Internet Engineering Task Force G. Bertrand
Internet-Draft E. Stephan
Intended status: Informational France Telecom - Orange
Expires: January 8, 2012 G. Watson
T. Burbridge
P. Eardley
BT
K. Ma
Azuki Systems
July 7, 2011
Use Cases for Content Delivery Network Interconnection
draft-bertrand-cdni-use-cases-02
Abstract
Content Delivery Networks (CDNs) are commonly used for improving the
footprint and the end-user experience of a content delivery service,
at a reasonable cost. This document outlines real world use-cases
(not technical solutions) for interconnecting CDNs. It provides the
business motivations for CDNI Working Group, which can be used to
validate different interconnection arrangements, and requirements of
the various CDNI interfaces.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 6
1.3. High Level Use Cases for Multi-CDN Systems . . . . . . . . 6
1.4. The Need for CDNI Standards . . . . . . . . . . . . . . . 8
2. Footprint Extension Use Cases . . . . . . . . . . . . . . . . 8
2.1. Geographic Extension . . . . . . . . . . . . . . . . . . . 8
2.2. Region to Region Interconnection . . . . . . . . . . . . . 9
2.3. Nomadic Users . . . . . . . . . . . . . . . . . . . . . . 9
2.4. Delivery Restrictions . . . . . . . . . . . . . . . . . . 9
3. Offload Use Cases . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Overload Handling and Dimensioning . . . . . . . . . . . . 10
3.2. Resiliency . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.1. Failure of Content Delivery Resources . . . . . . . . 11
3.2.2. Failure of Content Acquisition . . . . . . . . . . . . 11
3.3. Branding Consideration . . . . . . . . . . . . . . . . . . 11
4. CDN Capability Use Cases . . . . . . . . . . . . . . . . . . . 12
4.1. Device and Network Technology Extension . . . . . . . . . 12
4.2. Technology and Vendor Interoperability . . . . . . . . . . 13
4.3. QoE and QoS Improvement . . . . . . . . . . . . . . . . . 13
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
This document now merges input from [I-D.watson-cdni-use-cases] and
[I-D.ma-cdni-publisher-use-cases].
Content Delivery Networks (CDNs) are commonly used for improving the
footprint and the end-user experience of a content delivery service,
at a reasonable cost. This document outlines real world use-cases
(not technical solutions) for interconnecting CDNs. It provides the
business motivations for CDNI Working Group, which can be used to
validate different interconnection arrangements, and requirements of
the various CDNI interfaces.
There are many possible combinations for the relationships between
the different parties (Network Service Provider (NSP), CDN Provider,
Content Service Provider (CSP) and End User) involved in end-to-end
content delivery. However, in the context of interconnecting CDNs
the key relationships are listed below.
o How the CSP interacts with the CDN provider, so that the CDN
delivers content in a manner compliant with CSP's distribution
policies.
o How the End User interacts with the CSP and one or more CDNs to
request and receive content.
o How the different CDN providers, operating their CDNs, interact
with one another to deliver the CSP's content to the End User
while continuing to enforce the CSP's distribution policies.
This document describes a number of use cases that motivate CDN
Interconnection.
1.1. Terminology
We adopt the terminology described in
[I-D.jenkins-cdni-problem-statement], [RFC3466], and [RFC3568],
except for the terms defined below.
CDN Provider:
An administrative entity who operates a CDN over a NSP or over the
Internet.
Authoritative CDN (aCDN):
A CDN provider contracted by the CSP for delivery of content by its
CDN or by its downstream CDNs.
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Downstream CDN (dCDN):
A CDN provider which is contracted by an uCDN to achieve the delivery
of content to users.
Access CDN:
A CDN that is connected to the end-user's access and has information
about the end-user's profile and access capabilities.
Delivering CDN:
The CDN that delivers the requested content asset to the end-user.
In particular, the delivering CDN can be an access CDN.
CDN Interconnection (CDNI):
Relationship between two CDNs that enables a CDN to provide content
delivery services on behalf of another CDN. It relies on a set of
interfaces over which two CDNs communicate in order to achieve the
delivery of content to end-users by one CDN (the downstream CDN) on
behalf of another CDN (the upstream CDN).
