Abstract:
A bidirectional telephone communication system for supporting a multiplicity of subscriber lines between a downstream distribution terminal using only two of a multiplicity of pre-existing transmission line pairs connected between an upstream distribution terminal and a downstream distribution terminal. Said system including automatic initializing and monitoring circuitry for powering up a communication link and reestablishing the link if lost.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to telephone systems and more particularly to methods and apparatus for upgrading an existing tip and ring prior art telephone system which uses a pair of copper conductors for each bidirectional connection between two distribution terminals to a system which requires only two pairs of existing copper (or other metal) conductors for carrying a plurality (such as twenty-four) bidirectional communications between the two distribution terminals. The invention also relates to such methods and apparatus for upgrading a telephone system which, after being upgraded according to the teachings of this invention, is compatible for still further and future upgrades. 
     2. Description of Related Art 
     Over the last twenty years, the demands for “telephone”-type communications has increased at exponential rates. Telephone-type communications, or “telephony,” is no longer simply applicable to telephone voice communications. In fact, the demands on the infrastructure and existing telephone systems from other types of telephony such as faxes, computer modems, etc. and other broadband uses now exceed voice communications in most locations. 
     Consequently, telephone systems in these high-density areas now use many different high speed, broadband transmission techniques, including light transmission through optical fibers. Yet, even though there are areas of communications or physical locations demanding this very high-density type of service, there are likely to be other areas or communications or physical locations immediately adjacent where the demands on telephone service has increased only slightly from the demands of twenty years ago. Therefore, methods and equipment must be provided which interface various levels of service demands. 
     It is therefore not unusual to require different upgrade levels of a telephone system depending upon these highly varying needs. In addition, because new and different services which require high-speed and broad-band telephone communications seem to be hitting the market every day, it is also desirable to provide methods and apparatus for upgrading a telephone system, which upgrade will also allow for continuous and much expanded upgrades of service in the future with minimal change to the existing infrastructure. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide methods and apparatus to increase the number of communication channels carried by existing copper wire pairs. 
     It is yet another object of the present invention to provide methods and apparatus for efficient and cost effective upgrading to existing infrastructure copper wire communication pairs. 
     These and other objects can be achieved by the present invention which provides bidirectional telephone delivery circuitry and methods for supporting a multiplicity of telephone subscriber lines at a downstream distribution terminal using only two of a multiplicity of pre-existing transmission line pairs connected between an upstream distribution terminal and the downstream distribution terminal. The methods and apparatus comprise an upstream distribution terminal which may receive and transmit PCM telephone signals to and from one location. These PCM signals are transmitted to conversion circuitry which includes an HDSL driver and receiving circuit for receiving HDSL TDM signals from a downstream terminal and for transmitting corresponding HDSL TDM signals to the downstream terminal on a pair of transmission line pairs. A pair of HDSL isolation transformers are included and, according to one embodiment, each of the pair has an upstream side coil connected to the HDSL driver and receiver circuit and each also has a downstream side coil connected to one of two conductor pairs such as a pair of copper tip and ring conductors typically used for existing voice telephone service. Each of the downstream coils of the two transformers also includes a center tap. There is included power circuitry for providing a source of regulated and current limited DC power which has a power output terminal and a return terminal. The power output terminal is connected to the center tap of one of the pair of isolation transformers, and the power return terminal is connected to the center tap of the other one of the pair of isolation transformers. Two transmission line pairs are chosen from the existing, twenty-four conductor transmission line pairs typically used for tip and ring voice telephone service. The two transmission line pairs will typically be selected from the existing multiplicity of infrastructure telephone transmission lines located between the upstream distribution terminal and the downstream distribution terminal. As mentioned above, one of the transmission line pairs is connected to each side of the downstream coil of one of the isolation transformers and the other one of the transmission line pairs is connected to each side of the downstream coil of the other one of the transmission line pairs. The existing infrastructure at the downstream distribution terminal will typically include a multiplicity of telephone subscriber lines connected between a plurality of user locations such as homes or businesses and the downstream distribution terminal. Thus, the downstream distribution terminal is located between the two conductor transmission line pairs and the selected multiplicity of telephone subscriber lines. The downstream distribution terminal will also include a pair of isolation transformers and an HDSL TDM driver and receiver circuit substantially similar to that in the upstream distribution terminal which connects with the HDSL TDM driver and receiver circuit located in the upstream distribution terminal through the two transmission line pairs. The DC power distribution circuit provides a DC power source in the downstream distribution terminal and includes at least a pair of output terminals and an input power terminal connected to the center tap of the isolation transformer connected across one of the transmission line pairs and an input power return terminal connected to the center tap of the other isolation transformer connected across the other one of the transmission pairs so as to receive the source of regulated and current limited DC power from the upstream distribution terminal. 
