Abstract:
A line termination unit which supports Integrated Services Digital Network (ISDN) and high speed data (HSD) services such as asymmetric digital subscriber loop (ADSL) or XDSL services to a subcriber over a common two-wire subscriber line. The line termination unit has a line termination circuit that connects to the subscriber line and provides ISDN signals to the line. The line support circuit receives incoming ISDN and HSD signals from the line and transmits outgoing ISDN and HSD signals to the line. The received incoming analog signals are separated into first (ISDN information) signals and second (HSD information) signals. The first signals are converted into third digital signals having a format used for ISDN signals by an associated central office and transmitting the third digital signals to the central office. The second signals are converted into fourth digital signals having a format used for HSD signals by an associated central office and the fourth digital signals are transmitted to the central office.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 08/767,138 entitled “Telecommunication Equipment Support of High Speed Data Services” of Nye et al. filed Dec. 19, 1996 now U.S. Pat. No. 6,144,659. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to telecommunication line termination equipment and in particular to Integrated Services Digital Network (ISDN) line termination equipment. 
     There is an ever pressing need to provide consumers of telecommunication services with high speed data services. Many subscribers use plain old telephone services (POTS) lines to carry data communication signals between computer devices employing modems to communicate via the public switched telephonic network. Unfortunately, the maximum data rate using modems of a POTS subscriber line is limited by many factors including the sampling rate, bandwidth, and the analog to digital signal conversion rate for the line cards which terminate the POTS lines. 
     Other subscriber lines are available, however, which provide higher data rates. Integrated Services Digital Network (ISDN) lines provide a subscriber with telephone services generally at a higher data rate than conventional POTS lines. Subscribers utilize an ISDN line to carry digital signals controlled by a personal computer to another ISDN set, modem or ISDN modem pool via the public switched telephone network. It will be appreciated that the maximum data rate which can be transmitted using modems over an ISDN subscriber line is limited to 144 kilobits per second. 
     Subscribers can lease special lines from their telephone providers which accommodate higher data rates than are supported by conventional dial-up subscriber lines or by ISDN lines. Recently, Asymmetric Digital Subscriber Line (ADSL) technology has evolved which provide even higher data transmission speeds than ISDN technology. The known 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. Proper terminating equipment at the consumer location and the telephone service provider central office is required to employ ADSL technology. 
     Referring now to FIG. 1, currently available services for subscribers using conventional two wire copper loops are illustrated. Equipment to the right of dashed line  10  represents customer premises equipment (CPE); equipment to the left of line  10  represents central office line termination equipment. The ISDN line interface  12  also known as a line card, provides an interface between digital incoming and outgoing communication lines  14  and  16 , and analog signals carried on subscriber line  18 . For example, lines  14  and  16  may carry 2-64 kilobits per second (kbps) and 1-16 kbps signals representative of information received from and transmitted to line  18 . A main distribution frame (MDF)  20  is used to interconnect a plurality of incoming subscriber lines to various terminating equipment at the central office. In this example, line  18  is connected through an ISDN splitter  19  and MDF  20  to subscriber line  22 . A conventional ISDN station set or instrument  24  at the consumer&#39;s premises is connected through ISDN splitter  23  to subscriber line  22 . 
     FIG. 1 also illustrates another service to the subscriber which provides a high speed data capability. An ADSL interface circuit  26  provides an interface between the central office and the subscriber for transmitting and receiving data at rates up to several Megabits per second. Lines  28  and  30  provide inbound and outgoing digital data communications representative of information to and from the subscriber carried on line  32 . Line  32  is connected via ISDN splitter  19  and MDF  20  to subscriber line  22 . An ADSL interface  36  provides an interface between conventional digital data communicated with a user&#39;s personal computer  38  and ADSL analog format signaling communicated on line  37 . The ISDN splitter  23  couples the ADSL signal between ADSL interface  36  and subscriber line  22 . 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 ISDN line interface  12 . 
