MXPA96004854A - Method and apparatus to support the operation of multiple access of division of time (tdma) overhibited fiber (hfc) or other cana - Google Patents

Abstract

The present invention relates to a Time Division Multiple Access (TDMA) communication network comprising: a downstream channel synchronization element comprising: a time base timer to generate time markers comprising reference accounts programmable N-bit registers that are incremented at a previously determined frequency and reset to O when the count reaches a previously defined value, and at least one time marker insert unit, each time marker insert unit comprising a first input terminal for receiving a time division multiple access transport stream having a previously determined data rate and comprising data packets and media access control packets that are spread between the data packets to pre-determined intervals, a second input terminal to receive the markers of you generated by the time base timer and to insert a time marker account received at the time into a media access control (MAC) packet received at the time, and an output terminal to transmit the data stream from time division multiple access received with the time marker accounts inserted in the medium access control packets in a continuous output time division multiple access transport stream for the remote user terminals where the data entry markers time are independent of a data regime, a physical channel, and a channel protocol of the transport stream and are used to synchronize user terminals

Description

METHOD AND APPARATUS FOR SUPPORTING THE MULTIPLE TIME DIVISION ACCESS (TDMA) OPERATION ON HYBRID FIBER COAXIAL (HFC) OR OTHER CHANNELS FIELD OF THE INVENTION The present invention relates to a versatile and efficient Access Network that supports and synchronizes the time division multiple access operation (Time Division Multiple Access, TDMA) on hybrid fiber coaxial channels (HFC) and / or other channels such as wireless channels. Background of the Invention In an interactive communication system, a plurality of users or subscribers of the system are located in a previously determined region and are provided with the ability to interact with their televisions, personal computers, and so on. More particularly, the users are connected via a cable plant in a tree structure to the equipment in a Central Office. Various formats can be used to allow the plurality of users to share the resources of the cable plant and the Central Office equipment. One such format is the use, for example, of Multiple Access Time Division Frequency. United States Patent No. 5,138, 635 (Ballance), issued August 11, 1992, describes a technique for clock synchronization in a communications network. The network comprises a central exchange comprising a master clock, and a plurality of remote subscriber stations that are connected to the central exchange and communicate via data cells with the central exchange. The subscriber stations are arranged to retrieve a master clock frequency from the data received from the central exchange, and to transmit data to the central exchange on that master clock frequency. The central exchange comprises (a) a delay line arranged to receive the incoming data cells, (b) an element for sampling data from different terminals of the delay line, and (c) an element for determining from the sampled data which terminal of the delay line carries the data-optimally in the phase with the master clock and to select that data to produce a data cell accordingly. Therefore, the central exchange uses a single clock, but instead of trying to retrieve an appropriate clock for incoming data, the central exchange uses a delay line to provide a progressive delay for incoming data via the line delay, and then identify the terminal from the delay line that carries the incoming data that has an appropriate phase for the master clock. In this way, the central exchange handles the data transmitted from the subscriber stations with a phase that varies arbitrarily with respect to the master clock of the system. United States Patent No. 5,425,027 (Baran), issued June 13, 1995, discloses a cell network in fast packets of television cables and wide area fibers. The fiber portion of the network bidirectionally transmits cells committed to the Asynchronous Transfer Mode (ATM) on a digital fiber optic path from a head end unit to interconnect subscriber interface units (SIUs) to support the services digital in two directions with a coaxial feeder cable television system, where the television and digital signals are transmitted in different frequency bands. At the subscriber terminals, television and digital signals are filtered and processed separately. Each subscriber interface unit sends and receives a UHF signal that is converted to, and from, a digital signal, respectively, to transmit the cells of asynchronous transfer mode. Each cell of asynchronous transfer mode contains a local address of the source and the destination of that cell, and the subscriber interface unit only accepts those cells addressed to it. An allocation and capacity combination arrangement from a Fiber Termination Unit (FTU) at the head end is used. More particularly, the fiber termination unit initially measures the transit time in round trip of the signals sent to each subscriber interface unit. Each subscriber interface unit is assigned to a predetermined number of cells for transmission purposes that is monitored during transmissions and dynamically changed as required for the most efficient use of the transmission medium. The synchronization for the control of the subscriber interface units uses bit synchronization of a constant bit stream of the cells emanating from the fiber termination unit, wherein each subscriber interface unit ensures a local oscillator at its rate of bits to control the output cells of the subscriber interface unit. This same de-synchronization source also provides the frequency reference for the receiving section of each subscriber interface unit. Thus fiber termination units and subscriber interface units are essentially secured together with known measured transit time lags. The Patent of the United States of North America No. ,428,645 (Dolev et al.), Issued June 27, 1995, describes a technique for synchronizing a local time maintained at a node within a network architecture with a reference time. A burst, which includes a series of synchronization messages "k", is sent from a master node to remote child nodes, wherein each synchronization message includes a reference time stamp based on a reference time provided to the master node by a source of remote time. The secondary nodes synchronize themselves by first estimating a local time according to the calculation of the secondary node corresponding to the reference time determined in relation to the time stamps contained within the synchronization messages received. More particularly, the technique determines that a first time according to a first time scale falls between the second and third times according to a second time scale. The times are selected based on the synchronization messages sent in a burst-from a deposit of one of the time scales (ie, the reference time) carrying the time stamps according to a reference time scale. These synchronization messages are received by a local time deposit, such as a secondary node, which associates the local time stamps according to another time scale (ie, a local time scale). Due to the protocol of the synchronization messages, the temporal relationships are determined between the local time stamps and the reference time stamps within the messages of a burst. These first, second and third times are identified in the secondary node based only on the synchronization messages received within a burst. After the first, second and third times are identified, a time is selected in relation to the second and third times, preferably halfway between both, and a difference between the second and third selected times is determined. Finally, the local time is updated to compensate for that difference and is presumably accurate within half the distance between the second and third times. There is a problem in the time division multiple access communication access network of how to synchronize all the plurality of remote users arranged in a tree type architecture that can communicate with the central office equipment using channels which may have different protocols so that all users have a common reference and know what frequency (channel), frame length, and slot number (s) of time there is to transmit on which to operate with sufficient force and obtain a shared allocation of resources available. The synchronization of the plurality of users must be achieved by distributing a time reference that is independent of a data rate, a physical channel, and a channel code that is used in order to operate with any of the channel parameters that are available now for use or that will be available for future use.

