Abstract:
A hierarchical content distribution system includes a seeding server, a plurality of geographically distributed content platforms, and a distribution controller, all interconnected by a communications network. The seeding server initially receives content files for distribution to various content platforms that provide for the persistent storage of the content files. Each content platform includes a content file server responsive on-demand to requests for the transfer of content files. The distribution controller autonomously monitors the transfers of content files and selectively issues transfer directives to the content platforms to modify the distribution of content files among the content platforms. The content file servers respond to received transfer directives by issuing requests for the transfer of the directive identified content files, thereby conforming the specific distribution of content files to an optimal distribution pattern as determined by the distribution controller based on usage patterns.

Description:
REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 10/132,954, filed on Apr. 26, 2002, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is generally related to network-based content delivery systems and, in particular, to a streaming media content delivery system supporting multiple, concurrent, peer-based sources of multimedia content accessible subject to central mediation. 
     2. Description of the Related Art 
     The desire for high-quality, on-demand delivery of streaming multimedia and other rich digital content is a principal driving force in the continued development of the broadband Internet infrastructure. Indeed, with the growth of broadband connections, the number, scale, and diversity of multimedia content servers has rapidly increased. Streaming audio and video files, including entertainment, news broadcasts, and instructional programming are now sourced by a variety of mainstream Internet sites. Content delivery through streaming media is broadly recognized as one of the fastest growing technologies related to the Internet. 
     Despite the growth in interest and use, conventional content streaming systems have not been cost-effective or particularly reliable in delivering high-quality content. Streaming media content, including in particular high-quality audio and video, is naturally bandwidth intensive and fundamentally sensitive to varying delivery latencies. Whether due to transient transport overloads, functional interruptions in the network infrastructure, or bandwidth limitations of a content source site, the result is uniformly perceived by a recipient as a reduction in the quality of service of the content source site. 
     Because of the open and shared nature of the Internet, few practical mechanisms can ensure the uninterrupted delivery of broadband content, typically consisting of multi-megabyte files, over the entire delivery path from a source site to a recipient. Known schemes include the use of network edge caches distributed at strategic locations within the network infrastructure controlled by an individual service provider. These network edge caches can be operated to significantly reduce the network traffic through the local network space of the individual service provider. Large edge caches are naturally required to store any significant amount of streaming media content. Implementing a useful number of adequately scaled, geographically distributed edge caches requires a large capital infrastructure investment. 
     Quality of service issues within the domain of individual content source sites are relatively easier to manage. Over the past few years, highly scaled, geographically distributed and even multiply redundant content source system architectures have been developed. Conventionally, these very large-scale systems are considered a baseline requirement to ensure a consistent high quality of service from the source sites. These sites typically employ large-scale server farms, hosting extensive libraries of archived multimedia content, that cumulatively provide sufficient throughput to enable real-time responsiveness and continuous on-demand delivery. Very high-bandwidth Internet connections with sufficient capacity to accommodate peak-demand content access requirements are also required. 
     Unfortunately, conventional content delivery networks, including fully scaled content server systems and extensive edge cache networks, have not proven adequate to broadly ensure a high quality of service to all potential users of the systems. Ultimately, any media content must be delivered as an effectively continuous stream of multimedia data to the recipient computer. The continuity of the stream must remain within the buffer length tolerance supported by the media player on the recipient computer. Transient bandwidth bottlenecks can certainly occur anywhere beyond the scope of a conventional content delivery network. Bottlenecks and delivery latencies can occur even within the network, particularly whenever the stream data is not immediately available in a locally accessible edge cache. Such bottlenecks in the Internet infrastructure are unfortunately both common and unpredictable. 
     Transient bandwidth bottlenecks can also occur in within the content server system itself. The rate of content access requests is highly variable with unpredictable demand peaks. Whenever the access rate exceeds the capabilities of the content server system, connection requests, including ongoing streaming data transfers, are dropped or delayed. Whether due to network or server bottlenecks, the resulting latencies and gaps in the delivery of stream data packets ultimately to the recipient are uniformly seen as source-site quality of service failures. 
     Expanding the conventional content distribution networks to prevent significant transient bandwidth bottlenecks is generally recognized as not practical. Due to the size and diversity of the Internet and the growing demands for streaming content delivery, significantly expanding the edge cache network coverage and the capacity of all included edge caches and streaming media source sites is simply not cost-effective. Furthermore, the costs associated with high-bandwidth Internet access and server throughput grow proportional to peak access demands, which is disproportionately greater than the growth of average access demands. Conventionally, a minimum of 50 percent additional access and server bandwidth is required, if not more, to meet peak bandwidth requirements. This additional bandwidth, however, is unused typically in excess of 90 percent of the time. The capital and operating cost of this additional bandwidth is therefore not directly recoverable. Consequently, content sites and the content delivery network operators have been severely limited in being able to consistently and profitably deliver streaming media content with a high quality of service. 
