Method and apparatus for supporting TDMA operating over hybrid fiber coaxial (HFC) or other channels

Abstract

In a Time Division Multiple Access (TDMA) communication network, a central office (CO) provides interactive communication between a service provider and a plurality of user terminals. To synchronize transmissions of the user terminals, a timebase timer in the CO generates modulo N-bit cyclical reference counts as time markers. In a downstream direction to the plurality of user terminals, time marker insertion units in the CO receive both (a) separate digital TDMA transport streams having a predetermined data rate including data packets and Media Access Control (MAC) packets that are interspersed between the data packets at predetermined intervals, and (b) the time markers generated by the timebase timer, and insert a currently received time marker count into a concurrently received MAC packet. The resultant downstream TDMA transport streams with the inserted time marker counts in the MAC packets are transmitted in continuous TDMA output transport stream to the remote user terminals. The time markers are independent of a data rate, a physical channel, and a channel protocol of the transport stream. In each user terminal, a network interface module synchronizes itself by comparing received time markers and locally generated time marker counts for correcting a local oscillator frequency. Upstream channel units in the CO are synchronized using the timebase timer generated time markers for receiving and processing upstream data packets upon arrival at their pre-assigned channel unit.

What is claimed is:  
     
       1. A time division multiple access (TDMA) communication network comprising: 
       channel synchronizing means for synchronizing channels in a downstream direction towards users of the communication network comprising:  
       a timebase timer for generating time markers comprising modulo N-bit programmable cyclical reference counts that are incremented at a predetermined frequency and are reset to 0 when the reference counts reach a predefined value; and  
       at least one time marker insertion unit, each time marker insertion unit comprising a first input terminal for receiving a digital TDMA transport stream having a predetermined data rate and comprising data packets and Media Access Control (MAC) packets that are interspersed between the data packets at predetermined intervals, a second input terminal for receiving the time markers generated by the timebase timer and for inserting a currently received time marker count into a currently received MAC packet, and an output terminal for transmitting the received TDMA data stream with the inserted time marker counts in the MAC packet in a continuous output TDMA transport stream to remote user terminals where the time markers are independent of a data rate, a physical channel, and a channel protocol of the transport stream and are used for synchronizing the user terminals.  
     
     
       2. The TDMA communication network of  claim 1  wherein the downstream channel synchronizing means further comprises at least one modulator means, each modulator means modulating the digital TDMA transport stream transmitted by a separate one of the at least one time marker insertion unit into a separation analog output TDMA transport stream having a predetermined protocol for transmission to the remote user terminals. 
     
     
       3. The TDMA communication network of  claim 2  wherein the downstream channel synchronizing means comprises: 
       a plurality of time marker insertion units and two of the time marker inserting units receive digital TDMA transport streams having different predetermined data rates comprising data packets and Media Access Control (MAC) packets that are interposed between the data packets at predetermined intervals, and transmit the received TDMA transport stream with the inserted time marker counts in the MAC packets in a continuous digital output TDMA transport stream; and  
       a plurality of modulator means wherein two of the modulator means modulate the digital TDMA transport Streams stream transmitted by a separate ones one of the plurality of time marker insertion units into a separate analog output TDMA transport streams having different pre-determined protocols for transmission to the remote user terminals.  
     
     
       4. The TDMA communication network of  claim 1  wherein the downstream channel synchronizing means comprises a plurality of time marker insertion units, where two of the time marker insertion units receive separate digital TDMA transport streams having different predetermined data rates comprising data packets and MAC packets that are interspersed between the data packets at predetermined intervals, and transmit the received TDMA transport stream with the inserted time marker counts in the MAC packets in a continuous output TDMA transport stream to the remote user terminals. 
     
     
       5. The TDMA communication network of  claim 4  wherein the downstream channel synchronizing means further comprises a plurality of modulator means wherein two of the modulator means modulate the digital TDMA transport stream transmitted by a separate one of the plurality of time marker insertion units into a separate analog output TDMA transport stream having different predetermined protocols for transmission to the remote user. 
     
