Abstract:
A method includes receiving an indicator from a service provider via a network. The indicator is received with first media content and includes data to cause a selectable image to be displayed with the first media content. The selectable image indicates an availability of second media content that is different than the first media content. The method includes, in response to receipt of the indicator, displaying the selectable image with the first media content at a display device. The method further includes, in response to receiving a removal message before receiving an input indicating a selection of the selectable image, removing the selectable image from display at the display device.

Description:
CLAIM OF PRIORITY 
     The present application is a continuation of and claims priority from U.S. patent application Ser. No. 10/335,735, filed on Jan. 2, 2003 and entitled “SYSTEM AND METHOD FOR PROVIDING TELEVISION SERVICES”, which is a divisional of and claims priority from U.S. patent application Ser. No. 09/116,325, filed on Jul. 15, 1998 and entitled “SYSTEM AND METHOD FOR PROVIDING TELEVISION SERVICES”, now issued as U.S. Pat. No. 6,567,982, which is a continuation of and claims priority from U.S. patent application Ser. No. 08/428,718, filed on Apr. 25, 1995 and entitled “SYSTEM AND METHOD FOR PROVIDING TELEVISION SERVICES”, now issued as U.S. Pat. No. 5,818,438. The contents of U.S. patent application Ser. No. 10/335,735, U.S. patent application Ser. No. 09/116,325 and U.S. patent application Ser. No. 08/428,718 are expressly incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates in general to the field of television and in particular to the field of interactive television. 
     BACKGROUND 
     Advances in telecommunications and computing technology are leading to the provision of interactive television (TV) on a large scale. Interactive TV involves the use of video gateways and video transport of sufficient bandwidth for video programmers and enhanced video gateway providers to offer their services to residential and business subscribers. Where such facilities are available, subscribers will not only be able to access these services by passively receiving them, but will also be able for the first time to interact with the service providers by communicating requests and commands to the providers via the same path over which the programming services are provided (or even via other paths or drivers). 
     Interactive TV service is capable of supporting at least the following services: (1) traditional broadcast and cable television programming; (2) video services, such as pay-per-view (PPV), near video-on-demand (NVOD), video-on-demand (VOD), promo channels, electronic program guides, etc.; (3) cable delivered PC-based services; and (4) interactive services, through the use of a combination of compression and digital video technologies. Interactive TV service also permits menuing capabilities and upstream signaling from subscribers to service providers. A subscriber interactive TV connection may, for example, provide subscribers with a screen of available enhanced video gateway providers and/or video programmers and their telephone numbers, or a menu to interactively order services and/or programs. 
     Interactive television may be provided over any number of paths, including coaxial cable or optical fiber, hybrid fiber/coaxial, or any other suitable path that accommodates sufficient bandwidth for desired analog and digital video channels as well as other telecommunications services. Content Providers may include, for example, providers of interactive or non-interactive over-the-air programming such as commercial television stations, cable programming such as weather, travel and entertainment channels, game channels, and on-line services of various types. 
     Interactive video enables a subscriber to request that an “interactive session” be established between an “interactive server” or similar platform maintained by an interactive video service provider and a “client” terminal device at the subscriber&#39;s premises. An interactive session is a two-way communication relationship, and is a precondition to interactive video services being provided to a subscriber&#39;s terminal device. Such a session utilizes the necessary downstream bandwidth and resources (defined below) for delivering interactive video service and the necessary upstream bandwidth from the subscriber&#39;s terminal device to issue commands to the interactive server. The terminal device may take the form of what has been termed a “set top box” (STB), or may be any other device capable of performing at least the following functions: (1) exchanging messages (including video-related data) over a network with the interactive server; (2) receiving messages from a user input device, such as a hand-held remote control unit; (3) translating video signals from a network-native format into a format that can be used by the television or display device; and (4) providing a video signal to a television or other display device. A STB may also be capable of performing other functions, such as: (1) inserting alphanumeric or graphical information into the video stream in order to “overlay” that information on the video image; (2) providing graphic or audio feedback to a user; or (3) possibly the most basic function, simply routing a traditional broadcast signal to a viewing device to which the STB is connected. 
     The STB “client” is “served” by a facility which may be operated and maintained by the video service provider. This “interactive server” provides, in response to a subscriber request, access to an “application,” which may be something as straightforward as a video program, or may itself interact with the subscriber by transmitting, for example, a subscriber prompt or menu to allow the subscriber to assert a desired selection from among a set of given commands for the interactive server to carry out. 
     This added functionality is in large part the result of a historically unprecedented convergence of communications and computing technology. It makes possible, for the first time, features such as the following. In the game media environment, a subscriber may download video games or even play them interactively with the interactive server and/or with other subscribers. An interactive service subscriber may order “time shift TV,” in which a particular program may be viewed at a time following its ordinary broadcast time. A subscriber may also selectively view desired parts of transactional, informational or advertising services. For example, a subscriber may view information on the weather predictions for a given location or at a given time, gather information relating to a particular sporting event or team, obtain news on demand, or query a system regarding a particular real estate market. Alternatively, a subscriber may participate in interactive entertainment programs, such as interactive game shows, interactive lottery or gambling, or request musical selections. Subscribers interested in educational programming, such as a school or a family residence, may invoke interactive “edutainment” or “how-to” programs. Interactive communication services, such as online services historically provided by the public telephone network, may also be accessed via interactive TV, which permits not only the rapid transfer of files to the subscriber but also interaction with other subscribers. 
     The combination of broadcast and interactive applications over interactive TV (e.g., interactive programs) creates a new mode of communication in which a user, when informed of the availability of an interactive application relating to the subject matter of a broadcast program, may invoke the application to investigate that subject matter more thoroughly and according to his or her own tastes. 
     Additionally, television viewers, who are accustomed to choosing at will between the available channels with instantaneous results, will expect to pass from one medium (e.g., broadcast) to another (e.g., interactive) “seamlessly” with the push of a button. To accommodate their viewer&#39;s needs, programmers may wish to provide broadcast programming, such as a commercial advertisement or a news program, and make available in the context of that program a related interactive television program. 
     The means by which interactive television and broadcast television are provided, however, are generally quite different. The two media, for example, are typically supplied from different sources and use different modulation techniques over different transmission paths. The originating source of broadcast programming is likely to be remote from those subscribers interested in invoking an interactive service, making telecommunication between the parties over a dedicated network prohibitively expensive and complex. By contrast, interactive servers, in order to avoid the expense of high bandwidth communications over such distances, can be located geographically close to a corresponding set of subscribers, unlike the programming sources or “Content Providers.” An interactive server can therefore efficiently provide exclusive interactive access to a large number of applications by a large number of interactive subscribers. 
     The technical differences between broadcast programming and interactive applications, combined with the difficulties of providing interactive services at any rate, make the provision of a smooth transition between interactive and broadcast television a difficult proposition and a seamless transition from broadcast television to interactive television and back an elusive goal. 
     SUMMARY 
     The present disclosure provides an approach for viewer-friendly and virtually instantaneous transitioning from a first analog based television program to a second program, particularly an interactive application program, and further permits a similarly rapid and easily accomplished return to viewing the first program. 
     To accomplish this convenient and virtually instantaneous transition between programs such as a broadcast program and an interactive application or program, the present disclosure provides a system for permitting a provider of program content to furnish a video service provider with content, such as an interactive program or application, and for permitting the video service provider to transmit to the Content Provider an identifying code or address, such as an interactive callback address. The video service provider associates this identifying code or address with a location at which the program or application will be stored. The identifying code or callback address may be a program-specific code that can be used by subscribers to invoke the program from the video services provider directly. Alternatively, the identifying code may be a common identifying code or callback address (which might be called a “well-known callback address”), used by all subscribing viewers to access a program- or application-specific identifying code or callback address, which is in turn used to invoke the program. 
     According to the present disclosure, Content Providers may transmit the identifying code or callback address for a second program in coordination with a first program, so that viewers of the first program, who have access to systems operated by the video service provider, may invoke the second program, which may be an interactive program or application, using that identifying code or callback address. 
     Also according to the present disclosure, the Content Provider may transmit the identifying code or callback address in the first program signal, for example, in the vertical blanking interval of the video stream for that program. Alternatively, the identifying code or callback address could be provided in any other suitable out-of-band channel, especially one that is capable of being synchronized with the program signal, so that the identifying code or callback address may be transmitted at appropriate times during the program. 
     Additionally, the present disclosure permits the Content Provider to transmit with the identifying code or callback address additional information, such as information to be used at the subscriber site to generate a screen image indicating the availability of additional content from the video service provider. 
     The present disclosure also provides for an interactive server, which may be operated and maintained by the video service provider. The interactive server can service requests from Content Providers for identifying codes or callback addresses, such as interactive callback addresses, can store program content from Content Providers, such as interactive programs or applications, and can associate that content with an appropriate identifying code or address, such as an interactive callback address. The interactive server according to the present disclosure can also service requests for that content from subscribing viewers. 
     The subscribing viewers are provided with a set top box or similar device adapted to be coupled to a video distribution network to which one or more video service provider systems are also coupled, and also adapted to be coupled to a television, computer or any other suitable display device to reside either outside of, or within, the housing of the display device. The set top box includes a receiving set capable of receiving broadband signals over the video distribution network and possibly also over the air. The set top box also includes at least one processor coupled to the receiving set and programmed to detect the presence and content of an identifying code or callback address, such as an interactive callback address, received by the receiving set either in a program signal (typically in the vertical blanking interval of that signal) or possibly in an out-of-band signal. The set top box processor is also programmed to store the identity of the channel on which the program is being received in one of at least one information storage devices or memory means to which the processor is coupled. The processor is also programmed to detect and store information accompanying the transmission of the identifying code or callback address regarding an image to be displayed on the display device (such as a video screen “button” or “icon”) to indicate the availability of content, such as an interactive application, from a video service provider. Alternatively, such information regarding the image to be displayed on the television or other display device may be pre-stored in an appropriate information storage device to which the processor is coupled. The processor is also coupled to a means for generating a video image based on the received or pre-stored “button” or “icon” information, or alternatively, is programmed to generate the video signal and is coupled to the display device in such a manner as to provide such a signal to that device. 
