Abstract:
Apparatus and method for a central office data communications apparatus allows for combining the voice POTS and high speed modem data processing functions into one device at the central office. The combination of the signals allows for a single high-speed CODEC which samples both a POTS signal and the high-speed modem signals to be utilized. This eliminates the need for external POTS splitters and costly duplicative circuitry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Serial. No. 60/039,430, filed on Feb. 26, 1997, and entitled “Combined DSL/Channel Bank”. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to telecommunications and, more particularly, to an apparatus and method for combining POTS and DSL apparatus and function into one device. The combination uses a single highspeed CODEC which samples both the POTS signal and the DSL signal. 
     2. Description of the Invention 
     As known in the art, high-speed modems are able to transfer data at high rates over a local loop. In order to accomplish these high data rates, the high-speed digital modems use frequencies which are significantly higher than the voice band frequencies used in the plain old telephone system (“POTS”). 
     However, such modems require that the central office wire center utilize a POTS splitter device to separate the POTS voice band frequencies, occurring in the frequency spectrum between about 0 Hz and about 4 kHz, from the highspeed digital modem data using the frequency spectrum of between about 20 kHz and about 1 MHz. This setup also requires that there be duplicative hardware to process the POTS voice and digital modem frequencies. The hardware converts the voice data into digital data for transmission over a voice time division multiplexing (TDM) bus, and the digital signal that is processed by analog front end and coder/decoder (CODEC) devices converts the highspeed modem data from the analog frequencies back to digital data. Unfortunately, the manufacture and installation of POTS filters and duplicative coder/decoder and analog front end logic are expensive and their use sometimes requires the rewiring of the central office wire center. 
     Consequently, it would be desirable to avoid the use of the POTS splitter and duplicative analog front-end and coder/decoder logic, which saves space due to the reduced circuitry and avoids the expense the extra circuitry imposes. 
     SUMMARY OF THE INVENTION 
     Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     To achieve the advantages and novel features, the present invention is generally directed to a central office data communications apparatus and method, that allows a combined voice POTS and high speed modem processing functions into one device at the central office. The combination of the signals allows for a single high-speed CODEC which samples both a POTS signal and the high-speed modem signals to be utilized. This eliminates the need for external POTS splitters and costly duplicative circuitry. 
     One embodiment of the modem apparatus and method for a combined digital subscriber line (DSL) and voice system includes apparatus for processing the voice POTS signals and the speed modem signals through a common analog front end high-speed coder/decoder (CODEC) circuitry. The digital signals from the high-speed CODEC are provided to a DSP logic which provides for support of multiple voice lines. Once connected, voice POTS frequencies are not bursty, and therefore, need to be serviced on an eight kHz sample rate in both directions. The digital signal processor (DSP) provides this processing by filtering between voice and high speed modem data in the DSP itself. 
     The preferred embodiment includes a sample rate of 192 kHz. However, any sample rate is possible as long as it is a multiple of the eight kHz, because the voice POTS signal is always sampled at an eight kHz rate in order to interface to the public switched telephone network (PSTN) network. Since the conversion and filtering between voice and high speed modem data is not run time extensive, the DSP can service multiple subscriber lines simultaneously without saturation. 
     The invention can also be viewed as providing a method for allowing combined voice POTS and high speed modem processing functions in one device. In this regard, the method can be broadly summarized by the following steps: 
     interfacing to a local loop capable of simultaneously carrying both a POTS signal and high speed modem signals; 
     sampling both said POTS and said high speed modem signals with a single codec; and 
     processing both said sampled POTS and said sampled modem signals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is a schematic view of the central office (CO) wire centers and user premises layout. 
     FIG. 2 is a block diagram of the CO POTS interface, the POTS switch analog conversion card and the DSL modem apparatuses of FIG.  1 . 
     FIG. 3 is a schematic view of the CO wire centers and user premises layout with the modem bank, that combines the central office DSL modem and the POTS switch analog conversion card for voice data signals, apparatus of the present invention. 
     FIG. 4 is a block diagram of the modem bank of FIG.  3 . 
     FIG. 5 is a block diagram of the analog front end and subscriber line interface circuit, and the coder/decoder circuit of FIG.  4 . 
     FIG. 6 is a block diagram of the digital signal processor engine of FIG.  4 . 
     Reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings in which the reference numerals indicate like parts throughout several views, FIG. 1 illustrates the plain old telephone system (POTS) networks including data communication modems ( 16  and  45 ) of the prior art. The POTS network includes numerous user premises  41 , wherein each user premises is connected to a central office wire center  11 , via a subscriber line  27 . Each subscriber line  27  is connected to the user premises  41 , which further connects to a user premises line  47 , for distribution of POTS service throughout the user premises. Usually, there are numerous POTS devices connected to each user premises line  47 , such as telephones  44 , fax machines  42 , PCs  43 , and the like. It is also known, but not shown, that it is possible to have multiple subscriber lines  27  connected to each user premises, thereby creating two separate user premises lines  47  within each user premises. 
