Patent Abstract:
An out-of-band ranging technique is automatically initiated at a customer premises equipment unit when the equipment is installed, when power is restored after a power failure or interruption, upon verification of the equipment, upon reconnection after a disconnection of the equipment or the like. To this end, an out-of-band tone is employed that is automatically transmitted when the customer premises equipment that transmits the TDMA signal is powered ON, or transmitted in response to a specific command generated locally or remotely. Specifically, when ranging is being effected the customer premises equipment generates and transmits the out-of-band ranging tone until a message is received from a remote terminal indicating that the transmission of the ranging tone be terminated. The loop delay being determined is the delay interval between transmission of the termination message and detection that transmission of the ranging tone has terminated. Then, a message is transmitted to the customer premises equipment that contains the ranging delay interval that is to be used in all future transmissions to the remote terminal. In one embodiment of the invention, the customer premises equipment automatically switches to an idle standby state when the remote terminal removes its upstream transmission slot. In the standby state, the customer premises equipment is still capable of receiving data and is periodically polled by the remote terminal assigning it an upstream transmission slot. If a customer premises equipment in the standby state is not polled during a predetermined interval, it automatically switches to a verification state. Additionally, if the customer premises equipment does not respond when polled, the remote terminal transmits it a message putting it in the verification state. If a polled customer premises equipment responds with an out-of-band tone, which indicates that it is in the verification state, the remote terminal treats it as though it is verifying ranging. If the out-of-band tone is properly aligned, the customer premises equipment is switched to an active state.

Full Description:
RELATED APPLICATIONS 
     U.S. patent applications Ser. Nos. 09/356,978 and 09/356,979 were filed concurrently herewith. 
    
    
     TECHNICAL FIELD 
     This invention is related to Time Division Multiple Access (TDMA) communications and, more particularly, to ranging in the transmission of TDMA signals. 
     BACKGROUND OF THE INVENTION 
     In TDMA transmission of signals it is required that all the individual signal components of the TDMA transmission have equal transmission delay. Consequently, a delay interval must be determined for each signal included in the TDMA transmission which when added to the individual signal yields a common loop delay for that signal equal to individual loop delay of the other TDMA signal components. To determine the particular delay to be added to each of the TDMA signal components, a so-called “ranging” procedure is effected when an equipment unit which will transmit the signal is installed, relocated, or otherwise has a disruption in service. A popular prior known ranging procedure is so-called “in-band ranging”, where in-band ranging messages are employed to effect the ranging procedure. Unfortunately, the use of the in-band ranging messages requires that the transmission bandwidth be temporarily interrupted and used for transmitting the in-band ranging messages. Thus, in-band ranging is an intrusive procedure that interferes with normal bandwidth use. Additionally, it is necessary to schedule when the in-band ranging is to be done. Indeed, as the rate at which in-band ranging is scheduled is increased, more and more transmission bandwidth is lost. This is extremely undesirable because the bandwidth cannot be used for other purposes, for example, constant bit rate transmission. 
     SUMMARY OF THE INVENTION 
     These and other problems and limitations of the prior known in-band ranging procedure are addressed by employing a non-intrusive out-of-band ranging technique. Ranging is automatically initiated at a customer premises equipment unit when the equipment is installed, when power is restored after a power failure or interruption, upon verification of the equipment, upon reconnection after a disconnection of the equipment or the like. To this end, an out-of-band tone is employed that is automatically transmitted when the customer premises equipment that transmits the TDMA signal is powered ON, or transmitted in response to a specific command generated locally or remotely. 
     Specifically, when ranging is being effected the customer premises equipment generates and transmits the out-of-band ranging tone until a message is received from a remote terminal indicating that the transmission of the ranging tone be terminated. The loop delay being determined is the delay interval between transmission of the termination message and detection that transmission of the ranging tone has terminated. Then, a message is transmitted to the customer premises equipment that contains the ranging delay interval that is to be used in all future transmissions to the remote terminal. 
