3.2. Generic CDNI Metadata Object Properties

The HostMetadata and PathMetadata objects contain or can reference other CDNI Metadata objects that contain properties which describe how User Agent requests for content should be processed, for example where to acquire the content, authorization rules that should be applied, delivery location restrictions and so on. Each such CDNI Metadata object is a specialization of a CDNI GenericMetadata object. The GenericMetadata object abstracts the basic information required for Metadata override and Metadata distribution, from the specifics of any given property (e.g., property semantics, enforcement options, etc.).

The GenericMetadata object defines the type of properties contained within it as well as whether or not the properties are "mandatory-to-enforce". If the dCDN does not understand or support the property type and the property type is "mandatory-to-enforce", the dCDN MUST NOT serve the content to the User Agent. If the dCDN does not understand or support the property type and the property type is not "mandatory-to-enforce", then that GenericMetadata object may be safely ignored and the dCDN MUST process the content request in accordance with the rest of the CDNI metadata.

Although a CDN MUST NOT serve content to a User Agent if a "mandatory-to-enforce" property cannot be enforced, it may be "safe-to-redistribute" that metadata to another CDN without modification. For example, in the cascaded CDN case, a transit CDN may pass through "mandatory-to-enforce" metadata to a downstream CDN. For Metadata which does not require customization or translation (i.e., metadata that is "safe-to-redistribute"), the data representation received off the wire MAY be stored and redistributed without being natively understood or supported by the transit CDN. However, for Metadata which requires translation, transparent redistribution of the uCDN Metadata values may not be appropriate. Certain Metadata may be safely, though possibly not optimally, redistributed unmodified. For example, source acquisition address may not be optimal if transparently redistributed, but may still work.

Redistribution safety MUST be specified for each GenericMetadata. If a CDN does not understand or support a given GenericMetadata property type and the property type is not "safe-to-redistribute", before redistributing the metadata, the CDN MUST set the "incomprehensible" flag for the GenericMetadata property that it did not understand and was marked as not "safe-to-redistribute". The "incomprehensible" flag signals to a dCDN that the metadata was not properly transformed by the transit CDN. A CDN MUST NOT attempt to use metadata that has been marked as "incomprehensible" by a uCDN.

Transit CDNs MUST NOT change the value of "mandatory-to-enforce" or "safe-to-redistribute" when propagating metadata to a dCDN. Although a transit CDN may set the value of "incomprehensible" to true, a transit CDN MUST NOT change the value of "incomprehensible" from true to false.

The following table describes the action to be taken by a transit CDN (tCDN) for the different "mandatory-to-enforce" (MtE) and "safe-to-redistribute" (StR) cases, when the tCDN either does or does not understand the metadata in question:

The following table describes the action to be taken by a dCDN for the different "mandatory-to-enforce" (MtE) and "incomprehensible" (Incomp) cases, when the dCDN either does or does not understand the metadata in question:

3.3. Metadata Inheritance and Override

In the data model, a HostMetadata object may contain (or reference) multiple PathMetadata objects (via PathMatch objects). Each PathMetadata object may in turn contain (or reference) other PathMetadata objects. HostMetadata and PathMetadata objects form an inheritance tree where each node in the tree inherits or overrides the property values set by its parent.

GenericMetadata objects of a given type override all GenericMetadata objects of the same type previously defined by any parent object in the tree. GenericMetadata objects of a given type previously defined by a parent object in the tree are inherited when no object of the same type is defined by the child object. For example, if HostMetadata for the host "example.com" contains GenericMetadata objects of type LocationACL and TimeWindowACL, while a PathMetadata object which applies to "example.com/movies/*" defines an alternate GenericMetadata object of type TimeWindowACL, then:

• the TimeWindowACL defined in the PathMetadata would override the TimeWindowACL defined in the HostMetadata for all User Agent requests for content under "example.com/movies", and
• the LocationACL defined in the HostMetadata would be inherited for all User Agent requests for content under "example.com/movies".
• A single HostMetadata or PathMetadata object SHOULD NOT contain multiple GenericMetadata objects of the same type. If a list of GenericMetadata contains objects of duplicate types, the receiver MUST ignore all but the first object of each type.

4. Encoding-Independent CDNI Metadata Object Descriptions

Section 4.1 provides the definitions of each object type declared in Section 3. These objects are described as structural objects as they provide the structure for the inheritance tree and identify which specific properties apply to a given User Agent content request.