     As noted previously, each user premises is connected via a subscriber line  27  to a central office wire center  11 . The subscriber line  27  is connected to a POTS splitter device  15  that separates the analog POTS signals from data signals. The POTS signals are sent to a POTS switch  14  that is connected to the other central office wire centers, via the public switched telephone network (PSTN)  28 . Modem data signals are separated from the POTS analog signals at POTS splitter  15 , and are connected to modems  16  within the central office wire center  11 . Modems  16  are further connected to digital data networks such as the Internet  29 . 
     A brief discussion of an example for the signals generated in the applied system environment for the prior art from the user premises and transmitted through the central office wire center, via either the PSTN or Internet networks and back to a user premises will now be detailed. 
     When a user wishes to place a telephone call on device  44 , the user picks up the receiver and puts the subscriber line  27  in an off-hook condition that is detected at the central office wire center  11 , by closed switch hooks (not shown). The off-hook condition signals the central office wire center  11 , via subscriber line  27 , to accept an outgoing call by allowing a flow of D.C. current and a dial tone of 480 Hz to be sent to device  44 . The outgoing telephone call signals are transmitted, as described before, via subscriber line  27  to POTS splitter  15 . The analog POTS system signals are separated from the modem signals, and the POTS signals are directed towards the POTS switch  14  for transmission, via the PSTN network  28 , to the destination central office wire center  11  of the destination user premises  41 . The signal is further directed towards a POTS splitter  15  within the destination central office wire center  11 . The signal is transmitted, via subscriber line  27 , to the destination user premises  41 . The modem signal enters the destination user premises  41 , via subscriber line  27 , and is connected to the user premises line  47  that distributes the signal to be received throughout the destination user premises  41 . This is the path in which a plain old telephone system (POTS) call is transmitted. 
     Now, a description of digital signals to/from the user premises will be described. When a user desires to transmit data over a digital network via his personal PC  46 , digital phone  44 , or the like, the digital signals from the digital device, are transformed into analog signals, via modulation by modem  45 . The signals are transmitted over the user premises line  47  to the subscriber line  27  for final delivery to the local central office wire center  11 . The digitally modulated analog signals going into POTS splitter  15 , are separated from the analog POTS signals, and are directed to modems  16 . Modems  16  demodulate the analog signals back to their original digital data signals. The modems  16  transmit the digital data over the Internet  29 . The digital data signals sent via the Internet  29  are received at the destination central office wire center  11  by the modems  16 . The modems  16  modulate the digital signals into analog signals for transmission through the POTS splitter  15  and over destination subscriber line  27  to the destination user premises  41 . The modulated signals are received at the user premises line  47 , for distribution to all equipment connected to the user premises distribution line. The modulated signals are demodulated, within the destination modem  45 , back to a digital signals, which are transmitted to the digital device connected to the modem. 
     FIG. 2 illustrates the separate central office POTS interface, the POTS Switch analog conversion card, and the DSL modem apparatuses of the prior art. 
     The POTS splitter device  15  illustrated in FIG. 2 is connected to the subscriber line wire pair  27  which transmits both voice POTS and high-speed modem data into the central wire office  11 . The POTS splitter device separates the low voice POTS frequency spectrum of 0 kHz to 4 kHz and transmits them as described above to POTS switch  14 . The POTS switch  14  contains within it a voice line card  32 , comprising the subscriber line interface circuit  33  and CODEC  34 . 
     The CODEC  34  converts the analog voice signals into digital signals and transmits them, via the voice TDM bus  21 , across the PSTN network  28  to the destination central office wire center for transmission to the destination user premise  41 , as described above. The high-speed digital modem signals on the subscriber line wire pair  27  are separated from the voice signals and provided to a modem device  16  for processing. 
     The modem device  16  comprises an analog front end  35 , which transforms the two wire high speed analog data signals, utilizing the frequency spectrum of between about 20 kHz and 1 MHz into four wire loops, and transmits the analog signals over the four wire loops to the CODEC device  36  for conversion from analog signals into digital data. The high-speed digital data is then output from the CODEC  36  into the DSP digital signal processor (DSP)  37  logic for processing and further transmission via the digital data bus ( 22 ). As can be seen by FIG. 2, there is duplicate hardware in both the POTS switch  14  and the modem  16  devices which include the analog front end  35  and subscriber link interface circuit  33 , and the CODEC  34  and  36  devices. 
     FIG. 3 illustrates the plain old telephone system (POTS) networks including data communication modem and voice bank  60  of the present invention. It is shown that the present invention communication modem bank  60  can be substituted for the POTS splitter  15  and high-speed data modem  16 . The network is otherwise the same. 
     Referring now to FIG. 4, illustrated is a block diagram of the modem bank  60  that combines the voice POTS and high-speed modem data functionality into one device. The modem and voice bank  60  utilizes a single analog front end/subscriber link interface (AFE/SLIC) circuit  61  to interface to the subscriber link  27  which is connecte d to the user premise  41 . The AFE/SLIC  61  herein defined in further detail with regard to FIG. 5 provides for the hybrid circuits, ring indicator, off/hook detector, and line protection circuitry. The AFE/SLIC  61 , by utilizing the hybrid circuit, provides for a one way analog communication link for a signal in each direction on lines  67 A and  67 B. This a nalog signal is transmitted between the AFE/SLIC  61  and the CODEC  62 . The CODEC  62  herein defined in further detail with regard to FIG. 5 provides the actual coding of digital to analog signals and decoding of analog to digital signals. The digital signals from CODEC  62  are transmitted between the CODEC  62  are the DSP logic  63  across bus  75 . Bus  75  provides a multiplexing of digital signals from one of a plurality of operating CODECs  62  to the DSP logic  63  at any particular time. The DSP logic  63 , herein defined in further detail with regard to FIG. 6, processes the digital data received from line  75  and filters out the voice POTS signals from the digital data signals. 
