Abstract:
A system and method selectively establishes data communications, such as XDSL services, between data devices and a network switch. Status of the data devices are monitored and active data devices are connected to a data branch for data communications. Data devices which are inactive may remain connected to the data branch, if available, or may be switched to a pilot branch. While disconnected from the pilot branch, the system may detect a signal from the data device indicating that the device is going active. If pilot signals are being used, the pilot signals between a data device and the network switch are monitored to determine when the data device is going active. Once detected, the data device is connected to the data branch. Alternately, if pilot signals are not being used, the system monitors the connection with the data device for any signals, such as a wake-up signal, which indicates that the data device is going active.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to telecommunication equipment which terminates subscriber lines and supports high speed data services for subscribers. The invention is especially suited but not limited to providing high speed data services which exceed the capability of conventional POTS terminating equipment. 
   In the United States, subscribers are commonly provided with telephone services known as plain old telephone services (POTS). Such services include providing conventional dial tone and automated dialing features, including the use of dual frequency tone signaling to communicate dialed number information. Additional modem telephone features include conferencing, call waiting, incoming caller identification and other commercially available features. 
   Subscribers utilize a POTS line to carry conventional modem signals controlled by a personal computer to another modem via the public switch telephone network. Modems are currently available which support data communication rates up to 56 Kilobits per second (Kbps) over dial up analog subscriber lines. Those skilled in the art will understand that the maximum data rate which can be transmitted using modems over a POTS subscriber line is limited by the sampling rate, the band width of the channel, and the rate by which the analog signals are converted to digital signals by the line card units which terminate each POTS line at a central office. Thus, conventional modem data rates are limited by POTS line cards which terminate the subscriber lines. 
   Subscribers in the United States can lease special subscriber lines from their telephone service providers which accommodate higher data rates than are supported by conventional dial up subscriber lines. Such higher speed lines utilize different terminating circuitry at the central office to accommodate higher data rates. For example, integrated service digital network (ISDN) terminating equipment will provide a subscriber with a capability of higher data rates than a conventional POTS terminated line. For example, a known asynchronous digital subscriber line (ADSL) technique which is supported by available equipment provides a significantly higher data rate to a subscriber over a conventional copper two-wire subscriber line. Of course, the ADSL service requires proper terminating equipment at the central office and at the consumer premises to accommodate the greater throughput capabilities, i.e. data rates. 
     FIG. 1  illustrates some available services in the United States to subscribers using conventional two-wire copper loops. Equipment to the right of the dashed line  100  represents customer premise equipment (CPE). Equipment to the left of the dashed line  100  represents central office line termination equipment. A POTS line interface  102 , also known as a line card, provides an interface between digital incoming and outgoing communication lines  104  and  106 , and analog signals carried on subscriber line  108 . For example, communication lines  104  and  106  may carry 64 Kb per second pulse coded modulation (PCM) signals representative of analog information received from and transmitted to line  108 . A main distribution frame (MDF)  110  is used to interconnect a plurality of incoming subscriber lines to various terminating equipment at the central office. In this example, a line  108  is connected through a POTS splitter  112  and the MDF  110  to a subscriber line  114 . A conventional telephone instrument  116  at the consumer&#39;s premise is connected through a POTS splitter  118  to the subscriber line  114 . 
     FIG. 1  also illustrations another service to the subscriber which provides high speed data capability. An ADSL interface circuit  120  provides an interface between the central office and the subscriber for terminating the received data at rates up to several megabits per second (Mbps). Lines  122  and  124  provide inbound and outbound digital data communications, representative of information to and from the subscriber, carried on line  126 . Line  126  is connected via the POTS splitter  112  and the MDF  110  to the subscriber line  114 . An ADSL interface  128  provides an interface between conventional digital data, communicated with a subscriber&#39;s personal computer  130 , and ADSL analog format signaling communicated on a line  132 . The POTS splitter  118  couples the ADSL signal between the ADSL interface  128  and the subscriber line  114 . The advantage to the user is that the ADSL facilities support a substantially higher-data rate than would be available if the subscriber utilized communications terminated via the POTS line interface  102 . 