     A disadvantage illustrated in FIG. 1 is that ISDN splitters  19  and  23  are required. These known ISDN splitters function to separate the higher frequency signals associated with ADSL signaling from the lower frequency signals (typically &lt;80-110 kilohertz) associated with the conventional ISDN communications. The conventional ISDN splitter consist of a lattice of inductors and capacitors that provides the needed filtering while maintaining the ISDN signals. The components (inductors and capacitors) used in the ISDN splitter occupy a relatively large volume. Thus, a conventional ISDN splitter occupies a significant amount of space. 
     Unfortunately, conventional ISDN termination equipment is complex (especially in wiring devices) and is not highly integrated when employing ADSL technology. Moreover, bulky splitters are required taking up a significant amount of space in the terminating equipment cabinets. The size of the splitters and the wiring associated with connecting them to the MDF, ADSL interface and the ISDN line interface take up precious space which is limited. The problem is magnified as more and additional subscribers request services. Accordingly, there is a need to provide highly integrated equipment enabling high speed ADSL technology services on ISDN lines while minimizing space and wiring requirements. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to address the above referenced need by providing a solution which minimizes the space and wiring associated with the central office terminating equipment for high speed data services. 
     In accordance with one embodiment of the present invention, access interface units terminate subscriber lines by which the corresponding subscribers can utilize ISDN services and/or high speed data services such as ADSL. The access interface units support both types of service without utilizing a conventional ISDN splitter. The access interface units include a line support circuit wherein two way communications on the subscriber loop are separated into inbound and outbound communications on separate channels. The inbound communications are split into first and second signals. The first signal is low pass filtered and converted into digital format signals by a conventional ISDN receiver. The second signal is high pass filtered and converted into digital format signals by a high speed data receiver. The outbound communication is the summation of third and fourth analog signals from an ISDN transmitter and high speed data transmitter. An important aspect of this invention resides in the ability to use conventional low voltage, low current passive and active components for the low pass and high pass filters. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a conventional implementation in which a subscriber is provided ISDN and high speed data services by using an ISDN splitter to support line termination equipment; 
     FIG. 2 illustrates an embodiment of the present invention where an access interface unit accommodates ISDN and high speed data services over a single subscriber line without requiring a conventional splitter at the terminating central office equipment; 
     FIG. 3 illustrates an exemplary embodiment of the line support circuit as shown in FIG. 2; and 
     FIG. 4 illustrates another embodiment of the present invention in which a multiple line interface unit terminates several subscriber lines and shares high speed data resources among the subscriber lines. 
    
    
     DETAILED DESCRIPTION 
     In accordance with the present invention, a single subscriber line supports at least two different classes of subscriber services, e.g. ISDN and high speed data services such as XDSL. The “X” in XDSL represents one of a family of digital subscriber line services, such as ADSL (Asymmetric), ADSL lite, RDSL (Rate-adaptive), and VDSL (Very high speed). As used herein “high speed data interface” refers to apparatus that uses a signaling method to provide higher data transmission speeds than can be supported by conventional ISDN line terminating equipment. For further details of providing XDSL services for a subscriber, reference can 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 herein by reference. 
     Referring to FIG. 2, consumer premises equipment is located to the right of dashed line  40 ; central office equipment including line terminating equipment is located to the left of dashed line  40 . A two-wire copper subscriber line  42 , also known as a subscriber loop, connects consumer premises equipment located to the right of line  40  with central office terminating equipment to the left of line  40 . The subscriber may utilize a conventional ISDN instrument  44  which can be connected to subscriber line  42  via an ISDN splitter  43  to receive ISDN signals. The subscriber may elect to couple a high speed data interface, e.g., XDSL interface  46 , via ISDN splitter  43  to subscriber line  42  to support high speed data communications. A personal computer  48  is illustratively shown connected to XDSL interface  46 . It will be appreciated by those skilled in the art that equipment other than personal computer  48  may be utilized to transmit or receive a variety of data representing different types of information. 