SUMMARY OF THE INVENTION The present invention is directed to a method and apparatus that supports and synchronizes time division multiple access operation over hybrid fiber coaxial channels and / or wireless channels. More particularly, the present invention is directed to a technique for implementing a synchronization of a plurality of user equipment from a head end office using a time division multiple access format by distributing a time reference that is independent of the rate regime. data, the physical channel and the channel code used. Viewed from one aspect, the present invention is directed to a time division multiple access communication network comprising a synchronization element. of downstream channel comprising a time base timer and at least one time marker insert element. The time base timer generates time markers that comprise programmable cyclic reference accounts of modular N-bits that are incremented at a previously determined frequency and reset to 0 when the account reaches a redefined value. Each of at least one time marker insert element comprises a first and a second input terminal, and an exit terminal. The first input terminal receives a time division multiple access transport stream having a previously determined data rate including data packets and media access control packets that are spread at previously determined intervals between the data packets. The second input terminal receives the time markers generated by the time base timer and inserts a time marker account received at the time into a media access control packet received at the time. The output terminal transmits the Time Division Multiple Access data stream received with the time marker accounts in the medium access control packets in a continuous output data stream to the remote user terminals where the dialer markers. time are independent of a data regime, a physical channel, and a channel protocol of the transport stream and are used to synchronize the terminals of the users. Seen from another aspect, the present invention is directed to a time division multiple access communication network comprising a downstream channel synchronization element comprising a time base timer and a plurality of marker insertion elements. weather. The time base timer generates time markers comprising programmable cyclic reference accounts of modular N-bits that are incremented at a previously determined frequency and reset to 0 when the account reaches a redefined value. Each time marker insert element comprises a first and a second input terminal, and an output terminal. The first input terminal receives a digital time division multiple access transport stream having a previously determined data rate including data packets and media access control packets that are spread at pre-determined intervals between the packets of data . The second input terminal receives the time stamps generated by the time base timer and inserts a time stamp account received at the time into the media access control packet received at the time. The output terminal transmits the Time Division Multiplex Access data stream with the time marker accounts inserted in the media access control packets in a continuous output data stream to the 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 to synchronize the user terminals, where two of the time stamp insertion elements receive streams digital time division multiple access transport that have different data regimes previously determined.

Seen in still another aspect, the present invention is directed to a method of synchronization communications with a plurality of remote user terminals in a time division multiple access communication network. In a first step, the generation of a time marker sequence is generated by comprising the programmable cyclic reference numbers of modular N-bits that increase at a previously determined frequency and are reset to 0 when the account reaches a previously defined value. a time-based stopwatch In a second step, at least one downstream time division multiple access transport stream is received, wherein each transport stream comprises a previously determined frequency including, data packets and access control packets to the means that they are scattered at previously determined intervals between the data packets. In a third step, a time marker account received at the time generated in the first step is inserted into the access control packet to the medium received at the time in the second step in a time marker insertion element, and at least one time division multiple access data stream with the time stamp accounts in the medium access control packets are transmitted in a downstream data stream of continuous output to the terminals of the remote users, in where the time markers in the downstream data stream are independent of a data rate, a physical channel and a channel protocol of the downstream transport stream and are used by the plurality of user terminals to synchronize the data transmissions Upstream. The invention will be better understood from the following more detailed description taken together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a block diagram of a time division multiple access communication network according to the present invention. FIGURE 2 is a partial view of the time division multiple access communication network of the FIGURE 1 showing exemplary data transport streams including time stamps inserted therein according to the present invention. FIGURE 3 is a block diagram of a Network Interface Module for synchronizing a user terminal or subscriber to the time markers in a data transport stream received in accordance with the present invention. FIGURE 4 is a block diagram of an upstream Channel according to the present invention.

FIGURE 5 is a timing diagram for a late burst in the upstream channel of FIGURE 4; and FIGURE 6 is a timing diagram for an early burst in the upstream channel of FIGURE 4. Detailed Description It should be understood that the corresponding elements that perform the same function in each of the figures have been given the same number of designation. Referring now to FIGURE 1, a block diagram of an access network 10 (shown within a dotted line rectangle) according to the present invention is shown. The access network 10 comprises the equipment of the central office 11 (shown inside a dotted line rectangle) which is connected on a first side to a Service Provider (not shown), a cable plant 22 coupled to a second side of the equipment of the central office 10, and to a plurality of terminals of users or subscribers 32 (l) -32 (x) coupled to the cable plant 22. The equipment of the central office 11 comprises a plurality of Access Control Multiplexers. to the Media (MUX MAC) 14 (1) -14 (n), a plurality of Units of Insertion of Time Markers (TMIU) or elements 16 (1) -16 (n), a plurality of Generic Modulators (GEN MOD.) 18 (l) -18 (n), a Time Base Timer 20, a plurality of upstream 23 (l) -23 (n) channels comprising Burst Demodulators (BURST DEMOD) 24 (1) -24 (n), respectively, and the respective units of Real-Time Processing Module Upstream (UETM) 26 (1) -26 (n), a Packet Redirector 28, and a Network Interface and Control Unit 30. In a downstream portion of the Central Office equipment 11 going from the Remote Service Provider to the User Terminals 32 (l) -32 (x), the access control multiplexers to the means 14 (1) -14 (n) receive separate data streams at the first inputs from the remote service provider via the conductors 12 (l) -12 (n), respectively, and signals from the Control Unit and Network Interface 30 in the second inputs via a common conductor 40. The outputs from the control multiplexers of access to the means 14 (l) -l4 (n) are coupled to the first entries of the insertion units of time markers 16 (l) -16 (n), respectively, via the respective conductors 42 (l) -42 (n). The time base timer 20 is coupled to the second inputs of the time marker insertion units 16 (l) -16 (n), via a common conductor 48. The outputs from the time marker insertion units 16 (l) -16 (n) are coupled to the inputs of the Generic Modulators (GEN MOD) 18 (l) -18 (n), respectively, via the respective leads 44 (l) -44 (n).