     In one embodiment of the invention, the customer premises equipment automatically switches to an idle standby state when the remote terminal removes its upstream transmission slot. In the standby state, the customer premises equipment is still capable of receiving data and is periodically polled by the remote terminal assigning it an upstream transmission slot. If a customer premises equipment in the standby state is not polled during a predetermined interval, it automatically switches to a verification state. 
     Additionally, if the customer premises equipment does not respond when polled, the remote terminal transmits it a message putting it in the verification state. If a polled customer premises equipment responds with an out-of-band tone, which indicates that it is in the verification state, the remote terminal treats it as though it is verifying ranging. If the out-of-band tone is properly aligned, the customer premises equipment is switched to an active state. 
     An advantage of polling customer premises equipment in the idle standby state is that it enables system operations to distinguish between an idle customer premises equipment, power outages, disconnected or otherwise removed customer premises equipment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows, in simplified block diagram form, a video distribution system employing an embodiment of the invention; 
     FIG. 2 shows, in simplified block diagram form, details of an ONU ranging delay unit employed in practicing the invention; 
     FIG. 3 shows, in simplified block diagram form, details of an OLC ranging delay unit employed in practicing the invention; 
     FIGS. 4A,  4 B and  4 C when connected A—A, B—B, C—C, D—D, E—E and F—F form a flow chart illustrating the steps in the ranging delay procedure of the ONU ranging delay unit of FIG. 2; and 
     FIGS. 5A and 5B when connected A—A and B—B form a flow chart illustrating the steps in the ranging delay procedure of the OLC ranging delay unit of FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows, in simplified block diagram form, a video distribution system employing an embodiment of the invention. Specifically, shown is network  100  including video server  101  which supplies downstream video signals to broadband network  102 , in response to an upstream communication including a selection message. Broadband network  102  supplies the communications signals to and from optical line terminal  103 . At optical line terminal (OLT)  103 , optical line circuit (OLC)  104  interfaces to an optical fiber line. The optical fiber line is, for example, a power splitting passive optical network (PSPON) fiber including optical fibers  110  and  111  on which optical signals are transmitted using coarse wavelength division multiplexing. Transmission on the fiber lines  110  and  111  is achieved using two wavelengths, 1550 nano meters (nm) downstream, for example, to a home and 1310 nm upstream, for example, from the home. The PSPON fibers  110  may be split into a predetermined number of optical fibers, for example, 32 fibers  111 , thereby interfacing via associated ONUs  106  with 32 locations. Note that OLT  103  serves one or more OLCs  104 , namely,  104 - 1  through  104 -Z, coupled to a corresponding number of fiber lines, namely,  110 - 1  through  110 -Z, respectively, and that an OLC  104  serves one or more ONUs  106  via optical fibers  111 - 1  through  111 -W. In this example, the downstream transmission of video signals is in asynchronous transfer mode (ATM) cells via time division multiplex (TDM), while upstream transmission of communication is via time division multiple access (TDMA), and both downstream and upstream communications is at 155.52 Mb/sec. Efficient TDMA communications in the upstream direction requires all optical network units (ONUs)  106  to have equal loop delay in relationship to their associated OLC  104 . This is realized by employing a ranging procedure that is executed when each ONU  106  associated with a particular OLC  104  is installed, moved, returned to service, or the like. The ranging procedure defines an artificial delay that when added to the transmission loop delay of an ONU  106  yields the required common loop delay. The desired ranging delay is obtained, in this example, by employing a unique out-of-band ranging procedure, in accordance with the invention 
     Actually, OLT  103  is a special ATM switch including a traditional ATM fabric and input/output (I/O) ports. In this example, two types of I/O boards are required, namely, standard SONET (synchronous optical network) boards, e.g., OC-12 units, and OLC boards. Video signals received from OLT  103  as ATM cells from one or more SONET boards are distributed to the OLC boards. Because of this, upstream channel select messages being sent to a video services controller in video server  101  are intercepted within the OLT  103 , which accumulates the number of viewers of each video program that is OLT  103  wide. Only channel (program) selections that are not available within presently received SONET VCs are passed on to the video services controller  202  in video server  101 . Additionally, messages are sent by OLT  103  to video server  101  and, therein, to a video services controller therein (not shown) whenever a transmitted video program is no longer being viewed by any OLT  103  supported TV  107 . It is noted that each of OLC units  104  includes, in this example, a CPU and memory that may be a microprocessor with memory, as described below. 