     The power circuitry located in the upstream distribution terminal provides the regulated and current limited DC power to the downstream distribution terminal on two transmission line pairs which also carry HDSL TDM bidirectional telephone signals. The HDSL TDM circuitry comprises a pair of HSDL isolation transformers and the downstream coil of the isolation transformers each include center taps, each one connected to the power output terminal and the other center top connected to the power return terminal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the present invention will be more fully disclosed when taken in conjunction with the following Detailed Description of the Invention in which like numerals represent like elements and in which: 
     FIG. 1 is a prior art diagram of existing tip and ring telephone circuitry; 
     FIG. 2 shows a block diagram of the circuitry of the present invention utilizing some of the infrastructure of the prior art; 
     FIG. 3 is a block diagram of the system circuitry of the present invention located at an “upstream” distribution terminal; 
     FIG. 3A shows a pair of isolation transformers in the “downstream” distribution terminal used to receive DC regulated power at the center taps; 
     FIG. 4 is a block diagram of the HDSL signal driver and receiver circuitry shown in FIG. 3; 
     FIG. 5 shows a ETS1 ETR-152 data frame used to disguise PCM data packets according to the teachings of the present invention; 
     FIG. 6 shows how PCM data packets are mapped into a ETS1 data frame for transmission on two transmission line pairs according to the teachings of the present invention; and 
     FIG. 7 is a status and operational diagram showing the operational sequence and steps of the automatic initialization and monitoring features of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, there is shown a portion of the distribution circuitry for a prior art telephone system using a pair of electrical conductors for each channel of communication. As shown in the figure, there is an “upstream” distribution terminal  10  providing a multiplicity “N” of conductors pairs  12 ,  14 ,  16 ,  18 ,  20  and  22  to a “downstream” distribution terminal  24 . The multiplicity “N” of conductor pairs according to the infrastructure of a typical telephone system is equal to twenty-four. Downstream distribution terminal  24  provides a like number of “N” conductor pairs to end users or subscribers such as conductor pair  26  to a house  28  having a standard voice telephone connection  30 . The term “upstream” is used herein to indicate a distribution terminal closest to a control or central office and the term “downstream” is used to indicate a distribution terminal close to the end user. In this prior art system, it is seen that it was required to have at least as many conductor pairs between the “upstream” distribution terminal and the “downstream” distribution terminal as it was between the “downstream” distribution terminal  24  and each of the individual telephone services connected to the distribution terminal  24  as indicated by conductor pairs  26 ,  32 ,  34 ,  36 ,  38  and  40 . 
     Referring now to FIG. 2, there is shown a block diagram of the telephone service of the present invention which uses some of the infrastructure of the prior art system but in a much more efficient way that allows substantial increase in the number of communication channels. For example, the upstream distribution terminal  10  may be the same outside steel cabinet as used with the prior art and which has the same number or multiplicity of conductive pairs represented by line pairs  12 ,  14 ,  16 ,  18 ,  20  and  22  which represent pairs 1 through N between the “upstream” distribution terminal  10  and the “downstream” distribution terminal  24 . However, according to the present invention, it will only be necessary to use two transmission lines, such as pairs  12  and  14 , to service the same number of customers connected to the local or downstream distribution terminal  24  as was serviced by distribution terminal  24  in the prior art circuitry of FIG.  1 . Therefore, if, for example, there were twenty-four conductive pairs between the upstream distribution terminal  10  and the downstream or local distribution terminal  24  in the prior art, there will still be twenty-four conductive pairs between the two distribution terminals, but only two of the twenty-four pairs are necessary to provide all of the communication channels between remote or upstream distribution terminal  10  and local or downstream distribution terminal  24 . Thus, the other twenty-two pairs can be used for other purposes as indicated by second ENU (Electrical Network Unit)  42  which may be at a distance from local distribution terminal  24 . In addition to being connected to line pairs  12  and  14  from remote distribution terminal  10 , the ENU  44  in local distribution terminal  24  is also connected to the conductive pairs  26 ,  32 ,  34 ,  36  and  40  to the end users such as end user  28  on line  26  and end users  46  and  48  on lines  32  and  40 , respectively. 
