Abstract:
A method and apparatus for transport encoded asset data and content data, multiplexing the transport encoded content data with a plurality of NULL transport packets to provide “place holder” for the asset data transport packets, and replacing the NULL transport packets with asset data transport packets prior to transmitting the multiplexed transport stream to a set top box.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of pending U.S. patent application Ser. No. 09/458,896, filed on Dec. 10, 1999, which application claims benefit of U.S. Provisional Patent Application Ser. No. 60/127,126, which was filed on Mar. 31, 1999; both prior applications are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an information distribution system such as a video-on-demand (VOD) system. More particularly, the present invention relates to a method and apparatus for processing content and other assets such that the other assets may be injected into a subsequent content stream.  
         [0004]     2. Description of the Background Art  
         [0005]     Information distribution systems, such as video on demand (VOD) system providing content encoded according to the various Moving Pictures Experts Group (MPEG) standards are known. For example, a first standard known as MPEG-1 refers to ISO/IEC standards 11172, which is incorporated herein by reference in its entirety. A second standard known as MPEG-2 refers to ISO/IEC standards 13818, which is incorporated herein by reference in its entirety. Additionally, a compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, incorporated herein by reference.  
         [0006]     An interactive information distribution system provided by DIVA Systems Corporation of Redwood City, Calif. is described in more detail in U.S. Pat. No. 6,253,375, which is incorporated herein by reference in its entirety. Users or subscribers to the DIVA system select information offerings using a “Navigator” functionality, which is described in more detail in U.S. Pat. No. 6,253,375 and incorporated herein by reference in its entirety. Briefly, the Navigator utilizes a combination of MPEG content (such as MPEG video content and related MPEG audio content) and Navigator asset data to provide viewers with a means of selecting and ordering services. Navigator assets include bitmaps and navigation control scripts. As the set top box user is “navigating,” the set top box extracts the asset data from the transport stream and uses that data to provide bitmap overlays on top of the MPEG content. The control data within the assets is used to define the layout of the screen and to take actions based on viewer input.  
         [0007]     Assets, such as the aforementioned Navigator assets, are typically packaged as MPEG transport packets that are multiplexed along with content-representative MPEG packets to produce a single MPEG transport stream file. The file is then transported to and stored on each of, possibly, many servers for subsequent transmission to the users&#39; set top boxes.  
         [0008]     Unfortunately, embedding assets such as Navigation assets within the content places a severe limitation on changes to the assets. For example, if a bitmap asset must be changed to provide new graphic data, the content files for all navigation screens using that bitmap need to be re-multiplexed, redistributed, and re-loaded onto all servers. Additionally, the multiplexing of the Navigation assets and content results in a duplication of the Navigation asset data within each of a plurality of content streams including the data.  
         [0009]     Therefore, it is seen to be desirable to provide a method and apparatus for inserting assets, such as navigation assets, into a content stream in a manner avoiding the above-described problems.  
       SUMMARY OF THE INVENTION  
       [0010]     The disadvantages heretofore associated with the prior art are overcome by the present invention of a method and apparatus for transport encoding asset data and content data, multiplexing the transport encoded content data with a plurality of NULL transport packets to provide “place holder” for the asset data transport packets, and replacing the NULL transport packets with asset data transport packets prior to transmitting the multiplexed transport stream to a set top box.  
         [0011]     Specifically, in an information distribution system providing content data and asset data to at least one subscriber, an apparatus according to the invention comprises: a NULL packet inserter, for inserting NULL transport packets within a transport stream including content packets; and a transport processor, for replacing at least some of the NULL packets with asset packets to produce a transport stream including content packets and asset packets. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0013]      FIG. 1  depicts a high level block diagram of an interactive information distribution system;  
         [0014]      FIG. 2  depicts a graphical representation of several packetized streams useful in understanding the invention; and  
         [0015]      FIG. 3  depicts a flow diagram of a method for processing content and asset information according to the invention. 
     
    
       [0016]     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION  
       [0017]     While the invention will be primarily described within the context of an interactive information distribution system, it should be noted that the invention has broad applicability to any system in which a data stream generated by combining fixed packet length data sub-streams is subject to regeneration due to, illustratively, modifications or changes made to one of the data sub-streams.  