     An access interface unit (AIU)  50  terminates subscriber line  42  via MDF  52 . The AIU  50  is responsible for all interactions and communication signals transmitted to and received from subscriber line  42 . Additionally, AIU  50  is responsible for providing separate inbound and outbound data paths for communicating information with the central office switch such as utilizing ISDN digital signals or asynchronous transfer mode (ATM) format signals. Communication channels  54  and  56  carry inbound and outbound high speed digital information, respectively. Communication channels  58  and  60  similarly carry inbound and outbound conventional ISDN information, respectively. 
     Line support circuit  62  terminates subscriber line  42  and provides conventional ISDN subscriber line support facilities. The line support circuit  62  provides the simplex to duplex communications interface by which duplex communications on subscriber line  42  are separated into independent transmit and receive communications coupled to the central office. Line  64  carries information from the subscriber and line  66  carries information to be transmitted to the subscriber. Line  64  is coupled to signal splitter  68  which splits the information received from the subscriber into two substantially equal signals, one signal being applied to line  70  and the other signal being applied to line  72 . Line  70  is coupled to high pass filter  74  and line  72  is coupled to low pass filter  76 . The outputs from the high pass filter  74  and low pass filter  76  are coupled respectively to the XDSL receiver  78  and ISDN receiver  80 . The low pass filter  76  passes signals with frequencies relevant for conventional ISDN communication, such as below 80-120 Kilohertz, to the ISDN receiver which translates the ISDN signals into digital signals which are transmitted on line  58  to central office equipment. High pass filter  74  passes signals with frequencies above the cut-off frequency of filter  76 , e.g. above 80-120 Khz, as used in known XDSL over ISDN signal encoding (between about approximately 138 Kilohertz and 1100 Kilohertz for ADSL). The XDSL receiver  78  converts the high pass filtered signals into other conventional signals such as ATM signals transmitted on channel  54  to the central office equipment. 
     Information transmitted to subscriber line  42  is received from central office facilities on communication channels  60  and  56 . The ISDN transmitter  82  receives digital information, to be translated into conventional ISDN signals. Digital data, such as in ATM format, is received on communication channel  56  via XDSL transmitter  84  which converts this data into corresponding XDSL analog signals which are transmitted to signal combiner  86 . Likewise, the analog output from ISDN transmitter  82  is sent to combiner  86  which sums the input analog signals into a resulting output signal carried on line  66  to line support circuit  62 . 
     FIG. 3 is an illustrative embodiment of line support circuit  62 . The tip (T) and ring (R) conductors define subscriber line  42 . An over voltage protection device  100  is used to limit the maximum voltages which can appear across the subscriber line  42 . A source of DC current such as central office battery  102  provides a sealing current supplied to conventional ISDN subscriber lines. Operational amplifier  108  is connected with inputs to subscriber line  42  and provides an amplified signal replica of information transmitted from the subscriber to its output coupled to line  64 . Operational amplifiers  110  and  112  obtain an input signal from line  66  from the signal combiner. The respective outputs from amplifiers  110  and  112  are coupled to the tip and ring lines of subscriber line  42 . These amplifiers transmit signals from the central office to the subscriber line. There are alternate embodiments of the line support circuit, for example voltage addition circuits and/or current addition circuits may selectively be employed. 
     Additional details of operation concerning the circuit as show in FIG. 3 may be obtained by referencing U.S. Pat. No. 5,528,688, which is incorporated herein by reference. In accordance with the present invention, the capacitors shown in FIG. 3 in series with the input and output signals are selected to have a capacitance value when considered with the corresponding equivalent resistances to pass the required frequency bandwidth to handle both conventional ISDN services and XDSL services. That is, the components of this circuit are selected to provide a frequency bandwidth extending between approximately 20 hertz and 1.5 megahertz. When conventional ISDN class of services is being utilized, low pass filter  76  as shown in FIG. 2 is utilized to eliminate any unwanted higher frequency signal components which may be present due to the extended frequency bandwidth needed to accommodate XDSL signaling. 