     The DSP logic  63  then transmits the voice POTS signals to the POTS switch  14  (FIG. 3) for transmission across the PSTN network  28  to the destination central office wire center  11  POTS switch  14 . The digital data is filtered and transmitted on data bus  25 , and over the Internet  29  to the destination CO wire center  11 . DSP logic  63  is herein defined in further detail with regard to FIG.  6 . 
     Since it is assumed that DSP sharing is provided, multiple AFE/SLICs  61  and CODECs  62  can share the processing power of the DSP logic  63  which can support numerous simultaneous transmissions through the central office wire center. The DSP sharing includes voice sharing which assumes that the voice has a low peak busy hour rate, probably lower than data due to shorter hold times. Once connected, the voice signal is not bursty, therefore, it needs to be serviced on an eight kHz sample rate in both directions. This can be done because the voice processing, which converts  12  bit linear code into eight bit mu-law code, is done in this DSP logic  63  and is not run time extensive. Filtering between the voice signals and data signals is also done in DSP logic  63 , eliminating the need for a separate POTS filter. 
     Referring now to FIG. 5, illustrated is shown the AFE/SLIC  61  and the CODEC  62  functional block diagram. The subscriber line  27  is a bidirectional wire pair from the subscriber user premise  41  and is connected to a line protection circuitry  65 . Line protection circuit  65  protects the multi-channel communications device against line surges, lightening strikes and the like. Line protection circuit  65  is then further connected to the impedance and isolation circuit  66  via a communication link. The impedance and isolation circuit  66  contains circuitry for impedance control, isolation, hybrid circuits, ring indicator and off-hook detector (not shown). The AFE/SLIC  61  is then connected via communication link  67  to the CODEC  62 . 
     With further reference to FIG. 5, CODEC  62  receives analog signals via line  67 A for conversion from analog to digital receiver circuit  72 . Analog to digital receiver  72  is provided timing by timing circuit  71 . Timing circuit  71  provides timing signals to process the analog to digital and digital to analog transformations. The output of the analog to digital receiver  72  is digitized data which is placed on bi-directional bus  75 . 
     Digital communication link  75  and  25  can be comprised of  8 ,  16 ,  32 ,  64 ,  128  or other bit sized digital parallel communication link. Communication link  25  and  75  can also be comprised of a bit serial or other type of chip to chip signal communication links. Communication link  67 B transmits analog signals coded by the digital to analog driver  73 . The digital to analog driver  73  receives digital signals for transmission across digital communication link  75 . 
     Interface  68  carries the control and status information from the digital signal processor to the impedance control isolation circuitry  66  of AFE/SLIC circuitry  61 . 
     Referring now to FIG. 6, illustrated is the DSP  63  block diagram of the functionality of the DSP logic  63 . Digital signals are received on communication link  75  and are provided to the data demodulator  81  and to the decimator  82 . For the voice POTS signals, the decimator  82  reduces the voice sample rate to eight kHz. The signal is then sent through a low pass filter  83  which eliminates the high frequency data signals. A linear to mu-law converter  84  converts the voice signals for output onto a voice time division multiplexing (TDM) bus  21 . The voice POTS signal is combined with voice signals from other channels to make up the TDM bus. The digital demodulator  81  receives the high speed digital signals from the CODEC  62 , demodulates these signals, and transmits them across data bus  22  for further transmission over the Internet  29 . 
     The transmit path through the DSP logic  63  has the data modulator  86  receiving high speed digital data signals from the data bus  22 . The voice TDM bus  21  provides a digitized voice signal to the mu-law to linear converter  85 . The mu-law to linear converter  85  provides for encoding of the digitized voice POTS signal. In an alternative embodiment, A-law encoding may be utilized instead of mu-law encoding. The encoded voice POTS signal is then added to the data signal output from the data modulator  86  in circuitry  87 . The voice POTS signal is summed on an eight kHz sample rate while the combined voice and data signal is outputted to the digital to analog converter on a multiple of eight kHz sample rate. 
     The preferred embodiment provides for the sample rate to be 192K. The above description provides for operation of a single voice and data channel. Other embodiments include multiple AFE/SLIC  61  and multiple CODEC  62   s  (as shown in FIG. 4) and provides the ability to be active at the same time through DSP sharing using statistical properties of data as described in the U.S. Pat. No. 6,084,885 entitled “APPARATUS AND METHOD FOR DSP SHARING USING STATISTICAL PROPERTIES OF DATA”, Ser. No. 09/027,705 herein incorporated by reference. 
     The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled.