Patent Publication Number: US-2005138670-A1

Title: Digital video overlay for passive optical networks

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates in general to a passive optical network that is capable of delivering video, voice and data to end-users.  
      2. Description of Related Art  
      Referring to  FIG. 1 , there is a block diagram that shows the basic components of a traditional PON  100  that is capable of delivering video, voice and data to an end-user  102  (one shown). The PON  100  is made from well known components which include an optical line termination module (OLT)  104 , an optical distribution network (ODN)  106  and  15  multiple optical network termination modules (ONTs)  108  (five shown). As shown, the OLT  104  interfaces with a public switched telephone network (PSTN)  110  which enables voice to be delivered to the end-user  102  via a plain old telephone service (POTS) device  112  (e.g., telephone  112 ). In addition, the OLT  104  interfaces with an asynchronous transfer mode/internet protocol (ATM/IP) network  114  which enables data to be delivered to the end-user  102  via a personal computer (PC)  116 . Typically, the voice and data are transmitted to the end-user  102  on a 1480-1500 nm band (e.g., 1490 nm center-wavelength) and received from the end-user  102  on a 1260-1360 nm band (e.g., 1310 nm center-wavelength). Moreover, the OLT  104  interfaces with a video provider  118  which enables video to be delivered to the end-user  102  via a television  120 . A brief description is provided below that describes two known ways that the PON network  100  can be configured to deliver video to the end-user  102 .  
      One known way of configuring the traditional PON  100  so it can deliver video in addition to voice and data to end-users  102  is to use a wavelength division multiplexing (WDM) 1550 nm analog video overlay  122  (e.g., see the ITU-T G983.1 to 8 specification). There are several drawbacks associated with this particular traditional PON  100  including for example: (1) the WDM analog video overlay  122  is “analog”; (2) the WDM analog video overlay  122  does not support evolutions towards video-on-demand or high definition television (HDTV) very well; and (3) the WDM analog video overlay  122  is not compatible with inband video delivery systems that use for example an xDSL infrastructure. Another disadvantage is the cost of the WDM analog video overlay  122  where high power optics are required at the OLT  104  to feed the analog video signal to the ONTs  108 . The high power optics and their supporting amplifiers are expensive because they have high linearity requirements over a broad frequency range.  
      A second known way of configuring the traditional PON  100  so it can deliver video in addition to voice and data to end-users  102  is to integrate inband video streaming equipment  124  into the PON  100 . The main drawbacks associated with this particular traditional PON  100  is that the inband video streaming equipment  124  needs a complicated multicast protocol to avoid duplication of broadcast streams. In addition, the inband video streaming equipment  124  needs an enormous bandwidth to distribute the video signals. The complicated multicast protocol and the enormous bandwidth requirements have an adverse impact on the development resources and potential cost of the inband video streaming equipment  124 . As such, there is a need for a PON network that addresses and solves the aforementioned drawbacks associated with delivering video to an end-user using the traditional PONs. These needs and other needs are addressed by the PON, set-top box and methods of the present invention.  
     BRIEF DESCRIPTION OF THE INVENTION  
      The present invention includes a PON capable of using a WDM 1550 nm digital video overlay to deliver a digital video signal (e.g., analog broadcasted signal) from a video head-end to an end-user. The PON is also capable of transmitting voice and data on a 1480-1500 nm band to the end-user and further capable of receiving voice and data on a 1260-1360 nm band from the end-user. The present invention also includes a set-top box and several methods associated with using the PON. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:  
       FIG. 1  (PRIOR ART) is a block diagram that shows the basic components of a traditional PON that is capable of delivering video, voice and data to an end-user;  
       FIG. 2  is a block diagram that shows an enhanced PON that is capable of delivering video, voice and data to an end-user in accordance with the present invention;  
       FIG. 3A  is a block diagram that shows the basic components of the PON shown in  FIG. 2  that has been enhanced in accordance with a first embodiment of the present invention;  
