Abstract:
Highly asymmetrical nature of digital video allows a single Cable Modem Termination System (CMTS) like device to support the transmission over a thousand individual high-quality IP packetized video data channels terminating into low cost cable modem units. A Video Modem Terminating System (VMTS) unit handles housekeeping information. As the amount of upstream housekeeping data are small, even for 1000 simultaneous TV channels, the data can be inserted into the digital video cell streams and packaged within IP packet envelopes. The VMTS unit is equally effective for MPEG-2, MPEG-4, Microsoft Media 9 and other digital encoding of video and audio signals.

Description:
RELATED PATENTS  
       [0001]     This patent stems from a U.S. provisional patent application Ser. No. 60/531,655, and filing date of Dec. 23, 2003, entitled VIDEO MODEM TERMINATION SYSTEM, by inventor, DAVID BARAN. The benefit of the earlier filing date of the provisional patent application is claimed for common subject matter. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention reduces the cost of delivering digital IP video TV signals to the home over cable and systems in general, and more particularly, utilizing the asymmetrical nature of video transmission.  
       DESCRIPTION OF THE RELEVANT ART  
       [0003]     Cable operators desire to send digital video as Internet Protocol (IP) video, as used on the Internet, via their present inexpensive Data Over Cable Service Interface Specification (DOCSIS) cable modems, which uses IP packets. The cost limitation of video over DOCSIS channels is that a separate expensive Cable Modem Termination System (CMTS) is required for each 6 MHz downstream channel. The DOCSIS Cable Modem Terminating System (CMTS) is defined in ANSI/Society of Cable Television Engineers (SCTE) specifications 22-1, 22-2, 22-3, 23-1, 23-3 and additionally in CableLabs&#39; specifications SP-RFIv2.0, SP-OSSIv2.0, SP-BPI+, SP-BPI, SP-CMCI, and SP-CMTS-NSI and are manufactured by several companies. Highly similar units are made in accordance with the Euro-DOCSIS standard, which is defined by several appendices in the previously listed specifications, and are optimized for the European 8 MHz channelized cable systems instead of the 6 MHz channels used in North America. The term “CMTS”, as used herein, applies to devices constructed to either specification. A representative prior art CMTS unit is shown in  FIG. 1 . The CMTS unit includes a WAN/LAN interface  101 , a fast path processor  102 , a management processor  103 , a downstream modulator  104 , a DOCSIS media access and control processor  105 , an upstream receiver  106 , an up-converter  107 , and a subscriber&#39;s cable or video modem  108 . The WAN-LAN interface  101  is connected to the management processor  103  and the fast path processor  102 . The fast path processor is connected to the downstream modulator  104 , and the upstream receiver  106 . The management processor is connected to the DOCSIS access and control processor  105 . The downstream modulator  104  is connected to the up-converter  107  and the DOCSIS media access and control processor  105 . The DOCSIS media access and control processor  105  is connected to the upstream receiver  106 . The subscriber&#39;s cable or video modems  108  are connected to the upstream receiver  106  and the up-converter  107 .  
         [0004]     The upstream receiver  106  typically is a wideband digital receiver. The upstream receiver  106  has at least one, and may have six or more, wideband digital receivers. More may be used, for particular applications and alternative cable network topologies.  
         [0005]     The WAN/LAN interface  101  connects to Ethernet at 10/100/1000 data rates. Twisted pair or optical fiber currently are used as the physical media. The fast path processor  102  passes data from the upstream receiver  106  to the WAN/LAN interface  101 . The fast path processor  102  also passes data from the WAN/LAN interface  101  to the downstream modulator  104 . The term “fast path” comes from the fact that this processor is involved with all data transfers into or out of the CMTS, and thus must be “fast” to avoid producing undesirable packet latency or loss. The downstream modulator  104  passes the modulated data to the up-converter  107 , which sends data, typically in the radio frequency range greater than 80 MHz, to the subscriber&#39;s cable or video modems  108 . The management processor  103  is responsible for scheduling transmissions over the cable network as well as providing system status information using protocols such as SNMP.  
         [0006]     Received data, typically in the radio frequency range greater than 80 MHz, from the subscriber&#39;s cable or video modems  108 , are received by the downstream receiver  106 . SNMP and related management control are performed by management processor  103 . DOCSIS media access and control processor  105  controls the downstream modulator  104  and the upstream receiver  106 .  
