.2.8. ITU-T B.2.8. ITU-T
SG13 is developing standards related to the support of IPTV services SG13 is developing standards related to the support of IPTV services
(i.e.. multimedia services such as television/VoD/audio/text/ (i.e.. multimedia services such as television/VoD/audio/text/
graphics/data delivered over IP-based managed networks). graphics/data delivered over IP-based managed networks).
ITU-T Recommendation Y.1910 [Y.1910] provides the description of the ITU-T Recommendation Y.1910 [Y.1910] provides the description of the
IPTV functional architecture. This architecture includes functions IPTV functional architecture. This architecture includes functions
and interfaces for the distribution and delivery of content. This and interfaces for the distribution and delivery of content. This
architecture is aligned with the ATIS IIF architecture. architecture is aligned with the ATIS IIF architecture.
Based upon ITU-T Rec. Y.1910, ITU-T Rec. Y.2019 [Y.2019] describes in Based upon ITU-T Rec. Y.1910, ITU-T Rec. Y.2019 [Y.2019] describes in
more detail the content delivery functional architecture. This more detail the content delivery functional architecture. This
architecture allows CDN Interconnection: some interfaces (such as D3, architecture allows CDN Interconnection: some interfaces (such as D3,
D4) at the control level allow relationships between different CDNs, D4) at the control level allow relationships between different CDNs,
in the same domain or in different domains. Generic procedures are in the same domain or in different domains. Generic procedures are
described, but the choice of the protocols is open. described, but the choice of the protocols is open.
A.2.9. Open IPTV Forum (OIPF) B.2.9. Open IPTV Forum (OIPF)
The Open IPTV Forum has developed an end-to-end solution to allow any The Open IPTV Forum has developed an end-to-end solution to allow any
OIPF terminal to access enriched and personalized IPTV services OIPF terminal to access enriched and personalized IPTV services
either in a managed or a non-managed network[OIPF-Overview]. Some either in a managed or a non-managed network[OIPF-Overview]. Some
OIPF services (such as Network PVR) may be hosted in a CDN. 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: To that end, the Open IPTV Forum specification is made of 5 parts:
o Media Formats including HTTP Adaptive Streaming o Media Formats including HTTP Adaptive Streaming
o Content Metadata o Content Metadata
o Protocols o Protocols
o Terminal (Declarative or Procedural Application Environment) o Terminal (Declarative or Procedural Application Environment)
o Authentication, Content Protection and Service Protection o Authentication, Content Protection and Service Protection
A.2.10. TV-Anytime Forum B.2.10. TV-Anytime Forum
Version 1 of the TV-Anytime Forum specifications were published as 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 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 Services: Search, select, and rightful use of content on personal
storage systems ("TV-Anytime")". It includes the specification of storage systems ("TV-Anytime")". It includes the specification of
content metadata in XML schemas (ETSI TS 102 822-3) which define content metadata in XML schemas (ETSI TS 102 822-3) which define
technical parameters for the description of CoD and Live contents. technical parameters for the description of CoD and Live contents.
The specification is referenced by DVB and OIPF. The specification is referenced by DVB and OIPF.
The TV-anytime Forum was closed in 2005. The TV-anytime Forum was closed in 2005.
A.2.11. SNIA B.2.11. SNIA
The Storage Networking Industry Association (SNIA) is an association The Storage Networking Industry Association (SNIA) is an association
of producers and consumers of storage networking products whose goal of producers and consumers of storage networking products whose goal
is to further storage networking technology and applications. is to further storage networking technology and applications.
SNIA has published the Cloud Data Management Interface (CDMI) SNIA has published the Cloud Data Management Interface (CDMI)
standard ([SNIA-CDMI]). standard ([SNIA-CDMI]).
"The Cloud Data Management Interface defines the functional interface "The Cloud Data Management Interface defines the functional interface
that applications will use to create, retrieve, update and delete that applications will use to create, retrieve, update and delete
data elements from the Cloud. As part of this interface the client data elements from the Cloud. As part of this interface the client
will be able to discover the capabilities of the cloud storage will be able to discover the capabilities of the cloud storage
offering and use this interface to manage containers and the data offering and use this interface to manage containers and the data
that is placed in them. In addition, metadata can be set on that is placed in them. In addition, metadata can be set on
containers and their contained data elements through this interface." containers and their contained data elements through this interface."
A.3. Related Research Projects B.2.12. Summary of existing stanardization work
A.3.1. IRTF P2P Research Group The following sections will summarize the existing work of the
standard bodies listed earlier against the CDNI problem space.