   A disadvantage of the system shown in  FIG. 1  is that there is one ADSL interface  120  corresponding to each personal computer  130 . Additionally, as the number of ADSL subscribers increases, the number of ADSL interfaces connected to the subscriber lines, such as subscriber line  114 , must also increase. However, most ADSL service subscribers do not use ADSL services continuously. Thus, the ADSL interfaces  120  will be idle a significant amount of time. At the present, ADSL interface circuitry is expensive. This problem is magnified as more and more subscribers request ADSL service. Therefore, there is a need to provide high speed services, such as ADSL, while minimizing the cost of implementing the services. 
   SUMMARY OF THE INVENTION 
   The above need is satisfied and a number of technical advances are achieved in the art by implementation of a system and method in accordance with the present invention which supports routing of XDSL communication data between an XDSL interface branch and a pilot interface branch. 
   Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below. Since the following is for summary purposes only, none of the aspects present below should be considered essential to the present invention, which is solely defined by the appended claims. 
   In accordance with an aspect of the present invention, a system establishes data communications with a data device by monitoring whether the data device is active or inactive. If the data device is active, a controller circuit connects the active data device to a data branch to establish data communications. Preferably, the data communications are digital subscriber line communications. The controller circuit further monitors data devices already connected to the data branch to determine whether any of them are inactive. If the controller circuit detects an inactive data device, the controller circuit, if need be, may disconnect the inactive data device and connect a data device becoming active. The inactive data device may be connected to a pilot branch until it again becomes active. 
   In another aspect of the present invention, a method is provided for selectively connecting active data devices to a data branch to establish data communications. Inactive data devices are detected and either connected to a pilot branch or remains connected to the data branch, if there is available space. The method may detect when an inactive data device becomes active by monitoring pilot signals sent to and from the inactive device in accordance with the ITU standard for G.lite. Alternatively, if pilot tones are not being used, the method monitors the connection to the inactive data device for the presence of signals. 
   These and other features and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing advantageous features of the invention will be described in detail and other advantageous features will be made apparent upon reading the following detailed description that is given with reference to the several figures of the drawings in which: 
       FIG. 1  illustrates a prior art implementation in which a subscriber is provided POTS and high speed data services by using a POTS splitter to support line termination equipment; 
       FIG. 2  is a graphical representation of a system for providing POTS and XDSL services in accordance with an aspect of the present invention; and 
       FIG. 3  is a block diagram of another aspect of the present invention for providing POTS and XDSL services. 
   

   DETAILED DESCRIPTION 
   One or more specific versions of the present invention will be described below. In an effort to provide a concise description of these versions, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
   In accordance with a version of the present invention, a single subscriber line supports at least two different classes of subscriber service, such as POTS and XDSL or other high speed data services. The “X” in XDSL represents one of a family of digital subscriber line services such as ADSL (asynchronous), ADSL Lite, RDSL (rate-adaptive) and VDSL (very high speed). As used herein, high speed data interface refers to apparatus that use a signaling method to provide higher data transmission speeds than can be supported by conventional POTS line transmitting equipment. “X” could also be used in energy mode for SDSL, HDSL, HDSL II and SHDSL where POTS circuitry would not be present. 
   Now, referring to  FIG. 2 , consumer premises equipment (CPE)  135  is located to the right of a dashed line  132 . Central office equipment (COE), including central office line terminating equipment  137 , is located to the left of the dashed line  132 . A two-wire copper subscriber line (tip and ring)  134 , also commonly known as a subscriber loop, connects the CPE  135  with the central office terminating equipment  137 . A subscriber may utilize a conventional telephone instrument  136  (such as a telephone) which can be connected to the subscriber line  134  via a POTS splitter  138  to receive POTS signals. The subscriber may elect to couple a high speed data interface (an interface circuit), such as a XDSL interface  140 , via a POTS splitter  138  to the subscriber line  134  to support high speed data communications. A high speed data device, shown as a personal computer  142 , is illustratively shown connected to the XDSL interface  140 . For purposes of this disclosure, a data device may comprise the personal computer  142  and the XDSL interface  140 . It will be appreciated, however, by those skilled in the art that high speed data devices other than the personal computer  142  may be utilized to transmit or receive a variety of data representing different types of information. 