         [0007]     As CMTS units are very expensive, a separate CMTS unit or even a CMTS blade, i.e., a plug in card within a larger chassis, within a larger CMTS chassis required for each 6 MHz channel makes this approach economically infeasible for video distribution. Unlike the case for digital video CMTS units are cost effective for data because a single CMTS is able to handle more than a thousand data users reducing the cost per user. But as each 6 MHz channel supports only about 10 MPEG digital video channels using, for example, 64-QAM modulation, if an expensive CMTS unit was required for each 6 MHz channel, the resulting cost would be prohibitive.  
         [0008]     One alternative approach is to use a dedicated CMTS unit to deliver control information combined with an apparatus such as an edge QAM modulator, or one or more QAM modulators, to generate multiplicity of 6 MHz QAM modulated channels dedicated to carrying digital TV. This approach is workable, but two separate tuners are required for each set top unit. One tuner in each set top is needed for video and the other for DOCSIS control signals.  
         [0009]     Today&#39;s cable systems send digital video as MPEG cells, i.e., packets, on 6 MHz QAM modulated TV channels to set top units. As a separate set top is required for each separate TV set and as their cost is high, today&#39;s set top costs form an economic impediment to the all-digital cable evolution.  
       SUMMARY OF THE INVENTION  
       [0010]     A general object of the invention is to remove the need for a separate CMTS unit for each 6 MHz video channel.  
         [0011]     A second objective is to reduce the cost of the set-top unit by eliminating the need for a second tuner or cable modem in each set-top unit. This is accomplished by replicating the downstream cable modem control signals in each 6 MHz channel containing digital video date by interspersing it into unused cell positions and concatenating the upstream cable modem signal for all set-top units into a single dedicated Video Modem Terminating System (VMTS) unit, which controls all of the downstream channels.  
         [0012]     Accordingly, the present invention, as embodied and broadly described herein, takes advantage of the highly asymmetrical nature of digital video and uses a single CMTS-like device to support the transmission over a thousand individual high-quality IP packetized video data channels terminating into low cost cable modem units that essentially perform the major functions of the set-top unit. This new invention is called a video modem terminating system (VMTS). The VMTS unit provides a mechanism for delivering a high volume of downstream traffic both on dedicated DOCSIS downstream carriers as well as intermixed with MPEG2 video downstreams. In addition, VMTS unit manages the critical timing necessary to fully utilize the DOCSIS upstream. The VMTS unit handles housekeeping information. It will be appreciated that this approach is equally effective for MPEG-2, MPEG-4, Microsoft Media 9 and other digital encodings of video and audio signals.  
         [0013]     The invention includes an edge QAM modulator used with a plurality of set-top units. The invention reduces the equipment required for the downstream transmission of digital video data to a plurality of set-top units. The edge QAM modulator transmits a plurality of downstream radio frequency (RF) carriers. Each carrier conveys a multiplicity of video, audio and control packet streams, individually directed to each of the plurality of set-top units. This creates a virtual circuit to each set-top unit in the plurality of set top units  
         [0014]     Each set-top unit in the plurality of set top units includes a receiver tuner and circuitry for receiving and decoding the downstream signals uniquely addressed to each set-top unit in the plurality of set top units. Each set-top unit receives TV remote control signals and forming packets and directing the packets upstream to a single common shared CMTS unit.  
         [0015]     Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention, and together with the description serve to explain the principles of the invention.  
         [0017]      FIG. 1  is a block diagram of a prior art conventional CMTS unit;  
         [0018]      FIG. 2  is a block diagram of the preferred implementation of a VMTS system;  
         [0019]      FIG. 3  is a representation of MPEG digital packets showing the addition of headers and trailers as used in this invention;  
         [0020]      FIG. 4  is the same as  FIG. 3 , except that  FIG. 4  shows the addition of headers and trailers as used in this invention when the incoming packet is already an IP packet, as used by PC-based protocols such as Windows Media from Microsoft or Real Media from Real Networks;  
         [0021]      FIG. 5  is a block diagram showing the simultaneous processing of IP and MPEG packets in the downstream, to the user, direction;  
         [0022]      FIG. 6  is a flow chart of the processing within the VMTS;  
         [0023]      FIG. 7  is a representation of the contents of the MPEG-2 packet format used by the Data Over Cable Service Interface Specification (DOCSIS) protocol in the context of locating a media access and control (MAC) message with the underlying transport frame;  
         [0024]      FIG. 8  is a representation of the structure of a DOCSIS PDU packet;  
         [0025]      FIG. 9  is a block diagram showing the overall system configuration including the source of programming to the end set-top unit;  
         [0026]      FIG. 10  is the layout of a DOCSIS Media Access and Control (MAC) message packet; and  
         [0027]      FIG. 11  is the layout of the header fields of a DOCSIS MAC or data packet. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     Reference now is made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.  