     Furthermore, the set top box processor is adapted to establish communication over the video distribution network with the video service provider, upon receiving a request from the subscribing viewer in response to seeing the screen button or icon. The processor may first store in the information storage device the identity of the channel on which the program then being viewed is being transmitted. A communication session over the network to the video service provider is then established by transmitting a message including the identifying code or callback address, such as the interactive callback address. If the identification code or callback address is a common identification code (for example, a “well-known callback address”) the video service provider returns the program- or application-specific identification code or callback address, which the processor then may use to invoke from the video service provider the associated program or application. 
     The video service provider transmits to the set top box the identity of a network service (i.e., a network address) or a channel on which the requested program will be provided, and the set top box processor initiates a session with the indicated network service and/or causes the receiving set to tune to the channel. The set top box then receives the program or application from the video service provider. During that session, communication between the set top box and the video service provider may be two-way. 
     When the program or application is terminated, or when the user signals the set top box that viewing the second program or application is no longer desired, the communication session is terminated. The processor then retrieves the identity of the first program from the information storage device, and causes the receiving set to re-tune to the first program to which the viewer had been tuned. 
     It is accordingly an object of the present disclosure to provide a system for permitting a Content Provider to furnish a video service provider with program content, such as an interactive application or program, and for permitting the video service provider to transmit to the Content Provider an identifying code or address, such as an interactive callback address or a “well-known interactive callback address.” 
     It is an object of the present disclosure to provide a system for permitting a Content Provider to furnish an identifying code or callback address along with a program for directly invoking another program, such as an interactive program furnished to subscribing viewers by the video service provider. 
     It is a further object of the present disclosure to provide a system for permitting a Content Provider to furnish a common identifying code or callback address (such as a “well-known interactive callback address”), used by all subscribing viewers to access a program- or application-specific identifying code or callback address that, in turn, is used to invoke the program content from the video service provider. 
     It is an additional object of the present disclosure to permit a Content Provider to transmit the identifying code or callback address in coordination with the program signal, such as in the vertical blanking interval of the video stream. 
     It is a further object of the present disclosure to permit a Content Provider to optionally transmit the identifying code or callback address in coordination with the program signal, but in any suitable out-of-band channel. 
     It is yet another object of the present disclosure to permit the Content Provider to transmit with the identifying code or callback address additional information, such as information to be used at the subscriber site to generate a screen image indicating the availability of additional content from the video service provider. 
     A further object of the present disclosure is to provide an interactive server capable of servicing requests from Content Providers for identifying codes or addresses for program content and to receive and store such content in association with the identifying code. 
     An additional object of the present disclosure is to provide an interactive server according to the present disclosure that can service requests for program content from subscribing viewers. 
     Another object of the present disclosure is to provide subscribing viewers with a set top box for detecting the presence and content of an identifying code or callback address transmitted in coordination with a-program, to store for later retrieval the identity of the channel on which the program is being received, to generate a screen image for display on a display device based on information either pre-stored or transmitted with the identifying code, to establish a session with the video services provider using the code, and upon termination of the session, to fetch the identity of, and re-tune to, the channel the subscriber was originally watching. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high level functional block diagram of certain environment and components of a system according to a preferred embodiment of the present disclosure. 
         FIGS. 2A and 2B  are a flowchart for the operation of a first embodiment of a system according to the present disclosure. 
         FIGS. 3A and 3B  are a flowchart for the operation of a second embodiment of a system according to the present disclosure. 
         FIGS. 4A and 4B  are a flowchart for the operation of a third embodiment of a system according to the present disclosure. 
         FIGS. 5A and 5B  are a flowchart for the operation of a fourth embodiment of a system according to the present disclosure. 
         FIG. 6  is a high level diagram of an embodiment of an interactive server and certain environment according to the present disclosure. 
         FIG. 7A  is a diagram showing the format for an interactive callback address according to the present disclosure having error correction check bits. 
         FIG. 7B  is a diagram showing the contents of an interactive callback address according to the present disclosure, with the error correction check bits not shown. 
         FIG. 8  is a high level schematic diagram of a preferred embodiment of a set top box according to the present disclosure including input and output means. 
         FIG. 9  is a state diagram showing operating states of an embodiment of a set top box according to the present disclosure, corresponding to the embodiment of the system according to the present disclosure shown in  FIGS. 2A and 2B , and indicating conditions leading to state transitions and processing associated with the states and performed incident to the state transitions. 
         FIG. 10  is a state diagram showing operating states of an embodiment of a set top box according to the present disclosure, corresponding to the embodiment of the system according to the present disclosure shown in  FIGS. 3A and 3B , and indicating conditions leading to state transitions and processing associated with the states and performed incident to the transitions. 
         FIG. 11  is a state diagram showing operating states of an embodiment of a set top box according to the present disclosure, corresponding to the embodiment of the system according to the present disclosure shown in  FIGS. 4A and 4B , and indicating conditions leading to state transitions and processing associated with the states and performed incident to the transitions. 
         FIG. 12  is a state diagram showing operating states of an embodiment of a set top box according to the present disclosure, corresponding to the embodiment of the system according to the present disclosure shown in  FIGS. 4A and 4B , and indicating conditions leading to state transitions and processing associated with the states and performed incident to the transitions. 
     
    
    
     DETAILED DESCRIPTION 
     High-Level Architecture of an Embodiment of an Interactive Video Services Network 
       FIG. 1  shows the primary components used in a typical setting for implementing an embodiment of the systems, devices and methods according to the present disclosure. A video service provider  1 , responsible for providing interactive applications, operates and maintains a system equipped to receive signals as well as interactive applications and other content from one or more Content Providers A, B, C, . . . , N, respectively referred to by numerals  41 - 44 . The means by which interactive applications are furnished by the Content Providers to the video service provider  1  is discussed in detail below and in the section entitled “Assignment of Interactive Callback Address.” 
     Content Providers may be any original or secondary source of programming or information generally, including, for example, interactive or non-interactive over-the-air programming such as commercial television stations, cable programming such as weather, travel and entertainment channels, game channels, and on-line services of various types. Content Providers may alternatively broadcast directly to viewers, without the necessity of the broadcast being received and retransmitted to subscribers. 
     Over-the-air broadcast Content Providers such as commercial television stations, which may not provide programming by way of the video service provider  1  may nevertheless furnish the video service provider  1  with interactive applications associated with their broadcasts. An example of such a Content Provider is Content Provider A  41 . According to an approach described below, a video service provider  1  that has received an interactive application from Content Provider A  41  may then provide access to the interactive application to subscribers  70  of the video service provider  1 , in response to subscriber requests. 
     Content Providers that may not transmit programming to viewers over the air but which may provide it via cable, for example, such as weather, entertainment and game program providers, which may be represented by Content Provider B  42 , may provide programming to viewers via the video service provider  1 . This programming could be sent to the video service provider  1  in the form of an RF transmission, in which case the signal would be received and suitably processed by RF equipment  25 . Alternatively, the programming might be transmitted to the video service provider  1  over, for example, a network according to a cell- or packet-switching or other suitable protocol. In the latter event, the programming signal could be received at network provider  10  via the video service provider  1  and switch  12 . Switch  12  would in turn provide the received signal, along with numerous other signals it would in general handle, to signal processor  14 , which conditions the signal for receipt and transmission by RF equipment  25 . 
     Content Providers A-N may also furnish the video service provider  1  with one or more interactive applications which the video service provider  1  may in turn provide to subscribers  70  of the video service provider  1  in response to subscriber requests. 
     Other providers of television content such as advertisers, which may be represented by Content Provider C  43 , may not provide services to viewers but rather furnish content originating with them to broadcasters that incorporate that content into their own broadcasts. They may also furnish interactive applications to the video service provider  1 , as further described below. The video service provider  1  may then provide access by subscribers  70  to the interactive application. 
     Signals containing programming furnished by the Content Providers A-N (ref. numerals  41 - 44 ) may have inserted into them interactive callback addresses by one or more ICA insertion mechanisms. For example, ICA insertion mechanism  20  can be connected via suitable communication paths to Content Provider B  42  and to interactive server  5 . Insertion mechanism  20  can be any known equipment for inserting information in a television signal, for example, in line  21  of the vertical blanking interval of an NTSC video signal. Content Provider B  42  may decide to transmit a broadcast, such as a commercial, having an associated interactive component or application that may have been provided to the video service provider  1  and is stored in the interactive server  5 . Content Provider B  42  then queries interactive server  5  for the network address and application ID for the associated interactive component. In response to the query, the interactive server  5  identifies the network address and application ID for the associated interactive component which, together, constitute an interactive callback address or ICA. Content Provider B  42 , which is able to issue instructions to ICA insertion mechanism  20 , inserts the ICA received from the interactive server  5  into the transmission (e.g., of the commercial) when it is broadcast. As will be further described below, a properly equipped subscriber STB  100  will be able to sense the ICA on that broadcast channel and then display a button or icon on the viewing screen over the broadcast channel and also store the ICA. If the subscriber selects the displayed button, the STB  100  establishes a session with interactive server  5  and receives the interactive program or application associated with the broadcast. 
     An ICA may be inserted in a broadcast signal by other means. For example, ICA insertion mechanism  22  can be operated and controlled by the video service provider  1 . ICA insertion mechanism  22  can be any known mechanism for inserting information into a television signal (as with ICA insertion mechanism  20 ). A communication path is established between insertion mechanism  22  and interactive server  5 . ICA insertion mechanism  22  is also in communication with Content Provider B  42  and with RF equipment  25  in network provider  10 . Content Provider B  42  may decide to air a broadcast, such as a commercial, having an associated interactive component or application available on interactive server  5 . As shown in  FIG. 1 , Content Provider B  42  may broadcast directly to RF equipment  25  or through switch  12 . In the event that the broadcast will be directly to the RF equipment  25 , Content Provider B  42  prior to or during airing of the broadcast transmits a notice to video service provider  1  that the broadcast program is to be transmitted at a given time. In response to this notice, the interactive server  5  identifies the network address and application ID for the interactive component associated with the broadcast, which, together, constitute an interactive callback address or ICA. Interactive server  5 , which maintains control over the ICA insertion mechanism  22  inserts the ICA received from the interactive server  5  into the transmission (e.g., the commercial) when it is broadcast and communicates the resultant signal to RF equipment  25  of network provider  10 . 