         [0018]      FIG. 1  depicts a high level block diagram of an interactive information distribution system. Specifically,  FIG. 1  depicts a high level block diagram of an interactive information distribution system  100  containing the present invention. The system  100  contains service provider equipment  102 , a distribution network  104  and subscriber equipment  106   n , where n is an integer greater than zero.  
         [0019]     The service provider equipment  102  comprises a plurality of asset sources  110 , a first transport packetizer  120 , an asset storage module  125 , an encoded content source  130 , a second transport packetizer  135  including a null packet inserter  135 -NP, a content storage module  140  and a session controller  145  including a mapping data memory region  145 -MD, a count memory region  145 -C and a rate memory region  145 -R. The functionality of the service provider equipment  102  may be divided into those functions typically provided by a content development facility (CDF)  102 A and those functions provided by an interactive information distribution system (IIDS)  102 B. A content development facility receives encoded content from, for example, a content encoding facility where Navigation assets and/or other assets are developed or aggregated. The CDF formats the content and assets into, for example, MPEG-2 transport stream files and distributes the resultant files to IIDS locations. The CDF functionality comprises the asset sources  110 , the first transport packetizer  120 , the encoded content source  130  and the second transport packetizer  135 . The operation of the CDF  102 A and IIDS  102 B will be described within the context of a system  100  including all the relevant functions. However, it shall be noted that the CDF functions may be implemented in a CDF that is physically remote from the remaining functions of the system  100 . The CDF functions may also be performed prior to the actual need for the assets and/or content.  
         [0020]     The service provider equipment  102  processes content data and asset data to provide, respectively, a content data transport stream CONTENT and an asset data transport stream ASSETS. The asset data transport stream ASSETS includes a plurality of transport packets carrying asset data. The content data transport stream CONTENT includes a plurality of NULL transport packets interspersed with content transport packets such that the NULL packets “reserve” a portion of the content data stream sufficient to accommodate the asset data packets within the asset data stream ASSETS. The service provider equipment  102 , in response to a subscriber request for a content stream, provides a version of the requested content stream in which some or all of the NULL packets have been replaced by asset data packets. In this manner, the service provider equipment  102  is able to adapt the asset data provided to a subscriber without reprocessing the content data.  
         [0021]     The asset sources comprise, illustratively, bit map imagery  110 - 1 , control scripts  110 - 2  and other assets  110 - 3 . The bit map imagery  110 - 1 , control scripts  110 - 2  and other assets  110 - 3  are provided to the first transport packetizer  120  via respective stream or signal paths A 1 , A 2  and A 3 . The assets may comprise, e.g., Navigation assets that are used by a set top terminal to interactively navigate or view the offerings of the information distribution system  100 . The first transport packetizer  120  packages the received asset streams A 1 -A 3  into appropriate MPEG streams, such as video streams, audio streams, data streams and the like to produce a transport stream TA, illustratively an MPEG-2 transport stream, that is coupled to the asset storage module  125 . Specifically, the transport stream TA (including packaged assets) is distributed from the CDF  102 A to the asset storage module  125  of the IIDS  102 B. The asset storage module  125  communicates with the session controller  145  via an asset control signal ASC to provide storage location information associated with each stored asset stream.  
         [0022]     The encoded content source  130 , illustratively a means of receiving MPEG-2 encoded content and other content from a studio or other source of content, provides a content stream C to the second transport packetizer  135 .  
         [0023]     The second transport packetizer  135  packetizes the content stream C to produce a transport stream TC, illustratively an MPEG-2 transport stream, that is coupled to the content storage module  140 . In response to a control signal RESERVED BANDWIDTH, the null packet inserter  135 -NP of the second transport packetizer  135  operates to intersperse NULL packets with the content packets within the content transport stream TC.  
         [0024]     The number of NULL packets interspersed with the content data packets “reserves” a portion of the content data stream sufficient to, ideally, accommodate all of the asset data packets. That is, the amount of bandwidth to be reserved by interspersing NULL packets (e.g., 300 kilobits per second of a 3.6 Megabits per second bitstream) is indicated to the NULL packet inserter 135-NP via the control signal RESERVED BANDWIDTH. The number of NULL packets may be predetermined or calculated.  