     FIG. 4 illustrates an alternative embodiment of the present invention. In this embodiment, a multiple line interface unit (MLIU)  120  terminates subscriber lines  122 A,  122 B, . . .  122 N by corresponding subscriber interface units (SIU)  124 A,  124 B, . . .  124 N. Since each of the SIUs are identical and support ISDN service for each respective subscriber line, only SIU  124 A will be described. SIU  124 A includes a line support circuit (LSC)  126  such as shown in FIG.  3 . Inbound analog information from LSC  126  is coupled on line  128  to analog to digital converter  130  which sends the digitized information to digital signal processor (DSP)  132 . The DSP  132  processes the digitized information, converts it into a format used by the central office, and sends the signals to the central office on the inbound path of lines  134 . Outbound signals from the central office on the outbound path of lines  134 A,  134 B... 134 N are received by DSP  132  and converted back into digital signals which can be directly translated by digital to analog converter  136  into analog signals sent on line  138  to LSC  126 . Thus, each SIU supports ISDN for the respective subscriber line. 
     In accordance with this embodiment, a high speed data unit (HSDU)  140  supports high speed data services such as XDSL for a predetermined number of subscriber lines and is shared among the subscriber lines, i.e. among the SIUs. This is done to make the MLIU  120  more economical as compared with an approach where high speed data interfaces are provided on a one to one basis for each subscriber line. HSDU  140  includes XDSL interface units  142 A . . .  142 M which comprise XDSL transceivers that translate the digitized subscriber information into XDSL formatted information transmitted and received on lines  144 A . . .  144 M to the central office such as via ATM facilities. A selector  146  selects which of the interface units  142 A . . .  142 M will be connected via lines  148 A,  148 B, . . .  148 N to respective SIUs  124 A,  124 B, . . .  124 N. Since M is an integer less than N, not all SIUs can be concurrently provided with high speed data services. While this is a limitation, the number of subscribers requesting high speed data services at any given time can be forecast and the M/N ratio determined to provide a targeted class of service. 
     Lines  148 A . . .  148 N support the flow of digital information between the SIUs and HSDU. Filtering of unwanted high frequency components associated with the high speed data is incorporated using known digital filtering techniques by the DSPs on the SIUs. Similarly, the filtering of unwanted low frequency components associated with the high speed data can be incorporated into the interface units  142 A . . .  142 M. Alternatively, such filtering could be accomplished in the analog domain before conversion of the analog signals associated with the line support unit into digital signals. In that case, the filtered analog signals would be sent via lines  148 A . . .  148 N to the HSDU and the interface unit  142 A . . .  142 M would process the filtered analog signals. An important aspect of the invention resides in not having to provide such filtering at the “front end” of the line support circuit where large filter components would be required. 
     A controller  150  provides call processing communications and instructions among the central office via line  152 , HSDU  140  via line  154 , and the SIUs via line  156 . A microprocessor  158  is supported by read only memory (ROM)  160  and random access memory (RAM)  162 . The microprocessor  158  is connected to input/output interface  164  which supports the receipt and transmission of signals over lines.  152 ,  154  and  156 . Call processing instructions and status information are communicated on line  152  between the central office and MLIU  120  via controller  150 . Instructions are communicated on line  154  to HSDU  140  to control the path selections made by selector  146 . Call processing information is carried on line  156  between controller  150  and the SIUs. 
     It will be apparent to those skilled in the art that various implementations of the present invention is possible. For example, very large scale integration (VLSI) techniques could be used to construct a multiple line interface unit wherein the required functions in the SIUs could be provided in a common shared circuit. A DSP with sufficient power and capabilities could service several if not all of the SIUs. Further, common functions of the XDSL interface units suggest several if not all of these units could be combined into a shared processing circuit or chip. It is also contemplated that the functions of the HSDUs and the SIUs could be combined in whole or in part by a sufficiently powerful DSP or DSPs or a computing system. Alternatively, the internal components of the MLIU could be segregated by analog and digital functions. 