     Further, as will be appreciated by those skilled in the art, the use of modem communication techniques, such as, for example, PCM (Pulse Code Modulation), may provide a large number of telephone communication channels to be provided to upstream terminal  10  over a single cable  49 . However, a single twisted pair used for transmission does not provide adequate bandwidth for all of the “PCM” communication channels. Therefore, if the PCM communication data is to travel between terminal  10  and terminal  24  on two transmission line pairs instead of a single communication line, the format of the data must be changed. 
     Therefore, according to the present invention, remote distribution terminal  10  will now include new equipment such as the Matrix Distribution Shelf (MDS)  50 , a microprocessor  52  and a power source  54 . According to one embodiment, MDS  50  has sufficient slots to handle up to fourteen separate communication boards such as communication board  56 . Also, according to the present invention, each of the communication boards can handle four separate distribution circuits of the type shown in FIG.  3 . Each of the two circuits are connected to two transmission line pairs such as transmission line pairs  12  and  14 . Thus, according to the present invention, the communications board  56  on the Matrix Distribution Shelf  50  can receive transmission line pairs  12  and  14  connected to ENU  44  and transmission line pairs  16  and  18  to the second ENU  42 . As shown in FIG. 3, circuitry included on the communications board  56  includes a field programmable gate array  58 , HDSL signal driver and receiver  60 , Power Protection and Current Limiter Circuitry  62  and surge protection circuitry  64 . In addition to the circuitry located on the communication board  56 , as discussed above, the upstream distribution terminal itself also includes a microprocessor  52  and power supply  54 , which are connected in a similar manner to the other thirteen communication boards. 
     Thus, the two conductor pairs  12  and  14 , as will become clear hereinafter, by using the new and unique circuitry of this invention and a split HDSL transmission format, are now capable of carrying all twenty-four of the communication channels that were carried by the multiplicity of twenty-four conductive pairs required by the prior art circuitry. It should be understood that references to twenty-four communication channels is for convenience only since that is the number in many existing prior art telephone systems. The number can, of course, vary from twenty-four. In addition, it is seen that another multiplicity of twenty-four prior art communication channels can also be routed through downstream distribution terminal  24  to be carried by conductive pairs  16  and  18 . Furthermore, as is indicated by the optical transmission line  66 , completely new and different transmission methods, such as light transmission methods through optical fiber  66 , can be provided from the remote distribution terminal  10  to a different local distribution terminal  68 . As an example only, downstream distribution terminal  68  may be a completely optical system which receives a single optical fiber  66  carrying a large multiplicity of communication channels from the remote terminal  10  to the ONU or downstream distribution terminal  68 . ONU  68  may represent a local or downstream distribution terminal for new construction, office buildings, new residential subdivisions, etc. Thus, as shown in the drawing, there is also included at least one communication channel  70  between ONU  68  and subscriber location  72  with a telephone  74 . It will be appreciated that the communication channel between ONU  68  and subscriber  72  could be by means of an optical fiber or traditional communication pairs. 
     In addition to new equipment provided in the remote distribution cabinet  10 , it will also be necessary to provide new equipment such as ENU  44  in the downstream distribution terminal or cabinet  24 . As shown in the blown-up portion  76  of FIG. 2, ENU  44  will include a power supply source  78 , its own microprocessor  80 , an HIU (HDSL Interface Unit)  82  for receiving the split HDSL formatted communication data and an EIU or Electrical Interface Unit  84  which interfaces the two communication pairs  12  and  14  between upstream terminal  10  and downstream terminal  24  with the individual communication or channel quad cards  86   a  through  86   f . Each of the six channel cards  86   a  through  86   f  can handle up to four communication circuits and thus, the full original twenty-four circuits can receive the twenty-four different communication pairs from the original twenty-four customers. These twenty-four communication signals are then converted to an HDSL format so they can be handled by the two transmission pairs  12  and  14  connected between the upstream terminal  10  and the local or downstream terminal  24  rather than the twenty-four line pairs required by the prior art. 