     In the event that a Content Provider such as Content Provider B  42  is transmitting a broadcast via switch  12  in network provider  10 , ICA insertion mechanism  24  is in communication with interactive server  5 , Content Provider B  42 , and switch  12  of network provider  10 . As with the ICA insertion mechanism  24 , Content Provider B  42  prior to or during airing of the broadcast transmits a notice to video service provider  1  that the broadcast program is to be transmitted at a given time. In response to this notice, the interactive server  5  identifies the network address and application ID for the interactive component associated with the broadcast, which, together, constitute an interactive callback address or ICA. Interactive server  5 , which maintains control over the ICA insertion mechanism  24 , as well as ICA insertion mechanism  22 , inserts the ICA received from the interactive server  5  into the transmission (e.g., the commercial) when it is broadcast, and communicates the resultant signal to switch  12  of network provider  10 . 
     In one embodiment of the disclosure, a video service provider  1  provides its services using at least some of the components shown in  FIG. 1 . The services provided by video service provider  1  may include voice, data, and video services, including interactive TV and cable channel service, and including both service that is multi-cast (to all subscribers) and switched (to particular individual subscribers), which may be interactive in nature. The primary functionality of the service provider  1  in this embodiment is provided by interactive server  5 , which stores and manages the interactive applications provided by the Content Providers, and which responds to requests from subscribers  70  during interactive sessions subscribers  70  initiate. Interactive server  5  is shown and described in greater detail in  FIG. 6  and the accompanying text. 
     Although the present discussion focuses on the provision of interactive applications, the video service provider  1  may be an enhanced video gateway provider, offering service including menuing and navigation capabilities, billing and collections, information services, storage and order processing. As in the embodiment shown in  FIG. 1 , the “Level 2” or “L2” Service, presently defined, along with the subscriber  70  set top box (“STB”)  100 , by the Federal Communications Commission (“FCC”) as the unregulated portion of a video services network, is implemented by the video service provider  1 . In this embodiment, the video service provider  1  is physically separated from the “Level 1” or L1 service, defined by the FCC as the regulated portion of a video services network and the portion of the system known as “video dial tone,” functionality of which is implemented by network service provider  10  in  FIG. 1 . In this configuration, the L1 service might serve a number of such video service providers (although only one is shown and described for convenience). Alternatively, the video service provider  1  may at the same site provide both L1 and L2 services. 
     Interactive server  5 , which is part of the L2 Service, is linked to a switch  12 , part of the L1 service, for transferring data according to any desired protocol or scheme, such as the ATM cell-switching protocol, for example. The switch  12  may also switch video signals from Content Providers, as shown  FIG. 1  for Content Providers B-N (reference numerals  42 - 44 , respectively), to one or more video signal processors  20  for delivery to the network distribution facilities. In an embodiment of the disclosure, signal processing equipment  14 , network controller  16 , RF equipment  25  and electrical/optical converter  30  all serve to interface the switch  12  with the broadband distribution system  50 . 
     The signal processing equipment  14  receives digital video signals and transforms them into properly timed and mapped broadband signals for transmission to subscribers. One example of the standard according to which such transformation may be performed is the MPEG-2 standard (Moving Pictures Expert Group standard 2, an international video and audio compression and transmission standard described in ISO/IEC CD 13818-1, the contents of which are incorporated by reference herein); however, any other suitable standards, formats, protocols, data structures, sequences or organization schemes could also be employed just as easily and effectively. 
     Network controller  16  receives input via signal processor  14  from the STB  100  of subscriber  70  and sends output to the switch  12 , signal processor  14 , and to the interactive server  5  in order to establish network sessions that permit downstream transmission of broadcast and interactive applications from the interactive server  5 , as well as upstream signaling from STB  100  of subscriber  70 . The network controller  16  output to switch  12  and signal processor  14  also provisions network resources to achieve these functions. 
     The RF equipment  25  provides RF modulation and RF combining for transmission of video signals onto the broadband distribution system  50 . It receives input from the switch  12  in, for example, ATM format and may receive input directly from Content Providers, such as the Content Provider B  42 . It provides output in the form of RF transmission either directly (not shown) onto a broadband RF distribution network  50 , or if the broadband RF distribution network is implemented with optical fiber, it provides output to electrical/optical converter  30 . In this event, converter  30  transforms the input received from the RF equipment  25  and places it onto the broadband distribution system  50 . 
     The switch  12 , network controller  16 , RF equipment  25 , electrical/optical converting equipment  30  and broadband distribution system  50  together make up at least part of the L1 service provided by network service provider  10 . Network service provider  10  is responsible for setting up and maintaining a communications interface between the interactive server  5  and the STBs  100  of a node  60  of subscribers. Network service provider  10  receives an application transmission from the interactive server  5  in the downstream direction. Network service provider  10  receives application transmission in the upstream direction from subscriber STBs  100  (to be discussed at greater length below) via broadband RF transmission. 
     As shown in  FIG. 1 , provision of programming by the Content Providers  41 - 44  may be: directly to viewers, including one or more subscribers  70 , who may receive the signal, for example, with a conventional antenna (see Content Provider A  41 ); via the service provider without requiring digital switching or conversion to broadband, when the signal is already in broadband format which may be the case, for example, if the Content Provider is a provider of over-the-air or cable channel service (see Content Provider B  42 ); or via the service provider  1  through the switch  12  and signal processor  14 . Not shown in  FIG. 1 , but described below with reference to  FIGS. 6 and 7 , is the provision of interactive applications from the Content Providers  41 - 44  to the video service provider  1 , and the provision of an identifying code such as an interactive callback address from the video service provider  1  to the Content Providers  41 - 44 . 
     A video signal provided by, or by way of, the video service provider  1  is placed on the broadband distribution system  50 . Broadband distribution system  50  is most preferably a broadband network with bandwidth on the order of 750 Mhz, but it may feature a suitable bandwidth for the program content and functionality desired. In the presently described embodiment of the video dial tone system, the distribution is partitioned into a 50-750 Mhz downstream path for the provision of video services and a 5-42 Mhz upstream path for signaling by a subscriber  70  to the video service provider  1 . 
     Broadband distribution system  50  provides a link between the video service provider  1  and one or more nodes  60  of subscribers  70 . One such subscriber node  60  is shown in  FIG. 1 . In an embodiment of the video dial tone system, a subscriber node  60  may include a remote terminal  65 , which converts optical signals received over the network to electrical signals. The electrical signals are then provided on a coaxial distribution system  66  to a number of taps (not shown), each of which may serve a number of subscribers  70 . 
     Subscriber  70  is situated similarly to a typical television viewer in a number of respects. As shown in  FIG. 1 , the subscriber is equipped with one or more televisions  80 ,  90  or other suitable image monitoring devices. As depicted in the Figure, a television  90  may be connected directly to the coaxial distribution system  66 , rather than via the STB  100 , as in the case of television  80 . The subscriber is further equipped with a set top box  100  that is also coupled to the coaxial distribution system  66 . The STB  100  may be a device with certain similarities to conventional cable company STBs. However, the particular requirements of the STB  100  for implementing the present disclosure, including functionality not present in conventional STBs, are shown in greater detail in  FIG. 8 , which shows the components of an embodiment of an STB  100 , and  FIGS. 9 to 12 , which depict the logic flow for four embodiments of an STB  100  according to the present disclosure and corresponding respectively to  FIGS. 2A-B  to  5 A-B. 
     Operation of Several Embodiments of a System According to the Present Disclosure 
     An interactive application must be associated with an identifying code such as an interactive callback address if it is to be invoked by subscribers. The provision of this code or address to subscribers in the context of other programming is what allows a subscriber  70  with the proper equipment and data links to invoke the interactive application. The provision of an address in response to a request by a Content Provider can be accomplished in several ways, to be discussed at further length below. In addition, the address can be provided to the subscriber  70  in various ways, and the manner in which this address (and information regarding the availability of an interactive application) is provided determines to a certain extent the overall functioning of the system. Four illustrative approaches to providing an address, which may be referred to as an “interactive callback address” or “ICA,” will be discussed, along with the operation of systems according to the present disclosure for implementing these approaches, in relation to  FIGS. 2A ,  2 B,  3 A,  3 B,  4 A,  4 B,  5 A and  5 B. These Figures present each of the four approaches as a logic flow. The approaches are to be taken without limitation as examples of ways in which devices, systems, and methods according to the present disclosure may be carried out. The division of these logic flows into the boxes shown in the Figures is also by way of example, rather than of limitation (as is the remainder of this document). 
     Application-Specific Interactive Callback Address Transmitted with Broadcast and Identified by Standard Button Overlay 
     In  FIG. 2A , at  205 , an ICA is established (as further described below) for a particular interactive application associated with given programming. The ICA describes a logical address that would map to an interactive server&#39;s network address, includes an application ID, and may include a “timeout” period, which is the time that the button should be displayed on the broadcast screen. The STB  100  may also have a standard default timeout period, if no timeout is sent with the ICA. A subscriber&#39;s STB  100 , when equipped with this ICA, can call the interactive server  5  to establish a session with the interactive application associated with the program. 
     At  210 , the ICA is delivered to a medium (such as, for instance, a provider of program material such as video tape or live broadcast) and, in a preferred embodiment of the disclosure, is inserted or stored in the vertical blanking interval (VBI) of the desired program associated with the medium. As an alternative to providing the ICA in the VBI of a broadcast program, any other synchronized in-band or out-of-band transmission system may be used. As further described below, the ICA serves as a complete or partial basis for the STB  100  of a subscriber  70  to generate a signal representing a “button” for inclusion on the screen of the television  80  of subscriber  70 . The ICA is inserted in the program such that the interactive button may be generated by a subscriber&#39;s STB  100  to appear at the desired time on the screen of a subscriber  70  tuned to that program. A “remove button” message may also be inserted in the VBI (or, again, another synchronized in-band or out-of-band transmission system) at the point in time when the button should be removed by the STB  100 . Alternatively, the button may be removed if a new ICA is received, or if a timer expires, or finally, if the broadcast channel is changed. If, on the other hand, the button is to remain continuously on the screen, the ICA may be inserted at periodic intervals in the program. 
