Internet Engineering Task Force G. Bertrand, Ed.
Internet-Draft E. Stephan
Intended status: Informational France Telecom - Orange
Expires: September 27, 2012 G. Watson
T. Burbridge
P. Eardley
BT
K. Ma
Azuki Systems
March 26, 2012
Use Cases for Content Delivery Network Interconnection
draft-ietf-cdni-use-cases-04
Abstract
Content Delivery Networks (CDNs) are commonly used for improving the
End User experience of a content delivery service, at a reasonable
cost. This document focuses on use cases that correspond to
identified industry needs and that are expected to be realized once
open interfaces and protocols supporting interconnection of CDNs are
specified and implemented. The document can be used to guide the
definition of the requirements to be supported by CDNI interfaces.
Status of this Memo
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Rationale for Multi-CDN Systems . . . . . . . . . . . . . 5
2. Footprint Extension Use Cases . . . . . . . . . . . . . . . . 7
2.1. Geographic Extension . . . . . . . . . . . . . . . . . . . 7
2.2. Inter-Affiliates Interconnection . . . . . . . . . . . . . 7
2.3. ISP Handling of Third-Party Content . . . . . . . . . . . 8
2.4. Nomadic Users . . . . . . . . . . . . . . . . . . . . . . 8
3. Offload Use Cases . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Overload Handling and Dimensioning . . . . . . . . . . . . 9
3.2. Resiliency . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Failure of Content Delivery Resources . . . . . . . . 10
3.2.2. Content Acquisition Resiliency . . . . . . . . . . . . 10
4. CDN Capability Use Cases . . . . . . . . . . . . . . . . . . . 11
4.1. Device and Network Technology Extension . . . . . . . . . 11
4.2. Technology and Vendor Interoperability . . . . . . . . . . 12
4.3. QoE and QoS Improvement . . . . . . . . . . . . . . . . . 12
5. Enforcement of Content Delivery Policy . . . . . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Content Service Providers' Delivery Policies . . . . 15
A.1. Content Delivery Policy Enforcement . . . . . . . . . . . 15
A.2. Secure Access . . . . . . . . . . . . . . . . . . . . . . 16
A.3. Branding . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
Content Delivery Networks (CDNs) are commonly used for improving the
End User experience of a content delivery service, at a reasonable
cost. This document focuses on use cases that correspond to
identified industry needs and that are expected to be realized once
open interfaces and protocols supporting interconnection of CDNs are
specified and implemented. The document can be used to guide the
definition of the requirements to be supported by the various CDNI
interfaces defined in [I-D.ietf-cdni-problem-statement].
This document identifies the 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)
Then, the document highlights the need for interoperability to
exchange and enforce content delivery policies (Section 5).
1.1. Terminology
We adopt the terminology described in
[I-D.ietf-cdni-problem-statement], [I-D.davie-cdni-framework],
[RFC3466], and [RFC3568].
We extend this terminology with the following terms.
Access CDN:
A CDN that is directly connected to the End User's access. An Access
CDN may have specific information about the End User and the network,
for instance, End User's profile and access capabilities.
Delivering CDN:
The CDN that delivers the requested piece of content to the End User.
In particular, the Delivering CDN can be an Access CDN.
1.2. Abbreviations
o CDN: Content Delivery Network also known as Content Distribution
Network
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o CSP: Content Service Provider
o dCDN: downstream CDN
o DNS: Domain Name System
o DRM: Digital Rights Management
o EU: End User
o ISP: Internet Service Provider
o NSP: Network Service Provider
o QoE: Quality of Experience
o QoS: Quality of Service
o uCDN: upstream CDN
o URL: Uniform Resource Locator
o WiFi: Wireless Fidelity
1.3. Rationale 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 (decreased round-trip-time between the user and the
delivery server) and better robustness,
o reduce the network operator's costs; for instance, lower delivery
cost (reduced bandwidth usage) for cacheable content,
o reduce the Content Service Provider's (CSP) costs, such as
datacenter capacity, space, and electricity consumption, as
popular content is delivered through the CDN rather than through
the CSP's servers.
Indeed, many Network Service Providers (NSPs) 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.