     Consequently, there is a clear need for a content delivery network architecture that can reliably provide a high quality of service to content stream recipients and that is cost-effective to operate. 
     SUMMARY OF THE INVENTION 
     Thus, a general purpose of the present invention is to provide an efficient peer-to-peer content distribution network system architecture capable of efficiently providing a high quality of service in the delivery of multimedia data streams to end-users. 
     This is achieved in the present invention through provision of a hierarchical content distribution system, including a seeding server, a plurality of geographically distributed content platforms, and a distribution controller, all interconnected by a communications network. The seeding server initially receives content files for distribution to various content platforms that provide for the persistent storage of the content files. Each content platform includes a content file server responsive on-demand to requests for the transfer of content files. The distribution controller autonomously monitors the transfers of content files and selectively issues transfer directives to the content platforms to modify the distribution of content files among the content platforms. The content file servers respond to received transfer directives by issuing requests for the transfer of the directive identified content files, thereby conforming the specific distribution of content files to an optimal distribution pattern as determined by the distribution controller based on usage patterns. 
     An advantage of the present invention is that content is redundantly distributed in the form of discrete segments throughout a peer storage network, permitting retrieval of segments on a best quality-of-service basis determined relative to each computer system that requests a streaming media content file. Multi-source segmented delivery of content also distributes the transport load over multiple content sources while ensuring the availability of multiple sources for all segments. The perceived quality-of-service is both increased and reliably maintained. 
     Another advantage of the present invention is that centralized mediation of segmented file transfers permits strategic planning of the ongoing segmented file transfer load distribution. Central mediation combined with distributed segmented file storage enables the aggregate bandwidth of the content distribution network to be optimally utilized. The complexity and cost of the central content mediation system, including the scale of the network access connections to accommodate worst case usage requirements, are greatly reduced. 
     A further advantage of the present invention is that the mediation system can perform predictive seeding of the content delivery network and adaptive modification of segment distribution in response to changing content file demands. Historical demand patterns, peer node availability and bandwidth capabilities can be used to guide the strategic distribution of content segments throughout the content delivery network. Planned, periodic updates of the content distribution network segment caches can be used to pre-deliver content segments to multiple strategically selected network caches during off-hours, thus minimizing both seeding and subsequent end-user demand spikes. 
     Still another advantage of the present invention is that the content distribution network can include a multi-tiered hierarchy of content segment caches, including peer cache nodes, primary content distribution nodes, and seeding servers. Reliable access to content segments is ensured by wide distribution of the content segments within the segment cache storage tiers and across multiple tiers. 
     Yet another advantage of the present invention is that the central mediation system can be persistently connected to and monitor the state of the available, active peer nodes of the content distribution network. Changes in the availability and supported bandwidth of nodes within the content distribution network are dynamically detected and factored into the ongoing tactical utilization of the content distribution network as mediated by the central server system. 
     Still another advantage of the present invention is that the distribution of content segments is actively maintained by the mediation server system. The distribution of content segments within the content delivery network, which is continuously subject to redistribution as a consequence of content use requests, is tracked and managed by the mediation server system to strategically adapt the distribution pattern to optimally match demand patterns. 
     A yet further advantage of the present invention is that proprietary content is continuously protected by a combination of encryption and digital signatures applied to the content files and to the individual content file segments. The mediation server system maintains the integrity of the content file segments throughout the operations of file segment transport, cache storage, and streaming file assembly and playback. The integrity of content within the content distribution system is thus ensured by the management function of the mediation server system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages and features of the present invention will become better understood upon consideration of the following detailed description of the invention when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof, and wherein: 
         FIG. 1  is a block diagram of a content distribution network organized in accordance with a preferred embodiment of the present invention; 
         FIGS. 2A and 2B  provide detail views of the segmentation of a streaming media content file in accordance with preferred embodiments of the present invention; 
         FIG. 3  is a block diagram of a peer network client system constructed in accordance with a preferred embodiment of the present invention; 
         FIG. 4  is a block diagram of a peer network mediation server system constructed in accordance with a preferred embodiment of the present invention; 
         FIG. 5  is a flow diagram of a streaming media content file transfer executed with respect to a peer network client system in accordance with a preferred embodiment of the present invention; and 
         FIG. 6  provides a detailed flow diagram of the adaptive request process implemented in a peer network client system constructed in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The content distribution network (CDN) of the present invention provides a comprehensive system solution to delivering streaming media and other digital content files to end-user systems with a consistent, high quality of service. The end-user systems participate in a distributed network of peer computer systems, organized into a tiered set of content sources, that store and, on request, selectively forward content to any other peer computer system within the network. The distribution of content and the coordination of content requests is mediated through a centralized server system, which maintains a directory catalog of the available content and of the location of the content within the network. 