Section 4.2 provides the definitions for a base set of core metadata objects which may be contained within a GenericMetadata object. These objects are described as property objects, as they define the structure, semantics, and enforcement options for specific properties of the metadata being described. Property objects govern how User Agent requests for content are handled. Property objects may be composed of, or contain references to, other property sub-objects (i.e., property objects contained within or referenced by the property object that refers to that property sub-object). In those cases the value of the property sub-objects can be either a complete serialized representation of the sub-object, or a Link object that contains a URI and relationship that can be dereferenced to retrieve the complete serialized representation of the property sub-object.

Section 6.5 discusses the ability to extend the base set of metadata objects specified in this document with additional standards based or vendor specific property objects that may be defined in the future in separate documents.

Downstream CDNs MUST support parsing of all CDNI metadata objects specified in this document. A dCDN does not have to implement the underlying functionality represented by the metadata object, though that may restrict the content that a given dCDN can serve. uCDNs as generators of CDNI Metadata only need to support generating the CDNI metadata that they need in order to express the policies and treatment required by the content they are describing.

Note: In the following sections, the term "mandatory-to-specify" is used to convey which property sub-objects MUST be specified for a given structural or property object. When mandatory-to-specify is set to true on a sub-object, it implies that if the property object containing that property sub-object is specified, then the mandatory-to-specify property sub-object MUST also be specified, e.g., a HostMatch property object without a host to match against does not make sense, therefore, the host is mandatory-to-specify inside a HostMatch property object.

4.1. Descriptions of the CDNI Structural Metadata Objects

Each of the sub-sections below describe the structural objects defined in Table 2.

4.1.1. HostIndex

The HostIndex object is the entry point into the CDNI Metadata hierarchy. It contains (or references) a list of HostMatch objects. An incoming content request is checked against the hostname (or IP address) specified by each of the listed HostMatch objects to find the HostMatch object which applies to the request.

• Property: hosts
  • Description: List of HostMatch objects, in priority order.
  • Type: List of HostMatch objects
  • Mandatory-to-Specify: Yes.

4.1.2. HostMatch

The HostMatch object contains a hostname or IP address to match against content requests. The HostMatch object also contains or references a HostMetadata object to apply if a match is found.

• Property: host
  • Description: String (hostname or IP address) to match against the requested host.
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: host-metadata
  • Description: CDNI Metadata to apply when delivering content that matches this host.
  • Type: HostMetadata
  • Mandatory-to-Specify: Yes.

4.1.3. HostMetadata

A HostMetadata object contains (or references) the CDNI Metadata properties for content served for a particular host (defined in the HostMatch object) and possibly child PathMatch objects.

• Property: metadata
  • Description: List of host related metadata.
  • Type: List of GenericMetadata objects
  • Mandatory-to-Specify: Yes.

• Property: paths
  • Description: Path specific rules. Path patterns (PathMatch objects) MUST be evaluated in the order they appear and the first PathMatch object that matches the content request being process is applied.
  • Type: List of PathMatch objects
  • Mandatory-to-Specify: No.

4.1.4. PathMatch

The PathMatch object contains (or references) an expression given as a PatternMatch object to match against a resource URI path and contains or references a PathMetadata object to apply if a match is found.

• Property: path-pattern
  • Description: Pattern to match against the requested path, i.e., against the [RFC3986] path-absolute.
  • Type: PatternMatch
  • Mandatory-to-Specify: Yes.

• Property: path-metadata
  • Description: CDNI Metadata to apply when delivering content that matches this path.
  • Type: PathMetadata
  • Mandatory-to-Specify: Yes.

4.1.5. PathMetadata

A PathMetadata object contains (or references) the CDNI Metadata properties for content served with the associated URI path (defined in a PathMatch object) and possibly child PathMatch objects.

Note that if DNS-based redirection is employed, then any metadata at the PathMetadata level or below will be inaccessible at request routing time because only the content request hostname is available at request routing time.

• Property: metadata
  • Description: List of path related metadata.
  • Type: List of GenericMetadata objects
  • Mandatory-to-Specify: Yes.

• Property: paths
  • Description: Path specific rules. First match applies.
  • Type: List of PathMatch objects
  • Mandatory-to-Specify: No.