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An example is depicted in Figure 1. Two CDN Providers establish a
CDN Interconnection. 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 requests content from CSP-1, CDN-A considers that
delivery by CDN-B is appropriate, for instance, because CDN-B is an
Access CDN and the user is directly attached to it. CDN-A has
delegated the handling of requests for CSP-1's content through the
CDN Interconnection agreement, thus, the content is actually
delivered from CDN-B.
The End User benefits from this arrangement through a better Quality
of Experience (QoE), because the content is delivered from a nearby
Surrogate. CDN Provider 'A' benefits because it does not need to
deploy such an extensive CDN, whilst CDN Provider 'B' may receive
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 CSP-1 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 Interconnection
Figure 1
To extend the example, another Content Service Provider, CSP-2, 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-2
may not have distribution rights in the country where CDN Provider
'B' operates. This example illustrates that policy considerations
are an important part of CDNI.
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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 to its CSPs:
o without compromising the quality of delivery,
o without incurring additional transit and other network costs that
would result from serving content 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
these CDN Providers to provide their services beyond their own
footprint.
As an example, suppose a French CSP wants to distribute its TV
programs to End Users located in France and various countries in
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. Inter-Affiliates 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 technologies, 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. For example, the CDN Provider might want to expose a
single set of interfaces to the CSPs.
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2.3. ISP Handling of Third-Party Content
Consider an ISP carrying to its subscribers a lot of content that
comes from a third party CSP and that is injected into the access
network by an Authoritative CDN Provider. There are mutual benefits
to the Access CDN, the Authoritative CDN, and the CSP that would make
a case for establishing a CDNI agreement. For example:
o Allow the CSP to offer improved QoE and QoE services to
subscribers, for example, QoS and reduced round trip time.
o Allow the Authoritative CDN to reduce hardware capacity and
footprint, by using the ISP caching and delivery capacity.
o Allow the ISP to reduce traffic load on some segments of the
network by caching inside of the ISP network.
o Allow the ISP to influence and/or control the traffic ingestion
points.
o Allow the ISP to derive some incremental revenue for transport of
the traffic and to monetize QoE services.
2.4. Nomadic Users
In this scenario, a CSP wishes to allow End Users who move between
CDNs to continue to access their content. The motivation of this
case is to allow nomadic End Users to maintain access to content with
a consistent QoE, across a range of devices and/or geographic
regions.
This use case covers situations like:
o End Users moving between different CDN Providers, which may reside
within the same geographic region or different geographic regions,
o End Users switching between different devices or delivery
technologies, as discussed in Section 4.
The term "Nomadic" does not necessarily relate to geographic roaming.
Consider the following example, illustrated in Figure 2: End User A
has subscription to a broadband service from NSP A, her "home NSP".
NSP A hosts CDN-A. Ordinarily, when End User A accesses content via
NSP A (her "home NSP") the content is delivered from CDN-A, which in
this example is within NSP A's network.
However, while End User A is not connected to NSP A's network, for
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example, because it is connected to a WiFi provider or mobile
network, End User A can also access the same content. In this case,
End User A may benefit from accessing the same content but delivered
by an alternate CDN (CDN-B), in this case, hosted in the network of
the WiFi or mobile provider, rather than from CDN-A in NSP A's
network.
+-------+
|Content|
+-------+
|
,--,--,--. ,--,--,--.
,-' NSP A `-. ,-' NSP B `-.
( (CDN-A) )=====( (CDN-B) )
`-. ,-' `-. ,-'
`--'--'--' `--'--'--'
| |
+------------+ +---------------+
+ EU A (home)| | EU A (nomadic)|
+------------+ +---------------+
=== CDN Interconnection
Figure 2
The alternate CDN (CDN-B) is allowed to distribute the content of CSP
A to End User A; however, no other End Users in the region of CDN-B
are allowed to retrieve the content unless they too have such an
agreement for nomadic access to content.
Depending on CSP's content delivery policies (see Appendix A.1), a
user moving to a different geographic region may be subject to geo-
blocking content delivery restrictions. In this case, he/she may not
be allowed to access some pieces of content.
3. Offload Use Cases
3.1. Overload Handling and Dimensioning
A CDN is likely to be dimensioned to support an expected maximum
traffic load. However, unexpected spikes in content popularity
(flash crowd) 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
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CDNs as they can use the resources of each other during their
respective 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.