     In the preferred embodiments of the present invention, each unit of content, typically represented by a content file, is segmented into discrete parts that are each uniquely identified in the catalog maintained by the mediation server system. Multiple copies of each segment are preferably distributed to cache stores maintained throughout the network to ensure redundant sources of segments for any requesting peer computer system. The distribution of segments within the network of caches is determined by the mediation server system. While entire sets of segments may be distributed to individual peer computer systems, the mediation server system can also operate to ensure that only fragmentary portions of content units are stored by individual peer computer systems. Through fragmentary storage, the effective security of the corresponding content units is fundamentally increased. The redundant distribution of segments permits transfer of the entire set of segments to a requesting peer with an assured high quality of service. 
     The mediation server system preferably manages the transfer of content segments within and between the various storage tiers of content distribution network, including content seeding peer computer systems, dedicated content distribution platforms, and end-user client node computer systems. The seeding peers preferably operate as the source of new content segments for distribution to the content distribution network and as ultimate backup sources for segments of requested content. The dedicated content distribution platforms preferably operate as a middle tier for content distribution, affording a greater fan-out of the transfer load in distributing content segments to the end-user client systems. These content distribution platforms may also be used as dedicated sources of proprietary or other content that for licensing or other reasons will not be distributed for persistent storage in the end-user tier of content caches. Finally, the end-user client node tier is typically a highly heterogenous collection of typically independently operated computer systems, each used to host a segment storage cache and to participate on an ad-hoc basis in the content distribution network. Client node systems may support caches of varying size, network connections of varying capacity, and be available on independent schedules. 
     Requests for selected content units and cache content update requests are submitted to the mediation server through preferably persistent network connections. Manifest lists of the segments may be returned directly or indirectly through an identification of a location within the peer network where a copy of the manifest list is stored. Based on a manifest list, content segments are independently requested by and transferred to nodes of the content distribution system. The peer driven segment retrieval process is cooperatively monitored by the mediation server and, as needed, alternate source locations for segments are provided. Information on the performance of individual peers and the patterns of requests are collected and evaluated on a generally dynamic basis for the generation of request manifest lists. This information is also utilized as a basis for the generation of cache update manifest lists, used to control the background transfer and controlling the storage distribution of content segments throughout the network to optimize the delivery of content in anticipation of demand. 
     A preferred architecture of a CDN system  10 , consistent with the present invention, is shown in  FIG. 1 . The CDN system  10  preferably includes a central server system  12  and a peer content storage network  14 . While logically operating as a centralized system, the various server computer systems that cooperatively function as the central server system  12  can be remotely located, duplicated, and scaled as needed for management, performance, and commercial requirements. The operational functions of the central server system  12  include the preparation, including segmentation, of new content for publication, the distribution and management of content segments throughout the peer content storage network  14 , monitoring the effective performance and actual content segment transfers between various peer nodes within the content storage network  14 , and responding to content and cache update requests. 
     In the preferred embodiments of the present invention, new content is initially prepared through a content publisher system  16  by encoding or transcoding a new content file or other unit of content to one of several defined media content formats. The currently preferred formats include the Microsoft® WMA streaming media and the Motion Picture Experts Group MPG3 formats. Other formats can be equivalently processed and used. The content file is then encrypted through a license encoding server. In the preferred embodiments of the present invention, a Microsoft digital rights management (DRM) encryption system is utilized to encrypt the content and subsequently manage the serving of licenses by a license server  20 . A content unit identifier, uniquely corresponding to the encrypted, encoded content file, and the DRM generated license key are provided to the license server  20 . 
     Encrypted, encoded content files are segmented by a content segmentation server  22 . As illustrated in  FIG. 2A , representing a first preferred embodiment, a content file  24  is divided into segments  26   1-N , each with a defined segment size, generally within the range of 25 kilobytes and 2 megabytes and typically on the order of 100 kilobytes. Each segment is then assigned the unique content unit identifier  28  and a segment sequence identifier  30 , permitting a particular content file  24  to be reassembled in order from a collection of the content segments  26   1-N . The resulting construction of named segments  32  are then transferred to a seeding peer server  34  and stored in a seeding cache  36  for subsequent distribution further into the peer content storage network  14 . Preferably, the seeding peer server  34  is considered part of the peer content storage network  14 . 
     Segment catalog records  38   1-N  are generated in correspondence with the named segments  32   1-N . For a named segment  32   2 , the corresponding segment catalog record  38   2  includes a copy of the content unit identifier  28  and segment sequence identifier  30  of the named segment  32   2 . A security value  40 , based on the data content of the segment  26   2 , and a field  42  permitting storage of one or more location identifiers are also included in the segment catalog record  38   2 . Preferably, the security value  40  is an MD5 hash, multi-byte checksum, or other data value signature of the segment  26   2  sufficient to subsequently authenticate the data integrity of the segment  26   2 . 