The outputs from the generic modulators 18 (l) -18 (n) are coupled to the cable plant 22 for transmission to the inputs of a plurality of user terminals 32 (1) -32 (x). In an upstream portion of the equipment of the Central Office 11 going from the User Terminals 32 (l) -32 (x) to the Remote Service Provider, the user terminals 32 (l) -32 (x) transmit bursts of messages via the cable plant 22 to the Central Office team 11 where they are received in units of previously determined channels 23 (1) -23 (n). More particularly, the channel units 23 (l) -23 (n) comprise burst demodulators 24 (l) -24 (n) and upstream processing modules 26 (l) -26 (n), respectively, and the outputs of the burst demodulators 24 (l) -24 (n) are coupled to the inputs of the upstream real-time processing modules, respectively. The outputs of the upstream processing modules 26 (l) -26 (n) are coupled to the packet redirector inputs 28 via the conductors 49 (l) -49 (n), respectively, and the redirector packets 28 transmits signals to the remote Service Provider on the output channels 54. The Network Interface and Control Unit 30 receives information from the upstream control path from the packet redirector 28 via the conductor 52, and the base timer of time 20 exchanges information with the channel units 23 (l) -23 (n) and the Control Unit and Network Interface 30 via a bus 51. During the operation, the access control multiplexers to the means 14 ( l) -14 (n) receive pure digital data streams at the first inputs from a Service Provider via the conductors 12 (l) -12 (n), respectively, and the access control messages to the media that are generated by the Control and Interface unit d e Network 30 in the second inputs via bus 40. The pure data signals received by the access control multiplexers to the means 14 (l) -14 (n) from the Remote Service Provider can comprise any data stream. For example, Moving Picture Expert Group-2 (MPEG-2) or Asynchronous Transfer Mode (ATM), the standard data streams that have any suitable data regime previously determined. The access control messages to the medium are provided by the control unit and network interface 30 at a substantial periodic rate to the access control multiplexers to the means 14 (1) -14 (n), and comprise, for example , an empty packet or a packet containing control information previously determined for transmission to the user terminals 32 (l) -32 (x). Each of the access control multiplexers to the means 14 (l) -14 (n) multiplexes the data stream received from the remote Service Provider with the access control messages to the medium provided by the Control Unit and inter- face of Network 30 to generate a time-division multiple access output data stream at a previously determined data rate. It should be understood that one or more of the access control multiplexers 14 (l) -14 (n) may have output data streams - at a previously determined first data rate, another or more of the control multiplexers of access to the means 14 (1) -14 (n) may have output data streams at a second previously determined data rate, and still another or more of the access control multiplexers to the means 14 (1) - 14 (n) may have output data streams to a third predetermined data rate, etatetera, to adjust the services provided to the Users Terminals 32 (1) -32 (x). The output data streams multiplexed from the access control multiplexers to the means 14 (1) -14 (n) are received at the first inputs of the insertion units of the time marker or elements 16 (1) - 16 ( n), respectively, via the respective conductor 42 (l) -42 (n). In addition, the time marker insertion units 16 (1) -16 (n) receive the time markers (TM) in the second inputs from the time base markers 20 via a common conductor 48. Each of the units of insertion of time markers 16 (1-16 (n) detects the arrival of empty access control messages to the media in the multiplexed data stream received from the access control multiplexers to the means 14 (l) -14 (n) associated, and inserts a time base marker therein Referring now to FIGURE 2, a partial view of the Time Division Multiple Access communication network of FIGURE 1 comprising the insertion units of time markers 16 (l) -16 (n), the Generic Modulators 18 (l) -18 (n), and the time-based Stopwatch 20 to illustrate the operation of the marker insertion units of 16 (l) -16 (n) time according to the present invention The Marker of Time base 20 may comprise any suitable generating unit that generates Time Markers or Timestamps of N modular outputs in a predetermined rate. For example, the Time Base Timer 20 may comprise a local stable clock (not shown) or a Stratum clock source (not shown) that drives a programmable N module counter (not shown). In turn, the counter of N modules generates Time Markers that are distributed to the insertion units of time markers 16 (l) -16 (n) via the driver 48. More particularly the Time Base Stopwatch 20 generates a N-bit programmable reference count (for example, 32 bits) that increments to a frequency (for example, 1024 Mhz with 1 ppm stability) and resets to 0 when the account reaches a previously defined value. The Time Base Timer 20 can optionally support a Time of Day functionality, and transmits the Time of Day along with the Time Markers. More particularly, the Time Base Timer 20 generates a Time Marker sequence comprising a series of numbers of N cyclic modules from 0 to module N (of which only Time Markers 1-12 are shown in the FIGURE). 2) to a previously determined time marker regime. The Time Markers are transmitted via the driver 48 to the insertion units of time markers 16 (l) -16 (n). The 16 (l) -16 (n) units detect the occurrence of special time base access control messages (e.g., empty medium access control messages) that were inserted into the data streams by means of the access control multiplexers to the means 14 (l) -14 (n), respectively, and were received via the respective conductors 42 (l) -42 (n). During the detection of access control messages to the special time base means, each time stamp insertion unit inserts the number N of the Time Marker module that is being received on the driver 48 in that access control message to the special time base medium. For example, as shown in the output data stream from the insertion unit of time markers 16 (1) on conductor 44 (1), Time Markers (TM) 10, 25, and 47 were inserted within of the special time base access control message packets that occur between the sequential data packets (DT) received from the access control multiplexer to the means 14 (1) via the driver 42 (1) . Furthermore, as shown in the output data stream from the time stamp insertion unit 16 (2) in the conductor 44 (2), the Time Markers 08, 19, 25, and 49 were inserted into the the special time base medium access control message packets that occur between the sequential data packets received from the access control multiplexer to the means 14 (2) via the conductor 42 (2). Additionally, as shown in the output data stream from the insertion unit of time markers 16 (n) on the conductor 44 (n), the Time Markers 09, 23 and 37 were inserted into the Message packets of access control to the special time base means that occur between the sequential data packets received from the access control multiplexer to the means 14 (n) via the conductor 42 (n). It should be understood that the special time base access control message packets occur at a rate which is suitable for canceling any deviation from a counter of N local time base modules in a Network Interface Module 34 of a user terminal (e.g., User Terminal 32 (2) shown in FIGURE 1). The insertion of Time Markers by the insertion units of time markers 16 (1) -16 (n) occur in real time, and the true value of the Time Marker is adjusted to take into account