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Content delivery network (cdn) content server request handling mechanism with metadata framework supportRelated Patent Categories: Electrical Computers And Digital Processing Systems: Multicomputer Data Transferring, Distributed Data ProcessingContent delivery network (cdn) content server request handling mechanism with metadata framework support description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070250560, Content delivery network (cdn) content server request handling mechanism with metadata framework support. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a division of Ser. No. 09/835,663, filed Apr. 16, 2001, now U.S. Pat. No. 7,240,100, which application was based on and claimed priority to Ser. No. 60/197,211, filed Apr. 14, 2000. BACKGROUND OF THE INVENTION [0002] 1. Technical Field [0003] The present invention relates generally to high-performance, fault-tolerant HTTP, streaming media and applications delivery in a content delivery network (CDN). [0004] 2. Description of the Related Art [0005] It is well-known to deliver HTTP and streaming media using a content delivery network (CDN). A CDN is a self-organizing network of geographically distributed content delivery nodes that are arranged for efficient delivery of digital content (e.g., Web content, streaming media and applications) on behalf of third party content providers. A request from a requesting end user for given content is directed to a "best" replica, where "best" usually means that the item is served to the client quickly compared to the time it would take to fetch it from the content provider origin server. An entity that provides a CDN is sometimes referred to as a content delivery network service provider or CDNSP. [0006] Typically, a CDN is implemented as a combination of a content delivery infrastructure, a request-routing mechanism, and a distribution infrastructure. The content delivery infrastructure usually comprises a set of "surrogate" origin servers that are located at strategic locations (e.g., Internet Points of Presence, access points, and the like) for delivering copies of content to requesting end users. The request-routing mechanism allocates servers in the content delivery infrastructure to requesting clients in a way that, for web content delivery, minimizes a given client's response time and, for streaming media delivery, provides for the highest quality. The distribution infrastructure consists of on-demand or push-based mechanisms that move content from the origin server to the surrogates. An effective CDN serves frequently-accessed content from a surrogate that is optimal for a given requesting client. In a typical CDN, a single service provider operates the request-routers, the surrogates, and the content distributors. In addition, that service provider establishes business relationships with content publishers and acts on behalf of their origin server sites to provide a distributed delivery system. A well-known commercial CDN service that provides web content and media streaming is provided by Akamai Technologies, Inc. of Cambridge, Mass. [0007] CDNSPs may use content modification to tag content provider content for delivery. Content modification enables a content provider to take direct control over request-routing without the need for specific switching devices or directory services between the requesting clients and the origin server. Typically, content objects are made up of a basic structure that includes references to additional, embedded content objects. Most web pages, for example, consist of an HTML document that contains plain text together with some embedded objects, such as .gif or .jpg images. The embedded objects are referenced using embedded HTML directives, e.g., Uniform Resource Identifiers (URIs). A similar scheme is used for some types of streaming content which, for example, may be embedded within an SMIL document. Embedded HTML or SMIL directives tell the client to fetch embedded objects from the origin server. Using a CDN content modification scheme, a content provider can modify references to embedded objects so that the client is told to fetch an embedded object from the best surrogate (instead of from the origin server). [0008] In operation, when a client makes a request for an object that is being served from the CDN, an optimal or "best" edge-based content server is identified. The client browser then makes a request for the content from that server. When the requested object is not available from the identified server, the object may be retrieved from another CDN content server or, failing that, from the origin server. [0009] In some CDNs, such as Akamai FreeFlow.RTM. content delivery service, data about the content provider's (CP's) objects, or so-called "metadata," is often directly encoded "in-URL," namely in the HTML or SMIL directives that are modified during the content modification process. More specifically, metadata is the set of all control options and parameters that determine how a CDN content server will handle a request for an object. Such metadata may include, for example, a CP code or other internal tracking number used, for example, to facilitate billing, coherence information (e.g., TTL or fingerprint) about how CDN servers should cache the object and maintain its freshness, a unique serial number value that may be used for load balancing, access control data, a hostname identifying the origin server where a copy of the object may be located, and other feature-specific metadata. [0010] By including object metadata directly in the HTML or SMIL directives, content providers may set up their metadata as part of the publication process, i.e., without requiring changes in their web server or involving network operations personnel. The "in-URL" embedding technique ensures that any modified URL pointing to the CDN has, in a self-contained way, the information needed to serve the object. On the other hand, the modified URL generated by this process is often long and complex. In addition, some content providers may only have a need to specify site-wide or global metadata specifications. [0011] Thus, there remains a need to provide a framework that allows for both a simple method of creating modified URLs for sites with simple global metadata specifications, while allowing arbitrary complexity for sites with arbitrarily complex metadata needs. BRIEF SUMMARY OF THE INVENTION [0012] To serve content through a content delivery network (CDN), the CDN must have some information about the identity, characteristics and state of its target objects. Such additional information is provided in the form of object metadata, which according to the invention can be located in the request string itself, in the response headers from the origin server, in a metadata configuration file distributed to CDN servers, or in a per-customer metadata configuration file. CDN content servers execute a request identification and parsing process to locate object metadata and to handle the request in accordance therewith. Where different types of metadata exist for a particular object, metadata in a configuration file is overridden by metadata in a response header or request string, with metadata in the request string taking precedence [0013] More generally, the present invention specifies interfaces that control CDN content server behavior, and it further describes those behaviors. A preferred means of control is a metadata component, which preferably takes the form of a key/value pair, and which is used to communicate desired handling of an object to CDN content servers. These components can be associated with requests in a number of ways, including CDN-generated configuration files, customer (CP) configuration files, and request-based and response-based mechanisms. Other controls include request-URI rewriting to allow the request-URI itself to be changed when necessary. Requests themselves may take on a number of forms, depending on customer requirements. [0014] In an illustrative embodiment, the present invention describes a method that is operative in a content delivery network (CDN) wherein participating content providers identify content to be served from a set of CDN content servers in response to requests, and wherein the CDN uses metadata to determine how a CDN content server will handle a request for a given object. The method begins by establishing a framework that enables delivery of metadata to a given CDN content server either in-band or out-of-band. "In-band" means that the metadata is delivered in a request string for the object ("in-ARL") or within an HTTP response header, e.g., when a CDN content server contacts the participating content provider upon a cache miss the first time the object is requested from the CDN server. "Out-of-band" means that the metadata is delivered to a given content server in a separate configuration file. According to the method, when a request for the given object is given CDN content server, the request is parsed to identify a set of metadata. At least one precedence rule is then applied to the set to identify given metadata to be applied to the given content prior to serving a response. Preferably, in-band-delivered metadata overrides out-of-band metadata, and in-ARL metadata overrides HTTP response header metadata when both are available. [0015] The foregoing has outlined some of the pertinent features and advantages of the present invention. A more complete understanding of the invention is provided in the following Detailed Description of the Preferred Embodiment. BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG. 1 is a block diagram of a content delivery network in which the present invention may be implemented; [0017] FIG. 2 is an illustrative "long" form ARL; [0018] FIG. 3 is a simplified block diagram illustrating various metadata sourcing mechanisms; [0019] FIG. 4 illustrates how a CDN content server handles metadata, folding in overrides as they appear according to the present invention; [0020] FIG. 5 is a flowchart illustrating a CDN server request identification and parsing routine of the present invention; [0021] FIG. 6 is a block diagram of a CDN content server; and Continue reading about Content delivery network (cdn) content server request handling mechanism with metadata framework support... 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