       FIG. 3B  is a flowchart of the basic steps of a preferred method for using the PON shown in  FIG. 3A  to deliver video from a video head-end to an end-user in accordance with the first embodiment of the present invention;  
       FIG. 3C  is a block diagram that shows an exemplary protocol stack that can be used to implement the PON shown in  FIG. 3A  in accordance with the first embodiment of the present invention;  
       FIG. 3D  is a block diagram that illustrates the basic components of an ONT that is located within the PON shown in  FIG. 3A  in accordance with the first embodiment of the present invention;  
       FIG. 4A  is a block diagram that shows the basic components of the PON shown in  FIG. 2  that has been enhanced in accordance with a second embodiment of the present invention;  
       FIG. 4B  is a flowchart of the basic steps of a preferred method for using the PON shown in  FIG. 4A  to deliver video from a video head-end to an end-user in accordance with the second embodiment of the present invention; and  
       FIG. 4C  is a block diagram that shows an exemplary protocol stack that can be used to implement the PON shown in  FIG. 4A  in accordance with the second embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      Referring to  FIG. 2 , there is a block diagram that shows a PON  200  that is capable of delivering video, voice and data to an end-user  202  in accordance with the present invention. Like the traditional PON  100 , the PON  200  includes an OLT  204 , an ODN  206  and multiple ONTs  208  (five shown). The OLT  204  interfaces with a PSTN  210  which enables voice to be delivered to the end-user  202  via a POTS device  212  (e.g., telephone  212 ). The OLT  204  also interfaces with an ATM/IP network  214  which enables data and inband video to be delivered to the end-user  202  via a PC  216 . Typically, the voice and data are transmitted to the end-user  202  on a 1480-1500 nm band (e.g., 1490 nm wavelength) and received from the end-user  202  on a 1260-1360 nm band (e.g., 1310 nm wavelength). However in contrast to the traditional PON  100 , the PON  200  uses a WDM digital video overlay  218  to deliver a digital video signal  220  on a  1550  nm wavelength (for example) from a video head-end  219  to a television  221  used by the end-user  202 . To implement the WDM digital video overlay  218 , the PON  200  utilizes WDM filters, a modulator (e.g., QAM modulator), a data compression protocol (e.g., MPEG2, MPEG4) and a transport protocol (e.g., Ethernet). A more detailed description about how two different embodiments of the PON  200  can utilize the WDM filters, the modulator, the data compression protocol and the transport protocol to enable the WDM digital video overlay  218  are described in detail below with respect to  FIGS. 3 and 4 .  
      Referring to  FIGS. 3A-3D , there are shown three block diagrams and a flowchart associated with a first embodiment of the PON  200   a  in accordance with the present invention. The PON  200   a  includes an OLT  204   a,  an ODN  206   a  and multiple ONTs  208   a  (five shown). Certain details associated with the components within the OLT  204   a,  ODN  206   a  and ONT  208   a  are well known in the industry. Therefore, for clarity, the description provided below in relation to the PON  200   a  omits those well known details and components that are not necessary to understand the present invention.  
      As can be seen, the OLT  204   a  interfaces with a PSTN  210   a  which enables voice to be delivered to the end-user  202   a  via a POTS device  212   a  (e.g., telephone  212   a ). The OLT  204   a  also interfaces with an ATM/IP network  214   a  which enables data to be delivered to the end-user  202   a  via a PC  216   a.  Moreover, the OLT  204   a  interfaces with a video-head end  219   a  to deliver one or more digital video signals  220   a  to a set-top box  226   a  and display  228   a  (e.g., television  228   a ) which are used by the end-user  202   a.    
      The video-head end  219   a  is the video source for the PON  200   a.  The video-head end  219   a  interfaces with a broadcast receiver  230   a  and an enhanced video content provider  232   a . The broadcast receiver  230   a  is used to receive analog and digital broadcasted television signals (or high definition television signals). The analog broadcasted television signals need to be digitized. And, then the digitized analog and the digital broadcasted television signals are encoded with an appropriate video data compression encoding scheme such as MPEG2 or MPEG4 (for example). The digital signals  220   a  are then transported to a distribution device  234   a  that can be co-located with the OLT  204   a.  