     
       6. The TDMA communication network of  claim 1  further comprising upstream channel synchronizing means comprising at least one upstream channel unit, where each upstream channel unit comprises a programmable real time unit for (a) storing information related to a frame length and a number of time slots arbitrarily preassigned to each user terminal that is transmitting data packets via the upstream channel unit, and (b) receiving both an upstream TDMA transport stream comprising data packets at a predetermined data rate from the remote user terminals, and the time markers comprising the modulo N-bit programmable cyclical reference counts generated by the timebase timer for synchronizing the processing of the data packets in the upstream channel unit during their time of arrival at the upstream channel unit. 
     
     
       7. The TDMA communication network of  claim 6  wherein the each upstream channel unit in the upstream channel synchronizing means further comprises a burst demodulator for receiving both the upstream TDMA transport stream comprising data packets at a predetermined data rate directed to the upstream channel unit from the remote user terminals, and an aperture control signal from the programmable real time unit for measuring burst arrival times relative to the aperture control signal in the received upstream TDMA transport stream. 
     
     
       8. The TDMA communication network of  claim 6  wherein the upstream channel synchronizing means comprises a plurality of upstream channel units, and at least two of the upstream channel units receive and process upstream TDMA transport streams comprising different transport data stream protocols from certain ones of the user terminals. 
     
     
       9. The TDMA communication network of  claim 1  wherein each remote user terminal comprises a network interface module for performing network timing functions comprising: 
       synchronizing means for synchronizing a user terminal to time markers in a received data stream comprising:  
       a digitally controlled local oscillator for generating clock pulses at a preset frequency;  
       a counter for generating modulo N-bit programmable cyclical local oscillator counts from a received time marker in a downstream transport stream that are incremented at the preset frequency from the local oscillator between time marker reception times from the downstream transport stream; and  
       comparing means for comparing a time marker count currently received in a downstream TDMA transport stream from one of the at least one time marker insertion unit with a current modulo N count from the counter, and generating an error control output signal corresponding to a difference between a the currently received time marker count and a current count in the counter for transmission to the digitally controlled local oscillator for altering the preset frequency of the digitally controlled local oscillator in a predetermined direction.  
     
     
       10. A time division multiple access (TDMA) communication network comprising: 
       channel synchronizing means for synchronizing channels in a down stream directions towards users of the communication network comprising:  
       a timebase timer for generating time markers comprising modulo N-bit programming cyclical reference counts that are incremented at a predetermined frequency and are reset to 0 when the reference counts reach a predefined value; and  
       a plurality of time marker insertion units, each time marker insertion unit comprising:  
       a first input terminal for receiving a digital TDMA transport stream having a predetermined data rate and comprising data packets and Media Access Control (MAC) packets that are interspersed between the data packets at predetermined intervals;  
       a second input terminal for receiving the time markers generated by the timebase timer and for inserting a currently received time marker count into a currently received MAC packet; and  
       an output terminal for transmitting the received TDMA data stream with the inserted time marker counts in the MAC packets in a continuous TDMA output transport stream to remote user terminals, where the time markers are independent of a data rate, a physical channel, and a channel protocol of the TDMA output transport stream and are used for synchronizing the user terminals, where two of the time marker insertion units receive digital TDMA transport streams having different predetermined data rates.  
     
     
       11. The TDMA communication network of  claim 10  wherein the downstream channel synchronizing means further comprises a plurality of modulator means wherein two of the modulator means modulate the digital TDMA transport streams transmitted by separate ones of the plurality of time marker insertion units into separate analog downstream TDMA output transport streams having different predetermined protocols for transmission to the remote user terminals. 
     