         [0025]     In one embodiment of the invention a default number of NULL packets is inserted into the multiplexed transport stream including null packets and content packets. The default number of NULL packets may be fixed or may be defined as a ratio (e.g., one null packet for every four content packets).  
         [0026]     The session controller  145  (or session manager) provides session control of the information flowing to and from the content  140  and asset  125  storage modules, and may be generally described as a system providing or controlling communications between, e.g., a cable system head-end and one or more set top terminals. The session controller  145  produces an asset storage control signal ASC for controlling and communicating with the asset storage module  125 , a content storage control signal CSC for controlling and communicating with the content storage module  140 , and a transport processor control signal TPC for controlling and communicating with the transport processor  150 .  
         [0027]     The session controller  145  communicates with the asset storage module  125  and content storage module  140  to determine appropriate mapping of content streams or files stored on the content storage module  140  to asset streams or files stored on the asset storage module  125 . This mapping information is stored within the mapping data memory portion  145 -MD of the session controller  145 .  
         [0028]     In one embodiment of the invention, the session controller  145  provides an asset injection rate (AIR) signal and an asset injection count (AIC) signal to the transport processor  150 . The asset injection rate is stored in the rate memory location  145 -R, while the asset injection count is stored in the count memory location  145 -C.  
         [0029]     The asset injection rate (AIR) signal indicates to the transport processor  150  a desired rate at which asset packets should be injected into a content stream including NULL packets. The asset injection rate refers to the number of NULL packets to be utilized for asset transport. A maximum asset injection rate utilizes every NULL packet to transport an asset stream. In lower asset rates, some NULL packets are not utilized.  
         [0030]     The asset injection count (AIC) signal indicates to the transport processor  150  the number of times that a particular asset should be repeated. For example, in response to an AIC signal indicative of a count of three, the transport processor will insert each asset packet into the FATC three times. The three insertions may be consecutive or an entire asset stream may be injected three times.  
         [0031]     In response to a user request for a particular content file, the session controller  145  causes the requested content file to be streamed to the transport processor  150 . Additionally, the session controller  145  utilizes the mapping data  145 -MD to determine which asset data stream or file (if any) is associated with the requested content stream or file. The session controller  145  causes the requested asset file to be streamed to the transport processor  150  from the asset storage module  125 .  
         [0032]     The session controller  145  sends data, such as commands, encryption keys and the like to set top boxes via a forward data channel (FDC). The session controller  145  receives data, such as information stream requests and session initiation data (set top identification, capability, and the like) via a reverse data channel (RDC). The FDC and RDC are supported by the distribution network  104  and comprise relatively low bandwidth data channels, such as 1-2 megabits per second data channels utilizing QPSK, QAM or other modulation techniques. The FDC and RDC are also known as “out of band” channels, where a relatively high bandwidth forward application transport (FAT) channel is known as an “in-band” channel.  
         [0033]     The session controller  145  contains an interface device for sending control information via the forward data channel FDC and receiving control information via the reverse data channel RDC using so-called “out of band” carrier frequencies.  
         [0034]     The transport processor  150  accomplishes all of the forward content channel transmission interface requirements of the system  100  of  FIG. 1 . Specifically, the transport processor  150  is coupled to subscriber equipment via a forward applications transport channel (FATC). The forward application transport channel (FATC) is supported by the distribution network  104  and comprises a relatively high bandwidth communications channel well suited to carrying video, audio and data such as, for example, multiplexed MPEG-2 transport packets. The FATC is also known as the “in-band” communications channel. It should be noted that data normally conveyed to a set top box via the FDC may be included in the FATC data stream.  
         [0035]     The transport processor  150  contains a multiplexer or combiner for detecting NULL packets within the content stream CONTENT, and for replacing some or all of those NULL packets with asset packets from the asset stream ASSET to form a combined content and asset stream. The transport processor  150  also contains a modulator for modulating the combined content and asset stream onto one or more carrier frequencies for transmission on the FATC, the so-called “in band” carrier frequencies.  