CDN peering: A business relation between two CDN providers based on
one or more CDN interconnections.
Recursive request routing:
Recursive: Where a process is repeated, but embedded within the
original process. In the case of Request Routing, this means that
the initial request received by the Authoritative CDN is processed
downstream from one CDN to another and that the responses are send
back upstream to the Authoritative CDN which then replies to the
initial request.
Iterative request routing
Iterative: Where a process is repeated multiple times to make
progress towards a goal. In the case of Request Routing, this means
that the initial request is received by the Authoritative CDN, which
replies it with a redirection directive to a downstream CDN. When
the end-user sends its request to the downstream CDN, the same
process is repeated, until the request arrives to the delivering CDN.
Asymmetric Distribution:
A distribution scenario where different NSPs have distribution rights
to the same content, but at different levels of quality (e.g., high
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definition vs. low definition video), which places restrictions on
delivery delegation.
1.2. Abbreviations
[Ed. Note: List of abbreviations to be updated later]
o CSP: Content Service Provider
o dCDN: downstream CDN
o ISP: Internet Service Provider
o NSP: Network Service Provider
o PC: Personal Computer
o QoE: Quality of Experience
o QoS: Quality of Service
o SLA: Service Level Agreement
o STB: Set-Top-Box
o uCDN: upstream CDN
o UA: User Agent
o UE: User Equipment
o VoD: Video on Demand
o WiFi: Wireless Fidelity
1.3. High Level Use Cases for Multi-CDN Systems
Content Delivery Networks (CDNs) are used to deliver content because
they can:
o improve the experience for the End User; for instance delivery has
lower latency and better robustness,
o reduce the operator's costs; for instance lower delivery cost
(reduced bandwidth usage) for cacheable content,
o reduce the Content Service Provider costs, such as datacenter
capacity, space, and electricity consumption.
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Indeed, many network service providers and enterprise service
providers are deploying or have deployed their own CDNs. Despite the
potential benefits of interconnecting CDNs, today each CDN is a
standalone network. The objective of CDN interconnection is to
overcome this restriction: the interconnected CDNs should be able to
collectively behave as a single delivery infrastructure.
Let's take an example, as depicted in Figure 1. Two CDN Providers
establish a CDN Interconnect. The Content Service Provider CSP-1
reaches an agreement with CDN Provider A for the delivery of its
content. CDN Provider A and CDN Provider B agree to interconnect
their CDNs. When a User Agent that is connected to CDN Provider B's
network requests Content from CSP-1, the Content is actually
delivered from CDN-B, because handling of requests for CSP-1's
Content has been delegated as part of the CDN Interconnect agreement.
The End User benefits through a better quality of experience, because
the Content is delivered from a nearby Surrogate. CDN Provider A
benefits because it doesn't need to deploy such an extensive CDN,
whilst CDN Provider B receives some compensation for the delivery.
CSP-1 benefits because it only needs to make one business agreement
and one physical connection, with CDN Provider A, but its End Users
get a service quality as though it had also gone to the trouble of
making a business agreement with CDN Provider B.
+-------+ +-------+
| CSP-1 | | CSP-2 |
+-------+ +-------+
| |
,--,--,--. ,--,--,--.
,-' `-. ,-' `-.
( CDN Provider A )=====( CDN Provider B )
`-. (CDN-A) ,-' `-. (CDN-B) ,-'
`--'--'--' `--'--'--'
|
+------------+
| User Agent |
+------------+
=== CDN Interconnect
Figure 1
To extend the example, another Content Service Provider, CSP-3, may
also reach an agreement with CDN Provider A. But it does not want its
Content to be distributed by CDN Provider B, for example, CSP-3 may
not have distribution rights in the country where CDN Provider B
operates. This example illustrates that policy considerations are an
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important part of CDNI.
This document identifies three main motivations for a CDN Provider to
interconnect its CDN:
o CDN Footprint Extension Use Cases (Section 2)
o CDN Offload Use Cases (Section 3)
o CDN Capability Use Cases (Section 4)
1.4. The Need for CDNI Standards
Existing CDN interfaces are proprietary and an external CDN typically
cannot use them, especially if the two CDNs rely on different
solutions. Nevertheless, [I-D.bertrand-cdni-experiments] shows that
some level of CDN interconnection can be achieved experimentally
without standardized interfaces between the CDNs. The methods used
in these experiments are hardly usable in an operational context,
because they suffer from several limitations in terms of
functionalities, scalability, and security level.