     The location identifiers are preferably surrogate client identifiers assigned to the peer nodes within the content storage network  14 . These surrogate client identifiers are preferably resolvable by the central server system  12  to peer network storage cache addresses, preferably in a uniform resource identifier (URI) form. The current URI of a client node can be determined whenever the client node reconnects with the central server system  12 . In resolving a location identifier for a client computer system that is currently unavailable, a null URI is returned. Preferably, location identifiers uniquely correspond to peer nodes. In an alternate embodiment, where the location identifier further identifies a particular cache store of named segments  32 , the location identifier revolves to a URI identifying a node and cache combination. 
     The segment catalog records  38  are stored to a content catalog database maintained by a database server  44 . As created, the location field  42  of the segment catalog records  38  initially contain only the location identifier of the seeding peer  34 . Whenever a named segment  32  is copied to or deleted from a segment cache within the storage content network  14 , the location field  42  the corresponding segment catalog record  38  is updated to reflect the current set of location identifiers specifying the content caches from which the segment can be obtained. 
     In response to a content unit request, the corresponding segment catalog records  38  are prepared and returned as part of a content manifest. In preparing the content manifest, the individual segment catalog records  38  are expanded by resolving the location identifiers to the complete URIs for the referenced named segments  32 . The requesting peer thus receives the necessary information to directly retrieve and validate the named segments  32  needed to reconstruct the requested content file  24 . 
     A second preferred embodiment of content segmentation and cataloging is shown in  FIG. 2B . As before, named segments  32  are created from the content file  24 . Groups of segments, preferably representing contiguous portions of the content file  24  are transferred to the seeding peer  34  and subsequently distributed as segment groups to content segment caches within the content storage network  14 . 
     A content manifest file  38 ′ is generated in combination with the named segments  32 . The content manifest file  38 ′ includes the unique content unit identifier  28 , a list  30 ′ of the segment sequence identifiers for the named segments  32 , and the security values  40 ′ for each of the named segments  32 . In the preferred embodiment of the present invention, the content manifest file  38 ′ is distributed as an implied first member of each segment group. Alternately, the content manifest file  38 ′ may be distributed separately through the seeding peer  34  to the content segment caches of selected, typically high availability peer computer systems within the content storage network  14 . 
     A series of manifest catalog records  38 ″ X  are also created in combination with the named segments  32  and manifest content file  38 ′. Each manifest catalog record  38 ″ X  is established for a respective segment group for the content file  24 . A manifest catalog record  38 ″ X  includes the unique content unit identifier  28 , a list  30 ″ of the segment sequence identifiers for the corresponding sequence group of named segments  32 , a manifest security value  40 ″, and one or more location identifiers  42 ″ that specify the content caches storing the corresponding segment group of the content file  24 . 
     The manifest security value  40 ″ is preferably an MD5 hash, multi-byte checksum, or other data value signature of the content manifest file  38 ′ sufficient to subsequently authenticate the integrity of the content manifest file  38 ′. Where the content manifest file is separately distributed, an additional set of one or more location identifiers are included with the identification identifiers  42 ″ to specify available content segment caches that store copies of the content manifest  38 ′. The location identifiers  42 ″ as stored by the content catalog are updated as the content manifest  38 ′ and segment groups are copied between and deleted from content segment-caches within the content storage network  14 . 
     In response to a content unit request, the manifest catalog records  38 ″ X  are returned to the requesting peer computer system. The location identifiers  42 ″ are expanded URIs prior to returning the manifest catalog record  38 ″. The requesting peer computer system can then obtain a copy of the manifest content file  38 ′ and validate the copy against the manifest security value  40 ″. Individual named content segments  32  can then be requested from any peer computer system that persistently stores an encompassing segment group. 
     This second preferred embodiment of content segmentation and cataloging is presently preferred based on the reduced load incurred by the central server system  12 . The content manifest file  38 ′, due at least to the number and size of included security values  40 ′, may be an appreciable fraction of the size of the corresponding content file  24 . Distribution and retrieval of the content manifest file  38 ′ from the content storage network  14  greatly reduces the file transfer load imposed on the central server system  12 . 
     In the preferred embodiments of the present invention, the central server system  12  supports persistent connections established between the remotely distributed nodes of the peer content storage network  14  and a persistent network proxy server  46 . The persistent connections are preferably initiated by a client node of the peer connection storage network  14  to a defined TCP/IP socket supported by the persistent network proxy server  46 . These persistent connections are utilized to permit peer nodes to supply the central server system  12  with a then current surrogate client identifier, report status and performance information from the peer connection storage network  14  to the central server system  12  and to request and obtain manifests. 
