Patent Publication Number: US-2009235319-A1

Title: Video on Demand Gateway

Description:
This is a continuation patent application of U.S. patent application Ser. No. 10/010,719 entitled “Video On Demand Gateway” filed Nov. 8, 2001, for which priority is claimed and the contents of which are incorporated herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of video on demand (VOD) systems. 
     BACKGROUND OF THE INVENTION 
     A video on demand service permits a viewer to order a movie or other video program material for immediate viewing. In a typical broadcast satellite or cable television (CATV) system, the viewer is presented with a library of video choices. The VOD program material, such as for example movies, are referred to herein as assets, VOD assets or video assets. The viewer can search for desired videos by sorting the library according to actor, title, genre or other criteria before making a selection. More generally, assets include audio files, images and/or text. 
     In a true VOD system, a portion of the CATV spectrum is dedicated (on a per use basis) to transmit the requested video to the subscriber. The practice of assigning a portion of the CATV spectrum on a temporary basis is known as narrowcasting. Since the assigned video channel is dedicated to one viewer, VCR-like commands are possible. That is, for example, the purchased video may be paused, fast-forwarded, rewound or played in slow motion. Various vendors, known as VOD suppliers, provide systems and software that enable CATV operators to offer a VOD service to their subscribers. 
     In a typical VOID system, a software component (known as the VOD client) resides in the CATV set-top box (STB) at the viewer&#39;s home. A typical VOD system further includes a VOD server at the CATV system headend and a VOD pump. The VOD pump is a source of video signal. A common form of video signal is a digital MPEG stream. In addition to a VOD pump, a typical VOD system includes a VOD asset management system and a VOD business management system. 
     The VOD asset management system generates lists of movies that are available for VOD purchase. The VOD client communicates requests to the VOD management system at the CATV headend and sets up the VOD pump to transmit the movie to the viewer. Also, for billing purposes, the VOD business management system records the event of a video purchase and communicates the purchase event to a billing system through which the viewer pays for the video purchase. 
     The VOD server is a memory intensive system that stores the video library (video assets) at the headend and generates the VOD video stream for each subscriber. The video inventory in the VOD server may contain thousands of titles. The VOD server further generates one VOD video stream for each active VOD viewer. There may be thousands of simultaneous active VOD viewers. 
     As the video library expands, and as the number of VOD customers grows, the memory requirements and transmitting capacity of the VOD server is increased. Expansion of the VOD service means that the CATV operator must add equipment to expand the capabilities of the VOD server. 
     Generally, once a CATV operator selects a VOD system vendor, expansion of the system to accommodate a larger video inventory or a larger base of the VOD customers, requires that the CATV operator purchase compatible equipment from the same VOD systems vendor. Accordingly, the CATV operator is unable to take advantage of advances in VOD technology, such as advanced VOD memory storage or advanced VOD systems in general, unless the initially selected VOD systems vendor offers such advanced and/or reduced cost technology. 
     Furthermore, since the equipment offered by competing VOD systems vendors is not interoperable with exiting legacy systems, the VOD system of a given CATV operator must be all from the same VOD systems vendor. If the CATV operator elects to upgrade to more advanced (and possibly less expensive) VOD equipment, it often means that the CATV operator&#39;s legacy VOD equipment must be scrapped. 
     SUMMARY OF THE INVENTION 
     The present invention is embodied a system method and apparatus for use as a video on demand (VOD) gateway that allows multiple incompatible and non-interoperable VOD systems to function as a single unified VOD system. By use of the VOD gateway of the present invention, a CATV operator who has existing legacy VOD system equipment procured from a single VOD system vendor, may expand the existing legacy VOD system capacity by adding equipment from other VOD system vendors. In such manner, the CATV operator is able to take advantage of advanced technology and reduced costs offered by competing VOD system vendors without rendering existing legacy VOD system obsolete. 
     The present invention is further embodied in a VOD gateway system including a VOD asset gateway, a VOD session gateway and a VOD transaction gateway. The VOD gateway is located at the CATV headend or other transmitting station of a broadcast communications system. Furthermore, the present invention is embodied in generic VOD client software residing in a CATV set-top box or other receiving station of a broadcast communications system. 
     The VOD asset gateway aggregates video inventory from multiple VOD vendor&#39;s equipment and presents a single unified listing of VOD titles to the viewer. The VOD asset gateway reformats or translates the proprietary protocols used by multiple VOD vendor&#39;s equipment to a generic protocol describing all VOD assets. The VOD session gateway at the headend translates or reformats a subscriber request in a generic protocol for a VOD program to the specific protocol for a proprietary VOD system. Finally, the VOD transaction gateway distributes transactions reported by the set-top box so that VOD transactions are reported to the proper business management and/or billing for each type of VOD vendor&#39;s equipment. The VOD transaction gateway translates or reformats the transaction reporting protocol from the generic VOD client software residing in the CATV set-top box to the specific protocol used by the particular VOD vendor&#39;s business management system. 
     In an alternate embodiment, the VOD gateway of the present invention permits operators of multiple CATV systems to use multiple incompatible and non-interoperable VOD systems in each of a plurality of separate CATV systems. 