         [0036]     The distribution network  104  can be any one of a number of conventional broadband communications networks that are available such as a fiber optic network, a telephone network, existing cable television network and the like. For example, if the network is a hybrid fiber-coax network, the transmission transport technique used in both forward channels may be modeled after the Moving Pictures Expert Group (MPEG) transport protocol for the transmission of video data streams. In general, the transport mechanism for forward and reverse data channels that transport information to and from the set top terminal must be able to carry unidirectional, asynchronous packetized data such as that defined in the MPEG video and audio signal transmission protocol, and the like. There are a number of such transport protocols available.  
         [0037]     The subscriber equipment  106   n  comprises a subscriber or set top terminal or set top box  136 , a display device  140  (e.g., a conventional television) and a user input device  138  (e.g., a remote control). Each set top terminal  136  receives the data streams from the FATC, demodulates the received data streams and, in the case of video streams, processes the demodulated video streams for subsequent display on the display device  140 . In addition, the set top terminal  106  accepts commands from the remote control input device  138  or other input device. Those commands requiring processing at the lead end are formatted, modulated, and transmitted through the distribution network  104  to the session controller  145 . Typically, this transmission is accomplished through the RDC. These commands are preferably transmitted through the same network used to transmit information to the set top terminal. However, the RDC coupling the set top terminal to the server may be a separate network, e.g., a FATC through a television cable network and a RDC through a telephone network. The telephone network could also support the FDC.  
         [0038]     The session controller  145  interprets each command sent from the set top terminal through the RDC and adapts other functional elements (e.g., the storage modules) in response to the subscriber request (e.g., send a requested movie and associated asset data).  
         [0039]     Session control commands, such as navigation commands, are implemented by the session controller  145  with the set top terminal  136 . Each command is implemented by the execution of central scripts by the set top terminal  136 . The central scripts are transmitted to the set top terminal  136  (via the FATC) within the asset data in response to requests transmitted by the set top terminal  136  (via the RDC). It is noted that each control script includes links to other control scripts stored at the IIDS head end  102 B. In this manner, set top terminal memory is conserved. The control scripts control both information sessions, such as the presentation of video to the television screen, and navigator functions, such as menus facilitating selection of a video program. The graphical data and other asset data used to provide the user interface at the set top terminal  136  comprises asset data, such as navigator asset data that is processed by the service provider equipment  102  of the present invention.  
         [0040]      FIG. 2A  depicts a graphical representation of several packetized streams useful in understanding the invention. Specifically,  FIG. 2A  depicts graphical representations of an asset transport stream  210 , a content and NULL transport stream  220  and a content and asset transport stream  230 .  
         [0041]     The asset transport stream  210  is depicted as plurality of asset transport packets, where each transport packet includes a portion of the asset data. The asset data packets are denoted by the letter “A” within the asset stream representation  210 . Illustratively, referring to the system  100  of  FIG. 1 , the. NAVIGATION ASSETS stream provided by the asset storage module  125  to the transport processor  150  is structurally similar to the asset stream representation  210  of  FIG. 2A .  
         [0042]     The content and NULL transport stream  220  is depicted as a plurality of content data transport packets interspersed with NULL transport packets. Specifically, the content and NULL transport stream  220  comprises a repeating sequence of three content data packets followed by a single NULL packet. The content data packets are denoted by the letter “C” while the NULL packets are denoted by the NULL symbol (i.e., “Ø”). Illustratively, referring to the system  100  of  FIG. 1 , the CONTENT stream provided by the content storage module  140  to the transport processor  150  is structurally similar to the content and NULL stream representation  220  of  FIG. 2A .  
         [0043]     Each of the asset data packets A in the asset transport stream  210  is associated with a corresponding NULL packet Ø in the content and NULL transport stream  220 , as indicated by the correspondence arrows T 1 -T 9 . This correspondence is depicted for illustrative purposes only, since there need not be a strict correspondence of particular asset packets to particular NULL packets. It should be noted that NULL packets may be skipped (i.e. unutilized) such that a lower “asset injection rate” is provided. That is, the rate or utilization level of the NULL packets may be reduced by not inserting asset packets into every available NULL packet. The utilization level of the NULL packets may be described in terms of a percentage of available NULL packets, a percentage of available NULL packets for a given period of time (or bandwidth), or any other convenient metric. Moreover, asset packets may be inserted repeatedly into the asset and NULL transport stream, such that an “asset injection count” above unity is provided. That is, the entire asset packet stream may be repeatedly inserted such that a set top terminal may reacquire an asset stream that has been incorrectly acquired. NULL packets may be left unutilized, especially in the case of a relatively small asset stream.  