4.1.6. PatternMatch

A PatternMatch object contains the pattern string and flags that describe the PathMatch expression.

• Property: pattern
  • Description: A pattern for string matching. The pattern may contain the wildcards * and ?, where * matches any sequence of characters (including the empty string) and ? matches exactly one character. The three literals \ , * and ? should be escaped as \\, \* and \?. All other characters are treated as literals.
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: case-sensitive
  • Description: Flag indicating whether or not case-sensitive matching should be used.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is case-insensitive match.

• Property: ignore-query-string
  • Description: List of query parameters which should be ignored when searching for a pattern match. If all query parameters should be ignored then the list MUST be empty.
  • Type: List of String
  • Mandatory-to-Specify: No. Default is to include query strings when matching.

4.1.7. GenericMetadata

A GenericMetadata object is an abstraction for managing individual CDNI Metadata properties in an opaque manner.

• Property: generic-metadata-type
  • Description: CDNI Metadata property object type.
  • Type: MIME Type String (from Section 7.1)
  • Mandatory-to-Specify: Yes.

• Property: generic-metadata-value
  • Description: CDNI Metadata property object.
  • Type: Format/Type is defined by the value of generic-metadata-type property above.
  • Mandatory-to-Specify: Yes.

• Property: mandatory-to-enforce
  • Description: Flag identifying whether or not the enforcement of the property Metadata is required.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is to treat metadata as mandatory to enforce (i.e., true).

• Property: safe-to-redistribute
  • Description: Flag identifying whether or not the property Metadata may be safely redistributed without modification.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is allow transparent redistribution (i.e., true).

• Property: incomprehensible
  • Description: Flag identifying whether or not any CDN in the chain of delegation has failed to understand and/or failed to properly transform the Metadata.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is comprehensible (i.e., false).

4.2. Description of the CDNI Generic Metadata Objects

The property objects defined below are intended to be used in the GenericMetadata object generic-metadata-value field as defined in Section 4.1.7 and their generic-metadata-type property MUST be set to the appropriate Media Type as defined in Section 7.1.

4.2.1. Source Metadata

Source Metadata provides the dCDN information about content acquisition, i.e., how to contact an uCDN Surrogate or an Origin Server to obtain the content to be served. The sources are not necessarily the actual Origin Servers operated by the CSP but might be a set of Surrogates in the uCDN.

Endpoints within a source should be treated as equivalent/equal so one can specify a list of sources in preference order and for each source/preference rank one can specify a list of endpoints that are equivalent, e.g., a pool of servers that are not behind a load balancer.

• Property: sources
  • Description: Sources from which the dCDN can acquire content, listed in order of preference.
  • Type: List of Source objects
  • Mandatory-to-Specify: No. Default is to use static configuration, out-of-band from the metadata interface.

4.2.1.1. Source

A Source object describes the Source which should be used by the dCDN for content acquisition, e.g., a Surrogate within the uCDN or an alternate Origin Server, the protocol to be used and any authentication method.

• Property: acquisition-auth
  • Description: Authentication method to use when requesting content from this source.
  • Type: Auth
  • Mandatory-to-Specify: No. Default is no authentication required.

• Property: endpoints
  • Description: Origins from which the dCDN can acquire content. If multiple endpoints are specified they are all equal, i.e., the list is not in preference order, for example a pool of servers behind a load balancer.
  • Type: List of EndPoint objects
  • Mandatory-to-Specify: Yes.

• Property: protocol
  • Description: Network retrieval protocol to use when requesting content from this source.
  • Type: Protocol
  • Mandatory-to-Specify: Yes.

4.2.2. LocationACL Metadata

LocationACL Metadata defines location-based restrictions.

A LocationACL which does not include a locations property results in an action of allow, meaning that delivery can be performed regardless of the User Agent's location. The action from the first footprint to match against the User Agent's location is the action a CDN MUST take. If two or more footprints overlap, the first footprint that matches against the User Agent's location determines the action a CDN MUST take. If the locations property is included but is empty, or if none of the listed footprints matches the User Agent's location, then the result is an action of deny.

Although the LocationACL, TimeWindowACL, and ProtocolACL are independent GenericMetadata objects, they may provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the LocationACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed. Thus, in the example given, the request should be denied.