     Optical network unit (ONU)  106  terminates the PSPON  111  fiber and provides appropriate interfaces, in this example, to one or more television sets (TVs)  107 - 1  through  107 -N. Each of TVs  107 - 1  through  107 -N has an associated one of remote control (RC) units  108 - 1  through  108 -N, respectively. 
     Network  100  supplies, for example, via one or more video services controller units in video server  101  in response to specific program requests, conventional broadcast TV programs, programs similar to those supplied via cable TV providers, satellite TV providers, video on demand and the like. Procedures for requesting and transmitting video programs are described in greater detail below. 
     As shown in FIG. 1, a residential video subsystem includes an ONU  106  and one or more TVs  107  and associated RC units  108 . In this example, ONU  106  and TVs  107  are interconnected via coaxial (COAX) cable. 
     As indicated above, the desired ranging delay is effected by obtaining a measure of loop delay between an ONU  106  and its associated OLC  104 . This is realized, in this example, my employing a unique out-of-band ranging arrangement, in accordance with the invention. 
     To this end, ONU  106  includes an ONU ranging delay unit  200  including, in this example, apparatus as shown in FIG.  2 . Specifically, shown is PSPON transceiver  201  including PSPON interface  202  for interfacing PSPON optical fiber  111 , in well known fashion. Incoming optical signals from PSPON fiber  111  are supplied to optical/electrical (O/E) converter  203  where they are converted into electrical signals. In turn, the incoming electrical signals are supplied to controller  205  and, therein, to input interface  206 . Outgoing electrical signals are converted via electrical/optical (E/O) converter  204  to optical signals. In turn, the outgoing optical signals are supplied via PSPON interface  202  to PSPON optical fiber  111 . 
     Controller  205  includes central processor unit (CPU)  208  which may be a microprocessor, memory  209 , user input/output (I/O) units  210 , status register  211 , assigned time slot register  212 , start of down-stream frame register  213 , ranging delay register  214 , transmit burst control unit  215  and data first-in-first-out (FIFO) register  221 . Units  206 ,  208  through  215  and  221  are interconnected via bus  207 . A power ON status signal is supplied to one input of AND gate  216 , while an initialized status signal is supplied to an inhibit input of AND gate  216 , both from status register  211 . Thus, And gate  216  yields a high state output when power ON is a high state and initialized is a low state. This high state output from AND gate  216  is supplied via OR gate  217  to enable ranging tone oscillator  220  to supply as an output the desired out-of-band ranging tone. In this manner the ranging state is effected. Again, in this example, the out-of-band ranging tone is generated at 466.56 MHz. This ranging tone is supplied to summer  222  and, thereafter, to PSPON  111  via E/O  204  and PSPON interface  202 . 
     A verify status signal is supplied from status register  211  to an input of AND gate  218 , while a transmit burst control signal is supplied from transmit burst control  215  to a second input of AND gate  218 . And gate  218  is controlled via the supplied signals to enable transmission of the out-of-band ranging tone during the assigned time slot to effect the verify state. 
     An active status signal is supplied from status register  212  to an input of AND gate  219 , the transmit burst control signal is supplied to a second input of AND gate  219  and a clock (CLK) signal is supplied to a third input of AND gate  219 . And gate is controlled via the supplied signals to control supplying the CLK signal to data FIFO  221 , thereby enabling the active data state. The data output from data FIFO  221  is supplied via summer  222 , E/O  204  and PSPON interface  202  to PSPON fiber III. 
