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
Providers (CSPs).



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
content delivery.



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 
infrastructure.



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 seeks to deliver a targeted, deployable solution in a short timeframe. 

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 recharter.

The working group will focus on the following items:

- A specification for the "Named Footprint": specifying an object-based semantics to CDNI footpring advertisement and enabled RESTful implementation of the FCI protocol.

- Specifications for the "CDNI Logging interface" to allow CDN logging systems to exchange logging information   for accounting, analytics, monitoring, etc.

- A specification of the "CDNI Control interface" to allow an upstream CDN to remove or invalidate content
in a downstream CDN. 

- A specification for a "CDNI Metadata Expression Language". This will provide a flexible language for the specific purpose of describing parameters used in CDNI Interfaces. This expression language will allow flexible definition of values and evaluation of additional variables, for example in content request and response headers.  


- 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 for "CDNI Processing Stages Metadata". This
 document will define interfaces for content delivery that require the
flexible modification or synthesis of content to be delivered. This 
includes error messages.

The WG will discuss and address the security, management and operational
issues specific to CDNI, inside the above documents and specifications.



- A specification for "Protected Secrets":  Defining a simple mechanism for protected secret data (such as salt values or encryption keys) that may be embedded in configuration metadata or capabilities advertisements.

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
Agent;
- New protocols for ingestion of content or metadata between a CSP and a
CDN;

- 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, to 
realize the CDNI requirements and CDNI interfaces. For example, the ALTO protocol to enable
 down stream CDNs to exchange information that could aid an upstream CDN
 to make CDNI request routing decisions. The CDNI WG will also 
coordinate with relevant groups outside the IETF, if and where 
appropriate.