   A balanced access interface unit (BAIU)  144  terminates the subscriber line  134  via a MDF  146 . The BAIU  144  is responsible for all interactions and communication signals transmitted to and received from the subscriber line  134 . Additionally, the BAIU  144  is responsible for providing separate inbound and outbound data paths for communicating information with the central office switch via a network switch  148 , such as utilizing PCM-encoded digital signals or asynchronous transfer mode (ATM) formatted signals. Communication channels  150  and  152  carry inbound and outbound high speed digital information respectively and communication channels  154  and  156  similarly carry inbound and outbound conventional telephone information, respectively. Additionally, respective communication channels  158  and  160  carry inbound and outbound pilot signal information. 
   The BAIU  144  comprises a plurality of components such as a plurality of: POTS sections  162 ; XDSL receivers  164  and  166 ; pilot circuit receivers  168  and  170 ; XDSL transmitters  172  and  174 ; and pilot circuit transmitters  176  and  178 . The BAIU  144  also includes a transmit low voltage grid  180 , a receiver low voltage grid  182  and a controller  184 . 
   As will be discussed below, the XDSL receivers  164  and  166 , the XDSL transmitters  172  and  174  and the transmit and receiver grids  180  and  182  comprise a data branch for providing high speed data communications with the personal computer  142 . Additionally, the pilot circuit receivers  168  and  170 , the pilot circuit transmitters  176  and  178 , and the transmit and receiver grids  180  and  182  comprise a pilot branch for connecting with the personal computer  142  when the personal computer  142  is inactive, or in a sleep mode. The pilot branch and the personal computer  142  periodically communicate via pilot signals during a sleep mode period. The controller  184  and transmit and receiver grids  180  and  182  comprise a controller circuit which controls the connection of the data device. 
   The number M of POTS sections  162 , XDSL receivers  164  and  166 , pilot circuit receivers  168  and  170 , XDSL transmitters  172  and  174  and pilot circuit transmitters  176  and  178  is preferably determined by the central office based on the total number of subscribers using XDSL services. The value of M may selectively be chosen as 0, 4, 8, 16, 32, 64, 128 or greater. Thus, the present invention supports multiple POTS lines or no POTS. 
   The POTS section  162  comprises a number of subcomponents such as a line support circuit  186 , a signal splitter  188 , a high pass filter  190 , a low pass filter  192 , an analog to digital coder-decoder (A/D CODEC)  194 , a digital to analog coder-decoder (D/A CODEC)  196  and a combiner circuit  198 . All these components are described and reference should be made to U.S. patent application Ser. No. 08/767,138 of Nye et al., filed Dec. 19, 1996, entitled “Telecommunication Equipment Support of High Speed Data Services,” which is incorporated by reference herein. 
   Line support circuit  186  terminates the subscriber line  134  and provides conventional POTS subscriber line support facilities. The line support circuit  186  provides a simplex to duplex communications interface by which duplex communications on the subscriber line  134  are separated into independent transmit and receive communications coupled to the central office. Line  200  carries information from the subscriber and line  202  carries information to be transmitted to the subscriber. Line  200  is coupled to the signal splitter  188 , which splits the information received from the subscriber into two substantially equal signals, one signal being applied to line  204  and the other signal being applied to line  206 . Line  204  is coupled to the high pass filter  190  and line  206  is coupled to the low pass filter  192 . The outputs from the high pass filter  190  and the low pass filter  192  are coupled respectively to the receiver low voltage grid  182 , via line  208 , and to the A/D CODEC  194 . The low pass filter  192  passes signals with frequencies relevant to conventional voice communications, such as below 4 KHz, to the A/D CODEC  194  which translates the analog voice signals into digital signals, such as PCM, which are transmitted on line  154  to a far end CPE via the network switch  148 . The high pass filter  190  passes signals with frequencies above the cutoff frequency of the high pass filter  190 . The frequencies passed would typically be above 4 KHz as used in known XDSL signaling coding (between about 30 KHz and 1,500 KHz for ADSL). The XDSL receivers  164  and  166  (which are coupled to the receiver low voltage grid  182 ) convert the high pass filtered signals into other conventional signals, such as ATM signals, which are transmitted on channel  150  to the network switch  148 . 