     At  215 , the program is delivered on a given channel. If the ICA was inserted into the VBI, it will of course be included as part of the transmission. Alternatively, the ICA may be sent over another in-band or out-of-band transmission system synchronized with the program. 
     Referring to  FIG. 2B , at  220 , the STB  100 , which is tuned to a given channel, listens for the ICA in the VBI or other appropriate transmission. If an ICA is detected, at  225 , the STB  100 , at  230 , overlays a screen button having a standard predetermined configuration on the image displayed on the screen of TV  80  to which the STB  100  is connected. The provision and storage of the information required to generate the standard button is discussed at greater length below in the context of the STB  100 . Also at  230 , STB  100  sets an internal timer to a timer value sent as part of the ICA, or if no timer value is sent, to a standard timeout value. If no ICA is detected, the subscriber  70  continues watching the program, at  285 , and the STB  100  continues to listen for an ICA, at  220 . 
     As indicated at  235 , if the subscriber  70  has selected the displayed button, at the next step,  240 , STB  100  stores the identity of the current broadcast channel STB  100  then resolves the ICA from a logical address to a network address and then uses the ICA to establish an interactive session between itself and the interactive server  5  corresponding to the ICA. At this point the STB  100  stores the identity of the current channel for later retrieval, erases the button from the screen, and then tunes to the correct channel for maintaining the interactive session, which channel was received from the interactive server  5  according to standard protocols when STB  100  requested an interactive session. 
     As indicated at  245 , the interactive server  5  receives upstream data from the STB  100  and, in response, sends appropriate video screens, text, graphics, scripts, and/or other information downstream to the STB  100 . The STB  100 , at  250 , displays on the TV  80  the interactive session received from the interactive server  5 , and sends subscriber  70  responses upstream to the interactive server  5 . 
     As indicated at  255 , the STB  100  checks whether the interactive session has been terminated. This event will occur at the end of the interactive application, in which case the interactive server  5  terminates the session. Termination may also, of course, occur if the subscriber  70  requests it. If the session has been terminated, the STB  100  deletes the ICA, retrieves the identity of the channel that was previously being watched, and re-tunes the TV  80  to that channel. If the session has not been terminated, the interactive server  5  continues to receive upstream information from the STB  100  and to send video screens, text, graphics, scripts, and/or other interactive information downstream to the STB  100 , as shown at  245 . 
     At  265 , after the STB  100  has returned the TV  80  to the original program channel, at  260 , the STB  100  queries whether the button is still on the screen. If it is, the next query, at  270 , is whether the STB  100  has received a “remove button” message. If the STB  100  has received the “remove button” message, then, at  275 , it erases the button. Alternatively, if the STB  100  has not received the “remove button” message, but the timer has reached the timer value transmitted with the ICA indicating that the timeout period has elapsed (described in further detail below in connection with the STB  100  logic), the STB  100  erases the button. 
     If, at  235 , it had been determined by the STB  100  that the subscriber  70  did not select the displayed button, the STB  100  checks whether it has received a “remove button” message or if the timeout period has expired, at  270 . If either of these conditions has occurred, the STB  100  erases the button at  275  and deletes the ICA. Following  275  or  280 , the viewer continues watching the program, at  265 , and, returning to  220 , the STB  100  resumes listening for an ICA. 
     Well-Known Interactive Callback Address Transmitted with Program and Identified by Standard Button Overlay 
     An alternative to the application-specific callback addressing scheme described above in connection with  FIGS. 2A and 2B  is presented in  FIGS. 3A and 3B . These figures show the logical flow of an approach in which a single common identifying code or “well-known” interactive callback address is provided to all subscribers  70 , indeed all viewers, but which only the subscribers  70  use if they elect to invoke that application from the interactive server  5 . 
     At  305 , a program- or application-specific identifying code or ICA is established (as further described below) for a particular interactive application associated with a given program. As with the first approach, the ICA describes a logical address that would sap to an interactive server&#39;s network address, includes an application ID, and may include a “timeout” period, which is the time that the button should be displayed on the broadcast screen. Also, a well-known interactive callback address (“WKICA”) is established for all interactive applications associated with all programs. The WKICA generally includes the same sort of information as does the ICA. 
     The WKICA is a common address used by all STBs  100 . The STBs  100  call the WKICA to get the ICA information associated with the particular interactive application, (which would include the server ID if the subscriber were to have access to more than one interactive server). Once the STB  100 , using the WKICA, has obtained the desired ICA, it will call for the desired interactive application using that ICA. 
     At  310 , the WKICA is delivered to a medium (for instance, a provider of program material such as video tape or live broadcast) and, in a preferred embodiment of the disclosure, is inserted or stored in the VBI of the desired program associated with the program medium. As an alternative to providing the WKICA in the VBI of a program, any other in-band or out-of-band transmission system may be used if it is synchronized with the program. The WKICA is inserted so that it will appear on the TV  80  screen of subscriber  70  during the desired time in the program. A “remove button” and/or time expiration message may also be inserted in the VBI (or other synchronized transmission system) at the point in time when the button should be removed. If the button is to remain continuously on the screen, the WKICA may be inserted at periodic intervals throughout the program. 
     The program is then transmitted at  315 , on a particular channel. The WKICA is thus included in the VBI as part of the program transmission, or it may be sent on another in-band or out-of-band transmission system synchronized with the program. 
     Referring to  FIG. 3B , the STB  100 , tuned to a particular program channel, listens, at  320 , for the WKICA in the VBI or other appropriate transmission system. If at  325 , a WKICA in the VBI or other system is detected, an interactive session is established at  330 ; otherwise, the viewer continues watching the program and a timer is set, at  385 . 
     At  330 , the STB  100  calls the WKICA to establish an interactive session with the application identified by the WKICA. At the outset of the session, the STB  100  provides the application identified by the WKICA with the identity of the channel being viewed by the subscriber  70 . The STB  100  receives from the application specific information associated with the program channel, such as the type of button to display and the specific ICA to call to establish the appropriate interactive session, assuming the subscriber  70  selects it by pressing the button. The STB  100  sets the timer and displays on the screen of the TV  80  the type of button specified by the application associated with the WKICA and proceeds to wait for a “remove button” message or for the period for which the timer is set to expire. The STB  100 , using components and according to processing further described below, generates the button based in part on information previously stored, for example by software download, in the STB  100 . 
     The STB  100  also waits, at  335 , for the subscriber to select the button on the viewing screen. If a selected button is detected, the STB  100  at  340  stores the identity of the current broadcast channel in memory for later retrieval. It then calls the specific ICA it has received from the WKICA to establish the appropriate interactive session for the button that was pressed. The STB  100  also erases the button from the screen, and tunes to the appropriate channel for the interactive session. 
     During the interactive session, such as at  345 , the interactive server  5  receives upstream information from the STB  100  and sends downstream to the STB  100  text, graphics, scripts, and/or other information. As shown at  350 , the STB  100  displays the interactive session on the screen of TV  80 , and receives viewer commands and interactive responses and sends those signals upstream to the interactive server  5 . 
     The STB  100 , as indicated at  355 , determines whether the interactive session has been terminated, either at the subscriber&#39;s command, or if the end of the interactive application has been reached. If the interactive application has not been terminated, the STB  100  and the interactive server  5  continue providing the functionality in the states shown at points  345  and  350 . If the interactive session has been terminated, the STB  100  at  360  deletes the specific ICA and retrieves from memory the identity of the program channel the subscriber  70  had been viewing and re-tunes to that channel so that the subscriber  70 , at  365 , can continue viewing the broadcast program on that channel. 
     If at  335  the viewer had not selected the broadcast screen button, STB  100  would, at  370 , check whether a “remove button” message has been received or whether the timeout period has expired. If not, STB  100  returns to  335 , checking whether the displayed button has been selected. If a “remove button message” has been received or the timeout period expired, STB  100  erases the button, at  375 , and deletes the specific ICA. The viewer may then continue viewing the broadcast program at  365 , and the STB  100 , at  320 , continues listening for a WKICA in the VBI. 
     Application-Specific Interactive Callback Address Transmitted with Program and Identified by a Non-Standard Button Overlay 
     A third embodiment of a system and method according to the present disclosure is depicted in  FIGS. 4A and 4B . In  FIG. 4A  at  405  an interactive callback address package (ICAP) is established for an interactive application associated with a given program. This ICAP includes an ICA and may also include customized button information. This customized information may include: 
     a) type(s) of button(s); 
     b) characteristics of button(s); 
     c) location on the screen of button(s); 
     d) text of button(s); and 
     e) other unique characteristics of button(s). 
     The ICA describes a logical address that would map to an interactive server&#39;s network address, includes an application ID, and may include a “timeout” period, which is the time that the button should be displayed on the broadcast screen. As with the first described embodiment, the ICA will be used by the STB  100  to address a call to establish an interactive session associated with the program. 
     At  410 , the ICAP is delivered to a program medium (for instance, a provider of program material such as video tape or live broadcast) and, in a preferred embodiment of the disclosure, is inserted or stored in the vertical blanking interval (VBI) of the desired program associated with the program medium. As an alternative to providing the ICAP in the VBI of a program, any other synchronized in-band or out-of-band transmission system may be used. The ICAP is inserted in the program so that it will appear on the subscriber&#39;s  70  screen at the desired time. In addition to the ICAP, a “remove button” message may also be inserted in the VBI (or other transmission system) so that the button will be removed at the desired time. If it is desired that the button remain continuously on the viewing screen, the ICAP may be inserted at periodic intervals throughout the program. 
     At  415 , the program is transmitted on a given channel. Along with this program, the ICA may be included either in the VBI, or transmitted on another in-band or out-of-band transmission system synchronized with the program. 
     Referring to  FIG. 4B , an STB  100  tuned to the channel listens at  420  for the ICAP in the VBI or other appropriate transmission. At  425 , if an ICAP is detected, the STB  100 , at  430 , uses any customized button information contained in the ICAP to generate and overlay a customized button in a customized location over the image. If the ICAP does not contain information for a customized button, the STB  100  uses standard defaults that have been previously stored in the STB  100 , for example via software download. The STB  100  sets an internal timer to a timer value sent as part of the ICAP, or if no timer value is sent, to a standard timeout value. When the button is being displayed, the STB  100  listens for the remove button message to remove the button. 