     
       12. The TDMA communication network of  claim 10  further comprising upstream channel synchronizing means which comprises a plurality of upstream channel units, each upstream channel unit comprising a programmable real time unit for (a) storing information related to a frame length and a number of time slots arbitrarily preassigned to each user terminal that is transmitting data packets in an upstream TDMA transport stream via the upstream channel unit, and (b) receiving both the upstream TDMA transport stream comprising data packets at a predetermined data rate from the remote user terminals and the time markers comprising the modulo N-bit programmable cyclical reference counts generated by the timebase timer for synchronizing the processing of the data packets in the upstream channel unit during their time of arrival at the upstream channel unit. 
     
     
       13. The TDMA communication network of  claim 12  wherein each upstream channel unit in the upstream channel synchronizing means further comprising a burst demodulator for receiving both the upstream TDMA transport stream comprising data packets at a predetermined data rate from the remote user terminals, and an aperture control signal from the programmable real time unit for measuring data packet arrival times relative to the aperture control signal in the received upstream TDMA transport stream. 
     
     
       14. The TDMA communication network of  claim 12  wherein at least two of the upstream channel units receive and process upstream TDMA transport streams comprising different transport stream protocols. 
     
     
       15. The TDMA communication network of  claim 10  wherein the network further comprises: 
       a plurality of remote user terminals, each user terminal comprising a network interface module for performing network timing functions comprising synchronizing means comprising:  
       a digitally controlled local oscillator for generating modulo N-bit programmable cyclical local oscillator counts that are incremented at a predetermined frequency; and  
       a counter for generating modulo N-bit programmable cyclical local oscillator counts from a received time marker in a downstream transport stream that are incremented at the preset predetermined frequency from the local oscillator between time marker reception times from the downstream transport stream; and  
       comparing means for comparing a time marker count currently received in a downstream TDMA transport stream from one of the at least one time marker insertion unit with a central modulo N count from the counter, and generating an error control output signal corresponding to a difference between a currently received time marker count and a current count in the counter for transmission to the digitally controlled local oscillator for altering the preset predetermined frequency of the digitally controlled local oscillator in a predetermined direction.  
     
     
       16. A method of synchronizing communication between central office equipment and a plurality of remote user terminals in a TDMA communication network comprising the steps of: 
       (a) generating a time marker sequence comprising modulo N-bit programmable cyclical reference counts that are incremented at a predetermined frequency in a timebase timer and are reset to 0 when the counter reaches a predefined value;  
       (b) receiving at least one digital time division multiple access (TDMA) transport stream, each digital TDMA transport stream comprising a predetermined frequency including data packets and Media Access Control (MAC) packets that are interspersed between the data packets at predetermined intervals;  
       (c) inserting a currently received time marker count generated in step (a) into a MAC packet that is concurrently received in step (b) in each of the at least one digital TDMA transport streams in a time marker insertion unit; and  
       (d) transmitting each digital TDMA transport stream with the inserted time marker counts in the MAC packets from step (c) in a separate continuous analog downstream TDMA transport stream to remote user terminals, where the timer markers in each of the analog downstream TDMA output transport streams are independent of a data rate, a physical channel, and a channel protocol of the downstream TDMA output transport stream and are used by the plurality of user terminals for synchronizing their upstream data transmissions.  
     
     
       17. The method of  claim 16  comprising the further step of: 
       (e) modulating each of the at least one digital TDMA transport stream transmitted by the time marker insertion unit into a separate analog downstream TDMA output transport stream having a predetermined protocol for transmission to the plurality of remote user terminals.  
     
     
       18. The method of  claim 16  comprising the further steps of: 
       (e) storing separate control information related to a frame length and a number of time slots arbitrarily preassigned to predetermined user terminals in a programmable real time unit of an upstream channel unit that is assigned to receive data packets from the predetermined user terminals is an upstream direction in an upstream TDMA transport stream; and  
       (f) receiving both the time markers comprising the modulo N-bit programmable cyclical reference counts generated by the timebase timer in step (a) and the upstream TDMA transport stream comprising data packets at a predetermined data rate from the predetermined remote user terminals for synchronizing the processing the data packets from the predetermined user terminals in the upstream channel unit during their time of arrival at the upstream channel unit.  
     