     In the absence of specific activity, as an ongoing background activity, active client nodes utilize the persistent connections to signal a continuing availability to participate in segment data transfers within the peer content storage network  14 . In response to activity, client nodes also report outbound segment transfer load levels and other performance indicators affected by ongoing peer network participation, including any communication failures that may occur. Client nodes actively performing inbound segment data transfers from other nodes of the peer connection storage network  14  preferably also utilize the persistent connections to report network data transfer rates and latency information against other identified client nodes. The persistent network proxy server  46  preferably collects and records this status and performance information in a network status database maintained by the database server  44 . The data contained within the network status database, in effect, represents a peer network map useful to plan use of the peer content storage network  14 . 
     Content unit requests, as submitted by the client nodes, are directed through the persistent network proxy server  46  to a host broker server  48 . Each content unit request provides the unique content unit identifier for the requested content unit. A search of the content catalog database locates the catalog records corresponding to the content segments necessary to construct the requested content unit. The referenced locations identifiers are evaluated against the performance information represented by the network peer network map to select an optimal, redundant set of content segments. This evaluation preferably reflects a load-balancing of the ongoing segment data transfer demands on the potentially participating nodes of the peer connection storage network  14 . The evaluation also considers the reported network data transfer rates between the requesting client node or similarly situated client nodes and the potentially participating nodes. As a product of the evaluation, the host broker server  48  can produce a content records listing a set of content segments, collectively representing the requested content unit, that can be retrieved from specified locations within the peer content storage network  14 . The specified locations determined by the host broker server  48  thus collectively represent a mediated balancing of the need to broadly distribute the system-wide content segment transfer load across the available peer network nodes and ensure effectively uninterrupted delivery of each requested content unit to the requesting peer nodes. 
     Preferably, a complete content manifest-based working specification of the requested content unit is dynamically constructed by a requesting client node. The content manifest file is retrieved either from another client node or through the host broker server  48 . Based on the segment catalog records  38   X  or the segment group index records  38 ″ X , including the content unit and segment sequence identifiers, segment security values, and the expanded location identifiers  42 ,  42 ″, the working content manifest is constructed by the client node. Preferably, the expanded location identifiers are presented in a priority ordered by segment sequence number and relatively preferred location from which to transfer the segment as determined by the performance and load-balancing evaluation performed by the host broker server  48 . 
     The distribution of named content segments  32  throughout the peer connection storage network  14  is, in the preferred embodiments of the present invention, actively performed by the peer nodes of the peer connection storage network  14 . Named content segments  32  are placed by a content segmentation server  22 , individually or as members of segment groups, in the content segment cache  36  of one or more seeding peer servers  34 . The named content segments  32  are then dispatched typically through the Internet  50  in response to peer node requests to various dedicated content distribution network platforms  52 , client node platforms  54 ,  56 , and potentially other seeding servers  34 . 
     Preferably, all peer nodes within the peer connection storage network  14  implement content servers, such as peer node applications  58 ,  60 , to support the network transfer of named content segment  32  between respective local content segment caches  36 ,  62 ,  64 . The progressive distribution, including redistribution, of named content segments  32  is predominately effected by the peer node applications  58 ,  60  and any secondary seeding peer servers  34  directly requesting sets of named content segments  32  for storage in the associated content segment caches  36 ,  62 ,  64 . Additional distribution and redistribution of named content segments  32 , again individually or as members of segment groups, follows from the on-demand transfer of the named content segments  32  of content units requested by individual client nodes. As named content segments  32  are received by a requesting client node  54 , a copy is stored at least transiently in the associated content segment cache  64  pending streaming to a client media player  66 . 
     Strategic control over the distribution of the named content segments  32  is preferably performed by a manifest manager server  68 . In accordance with the present invention, at least the dedicated content distribution network platforms  52  and client node platforms  54 ,  56  periodically issue cache update manifest requests to the central server system  12  through the persistent connections with the network proxy server  46 . Cache update manifest requests are also preferably issued on each initiation of a persistent connection. A content unit request may also be treated as a cache update manifest request. 
     In the preferred embodiments of the present invention, the manifest manager server  50  determines a distribution pattern of named content segments  32  based on an ongoing analysis of the peer network map, a log of the recent content unit requests and segment transfers, as stored by the broker server  48  to the database server  44 , and optionally constraints and hints provided by central server system  12  administrators. In general, the goal of the analysis is to maximize the availability of named content segments  32  to likely requesting peer nodes over network connections of sufficient, reliable bandwidth, subject to the segment cache storage size, load limitations, and reported peer node relative network connection bandwidth of individual peer nodes. While, in a present implementation, this dynamic analysis is performed on a progressive batch basis, a near real time evaluation and analysis of the collected data is preferred. 