         [0029]     Today&#39;s inexpensive standard Data Over Cable Service Interface Specification (DOCSIS) 1.1 cable modems are generally able to support a 100 Mbps Ethernet connection, while the actual data stream delivered today, is restricted to 1 to 2 Mbps, peak for the cable operator&#39;s convenience. Each 6 MHz RF channel presently supports up to about 40 Mbps per 6 MHz channel using 256 QAM modulation. The approach described here also is applicable to the EuroDOCSIS standard, which uses an 8 MHz channel to achieve a 25% higher data rate. In the present invention a single Video Modem Terminating System (VMTS) unit is used to handle the housekeeping information and synchronization data, while the bulk video is sent in the form of IP packets over a plurality of 6 MHz channels without requiring a CMTS to be used. For each channel, the standard DOCSIS cable modem is able to handle these packets and output them to an Ethernet connector, which is the most common interface, used. The interface may include a low voltage data signal (LVDS). The DOCSIS cable modem uses the Baseline Privacy (BPI) security arrangement as part of the DOCSIS specification to provide a very secure path. Each DOCSIS system also includes a mechanism for preventing counterfeiting of customer premise equipment through a digital certificate hierarchy known as BPI+. Together, these methods provide a very strong security mechanism against signal theft and service theft. In the pre-digital area, theft of this nature has been known to constitute about 11% of a cable operator&#39;s subscriber base. Thus in the present invention the digital video can be securely transmitted and the necessity for the non-standard encryption process presently used by Conditional Access systems is no longer needed. The term Conditional Access relates to the means used by a cable system to ensure that only authorized subscribers&#39; set-top units are able to receive particular content to which they are entitled.  
         [0030]     In the exemplary arrangement shown in  FIG. 2 , the VMTS includes, by way of example, a plurality of ASI or Gigabit Ethernet inputs  205 ,  211 ,  215 ,  219 , a plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220 , a MPEG stream multiplexer  207 , a plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221 , a plurality of up-converters  209 ,  214 ,  218 ,  222 , an output-to-cable network combiner  210 , a WAN/LAN interface  101 , a management processor  103 , a DOCSIS media access and control processor  105 , an upstream receiver  106 . The upstream receiver  106  and the output-to-cable network combiner  210  are connected to a subscriber&#39;s cable or modem  108 . The WAN/LAN interface is coupled through the management processor  103  and the DOCSIS media access and control processor  105  to the upstream receiver  106 . ASI refers to the “asynchronous serial interface” of the MPEG transport stream protocol. Annexes of the ITU-J83 specification describe forward error correction and encoding used.  
         [0031]     The plurality of ASI inputs  205 ,  211 ,  215 ,  219  is connected to the plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220 , respectively. The plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220  is connected to the MPEG stream multiplexer  207 . The MPEG stream multiplexer  207  is connected to the DOCSIS media access and control processor  203  and to the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221 . The plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  is connected to the plurality of up-converters  209 ,  214 ,  218 ,  222 , respectively. The plurality of up-converters  209 ,  214 ,  218 ,  222  is connected to the output-to-cable network combiner  210 .  
         [0032]     Received data from the subscriber&#39;s cable or video modems  108  are received by upstream receiver  106 . The received data are pass through the DOCSIS media access and control processor  105 , through the management processor  103  to the WAN/LAN interface  101 .  
         [0033]     Data from the plurality of ASI inputs  205 ,  211 ,  215 ,  219  are passed to the plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220 , respectively. Wrapped data from the plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220  are passed to the MPEG stream multiplexer  207 . Data from the MPEG stream multiplexer  207  are passed to the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221 . Data from the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  are up-converted to an appropriate RF frequency, currently above 80 MHz, by the plurality of up-converters  209 ,  214 ,  218 ,  222 , respectively. The up-converted data from the plurality of up-converters  209 ,  214 ,  218 ,  222  are combined by output-to-cable network combiner  210 , and then sent to the subscribers&#39; cable or video modems  108 .  
         [0034]     A second preferred implementation replaces the separate CMTS core with demodulator which is connected to an existing CMTS, which allows reuse of already purchased CMTS equipment. This implementation demodulates QAM data from the CMTS&#39;s downstream output. The demodulated data includes of a MPEG transport stream, which can then be fed to the MPEG stream multiplexer  207  and then to the endcoders and modulators as described previously.  