     That is, by the use of the VOD gateway of the present invention a CATV multiple systems operator (MSO) can purchase VOD equipment from a plurality of manufacturers and place such VOD equipment in any one of a plurality of CATV systems. In such case, even though each CATV system uses only one type of VOD equipment, the VOD gateway of the present invention permits the MSO to place (and replace) VOD equipment from any manufacturer in any CATV system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a VOD system in accordance with the prior art. 
         FIG. 2A  is a block diagram of a VOD gateway system in accordance with the present invention. 
         FIG. 2B  is a block diagram of an alternate embodiment of a VOD gateway system in accordance with the present invention. 
         FIG. 3  is a block diagram illustrating further details of a VOD gateway system in accordance with the present invention. 
         FIG. 4  is a block diagram illustrating a VOD asset gateway in accordance with the present invention. 
         FIG. 5A  illustrates an embodiment of a VOD session gateway operated in server mode in accordance with the present invention. 
         FIG. 5  illustrates an alternate embodiment of a VOD session gateway operated in client mode in accordance with the present invention. 
         FIG. 6  is a signal flow diagram illustrating the signal flow through a VOD session gateway in accordance with the present invention. 
         FIG. 7  is a timing diagram illustrating the various time windows for delivering a VOD program. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a prior art VOD system  10  located in the headend  12  of the CATV system includes a VOD server  14 , a VOD asset management system  16  and a VOD business management system  18 . A CATV set-top box  20  is located in the home of the TV viewer and includes a VOD client software program  22  running in the set-top box  20 . 
     Generally, the VOD client software  22  communicates with the VOD asset management system to display lists of available video programming to the CATV subscriber. The subscriber selects a video for viewing, and the VOD server  14  delivers the selected video to the set-top box  20 . The resulting transaction (purchase of the video) is processed by the VOD business management system  18  whereby the viewer pays or is billed for the purchased video. 
     As indicated above, in order to expand the VOD system  10 , additional VOD servers  14  need to be added. However, since the VOD client software  22  will only work with VOD server  14 , only VOD servers that are compatible with the existing VOD server  14  may be used. In order to take advantage of advanced technology or less expensive VOD systems, the VOD client software  22  and the VOD system  10  must be changed. Changing to a new VOD system results not only in the obsolescence of the existing VOD system  10 , but also locks the CATV operator into yet another technology. 
     A VOD gateway  70  in accordance with the present invention is shown in the block diagram of  FIG. 2A . A CATV headend  32  includes VOD systems from multiple vendors such as VOD system  30  from vendor A, VOD system  50  from vendor B and VOD system  60  from vendor N. All of the distinct, proprietary and incompatible VOD systems  30 ,  50 ,  60  communicate to the same set-top box  40  through a generic VOD client software  42  via a common VOD gateway  70 . The VOD gateway  70  includes a VOD asset gateway  72 , a VOD session gateway  74  and a VOD transaction gateway  76 . 
     In operation, the VOD asset gateway  72  communicates with each VOD system  30 ,  50 ,  60  in order to aggregate all of the separate VOD videos from all vendors into a single listing of VOD assets. The unified lists of VOD assets is presented at the set-top box  40  via CATV system  34  and the generic VOD client  42 . 
     The subscriber at the CATV set-top  40  selects a given video for viewing. The VOD session gateway  74  receives the request for the given video from the subscriber and communicates with the appropriate VOD system  30 ,  50 ,  60  that serves the particular given video selected by the subscriber. The VOD pump within the selected VOD system  30 ,  50 ,  60  delivers the purchased video to the set-top box  40  over the CATV system  34 . 
     The transaction (purchase of the given video) is processed by the VOD transaction gateway  76 . The transaction is communicated to the appropriate VOD system  30 ,  50 ,  60  that provided the particular given VOD selection to the subscriber. 
     In such manner, incompatible and non-interoperable VOD systems  30 ,  50 ,  60  form a single VOD system. The respective VOD video inventories are made available to the set-top box  40  as a single VOD service. Thus, VOD systems from different vendors, using different technology may be mixed and matched without changing the generic VOD client software  42 . 
     An alternate embodiment of a system employing the VOD gateway of the present invention is shown in the block diagram of  FIG. 2B . A CATV multiple systems operator distributes satellite  75  signals to multiple CATV headends  32 A,  32 B,  32 N. Each CATV headend  32 A,  32 B,  32 N includes a VOD system from one of multiple VOD vendors such as VOD system A  30 A from vendor A, VOD system B SOB from vendor B and VOD system  60 N from vendor N. All of the distinct, proprietary and incompatible VOD systems  30 A, SOB,  60 N communicate with each respective set-top box  40 A,  40 B,  40 N through the same generic VOD client software  42 A,  42 B,  42 N via a respective VOD gateway  70 A,  70 B,  70 N. The VOD gateways  70 A,  70 B,  70 N in  FIG. 2B  are substantially identical to each other and each include a respective VOD asset gateway, a VOD session gateway and a VOD transaction gateway, similar to that shown in  FIG. 2A . 
     In such manner, the CATV multiple system operator may purchase and use incompatible and non-interoperable VOD systems  30 A, SOB,  60 N. Each of the incompatible VOD systems  30 A, SOB,  60 N may be placed in operation in any of the CATV headends  32 A,  32 B,  32 N without changing the VOD client  42 A,  42 B,  42 N. In each case, the respective VOD gateway  70 A,  70 B,  70 N assures compatibility with a respective substantially identical generic VOD client  42 A,  42 B,  42 N. Thus, VOD systems from different vendors, using different technology may be mixed and matched in any of the MSOs CATV systems  32 A,  32 B,  32 N without changing the generic VOD client software  42 A,  42 B,  42 N or the VOD gateway  70 A,  70 B,  70 N. 