The aim of the CDNI standards work is therefore to overcome such
shortcomings; a full list of requirements is being developed in
[I-D.lefaucheur-cdni-requirements].
2. Footprint Extension Use Cases
Footprint extension is expected to be a major use case for CDN
interconnection.
2.1. Geographic Extension
In this use case, the CDN Provider wants to extend the geographic
distribution that it can offer CSPs, without
o compromising the quality of delivery
o attracting transit and other network costs by serving from
geographically or topologically remote surrogates.
If there are several CDN Providers that have a geographically limited
footprint (e.g., restricted to one country), or do not serve all end-
users in a geographic area, then interconnecting their CDNs enables
CDN Providers to provide their services beyond their own footprint.
As an example, suppose a French CSP wants to distribute its TV
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programs to End Users located in various countries in Europe and
North Africa. It asks a French CDN Provider to deliver the content.
The French CDN Provider's network only covers France, so it makes an
agreement with another CDN Provider that covers North Africa.
Overall, from the CSP's perspective the French CDN Provider provides
a CDN service for both France and North Africa.
In addition to video, this use case applies to other types of content
such as automatic software updates (browser updates, operating system
patches, virus database update, etc).
2.2. Region to Region Interconnection
In the previous section, we have described the case of geographic
extension between CDNs operated by different entities. A large CDN
Provider may also operate CDNs from several subsidiaries (which may
rely on different CDN solutions, see Section 4.2). In certain
circumstances, the CDN Provider needs to make its CDNs interoperate
to provide a consistent service to its customers on its whole
footprint.
2.3. Nomadic Users
In this scenario a CSP wishes to allow users who move to other
geographic regions to continue to access their content. The
motivation in this case is to allow nomadic users to maintain access,
rather than to allow all residents within a region access to the
content.
This use case covers situations like users moving between different
CDN Providers within the same geographic region, or users switching
between different devices, as discussed in Section 4.
2.4. Delivery Restrictions
The content distribution policies that a CSP attaches to a content
asset depend on many criteria. Distribution rights for audiovisual
content are often negotiated using a combination of temporal
licensing (e.g., available for 24 hours, available 28 days after DVD
release, etc.), resolution-based licensing (e.g., high definition vs.
standard definition), and geo- location-based licensing (e.g., per
country).
"Geo-blocking" rules may specify:
o the geographic regions where content can be delivered from (i.e.
the location of the Surrogates), or
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o geographic locations where content can be delivered to (i.e., the
location of the End Users).
Hence, the exchange through the CDN interconnection of information
for controlling the footprint of the delivery is an important use
case.
The delivery of content may be further influenced by policies which
may include time-based rules that specify:
o an activation time (i.e., the time when the content should become
available for delivery),
o a deactivation time (i.e., time after which the content should no
longer be delivered), or
o an expiration time (i.e., the time at which the content files
should be expunged from all CDN storage).
The delivery of content may be further influenced by policies which
may include quality of service rules that specify:
o the maximum resolution deliverable to specific devices,
o the maximum resolution deliverable though a specific NSP, or
o the maximum resolution deliverable to users based on their
subscription levels.
The enforcement of CSP licensing rules when making CDN delegation
decisions is another important use case for CDN interconnection.
3. Offload Use Cases
3.1. Overload Handling and Dimensioning
A CDN is likely to be dimensioned to support the prime-time traffic.
However, unexpected spikes in content popularity may drive load
beyond the expected peak. The prime recurrent time peaks of content
distribution may differ between two CDNs. Taking advantage of the
different traffic peak times, a CDN may interconnect with another CDN
to increase its effective capacity during the peak of traffic. This
brings dimensioning savings to the CDNs as they can use the resources
of each other during their peaks of activity.
Offload also applies to planned situations where a CDN Provider needs
CDN capacities in a particular region during a short period of time.