• Property: locations
  • Description: Access control list which allows or blocks delivery based on client location.
  • Type: List of LocationRule objects
  • Mandatory-to-Specify: No. Default is allow all locations.

4.2.2.1. LocationRule

A LocationRule contains or references a list of Footprint objects and the corresponding action.

• Property: footprints
  • Description: List of footprints to which the rule applies.
  • Type: List of Footprint objects
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies locations to allow or deny.
  • Type: Enumeration [allow|deny]
  • Mandatory-to-Specify: No. Default is deny.

4.2.2.2. Footprint

A Footprint object describes the footprint to which a LocationRule may be applied by, e.g., an IPv4 address range or a geographic location.

• Property: footprint-type
  • Description: Registered footprint type (see Section 7.1.1.1).
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: footprint-value
  • Description: Footprint object conforming to the specification associated with the registered footprint type.
  • Type: String
  • Mandatory-to-Specify: Yes.

4.2.3. TimeWindowACL Metadata

TimeWindowACL Metadata defines time-based restrictions.

A TimeWindowACL which does not include a times property results in an action of allow, meaning that delivery can be performed regardless of the time of the User Agent's request. The action from the first window to match against the current time is the action a CDN MUST take. If two or more windows overlap, the first window that matches against the current time determines the action a CDN MUST take. If the times property is included but is empty, or if none of the listed windows matches the current time, then the result is an action of deny.

Although the LocationACL, TimeWindowACL, and ProtocolACL are independent GenericMetadata objects, they may provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the LocationACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed. Thus, in the example given, the request should be denied.

• Property: times
  • Description: Description: Access control list which allows or blocks delivery based on request time.
  • Type: List of TimeWindowRule objects
  • Mandatory-to-Specify: No. Default is allow all time windows.

4.2.3.1. TimeWindowRule

A TimeWindowRule contains or references a list of TimeWindow objects and the corresponding action.

• Property: windows
  • Description: List of time windows to which the rule applies.
  • Type: List of TimeWindow objects
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies time windows to allow or deny.
  • Type: Enumeration [allow|deny]
  • Mandatory-to-Specify: No. Default is deny.

4.2.3.2. TimeWindow

A TimeWindow object describes a time range which may be applied by an TimeWindowACL, e.g., start 946717200 (i.e., 09:00AM 01/01/2000 UTC), end: 946746000 (i.e., 17:00AM 01/01/2000 UTC).

• Property: start
  • Description: The start time of the window.
  • Type: Time
  • Mandatory-to-Specify: Yes.

• Property: end
  • Description: The end time of the window.
  • Type: Time
  • Mandatory-to-Specify: Yes.

4.2.4. ProtocolACL Metadata

ProtocolACL Metadata defines delivery protocol restrictions.

A ProtocolACL which does not include a protocol-acl property results in an action of allow, meaning that delivery can be performed regardless of the protocol of the User Agent's request. The action from the first protocol to match against the request protocol is the action a CDN MUST take. If two or more request protocols overlap, the first protocol that matches thre request protocol determines the action a CDN MUST take. If the protocol-acl property is included but is empty, or if none of the listed protocol matches the request protocol, then the result is an action of deny.

Although the LocationACL, TimeWindowACL, and ProtocolACL are independent GenericMetadata objects, they may provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the LocationACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed. Thus, in the example given, the request should be denied.

• Property: protocol-acl
  • Description: Description: Access control list which allows or blocks delivery based on delivery protocol.
  • Type: List of ProtocolRule objects
  • Mandatory-to-Specify: No. Default is allow all protocols.

4.2.4.1. ProtocolRule

A ProtocolRule contains or references a list of Protocol objects. ProtocolRule objects are used to construct a ProtocolACL to apply restrictions to content acquisition or delivery.

• Property: protocols
  • Description: List of protocols to which the rule applies.
  • Type: List of protocol objects
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies protocols to allow or deny.
  • Type: Enumeration [allow|deny]
  • Mandatory-to-Specify: No. Default is deny.

4.2.5. DeliveryAuthorization Metadata

Delivery Authorization defines authorization methods for the delivery of content to User Agents.

• Property: delivery-auth-methods
  • Description: Options for authorizing content requests. Delivery for a content request is authorized if any of the authorization method in the list is satisfied for that request.
  • Type: List of Auth objects
  • Mandatory-to-Specify: No. Default is no authorization required.