     Operation of ONU ranging delay unit  200  is described below in conjunction with the flow chart of FIG.  4 . 
     FIG. 3 shows, in simplified block diagram form, details of an OLC ranging delay unit employed in practicing the invention. Specifically, shown is PSPON transceiver  301  including PSPON interface  302  for interfacing PSPON optical fiber  110 , in well known fashion. Incoming optical signals from PSPON fiber  110  are supplied to optical/electrical (O/E) converter  303  where they are converted into electrical signals. In turn, the incoming electrical signals are supplied to diplexer  306 , which extracts and supplies the in-band data signals to controller  305  and, therein, to I/O  308 . Diplexer  306  also extracts the out-of-band ranging tone and supplies it to tuned detector  307 . A high state output from detector  307  indicating the reception of the out-of-band ranging tone is supplied to one input of AND gate  316 . 
     Controller  305  includes I/O  308 , CPU  310 , which may be a microprocessor, memory  311 , enable register  312 , reset register  313 , clock  314  and ranging delay register  315 , all interconnected via bus  309 . 
     An output from enable register  312  is supplied to a second input of AND gate  316  and when it is a high state signal and the high state tone detection signal is present, AND gate  316  supplies an enable high state signal to ranging delay timer  317 . This enables timer  317  to count the clock output from clock  314 . As described below, when the out-of-band ranging tone is no longer detected the count in timer  317  represents the loop delay for a particular ONU associated with this OLC. The loop delay interval is supplied to ranging delay register  315 . A reset signal from reset register initializes ranging delay timer  317 . 
     Operation of OLC ranging delay unit  300  is described below in conjunction with the flow chart of FIG.  5 . 
     FIGS. 4A,  4 B and  4 C when connected A—A, B—B, C—C, D—D, E—E and F—F form a flow chart illustrating the steps in the ranging delay procedure of the ONU ranging delay unit of FIG.  2 . The ONU  106  ranging delay procedure is begun at  401 . Thereafter, step  402  tests to determine if ONU power is ON. If the test result is NO, step  402  is repeated until it yields a YES result. Then, step  403  tests to determine if the ONU is initialized. If the test result is YES, ONU  106  is in the initialized state and control is transferred to step  408 . If the test result in step  403  is NO, ONU  106  has not been initialized and is in the ranging state, and step  404  causes the out-of-band ranging tone to be transmitted. Again, in this example, the ranging tone is generated at 466.56 MHz, which is outside the normal in-band message transmission band. Step  405  tests to determine if a broadcast message as been received by ONU  106 . If the test result is NO, step  405  is repeated until a YES result is obtained. Note that the received broadcast message includes an instruction for the ONU to stop transmission of the ranging tone and that the ONU assume an ID. Then, step  406  causes the transmission of the ranging tone to be terminated. Step  407  sets the ID for ONU  106  to ONUID. Step  408  tests to determine if a unicast message has been received including the ranging delay determined for the ONUID, namely, “F” which is the number of frames, “B” which is the number of bytes and “b” which is the number of bits. In this example, F is a 0, 1 or 2 frame, B is between 0 and 2429 bytes, inclusive, and b is between 0 and 7 bits, inclusive. Step  409  causes the ranging delay for the ONUID to be set to the received values of F, B and b. Step  410  tests to determine if the up-stream time slot assignment for the ONUID has been received. If the test result is NO, step  410  is repeated until it yields a YES result indicating that the assigned