     A VOD gateway for use in the CATV system in accordance with the present invention is shown in further detail in  FIG. 3 . There are two VOD gateway configurations: digital storage media command and control (DSM-CC) configuration and real time streaming protocol (RTSP) configuration. Digital storage media command and control (DSM-CC) signaling is widely used in a majority of VOD service trial and deployments today. In the real time streaming protocol (RTSP) based VOD Gateway Integration, the VOD Gateway is integrated with multiple VOD server vendors through the same asset and transaction integration as in the case of digital storage media command and control (DSM-CC). The only difference is that real time streaming protocol (RTSP) protocol is supported via the session gateway for session signaling and stream control. 
     The VOD gateway  100  includes an asset gateway  124 , a transaction gateway  126  and a session gateway  134 . The VOD gateway  100  is coupled to a Liberate Command server  106  and Liberate Datapoint server  104 . The Liberate Command server (provided by Liberate Technologies)  106  provides configuration management for all headend servers. The Liberate Datapoint server  104  stores the data characterizing the subscriber&#39;s account and capabilities of the set-top box  102 . The set-top box  102  generally has limited persistent storage for holding characterizing data. The Liberate Datapoint server  104  holds data needed by the set-top box  102 , including client VOD configuration data. 
     The asset gateway  124  is composed of an asset data manager  124 A and a cache portal  124 B. The asset data manager  124 A is coupled to a VOD asset management system  116  and a VOD asset distribution system  112  via asset APIs and custom interface programs  120 . A specialized custom designed interface program  120  is provided for each type of VOD vendor equipment. That is, one customized program is written for each VOD equipment manufacturer, such as SeaChange, nCube, Concurrent etc. 
     The transaction gateway  126  is coupled to a VOD business management system  118  and a VOD billing system  114  via transaction APIs and custom plugins  122 . Depending upon the VOD business management system used by the service provider, a specialized custom designed BMS (Business Management System) plugin  122  is written for each business management systems provider. In some cases, the VOD equipment supplier provides a business management system. In other cases, the VOD equipment supplier relies on a third party to provide a business management system  118  and billing system  114 . In either case a BMS plugin  122  is required so that the transaction gateway  126  can report VOD transactions. For this purpose, a transaction servlet  124 C report VOD transactions via a suitable client API  136 . 
     The transaction gateway  126  is intended to be a stateless entity. However, the transaction gateway  126  may need to access client transaction related data. In order to provide a memory of each subscriber client&#39;s transaction status, an external database memory  121  (persistence) is provided to store client states and client transaction related data. 
     The session gateway  134  is coupled to a VOD server comprising VOD manager  128  and VOD pump  130  via session APIs and custom interface programs  138 . As in the case for the asset gateway  124  and the transaction gateway  126 , specialized custom designed interface programs  138  are provided for each type of VOD vendor equipment. The session gateway  134  communicates with the set-top box  102  using the Session Resource Management (SRM)  152  and the Session Set up Protocol (SSP 1.0). Session APIs interface with external VOD servers for session signaling protocol conversion with the settop client, including session setup and tear down. The Session Resource Management performs such functions as determining the bandwidth required for given session and allocating the necessary frequency spectrum as required for the session. The Session Resource Management communicates the assigned VOD channel to the VOD client in the set-top box. In such manner, the set-top box tuner is able to tune to the channel containing the video that was ordered by the subscriber. 
     The VOD manager  128  is also coupled to the asset management system  116  and the VOD business management system  118 . The subscriber selects a video by the use of the asset management system  116 . The subscriber pays for the video by the use of the VOD business management system  118 . In response to selection of a video by the subscriber and payment authorization by the VOD billing system  114 , the VOD manager  128  enables VOD pump  130 , which delivers the requested video. The requested video is transmitted as a digital data stream controlled by either the Lightweight Stream Control Protocol (LSC 1.0) or Real-time Streaming Protocol (RTSP). 
     The set-top box  102  includes a master application  140  (executive program) on top of which various applications such as VOD application  142  is run. The VOD application program  142  calls upon session stream APIs  144  (client session stream extender interface) and asset APIs  146  (client asset extender interface). A Liberate TV Navigator program  148  (provided from Liberate Technologies) controls the general look and feel of the set-top box  102 , i.e. the manner in which the subscriber controls the programs and features of the set-top box  102 . Below the master application  140  is the Liberate Porter and operating system and drivers  150  which match the software to the set-top box hardware. 
     In addition, the VOD application  142  retrieves data and graphics for the VOD presentation on the set-top box. In particular, VOD application  142  uses the program related data (such as an Internet URL) to communicate via connect servers  110  to a VOD application server  108 . Graphics and presentation images needed by the VOD application  142  are received from VOD application server  108 . The VOD application  142  also calls upon transaction APIs  142 A to report VOD transactions through the asset gateway transaction servlet  124 C. 