     As will be appreciated by those skilled in the art, the addition of electronic equipment, such as is located in ENU  44  at terminal  24  and which allows a significant increase in communication channels without any increase in transmission wire pairs to the cabling infrastructure, requires a stable and dependable power source. Therefore, unless each downstream terminal, such as terminal  24  is connected to a power source and includes its own regulated power supply circuitry for operating the electronic equipment, it is necessary that the stable and dependable power source be provided from the upstream terminal  10  which may be located at a significant distance from downstream terminal  24 . 
     According to the present invention, a regulated and current limiter power source is provided from the upstream distribution terminal  10  to a power distribution panel  78 , which in turn is connected to microprocessor  80 , HIU  82  and the six channel cards  86   a  through  86   f . As was discussed above, regulated power is connected to the center taps  88  and  92  of the two isolation tranformers  90  and  94  which transformers are connected across the two transmission line pairs  12  and  14 . As shown in FIG. 3A, two isolation transformers  90 A and  94 A are connected across the same two transmission line pairs which extend between the “upstream” distribution terminal  10  and the “downstream” distribution terminal  24 . Thus, the regulated power provided from the “upstream” terminal is accessed at the “downstream” terminal  24  by center taps  88 A and  92 A. This regulated power is connected to power distribution panel where it is available to the circuitry in “downstream” distribution terminal  24  as discussed above. Circuitry  62  provides a stable and dependable source of power to one or more downstream distribution terminals located at distances up to 12,000 feet, such as, for example, downstream or local distribution terminal  24 . 
     It will also be appreciated by those skilled in the art that the actual HDSL TDM communication signals are also carried by the same two transmission pairs  12  and  14 . Therefore, referring now to FIG. 4 there is shown a block diagram of one of the communication boards  56  of FIG.  2 . There are four of the HDSL Driver and Receiver Circuits  60  of FIG. 3 on each communication board  56 . As shown in FIG. 4, there is an Interface and Framing FPGA (Field Programmable Gate Array)  102  connected to a first pair of DSP&#39;s (Digital Signal Processor)  104  and  106  (one DSP for each transmission line) which are in turn connected to signal processing circuits  108  and  110 , respectively, which, among other functions, provide digital-to-analog (D/A) conversion. The DSP&#39;s  104  and  106  along with their corresponding signal processors  108  and  110  comprise the HDSL signal driver and receiver circuitry  60  shown in FIG.  3 . Also as shown, the isolation transformers  90  and  94  discussed above, are connected to the signal processors  108  and  110 , respectively, of HDSL signal driver and receiver circuitry  60 . The three remaining HDSL signal driver and receiver circuits  60 A,  60 B and  60 C, along with the corresponding pairs of isolation transformers, are identical as to components and operation to HDSL signal driver and receiver circuit  60 . These HDSL signal driver and receiver circuits are also connected to Interface and Framing FPGA  102  in the same manner as circuit  60  and will not be discussed further. 
     Communication board  56  also includes a crystal oscillator  112  for clocking and synchronization purposes and a SRAM  114  for selecting and providing framing data and addresses to the DSP&#39;s  104  and  106 . In addition, Interface and Framing FPGA  102  is also connected to a Backplane Interface  116 . Backplane Interface  116  is also connected to the telephone receiving and transmitting PCM lines  118  and  120 , respectively, along with various control signals, including a sync signal on line  122  and addressing data represented by line  124 . 
     Referring again briefly to FIG. 2, as discussed above, it will be appreciated by those skilled in the art that according to the present invention, the communication board  56  will convert communications data received at terminal  10  on line  49  from another location to a format suitable for transmission on two transmission twisted line pairs such as is present in the existing infrastructure. Furthermore, if it is necessary or desirable to amplify the HDSL communications signals traveling between terminals  10  and  24 , it would be highly desirable to transmit the communication data between terminals  10  and  24  in a format that would allow the use of existing and commercially available repeaters and amplification equipment. To this end, it has been found that redefining the HDSL data so that it is disguised in ETS1 ETR-152 as standard European format, readily available level one EDSP repeaters, demonstration boards and line test equipment may be used. Therefore, according to this invention, DSP&#39;s  104  and  106  receive the PCM data, and in response to firmware instructions from Interface and Framing FPGA  102 , redefine and map the data into the basic ETS1 ETR-152 data frame format represented by FIG.  5 . Thus, this basic ETS1 data frame format is transmitted in both directions between terminals  10  and  24  on both line pairs  12  and  14  such that each transmission line pair carries one-half the data packets moving between the two distribution terminals. Since the communication data is being transmitted over the same two transmission line pairs in both directions and at the same time, it is necessary that data traveling in one direction be separated from data traveling in the opposite direction, and as will be appreciated by those skilled in the art, one effective technique is by echo cancellation. That is, the data being transmitted at a first location is subtracted from the total data present on the line at that first location. This, of course, leaves only the data transmitted from a second or remote location and received at the first location. This received data is then amplified and processed by the DSP&#39;s and returned to standard PCM format. 