The transport protocol can be Gigabit Ethernet (for example). Whereas, the video content provider  232   a  can supply digital video signals  220   a  (including high definition television signals  220   a ) from services like Video On Demand (VoD) and Pay Per View (PPV). The video content provider  232   a  typically supplies digital video signals  220   a  that are already digitized and encoded in the appropriate format. However, the video-head end  219   a  may need to encrypt the VoD and PPV digital video signals  220   a  to ensure privacy and to prevent unauthorized end-users  202   a  from viewing the material without payment. Moreover, the video head-end  219   a  may need to receive information (authorization and authentication information) about the appropriate end-users  202   a  to determine the destinations of those end-users  202   a  before it can supply VoD and PPV digital video signals  220   a.  This information could be provided via an upstream PON data link from the ONT  208   a  (see  FIG. 3D ).  
      As described above, the video-head end  219   a  interfaces with the distribution device  234   a  which is typically co-located with the OLT  204   a.  The distribution device  234   a  includes an optical transmitter  236   a  that transmits the digital video signals  220   a  to a WDM filter  238   a.  The optical transmitter  236   a  feeds the WDM filter  238   a  using the appropriate wavelength (e.g., 1550 nm center-wavelength) to fit into the WDM scheme specified by the PON  200   a.  It should be appreciated that Gigabit Ethernet has been specified for several wavelengths, one of them being 1550 nm. In the case of distributing specialized video content such as VoD or PPV digital video signals  220   a,  the distribution device  234   a  may need to perform port selection tasks to select the correct ports which select the correct PON trees that serve the appropriate end-users  202   a . This information could be provided by the video head-end  219   a.    
      After the WDM filter  238   a  receives (step  302  in  FIG. 3B ) the digital video signals  220   a  (e.g. MPEG2 encoded PPV digital video signals  220   a ) from the video-head end  219   a  and the distribution device  234   a.  Then the WDM filter  238   a  multiplexes (step  304 ) the digital video signals  220   a  and outputs (step  306 ) a multiplexed digital video signal  220   a  on an optical fiber  239   a  to the ONT  208   a.  The ONT  208   a  and in particular a WDM filter  240   a  receives and demultiplexes (step  308 ) the multiplexed digital video signal  220   a  from the data signal and voice signal. The WDM filter  240   a  then outputs demultiplexed digital video signals  220   a  to a modulator  242   a  (e.g., QAM modulator  242   a ) shown located in the ONT  208   a.  The modulator  242   a  receives and modulates (step  310 ) the demultiplexed digital video signals  220   a  and then outputs (step  312 ) the modulated digital video signals  220   a  over a co-axial cable  243  (for example) to the set-top box  226   a.    
      The set-top box  226   a  includes a tuner  244   a  that downconverts to baseband a selected carrier of one of the modulated digital video signals  220   a  based on a channel selected by the end-user  202   a . The set-top box  226   a  also includes a demodulator  246   a  (e.g., QAM demodulator  246   a ) that translates the baseband video signal  220   a  back into a digital video signal  220   a.  This digital video signal  220   a  is then decoded with a decoder  248   a  (e.g., MPEG decoder  248   a ). The decoded video signal  220   a  is fed over a co-axial cable (for example) to a video port or S-video port in the television  228   a.  Or, the decoded digital video signal  220   a  can be RF modulated (NTSC or PAL) and sent to the television  228   a.  For a more detailed discussion about one way to implement this WDM digital video overlay reference is made to the description provided below that is associated with  FIG. 3C  which shows the protocol stack for the PON  200   a.    
      Referring to  FIG. 3C , there is a diagram illustrating in greater detail exemplary protocol stacks associated with the video-head end  219   a,  the PON  200   a,  the set-top box  226   a  and the television  228   a.  It should be understood that for clarity many of the details associated with each protocol are well known to those skilled in the art and as such are not described in detail herein.  
      The video-head end  219   a  has a protocol stack which includes at least the following layers:  
                               Video-head end 219a                                            Video Source           MPEG Encode           IP           Ethernet           P2P fiber                      
 