   Information transmitted to the subscriber line  134  is received from the central office facilities and communication channels  156  and  152 . The D/A CODEC  196  receives digital information such as PCM-formatted voice or data to be translated into conventional POTS analog signals. Digital data which may be in ATM format is received on the communication channel  152  via the XDSL transmitter  174 , which converts this data into corresponding XDSL analog signals. The XDSL analog signals are then transmitted to the signal combiner  198  via the transmit low voltage grid  180 . Likewise, the analog output from the A/D CODEC  194  is sent to the singal combiner  198  which sums the analog signals into a resulting output signal carried on line  202  to the line support circuit  186 . 
   The pilot circuit receivers  168  and  170 , pilot circuit transmitters  176  and  178 , receiver low voltage grid  182  and transmit low voltage grid  180  are components which allow the central office to balance the use of the XDSL receivers  164  and  166  and the XDSL transmitters  172  and  174 . There are N number of XDSL receivers  164  and  166  and XDSL transmitters  172  and  174 . The value of N is less than the value of M because preferably not all XDSL subscribers will employ XDSL services simultaneously. Thus, the controller  184  may selectively balance the use of the XDSL branches (receivers  164  and  166  and transmitters  172  and  174 ) versus the pilot branches (receivers  168  and  170  and transmitters  176  and  178 ). 
   The pilot circuits on the pilot branch such as the receivers  168  and  170  and transmitters  176  and  178  are less complex circuits, and therefore typically less expensive, than the corresponding XDSL circuits on the data branch because they are required to process less data. When the personal computer  142  does not communicate with the XDSL interface  140  within a specified time, the XDSL interface  140  goes into a sleep mode. While in sleep mode the XDSL interface  140  does not need to communicate with the network switch  148  through a data, or XDSL, branch. However, communication between the XDSL interface  140  and the network switch  148  can be maintained in sleep mode by using the pilot branch. The pilot branch allows the XDSL interface  140 , and thus the personal computer  142 , and the network switch  148  to communicate in a very basic manner without having to use the expensive XDSL branch. The pilot branch may be alternatively implemented as a single digital signal processor (DSP) and a single A/D D/A converter. Such a DSP and A/D D/A converter may be capable of processing a plurality of lines. 
   This basic communication is preferably via pilot tones. A pilot tone is a single tone carrier signal which carries modulated information data. One description of sleep mode, and in particular, the use of pilot tones, is set forth in a G.lite ADSL draft standard from the International Telecommunications Union (ITU). The ITU has further issued a G.lite ADSL standard which operates in a level 3 (L3) mode as discussed below. Additionally, new low power modes are being developed by the telecommunications industry. For example, a level 1 (L1) mode operation in G.lite is being developed as a low power mode. Another mode is commonly designated as Quiescent mode (Qmode). Further, Qmode is being considered for standards other than G.lite, as well. As those skilled in the art will readily comprehend, the present invention may be advantageously implemented in any number of low power modes, including both those which utilize pilot tones and those which do not. 
   In accordance with the present invention, the XDSL pilot circuit receivers  168  and  170  receive pilot tones from the XDSL interface  140  while the XDSL interface  140  is in a sleep mode. When the XDSL interface  140  is ready to transmit information, it transmits a pilot tone (wake-up signal) indicating a desire to transmit XDSL information. One of the XDSL pilot circuit receivers  168  or  170  detects the wake-up signal and signals to the controller  184  that the XDSL interface  140  desires to transmit XDSL information. The controller  184  then instructs the receiver low voltage grid  182  and the transmit low voltage grid  180  to switch the connection with the XDSL interface  140  to the XDSL branch. In response to these instructions, the receiver low voltage grid  182  connects the XDSL interface  140  to one of the XDSL receivers  164  and  166 . Similarly, the transmit voltage grid  180  connects the XDSL interface  140  to one of the XDSL transmitters  172  and  174 . After these connections, the XDSL interface  140  is ready to transmit and receive XDSL communications. 