     According to one embodiment, and as shown in FIG. 6, transmission line pair one carries the “odd”-numbered PCM data packets and the other line pair carries the “even”-numbered data packets. Except for a sync data location and four locations carrying overhead information, the standards for the ETS1 data frame format only define the number of locations in a data frame and the size of the location. Therefore, it is possible to disguise a number of PCM data packets as ETS1 data packets. Referring again to FIG. 5, the ETS1-ETR data frame initially includes sync word location  126 . Then, as will be appreciated, this sync location is followed by an HOH (HDSL overhead) location  128  which will include various status bits of overhead or housekeeping information. HOH location  128  is then followed by data locations such as data location B 01  having reference number  130  through data location B 12  having reference number  132 . Data location  132  is then followed by another HOH location  134  and another twelve data locations B 13  having reference number  136  through data location B 24  having reference number  138 . Data locations up to location  138  represent one-half of the ETS1 ETR-152 data frame. The second half of the data frame starts with HOH location  140  followed by data location B 25  having reference numbers  142  through B 36  having reference number  144 , and the HOH location  146  followed by data locations  148 - 150 . 
     In keeping with the European standard ETS1 format, the data frame shown in FIG. 5 is described with respect to quats. A quat is equal to two bits. Therefore, sync word  126  is shown to be seven quats or fourteen bits. Likewise, HOH slot  128  is one quat or two bits. HOH slots  134 ,  140  and  146  are five quats or ten bits each. Each of the data slots B 01 , B 02 —through B 48  are 72.5 quats or 145 bits each. It should also be appreciated that each of the ETS1 data slots B 01  through B 48  each accommodate twenty-four PCM data packets plus various control and information packet slots as will be discussed below. Therefore, in the format set out in FIG. 6, the twenty-four PCM data packets each represent a slice of one of the twenty-four analog telephone or communication links in digital format. Therefore, each ETS1 frame carries forty-eight consecutive slices of twenty-four different communication links. The forty-eight packets are substantially 125 microseconds each and therefore the ETS1 data frame is six milliseconds (125 microseconds×48=6 milliseconds), plus or minus two “stuffing quats”  147  and  149 , as indicated by double-headed arrow  151 . Stuffing quats  147  and  149  allow for timing adjustments of each frame by automatically adding or not adding, as appropriate, the stuffing quats to slow the transmission if necessary. In any event, the two stuffing quats  147  and  149  will be added as necessary to assure two consecutive ETS1 frames will be twelve milliseconds or an average of six milliseconds each. 
     Since, according to one embodiment, each one of the data ETS1 locations  130 - 132 ,  136 - 138 ,  142 - 144  and  148 - 150 , can carry a multiplicity of PCM data packets, such as twenty-four packets, it is necessary to provide additional information in housekeeping instructions in addition to the HOH data frame information carried by locations  128 ,  134 ,  140  and  148 . 
     Therefore, referring now to FIG. 6, there is shown twenty-four PCM communication data packets mapped into each of the ETS1 memory locations shown in FIG.  5 . As shown, each of the ETS1 locations shown in FIG. 5 are subdivided into a total of eighteen separate locations per transmission line (twelve data and six overhead) and a EST1 overhead location “Z,” carrying reference number  150 . Also, transmission line pair one, which may for example be line  12  as shown in FIG. 3, carries the twelve odd-numbered packets of the twenty-four total of PCM communication data packets (PCM data packet  1  indicated by reference number  152  through PCM data packet  23  indicated by reference number  154 ) and transmission line pair two (such as transmission line pair  14 ) carries the twelve even-numbered PCM data packets—PCM  2  indicated by reference number  156  through PCM  24  indicated by reference number  158 . It is also noted that instead of PCM data packets, the last four locations provide or carry selected status values or housekeeping instructions. 