     
       19. The method of  claim 18  wherein in performing step (f) receiving both the upstream TDMA transport stream comprising data packets at a predetermined data rate from the predetermined remote user terminals and an aperture control signal from the programmable real time unit for measuring data packet arrival times relative to the aperture control signal in the received TDMA transport stream. 
     
     
       20. The method of  claim 19  wherein the TDMA communication system comprises a plurality of upstream channel units, and in performing step (f), at least two of the upstream channel units receive and process separate upstream TDMA transport streams comprising different transport stream protocols. 
     
     
       21. The method of  claim 16  wherein each of the plurality of remote user terminals comprises a network interface module for performing the steps of: 
       (e) generating clock pulses at a preset frequency in a digitally controlled local oscillator;  
       (f) generating modulo N-bit programmable cyclical local oscillator counts from a received time marker in a downstream transport stream in a counter that are incremented at the preset frequency from the local oscillator between time marker reception times from the downstream transport stream; and  
       (g) comparing a time marker count currently received in a downstream TDMA transport stream with a current modulo N count from the counter in a comparing device, and generating an error control output signal corresponding to a difference between a currently received time marker count and a current count in the counter for transmitting to the digitally controlled local oscillator for altering the preset frequency of the digitally controlled local oscillator in a predetermined direction; and  
       (h) altering the predetermined frequency of the digitally controlled local oscillator in a predetermined direction in response to the error control output signal generated in step (g).  
     
     
       22. Central office equipment for a time division multiple access ( TDMA )  communication network for supporting upstream and downstream communications including:    
       
         means for generating time markers which are independent of a data rate, a physical channel, and a channel protocol of a data transport stream; and  
       
         a time marker insertion unit including a first input for receiving a channel specific data transport stream, a second input for receiving generated time markers, and an output for outputting the channel specific data transport stream with inserted time markers for downstream communication wherein a time base timer generates said time markers as modulo N - bit programmable cyclical reference counts that are incremented at a predetermined frequency and are reset to zero  (   0   )  when the reference counts reach a predefined value.   
     
     
       23. Central office equipment according to  claim 22  wherein said first input receives a digital TDMA transport stream having a predetermined data rate, said transport stream including data packets and Media Access Control ( MAC )  packets that are interspersed between the data packets at predetermined intervals, and said time marker insertion unit inserts time markers into Media Access Control  ( MAC )  packets and outputs the TDMA data stream with the inserted time marker counts in the MAC packets.   
     
     
       24. Central office equipment for a time division multiple access ( TDMA )  communication network for supporting upstream and downstream communications including:    
       
         means for generating time markers which are independent of a data rate, a physical channel, and a channel protocol of a data transport stream; and  
       
       
         a time marker insertion unit including a first input for receiving a channel specific data transport stream, and a second input for receiving generated time markers, and an output for outputting the channel specific data transport stream with inserted time markers for downstream communication; and  
       
         at least one upstream channel unit having a programmable real time unit for  ( a )  storing information related to a frame length and a number of time slots arbitrarily preassigned to an upstream channel,  ( b )  receiving an upstream TDMA transports stream of data packets at a predetermined data rate from a remote user terminal, and  ( c )  using said generated time markers to generate an aperture control signal for synchronizing the processing of the data packets in the upstream channel unit.   
     
     
       25. Central office equipment according to  claim 24  wherein said upstream channel unit further includes a burst demodulator for receiving both the upstream TDMA transport stream of data packets at a predetermined data rate and the aperture control signal from the programmable real time unit for measuring burst arrival times relative to the aperture control signal in the received upstream TDMA transport stream. 
     
     
       26. Central office equipment for a time division multiple access ( TDMA )  communication network for supporting upstream and downstream communications including:    
       
         means for generating time markers which are independent of a data rate, a physical channel, and a channel protocol of a data transport stream; and  
       
       
         a time marker insertion unit including a first input for receiving a channel specific data transport stream, a second input for receiving generated time markers, and an output for outputting the channel specific data transport stream with inserted time markers for downstream communication; and  
       
       
         a plurality of upstream channel units each having means for synchronizing an upstream channel using said generated time markers, and at least two of the upstream channel units receive and process upstream TDMA transport steams having different transport data stream protocols. 
       