   Before the XDSL interface  140  is switched from the pilot branch to the XDSL branch, it may be necessary to switch another XDSL interface from the XDSL branch to the pilot branch. The controller  184  thus checks for an inactive XDSL interface which is connected to the XDSL branch. When such an inactive XDSL interface is identified, the controller  184  instructs the transmit low voltage grid  180  and the receiver low voltage grid  182  to switch the inactive XDSL interface to the pilot branch. In this manner, inactive XDSL interfaces can be connected to the relatively simple and inexpensive pilot branch until they activate. Consequently, the BAIU  144  can consist of less of the components in the complex and expensive XDSL branch while still providing XDSL service to numerous XDSL interfaces. 
   Alternatively, the BAIU  144  may have excess capacity in the XDSL branch and/or the pilot branch. In such a situation, it may not be necessary to “switch” both active and inactive XDSL interfaces. In other words, there may be an open XDSL branch which to connect the XDSL interface  140 . 
   Although the description herein is made in reference to various hardware and software systems, it should be appreciated that the teachings of the present invention are not limited for use with only such systems and that, instead, the teaching of the present invention is applicable to a large number of possible hardware and software embodiments. For example, different combinations of multiple pilot branches and/or multiple XDSL branches may be implemented on a single DSP. The DSP could then allocate its resources automatically as needed on the multiple channels. Similarly, multiple channels of POTS signals may be supported by a single DSP. Alternatively, POTS may not be supported in the present invention. The present invention provides reduced services (i.e. less than full service) with less resources when the CPE is not operating at full usage. Experience has shown that a typical CPE operates at less than full usage a high percentage of the time, thus the present invention results in a cost savings. 
   Referring now to  FIG. 3 , a block diagram illustrates a system  300  in accordance with another aspect of the present invention which is adapted for use with the L3 mode of operation of G.lite as described in the ITU ADSL standards. It should be appreciated that many of the block diagrams illustrated in  FIG. 3  may correspond to one or more components described with respect to  FIG. 2 . In the L3 mode, pilot tones are not transmitted during sleep mode. The CPE  135  is comprised of the POTS splitter  138 , the XDSL interface  140 , the telephone instrument  136  and the personal computer  142  as described above. The XDSL interface  140  communicates with a signal splitter  304  via the POTS splitter  138 . The signal splitter  304  transmits POTS signals to and from the POTS system  306  and transmits XDSL signals to and from a data system  308 . 
   The data system  308  comprises a crosspoint grid  310  for routing the XDSL signals in response to a switch circuit  312  in a controller  314 . The controller  314  further comprises an active/inactive detector  316  for detecting which of data, or XDSL branches  317  are active and inactive. A signal detector  318  in the controller  314  detects when wake-up signals arrive from the XDSL interface  140 . As noted, the XDSL interface  140  is not transmitting any pilot tones when in sleep mode in L3 operation. When XDSL communications are desired, the XDSL interface  140  transmits a wake-up signal to the signal splitter  304  which routes the wake-up signal to the crosspoint grid  310 . 
   The signal detector  318  of the controller  314  senses the wake-up signal and notifies the active/inactive detector  316 . The active/inactive detector  316  checks the XDSL branches  317  to determine which are inactive, or have been inactive for a set time period. Once an inactive XDSL branch  317  is identified, the controller  314 , through the switch circuit  310 , instructs the crosspoint grid  310  to connect the XDSL interface  140  to the inactive XDSL branch  317 . Although not shown, the controller  314  also notifies the network switch  148  that the XDSL interface  140  is being connected to the inactive XDSL branch  317 . Other than described above, the components in  FIG. 3  operate in a similar manner as those described with respect to  FIG. 2 . 
   For clarity and ease of description, the structure, control and arrangement of the conventional components and circuits have, for the most part, been illustrated in the drawings by readily understandable block representations and schematic diagrams, which show only those specific details that are pertinent to the present invention. These block representations and schematic diagrams have been employed in order not to obscure the disclosure with structural details which will be readily apparent to those skilled in the art having the benefit of the description herein. 
   While the specification in the invention is described in relation to certain implementations or versions, many details are set forth for the purpose of illustration. Thus, the foregoing merely illustrates the principles of the invention. For example, this invention may have other specific forms without departing from its spirit or essential characteristics. The described arrangements are illustrated and not restricted. To those skilled in the art the invention is susceptible to additional implementations or embodiments and certain of the details described in this application can be varied considerably, without departing from the basic principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention. They are thus within the spirit and scope of the present invention.