     It should be noted, and will be explained hereinafter, that the formatting instruction available on transmission line pair one is the same for all of the forty-eight ETS1 data locations whereas the last six slots in each ETS1 location on transmission line pair two is different for ETS1 location B 01  and B 25  (reference nos.  130  and  142 ) and carries different information than those slots in the remaining ETS1 data locations carry. For example, location  160  carries DCHAN 1-4 information and location  162  carries DCHAN 9-12 information. “DCHAN” information represents instructions and over head in the event the transmission line pair is to carry ISDN digital data rather han carry analog POTS (Plain Ole Telephone Service) analog data. In addition to the time slots  160  and  162 , it will be seen that transmission line pair two also includes time slot  164  which carries DCHAN 5-8 information. This is necessary since the ISDN digital data requires twice the bandwidth per channel as the PCM POTS data. Therefore, two transmission line pairs can only carry twelve ISDN communication channels and not the twenty-four communication channels that can be carried if its transmissions are for POTS service. The last four slots carry CUDL 1-CUDL 7 information. However, the last six slots are different for slots B 01  and B 25  on transmission line pair two than for transmission line pair one. For example, after the DCHAN  5 - 8  slot  164  and the HDLC slot  166  (which is the same for both transmission line pairs), the B 24  and B 26 -B 48  slots for line pair  2  carry further CUDL information in the same manner as transmission line pair  1 . 
     However, the ETS1 time slots B 01  and B 25  carry different information in their last four locations,  168 ,  170 ,  172  and  174  on line pair  2  than all of the other ETS1 time slots carry in the last four locations. 
     More specifically, the HDLC slots  166  are dedicated to carrying status and operational information between the microprocessor  52  in the MDS shelf and the microprocessor  80  in the ENU as shown in FIG.  2 . 
     The CUDL  1  through CUDL  8  overhead slots (CUDL is an acronym for Channel Unit Data Link) carry proprietary information to set up the link for each of the standard voice telephone or POTS communication links. 
     The CUDL CRC slots  169  and  170  which are present only in the B 01  and B 24  ETS1 time slots provide additional CRC (Cyclic Redundancy Checks) critical information so that it is not necessary to wait for the next ETS1 frame or a full six milliseconds to verify the integrity of the communication transmissions. As will be appreciated by those skilled in the art, the transmission integrity is verified by calculating a CRC value from the data stream and then comparing this calculated at the other end of the transmission line by the transmitting hardware. If the values are the same, the communication link is verified. Thus, the integrity of the communication line is verified at significantly shorter time periods than every six milliseconds, which is the time period of each ETS1 data frame. 
     The continuing and almost exponential demand growth for additional communication channels has, of course, increased the potential failures and down time of equipment. However, because of the new and complex communications technology now being used, a line failure no longer only affects a single communication channel. For example, according to the system of the present invention, if either one of the transmission line pairs  12  or  14  were to fail due to invention, if either one of the transmission line pairs  12  or  14  were to fail due to outside forces such as being cut or hit by lightning, all twenty-four communication channels would fail. Therefore, since a single equipment failure may result in the inoperability of a large number of telephone communication channels, it is important that the equipment be as automated as possible. This is true not only for normal operations but also for automatically getting the equipment up, back online and operating as quickly as possible. 
     Therefore, according to the present invention, the FPGA in interface and framing-FPGA  102  includes a memory portion programmed to initialize, systematically power-up or turn on, and monitor the equipment. 
     Referring now to the status and automatic sequencing diagram of FIG. 7, there is an Idle or off condition indicated by circle  170 . This is a situation or condition before the circuitry is initially activated after being installed, or when it has intentionally been turned off or deactivated for maintenance or repairs. The equipment may, of course, remain in this condition and not be used indefinitely. 
     However, at some point in time, the equipment will be turned on or powered-up as indicated by status condition  172 . It should also be noted that each of the links (lines) between different statuses (circles) conditions include an arrow pointing from one status condition to another status condition. The arrow indicates that the link is “one way.” That is, it is only possible to travel along link  172  from the Idle condition  170  to the power-up status condition  172 . It is not possible to go along link  174  from the power-up status  172  to the Idle status  170 . However, as will be discussed, it is possible to go from power-up status  172  to Idle status  170  along another link  176 . 