     
     
       27. Central office equipment for a time division multiple access ( TDMA )  communication network for supporting upstream and downstream communications including:    
       
         means for generating time markers which are independent of a data rate, a physical channel, and a channel protocol of a data transport stream; and  
       
       
         a time marker insertion unit including a first input for receiving a channel specific data transport stream, a second input for receiving generated time markers, and an output for outputting the channel specific data transport stream with inserted time markers for downstream communication; and  
       
       
         a plurality of time marker insertion units, each insertion unit including a first input for receiving a channel specific data transport stream of a channel different than the others of the plurality of time marker insertion units, a second input for receiving generated time markers, and an output for outputting the channel specific data transport stream with inserted time markers for downstream communication. 
       
     
     
       28. Central office equipment according to  claim 27  wherein a time base timer generates said time markers as modulo N- bit programmable cyclical reference counts that are incremented at a predetermined frequency and are reset to zero  (   0   )  when the reference counts reach a predefined value.   
     
     
       29. Central office equipment according to  claim 28  wherein said first input of each insertion unit receives a digital TDMA transport stream having a predetermined data rate, said transport stream including data packets and Media Access Control ( MAC )  packets that are interspersed between the data packets at predetermined intervals, and said time marker insertion units insert time markers into Media Access Control  ( MAC )  packets and output the TDMA data stream with the inserted time marker counts in the MAC packets.   
     
     
       30. Central office equipment according to  claim 29  further including: 
       
         a plurality of modulator means each for modulating the output of one of said insertion units to produce analog output TDMA transport streams for transmission to remote user terminals, and  
       
       
         at least two of the modulator means modulate the digital TDMA transport streams to produce analog output TDMA transport streams having different predetermined protocols for transmission to remote user terminals. 
       
     
     
       31. Central office equipment according to  claim 27  further including at least one upstream channel unit having a programmable real time unit for ( a )  storing information related to a frame length and a number of time slots arbitrarily preassigned to an upstream channel,  ( b )  receiving an upstream TDMA transport stream of data packets at a predetermined data rate from a remote user terminal, and  ( c )  using said generated time markers to generate an aperture control signal for synchronizing the processing of the data packets in the upstream channel unit.   
     
     
       32. Central office equipment according to  claim 31  wherein said upstream channel unit further includes a burst demodulator for receiving both the upstream TDMA transport stream of data packets at a predetermined data rate and the aperture control signal from the programmable real time unit for measuring burst arrival times relative to the aperture control signal in the received upstream TDMA transport stream. 
     
     
       33. Central office equipment according to  claim 27  including a plurality of upstream channel units each having means for synchronizing an upstream channel using said generated time markers, and at least two of the upstream channel units receive and process upstream TDMA transport streams having different transport data stream protocols. 
     
     
       34. A remote user terminal for TDMA communication network for supporting upstream and downstream communications from central office equipment including: 
       
         time marker detector means for detecting time markers in a received data stream and outputting a signal responsive to detected time markers;  
       
       
         variably controllable oscillator means for controlling the timing sequence of the processing of the received data stream; and  
       
       
         said variably controllable oscillator means operatively associated with said time marker detector means for varying the timing in response to detected time markers wherein:  
       
       
         said variable controllable oscillator means includes a digitally controlled local oscillator for generating clock pulses;  
       
         a counter is provided for generating modulo N - bit programmable cyclical local oscillator counts by incrementing a received time marker count at the frequency from the local oscillator between time marker reception times; and    
       
         comparing means are provided for comparing a received time marker count with a previously received time marker count which has been incremented by the counter, and generating an error control output signal corresponding to a difference between the received time marker count and the incremented count for adjusting the frequency of said digitally controlled local oscillator.