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For example, a CDN can offload traffic to another CDN during a
specific maintenance operation or for covering the distribution of a
special event. For instance, consider a TV-channel which has
exclusive distribution rights on a major event, such as a
celebrities' wedding, or a major sport competitions. The CDNs that
the TV-channel uses for delivering the content related to this event
are likely to experience a flash crowd during the event and to need
offloading traffic, while other CDNs will support a more usual
traffic load and be able to handle the offloaded traffic load.
3.2. Resiliency
3.2.1. Failure of Content Delivery Resources
It is important for CDNs to be able to guarantee service continuity
during partial failures (e.g., failure of some Surrogates). In
partial failure scenarios, a CDN Provider could redirect some
requests towards another CDN, which must be able to serve the
redirected requests or, depending on traffic management policies, to
forward these requests to the CSP's origin server.
3.2.2. Failure of Content Acquisition
Source content acquisition is typically handled in one of two ways:
o CDN origin, where a downstream CDN acquires content from an
upstream CDN, and the authoritative CDN acquires content from an
origin server of the CSP, or
o CSP origin, where the CDNs acquire content directly from an origin
server of the CSP.
Resiliency may be required against failure to ingest content from the
CSP. If a CDN is unable to retrieve the content, it may be that the
CSP's origin server is inaccessible to only this CDN, in which case
redirection of the end-users to an alternative CDN may circumvent the
problem. A CSP may also choose to specify one or more backup origin
servers.
3.3. Branding Consideration
There are situations where one CDN Provider cannot or does not want
to operate all the functions of a CDN. For instance, it always acts
as an uCDN and offloads the content delivery to dCDNs, i.e., it uses
the surrogates of other CDSPs. In this model, the uCDN acquires
content and receives the initial routing requests from the user
agent; whereas, the dCDNs operate the content delivery functions.
The uCDN also retrieves and presents the logging for the CSP.
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Preserving branding elements could interest the CSP or CDSPs. The
CSP might desire to offer content services under its name, even if
the associated CDN service involves other organizations. Therefore,
the CSP could request that the name of the CDSPs does not appear in
the URLs. Similarly, in offload situations, the uCDN might want to
offer CDN services under its own branding. This highlight a
requirement for exchanging branding related constraints over a CDNI.
4. CDN Capability Use Cases
4.1. Device and Network Technology Extension
In this use case, the CDN Provider may have the right geographic
footprint, but wishes to support the delivery of content to
alternative devices, such as smartphones connected to a mobile
network. In this case, the CDN Provider may federate with another
CDN Provider that offers service to these devices.
Consider the scenario shown in Figure 2. In this example, a nomadic
user switches from a TV going through a cable provider to a
smartphone going through a mobile operator. The CDN Provider on the
cable network may wish to delegate delivery of Content to the CDN
Provider on the mobile network. There are several possible
differences that may arise in this use case compared with the ones
discussed earlier, for example:
o the phone may require the Content at lower resolution than the TV;
o the CSP may want to license only lower resolution Content to CDN
Provider 2;
o the CSP may not want CDN Provider 2 to deliver Content if the
connection quality is below some threshold;
o the CSP may want to tailor the Content in some special way
depending on whether the End User is on cable or mobile, for
example, different adverts / DRMs / codecs / container formats /
delivery protocols...
These examples suggest the requirement for Asymmetric Distribution of
Content across the CDN interconnect. In the nomadic scenario, the
switch of CDN should be as seamless as possible from the End User's
perspective.
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+-----+
| CSP |
+-----+
|
,--,--,--. ,--,--,--.
,-' `-. ,-' `-.
( CDN Provider A )=====( CDN Provider B )
`-. Fixed ,-' `-. Mobile ,-'
`--'--'--' `--'--'--'
| |
+----+ +-------+
| TV |(1) | Phone |(2)
+----+ +-------+
=== CDN Interconnect
Fixed-Mobile Session Shifting
Figure 2
4.2. Technology and Vendor Interoperability
A CDN Provider may deploy a new CDN to run alongside its existing
CDN, as a simple way of migrating its CDN service to a new
technology. A CDN Provider may have a multi-vendor strategy for its
CDN deployment. A CDN Provider may want to deploy a separate CDN for
a particular CSP or a specific network. In all these circumstances,
CDNI benefits the CDN Provider, as it simplifies or automates some
inter-CDN operations (e.g., migrating the request routing function
progressively).