any delay of the waiting line of a control message accessing the special time base medium. Turning now to FIGURE 1, the output data streams of the insertion units of time markers 16 (l) -16 (n) are received by the generic modulators 18 (l) -18 (n), respectively, via the respective conductors 44 (1) -44 (n). The generic modulators 18 (1) -18 (n) transform the digital bit streams received via the conductors 44 (l) -44 (n), respectively, into analog Radio Frequency (RF) signals for efficient transmission over the plant of cables 22 to the Users Terminals 32 (l) -32 (x). As mentioned hereinabove, one or more of the output data streams from the access control multiplexers to the means 14 (1) -14 (n) may have a first data rate determined previously, another or more of the output data streams of the access control multiplexers to the means 14 (1) -14 (n) may have a second predetermined data rate, and still another or more of the output data streams from the access control multiplexers to the media 14 (l) -14 (n) may have a third predetermined data regime, etcetera, to adjust the services provided to the Users Terminals 32 (l) -32 (x) . For purposes of illustration, it is assumed, hereinafter, that the generic modulator 18 (1) receives a digital bit stream at a data rate of 27 Mbit / s and generates an output analog data stream using 64 bits of data. Quadrature Amplitude Modulation (QAM), the generic modulator 18 (2) receives a stream of digital bits at a data rate of 2 Mbit / second and generates an output analog data stream using Quadrature Phase Displacement Modulation ( QPSK) and the generic modulator 18 (n) receives a stream of digital bits at a data rate of 64 Kbits / second and generates an output analog data stream using, for example, Frequency Shift Modulation (FSK). It should be understood that the present invention provides the ability to transmit time stamp messages in any type of transport data stream having a specific data rate. This provides strength in the network 10 that allows any present or future data rate transport data stream to be adjusted and allows the User Terminals 32 (l) -32 (x) to be synchronized in an access tree type architecture. multiple time division with a common synchronization reference that is independent of the data rate, physical channel, and channel coding or transport stream protocol. User Terminals 32 (l) -32 (x) can comprise any suitable device such as a Digital Cable Terminal (DCT), a personal computer, and so on. The User Terminal 32 (2) illustrates a typical user terminal comprising a Network Interface Module (NIM) 34 and an Application Module (APPLN MODULE) 36. The network interface module 34 provides network services to the module of applications 36, and comprises transmission elements (not shown) such as tuners, modems, error correction devices, access control elements (not shown), and access interface equipment and network applications (not shown). In accordance with the present invention, the network interface module 34 further comprises elements for synchronizing the user terminals 32 (2) with the time markers received in one or more of the data streams from the cable plant 22. Referring now to FIGURE 3, a block diagram of a synchronization device 70 is shown. (shown within a dotted line rectangle) that is part of a Network Interface Module 34 (shown in FIGURE 1) for synchronizing a User Terminal [e.g., a 32 (2) User Terminal] for Internet Markers. Time in a data stream received in accordance with the present invention. The synchronization device 70 comprises a Time Base Marker Detector (TBM DETECTOR) 71, a Series-to-Parallel Displacement Register (S / P SHIFT REGISTER) 72, a Local Oscillator (LO) 74, a Controlled Oscillator Digitally (DCO) 76, A Local Time Base Counter (LTB COUNTER) 78, an Adder 80, and a Lock 82. Structurally, the inputs of the Time Base Marker Detector 71 and the serial shift register-a Parallel 72 are coupled to the cable plant 22. A first output of the time base marker detector 71 is coupled to an input of each of the local time base counter 78 and the Lock 82, and a second output of the Time base marker detector 71 is coupled to a second input of serial-to-parallel shift register 72. An output of serial-to-parallel shift register 72 is coupled to a second input of the time base counter local 78 and one input of the 80th Summer. a of the Local Oscillator 74 is coupled to a first input of the digitally controlled oscillator 76. An output of the latch 82 is coupled to a second input of the digitally controlled oscillator 76. The first and second outputs of the digitally controlled oscillator 76 are coupled to a third one. input of the local time base counter 78 and a clock output (CLK) of the synchronization device 70, respectively. An output of the local time base counter 78 is coupled to a second input of the adder 80. An output of the adder 80 is coupled to a second input of the latch 82. During the operation, the local oscillator 74 generates clock sequence pulses. at a predetermined frequency, and the digitally controlled oscillator 76 is initially operated at a fixed division of the frequency of the Local Oscillator 74. The output of the digitally controlled oscillator 76 is a predetermined initial local time base clock frequency and is transmitted at an input of the local time base counter 78. Each pulse of the local time base clock of the digitally controlled oscillator 76 increments the local time base counter 78 by 1. The time base marker detector 71 and the time register series-to-parallel offset 72 each receives a channel data stream from the 'cable plant 22. The time base marker detector 71 detects each of the timestamp messages in the channel data stream received from the cable plant 22, and generates a trimmed output signal for the local time base counter 78 and the latch 82, and a control signal enabled for the serial-to-parallel shift register 72. The shift register s / p 72 receives the data stream and, in response to the control signal enabled from the time base marker detector 71, stores and converts the timestamp of N modules received in series in the received data stream in a parallel output signal for transmission to the local time base counter 78 and the adder 80. The output signal in parallel from the shift register S / P 72 contains the count of N time base modules in the most recent time dialer message received in the data stream from the cable plant 22. The output signal cut out from the battery marker detector time 71 causes a current account comprising a time marker account previously stored in the local time base counter 78 plus some provisional account added thereto by the output from the digitally controlled oscillator 76 to exit to the adder 80 . Along with this, the time stamp count received at the time in the serial-to-parallel shift register 72 is input into the local time base counter 78 and the adder 80. The adder 80 subtracts the number N from the module in the time stamp account received at the time of the serial-to-parallel shift register 72 from the counter output of the time counter of the local time base counter 78. The output signal from the adder 80 represents a count of error between the two input count signals that are locked in the Lock 82. An error count output signal from the Lock 82 is transmitted to the digitally controlled oscillator 76 which responds to the error count signal to correct the frequency of the error. Digitally controlled oscillator output in a direction that decreases any error to more closely track the time stamp accounts received from the Central Office team 11. This process is repeated with the detection of each time stamp message received by the time base marker detector 71 and the series-to-parallel shift register 72 