     At the client (settop box) side, a generic software client is provided as the extenders for a standard Liberate TV Navigator platform  148 . The generic client includes the following modules and interface APIs to the VOD application developer: 
     Session extender and APIs  144  provide either digital storage media command and control (DSM-CC) user network signaling based on the session setup protocol (SSP) or real time streaming protocol (RTSP) protocol for VOD session signaling. 
     Stream extender and APIs  144  provide the VOD trick modes (play, pause, fast forward, rewind, etc.) enabled via the Stream Control Protocol. Two versions are supported: digital storage media command and control (DSM-CC) based Lightweight Stream Control Protocol (LSCP) or real time streaming protocol (RTSP). 
     Asset extender and APIs  146  provide JavaScript and Java based interfaces for asset metadata query for the client VOD application. In addition to the raw content of an asset, metadata is also a part of an asset object that describes characteristics of the asset. Metadata includes inherent attributes of the asset such as format, duration size or encoding method. The asset list can be cached at the settop box, retrieved from data carousel, or fetched via HTTP two-way interface through DOCSIS or out-of-band channels. 
     Using the VOD Gateway approach of the present invention, only a single client (supporting either digital storage media command and control (DSM-CC) or real time streaming protocol (RTSP)) needs to be provided and maintained no matter which VOD server will be used. In addition, the VOD client allows the integration with third party VOD application through Internet standard interfaces such as HTML (hypertext markup language) and JavaScript and Java. 
     The VOD Gateway architecture of  FIG. 3  uses either digital storage media command and control (DSM-CC) or real time streaming protocol (RTSP) configuration. The key modules are defined as: 
     Asset data manager  124 A manages the asset metadata with external sources and distributes the metadata to the cache portal  124 B. 
     Cache Portal  132  manages the client query of asset list and downloads the asset metadata to the client through a data carousel or HTTP. 
     Session Gateway  134  provides the protocol conversion from generic session protocol to VOD vendor specific protocols. Another purpose of session gateway can be to provide authentication interfaces for session set-up or tear down. 
     Transaction Gateway  126  provides transaction interaction such as a movie purchase with backoffice VOD billing system  114 . 
     Asset Gateway Architecture 
       FIG. 4  is a block diagram illustrating further details of a VOD asset gateway  302 . The VOD asset gateway  302  includes an asset manager  303  ( 124 A in  FIG. 3 ) and a cache portal  305  ( 124 B in  FIG. 3 ). The asset manager  303  includes an asset plugin  304  for retrieving lists of assets from the VOD asset database interface  314  in VOD vendor equipment  308 A. The asset plugin  304  retrieves the VOD asset data from the VOD asset database  314  and remaps the VOD data according to a unified generic schema. 
     The reformatted VOD asset data is cached in a cache portal  305  and made available as VOD data to the set-top box  310 . The set-top box  310  further communicates with a Liberate Datapoint server  301  wherein it is provided with data and parameters to enable a VOD service. Additionally, the set-top box  310  includes VOD applications which retrieves graphics and presentations from a VOD application Web server  312 . 
     The following sections describe a generic Movie On Demand asset metadata format that is used to describe Movie On Demand assets for the VOD Gateway. 
     Movie On Demand Asset Metadata is used to describe the properties of movie content contained in the asset, such as the movie title, preview, and poster etc. Metadata consists of keyword-value pairs and is described in XML (extensible markup language) format. The format allows for easy extensions with respect to new metadata entries. A DTD file is used to describe the syntax of XML asset metadata file. 
     The VOD asset gateway is ignorant of the assets that it hosts. As used herein, VOD program material (assets) may be video, audio, graphic or text programming. All assets are treated as a Product, Service, or Offering Entity. Product entities may be movies, news clips, games, and/or any other MIME type supported by the Liberate TV Navigator Client. Service entities are logical groupings of runtime behaviors and rules such as Basic Movies-On-Demand Service, Premium Movies-On-Demand Service, Music Videos-On-Demand Service, and so on. Offering entities relate Product entities to Service entities, similarly to the way foreign keys work in a relational databases. A Product must be “offered” to one or more Services via Offerings, in order to be utilized by a Liberate TV Navigator VOD application. 
     For example, a Product of type Movie Title may have two Offerings. One Offering is for a Service called “Basic Movies-On-Demand” and another Offering is for “Premium Movies-On-Demand”. The “Basic Movie-On-Demand” Service may have rules that do not allow stream control (trick-mode) support when viewing the movie. The “Premium Movies-On-Demand” Service may enable these controls. 
     Product 
     Products may have Parameters and Metadata. A Parameter is a data name/value pair that is predefined, and represents some relevant descriptive attribute about the Product. Parameters may be validated by the asset data manager. Metadata is also a name/value pair, but is NOT validated by the asset data manager. Metadata may be passed down to the Liberate TV Navigator client with no checks. 
     For example: A Move Title Product: 
     This Product may have the following Parameters:
         title—The title of the Movie Title.   rating—Movie Title rating.   short_summary—A short summary of the Movie.   year—The year of the Movie release.   actors—A list of actors/actresses.   genre—A list of genres associated with the Movie.   director—The Director&#39;s name.   studio—The Studio name.   run_time—the length of the Movie (HH:MM:SS)   poster_id—the Url of the Poster image   movie_id—The unique id used to identify the video on the stream server.   rental_period—The length of time allowed for viewing the video stream.       