         [0035]     A number of alternative arrangements may be used to convert the Ethernet stream into video. One case might be to use a home computer with an Ethernet connection as the set top device terminating into a common LCD display. Most home computers today contain digital video decoding capabilities for MPEG2 and Microsoft&#39;s Windows Media 9 encoded data streams. The LCD display could be used to display the digital TV, or it might be used to display the Interactive Program Guide (IPG) and the output going to a remotely connected video monitor. If the computer were capable of displaying DVB disks, then the computer would have the capability needed to convert the digital video into a usable display.  
         [0036]     Alternatively, a video MPEG decoder chip connected to an Ethernet chip would form an inexpensive tiny set top unit for driving a very low cost set top unit. Cable modems are inexpensive today because the cable industry created a standard that caused cable modems to become commodity electronics, with very low margins. They can be purchased for as little as $35 each in quantity at this time, while today&#39;s proprietary digital two-way set-top units sell in the $150+ range.  
         [0037]     In the preferred embodiment of this invention, a VMTS in some ways resemble a CMTS, but is differentiated to support an extremely high data delivery rate in the downstream, head end to consumer, direction. Video over IP traffic differs from traditional data traffic, and the differences between a CMTS and an VMTS are listed in the following table.  
                                         TABLE                                   CMTS   VMTS                                    TRAFFIC FLOW   About the same   Far greater           volume of upstream   downstream traffic           and downstream   than upstream           traffic   traffic       TYPE OF TRAFFIC   Personal computer   Control messages           user data   from set top box               (e.g., user hit the               “fast forward”               button on their               remote, user turned               off the TV, time               for a new traffic               encryption key               (TEK) in accordance               with the DOCSIS BPI               specification,               etc.).       NUMBER OF DOWN-   One   Many       STREAMS PER MAC       DOMAIN       TRAFFIC FILTERING   High   Low       REQUIREMENTS       (SECURITY)       ROUTING   High   Low       INTEGRATION       REQUIREMENTS       PACKET FLOW RATE   Unpredictable   Predictable       JITTER TOLERANCE   Medium   Low       LATENCY TOLERANCE   High   Low       DATA CONVERSION   None   MPEG-2/4, etc.       REQUIRED       (from video server)               to IP                  
 
         [0038]     In  FIG. 2 , the traffic through the DOCSIS core is limited solely to set-top box control functions, baseline privacy interface messages, etc. All video traffic bypasses the core, eliminating an expensive processor and extensive routing software. The standard DOCSIS messages from the media access and control (MAC) chip emerge as MPEG-2 cells, and the MPEG-2 cells are multiplexed by MPEG stream multiplexer  207  into a common dense QAM multiplexer/modulator that handles the video traffic. See co-pending U.S. patent application Ser. No. 10/328,868, with filing date of Dec. 23, 2002 by Baran et al., which is incorporated herein by reference.  
         [0039]     The plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  encapsulates data from CMTS&#39;s control information, as well as video-over-IP data together with control information from the VMTS. The plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  is designed to also encapsulate traffic, which may arrive as MPEG frames or standard IP packets. In the case of MPEG frames, as illustrated in  FIG. 3 , incoming MPEG cells  301  from the plurality of ASI inputs  205 ,  211 ,  215 ,  219  are concatenated together, wrapped with an IP header  302 ,  303  by the plurality of MPEG to DOCSIS PDU wrapper processors  206 ,  212 ,  216 ,  220 , respectively, converted to MPEG-2 cell contents by adding DOCSIS headers  305  using the DOCSIS protocol  304 . The resulting MPEG cells carrying the wrapped data are passed to the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  for delivery on the cable to subscribers&#39; cable or video modems  108 . See  FIGS. 2-5 . In the case of IP packets which contain encoded video, such as packets containing Microsoft&#39;s Windows Media 9, the IP packets may be concatenated together and optionally wrapped with a second IP header. Then the concatenated IP packets wrapped with the second IP header are converted to MPEG-2 cells which are passed to the multiplexer  207  and the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  and then to the plurality of up-converters  209 ,  214 ,  218 ,  222 , respectively, for delivery on the cable.  FIG. 4  and  FIG. 5  describe the processing prior to QAM multiplexing/modulation.  