     If, at  425 , no ICAP was detected, the subscriber  70  simply continues watching the program, at  485 , and the STB  100  continues to listen for the ICAP, at  420 . 
     If the subscriber  70  selects the displayed button, at  435 , the STB  100 , at  440 , stores in memory the identity of the current channel. The STB  100  then uses the ICA from the ICAP it has received to establish an interactive session between the STB  100  and the appropriate interactive server  5 . The STB  100  erases the button from the screen, and tunes to the correct channel for the interactive session, which channel was received from the interactive server  5  according to standard protocols when STB  100  requested an interactive session. 
     When the interactive session has been established, the interactive server  5 , at  445 , receives upstream information from the STB  100  and sends video screens, text, graphics, scripts, and/or other information downstream to the STB  100 . As shown at  450 , the STB  100  displays the interactive session on the screen of the TV  80 . The STB  100  also receives viewer interactive responses and sends responses upstream to the interactive server  5 . 
     If the interactive session is terminated, which may be a result of the subscriber  70  issuing a termination command, or simply as a result of the completion of the interactive application, STB  100  detects this event at  455  and, at  460 , deletes the ICAP and re-tunes to the channel that was originally being watched and the subscriber  70  continues watching the program on that channel, at  465 . If a termination is not detected, the interactive session continues at  445  and  450 . 
     If, at  435 , it had been determined by the STB  100  that the subscriber  70  did not select the displayed button, the STB  100  determines, at  470 , whether it has received a remove-button message or whether the timer has expired. If neither event has occurred, the STB  100  continues checking whether viewing subscriber  70  has selected the button, at  435 . If a remove button message has been received at  470 , the STB  100  erases the button and deletes the ICAP, at  475 ; if it has not, the STB  100  at  475  erases the button and deletes the ICAP only if a button timeout period has been exceeded, at  470 . After the STB  100  erases the button and deletes the ICAP, the viewing subscriber  70  continues watching the broadcast program, at  465 . Also, the STB  100  resumes listening for the ICAP at  420 . 
     Application-Specific Interactive Callback Address and Button Overlay Both Transmitted with Program 
     In a fourth embodiment of a system and method according to the present disclosure, the logical flow of which is illustrated at  FIGS. 5A and 5B , an application-specific ICA is transmitted with the program, along with a button inserted on the video program at the point of transmission. 
     Referring to  FIG. 5A , at  505 , an ICA is established for a particular interactive application associated with a given program. As with the previously described embodiments, the ICA describes a logical address that would map to an interactive server&#39;s network address, includes an application ID, and may include a “timeout” period, which is the time that the button should be displayed on the broadcast screen. The ICA ultimately will be used by the STB  100  of the subscriber  70  viewing the program to invoke an interactive session associated with that program. 
     At  510 , the ICA is delivered to a medium (for instance, a provider of material such as video tape or live broadcast) and, in a preferred embodiment of the disclosure, it is inserted or stored in the vertical blanking interval (VBI) of the desired program associated with the medium. As an alternative to providing the ICA in the VBI of a program, any other in-band or out-of-band transmission system may be used if it is synchronized with the program. The ICA is inserted into the program so that it will appear at the desired point in the program, and the button is also inserted into the program so that it will appear at that desired time on the screens of all viewers receiving the program, including viewers that are not subscribers and that lack an STB  100 . When the button is removed from the program image (and thus the viewers&#39; screens), a “remove button” message is inserted in the VBI. When the STB  100  of a viewing subscriber  70  receives this message, the STB  100  deletes the ICA. The timeout period can be sent with the ICA if the duration of the button display, and hence how long the ICA is to be active, is predetermined. 
     The program, at  515 , is transmitted on a particular channel. As described above in connection with  510 , the ICA may either have been incorporated in the transmission, or be sent on an in-band or out-of-band transmission system that is synchronized with the program. 
     STB  100  at  520  checks for an ICA in the VBI of the video stream (or in another suitable preselected transmission). As indicated at  525 , if an ICA is detected, the STB  100  does not overlay a button, at  530 , since the button is overlaid at the broadcast source and has appeared on the screen when the ICA arrived at the STB  100 . Rather the STB  100  sets the timer and begins checking for a “delete ICA” message or timeout. 
     If the ICA was not detected, the subscriber  100  simply continues watching the program, at  565 . 
     The STB  100 , at  535 , checks whether the subscriber  100  has selected the displayed button. If selection of the button is detected, the STB  100  stores the identity of the broadcast channel being viewed. It then uses the ICA to establish an interactive session, at  540 , with the appropriate interactive server  5 . The STB  100  receives and then tunes to the correct channel for an interactive session. 
     If, at  535 , the subscriber  70  had not selected the button displayed on the screen of the TV  80 , the STB  100  continues checking, as shown at  570 , whether a “delete ICA” message has been received or if the timer has expired. If either or both these events have occurred, then the STB  100 , at  575 , deletes the ICA. After  575 , the viewer continues watching the program, at  565 . 
     During the interactive session, the interactive server  5 , at  545 , receives upstream information from the STB  100  and sends video screens, text, graphics, scripts, and/or other information downstream to the STB  100 . At  550 , the STB  100  displays the interactive session on the screen of the TV  80 . It also receives viewer interactive responses and commands and sends them upstream to the interactive server  5 . 
     The STB  100  checks, at  555 , whether the interactive session has been terminated. If it has not, the interactive session continues, at  545  and  550 . If the session has been terminated, which may have occurred as a result of a command issued by viewing subscriber  70 , or due to the end of the interactive application having been reached, the STB  100  deletes the ICA, retrieves the identity of the channel, which subscriber  70  had been watching, and re-tunes to that channel. 
     The subscriber  70  continues watching the program, at  565 . The STB  100  continues to listen for the ICA, at  520 , in the VBI or other appropriate transmission. 
     Assignment of Interactive Callback Address 
     An interactive callback address (ICA) is associated with an interactive application to enable subscribers to invoke an interactive application, as well as to uniquely identify an interactive application for any number of additional reasons. The ICA describes a logical address that maps to an interactive server&#39;s network address, includes an application ID, and may also include a “timeout” period message, which indicates the amount of time that a button indicating the availability of an interactive application or program should be displayed on the broadcast screen. The ICA may be furnished in association with a program to subscribers in a variety of ways, two of which are described below. Once the ICA is received by a subscriber terminal device such as an STB  100 , the ICA may be stored so that it will be available at the request of subscriber  70  to call and establish with an interactive server  5  an interactive session associated with a program. The ICA may be assigned in a number of ways, two of which are described below, with reference to  FIG. 1 ,  FIG. 6  and  FIGS. 7A and 7B . 
     Case I: Locally Assigned Interactive Callback Addresses 
     When content, such as an interactive news program or a commercial advertisement, is specifically developed for an interactive platform, as may be the case for locally originating programming, a Content Provider  45  requests an ICA from a video service provider  1  operating an interactive server  5  linked to one or more nodes  60  of subscribers  70 . This request may be made by any suitable means. It could be done simply by making a telephone call to the video service operator  2 , or it could be done by purely electronic means, such as e-mail, or automatically, or remotely invoking an application on the interactive server  5  designed for this purpose. The Content Provider  45  also then transmits to the video service provider  1  the interactive application. This transmission may be done by physically sending the interactive application to the video service provider  1  on tape, magnetic disk, optical disk or other suitable medium; alternatively, it could be done by electronic or optical transmission of the data, such as over a network. 
     After receiving the request for the ICA, the interactive server  5  assigns an ICA consistent with the state of the interactive server  5  and its memory  8  and other storage devices  8 A and  9 . The video service provider  1  also stores the application received from the Content Provider in a suitable storage device, such as video storage  9 , and stores the ICA and perhaps information relating to the interactive application in a database maintained, for example, in disk storage  8 A. Such additional information may include an application ID selected by the video service provider  1 . 
     If the interactive server  5  is called by a subscriber  70  with an ICA, the interactive server  5  may thus retrieve using the ICA any information necessary for locating and running the interactive application. The new ICA may be selected according to any suitable scheme. In one embodiment of the present disclosure, the ICA has a format of the form shown in  FIGS. 7A and 7B . As shown in  FIG. 7A , but without limitation, the ICA preferably comprises 32 bits. According to an error correction scheme, such as a Hamming code or other suitable approach, a number of checkbite or parity-type bits are incorporated into the ICA. In  FIG. 7A , 6 such bits  110 - 115  are shown as bits  1 ,  2 ,  4 ,  8 ,  16 , and  32  corresponding to the ICA content shown in  FIG. 7B . Hence 38 bits are used to transmit the ICA, with a coding rate of about 0.84. Any error correction schemes suitable for minimizing errors in the transmission of an ICA having a known format may be used. 
     In  FIG. 7B , the components of the ICA are shown. Bits  9 - 32  contain a program identifier  120 , including a server ID and an application ID. Bits  3 - 8  are used for an industry code  125 , which is assigned to large Content Providers to uniquely identify them. Bits  1  and  2  correspond to time cycle identifier  130 , which facilitates re-cycling of program identifiers: when a particular application no longer is being provided by the Content Provider identified by a particular industry code, the Content Provider can re-use a particular program identifier. Time cycle identifier  130  is prefixed to ensure uniqueness of the ICA when a program identifier is used an additional time. Where, as shown, the time cycle identifier  130  is allocated two bits, a given program identifier  120  may be used uniquely four times. 
     When the interactive application has been stored, a new ICA has been selected for the interactive application, and the ICA and interactive application information have been stored in a database, the video service provider  1  or interactive server  5  sends a message to the Content Provider  45 . This message may include a description of the type of application, an ICA confirmation including the ICA itself, an application ID (including a server number and application number), any other information, such as billing information, and a timeout value for specifying the length of time a screen button should persist. 