     These parameters may be required for a Movie-On-Demand Application. 
     The Product may also have Metadata associated with it. The data may not be part of the Movie Title, but added in to compliment an application. For example:
         more_info url—a Url that references an Internet source to give more details about the Movie Tile.   special_offer_advertisment_url—a Url that references special advertisements relevant to the Movie Tile.   chat_group_url—a Url that references a chat group dedicated to movie reviews.       

     Service 
     The VOD Service Provider may define Service entities. Services allow providers to set business rule parameters, which are used by the VOD application. Products offered to a particular Service is then governed by those rules set in that Service. Similarly to Product entities, Service entities also have Parameters and Metadata. 
     For example: A Movie-On-Demand Service may have the following Parameters:
         title—the title of the Service (i.e. Basic or Premium Movies-On-Demand).   stream_control_enabled—this parameter may be a true/false flag telling the client application to enable or disable the “VCR-controls” at run-time.   advertisment_window_enabled—this parameter may be used to trigger intrusive advertisements during the session setup period.       

     Again, like Product entities, a Service may also have associated Metadata.
         on_pause_url—a Url that is fetched on a stream pause event.       

     Offering 
     Offering entities are similar to both Products and Services in that they have Parameters and Metadata, however, Offerings have two additional attributes: a “pref” (Product Reference) and an “sref” (Service Reference). The Product Reference attribute is the foreign key of its related Product entity. The Service Reference attribute is the foreign key of its related Service entity. An offering must have a one pref and one sref attribute. 
     Offering Parameters should relate to the context of that particular offering. For example an Offering of a Movie Title Product may have the following Parameters.
         offer_period_start_date—offering becomes valid to subscribers on this date.   offer_period end_date—offering expires on this date.   discount—the discount rate to be applied to the Product&#39;s “rental_price” Parameter.       

     Metadata usage is the same as Product and Service. 
     The VOD asset gateway uses Product, Service, and Offering entities to describe asset data and to set runtime values for VOD applications. Each entity supports Parameters and Metadata. Data is considered a Parameter, if it is required for the application to function. 
     Session Gateway Architecture 
     The Session Gateway is a server component of the VOD gateway. It is designed to allow full configuration based on standard protocols such as digital storage media command and control (DSM-CC) and real time streaming protocol (RTSP). The Session Gateway is introduced to provide two main functions: 
     (1) It provides protocol translation between the generic session protocol and the VOD vendor specific session protocols. A single generic client extender for session signaling is thus used for multiple VOD vendors.
 
(2) It facilitates a unified approach for authorization, statistics collection, and monitoring of VOD sessions. The latter is accomplished through the interface between the session gateway and transaction gateway, that is further integrated with external VOD backoffice system.
 
     The VOD gateway is designed to have two fully configurable modes of operations for Session Gateway: digital storage media command and control (DSM-CC) and real time streaming protocol (RTSP). It is not likely that the digital storage media command and control (DSM-CC) and real time streaming protocol (RTSP) are supported by a particular cable system VOD deployment at the same time. Therefore, VOD gateway is designed to be configurable to either digital storage media command and control (DSM-CC) or real time streaming protocol (RTSP) at the system installation stage. 
     Only the digital storage media command and control (DSM-CC) session signaling messages are handled through the Session Gateway while the stream control messages are always sent directly between the client and VOD server. It is usually the case that the DSM-CC stream control messages are the same across all the VOD vendors therefore it is handled directly for better scalability. 
     The Session Gateway can be scaled and deployed as an independent component of VOD gateway in the master or remote headends. 
     Digital Storage Media Command and Control (DSM-CC) Session Gateway Architecture 
     There are three logical entities in the digital storage media command and control (DSM-CC) model, Client, Server, and Network. The Network entity is always the session resource manager (SRM) that will be provided by headend provider or VOD vendor. It is responsible for assigning the network resources such as MPEG channels for VOD sessions. The Client entity is provided by generic client extender and is responsible for initiating the session setup request/release and the Server entity is provided by VOD vendors and is responsible for negotiating with session resource manager (SRM) for network resources and assigning the streaming server for the client. 
     There are two modes of operation for the digital storage media command and control (DSM-CC) Session Gateway: Server Mode and Client Mode. In the Server Mode (illustrated in  FIG. 5A ), the Session Gateway sits between the session resource manager (SRM) and VOD Server. In the Client Mode (illustrated in  FIG. 5B ), the Session Gateway sits between the Client and session resource manager (SRM). The mode is fully configurable upon the installation of the Session Gateway. The decision of which mode to use is based on the combination of headend and VOD vendors used as part of the integration and deployment planning. 
     Server Mode digital Storage Media Command and Control (DSM-CC) Session Gateway 
       FIG. 5A  illustrates the Server Mode digital storage media command and control (DSM-CC) session gateway architecture with the Session Setup scenario. In Server Mode, the session gateway  502  serves as the translation engine for the server side digital storage media command and control (DSM-CC) messages between the session resource manager (SRM)  504  and VOD server  508 . The VOD client extender  506  communicates with the Session Resource Management  504 . 
     The communication between client and session resource manager (SRM) uses the UDP protocols while the communication between session resource manager (SRM) and Session Gateway as well as between Session Gateway and VOD server uses TCP protocol. 
     The message flow of session setup scenario for Server Mode digital storage media command and control (DSM-CC) Session Gateway is described in the following: 
     Step 1: Start session setup
 
Step 2: Generic client extender sends ClientSessionSetupRequest message to session resource manager (SRM) with Client ID (OSI network service access point address including IP address and Media Access Control address), NodeGroup ID private descriptor, and Asset ID private descriptor. Session ID is determined by the client.
 