         [0044]     The content and asset transport stream  230  is depicted as a plurality of content data transport packets interspersed with asset transport packets. Specifically, the content and asset transport stream  230  comprises a repeating sequence of three content data packets followed by a single asset packet. The content data packets are denoted by the letter “C” while the asset packets are denoted by letter “A.” Illustratively, referring to the system  100  of  FIG. 1 , the FATC stream provided by the transport processor to the subscriber equipment  106  includes information streams that are structurally similar to the content and asset stream representation  230  of  FIG. 2 .  
         [0045]     It should be noted that it is not necessary for each NULL packet to be replaced by an asset packet. However, it is preferable to have a sufficient number of NULL packets within the content and NULL packet stream to provide for all of the asset packets to be included in the stream provided to the subscriber. Thus, the transport processor  150  of  FIG. 1  operates to replace either some or all of the NULL packets with the content and NULL packet stream to provide a content and asset stream.  
         [0046]      FIG. 2B  depicts a graphical representation of several packetized streams useful in understanding the invention. Specifically,  FIG. 2B  depicts graphical representations of an asset transport stream  240 , a content and NULL transport stream  250 , and a content and asset transport stream  260 .  
         [0047]      FIG. 2B  differs from  FIG. 2A  in that the content and NULL transport stream  250  includes more frequently interspersed NULL packets (i.e., one NULL packet after every two content packets), and the terminal or end portion of the asset transport stream  240  is depicted. Thus, it is noted that after replacing NULL packets in the content and NULL stream  250  with asset packets found in the asset transport stream  240 , the resulting content and asset transport stream  260  includes a plurality of remaining NULL packets  261 ,  262 .  
         [0048]     With respect to the content and NULL packet transport streams  220  and  250 , it is important to note that the content and NULL transport stream  250  of  FIG. 2B  allocates a larger portion of bandwidth to the transport of asset packets. As previously discussed, a control signal RESERVED BANDWIDTH provided to the second transport packetizer  235  is indicative of an amount of bandwidth to be reserved for the transport of asset packets. Thus, this control signal caused a higher bandwidth allocation for the content and NULL transport stream  250  than for the content and NULL transport stream  220 .  
         [0049]      FIG. 3  depicts a flow diagram of a method for processing content and asset information according to the invention. The method  300  of  FIG. 3  may be considered as several separate methods. Specifically, steps  305  through  320  define a method for processing content information, steps  305  and  330  through  335  define a method for processing asset information and steps  340  through  365  define a method for providing processed content and asset information to a set top terminal.  
         [0050]     At step  305  the MPEG content and navigator aspects for a navigator screen are defined or created. That is, at step  305  the video information, control information and graphical information for, e.g., a navigator screen having respective control, video and graphics layer is defined or created. The method  300  then proceeds to step  310 .  
         [0051]     At step  310  the MPEG content is packetized. That is, at step  310  the MPEG video information defined or created at step  305  is converted into a plurality of information packets, such as MPEG transport packets. This function may be performed by the transport packetizer  135  of the information distribution system  100  of  FIG. 1 . The method  300  then proceeds to step  315 .  
         [0052]     At step  315  the, illustratively, MPEG transport packets including content information are multiplexed with a plurality of null packets. A null packet comprises an MPEG transport packet having no useful information and serving the sole purpose of occupying space within an MPEG transport stream. This function may be performed by the null packet inserter  135 -NP of the system  100  of  FIG. 1 . The method  300  then proceeds to step  320 .  
         [0053]     At step  320  the multiplexed content/null packet stream is stored in, illustratively, the content storage module  140 . The method  300  then proceeds to step  340 .  
         [0054]     The above-described steps ( 310 - 320 ) describe the processing of the content defined or created at step  305 . The asset information defined or created at step  305  is similarly processed as will now be described. It should be noted that the asset processing and content processing may occur sequentially in either order or simultaneously.  