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 competition. 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.
In this use case, the Delivering CDN on which requests are offloaded
should be able to handle the offloaded requests. Therefore, the uCDN
might require information on the dCDNs to be aware of the amount of
traffic it can offload to every dCDN.
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 has at least two options:
(1) depending on traffic management policies, forward some requests
to the CSP's origin servers, and (2) redirect some requests toward
another CDN, which must be able to serve the redirected requests.
The second option is a use case for CDNI.
3.2.2. Content Acquisition Resiliency
Source content acquisition may be handled in one of two ways:
o CSP origin, where a CDN acquires content directly from the CSP's
origin server, or
o CDN origin, where a downstream CDN acquires content from a
Surrogate within an upstream CDN.
The ability to support content acquisition resiliency, is an
important use case for interconnected CDNs. When the content
acquisition source fails, the CDN might switch to another content
acquisition source. Similarly, when several content acquisition
sources are available, a CDN might balance the load between these
multiple sources.
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Though other server and/or DNS load balancing techniques may be
employed in the network, interconnected CDNs may have a better
understanding of origin server availability and be better equipped to
both distribute load between origin servers and attempt content
acquisition from alternate origin servers when acquisition failures
occur. When normal content acquisition fails, a CDN may need to try
other origin server options, e.g.:
o an upstream CDN may acquire content from an alternate CSP origin
server,
o a downstream CDN may acquire content from an alternate Surrogate
within an upstream CDN,
o a downstream CDN may acquire content from an alternate upstream
CDN, or
o a downstream CDN may acquire content directly from the CSP's
origin server.
Though content acquisition protocols are beyond the scope of CDNI,
the selection of content acquisition sources should be considered.
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 may wish to extend the supported range of devices and
User Agents or the supported range of delivery technologies. In this
case, a CDN Provider may interconnect with a CDN that offers
services:
o that the CDN Provider is not willing to provide or,
o that its own CDN is not able to support.
The following examples illustrate this use case:
1. CDN-A cannot support a specific delivery protocol. For instance,
CDN-A may interconnect with CDN-B to serve a proportion of its
traffic that requires HTTPS. CDN-A may use CDN-B's footprint
(which may overlap with its own) to deliver HTTPS without needing
to deploy its own infrastructure. This case could also be true
of other formats, delivery protocols (RTMP, RTSP, etc.) and
features (specific forms of authorization such as tokens, per
session encryption, etc.).
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2. CDN-A has footprint covering traditional fixed line broadband and
wants to extend coverage to mobile devices. In this case, CDN-A
may contract and interconnect with CDN-B who has both:
* physical footprint inside the mobile network,
* the ability to deliver content over a protocol that is
required by specific mobile devices.
These cases can apply to many CDN features that a given CDN Provider
may not be able to support or not be willing to invest in, and thus,
that the CDN Provider would delegate to another CDN.
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. In addition, a CDN Provider may have a multi-vendor
strategy for its CDN deployment. Finally, 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 requirements. As a result, the CDN Provider may
establish a CDN Interconnection agreement with another CDN Provider
that can provide the expected QoE to the End User, e.g., via an
Access CDN able to deliver content from Surrogates located closer to
the End User and with the required service level.
5. Enforcement of Content Delivery Policy
An important aspect of the above use cases is that CSPs commonly want
to enforce content delivery policies. A CSP may want to define
content delivery policies that specify when, how, and/or to whom the
CDN delivers content. These policies apply to all interconnected
CDNs (uCDNs and dCDNs) in the same or similar way that a CSP can
define content delivery policies for content delivered by a single,
non-interconnected CDN. Appendix A provides examples of CSP defined
policies.
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6. Acknowledgments
The authors would like to thank Kent Leung, Francois Le Faucheur, Ben
Niven-Jenkins, and Scott Wainner for lively discussions, as well as
for their reviews and comments on the mailing list.
They also thank the contributors of the EU FP7 OCEAN and ETICS
projects for valuable inputs.
7. IANA Considerations
This memo includes no request to IANA.
8. Security Considerations
CDN Interconnection, as described in this document, has a wide
variety of security issues that should be considered.