4.2.6. Cache

A Cache object describes the cache control parameters to be applied to the content by intermediate caches.

• Property: ignore-query-string
  • Description: Allows a cache to ignore URI query string parameters while comparing URIs for equivalence. Each query parameter to ignore is specified in the list. If all query parameters should be ignored, then the list MUST be specified and MUST be empty.
  • Type: List of String
  • Mandatory-to-Specify: No. Default is to consider query string parameters when comparing URIs.

4.2.7. Grouping

A Grouping object identifies a large group of content to which a given asset belongs.

• Property: ccid
  • Description: Content Collection identifier for an application-specific purpose such as logging.
  • Type: String
  • Mandatory-to-Specify: No. Default is an empty string.

• Property: sid
  • Description: Session identifier for an application-specific purpose such as logging.
  • Type: String
  • Mandatory-to-Specify: No. Default is an empty string.

4.3. CDNI Metadata Simple Data Type Descriptions

This section describes the simple data types that are used for properties of CDNI Metadata objects.

4.3.1. Link

A link object may be used in place of any of the objects or properties described above. Links can be used to avoid duplication if the same metadata information is repeated within the metadata tree. When a link replaces an object, its href property is set to the URI of the resource and its type property is set to the type of the object it is replacing.

• Property: href
  • Description: The URI of the addressable object being referenced.
  • Type: URI
  • Mandatory-to-Specify: Yes

• Property: type
  • Description: The type of the object being referenced.
  • Type: String
  • Mandatory-to-Specify: No

4.3.2. Protocol

Protocol objects are used to specify registered protocols for content acquisition or delivery (see Section 7.1.1.2).

Type: String

4.3.3. Endpoint

A hostname (with optional port) or an IP address (with optional port).

Note: All implementations MUST support IPv4 addresses encoded as specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] and MUST support all IPv6 address formats specified in [RFC4291]. Server implementations SHOULD use IPv6 address formats specified in [RFC5952].

Type: String

4.3.4. URI

A URI as specified in [RFC3986].

Type: String

4.3.5. Time

A time value expressed in seconds since Unix epoch in the UTC timezone.

Type: Integer

4.4. Auth

An Auth object defines authentication and authorization methods to be used during content acquisition and content delivery, respectively.

• Property: auth-type
  • Description: Registered Auth type (see Section 7.1.1.3).
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: auth-value
  • Description: An object conforming to the specification associated with the Registered Auth type.
  • Type: String
  • Mandatory-to-Specify: Yes.

4.4.1. CredentialAuth Type

CredentialAuth is a Registered Auth type defining an object for encapsulating user credentials (i.e., username and password) (see Section 7.1.1.3). The CredentialAuth object contains the following properties:

• Property: username
  • Description: Identification of user.
  • Type: String
  • Mandatory-to-Specify: Yes.
• Property: password
  • Description: Password for user identified by username property.
  • Type: String
  • Mandatory-to-Specify: Yes.

5. CDNI Metadata Capabilities

CDNI Metadata is used to convey information pertaining to content delivery from uCDN to dCDN. For optional metadata, it may be useful for the uCDN to know if the dCDN supports the metadata, prior to delegating any content requests to the dCDN. If optional-to-implement metadata is "mandatory-to-enforce", and the dCDN does not support it, any delegated requests for that content will fail. The uCDN will likely want to avoid delegating those requests to that dCDN. Likewise, for any metadata which may be assigned optional values, it may be useful for the uCDN to know which values a dCDN supports, prior to delegating any content requests to that dCDN. If the optional value assigned to a given piece of content's metadata is not supported by the dCDN, any delegated requests for that content may fail, so again the uCDN is likely to want to avoid delegating those requests to that dCDN.

The CDNI Footprint and Capabilities Interface (FCI) [I-D.ietf-cdni-framework] provides a means of advertising capabilities from dCDN to uCDN. Support for optional metadata and support for optional metadata values may be advertised using the FCI.

6. CDNI Metadata interface

This section specifies an interface to enable a Downstream CDN to retrieve CDNI Metadata objects from an Upstream CDN.