     An example of a subscriber receiving XDSL services is explained below with regard to the embodiment shown in FIG.  4 . The following steps describe providing XDSL services for the subscriber as the called party. 
     1. The central office equipment sends a call setup message by channel  152  to controller  150 . The central office setup message identifies the subscriber line to which high speed data services is to be provided. Controller  150  maintains a stored table that correlates subscriber lines to corresponding subscriber interface units, and hence the SIU to receive XDSL information is known based on the identity of the subscriber line. 
     2. Controller  150  generates a command transmitted via communication path  156  to SIU  124 A supporting subscriber line  122 A. The subscriber served by subscriber line  122 A is the party to receive XDSL communications in this illustrative example. 
     3. Controller  150  generates another command signal transmitted on line  154  to the HSDU  140  (selector  146 ) which identifies input line  148 A to be utilized to provide XDSL communications with line interface unit  124 A. Controller  150  stores a table of availability of the interface units  142 A . . .  142 M and assigns a not in use high speed interface unit such as  142 A to handle the XDSL communications with subscriber line  122 A. 
     4. Following the establishment of a communication path between the subscriber line  122 A and the HSDU  140 , controller  150  sends a reply message via channel  152  to the central office equipment confirming that the requested XDSL communication path has been established and identifying the high speed data unit  142 A and corresponding line  144 A which will carry the subject XDSL communication between the central office equipment and MLIU  120 . Thus, a completed path to the central office is now available to carry XDSL communications with customer premises equipment coupled to subscriber line  122 A. 
     In the above example, the controller  150  maintains a database of the availability of the interface units  142 A . . .  142 M to handle an XDSL service request. Alternatively, the central office could maintain a table or database of interface unit availability and provide controller  150  with the identification of the interface unit to be used. 
     The following steps illustrate the origination of a request by a subscriber for XDSL services implemented on an on demand basis. 
     1. For this illustrative example, assume that the subscriber requesting XDSL services is associated with subscriber line  122 A. Utilizing customer premises equipment coupled to subscriber line  122 A, the subscriber will initiate a request for XDSL communications such as by sending a request for services signal to the associated SIU  124 A. 
     2. Using known signal detection techniques, the DSP  132  of SIU  124 A will recognize the request for services signal. 
     3. SIU  124 A will then generate a command on line  156  advising controller  150  of the request for XDSL services by the subscriber associated with line  122 A. 
     4. The controller  150  transmits a service request on line  152  to the central office. The central office after checking the availability of one of lines  144 A . . .  144 M sends an instruction to controller  150  advising of the line, e.g.  144 A, to be used in accommodating this request for services. 
     5. The controller  150  transmits a command signal on line  154  to HSDU  140  (selector  146 ) indicating the XDSL interface unit  142 A to be connected to SIU  124 A via line  148 A. 
     6. The controller  150  preferably further generates a command signal on line  156  to SIU  124 A to advise of the path completion. 
     7. Thus, an XDSL communication path is established between the subscriber&#39;s customer premise equipment associated with subscriber line  122 A and high speed data line  144 A which carries simplex inbound and outbound communications to the central office equipment. 
     It is also contemplated that the high speed services could be provisioned by a telecommunication system administrator, e.g. so called “nailed up”. In this circumstance, one of lines  144 A . . .  144 M would be assigned on a good until changed basis to one of the SIUs and hence to a subscriber served by that SIU. In this arrangement, the subscriber would always have immediate access to high speed facilities. 
     While the specification in this invention is described in relation to certain implementations or embodiments, many details are set forth for the purpose of illustration. Thus, the foregoing merely illustrates the principles of the invention. For example, this intervention may have other specific forms without departing from its spirit or essential characteristics. The described arrangements are illustrative and not restrictive. 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 are thus within its spirit and scope. 
     Although an explanation of embodiments of the present invention have been made above with reference to the drawings, the scope of the invention is defined by the claims which follow.