In addition to the security considerations within the uCDN and dCDN,
four contexts involve security and trust issues:
a. The relationship between the CSP and the uCDN: the main contract
arrangement for distribution, which authorizes the uCDN to
acquire content on CSP's origin servers and to deliver it,
potentially with content delivery restrictions.
b. The relationship between the uCDN and dCDN: the transitive trust
relationship that extends the contract defined in (a) above and
that authorizes the dCDN to acquire content on uCDN's or CSP's
origin servers and to deliver it, potentially with content
delivery restrictions.
c. The relationship between the End User and dCDN: the recognition
of right to download predicated on (b) above.
d. The relationship between the End User and the CSP: the contract
that authorizes the End User to access the content.
CDNI should enable the four parties (CSP, uCDN, dCDN, End User) to
negotiate a security method or a method for confirming authorization
along the chain of trust (CSP -> uCDN -> dCDN -> End User).
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
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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 situations 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. CDNI interfaces and protocols should attempt to
minimize overhead for dCDNs.
This document focuses on the motivational use cases for CDN
Interconnection, and does not analyze these threats in detail.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.davie-cdni-framework]
Davie, B. and L. Peterson, "Framework for CDN
Interconnection", draft-davie-cdni-framework-01 (work in
progress), October 2011.
[I-D.ietf-cdni-problem-statement]
Niven-Jenkins, B., Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", draft-ietf-cdni-problem-statement-04 (work in
progress), March 2012.
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[I-D.ietf-cdni-requirements]
Leung, K. and Y. Lee, "Content Distribution Network
Interconnection (CDNI) Requirements",
draft-ietf-cdni-requirements-02 (work in progress),
December 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.
Appendix A. Content Service Providers' Delivery Policies
CSPs commonly apply different delivery policies to given sets of
content assets delivered through CDNs. Interconnected CDNs need to
support these policies. This annex presents examples of CSPs'
delivery policies and their consequences on CDNI operations.
A.1. Content Delivery Policy Enforcement
The content distribution policies that a CSP attaches to a content
asset may depend on many criteria. For instance, distribution
policies for audiovisual content often combine:
o temporal constraints (e.g., available for 24 hours, available 28
days after DVD release, etc.),
o resolution-based constraints (e.g., high definition vs. standard
definition), and
o geolocation-based constraints (e.g., per country).
dCDN delegation and Surrogate selection decisions are influenced by
these policies:
o dCDN delegation and/or Surrogates selection may fail if the
availability window for the requested content is not active,
o dCDN delegation may fail if the content resolution has been
specified by the CSP as being too high for distribution via the
dCDN,
o Surrogate selection may fail if the content resolution has been
specified by the CSP as being too high for distribution via the
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current CDN,
o dCDN delegation may fail if the footprint of the dCDN is outside
of the delivery footprint for the requested content, or
o Surrogate selection may fail if the footprint of the current CDN
is outside of the delivery footprint for the requested content.
These policy considerations permit preventing premature access to
pre-positioned content, preventing content licensing violations, and
enforcing geo-blocking policies.
A.2. Secure Access
Many protocols exist for delivering content to End Users. CSPs may
dictate a specific protocol or set of protocols which are acceptable
for delivery of their content, especially in the case where content
protection or user authentication is required (e.g., must use HTTPS).
CSPs may also perform per-request authentication/authorization
decision and then have the CDNs enforce that decision (e.g., must
validate URL signing, etc.).
A.3. Branding
Preserving the branding of the CSP throughout delivery is often
important to the CSP. CSPs may desire to offer content services
under their own name, even when the associated CDN service involves
other CDN Providers. For instance, a CSP may desire to ensure that
content is delivered with URIs appearing to the End Users under the
CSP's own domain name, even when the content delivery involves
separate CDN Providers. The CSP may wish to prevent the delivery of
its content by specific dCDNs that lack support for such branding
preservation features.
Analogous cases exist when the uCDN wants to offer CDN services under
its own branding even if dCDNs are involved. Similarly, a CDN
Provider might wish to restrict the delivery delegation to a chain
that preserves its brand visibility.
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Authors' Addresses
Gilles Bertrand (editor)
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.com
Stephan Emile
France Telecom - Orange
2 avenue Pierre Marzin
Lannion F-22307
France
Email: emile.stephan@orange.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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