     While in the “power-up” status as indicated at circle  172 , the equipment will be directed or controlled by the FPGA to follow a predetermined “power-up” or turn on sequence including properly configuring all of the EDSP registers in DSP&#39;s  104  and  106  and the applying of power to equipment in both the upstream and downstream terminals  10  and  24 . Handshaking, similar to that when two computer or two fax machines establish a communication link, is then carried out between DSP&#39;s  104  and  106  in terminal  10  and then their similar companion DSP&#39;s at the downstream terminal  24 . Once the operating parameters are established and agreed to between the DSP&#39;s at each end of the transmission lines, the “low level” data link is established. This should occur within a preselected time period, which according to one embodiment is selected to be about 45 seconds. That is, all of the housekeeping, formatting and synchronized data is transmitted and evaluated in both directions between the upstream and downstream terminals. At this point, and as an example only, there is no high level (actual telephone communications—voice or otherwise) data being transmitted. Once all of the transmission parameters for the low level data have checked out as operating properly, which means all of the DSP&#39;s and other hardware equipment are operating correctly, CRC calculations are verified (as discussed above with respect to FIG. 6) to assure the integrity of the communication link. 192 milliseconds are allowed to complete the verification of system integrity. If verification is complete in the 192 milliseconds, the system is switched to actual and normal operation as indicated by link  178  by moving to the “active” status condition  180 . 
     It will be appreciated, of course, that if the equipment experiences a serious equipment problem such that it will not operate properly, it may be automatically and completely shut down. Such a shutdown could occur, for example, if a circuit breaker were overloaded and tripped. It is also possible that the equipment could be manually turned off before it has time to switch to active status  180  or normal operation. This is indicated by the equipment switching from the power-up status  172  to the Idle status  170  along link  176 . 
     It is also, of course, possible that, although none of the power-up tests failed and the equipment appears to be in operating condition, for various reasons a proper low level link simply is not established before the expiration of the preset time period. If the link is not established and the equipment does not switch to the active status  180  before the expiration of the preset time limit, the equipment instead switches to a “reset” status  182  as indicated at link  184 . 
     Referring again to the “active” status  180  condition, it is seen that once operating normally as indicated by status  180 , the equipment can be switched along two possible paths. The equipment can be switched off and returned to the “Idle” status  170  as indicated by link  186 , or if it loses sync or otherwise momentarily loses the communication link for a selected period of time, such as, for example, only 2.88 seconds, the equipment switches to the “reset” status  182  by means of link  188 . Requiring a signal loss to exist for a time period such as 2.88 seconds avoids the same lengthy shutdown required by a complete reset and power up sequence when the signal loss is only a very short term signal lost with immediate reacquisition. 
     Once switched to the “reset” status  182  from links  184  or  188  as discussed above, or from link  190  to be discussed below, the equipment is either turned off and returned to the Idle status  170  as indicated by link  192  or it is reset to its initial condition and then placed in a waiting state for a selected period of time such as for example one-and-a-half minutes to allow it to stabilize as indicated by the “I-limit” status  194  and link  196 . Thus, if the link is not reestablished in 2.88 seconds, it will be down for the full one-and-a-half minutes. This is to allow minimum interruption of signals on adjacent transmission lines which would be affected by significant noise cross talk if the power, which is also carried by the two transmission line pairs, were to be repeatedly switched on and off in an attempt to power up the system when shut down by a power short. 
     Once the predetermined time period allowed for stabilization as indicated by status condition  194  has expired, the equipment is then switched to the “link lost” status  198  as indicated by link  200 . Unless it was intentionally powered-down and returned to the Idle status  170  as indicated by link  202 , the “link lost” status  198  is substantially the same status as the “power-up” status  172  except that it has incremented a counter indicating that the link had been operating and was lost at least one time. Thus, while in the “link lost” status  198 , the equipment goes through the same sequence discussed with respect to the “power-up” status  172  above. Consequently, the links switching from the “link lost” status  198  are the same as the links switching from the “power-up” status  172 . For example, link  202  switches the equipment back to the “Idle” state  170  in the same manner as link  176 . Link  204 , on the other hand, switches the equipment to the “active” status  180  in the same manner as link  178 . Finally, link  190  switches the equipment to the “reset” status  192  if the “active” status cannot be established in the allowed predetermined time period. This is in the same manner as link  184 . It can also be seen that in trying to establish an active operating condition, the equipment can repeatedly follow links  190 ,  196  and  200  until a good link is established, or alternately, if a good link is repeatedly established and then lost, the equipment can continually switch between active status  180 , reset status  182 , high-limit status  194  and link lost status  198 . 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material or act for performing the function in combination with other claimed elements as specifically claimed.