The interface can be used by a Downstream CDN to retrieve CDNI Metadata objects either

• Dynamically as required by the Downstream CDN to process received requests. For example in response to a query from an Upstream CDN over the CDNI Request Routing Redirection interface (RI) [I-D.ietf-cdni-redirection] or in response to receiving a request for content from a User Agent. Or;
• In advance of being required. For example in the case of Pre-positioned CDNI Metadata acquisition.

The CDNI Metadata interface is built on the principles of RESTful web services. In particular, this means that requests and responses over the interface are built around the transfer of representations of hyperlinked resources. A resource in the context of the CDNI Metadata interface is any object in the Data Model (as described in Section 3 through Section 4).

To retrieve CDNI metadata, a CDNI Metadata client (i.e., a client in the dCDN) first makes a HTTP GET request for the URI of the HostIndex which provides the CDNI Metadata client with a list of Hostnames for which the upstream CDN may delegate content delivery to the downstream CDN. The CDNI Metadata client can then obtain any other CDNI Metadata objects by making a HTTP GET requests for any linked Metadata objects it requires.

CDNI Metadata servers (i.e., servers in the uCDN) are free to assign whatever structure they desire to the URIs for CDNI Metadata objects and CDNI Metadata clients MUST NOT make any assumptions regarding the structure of CDNI Metadata URIs or the mapping between CDNI Metadata objects and their associated URIs. Therefore any URIs present in the examples below are purely illustrative and are not intended to impose a definitive structure on CDNI Metadata interface implementations.

6.1. Transport

The CDNI Metadata interface uses HTTP as the underlying protocol transport.

The HTTP Method in the request defines the operation the request would like to perform. A server implementation of the CDNI Metadata interface MUST support the HTTP GET and HEAD methods.

The corresponding HTTP Response returns the status of the operation in the HTTP Status Code and returns the current representation of the resource (if appropriate) in the Response Body. HTTP Responses from servers implementing the CDNI Metadata interface that contain a response body SHOULD include an ETag to enable validation of cached versions of returned resources.

The CDNI Metadata interface specified in this document is a read-only interface. Therefore support for other HTTP methods such as PUT, POST and DELETE etc. is not specified. A server implementation of the CDNI Metadata interface SHOULD reject all methods other than GET and HEAD.

As the CDNI Metadata interface builds on top of HTTP, CDNI Metadata server implementations MAY make use of any HTTP feature when implementing the CDNI Metadata interface, for example a CDNI Metadata server MAY make use of HTTP's caching mechanisms to indicate that the returned response/representation can be reused without re-contacting the CDNI Metadata server.

6.2. Retrieval of CDNI Metadata resources

In the general case a CDNI Metadata server makes each instance of an addressable CDNI Metadata object available via a unique URI and therefore in order to retrieve CDNI Metadata, a CDNI Metadata client first makes a HTTP GET request for the URI of the HostIndex which provides the CDNI Metadata client with a list of Hostnames for which the upstream CDN may delegate content delivery to the downstream CDN.

In order to retrieve the CDNI Metadata for a particular request the CDNI Metadata client processes the received HostIndex object and finds the corresponding HostMetadata entry (by matching the hostname in the request against the hostnames in the HostMatch). If the HostMetadata is linked (rather than embedded), the CDNI metadata client then makes a GET request for the URI specified in the href property of the Link object which points to the HostMetadata object itself.

In order to retrieve the most specific metadata for a particular request, the CDNI metadata client inspects the HostMetadata for references to more specific PathMetadata objects. If any PathMetadata match the request (and are linked rather than embedded), the CDNI metadata client makes another GET request for the PathMetadata. Each PathMetadata object may also include references to yet more specific metadata. If this is the case, the CDNI metadata client continues requesting PathMetadata recursively.

Where a downstream CDN is interconnected with multiple upstream CDNs, the downstream CDN needs to determine which upstream CDN's CDNI metadata should be used to handle a particular User Agent request.

When application level redirection (e.g., HTTP 302 redirects) is being used between CDNs, it is expected that the downstream CDN will be able to determine the upstream CDN that redirected a particular request from information contained in the received request (e.g., via the URI). With knowledge of which upstream CDN routed the request, the downstream CDN can choose the correct metadata server from which to obtain the HostIndex. Note that the HostIndex served by each uCDN may be unique.