Appendix B.2.12.1 summarizes existing interfaces that could be
leveraged for content acquisition between CDNs and Appendix B.2.12.2
summarizes existing metadata specifications that may be applicable to
CDNI. To date we are not aware of any standardization activities in
the areas of the remaining CDNI interfaces (CDNI Request Routing,
CDNI Control and CDNI Logging).
B.2.12.1. 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 Content on Demand
(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 IIF 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
working group 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. 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 the CDNI working group. The CDNI working group
may only concern itself with the negotiation/selection aspects of the
acquisition protocol to be used in a CDN interonnect scenario.
B.2.12.2. 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
be associated with data that is stored by a cloud storage provider.
While the metadata currently defined do not match the needs of CDN
Interconnection, 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).
B.3. Related Research Projects
B.3.1. IRTF P2P Research Group
Some information on CDN interconnection motivations and technical Some information on CDN interconnection motivations and technical
issues were presented in the P2P RG at IETF 77. The presentation can issues were presented in the P2P RG at IETF 77. The presentation can
be found in [P2PRG-CDNI]. be found in [P2PRG-CDNI].
A.3.2. OCEAN B.3.2. OCEAN
OCEAN (http://www.ict-ocean.eu/) is an EU funded research project OCEAN (http://www.ict-ocean.eu/) is an EU funded research project
that started in February 2010 for 3 years. Some of its objectives that started in February 2010 for 3 years. Some of its objectives
are relevant to CDNI. It aims, among other things, at designing a are relevant to CDNI. It aims, among other things, at designing a
new architectural framework for audiovisual content delivery over the new architectural framework for audiovisual content delivery over the
Internet, defining public interfaces between its major building Internet, defining public interfaces between its major building
blocks in order to foster multi-vendor solutions and interconnection blocks in order to foster multi-vendor solutions and interconnection
between Content Networks (the term "Content Networks" corresponds between Content Networks (the term "Content Networks" corresponds
here to the definition introduced in [RFC3466], which encompasses here to the definition introduced in [RFC3466], which encompasses
CDNs). CDNs).
OCEAN has not yet published any open specifications, nor common best OCEAN has not yet published any open specifications, nor common best
practices, defining how to achieve such CDN interconnection. practices, defining how to achieve such CDN interconnection.
A.3.3. Eurescom P1955 B.3.3. Eurescom P1955
Eurescom P1955 was a 2010 research project involving a four European Eurescom P1955 was a 2010 research project involving a four European
Network operators, which studied the interests and feasibility of Network operators, which studied the interests and feasibility of
interconnecting CDNs by firstly elaborating the main service models interconnecting CDNs by firstly elaborating the main service models
around CDN interconnection, as well as analyzing an adequate CDN around CDN interconnection, as well as analyzing an adequate CDN
interconnection technical architecture and framework, and finally by interconnection technical architecture and framework, and finally by
providing recommendations for telcos to implement CDN providing recommendations for telcos to implement CDN
interconnection. The Eurescom P1955 project ended in July 2010. interconnection. The Eurescom P1955 project ended in July 2010.
The authors are not aware of material discussing CDN interconnection The authors are not aware of material discussing CDN interconnection
protocols or interfaces made publically available as a deliverable of protocols or interfaces made publicly available as a deliverable of
this project. this project.
B.4. Relationship to relevant IETF Working Groups
B.4.1. 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 working group 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 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 current 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 working
group. One area for further study is whether additional information
should be provided by an ALTO service to facilitate CDNI CDN
selection.
B.4.2. 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 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.
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.
B.4.3. 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 working
group 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.
Authors' Addresses Authors' Addresses
Ben Niven-Jenkins Ben Niven-Jenkins
Velocix (Alcatel-Lucent) Velocix (Alcatel-Lucent)
326 Cambridge Science Park 326 Cambridge Science Park
Milton Road, Cambridge CB4 0WG Milton Road, Cambridge CB4 0WG
UK UK
Email: ben@velocix.com Email: ben@velocix.com
Francois Le Faucheur Francois Le Faucheur
Cisco Systems Cisco Systems
Greenside, 400 Avenue de Roumanille Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410 Sophia Antipolis 06410
France France
Phone: +33 4 97 23 26 19 Phone: +33 4 97 23 26 19
Email: flefauch@cisco.com Email: flefauch@cisco.com
Nabil Bitar Nabil Bitar
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