     Constraint information may be employed in the analysis to restrict the distribution of the named content segments  32  of particular content units to defined dedicated content distribution network platforms  52 , as may be externally determined appropriate for certain types of content. Constraint information may also specify language or other meta-data attributes of content units that can be actively considered in the analysis to determine an appropriate distribution pattern for content units. Other constraint information may be provided to specify periods within which specific content units will be available, permitting controlled, progressive distribution of content segments prior to a release date and subsequent retirement after a close date. 
     Hinting information is preferably provided to the manifest manager  70  to peremptorily drive the distribution of named content segments  32 . The hinting information may be specified in terms of the priority and prevalence of the distribution of named content segments  32  corresponding to particular content units. The prevalence hints may indicate desired levels of redundant copy distribution over geographic and other domains. Alternately, or in addition, the hinting information may be specified by associating empirical and historically-derived distribution patterns with specified content units. Particularly in the case of historically-derived patterns, the distribution of previously distributed content units can be used as a reference for projecting the likely demand distribution of newly released content units. 
     The central server system  12  preferably includes one or more web servers  72 , which may be geographically distributed, to provide typically end-user accessible interfaces for the selection of content units. The web servers  72  connect through network connections to the database server  44  to obtain browsable and searchable lists of the content units available through the mediating operation of the central server system  12 . In accordance with the present invention, select web servers  72  may be designated as the sole or limited selection source for defined content units. Consequently, these select web servers  72  may be operated as the apparent source of proprietary or branded content, at least from the perspective of end-users, yet obtain the full use and benefit of the CDN system  10  in distributing the proprietary and branded content units. 
     A preferred embodiment of a peer application  60  is detailed in  FIG. 3 . Executed as a component of a system application on a client platform  54 , a system manager  80  implements the top-level procedural logic of the peer application  80 . A network connection agent  82  provides a persistent proxy interface to the network proxy  46 , supporting the bidirectional transfer of control messages  84 , such as content unit and cache management requests, and data  86 , including request and cache update manifests. Named content segments  32  are requested and received, in a preferred embodiment of the peer application  60 , through an HTTP client component  88  from remote peers. A file receiver component  90 , supervised by the system manager  80 , performs the detailed transfer control of data files and named content segments  32  through the connection agent  82  and HTTP client  88  relative to a local content segment cache  64 . 
     As each named content segment  32  is received, a security value is regenerated based on the data of contained segment  26  and compared against a corresponding security value  40 ,  40 ′, as provided in the current request or cache update manifest. A comparison failure with the security value  40 ,  40 ′ indicates a corrupt named content segment  32 , which is discarded. Valid named content segments  32  are stored to a content segment cache  64  under the management control of a cache manager component  92  and the system manager  80 . Preferably, the content segment cache  64  is encrypted subject to a DRM license. Accesses to the named content segments  32  require an encryption key acquired through a license manager component  94 , which provides an interface  96  to a conventional DRM client  68  and, as required through the connection agent  82 , to the remote license server  20 . 
     The peer application  60  preferably implements an HTTP server  98  to provide conventional streaming content connectivity to an external client media player  66  or other streaming media content client. A streaming content component  100  coordinates between the system manager  80 , for initial set-up of the content streaming session, and the cache manager  92 , for the ordered retrieval of named content segments  32  corresponding to a requested content unit. Retrieved named content segments  32  are progressively passed by the streaming server  100  from the local content segment cache  64  to the HTTP server  98  for relay to a media player  66 . 
     The HTTP server  98  also supports named content segment  32  transfer requests from other peer nodes of the peer connection storage network  14 . A segment server component  102  is utilized to manage named content segment  32  transfers, subject to segment transfer session management performed by the system manager  80 . The transfer of named content segments  32  to the HTTP server  98  is coordinated by the segment server  100  with the cache manager  92  for selection of the request identified named content segments  32  from the content segment cache  64 . 
     A preferred architecture  110  of a content delivery network central server system  12 , exclusive of segment preparation and publication components, is shown in  FIG. 4 . A conventional hardware-based network connection load balancer  112  supports a scalable set of CDN server systems  114 ,  116 . Each CDN server systems  114 ,  116  implements a set of executable server components that are implemented on one or more conventional network connected server computer systems. The CDN server systems  114 ,  116  share access to a CDN database  118  configured to store OLTP accessible data and an archive database providing storage of recently logged and historical data that can be used for analytic and reporting purposes. 
     A client proxy component  120  maintains the direct socket connections for the persistent client sessions established against the active peer nodes of the peer connection storage network  14 . A startup message is received by the client proxy component  120  from each peer node upon joining the peer connection storage network  14 . Completion messages are received as different processes are completed by the peer nodes. 