         [0040]      FIG. 4  shows the case where an incoming cell  401  already has an IP header, and adding a DOCSIS PDU header  402  generates the required cell  403  for the multiplexer  207  and the plurality of Annex A/B/C encoders and modulators  208 ,  213 ,  217 ,  221  and then to the plurality of up-converters  209 ,  214 ,  218 ,  222 , respectively, for delivery on the cable.  
         [0041]      FIG. 5  illustrates the simultaneous processing of IP and MPEG packets in the downstream, to the user, direction. IP packets  501  in to the system pass through the DOCSIS PDU encapsulator  502 . The DOCSIS PDU encapsulator  502  includes baseline privacy encryption, when required. The encapsulated IP packets pass to the MPEG packetizer  503 , to the MPEG stream multiplexer  207  and then to the plurality of QAM modulators  506 ,  516 ,  526 ,  536 ,  546 ,  556 ,  566 ,  576 ,  586 . Alternatively, MPEG-2/4 video packets  511  pass to the IP encapsulator  512 , the DOCSIS PDU encapsulator  403 , and then to the MPEG packetizer  513 . The packetized encapsulated video packets then pass to the MPEG stream multiplexer  207  and then to the plurality of QAM modulators  506 ,  516 ,  526 ,  536 ,  546 ,  556 ,  566 ,  576 ,  586 . The CMTS core  521  maintains data regarding which customer devices are online and necessary timing and encryption information required by the DOCSIS protocol, and the CMTS MPEG stream passes to the MAC message processor  522  and then to the MPEG stream multiplexer  207  and then to the plurality of QAM modulators  506 ,  516 ,  526 ,  536 ,  546 ,  556 ,  566 ,  576 ,  586 .  
         [0042]     Given the nature of DOCSIS control information, the multiplexing process is somewhat complicated.  FIG. 6  illustrates the logic flow necessary to properly multiplex, by MPEG stream multiplexer  207 , the messages onto the appropriate downstream channel. In general, the VMTS transmits MPEG null packets if the VMTS does not have any downstream data to be transmitted. The MPEG null packets may be removed by the multiplexer logic if doing so will improve downstream traffic flow, i.e., if data were to be sent from a non-VMTS source, the non-VMTS data will take precedence over the null frames from the VMTS.  
         [0043]     More particularly, packets received  601  by the MPEG stream multiplexer  207  are checked to determine  603  if the received packet is a null MPEG cell. If yes, then the VMTS discards  602  the null MPEG cell. If no, then the VMTS checks  604  if a payload unit start indicator bit is set. If the payload unit start indicator bit were not set, then the VMTS uses  605  the first byte of payload section as start of DOCSIS packet header. If the payload unit start indicator bit were set, then the VMTS uses  606  the first byte of payload section as a pointer to find start of the DOCSIS packet header. The VMTS then checks  607  if the frame control indicates ATM or reserved packet. If the frame control indicates ATM or reserved packet, then the VMTS determines  608  if the user requested mode for ATM/reserved packets are to be discarded. If no, then the VMTS locates and examines  609  destination address. The VMTS then determines  610  if the destination address is a unicast address. If these packets are to be discarded, then proceed back to  601 . If they are to be passed, then send them to all downstream channels  611 . If the packet were not the ATM or reserved packet, then the VMTS replicates  611  packets across all downstream channels, and then goes to receive another MPEG cell  601 . If the packet were the ATM or reserved packet, then the packet is unicast, then the VMTS determines  612  which downstream channel is used by the modem by consulting the VMTS&#39;s station maintenance data, om the DOCSIS CMTS core, and the DOCSIS down channel frequency value for the particular modem. The VMTS then sends  613  the packet to the proper channel, and then receives another MPEG cell  601 .  
         [0044]     If the MPEG packet  701 , shown in  FIG. 7 , received by the MPEG stream multiplexer  207  from a DOCSIS VMTS source has, in the header  702 , the Payload Unit Start Indicator bit set, PUSI; then the packet contains a DOCSIS Media Access and Control (MAC) Message. When this occurs, the multiplexer must use the pointer_field byte to determine where the MAC message begins within the MPEG frame. This is the first byte which follows the MPEG header when the PUSI bit is 1, and is thus the 5 th  byte of a MPEG packet. This offset points to the frame control (FC) field  801  of  FIG. 8 , which defines the type of MAC message.  
         [0045]     The single byte of FC information  801  includes three subfields  802 : FC_TYPE, most significant two bits; FC_PARAM, 5 bits to right of FC_TYPE; and, EHDR_ON, 1 bit; see  FIG. 8 . The packet in  FIG. 8  includes the MAC-PARM  805 , LEN  806 , HCS  807  and PACKET PDU  805 . The packet PDU includes five subfields  804 : DA, SA, TYPE/LEN, USER DATA and CRC.  