time slot identified by its offset and size has been received. The offset is the number of bytes from the start of each frame and the size is the time slot length in bytes. Step  411  indicates that the unicast message to this ONUID including the assigned time slot has been received and causes the assigned time slot to be set to the received offset and size. Then, this ONU is in the verify state and step  412  causes the transmission of the out-of-band tone in the assigned time slot. Then, step  413  tests to determine if a unicast message to this ONUID has been received. If the test result is NO, step  413  is repeated until it yields a YES result. Step  414  tests to determine if the received message includes the ranging delay for this ONUID. If the test result is YES, step  415  causes the ranging delay for this ONUID to be set to the received F, B and b. Note that in the verify state, the ranging delay value may be fine tuned through the reception of new values for F, B and b. Thereafter, steps  412  through  415  are iterated until step  414  yields a NO result. Then, step  416  causes the ONU to be set to the data state. Step  417  causes the in-band data burst to be transmitted in the assigned time slot. This is the ONU active data state. Step  418  tests to determine if a unicast message for this ONUID has been received. If the test result is NO, step  418  is repeated until it yields a YES result, if at all. Then, step  419  tests to determine if the received unicast message is switch to verify state. If the test result is YES, the ONU reenters the verify state, control is transferred to step  412  and steps  412  through  419  are iterated until step  419  yields a NO result. Note that the verification state may be reentered because of some particular event being detected in ONU  106 , for example, power failure, or from a control message from OLC  104 . Thereafter, step  420  causes the assigned time slot to be set to zero (0). This is the ONU idle state. Step  421  causes the ONU to be set to poll for status timer. In this example, the time-out interval for the status timer is one (1) second. Then, step  422  tests to determine if the status timer has timed-out. If the test result in step  422  is YES, control is transferred to step  408  and appropriate ones of steps  408  through  422  are iterated until step  422  yields a NO result. Step  423  tests to determine if a unicast message for this ONUID has been received. If the test result is NO, steps  422  and  423  are repeated until either of them yields a YES result. If step  422  yields a YES result, operation is as described above. If step  423  yields a YES result, step  424  tests to determine if the received unicast message is switch to verify state. If the test result is YES, control is transferred to step  412  and appropriate ones of steps  412  through  424  are iterated until step  424  yields a NO result. Then, step  425  causes the assigned time slot to be set to a new assigned time slot, namely, a new offset and size. Thereafter, control is transferred to step  417 , appropriate ones of steps  417  through  425  iterated and if necessary appropriate ones of steps  408  through  425  are iterated until the ONU again enters the active data state, i.e., its normal operational state. 
     Thus, it is seen that if the polled ONC responds with transmission of the out-of-band ranging tone, that is an indication that the ONU is already in the verify state and the associated OLC treats the ONU as though it was verifying ranging. If the out-of-band tone is properly aligned in the assigned time slot, the ONU is caused to switch to the active data state. 
     Additionally, requiring an idle ONU to be polled, enables system operations to distinguish among an idle ONU, a power outage and a relocated ONU, as described below in relationship to the operation of the OLC ranging unit. 
