A Content Delivery Network (CDN) is an infrastructure of network
elements operating at layer 4 through layer 7, arranged for the
efficient distribution and delivery of digital content. Such content
includes, but is not limited to, web pages and images delivered via
HTTP, and streaming of continuous media delivered via HTTP, RTSP, RTMP,
etc. CDNs typically provide services to multiple Content Service
CDNs provide numerous benefits: a shared platform for multi-service
content delivery, reduced transmission costs for cacheable content,
improved quality of experience for end users and increased robustness of
delivery. For these reasons they are frequently used for large-scale
As a result of the significant growth in content delivered over IP
networks, existing CDN providers are scaling up their infrastructure and
many Network Service Providers and Enterprise Service Providers are
deploying their own CDNs. Subject to the policy of the CSP, it is
generally desirable that a given item of content can be delivered to an
end user regardless of that end user's location or attachment network.
This creates a need for interconnecting (previously) standalone CDNs so
they can interoperate and collectively behave as a single delivery
The goal of the CDNI Working Group is to allow the interconnection of
separately administered CDNs in support of the end-to-end delivery of
content from CSPs through multiple CDNs and ultimately to end users (via
their respective User Agents). The CDNI WG aims at delivering a
targeted, deployable solution in a short timeframe as
needed by the industry. It is expected that the CDNI interfaces will be
realized using existing IETF protocols for transport and message
exchange, and using existing object notation grammars/languages for the
definition of CDNI objects and semantics. In the event that protocol
extensions or new protocols are deemed necessary by the WG, the WG will
The working group will focus on the following items:
- A "requirements" document. This document lists the requirements for
the CDNI architecture and the CDNI interfaces. In particular, this
document will focus on identifying a reasonable set of more urgent and
important requirements that will be addressed in the initial set of
CDNI protocols and solutions produced by the working group. This
document will list the requirements stemming from the threat analysis
and to be met by each of the CDNI interfaces.
- A "framework" document providing a description of the different
components of the CDNI architecture and how they interact with one
another. This document will also include a "threat analysis"
discussing the security concerns and threats, the trust model and
privacy issues specific to CDNI.
- A specification of the "CDNI Request Routing Redirection interface".
This interface will allow an upstream CDN Request Routing system to
obtain from the downstream CDN the information necessary to perform
request redirection. It is actually a logical bundling of two separate
but related interfaces:
* Footprint & Capability Advertisement interface: Asynchronous
operations to exchange routing information (e.g., the network
footprint and capabilities served by a given CDN) that enables CDN
selection for subsequent user requests; and
* Request Routing Redirection interface: Synchronous operations to
select a delivery CDN (surrogate) for a given user request.
- A specification of the "CDNI Metadata interface". This interface will
allow the CDNs to exchange content distribution metadata of inter-CDN
scope. Content distribution metadata refers to the subset of content
metadata that is relevant to the distribution of the content and
therefore is to be processed by CDNs (for example, this may include
information enabling: content acquisition, geo-blocking, enforcement
of availability windows or access control).
- A specification of the "CDNI Logging interface". This interface will
allow CDN logging systems to exchange logging information associated
with actions that are relevant across CDNs (such as content
distribution, content delivery and content routing actions) for
purposes of accounting, analytics, monitoring, etc.
- A specification of the "CDNI Control interface". In particular, this
interface will allow an upstream CDN to remove or invalidate content
in a downstream CDN.
- A specification for "CDNI URI Signing". This document will specify a
mechanism that allows interconnected CDNs to support access control
by signing content URIs. This may involve extensions to the CDNI
interfaces (e.g. CDNI Metadata interface, CDNI Logging interface).
The WG will discuss and address the security, management and operational
issues specific to CDNI, inside the above documents and specifications.
The working group will only define solutions for aspects of the CDN
Interconnection problem space that require direct communication or
interoperation between CDNs.
In particular, the WG will not define:
- New session, transport or network protocols.
- New protocols for delivering content from a CDN to an End User/User
- New protocols for ingestion of content or metadata between a CSP and a
- New protocols for acquiring content across CDNs.
- Protocols and algorithms for intra-CDN operations.
- Support for Transparent Caching across CDNs.
- New applications consuming CDNI logs.
- Digital Right Management (DRM) mechanisms.
The CDNI WG will work with other IETF WGs to assess, and where
appropriate, leverage protocols developed by those WGs, in order to
realize the CDNI requirements and CDNI interfaces. For example, the WG
may assess the suitability of the ALTO protocol as a protocol to enable
downstream CDNs to exchange information which may aid an upstream CDN
with making CDNI request routing decisions. The CDNI WG will also
coordinate with relevant groups outside the IETF, if and where