4.3. QoE and QoS Improvement
Some CSPs are willing to pay a premium for enhanced delivery of
Content to their End Users. In some cases, even if the CDN Provider
could deliver the content to the end users, it cannot meet the CSP's
service level agreement. So, it makes a CDN Interconnect agreement
with another CDN Provider that can meet the SLA, for instance an
Access CDN, which is able to deliver content from Surrogates located
closer to the end-user.
5. Acknowledgments
The authors would like to thank Francois Le Faucheur and Ben Niven-
Jenkins for lively discussions.
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They also thank the contributors of the EU FP7 OCEAN and ETICS
projects for valuable inputs.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
CDN interconnect, as described in this document, has a wide variety
of security issues that should be considered. The security issues
fall into three general categories:
o CSP Trust: where the CSP may have negotiated service level
agreements for delivery quality of service with the uCDN, and/or
configured distribution policies (e.g., geo-restrictions,
availability windows, or other licensing restrictions), which it
assumes will be upheld by dCDNs to which the uCDN delegates
requests. Furthermore, billing and accounting information must be
aggregated from dCDNs with which the CSP may have no direct
business relationship. These situtations where trust is delegated
must be handled in a secure fashion to ensure CSP confidence in
the CDN interconnection.
o Client Transparency: where the client device or application which
connects to the CDN must be able to interact with any dCDN using
its existing security and DRM protocols (e.g., cookies,
certificate-based authentication, custom DRM protocols, URL
signing algorithms, etc.) in a transparent fashion.
o CDN Infrastructure Protection: where the dCDNs must be able to
identify and validate delegated requests, in order to prevent
unauthorized use of the network and to be able to properly bill
for delivered content. A dCDN may not wish to advertise that it
has access to or is carrying content for the uCDN or CSP,
especially if that information may be used to enhance denial of
service attacks. In general, CDNI interfaces and protocols should
minimize overhead for dCDNs.
This document focuses on the motivational use cases for CDN
interconnect, and does not analyze these threats in detail.
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[I-D.bertrand-cdni-experiments]
Bertrand, G., Faucheur, F., and L. Peterson, "Content
Distribution Network Interconnection (CDNI) Experiments",
draft-bertrand-cdni-experiments-00 (work in progress),
February 2011.
[I-D.jenkins-cdni-problem-statement]
Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", draft-jenkins-cdni-problem-statement-02 (work
in progress), March 2011.
[I-D.lefaucheur-cdni-requirements]
Faucheur, F., Viveganandhan, M., Watson, G., and Y. Lee,
"Content Distribution Network Interconnection (CDNI)
Requirements", draft-lefaucheur-cdni-requirements-01 (work
in progress), March 2011.
[I-D.ma-cdni-publisher-use-cases]
Nair, R. and K. Ma, "Content Distribution Network
Interconnection (CDNI) Publisher Use",
draft-ma-cdni-publisher-use-cases-00 (work in progress),
March 2011.
[I-D.watson-cdni-use-cases]
Watson, G., "CDN Interconnect Use Cases",
draft-watson-cdni-use-cases-00 (work in progress),
January 2011.
[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.
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Authors' Addresses
Gilles Bertrand
France Telecom - Orange
38-40 rue du General Leclerc
Issy les Moulineaux, 92130
FR
Phone: +33 1 45 29 89 46
Email: gilles.bertrand@orange-ftgroup.com
Stephan Emile
France Telecom - Orange
2 avenue Pierre Marzin
Lannion F-22307
France
Email: emile.stephan@orange-ftgroup.com
Grant Watson
BT
pp GDC 1 PP14, Orion Building, Adastral Park, Martlesham
Ipswich, IP5 3RE
UK
Email: grant.watson@bt.com
Trevor Burbridge
BT
B54 Room 70, Adastral Park, Martlesham
Ipswich, IP5 3RE
UK
Email: trevor.burbridge@bt.com
Philip Eardley
BT
B54 Room 77, Adastral Park, Martlesham
Ipswich, IP5 3RE
UK
Email: philip.eardley@bt.com
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Kevin Ma
Azuki Systems
43 Nagog Park
Acton, MA 01720
USA
Phone: +1 978 844 5100
Email: kevin.ma@azukisystems.com
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