      The video-head end  219   a  is connected to the OLT  204   a  which has a protocol stack with at least the following layers:  
                               OLT 204a                                                Ethernet   Ethernet           P2P Fiber   WDM/PON                      
 
      This exemplary protocol stack indicates that the OLT  204   a  converts the physical layer from point-2-point fiber (such as Gigabit Ethernet) to WDM over PON while the layer above (such as Ethernet) remains untouched. The OLT  204   a  is connected to the ONT  208   a  which has a protocol stack with at least the following layers:  
                               ONT 208a                                                IP               Ethernet   QAM Mod.           WDM/PON   COAX                      
 
      This exemplary protocol stack indicates that the transport layers (IP and Ethernet) are terminated in the ONT  208   a  and the video channels  220   a  are modulated and then transported further using COAX. The ONT  208   a  is connected to the set-top box  226   a  which has a protocol stack with at least the following layers:  
                               Set-top box 226a                                                Digital/Analog               MPEG Decoding           QAM Demodulation   RF Modulation           COAX   COAX                      
 
      It should be appreciated that the set-top box  226   a  can be a legacy set-top box  226   a  such as “commodity” satellite receiver set-top box which has a large bandwidth capability. If a legacy set-top box  226   a  is used then the modulator  242   a  would need to be selected to interface with the set-top box  226   a.  The set-top box  226   a  is connected to the television  228   a  which has a protocol stack with at least the following layers:  
                               Television 228a                                            Television           COAX                      
 
      As shown in  FIG. 3C , it can be seen that the connection between the video-head end  219   a  and the ONT  208   a  is basically Ethernet (with on top of that maybe IP). This architecture has some advantages such as: 
          Maximum reuse of commodity Ethernet technology including the optics feeding into the WDM filter  238   a.       Flexible topology allows for multiple video sources to interface with the PON  200   a.  This architecture is very suitable for the model where both broadcast video and specialized video (such as PPV, VoD) can be delivered to the end-user  202   a .        