         [0055]     At step  330  the asset streams A 1 -A 3  are packetized into, illustratively, MPEG-2 transport packets and multiplexed to produce a packetized asset stream TA. This function is performed by the first transport packetizer  120  of the system  100  of  FIG. 1 . The method  300  then proceeds to step  335 , where the packetized asset stream TA produced by the transport packetizer  120  is stored in, illustratively, the asset storage module  125 . The method  200  then proceeds to step  340 .  
         [0056]     At step  340  mapping data linking the content and asset data (e.g., navigation screens, MPEG content and navigation assets) is generated. That is, mapping data, which is used to link the multiplexed content/null packet stream stored in the content storage module  140  to the packetized asset stream stored in the asset storage module  125 , is generated such that subsequent processing of the streams by the transport processor  150  may be used to combine video, associated audio, and assets, such as navigation assets. The method  300  then proceeds to step  345 .  
         [0057]     It should be noted that the generation of mapping data is depicted as occurring after the storage of the content TC and asset TA transport streams in the asset storage  125  and content storage  140  modules respectively. However, it will be appreciated by those skilled in the art that mapping data may be produced contemporaneously with the generation of those streams.  
         [0058]     At step  345  the method  300  waits for an set top terminal content request. That is, at step  345  the session controller  145  interacting with a subscriber terminal  136  waits for a request from that subscriber terminal for content stored within the content storage module  140 . The method  300  then proceeds to step  350 .  
         [0059]     At step  350 , in response to the set top terminal content request, mapping data for the requested content is retrieved from the mapping data memory portion  145 -MD of the session controller  145 . The retrieved mapping data is used to identify which packetized asset stream within the asset storage module  125  is associated with the content/null packet stream within the content storage module  140  that has been requested by the set top terminal. The method  300  then proceeds to step  353 .  
         [0060]     At optional step  353 , the session controller  145  provides to the transport processor  150  one or both of the asset injection rate (AIR) parameter and the asset injection count (AIC) parameter. In response, the transport processor  150  adjusts the asset injection rate and/or the number of times an asset is injected (asset injection count).  
         [0061]     At step  355  the stored multiplex/content null packet stream requested by the subscriber and the stored packetized asset stream associated by the mapping data are coupled to the transport processor  150  to be combined.  
         [0062]     At step  360 , null packets within the content/null packet stream retrieved from the content storage module  140  are replaced, as necessary, with asset packets from the packetized asset stream retrieved from the asset storage module  125  (as defined by the mapping data). Thus, in the case of a multiplexed content/null packet stream in which every, for example, fourth transport packet comprises a null packet, sufficient null packets to accommodate the asset packets retrieved from the asset storage module  125  are replaced. Ideally, every null packet will be replaced by an asset packet such that no bandwidth is wasted. However, since it is important to assure adequate levels of system performance and adequate quality of interaction from the point of view of a subscriber, it is likely that an excess number of null packets is advantageously provided such that unusually large asset streams may be accommodated without unduly degrading system performance.  
         [0063]     At step  365  the content stream including the asset packets is provided to the subscriber terminal or STT via the appropriate physical and logical channels. These physical and logical channels are determined at the time the set top terminal establishes a session with the session controller  145 .  
         [0064]     Various modifications to the above-described embodiments are contemplated by the inventor. For example, while the asset and content storage functions are depicted in  FIG. 1  as being implemented using separate asset  125  and content  140  storage modules, a single storage module may be utilized to realize these functions. Moreover, within the context of an information distribution system having a plurality of information servers, these functions may be distributed over several information servers. For example, a central or asset server may be used to hold a “gold” copy of asset data that is periodically used to update asset data stored in other servers along with content data.  
         [0065]     It should be noted that while the function of mapping data between content and asset data is performed with respect to the depicted mapping data  145 -MD element of the session controller  145 , the mapping data  145 -MD may be stored in the single storage module or either of the asset and content storage modules. It is only necessary that the entity controlling the distribution of the content stream CONTENT and the asset stream ASSET utilize the mapping data  145 -MD such that the asset stream appropriate to a requested content stream is provided to the transport processor  150  along with the requested content stream.  
         [0066]     Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.