     A proxy manager  122  monitors the connections established with the client proxy component  120  to maintain a data structure representing the peer nodes that are currently active and accessible. Periodic status messages are exchanged to actively monitor the state of the connected peer nodes. Failures in the status exchange are preferably analyzed with the result of redirecting a peer node to another CDN server system  114 ,  116 , which may be able to establish a more reliable network connection, or the connection is disconnected and the peer node is identified as inactive. 
     A client session component  124  establishes defined contexts for communications with each of the peer nodes connected to the client proxy  120 . Within each context, information is gathered through various progress, status, and logging messages received from the peer nodes. The collected information, as well as the activity state information managed by the proxy manager, is stored to the CDN database  118  for subsequent use in performance analysis and activity reporting. 
     A host broker component  126  receives, through the client proxy  120 , the peer node content unit requests. Through OLTP database accesses, the host broker determines an optimal set of peer nodes from which the requesting peer node can download the named content segments  32  corresponding to the requested content unit. Preferably, the host broker selects all active peer nodes that store named content segments  32 , individually or in segment groups, of the requested content unit and then orders identical copies of the named content segments  32  by the load level of the source peer node and the evaluated connection speed between the source and requesting peer nodes. The top segment catalog record  38 ,  38 ″ entries for named content segments  32  are selected and provided in one or more request catalog messages that are then returned to the requesting peer. 
     A file session component  128  actively monitors the ongoing named content segment  32  download and streaming operations of the individual peer nodes within corresponding client sessions. In conjunction with the host broker component  126 , a unique file session identifier is provided in each content unit request manifest. Unique file session identifiers are also provided in each cache update manifest. When a streaming content unit transfer is terminated, the peer node provides a session finished message to the file session component  128 . A file session finished message is also provided when a peer node has completed a content segment cache update, based on a provided cache update manifest. 
     A file session finished message includes the request or cache update manifest corresponding file session identifier and information detailing the required transfer time, number of source peer nodes used, and other statistically relevant information. Network communications failures with particular source peer nodes and other error conditions are also reported. The acquired information is stored to the CDN database  118  for subsequent use in performance analysis and activity reporting. 
     A cache manifest manager  130  is responsible for establishing the distribution of named content segments throughout the peer connection storage network  14 . The collected information stored by the CDN database  118  is periodically evaluated on a daily or shorter basis. Newly available content units, as represented by stored segment catalog records  38 , are considered in the evaluation. An updated distribution plan is ultimately produced and stored by the cache manifest manager  130  to the CDN database  118 . 
     A peer cache update manager  132  is responsive to cache update manifest requests, as periodically issued by the peer nodes. Based on the segment distribution plan determined by the cache manifest manager  130  and preferably further qualified by recognition of the ongoing named content segment  32  transfers dynamically reported to the file session component  128 , a cache update manifest specific to the requesting peer node is generated and returned. 
     A license manager component  134  is responsive to license request messages issued by client nodes in connection with content unit requests. The request manifest, in addition to providing a requisite set of segment catalog records  38 , preferably identifies the type of licensing encryption, if any, applied to the requested content unit. A license request message includes the request corresponding content unit identifier  28 , a license location identifier, which specifies the licensing authority for the requested content and requesting client node, and the license type identifier. 
     The specified license type permits the license manager  134  to validate the requested content unit license against the typically external licensing authority. In the preferred embodiments of the present invention, the license manager  134  utilizes a conventional Microsoft digital rights manager. Where validated, a license key is generated by the license manager  134  and provided to a license server  136 . The license is thus available to the client media player  66  for use in decrypting the streaming media content unit as received through the client peer application  60 . A license response message is also returned through the client proxy  120  to the requesting peer node in response to the license request message. The license response message either acknowledges the availability of the license key or provides a validation failure explanation. 
     The preferred process  140  implemented by a client peer application  60  is shown in  FIG. 5 . In connection with the execution of the peer application  60 , a client media player  66 , Web browser or other client application, executed on the client platform  54 , permits an end-user to select and login  142  to a chosen Web server  72 . Preferably, a list of available content units is displayed for selection  144  by the end-user. Based typically on an end-user selection, a content unit request is issued  146  to the CDN server system  114  currently supporting the persistent connection to the peer application  60 . The content unit request is brokered  148  and a request manifest  150  is returned. 
     Upon receipt of the request manifest, the client peer application  60  determines whether an encryption license applies to the requested content unit. A license validation  154  is obtained where required. The segment catalog records  38 ,  38 ″ provided by the request manifest are parsed and corresponding named content segment  32  transfer requests are progressively issued  156  to the segment catalog record  38 ,  38 ″ identified peer nodes. As the requested named content segments  32  are received  158 , the integrity of each named content segment  32  is checked  160 . Valid named content segments are preferably at least transiently stored  162  to the content segment cache  64 . An updated cache update manifest provided in combination with the request manifest can determine which named content segments  32  are to be persistently retained in the content segment cache  64 . Named content segments  32  that fail the integrity check are re-requested from the same or an alternate peer node. 