      A drawback of the architecture shown in  FIG. 3C  is that each ONT  208   a  needs to have a modulator  242   a  (e.g., QAM video modulator  242   a ) designed to interface with the set-top box  226   a  (e.g., “commodity” set-top box  226   a ). And, if a QAM video modulator  242   a  is used then it needs to model somewhere between  40  to  150  carriers which involves a lot of digital signal processing. A possible solution to the drawback associated with the QAM modulator  242   a  would be to only modulate the digital video signals  220   a  (channels) that the set-top box  226   a  has selected to demodulate but this would require a management channel between the set-top box  226   a  and ONT  208   a.    
      Referring now to  FIG. 3D , there is shown a block diagram that illustrates in greater detail the basic components of the ONT  208   a.  Certain details associated with the components like the E/O receiver  250   a,  the PON-PHY (such as BPON, EPON or GPON)  252   a , the PON TC  254   a,  the Ethernet component  256   a  and the CODEC &amp; SLICS  258   a  within the ONT  208   a  are known in the industry. Therefore, for clarity, the description provided below in relation to the ONT  208   a  omits details about those components and other components not necessary to understand the present invention.  
      As can be seen, the ONT  208   a  in addition to components  250   a,    252   a ,  254   a,    256   a  and  258   a  includes the WDM filter  240   a  which is used to separate the voice/data upstream and downstream from the digital video signal overlay downstream. The ONT  208   a  also includes a digital video receiver  260   a  that receives the digital video signal  220   a  on the 1550 nm wavelength (for example) and synchronizes the datastream of the received digital video signal  220   a  using basic framing applied on a physical layer. Once synchronization is established, the digital video receiver  260   a  filters the digital video signal  220   a  that is then sent to the modulator  242   a  which manipulates the video signal  220   a  so that is interoperable with the set-top box  226   a.  In the situation where the digital video signals  220   a  are VoD or PPV digital video signals  220   a,  then the digital video receiver  260   a  may need to receive information from the inband PON data stream (e.g., Ethernet device  256   a ) so that it can de-encrypt the VoD or PPV digital video signal  220   a.  Alternatively, the set-top box  226   a  can decode the encrypted VoD and PPV video signals  220   a.    
      As described above, the modulator  242   a  can be a QAM modulator  242   a  which is able to modulate the digital video signals  220   a  into the available frequency spectrum so they can be transported to the set-top box  226   a.  It is well known that the capacity of a single QAM modulated signal depends on constellation size and symbol-rate. And, that a higher constellation size is more spectral efficient and as such allows more data capacity. However a higher constellation size also requires a larger signal-to-noise (SNR) ratio to maintain the desired SNR ratio. In view of these facts and since the set-top box  226   a  is typically located relatively close to the television  228   a  this allows the use a very large bandwidth such as 2 GHz (for example). Consequently, the QAM symbol rate can be very large (e.g., up to 45 Msps) which allows for very small constellation sizes. BPSK and QPSK are other modulation schemes that could be used this environment. And, in the application where a coax-cable or terrestrial distribution network is used to connect the set-top box  226   a  to the television  228   a  then the available bandwidth would be more restrictive. In this case, the QAM modulated carriers are restricted to 6, 7 or 8 MHz in order to remain compatible with the analog RF modulated NTSC, PAL or SECAM video channels. In these environments 64-QAM or 256 QAM are the typical modulation schemes that can be used to achieve a higher spectral efficiency. Again, the choice of modulation schemes such as QAM, BPSK or QPSK used by the modulator  242   a  can be dictated by the type of set-top box  226   a  selected to be used in the present invention.  