     Case II: Content-Defined Interactive Callback Addresses 
     In case I, an interactive application may have been developed for a particular interactive server and was to be assigned an address by that server. As an alternative to case I, interactive applications associated with pre-developed content (that is, created specifically to be associated with the interactive application) may already be associated with and labeled with an ICA by the Content Provider  45 . This may be, but is not necessarily, the case for nationally originating programmers. For such content-defined ICAs, the interactive application and the pre-assigned ICA are both transmitted to the desired video service providers. The transmission may be done simply by shipping a tape, magnetic disk, optical disk or other suitable medium to the video service provider, or alternatively, may be electronically or optically transmitted over a network. The receiving video service provider  1  or interactive server  5  stores the interactive application, then adds the ICA and assigns an application ID. An application ID is an identifier for purposes of internal organization and tracking by the video service provider  1 . Thus, for a nationally originating program in which the ICA identifying the program is national, the interactive server  5  of (local) video service provider  1  translates the (national) ICA to a local server address of its internal database, for example on disk storage  8 A. Once this information has been stored, a receiving video service provider  1  sends a confirmation message to the Content Provider  45 , including what it has recorded as the ICA, the application ID, and a description of the application. As an alternative scheme, not shown in the Figures, the (local) video service provider  1  is linked to a national server running the interactive application, and the local server using the ICA provides a link from the subscriber to the national interactive server. 
     The Interactive Server 
     One or more interactive servers  5  may be maintained as part of the Level 2 service (L2, defined above in connection with  FIG. 1 ) in order to provide service to subscribers in a particular geographical area. An embodiment of the interactive server  5  according to the present disclosure may be coupled to one or more transmission paths, such as a satellite downlink, for receiving programs. The interactive server  5  is also coupled to a level 1 network (L1, defined in connection with  FIG. 1 ), through which it interacts with subscribers  70 , receiving program requests and commands, and sending programming as requested by each subscriber. 
     An embodiment of an interactive server  5  is shown in  FIG. 6 . The interactive server  5  may include, for example, one or more processors  7 , one or more memory devices  8 , and one or more storage devices such as disk storage  8 A. These components may be linked to one another by a data bus  6 . The interactive server  5  may also include a video storage medium  9 , in which device interactive applications supplied by Content Providers may be stored for retrieval upon request by a subscriber  70 . 
     The interactive server  5  may receive input and provide output to a video service operator, represented schematically at reference numeral  2 , or over data link  11  to the switch  12 , or over data link  3 A directly to a Content Provider  45 . In response to a request by a Content Provider  45  for an ICA to be associated with a program, for example, the video service provider  1  may interact with the interactive server  5  via I/O mechanism  4  in order to obtain an interactive application address, at which an interactive application will be found when stored with the interactive server  5 , and, if necessary, a port address, to combine with the address of the interactive server  5  itself for transmission to the Content Provider  45  via a communication link  3 . Under an alternative scheme, a Content Provider  45  could establish a link with the interactive server  5  itself over communications link  3   a  and obtain an ICA directly. 
     When a video service provider  1  has received an interactive application from a Content Provider  45 , the video service provider  1 , via I/O mechanism  4 , loads the interactive application into an appropriate storage medium, such as video storage  9 , which-may be a separate storage medium from the interactive server memory  8  or the interactive server disk storage  8 A, such that the interactive application may be retrieved using the interactive application address portion of the ICA furnished to the Content Provider  45 . 
     The video service provider  1  may also interact with the interactive server  5  to perform system management functions such as data storage management, if such functions are not carried out automatically. 
     Set Top Box Architecture 
     A subscriber  70  to an interactive video service will be equipped with an STB  100  for receiving transmissions and initiating an interactive session. The functionality of the STB  100  may reside in a stand-alone device, literally a box that can be placed on, or at least near, the television, that is similar in outward form to conventional devices for receiving cable programs. The STB  100  functionality could alternatively be performed by hardware resident elsewhere, such as within the television or display console, or by any suitably equipped terminal device. Since the hardware may be proprietary to the interactive video provider and may generally be a physically independent device, the term set top box is used here, but the disclosure is not so limited. 
     The components of an embodiment of an STB  100  that may be used to implement the system and method according to the present disclosure are shown in  FIG. 8 . STB  100  is coupled to coaxial distribution system  66 , as was briefly described in connection with  FIG. 1 . Input to STB  100  received over coaxial distribution system  66  is handled by receiving set components, either analog tuner  1210  or digital tuner/demodulator  1218 . Analog tuner  1210  may be any conventional tuner suitable for use in receiving video signals over a cable distribution system or the like. Analog signals on coaxial distribution system  66  having a particular carrier frequency are received by analog tuner  1210  if it is tuned to that frequency. Analog tuner  1210  is coupled to secure processor subsystem  1212 . Secure processor subsystem  1212  may be any known system for receiving scrambled or otherwise secured analog signals over a private distribution system. Typically, the secured processor subsystem  1212 , its components, and their functionality are compatible with remote terminal  65  (at the head end of the coaxial distribution system  66  and shown in  FIG. 1 ). Secure processor subsystem  1212  includes a conventional analog descrambler  1216  for descrambling signals received and forwarded by analog tuner  1210 . Secure processor subsystem  1212  also includes a non-volatile memory subsystem  1214  for storing information necessary for decoding received transmissions, including normal cable program transmissions, pay-per-view program transmissions and the like. 
     Digital signals on cable distribution system  66  are received by digital tuner/demodulator  1218  if they are in a band to which the digital tuner/demodulator  1218  is tuned. Digital tuner/demodulator  1218 , which can be any suitable conventional component, demodulates signals it is tuned to receive in order to reconstruct the desired digitized analog signal. This resulting signal is transmitted to video decoder  1220 , a conventionally available device that interprets the input stream. Video decoder  1220  thereby recovers the compressed signal to produce a video signal. 
     Analog descrambler  1216  and video decoder  1220  are both coupled to graphics assist module  1222 . Graphics assist module  1222  can be any conventionally available graphics processor suitable for adding a graphics overlay onto the video signals received from the video decoder  1220  and/or the analog descrambler  1216  in response to instructions implemented by software running on CPU  1228 . The functionality of graphics assist module  1222  could be implemented by CPU  1228  if it were suitably programmed and capable of sufficient throughput. As will be further described below, graphics assist module  1222 , in response to instructions received over system bus  1224 , generates a video signal overlaid on the existing television signal indicating the availability of an interactive program. For example, graphics assist module  1222  may generate a button image, or a logo or other pattern or symbol, and inject the image into the video stream such that the image appears in a designated portion of the screen. Information used in generating this button, as described below, may be available in the signal received over coaxial distribution system  66 , or may use information stored in the STB  100 , such as in static memory  1229 , in which the button information may be pre-loaded. 
     The video stream emerging from analog descrambler  1216  or video decoder  1220 , and from graphics assist module  1222 , is provided to NTSC signal generation module  1226 . As an alternative to NTSC, signal generation module  1226  could generate signals according to any available and desired video format. NTSC signal generation module  1226  is conventional circuitry for transforming the output of analog descrambler  1216 , video decoder  1220  and graphics assist  1222  into the standard foam usable by a conventional television or monitor (not shown in this view). This functionality could, alternatively, convert input signals to any suitable standard format. As shown in  FIG. 8 , NTSC signal generation module  1226  generates a set of coordinated signals and provides them on channel 3 or 4,  1226 A, to a monitor adapted to receive and display television signals (not shown). Also transmitted by NTSC signal generation module  1226  to the monitor or television (not shown) is a composite/Svideo Out signal,  1226 B, and left and right audio signals,  1226 C. 
     In addition to the previously described components and functionality, which have to do with the receipt and provision of television signals, possibly with inserted graphics, STB  100  includes a number of components and implements several additional functions. 
     The processing associated with managing and controlling the functions of the set top box  100  is performed by CPU  1228 . CPU  1228  may be any suitable commercially available processor and preferably one capable of performing in excess of 30 Mips, such as a Power PC or Pentium chip. In running system software stored in static memory  1229  (which may be an EEPROM, ROM or the like), CPU  1228  has access via system bus  1224  to static memory  1229  and to dynamic memory  1230 , (which may be conventionally available memory, preferably with a storage capacity of at least about 4-5 MB). CPU  1228  also has access via system bus  1224  to information regarding the current channel, to the graphics assist  1222  regarding screen button or other graphical display signals, and to video decoder  1220  and digital tuner/demodulator  1218 , as well as to secure processing subsystem  1212  and analog tuner  1210  in order to assert command messages to those components. 
     Interaction by subscriber  70  with STB  100  may be by any suitable means, but is preferably by conventional infrared (IR) remote control. IR controller  1232  receives signals from subscriber-controlled remote control input device  1233  via an IR receiver and associated circuitry (not shown). Instructions received by IR controller  1232  may be asserted via system bus  1224  as commands to secure processor subsystem  1212  and analog tuner  1210 , as well as to video decoder  1220  and digital tuner demodulator  1218 . IR controller  1232  can also send messages to CPU  1228  when, for example, subscriber  70  requests an interactive program or other service. 
     Interaction by the STB  100  upstream via coaxial distribution system  66  and to video service provider  1  is conducted by CPU  1228  through WAN communications processor  1234 . WAN communications processor  1234  can be any conventional device suitable for converting messages received via system bus  1224  into a WAN-compatible protocol, such as IP (internet protocol). Upstream modulator  1236 , which can be any conventional device, modulates signals received from WAN communications processor  1234  for transmission over coaxial distribution system  66  and via remote terminal  65  and network provider  10  to interactive server  5  of video services provider  1  (as shown in  FIG. 1 ). 
     STB Processing Associated with Operation of Several Embodiments of a System According to the Present Disclosure 
     In  FIGS. 9-12 , the processing associated with four embodiments of the STB  100  according to the present disclosure is shown in the form of diagrams depicting the processing states of the STB  100 , conditions for transitioning between those states and processing associated with each state and incident to the state transitions. The embodiment shown in  FIG. 9  corresponds to the embodiment of the disclosure shown in  FIGS. 2A  and B,  FIG. 10  corresponds to  FIGS. 3A  and B,  FIG. 11  to  FIGS. 4A  and B, and  FIG. 12  to  FIGS. 5A  and B. The processor states and processing carried out by STB  100  are implemented by CPU  1228 , shown in  FIG. 8 . As has been described with reference to that figure, CPU  1228  has access via system bus  1224  to signals received over coaxial distribution system  66  that have been descrambled or decoded as necessary by either of video decoder  1220  or analog descrambler  1216 . CPU  1228  is easily capable of sampling these sources sufficiently frequently to detect the receipt of new video frames and to detect the presence and content of information in the VBI of received video signals. In alternate embodiments of the present disclosure, the STB  100  could receive and analyze information received via other in-band or out-of-band transmission paths. 