until a secured condition is determined. For example, if it is assumed that all user terminals 32 (l) -32 (x) receive the same sequence of time markers of 10, 25, 47, and so on, [as shown in the output of the insert unit of time marker 16 (1) in FIGURE 2], the operation of each user terminal 32 (l) -32 (x) can be described as follows. Each user terminal 32 (l) -32 (x) first receives, detects, and stores the current time marker count of "10" in response to the clock pulses in sequence from the digital controlled oscillator 76. With the reception and subsequent detection of the number "25" of the time marker in the data stream from the cable plant 22, the number "25" is effectively compared to an account number (eg, a number "28") found in the moment in the local time base counter 78. More particularly, the number "28" occurred in the local time base counter 78 because the clock pulses from the digitally controlled oscillator 76 have a slightly faster rate than time marker counts generated by the time base timer 20 shown in FIGURE 1. The comparison between the two numbers is effectively done by subtracting the number "25" from the time marker received at the time from the region. series-to-parallel offset stroke 72 of the number "28" of the local time base counter 78. A difference of "+3" between the two numbers of the time marker is the resulting error that is transmitted to the digitally controlled oscillator 76. The digitally controlled oscillator responds to an "+3" error signal to slightly decrease the frequency of the output clock pulses for the local time base counter 78. With the subsequent reception of the marker number "47" ', the number "47" is effectively compared to an account number (for example a number "45") currently in the local time base counter 78. That comparison is effectively performed by subtracting the number "47" from the time marker received at the time of the serial-to-parallel shift register 72 of the number "45" from the local time base counter 78. A difference of "-2" between the two timestamp numbers is the resulting error that is trans limit the digitally controlled oscillator 76. The digitally controlled oscillator 76 responds to an "-2" error signal to slightly increase the frequency of the output clock pulses for the local time base counter 78. That process continues until the output of the digitally controlled oscillator is declared in an "insured" condition. It should be understood that in reality each of the User Terminals 32 (l) -32 (x) is synchronized to itself using time markers found in one or more of the transport streams propagating over the cable plant 22. For example, User Terminals 32 (2) and 32 (4) can be used in time markers 10, 25, 47, etc., found in the transport stream from General Modulator 18 (1) (shown in FIGURE 2) ), the user terminals 32 (1) and 32 (3) can use the time stamps 08, 19, 35, 49, et cetera, found in the transport stream from the general modulator 18 (2) (shown in FIGURE). 2), and the user terminal 32 (x) can use the time stamps 09, 23, 37, et cetera, found in the transport stream from the general modulator 18 (n) (shown in FIGURE 2. It should be understood that the digitally controlled oscillator can comprise any suitable device.

For example, a programmable counter (not shown) can be used that inserts or removes cycles from the local oscillator 74 to a clock over a binary counter. Alternatively, a direct digital synthesis (DDS) device (not shown) can be used to generate a secured local clock. This alternative technique uses a phase accumulator (not shown) and a compensation register / adder (not shown (without a lookup table or square wave generation) in any arrangement of the digitally controlled oscillator 76, to avoid a long-term attempt to For an assured phase cycle (PLL), an accurate estimation of the frequency error (l / error count) is required Ideally, you want to linearly distribute a correction for this error over a next time interval. a final error of less than one local time base counter clock cycle 78. Once the user terminal [eg, 32 (1)] is closed in synchronization with the downstream time markers, the terminal The user can request interactive service requests via upstream communications, returning now to FIGURE 1, in an upstream direction from the user terminals 32 (l) -32 (x) to the provider. remote service provider, to initiate any upstream communication from the user terminals 32 (l) -32 (x) to the Central Office equipment 11 and the Remote Service Provider, a user terminal [eg 32 ( 2)] transmits an interactive service request via the cable plant 22 and by a previously determined or implicit upstream channel [eg channel 23 (1)] to the Control Unit and Network Interface 30. The Control Unit and Network Interface manages the underlying physical cable plant 22 on behalf of a Network Administrative Entity (not shown). The use of the bandwidth in the cable plant 22 is maximized substantially over space (nodes in a tree-like architecture), frequency (radiofrequency bearers), and time domains (TDM). In response to a service request from a remote User Terminal, the Network Interface and Control Unit 30 dynamically assigns an upstream channel to the user terminal requesting the interactive service request for subsequent communications. More particularly, the Control Unit and Network Interface 30 allocates a channel frequency, a frame length, and a number of time slots (packets) for the upstream transmission to the User Terminal for communication with the Provider of Remote service This information is transmitted to the User Terminal via an access control message to the medium provided to the access control multiplexers to the means 14 (l) -14 (n) in the downstream direction. Once set, the User's terminal communicates with the Remote Service Provider using the channel frequency, the frame length and the assigned time slots in the upstream transmission direction. The plurality of upstream channels 23 (1) - 23 (n) in the Central Office equipment 11 comprises Burst Demodulators 24 (l) -24 (n), respectively, and the respective Upstream Real Time Modules (URTM) ) 26 (l) -26 (n) in sequence. The Burst Demodulators 24 (1) -24 (n) work in reverse • with respect to the Generic Modulators 18 (l) -18 (n) to recover the digital bit current bursts of the modulated Frequency or Frequency carriers intermediate from the User Terminals 32 (l) -32 (x). In addition, Burst Demodulators 24 (l) -24 (n) measure the signal strength of each burst propagating through them, and both add a byte to the burst that contains the signal power measurement of the burst and use the power measurements to perform energy control functions. The Burst Demodulators 24 (l) -24 (n) can optionally measure the arrival times of the bursts relative to an Aperture control signal received from the Real-Time Modules Upstream 26 (l) -26 (n), respectively, in symbol time units, and join a burst arrival time measurement, for example, to the tail (end) of the burst after the power measurement byte of the signal. Alternatively, an external entity (not shown) may perform the burst arrival timer measurements relative to the Aperture control signal. For optimal operation, the Aperture control signal is used to enable the burst demodulation operation while operating in the time division multiple access environment. Enabling the Demodulators 24 (l) -24 (n) around an expected window of each burst received in a Burst Demodulator decreases the probability of a false burst detection. Referring now to FIGURE 4, a block diagram of an upstream channel 23 (1) operating with a network interface and control unit 30 and a time base timer 20 (shown in FIGURE 1) is shown. according to the present invention. It should be understood that each of the other