      Referring to  FIGS. 4A-4C , there are shown two block diagrams and a flowchart associated with a second embodiment of the PON  200   b  in accordance with the present invention. The PON  200   b  includes an OLT  204   b,  an ODN  206   b  and multiple ONTs  208   b  (five shown). Again, certain details associated with the components within the OLT  204   b,  ODN  206   b  and ONT  208   b  are well known in the industry. Therefore, for clarity, the description provided below in relation to the PON  200   b  omits those well known details and components that are not necessary to understand the present invention.  
      As can be seen, the OLT  204   b  interfaces with a PSTN  210   b  which enables voice to be delivered to the end-user  202   b  via a POTS device  212   b  (e.g., telephone  212   b ). The OLT  204   b  also interfaces with an ATM/IP network  214   b  which enables data to be delivered to the end-user  202   b  via a PC  216   b.  Moreover, the OLT  204   b  interfaces with a video-head end  219   b  (similar to video-head end  219   a ) to deliver one or more digital video signals  220   b  to the end-user  202   b  via a set-top box  226   b  (similar to set-top box  226   a ) and a display  228   b  (e.g., television  228   b ). To accomplish this, the OLT  204   b  and in particular a co-located modulator  242   b  (e.g., QAM modulator  242   b  shown within the distribution device  234   b ) receives (step  402  in  FIG. 4B ) the digital video signals  220   b  (e.g. MPEG2 encoded PPV digital video signals  220   b ) from the video-head end  219   b  and the distribution device  234   b.  Then the modulator  242   b  modulates (step  404 ) the digital video signals  220   b  and outputs modulated digital video signals  220   b  to the WDM filter  238   b.  The WDM filter  238   b  multiplexes (step  406 ) the modulated digital video signals  220   b  and outputs (step  408 ) a multiplexed modulated digital video signal  220   b  on an optical fiber  239   b  to the ONT  208   b.  The ONT  208   b  and in particular a WDM filter  240   b  receives and demultiplexes (step  410 ) the multiplexed modulated digital video signal  220   a  from the data signal and voice signal. The WDM filter  240   a  then outputs (step  412 ) the demultiplexed modulated digital video signals  220   b  over a co-axial cable (for example) to the set-top box  226   b.    
      The set-top box  226   b  includes a tuner  244   b  that downconverts to baseband a selected carrier of one of the modulated digital video signals  220   b  based on a channel selected by the end-user  202   b.  The set-top box  226   b  also includes a demodulator  246   b  (e.g., QAM demodulator  246   b ) that translates the baseband video signal  220   b  back into a digital video signal  220   b.  This digital video signal  220   b  is then decoded with a decoder  248   b  (e.g., MPEG decoder  248   b ). The decoded video signal  220   b  is fed over a co-axial cable (for example) to a video port or S-video port in the television  228   b.  Or, the decoded digital video signal  220   b  can be RF modulated (NTSC or PAL) and sent to the television  228   b.  For a more detailed discussion about one way to implement this WDM digital video overlay reference is made to the description provided below that is associated with  FIG. 4C  which shows the protocol stack for the PON  200   b.    
      Referring to  FIG. 4C , there is a diagram illustrating in greater detail exemplary protocol stacks associated with the video-head end  219   b,  the PON  200   b,  the set-top box  226   b  and the television  228   b.  It should be understood that for clarity many of the details associated with each protocol are well known to those skilled in the art and as such are not described in detail herein.  
      The video-head end  219   b  is associated with a protocol stack which includes at least the following layers:  
                               Video-head end 219b                                            Video Source           MPEG Encode           IP           Ethernet           P2P fiber                      
 