     The processes shown in these figures could also be represented as logic flow diagrams. Moreover, the exact ordering of the numbered boxes of the flowcharts is not a limitation of the disclosure, but merely an illustration of one way in which the depicted function of each embodiment of this aspect of the present disclosure may be carried out. 
     STB Processing Where an Application-Specific Interactive Callback Address is Transmitted with Program and Identified by a Standard Button Overlay 
     Processes performed by STB  100  in carrying out the first embodiment the system and method according to the present disclosure are shown in  FIG. 9 . As shown, the STB  100  process begins when the subscriber  70  turns on the STB  100  to view a program. The STB  100  process at that time initializes into the idle state,  700 . While in the idle state  700 , the STB  100  checks a number of conditions: it checks whether a video frame has been received; whether a screen button has been selected by viewing subscriber  70 ; whether a “remove button” message has been received with a video frame; and whether a button timer has exceeded a threshold value and thus expired. 
     If a video frame has been received,  702 , STB  100  enters a new state,  704 , in which it tests the video frame, particularly the VBI of that frame, for the presence of an ICA. As described elsewhere in this application, according to the present disclosure, the ICA could alternatively be transmitted to the STB  100  by any suitable in-band or out-of-band means. 
     If no ICA is detected in the given frame by STB  100  at  706 , the process returns to idle state  700 . However, if an ICA is detected in the received frame at  708 , STB  100  at  710  stores the ICA, for example in dynamic memory  1230  (shown in  FIG. 8 ). STB  100  then enters a new state,  712 . 
     In state  712 , STB  100  tests the detected ICA for the presence of information relating to the drawing of a screen button to indicate to viewing subscriber  70  that an interactive program is available. If such information related to the configuration of the screen button is found, at  718 , then STB  100  draws a custom button according to this information, at  720 . Also at  720 , STB  100  sets a timer for the screen button, which STB  100  will check to ensure that the button remains on the screen no longer than a desired maximum time. If the button information was not found in the ICA,  714 , then STB  100  at  716  draws a standard button on the basis of information stored in static memory  1229 , shown in  FIG. 8 . STB  100  at  716  also sets the timer to be later checked in order to ensure that the standard screen button is timely erased. After the button is drawn and the timer is set at  716  or  720 , idle state  700  is resumed. 
     When in the idle state  700 , in addition to testing whether a video frame has been received, as described above, STB  100  also tests whether a screen button, if present on the screen, has been selected by subscribing viewer  70 . STB  100  can access this information available from IR controller  1232  via system bus  1224 , as shown in  FIG. 8 . If a button has been selected,  722 , STB  100 , at  724 , saves in dynamic memory  1230  (shown in  FIG. 8 ) the identity of the channel currently being viewed by subscriber  70 . STB  100  at  724  also erases the screen button, which provides feedback to subscriber  70  that the button has been selected. 
     After the channel has been saved and the button erased at  724 , STB  100  enters the interactive application state  726 . In interactive application state  726 , STB  100  establishes an interactive session with interactive server  5  of video service provider  1  over the network by sending a message containing the ICA using WAN communications processor  1234  and upstream modulator  1236  (shown in  FIG. 8  and described above) over coaxial distribution system  66 , and via remote terminal  65  and network service provider  10  to interactive server  5  of video service provider  1  (shown in  FIG. 1 ). 
     STB  100  remains in the interactive application state  726  as long as the interactive application invoked by the ICA and provided by video service provider  1  has not ended or been terminated by subscribing viewer  70  via IR controller  1232 . If either of these events are detected by STB  100  at  728 , however, STB  100  at  730  retrieves from dynamic memory  1230  the earlier-stored identity of the channel originally being watched and issues a command to either video decoder  1220  and digital tuner/demodulator  1218  or secure processor subsystem  1212  and analog tuner  1210  to re-tune to that original channel. Also at  730 , STB  100  deletes the ICA from dynamic memory  1230 . STB  100  then returns to the idle state  700 . 
     While in idle state  700 , and in addition to testing for the reception of video frames and whether a screen button has been selected, STB  100  also checks, when a video frame has been received at  702 , but no ICA has been detected at  706 , for a “remove button” message in the VBI of the video frame (or in any other suitable in-band or out-of-band signaling path). STB  100  also periodically checks whether the timer, set at  716  or  720 , has expired. If either a “remove button” message has been received or the expiration of the timer has been detected, at  732 , then STB  100 , at  734 , erases the screen button and deletes the ICA from dynamic memory  1230 , if one had been previously stored. STB  100  then returns to its idle state  700  and continues checking for video frames, the selection of a screen button, remove button messages and timer expirations. 
     STB Processing Where a Well-Known Interactive Callback Address is Transmitted With a Program and Identified by Standard Button Overlay 
     In  FIG. 10 , processes performed by STB  100  in connection with a second embodiment of the system and method according to the present disclosure are shown in state diagram form. The STB  100  process begins when the subscriber  70  turns on the STB  100  to view a program. The STB process initializes into the idle state,  800 . While in the idle state  800 , the STB  100  checks a number of conditions: it checks whether a video frame has been received; whether a screen button has been selected by viewing subscriber  70 ; whether a “remove button” message has been received with a video frame; and whether a button timer has exceeded a threshold value and thus expired. 
     If a video frame has been received, at  802 , STB  100  enters a new state,  804 . In this state, it tests the video frame, particularly the VBI of that frame, for the presence of a WKICA (i.e., a well-known interactive callback address, described above) associated with the program being viewed. As discussed elsewhere in this application, according to the present disclosure, the WKICA could alternatively be transmitted to the STB  100  by any suitable in-band or out-of-band means. 
     If STB  100  detects at  806  no WKICA in the given frame, the process returns to state  800 . However, if a WKICA is detected in the received frame, at  808 , STB  100 , at  810 , stores the WKICA, for example in dynamic memory  1230  (shown in  FIG. 8 ). STB  100  then calls the WKICA, establishes an interactive session with the WKICA, and sends the WKICA application the identity of the broadcast channel on which it received the WKICA. STB  100  then receives from the WKICA application the specific ICA, which it must call if the associated button on the screen is selected. STB  100  stores the ICA, for example in dynamic memory  1230  (shown in  FIG. 8 ) and then enters a new state,  812 . 
     In state  812 , STB  100  tests information downloaded from the WKICA interactive session for the presence of information relating to the drawing of a screen button to indicate to viewing subscriber  70  that an interactive program is available. If such information related to the configuration of the screen button is found, at  818 , then STB  100  draws a custom button according to this information, at  820 . Also at  820 , STB  100  sets a timer for the screen button, which it will check to ensure that the button remains on the screen no longer than a desired maximum time. If the button information was not received from the WKICA interactive session, at  814 , then STB  100 , at  816 , draws a standard button on the basis of information stored in static memory  1229 , shown in  FIG. 8 . STB  100 , at  816 , also sets the timer to be later checked in order to ensure that the standard screen button is timely erased. After the button is drawn and the timer is set at  816  or  820 , idle state  800  is resumed. 
     When in the idle state  800 , in addition to testing whether a video frame has been received, as described above, STB  100  also tests whether a screen button, if present on the screen, has been selected by viewing subscriber  70 . STB  100  can access this information, available from IR controller  1232 , via system bus  1224 , as shown in  FIG. 8 . If a button selection has been selected,  822 , STB  100  at  824  saves in dynamic memory  1230  (shown in  FIG. 8 ) the identity of the channel currently being viewed by subscriber  70 . STB  100 , at  824 , also erases the screen button, thus providing feedback to subscriber  70  that the button has been selected. 
     After the channel has been saved and the button erased, at  824 , STB  100  calls the specific ICA and enters the interactive application state,  826 . In interactive application state  826 , STB  100  initiates an interactive session with interactive server  5  of video service provider  1  over the network by sending a message containing the ICA using WAN communications processor  1234  and upstream modulator  1236  (shown in  FIG. 8  and described above) over coaxial distribution system  66 , and via remote terminal  65  and network service provider  10  to interactive server  5  of video service provider  1  (shown in  FIG. 1 ). 
     STB  100  remains in the interactive application state  826  as long as the interactive application invoked by the ICA and provided by video service provider  1  has not ended or been terminated by subscribing viewer  70  via IR controller  1232 . If either of these events are detected by STB  100 , at  828 , at  830  it retrieves from dynamic memory  1230  the earlier-stored identity of the channel originally being watched and issues a command to either video decoder  1220  and digital tuner/demodulator  1218  or secure processor subsystem  1212  and analog tuner  1210  to re-tune to that original channel. Also at  830 , STB  100  deletes the ICA from dynamic memory  1230 . STB  100  then returns to the idle state  800 . 
     In addition to testing in idle state  800  for the reception of video frames and whether a screen button has been selected, STB  100  also conducts a further check. If, at  802 , a video frame has been received, but no WKICA has been detected at  806 , STB  100  checks for a “remove button” message in the VBI of the video frame (or in any other suitable in-band or out-of-band signaling path). STB  100  also periodically checks whether the timer, set at  816  or  820 , has expired. If either a “remove button” message has been received or the expiration of the timer has been detected, at  832 , then STB  100 , at  834 , erases the screen button and deletes the ICA from dynamic memory  1230 , if one had been previously stored. STB  100  then returns to its idle state  800  and continues checking for video frames, the selection of a screen button, remove button messages and timer expirations. 
     STB Processing Where an Application-Specific Interactive Callback Address Package is Transmitted with Program and Identified by a Non-Standard Button Overlay 
     A third embodiment of the processing performed by STB  100  in implementing the system and method according to the present disclosure is shown in  FIG. 11 . The STB  100  process begins when the subscriber  70  turns on the STB  100  to view a program. The STB  100  process initializes into the idle state,  900 . While in the idle state,  900 , the STB  100  checks a number of conditions: it checks whether a video frame has been received; whether a screen button has been selected by viewing subscriber  70 ; whether a “remove button” message has been received with a video frame; and whether a button timer has exceeded a threshold value and thus expired. 