         [0046]     Packets with an FC_PARAM of 00 are data packets which are destined for a particular DOCSIS modem. In the preferred embodiment, the video set-top needs only a single tuner that is tuned to a selected downstream frequency. By examining the destination address field, 6 bytes; see  FIG. 8 , and using a database of modem to channel mapping information provided by the RetroVue controller, B in  FIG. 9 , the multiplexer determines to which QAM stream each particular packet is directed.  
         [0047]     Packets with an FC_PARAM of 01 or 10 are ATM data or reserved for future use, respectively, and should be replicated onto all downstreams by the multiplexer or discarded completely, as configured by the user.  
         [0048]     Packets  13  with an FC_PARAM of 11 are MAC messages of the format shown in  FIG. 10 . If the destination address, DA  14  in  FIG. 10 , were 01-E0-2F-00-00-01 or FF-FF-FF-FF-FF-FF, then the MAC message should be multiplexed/delivered on ALL QAM channels that are under the control of the VMTS. If the destination address were in the database of to channel mapping information provided by the RetroVue controller, B in  FIG. 9 , then the MPEG stream multiplexer  207  determines on which single QAM channel the particular packet should be delivered. If the destination address were not that of a particular modem, then the MAC message may be multiplexed by the MPEG stream multiplexer  207  across ALL downstream channels with active modems or discarded at the user&#39;s discretion.  
         [0049]      FIG. 9  shows a system block diagram. Programming or content may be received from a satellite through satellite dish  51 , and converted to appropriate frequency by input converter  53 . Programming or content alternatively make arrive from an antenna  52  and converted by input converter  53 . Programming or content from input converter  53  may be in digital form, and sent over a high speed data link, such as Gigabit Ethernet, to switch  54 . Switch  54  routes data to any of encryptor and RF modulator  56  and to or from controller  57  and to or from storage  55 . Controller  57  routes data between switch  54  and legacy devices such as a conditional access key generator  501  and a management platform  502  and the encryptor and RF modulator  56 . CMTS  59  exchanges data from HFC network  22  with the switch  54 , which can in turn pass data to controller  57 , application server  58 , encryptor and RF modulator  56 , wide area network  21  such as the Internet, and the storage unit  55 . Data may be sent over hybrid fiber and/or coax cable network  22  to a user, set top box  23 . The set top box  23  is connected to a television, as is well known in the art.  
         [0050]     Packets with an FC_PARAM of 00 are data packets which are destined for a particular DOCSIS modem. The video set-top needs only a single tuner that is tuned to a selected downstream frequency. By examining the destination address field, 6 bytes; see  FIG. 8 , and using a database of modem to channel mapping information provided by the RetroVue controller, B in  FIG. 9 , the multiplexer determines to which QAM stream each particular packet is directed.  
         [0051]     Packets with an FC_PARAM of 01 or 10 are ATM data or reserved for future use, respectively, and should be replicated onto all downstreams by the multiplexer or discarded completely, as configured by the user.  
         [0052]     Packets  13  with an FC_PARAM of 11 are MAC messages of the format shown in  FIG. 10 . If the destination address, DA  14  in  FIG. 10 , were 01-E0-2F-00-00-01 or FF-FF-FF-FF-FF-FF, then the MAC message should be multiplexed/delivered on ALL QAM channels that are under the control of the VMTS. If the destination address were in the database of to channel mapping information provided by the RetroVue controller, B in  FIG. 9 , then the MPEG stream multiplexer  207  determines on which single QAM channel the particular packet should be delivered. If the destination address were not that of a particular modem, then the MAC message may be multiplexed by the MPEG stream multiplexer  207  across ALL downstream channels with active modems or discarded at the user&#39;s discretion.  
         [0053]      FIG. 11  shows a more detailed portion of the header  15 , with the FC  16  as one byte, broken out in terms of FCTYPE, FC PARM and EHDR_ON.  
         [0054]     Reference is made to ANSI/SCTE Specification  23 -1 Data-Over-Cable Systems Radio Frequency Interface Specification 1.1 to better understand some of the DOCSIS details.  
         [0055]     It is apparent to those skilled in the art that various modifications can be made to the video modem termination system and method of the instant invention without departing from the scope or spirit of the invention, and it is intended that the present invention cover modifications and variations of the video modem termination system and method provided they come within the scope of the appended claims and their equivalents.