In the case of DNS redirection there is not always sufficient information carried in the DNS request from User Agents to determine the upstream CDN that redirected a particular request (e.g., when content from a given host is redirected to a given downstream CDN by more than one upstream CDN) and therefore downstream CDNs may have to apply local policy when deciding which upstream CDN's metadata to apply.

6.3. Bootstrapping

The URI for the HostIndex object of a given upstream CDN needs to be either configured in, or discovered by, the downstream CDN. All other objects/resources are then discoverable from the HostIndex object by following the links in the HostIndex object and the referenced HostMetadata and PathMetadata objects.

If the URI for the HostIndex object is not manually configured in the downstream CDN then the HostIndex URI could be discovered. A mechanism allowing the downstream CDN to discover the URI of the HostIndex is outside the scope of this document.

6.4. Encoding

Objects are resources that may be:

• Addressable, where the object is a resource that may be retrieved or referenced via its own URI.
• Embedded, where the object is contained within a property of an addressable object.

The descriptions of objects use the phrase "X contains Y" to mean that Y is either directly embedded in X or is linked to by X. It is generally a deployment choice for the uCDN implementation to decide when and which CDNI Metadata objects to embed and which are made separately addressable.

6.4.1. MIME Media Types

All MIME types for CDNI Metadata objects are prefixed with "application/cdni.". The MIME type for each object then contains the object name of that object as defined by this document. The object type name is followed by ".v" and the version number of the object type (e.g., “.v1”). Finally, the encoding type "+json" is appended. Table 3 3 lists a few examples of the MIME Media Type for some object (resource) that are retrievable through the CDNI Metadata interface.

{
  "hosts": [
    {
      "host": "video.example.com",
      "_links": {
        "host-metadata" : {
          "type": "application/cdni.HostMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234"
        }
      }
    },
    {
      "host": "images.example.com",
      "_links": {
        "host-metadata" : {
          "type": "application/cdni.HostMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host5678"
        }
      }
    }
  ]
}

{
  "metadata": [
    {
      "generic-metadata-type": "application/cdni.SourceMetadata.v1+json",
      "generic-metadata-value": {
        "sources": [
          {
            "_links": {
              "acquisition-auth": {
                "auth-type": "application/cdni.Auth.v1+json",
                "href": "http://metadata.ucdn.example/auth1234"
              }
            },
            "endpoint": "acq1.ucdn.example",
            "protocol": "ftp"
          },
          {
            "_links": {
              "acquisition-auth": {
                "auth-type": "application/cdni.Auth.v1+json",
                "href": "http://metadata.ucdn.example/auth1234"
              }
            },
            "endpoint": "acq2.ucdn.example",
            "protocol": "http"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "application/cdni.LocationACL.v1+json",
      "generic-metadata-value": {
        "locations": [
          {
            "footprints": [
              {
                "footprint-type": "IPv4CIDR",
                "footprint-value": "192.168.0.0/16"
              }
            ],
            "action": "deny"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "application/cdni.ProtocolACL.v1+json",
      "generic-metadata-value": {
        "protocol-acl": [
          {
            "protocols": [
              "ftp"
            ],
            "action": "deny"
          }
        ]
      }
    }
  ],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/video/trailers/*"
      },
      "_links": {
        "path-metadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234/pathABC"
        }
      }
    },
    {
      "path-pattern": {
        "pattern": "/video/movies/*"
      },
      "_links": {
        "path-metadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": "http://metadata.ucdn.example/host1234/pathDCE"
        }
      }
    }
  ]
}

{
  "metadata": [],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/videos/movies/hd/*"
      },
      "_links": {
        "pathmetadata": {
          "type": "application/cdni.PathMetadata.v1+json",
          "href": 
            "http://metadata.ucdn.example/host1234/pathABC/path123"
        }
      }
    }
  ]
}

{
  "metadata": [
    {
      "generic-metadata-type": "application/cdni.TimeWindowACL.v1+json",
      "generic-metadata-value": {
        "times": [
          "windows": [
            {
              "start": "1213948800",
              "end": "1327393200"
            }
          ],
          "action": "allow"
        ]
      }
    }
  ]
}

Grant Watson
Velocix (Alcatel-Lucent)
3 Ely Road
Milton, Cambridge  CB24 6AA
UK

Email: gwatson@velocix.com

Kent Leung
Cisco Systems
3625 Cisco Way
San Jose, 95134
USA

Email: kleung@cisco.com