     If a video frame has been received, at  902 , STB  100  enters a new state,  904 , in which it tests the video frame, particularly the VBI of that frame, for the presence of an ICAP associated with the program being viewed. As described above in connection with  FIGS. 4A and 4B , an ICAP is an interactive callback address package, described above as optionally including non-standard or customized button information such as: a) type(s) of buttons; b) description of buttons; c) location of button(s) on screen; d) text of button(s); and e) other characteristics of buttons. As discussed elsewhere in this application, according to the present disclosure, the ICAP could alternatively be transmitted to the STB  100  by any suitable in-band or out-of-band means. 
     If STB  100 , at  906 , detects no ICAP in the given frame, the process returns to state  900 . However, if an ICAP is detected in the received frame, at  908 , STB  100  at  910  stores the ICAP, for example in dynamic memory  1230  (shown in  FIG. 8 ). STB  100  then enters a new state,  912 . 
     At  912 , STB  100  tests the detected ICAP for the presence of custom information relating to the drawing of a screen button to indicate to viewing subscriber  70  that an interactive program is available. If such information related to the configuration of the screen button is found, at  918 , then STB  100  draws a custom button according to this information, at  920 . Also at  920 , STB  100  sets a timer for the screen button, which it will check in order to ensure that the button remains on the screen no longer than a desired maximum time. If the button information was not found in the ICAP, at  914 , then STB  100 , at  916 , draws a standard button on the basis of information stored in static memory  1229 , shown in  FIG. 11 . STB  100 , at  916 , also sets the timer to be later checked in order to ensure that the standard screen button is timely erased. After the button is drawn and the timer is set at  916  or  920 , idle state  900  is resumed. 
     When in the idle state  900 , in addition to testing whether a video frame has been received, as described above, STB  100  also tests whether a screen button, if present on the screen, has been selected by subscribing viewer  70 . STB  100  can access this information, available from IR controller  1232 , via system bus  1224 , as shown in  FIG. 8 . If a button has been selected,  922 , STB  100  at  924  saves in dynamic memory  1230  (shown in  FIG. 8 ) the identity of the channel currently being viewed by subscriber  70 . STB  100 , at  924 , also erases the screen button, thus providing feedback to subscriber  70  that the button has been selected. 
     After the channel has been saved and the button erased, at  924 , STB  100  enters the interactive application state,  926 . In interactive application state  926 , STB  100  establishes an interactive session with interactive server  5  of video service provider  1  over the network by sending a message containing the ICAP using WAN communications processor  1234  and upstream modulator  1236  (shown in  FIG. 8  and described above) over coaxial distribution system  66 , and via remote terminal  65  and network service provider  10  to interactive server  5  of video service provider  1  (shown in  FIG. 1 ). 
     STB  100  remains in the interactive application state,  926 , as long as the interactive application invoked by the ICAP and provided by video service provider  1  has not ended or been terminated by subscribing viewer  70  using IR controller  1232 . If either of these events are detected by STB  100 , at  928 , STB  100 , at  930 , retrieves from dynamic memory  1230  the earlier-stored identity of the channel originally being watched and issues a command to either video decoder  1220  and digital tuner/demodulator  1218 , or to secure processor subsystem  1212  and analog tuner  1210  to retune to that original channel. Also at  930 , STB  100  deletes the ICAP from dynamic memory  1230 . STB  100  then returns to the idle state  900 . 
     In addition to testing in idle state  900  for the reception of video frames and whether a screen button has been selected, STB  100  also conducts a further check. If, at  902 , a video frame has been received but no ICAP has been detected, at  906 , STB  100  checks for a “remove button” message in the VBI of the video frame (or in any other suitable in-band or out-of-band signaling path). STB  100  also periodically checks whether the timer, set at  916  or  920 , has expired. If either a “remove button” message has been received or the expiration of the timer has been detected at  932 , then STB  100  at  934  erases the screen button and deletes the ICAP from dynamic memory  1230 , if one had been previously stored. STB  100  then returns to its idle state  900  and continues checking for video frames, the selection of a screen button, remove button messages and timer expirations. 
     STB Processing Where an Application-Specific Interactive Callback Address and Button Overlay are Both Transmitted with the Program 
     Referring to  FIG. 12 , processing by STB  100  in connection with the fourth embodiment of the system and method according to the present disclosure is shown. In this embodiment, the button indicating the availability of an interactive program is inserted into the signal at its point of origin and thus need not be overlaid by STB  100 . 
     The STB  100  process begins when the subscriber  70  turns on the STB  100  to view a program. The STB  100  process initializes into the idle state,  1000 . While in the idle state,  1000 , the STB  100  checks a number of conditions: it checks whether a video frame has been received; whether a screen button has been selected by viewing subscriber  70 ; and whether a timer has expired by exceeding a threshold value. 
     If a video frame has been received,  1002 , STB  100  enters a new state,  1004 , in which it tests the video frame, particularly the VBI of that frame, for the presence of an ICA associated with the program being reviewed. As discussed elsewhere in this application, according to the present disclosure, the ICA could alternatively be transmitted to the STB  100  by any suitable in-band or out-of-band means. 
     If STB  100  detects, at  1006 , no ICA in the given frame, the process returns to the idle state,  1000 . However, if an ICA is detected in the received frame,  1008 , STB  100 , at  1010 , stores the ICA, for example in dynamic memory  1230  (shown in  FIG. 8 ). STB  100 , also at  1010 , sets the timer. The STB  100  then returns to the idle state,  1000 . No button needs to be drawn, since a button will be present, if at all, in the received broadcast signal and thus on the screen. 
     When in the idle state,  1000 , in addition to testing whether a video frame has been received, as described above, STB  100  also tests whether a screen button, if present on the screen, has been selected by subscribing viewer  70 . STB  100  can access this information, available from IR controller  1232 , via system bus  1224 , as shown in  FIG. 8 . If a button has been selected, at  1012 , STB  100 , at  1014 , saves in dynamic memory  1230  (shown in  FIG. 8 ) the identity of the channel currently being viewed by subscriber  70 . STB  100 , at  1014 , need not erase the screen button, since it was not responsible for overlaying the button. Rather, at the desired time, the button is removed at the point of origin, where it was inserted into the video stream. 
     After the channel has been saved at  1014 , STB  100  enters the interactive application state,  1016 . In the interactive application state,  1016 , STB  100  establishes an interactive session with interactive server  5  of video service provider  1  over the network by sending a message containing the ICA. STB  100  sends the message containing the ICA using WAN communications processor  1234  and upstream modulator  1236  (shown in  FIG. 8  and described above) over coaxial distribution system  66 , and via remote terminal  65  and network service provider  10  to interactive server  5  of video service provider  1  (shown in  FIG. 1 ). 
     STB  100  remains in the interactive application state  1016  as long as the interactive application invoked by the ICA and provided by video service provider  1  has not ended or been terminated by subscribing viewer  70  using IR controller  1232 . If either of these events are detected by STB  100 , at  1018 , however, STB  100  at  1020  retrieves from dynamic memory  1230  the earlier-stored identity of the channel originally being watched. STB  100  then also issues a command to either video decoder  1220  and digital tuner/demodulator  1218 , or to secure processor subsystem  1212  and analog tuner  1210 , to re-tune to the original channel. Also at  1020 , STB  100  deletes the ICA from dynamic memory  1230 . STB  100  then returns to the idle state  1000 . 
     In addition to testing in idle state  1000  for the reception of video frames and whether a screen button has been selected, STB  100  also conducts a further check. If at  1002  a video frame has been received but no ICA has been detected at  1006 , STB  100  checks periodically whether the timer, set at  1010 , has expired. If either the screen button has been removed from the broadcast image at its source or the expiration of the timer has been detected at  1022 , then STB  100  at  1024  deletes the ICA from dynamic memory  1230 , if one had been previously stored. STB  100  then returns to its idle state  1000  and continues checking for video frames, the selection of a screen button, remove button messages and timer expirations. 
     Signaling Between the Set Top Box and the Interactive Server Associated with Establishing an Interactive Session 
     When a subscriber  70  has seen an icon or button on the screen during a particular program, and wishes to view the interactive application, he or she “pushes the button” by sending the appropriate signal to the STB  100  using a suitable user input device, such as IR remote input device  1233 . The signal may be any preselected signal the input device is capable of generating, and the STB  100  is capable of receiving. It could, for example, be one or more existing keys on the IR remote input device  1233 . When the STB  100  receives this preselected signal while in state  712 ,  812 ,  912  or  1012 , depending on the embodiment (in which state STB  100  tests for the selection of a button by viewing subscriber  70 , as described), the STB  100  saves the present channel number in dynamic memory  1230 , initiates an application for setting up an interactive session, including sending a session request message to the network service provider  10 . As defined above, the L1 service, or video dial tone, provided by network service provider  10  represents the data communications phase of a system for providing video services and is the part of that system that is regulated by the FCC. As described above in connection with  FIG. 1 , the network service provider  10  operates the following components: the switch  12 , the network controller  16 , the signal processing equipment  14 , and the RF equipment  25 , and interfaces with the distribution network  50 . 
     The network service provider  10  at the request of STB  100 , is responsible for establishing a session between STB  100  and the interactive server  5 . If a connection with the interactive server  5  is properly established by the network service provider  10  and the interactive server  5  is up and capable of conducting an interactive session, the interactive server  5  sends a session accept message back to the network service provider  10 , which in turn sends a session accept message to the STB  100 . 
     Once the STB  100  has received the session accept message from the interactive server  5  by way of the network service provider  10 , it uses the ICA to send an application ID request message directly via the network service provider  10  (i.e., the network service provider  10  service needs only to transmit but not process the message) indicating the application server  5  with which the session is requested. The network service provider  10  sets up an interactive session with the indicated interactive server  5  and sends a confirmation to the STB  100 . When it has received this confirmation the STB  100  issues a request to the network service provider  10  to connect with the interactive serve  5 . The network service provider  10  then notifies the interactive server  5  of the request. If the interactive server  5  is able to respond to the request, the network service provider  10  establishes a connection between the interactive service  5  and the STB  100 , and the interactive session proceeds. 
     The foregoing describes a preferred embodiment of the present disclosure. Various changes and modifications to what is disclosed may be adopted or implemented without departing from the scope of the disclosure.