      The video-head end  219   b  is connected to the OLT  204   b  which has a protocol stack with at least the following layers:  
                               OLT 204b/Distribution Device 234b                                                IP               Ethernet   QAM Modulator           P2P Fiber   WDM/PON                      
 
      The OLT  204   b /distribution device  234   b  is connected to the ONT  208   b  which has a protocol stack with at least the following layers:  
                               ONT 208b                                                WDM/PON   COAX                      
 
      The ONT  208   b  is connected to the set-top box  226   b  which has a protocol stack with at least the following layers:  
                               Set-top box 226b                                                Digital/Analog               MPEG Decoding           QAM Demodulation   RF Modulation           COAX   COAX                      
 
      Again, it should be appreciated that the set-top box  226   b  can be a legacy set-top box  226   b  such as “commodity” satellite receiver set-top box which has a large bandwidth capability. The set-top box  226   b  is connected to the television  228   b  which has a protocol stack with at least the following layers:  
                               Television 228b                                            Television           COAX                      
 
      As shown in  FIG. 4C , it can be seen that the QAM complexity is reduced in PON  200   b  because one QAM modulator  242   b  is used by the OLT  204   b  as compared to the first embodiment of the PON  200   a  which has a QAM modulator  242   a in each one of the ONTs  208   a  (see  FIG. 4A ). One possible drawback of associating the QAM modulator  242   b  with the OLT  204   b  is that the linearity and SNR requirements are increased on the optical transmitter  236   b  that feeds the digital video signals  220   b  into the WDM filter  238   b.  Nevertheless these requirements are still quite relaxed as compared to the traditional PON  100  that uses the WDM analog video overlay  122  (see  FIG. 1 ). It should also be appreciated that the PON  200   b  could use ONTs  208   b  that are similar to the ONTs used in the traditional PON  100  that uses the WDM analog video overlay  122  so long as the utilized spectrum by the centralized QAM modulator  242   b  associated with the OLT  204   b  corresponds to the band in the analog path which can be up to 550-750 MHz for NTSC.  
      It should be appreciated that protocols used to describe the two PONs  200   a  and  200   b  above are exemplary and that there are many different types of protocols that could be used to implement the PONs  200   a  and  200   b.    
      Referring to both embodiments of the PON  200 , it can be seen that the WDM digital video overlay can reuse mature technologies such as MPEG2 and MPEG4 for data-compression and Ethernet as a transport protocol. By reusing these technologies, the WDM digital video overlay can be implemented with minimal changes to the basic PON. In addition, since MPEG2 is already used to compress digital video signals for satellite broadcast this means that the set-top box  226  can be the same as or similar to a traditional satellite set-top box. Moreover, since Gigabit Ethernet which has a payload of 1 Gbps is already used to connect Local Area Networks (LANs) and IP switches this means that the distribution of digital video signals  220  could be implemented by reusing off-the shelf Gigabit Ethernet switches. If Gigabit Ethernet is used it can deliver up to 250 TV channels or 50 HDTV channels or any linear combination of these two simply by allocating 4 Mbps for a normal TV channel and 20 Mbps for a HDTV channel. And, as the data compression technology evolves it is believed that the next generation Ethernet standard will be able to deliver 10 Gbps which enables the amount of channels that can be delivered via this infrastructure to grow dramatically over the next few years.  
      In addition, if the PON  200  utilizes an Ethernet based WDM digital signal overlay then the PON  200  can reuse some parts of the IEEE EFM EPON specification. For example, the EPON specification requires that every ONT receives the full digital signal content. And, if the PON  200  reuses the ONT that is based on the EPON specification then the specialized content like VoD and PPV digital video signals  220  destined for specific users  202  would have to be filtered in the ONT  208 . However, this is not believed to be a security risk since the same digital signal broadcast concept with content filtering in the ONT is also applied for the data path in both the EPON and APON specifications.  
      Lastly, it should be noted that since the PON  200  has a downstream digital video broadcast then there is no need for a point-2-multipoint TDMA based MAC layer, no management to guarantee fair upstream bandwidth allocation, not even an ONT ranging protocol. In other words, the architecture of the PON  200  can be characterized as a “dumb”, always on downstream video channel or as a big “dumb” bitpipe if you will, with basic framing on the Physical layer to enable each ONT  208  to ‘lock in’ without requiring direct feedback to the digital OLT  204 . This “dumb” bitpipe can be considered as a satellite replacement delivery vehicle.  
      Following is a list of some of the other features and advantages associated with the present invention: 
          The PON that utilizes the WDM digital video overlay can be used with any standard and is not restricted to any particular standard or specification such as the EPON (specified by IEEE), the APON and the GPON (per ITU-T recommendations).     The PON using the WDM digital video overlay can effectively lower the required bandwidth in the PON-OLT Telecom Equipment while still delivering digital broadcast video.     The television can be any ‘off the shelf’ device that translates the video signal provided by the set-top box into video and audio that can be viewed and heard by the end-user.     The set-top box can be a satellite receiver which can handle a relatively large bandwidth (2000 MHz) and use BPSK or QPSK modulation. As such, the satellite receiver set-top boxes may be a better match for a PON platform that has virtually ‘unlimited’ bandwidth potential. One exemplary satellite receiver set-top box that is commercially available is the Conextant CX24110 which has a QPSK/BPSK demodulator IC with internal dual analog-to-digital converters, digital demodulation, and forward-error correction (FEC). The demodulator IC provides digital derotation, digital filtering, equalization, and Viterbi/Reed-Solomon FEC. This satellite receiver set-top box is also compliant with the DVB (ETS  300 - 421 ) specification for satellite transmission.     The PON that delivers video signals using a digital video overlay via WDM can use the same 1550 nm wavelength as would be used if the PON implemented an analog video overlay via WDM.     This architecture provides a quick and economical roadmap to broadcast video delivery over the PON network while at the same time allowing more enhanced video services such as HDTV and Video-On-Demand.        

      Although several embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.