     FIGS. 5A and 4B when connected A—A and B—B form a flow chart illustrating the steps in the ranging delay procedure of the OLC ranging delay unit of FIG.  3 . The OLC ranging delay procedure is started in step  501 . Thereafter, step tests to determine if a ranging tone has been received by the OLC from ONUID. If the test result is NO, step  502  is repeated until it yields a YES result. Then, step  503  causes a message to be transmitted to the ONUID causing it to stop transmitting the ranging tone and to assign the ONU ID as ONUID. Step  504  causes the ranging delay timer to be set. Then, step  505  tests to determine if the transmission of ranging tone has stopped. If the test result is NO, step  505  is repeated until it yields a YES result. Step  506  causes the ranging delay timer to be stopped. The accumulated time interval of the ranging delay timer is the ranging delay for the ONUID. That is, the interval between the terminate transmission of ranging tone message is sent by the OLC and detection that it has terminated is the loop delay for the ONUID. Then, step  507  causes the transmission of a unicast message to the ONUID including the determined ranging delay, namely, F, B and b. Step  508  causes the transmission of a message to the ONUID including assignment of an up-stream time slot, namely, offset and size. Step  509  tests to determine if an out-of band ranging delay tone presently being received in the assigned time slot is aligned with the assigned time slot. If the test result is NO, step  510  causes a message to be transmitted to the ONUID to adjust the ranging delay of the ONUID. Thereafter, step  509  again tests to determine if the out-of-band tone is aligned with the assigned time slot as adjusted. If the test result is NO, steps  510  and  509  are iterated until step  509  yields a YES result. Then, step  511  causes a message to be transmitted to the ONUID indicating that the ONU switch to the active data state. Step  512  tests to determine if up-stream data is being received from any ONU associated with this OLC. If the test result is NO, step  512  is repeated until it yields a YES result. Then, step  513  tests to determine if the data is in the proper time slot assigned to ONUID transmitting the data. If the test result is YES step  513  is repeated until it yields a NO result. Step  514  tests to determine if there is a loss of signal. If the test result is YES, step  515  causes a message to be transmitted to the ONUID switching it to the verify state. Then, control is transferred to step  508  and appropriate ones of steps  508  through  515  are iterated until step  514  yields a NO result. Step  516  tests to determine if there is a large time slot drift. If the test result is YES, control is transferred to step  515  and appropriate ones of steps  508  through  516  are iterated until step  516  yields a NO result. Then, step  517  tests to determine if there is a severe unadjustable problem. If the test result is YES, step  518  causes a message to be transmitted to the ONUID causing it to enter the uninitialized state. Returning to step  517 , if the test result is NO, step  519  tests to determine if the time slot drift is minor. If the test result is NO, control is returned to step  512  and appropriate ones of steps  512  through  519  are iterated, and if necessary appropriate ones of steps  508  through  519  are iterated, until step  519  yields a YES result. Then, step  520  causes a message to be transmitted to the ONUID including a new ranging delay, namely, a new F, B and b. 
     Note that if a power outage renders one or more ONU associated with the OLC to be inoperative, a so-called “self-aware” system must re-establish a correct state of operation of the one or more associated ONUs automatically when power is restored. An ONU that loses power stops transmitting data and reverts to the verify state. The associated OLC detects the “loss of signal” from the one or more ONU that lost power, and deletes them from a list of up-stream time slot assignments. Then, the list of ONCs that are not in the active state are polled, as described above. Consequently, when power is restored, the ONUs are brought on-line one at a time. 
     If an ONU is moved or otherwise disconnected, it is placed into the un-iniatilized state by clearing its ranging delay. When the ONU is reconnected, it will automatically initiate the ranging procedure, as described above. 
     In certain instances an ONU can be disconnected or moved without prior knowledge of the system operators. For example, an ONU can be disconnected and, then, reconnected at some other location without notification to the system operators. When the ONU is disconnected it loses power and switches to the verify state, as described above. When an attempt is made to reconnect and reactivate the ONU, however, its out-of-band ranging tone will be positioned incorrectly in the up-stream frame. That is, the out-of-band tone will be in the wrong time slot. Because of this, the associated OLC generates a message and send it to the ONU, which resets the ONC to the un-initialized state. This, in turn, results in the automatic activation of the ranging procedure. That is, the ONU is treated as a newly connected ONU. 
     As shown, out-of-band ranging has no impact on up-stream bandwidth management, i.e., it is non-intrusive. Additionally, the probability of a “ranging” collision is minimized because an ONU ranges immediately upon it being connected to the network and powered on. Moreover, an out-of-band ranging tone offers additional capabilities for non-intrusive verification, handling power outages, switching an ONU to a low power standby state and ONU location moves, as described above. 
     The above-described embodiments are, of course, merely illustrative of the principles of the invention. Indeed, numerous other methods or apparatus may be devised by those skilled in the art without departing from the spirit and scope of the invention.

Technology Classification (CPC): 7