upstream channels 23 (2) -23 (n) (shown in FIGURE 1) have block diagrams corresponding to that shown in FIGURE 4 and operate with the network interface and control unit 30 and a time base timer 20 in the same way. The upstream channel 23 (1) comprises a real-time processing module unit 26 (1) and a burst demodulator 24 (1). The upstream processing real-time processing module unit 26 (1) comprises a Channel Manager Unit (CHAN MGT) 90, a Burst Synchronization Entity 92, and a Cyclic Redundancy Verification Unit / forward Error Correction. (FEC / CRC) 94. Within the Channel 23 (1) unit, the burst synchronization entity 92 sends opening control signals to the burst demodulator 24 (1) via the conductor * 96, and receives detection signals. of bursts from the demodulator 24 (1) via the driver 97. The burster demodulator 24 (1) also transmits "receipt data" and "receipt clock" signals to the redundancy check / forward error correction unit 94 via conductors 98 and 99, respectively. The channel unit 23 (1) receives the signals from the time base clock and the time base marker from the time base timer 20 via bus 48, and radio frequency or intermediate frequency signals from the plant of cables 22 via conductor 50 (1). More particularly, the burst demodulator 24 (1) can receive radiofrequency signals directly from the cable plant 22. Alternatively, a converter (not shown) can be inserted between the cable plant 22 and the burst demodulator 24 ( 1) for converting the modulated radiofrequency signal received from the cable plant 22 into a modulated intermediate frequency signal for transmission to the burst demodulator 24 (1). Still further, the channel unit 23 (1) transmits packets (e.g., asynchronous transfer mode packets) to the packet redirector 28 via the conductor 49 (1), and interacts with the control unit and network interface 30 via the bus 51 and also via the conductor 49 (1), the packet redirector 28, and the conductor 52 (shown in FIGURE 1). Once a user terminal [e.g., 32 (2) in FIGURE 1] makes an interactive question and the network interface and control unit 30 allocates a frame length, time slots, and frequency for the terminal of use 32 (2) to use it via an access control message to the downstream medium as described hereinabove, the control unit and network interface 30 establishes the appropriate channel unit [eg, channel unit 23 ( 1)] by sending suitable establishment signals to the channel unit 23 (1) via bus 51. More particularly, the control unit and network interface 30 control unit and network interface 30 transmits signals via bus 51 for charging or configure the channel management unit 90 with certain parameters such as, for example, time slots and frame parameters (how many slots / frame), etc, for channel unit 23 (1). /// & The channel management unit 90 is basically a processor that controls the operation of the burst synchronization entity 92 and the cyclic redundancy check / forward error correction unit 94. For example, the channel management unit 90 maintains the statistics track for channel unit 23 (1) so, for example, the number of errors in each received time slot, power levels, etc. such as those obtained from the cyclic redundancy check / forward error correction unit 94. The actual data packets transmitted by the channel management unit 90 include locally generated statistics data on the packets in each slot containing the number average of errors and the power level seen in each slot or package. That information is sent to the Control Unit and Network Interface 30 in the form of, for example, an asynchronous transfer mode packet via the packet redirector 28. More particularly, the asynchronous transfer mode packets transmitted by the channel management unit 90 contain statistical information for the network interface and control unit. and they are transmitted via the driver 49 (1) to the packet redirector 28 which redirects these packets of statistical information to the control unit and network interface 30 via the driver 52 (shown in FIGURE 1). The forward error correction / redundancy check unit 94 functions to receive data or clock packets from the Burst Demodulator 24 (1) via leads 98 and 99, respectively and perform forward error checking (FS) or a cyclic redundancy checker CRC, or any other desirable error checking technique on the data of the clock packets. The corrected error data packets are transmitted via the driver 49 (1) to the packet redirector 28 where they are placed on an appropriate channel for transmission to the remote Service Provider via the conductors 54 (shown in FIGURE 1). More particularly, the packet redirector 28 determines whether a packet is a packet of data that must be redirected to the remote Service Provider via the conductors 54, or a packet of statistical information that must be sent back to the Control Unit and Network Interface 30 via the driver-52 displaying differentiated codes that were entered in the header field by the forward error correction / redundancy verification unit 94 and the Channel Management Unit 90, respectively. To achieve synchronization in the upstream Channel Unit 23 (1) the Burst Synchronization Entity 92 generates an Aperture control signal for transmission via the conductor 96 to the Breakaway demodulator 24 (1), and receives a signal from bursts detection from the burster demodulator 24 (1) via the driver 97. The burster synchronization entity 92 uses the time base clock and the time base marker signals from the time base clock via the busbar 48 to determine when there should be a burst and to generate the aperture control signal from the time base clock and the time base marker signals. Referring now to FIGURES 5 and 6, FIGURE 5 shows a timing diagram for a late burst in the upstream channel unit 23 (1) of FIGURE 4, and FIGURE 6 shows a burst timing diagram early in the upstream channel unit 23 (1) of FIGURE 4. More particularly, the burst synchronizing unit 92 generates a time reference (tS (0t) for each time slot in the form of a control signal for the burst demodulator 24 (1) via the conductor 96, and receives a burst detection signal from the burst demodulator 24 (1) via the conductor 97. The time slot (ts) or ot) is a function of the time base marker signals received through the Burst Synchronization Entity 92 from the time base timer 20 via bus 48 and the parameters of the associated channels loaded by the control unit and network interface 30 in l to channel management unit 90 via bus 51. The position of the opening signal (tapr) with respect to the signal of the time slot is programmable via the control unit and network interface 30. The arrival time of the head end of a burst is shown as tarv in FIGURES 5 and 6. An incoming synchronization error of a burst (terr) is defined in equation 1 as: Then, if terr <; 0 (as shown in FIGURE 5), the burst is late, and if the tcrr > 0 (as shown in FIGURE 6), the burst is early. Normal operations require | terr | < tg, where tg (not shown) is a guard time between bursts. For systems comprising elements with a negligible processing delay variation, terr is a correction factor that can be used by any suitable classification algorithm. More particularly, classification is defined as a procedure or technique used to determine a time correction required to compensate for all system synchronization deviations such as processing delays, channel delays, transport delays, packet tremors, and precision of the oscillator. This is necessary to optimize the bandwidth in a time domain. Without classification, a dominant factor in the determination of guard time is determined by the worst propagation delay of the case that determines a minimum slot width tS | lw, where tsioiw = burst length + worst case propagation delay (Ec . 2) .