     In the preferred embodiments of the present invention, once at least the initial named content segment  32  has been received, streaming  164  of the requested content unit is enabled to the attached client media player  66 . As permitted by the client media player  66 , Web browser or other client application, a new content unit can be selected  144  at any time, terminating the current transfer, and causing a new content unit request to be issued  146 . 
     Periodic updates of the content segment cache  64  are scheduled by the client peer application  60 . Cache update requests are preferably issued  166  automatically by the peer application  60  to the currently connected CDN server system  114 . A cache update manifest is generated  168  and returned  170  to the requesting client peer application  60 . The cache update manifest is parsed by the client peer application  60  to identify any named content segments  32 , as specified by corresponding segment catalog records  38 , that are not currently stored by the content segment cache  64 . Requests for the non-resident named content segments are issued  156  and the named content segments  32  are received  158  and stored  162  to the content segment cache  64 . 
     In an alternate embodiment of the present invention, the cache update manifest provides meta-information that is used by the client peer application  60  to qualify cache update operations. The cache update manifest meta-information is utilized to specify the schedule of cache update requests and the location of the CDN server system  114 ,  116  to use as the target of the next cache update request. The meta-information may also be provided to specify a delay schedule for issuance of named content segment  32  transfer requests. This allows the cache update manager  132  to fully mediate the data transfer load on the peer content storage network  14  both in terms of selecting the transfer source peer nodes utilized and the temporal distribution of the load imposed on those nodes. Such mediation is particularly valuable to optimally schedule the load placed on the seeding peers  34  and dedicated CDN platforms  52  particularly where the peer content storage network  14  includes a large number of peer nodes. 
     The managed client peer process  180  of named content segment request and retrieval is shown in greater detail in  FIG. 6 . The contents of request and cache update manifests, including meta-information, are initially parsed  182  upon receipt of the manifests. Deferred operations are preferably handled through a periodic re-parsing of the manifests at the deferred time intervals. In anticipation of the receipt of new named content segments  32  beyond a client platform  54  defined cache size, named content segments  32  no longer identified in the current cache update manifest are deleted  184  from the content segment cache  64 . 
     Preferably, multiple named content segments  32  are requested  156  concurrently from the peer content storage network  14 . Each concurrently requested named content segment  32  is also redundantly requested from multiple peer node locations. The total number of concurrent named content segment  32  transfers allowed is a dependent on the maximum acceptable load permitted on the client platform  54 . Excluding the redundant transfers, a default limit is set at four concurrent transfers of unique named content segments  32 . As redundant copies of named content segments are received  158 , the transfer bandwidths of each are monitored. Once a reasonably stable gauge of the transfer bandwidths can be determined, adjusted potentially for different transfer start times and the anticipated remaining length of the named content segment  32 , only the highest bandwidth transfer for each named content segment  32  is maintained. A failure to complete any of these remaining transfers is detected  186 . A severe reduction in the transfer bandwidth is also preferably treated as a transfer failure. Redundant requests for the same named content segment  32  are again reissued  188  to multiple peer node locations determinable from the manifests. 
     Named content segments  32  are stored  162  to the content segment cache  64  as received  158 . A security value for the segment data may be accumulated as the named content segment  32  is received or computed once the named content segment  32  once the transfer is completed. This actual security value is then compared  190  to the security value  40  provided in the corresponding segment catalog record  38 . On a comparison failure, the received named content segment  32  is deleted from the content segment cache  64 . Redundant requests for the named content segment  32  are again reissued  188 . 
     Preferably, detailed information, including the connection latency, average bandwidth and reliability of transferring named content segments  32  relative to the requesting client platform  54 , is collected by the client peer application  60 . Information detailing transfer failures and data integrity failures, along with the identity of the peer nodes participating in the failed transactions, is also collected. This performance information is reported to the connected CDN server system  114 ,  116 , preferably in connection with the transfer completion of each content unit transfer and cache update. 
     Thus, an efficient peer-to-peer content distribution network system architecture capable of efficiently providing a high quality of service in the delivery of multimedia data streams to end-users has been described. While the present invention has been described particularly with reference to operation over the public Internet, the present invention is equally applicable to the distribution over other public and private communications networks. Additionally, the present invention is also applicable to the rapid and efficient distribution of digital information that may have use other than as streaming media content. 
     In view of the above description of the preferred embodiments of the present invention, many modifications and variations of the disclosed embodiments will be readily appreciated by those of skill in the art. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.