Step 3: session resource manager (SRM) sends ServerSessionSetupIndication message to Session Gateway.
 
Step 4: Session Gateway translates the user private data field of the generic digital storage media command and control (DSM-CC) message to the VOD vendor specific format and forwards the modified ServerSessionSetupIndication message to VOD server.
 
Step 5: VOD server requests the network resource with required Resource Descriptor in the ServerAddResourceRequest message to Session Gateway.
 
Step 6: Session Gateway forwards ServerAddResourceRequest to session resource manager (SRM) (with reformatting if necessary)
 
Step 7: session resource manager (SRM) assigns the network resource to the session and sends ServerAddResourceConfirm message to Session Gateway
 
Step 8: Session Gateway forwards the ServerAddResourceConfirm message to VOD server (with reformatting if necessary).
 
Step 9: VOD Server sends ServerSessionSetupResponse to Session Gateway
 
Step 10: Session Gateway forwards the ServerSessionSetupResponse to session resource manager (SRM) (with reformatting if necessary)
 
Step 11: session resource manager (SRM) inserts client view of resource descriptor and sends ClientSessionSetupConfirm message to the generic client extender.
 
Step 12: Client retrieves resource descriptor with tuning information such as Frequency and ServiceID as well as stream control IP address. And the session is established.
 
     Client Mode Digital Storage Media Command and Control (DSM-CC) Session Gateway 
       FIG. 5B  illustrates the Client Mode digital storage media command and control (DSM-CC) session gateway architecture with the Session Setup scenario. In  FIG. 5A , the session gateway  502  communicates with the Session Resource Management  504 , which in turn communicates with the VOD client extender  506  in the set-top box. In comparison, the session gateway  522  in  FIG. 5B  is operated in a client mode. That is, the VOD client extender  524  in the set-top box communicates with the session gateway  522 , which in turn communicates with the Session Resource Management  520 , which provides the interface to the VOD digital storage media command and control (DSM-CC) server  526 . 
     In client mode shown in  FIG. 5 , the session gateway  522  serves as the translation engine for the client side digital storage media command and control (DSM-CC) messages between the client  524  and session resource manager (SRM)  520 . 
     In the client mode case, the communication between client and Session Gateway as well as between Session Gateway and session resource manager (SRM) uses the UDP protocols while the communication between session resource manager (SRM)  520  and VOD server  526  uses TCP protocol. 
     The message flow of session setup scenario for Client Mode digital storage media command and control (DSM-CC) Session Gateway is described in the following: 
     Step 1: Start session setup
 
Step 2: Generic client extender sends ClientSessionSetupRequest message to Session Gateway with Client ID (OSI network service access point address including IP address and Media Access Control address), NodeGroup ID private descriptor, and Asset ID private descriptor. Session ID is determined by the client.
 
Step 3: Session Gateway translates the user private data field of the generic digital storage media command and control (DSM-CC) message to the VOD vendor specific format and forwards the modified ClientSessionSetupRequest message to session resource manager (SRM).
 
Step 4: session resource manager (SRM) sends ServerSessionSetupIndication message to VOD server.
 
Step 5: VOD server requests the network resource with required Resource Descriptor in the ServerAddResourceRequest message to session resource manager (SRM).
 
Step 6: session resource manager (SRM) assigns the network resource to the session and sends ServerAddResourceConfirm message to VOD server
 
Step 7: VOD Server sends ServerSessionSetupResponse to session resource manager (SRM).
 
Step 8: session resource manager (SRM) inserts client view of resource descriptor and sends ClientSessionSetupConfirm message to Session Gateway.
 
Step 9: Session Gateway translates the VOD vendor specific user private descriptors and resource descriptor if necessary and forwards the ClientSessionSetupConfirm message to the generic client extender.
 
Step 10: Client retrieves resource descriptor with tuning information such as Frequency and ServiceID as well as stream control IP address. And the session is established.
 
     Real Time Streaming Protocol (RTSP) Session Gateway Architecture 
     Real time streaming protocol (RTSP) supported by VOD gateway is based on the Internet Engineering Task Force RFC 2326 standard with the hybrid fiber coax (HFC) extensions proposed by nCUBE. Several VOD vendors have adopted real time streaming protocol (RTSP) for trial and deployment of VOD services. Real time streaming protocol (RTSP) protocol has its unique capabilities when used for VOD systems: 
     Real time streaming protocol (RTSP) protocol supports multiple Asset streaming per session instead of digital storage media command and control (DSM-CC) (session setup protocol (SSP)) that only allows one Asset per Session 
     Real time streaming protocol (RTSP) has HTTP like syntax that is easy for developer to implement. 
     The hybrid fiber coax (HFC) extension of real time streaming protocol (RTSP) supports MPEG resource parameter. 
     The basic architecture for real time streaming protocol (RTSP) Session Gateway is to use the Session Gateway to handle both session and stream related real time streaming protocol (RTSP) messages and to perform protocol translation between generic real time streaming protocol (RTSP) message initiated from the client and VOD vendor specific messages. In such manner, a generic real time streaming protocol (RTSP) extender is maintained for all the VOD vendors. The operation is similar to the operation of HTTP Proxy server. Also, the VOD server does not require IP level message authentication. 
     The detailed real time streaming protocol (RTSP) message flows are illustrated in  FIG. 6 . 
     Transaction Gateway Architecture 
     The purpose of the Transaction Gateway is to authorize the delivery of media services to a set-top user. It also abstracts the external components (such as Billing) away from set-top client implementation. 
     The concept of a “Transaction” is used to represent a rental-period or time period, which a set-top user would have to view a given media asset. The Transaction gateway offers the following:
         1. Authorization Interface: provide an authorization pathway allowing authorization requests to be routed to an external authorization processor. This is integrated with the information from the Asset Manager.   2. Purchase history: provide purchase history of completed Transactions.   3. Active or Suspended Sessions: a means for both the set-top client software and external server components of the back office to interact with Transactions that are currently in progress or currently stalled or stopped Transactions. This information can be used for billing implementations, advertisement insertion, tracking and usage collection.       