It should be appreciated and understood that the specific embodiments of the invention described hereinabove are merely illustrative of the general principle of the invention. Those skilled in the art can make various modifications which are consistent with the principles set forth above, for example, other time marker formats that are independent of a data rate, a physical channel, and a channel protocol can be used. the transport stream to synchronize the user terminals.

Claims (21)

1. A Time Division Multiple Access (TDMA) communication network comprising: a downstream channel synchronization element comprising: a time base timer to generate time markers comprising programmable N-bit cyclic reference counts Modules that increase at a previously determined frequency and reset to 0 when the account reaches a previously defined value; and at least one time marker insertion unit, each time marker insert unit comprising a first input terminal for receiving a time division multiple access transport stream having a previously determined data rate and comprising data packets and access control packets to the media that are spread between the data packets at previously determined intervals, a second input terminal to receive the time markers generated by the time base timer and to insert an account of time marker received at the time in a medium access control pack (MAC) received at the time, and an output terminal for transmitting the time division multiple access data stream received with the time stamp accounts inserted in the access control packages to the medium in a multiple-access transport stream of division of tie continuous output mpo for remote user terminals where time markers are independent of a data rate, a physical channel, and a transport stream channel protocol and are used to synchronize user terminals.

2. The time division multiple access communication network of claim 1, wherein the downstream channel synchronization element also comprises at least one modulating element, each modulating element modulating the multipath division multiple access transport stream. digital time transmitted by at least one separate time marker insertion unit in a separate analog output time division multiple access transport stream having a protocol previously determined for transmission to remote user terminals.

3. The time division multiple access communication network of claim 2, wherein the downstream channel synchronization element comprises: a plurality of time marker insertion units and two of the marker insertion units of time receive digital time division multiple access transport streams having different previously determined data regimes comprising data packets and access control packets to the Media that are spread between the data packets at previously determined intervals, and transmit the time division multiple access transport stream received with the time stamp accounts in the media access control packets in a continuous digital output time division multiple access transport stream; and a plurality of modulator elements wherein two of the modulator elements modulate the digital time division multiple access transport streams transmitted by the separate units of the plurality of time marker insertion units in access transport streams time division multiple of a separate analog output that have different protocols previously determined for transmission to remote user terminals. The time division multiple access communication network of claim 1, wherein the downstream channel synchronization element comprises a plurality of time marker insertion units, wherein two of the time marker units receive separate digital time division multiple access transport streams having different previously determined data regimes comprising data packets and media access control data packets that are spread between the data packets at previously determined intervals, and transmits the time division multiple access transport stream received with the time marker accounts inserted into the medium access control packets in a continuous access time division multiple access transport stream for the terminals of remote users. The time division multiple access communication network of claim 4, wherein the downstream channel synchronization element further comprises a plurality of "modulator" elements wherein two of the modulator elements modulate the transport stream digital time division multiple access transmitted by a separate unit of the plurality of time marker insertion units in a separate analog output time division multiple access transport stream having different protocols previously determined for transmission to the remote user terminals 6. The time division multiple access communication network of claim 1, further comprising an upstream channel synchronizing element, comprising at least one upstream channel unit, wherein each Upstream channel unit comprises a real-time unit programmed friendly to (a) store information related to a frame length and a number of time slots previously assigned arbitrarily to each user terminal that is transmitting data packets via the upstream channel unit, and (b) receive both an upstream time division multiple access transport stream, comprising data packets at a predetermined rate from the remote user terminals, such as the time stamps comprising the programmable cyclic reference accounts of modular N-bits generated by the time-based timer to synchronize the processing of the data packets in the upstream channel unit during its arrival time to the upstream channel unit. The time division multiple access communication network of claim 6, wherein each upstream channel unit in the upstream channel synchronization element further comprises a burst demodulator to receive both the access transport stream upstream time division multiple, comprising the data packets at a predetermined data rate directed to the upstream channel unit from the remote user terminals, as an open control signal from the programmable real-time unit for measuring burst arrival times relative to the opening control signal in the upstream time division multiple access transport stream. The time division multiple access communication network of claim 6, wherein the upstream channel synchronization element comprises a plurality of upstream channel units, and at least two of the upstream channel units receive and processing upstream time division multiple access transport streams comprising different transport data stream protocols from some of the plurality of user terminals. The time division multiple access communication network of claim 6, wherein each user terminal comprises a network interface module for performing network synchronization functions comprising: a synchronization element comprising: a local oscillator digitally controlled to generate clock pulses at a previously set frequency; a counter for generating modular N-bit programmable cyclic local oscillator accounts from a time marker received in a downstream transport stream that increases at a frequency previously established from the local oscillator between the reception times of the marker of time from the downstream transport stream; and a comparison element for comparing a time marker account received at the time in a downstream time division multiple access transport stream from at least one time marker insertion unit with an account of N current modules to starting from the counter, and generating an error control output signal corresponding to a difference between a received time marker account and a current account in the counter for transmission to the digitally controlled local oscillator, to alter the previously established frequency of the local oscillator digitally controlled in a previously determined direction. 10. A time division multiple access communication network comprising: a current downstream channel synchronization element comprising: a time base timer to generate time markers comprising programmable N-bit cyclic reference counts Modules that are incremented at a previously determined frequency and reset to O when the account reaches a previously defined value; and a plurality of time marker insertion units, each time marker insertion unit comprising: a first input terminal for receiving a time division multiple access transport stream having a previously determined data rate and comprises data packets and media access control packets that are spread between the data packets at previously determined intervals; a second input terminal for receiving the markers generated by the time base timer and for inserting a time marker account received at the time for a media access control packet received at the time; and an output terminal for transmitting the timeslot multiple access data stream received with the time stamp accounts inserted in the media access control packets in a split-stream multiple access output stream. time continues to the terminals of remote users, where the time markers are independent of a data rate, a physical channel, and a channel protocol of the time-division multiple access output transport stream and are used for synchronizing the user terminals, wherein two of the time stamp insertion units receive digital time division multiple access transport streams having different previously determined data rates. The time division multiple access communication network of claim 10, wherein the downstream channel synchronization element further comprises a plurality of modulator elements wherein two of the modulator elements modulate the transport streams of the modulator. digital time division multiple access transmitted by separate units of the plurality of time marker insertion units into separate analog downstream time division multiple access output