     Authorization 
     No attempt is made within the VOD gateway to define the business rules for authorizing services and billing to customers. The logical decision to authorize a particular request is made by an external authorization implementation listening to an interface on the VOD gateway. The VOD gateway provides a way to host many such authorization requests concurrently, integrating the request information with that of the Asset Manager and routing the request to the appropriate authorization implementation. Once a Transaction is authorized, the Transaction can be stopped and restarted without the interaction of the external authorization component. 
     Active Transactions 
     Once a Transaction becomes authorized from the appropriate external authorization implementation, it becomes an “active” Transaction. Active Transactions contain all the default information about the Transaction and any custom information inserted by the set-top client software or an external server-side component. The default information within the Transaction indicate what set-top, service, application, offering is being delivered. The Transaction remains “active” for the duration of the rental-period. 
     Purchase History 
     Once a Transaction has gone beyond it&#39;s rental-period, it transitions to being a “completed” Transaction. In this state, the set-top client can request information about all or individual previous sessions. 
     Billing 
     When an external billing implementation registers with the VOD gateway for the first time, the registration is remembered by the VOD gateway. Based on the registration criteria, all messages defined in the registration are held within the VOD gateway for delivery to this implementation. Once these messages are delivered, they can be dropped by the VOD gateway going forward. In this way, the billing implementation can still operate in a batch mode. 
     The Transaction interface operates in a similar fashion to Billing but does not offer any durability or holding of messages from the past. 
     Transaction Lifecycle 
     The following sequence diagram captures a possible scenario for the setup and teardown of a video session with the Session Gateway from a set top client. Some detail has been left out for simplicity. This attempts to show how the transaction flows through to the VOD gateway. 
     Session Setup Request/Authorization 
     Before the Session Gateway sets up the session on the VOD server, it first gets authorization from the Transaction Gateway component. 
     Upon receiving an Authorization request, the Transaction Manager performs the following processing:
         1. Checks the required parameters are present for starting/re-starting a Transaction. These are: machine, application and offering identifiers. If the required parameters are missing from the request an immediate denial is sent to the requester.   2. Fetches other details like product and service by using the Delivery CachePortal.   3. Attempts to find a stalled Transaction.   4. If no stalled session exists, the augmented request is sent to the correct Authorization interface and its reply is forwarded to the requestor.   5. If a stalled Transaction exists, then this is forwarded to the requestor.       

     Both the original augmented request and any Authorization interface reply are published to the Transaction topic. 
     Upon the authorization of VOD session, the Session Gateway can then set up the session with the specific vendor VOD server. The Session Gateway could then send a message indicating that the session has started. 
     The client upon successfully initiating streaming can send updates about the “session” to the DeliveryServlet. The DeliveryServlet posts this information to the Transaction Gateway where this information is published to the Transaction topic. 
     Billing Rules/Purchase 
     The external Billing implementation subscribes to the Billing interface. Whether the Billing system chooses to initiate billing and add a line item on a customer&#39;s monthly bill is entirely up to each system. The flexibility is achieved by passing a filter/query string to the register method on the interface (more detail below). This will restrict the reception of messages to those specifically defined in the query. For a given deployment this can be a sessionState=Started event or an event driven by the client UI application in the set-top, i.e. deliveryState=ViewingWindow. 
     The billing rules can be partially supported on the client via the HTML and JavaScript and Java environment during the duration of the video session. The client can change the values of the “deliverystate” within the Transaction to reflect the current condition and state, e.g.: CancelWindow or ViewingWindow. 
       FIG. 7  illustrates the control over the viewing window for a VOD program. The stream length  612  is equal to the duration of the VOD program ordered. The total rental window  610  however, is longer than the total stream length  612  of the VOD program. After the VOD program begins to play  620  there is a cancel window  614  during which the consumer may decide to cancel  622  the VOD program. After the cancel window  614  has passed, the VOD video is regarded as having been purchased  624  and the viewer is billed for the purchase. Initially, trick mode (pause, rewind, etc.) is available to the viewer. However, after the viewing window  616 , the trick mode disable window  618  disables trick mode to guarantee that the stream length  612  will fit within the rental window  610 . In such manner, the movie can run completely with in the rental window  610 . 
     The movie stream ends, or the user stops the movie but the session is torn down eventually. If the connection to the client is lost, the Session gateway may tear down the disconnected session. In any event, the Session gateway notifies the Transaction gateway, thus completing the Session gateway&#39;s role and responsibilities with respect to the Transaction gateway. 
     Transaction Gateway Interface Definitions 
     The interfaces used by Transaction Gateway are Authorization, Billing, Transaction, PersistedTransaction, and DeliveryRequestor. 
     The Authorization and Billing interfaces are used by external systems to perform these specific tasks. 
     The progress and control of current transactions can be achieved by connecting to the Transaction interface. History of all previous purchase activity can be collected from the Transaction interface. History information can then be made available to the VOD gateway from an external system hosting the PersistedTransaction interface. 
     The Delivery section details the main functionality of this component, namely to track the activity of all active media transactions. The Delivery interface as detailed here is used by other VOD gateway components to drive information through the Transaction gateway. 
     All the interfaces for the Transaction Gateway use a common message format. This message format or DeliveryMessage has some predefined parameters and states. 
     Transaction Usage Interface 
     The Transaction represents the delivery of a Product (asset) to a user and thus can have many video sessions started and stopped during its lifetime. This time-to-live window is set from the imported product or the default in Command. 
     The Transaction definition below is what the client can use in request-queries for currently running Transactions. Once a Transaction is started via the extender and the Session Gateway, this information is available for the session. 
     The client can push any name-value pair into the DeliveryMessage and have this be available for later use. An external component can also push name-value pairs into the Transaction. 
     A typical query to the DeliveryRequestor interface with the request method would include the mid, appid, sid. This would retrieve all the current Transaction or stalled sessions. 
     Any pre-defined parameter can be used for building “selectors” or when filtering messages coming through the interfaces. These are defined below and as constant String(s) in the DeliveryConstants class. The various states have their own definition interface classes. 
     Authorization Interface 
     The Authorization interface is hosted within the VOD gateway. External implementations for authorization processing are clients to this interface. 
     Billing Interface 
     The billing interface is hosted within the VOD gateway. External implementations of billing are clients to this interface. It allows an external billing system to receive and send billing related messages from/to the VOD gateway. 
     Transaction Interface 
     The Transaction interface is hosted within the VOD gateway. External components are clients to this interface. This interface allows external systems to receive and send specific messages from and to the VOD gateway. 
     PersistedTransaction Interface 
     This interface is hosted outside the VOD gateway. The VOD gateway is a client to this interface and the class or implementation is loaded at run time. This interface allows an external system to host and store specific messages for the VOD gateway. The implementation for this interface is not part of the VOD gateway. The Transaction Gateway expects that PersistedTransaction interfaces named “ActiveSessions” and “PreviousSessions” will exist. It attempts to connect to these before initiating service. Failures to these connections are ignored with the information lacking from within the Transaction Gateway. 
     DeliveryRequestor Interface 
     This interface feeds and listens to the external interfaces described above but also presents a client-centric interface within the VOD gateway. The following table shows the internal services provided within the VOD gateway. 
     Generic Client Extender and APIs 
     The Liberate TV Navigator standard architecture provides several VOD Extenders and JavaScript and Java libraries for facilitating quick development of Video On Demand Application on top of the middle-ware. In the current Liberate TV Navigator Standard architecture there are two extenders that provides a JavaScript and Java based interface for VOD Application developer and they are:
         VOD Session and Stream Extender.   VOD Asset Extender.       

     The VOD Session and Stream Control Extender provides a generic Session class interface that allows to applications to setup and tear-down dynamic VOD sessions and also provide an interface for creating new Stream objects that can used to control VOD streasset management system through specified methods for Play, Fast Forward, Rewind, Stop. The current version of the Extender supports DSMCC based session setup protocol (SSP) (Session Setup Protocol) and real time streaming protocol (RTSP) protocols for session management and supports LSC and real time streaming protocol (RTSP) protocol for stream control/management. In near future, this interface is intended to extend support for additional user specified fields in both the session and stream management protocols. 
     The VOD Asset Extender interacts with the VOD gateway server to download all the VOD program asset related information and efficiently manages all such information in memory, on the set top box. The Asset Extender also provides a JavaScript and Java based interface for the VOD application to query information about various categories of prograsset management system available on the server, a short summary of the program with purchase information as well as more detailed information related to the program itself. 
     The Asset Extender provides three JavaScript and Java Classes: Categories, Offerings and ProgramInformation that provides good abstraction for the Application to efficiently query, manage and use VOD program related information. The schema definition for the VOD Asset database is loaded dynamically and can be changed to add any additional user/deployment specific fields. The actual VOD Asset meta-data is downloaded to the client in proposed XML format from the VOD gateway either through a two-way dedicated TCP connection or through a HTTP interface or the information can be broadcast to all the clients using the mediacast carousel. Also, the JavaScript and Java interface is intended to provide support for any additional user specified or deployment specific fields for Categories, Offerings and Program Information. 
     Depending on the client hardware profile the Asset Extender is designed to support very advanced searches and sorts on the server side at the VOD gateway. Such optimization are necessary depending on the limited amount of memory and processing power available on the digital set top box. In case where the VOD Asset database is much bigger than the memory available to the Asset Extender on the set top, the VOD Asset extender will only cache information based on the current application context and will swap information from the memory as this context changes. context and will swap information from the memory as this context changes.