streams having different previously determined protocols for transmission to the terminals of remote users. The time division multiple access communication network of claim 10, further comprising an upstream channel synchronization element, comprising a plurality of upstream channel units, each upstream channel unit comprising a unit Real-time programmable for (a) storing information related to a frame length and a number of time slots previously arbitrarily assigned to each user terminal that is transmitting data packets in a multipath division multiple access transport stream. upstream time via the upstream channel unit, and (b) receiving both the upstream time division multiple access transport stream comprising data packets at a predetermined data rate from the remote user terminals, and the time markers comprising the reference accounts. cyclic programmable modular N-bits generated by the time-based timer to synchronize the processing of the data packets in the upstream channel unit during its arrival time to the upstream channel unit. The time division multiple access communication network of claim 12, wherein each upstream channel unit in the upstream channel synchronization element further comprises a burst demodulator to receive both the access transport stream upstream time division multiple comprising the data packets at a data rate previously determined from the remote user terminals, as an open control signal from the programmable real-time unit for measuring the arrival times of the packets of data relative to the opening control signal in the received upstream time division multiple access transport stream. The time division multiple access communication network of claim 12, wherein at least two of the upstream channel units receive and process the upstream time division multiple access transport streams comprising different protocols of transport streams. The time division multiple access 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 synchronization functions of network comprising synchronization elements comprising: a digitally controlled local oscillator for generating modular N-bit programmable cyclic local oscillator accounts that increase at a predetermined frequency; and a counter for generating modular N-bit programmable cyclic local oscillator accounts from a time marker received in a downstream transport stream that increases at the frequency previously established from the local oscillator between the times of reception of the marker of time from the downstream transport stream; and a comparison element for comparing a time marker account received at the time, in a downstream time division multiple access transport stream, from one of at least one time marker insert unit, to an account of N current modules from the counter, and generating an error control output signal corresponding to a difference between a received time marker count and a current account in the counter for transmission to the digitally controlled local oscillator to alter the previously established frequency of the local oscillator digitally controlled in a previously determined direction. 16. A method for synchronizing communications between a central office computer and a plurality of remote user terminals in a time division multiple access communication network comprising the steps of: (a) generating a time marker sequence which comprises modular N-bit programmable cyclic reference counts that are incremented at a predefined frequency in a time base timer and reset to 0 when the account reaches a previously defined value. (b) receiving at least one time division multiple access transport stream, each digital time division multiple access transport stream comprising a predetermined frequency that includes data packets and access control packets to the means that they are scattered among the data packets at previously determined intervals; (c) inserting a time stamp account received at the time generated in step (a) into a media access control packet that is received at the time in step (b) in each of at least one time division multiple access transport stream in a time marker insert unit; and (d) transmitting each digital-time division multiple access transport stream with the time marker accounts inserted in the media access control packets from step (c) in a multiple access transport stream. separate continuous downstream time division division, to the remote user terminals, where the time stamps in each of the analog access downstream time division multiple access output streams are independent of a data rate , a physical channel, and a channel protocol of the downstream time division multiple access output stream and are used by the plurality of user terminals to synchronize their upstream data transmissions. The method of claim 16, comprising the additional step of: (e) modulating each of at least one digital time division multiple access transport stream transmitted by the time marker insert unit, in one separate analog downstream time division multiple access output transport stream, having a pre-determined protocol for transmission to the plurality of remote user terminals. The method of claim 16, further comprising the steps of: (e) storing separate control information related to a frame length and a number of time slots previously arbitrarily assigned to user terminals previously determined in a programmable real-time unit of an upstream channel unit that is assigned to receive data packets from previously determined user terminals in an upstream direction in an upstream time division multiple access transport stream; and (f) receiving both the time markers comprising the programmable cyclic reference counts of modular N-bits generated by the time base timer in step (a) and the current time division multiple access transport stream. above comprising data packets at a previously determined data rate from the remote user terminals previously determined for the synchronization of the processing of the data packets from the user terminals previously determined in the upstream channel unit during their arrival time to the upstream channel unit. The method of claim 18, wherein in the embodiment of step (f) receiving both the upstream time division multiple access transport stream, comprising data packets at a data rate previously determined from the remote user terminals previously determined, as an opening control signal from the programmable real-time unit for measuring the arrival times of the data packets relative to the opening control signal in the multiple access transport stream of time division. The method of claim 19 wherein the time division multiple access communication system comprises a plurality of upstream channel units, and in the embodiment of step (f), at least two of the current channel units up receive and process separate upstream time division multiple access transport streams comprising different transport stream protocols. The method of claim 16, wherein each of a plurality of remote user terminals comprises a network interface module for performing the steps of: (e) generating clock pulses at a frequency previously established in a local oscillator Digitally controlled (f) generating modular N-bit programmable cyclic local oscillator accounts from a time marker received in a downstream transport stream that increases to the frequency previously established from the local oscillator between the receive times of the time from the current-transport downstream; and (g) comparing a time marker account received at the time in a downstream time division multiple access transport stream, with a count of N current modules from the counter, and generating a control output signal error corresponding to a difference between a received time marker account and a current account in the counter for transmission to the digitally controlled local oscillator to alter the previously established frequency of the digitally controlled local oscillator in a previously determined direction. (h) altering the previously determined frequency of the digitally controlled local oscillator in a previously determined direction in response to the error control output signal generated in step (g). SUMMARY 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 from user terminals, a time-based stopwatch in the central office generates cyclic reference N-bit modular accounts as time markers. In a downstream direction towards the plurality of user terminals, the insertion units in the time stamp in the central office receive both (a) separate time division-digital multiple access transport streams having a data rate previously determined that includes data packets and media access control (MAC) packets that are spread between the data packets at previously determined intervals, such as (b) the time markers generated by the time base timer, and insert a time marker account received at the time into a media access control package received at the time. The resulting downstream time division multiple access transport streams with the time marker accounts inserted in the media access control packets are transmitted in a continuous time division multiple access output transport stream. to the terminals of remote users. The time markers are independent of a data rate, a physical channel, and a channel protocol of the transport stream. At each user terminal, a network interface module is self-synchronized by comparing received time markers and locally generated time marker accounts to correct the frequency of a local oscillator. The upstream channel units in the central office are synchronized using the time markers generated by the time base timer to receive and process the upstream data packets during their arrival at their previously assigned channel unit. * * * * *