Abstract:
A signal matching apparatus for exchanging signals between a digital switching system and a two-wire long distance subscriber line signal switching system comprises a first PCM equipment for converting a 4-wire E1 signal of the digital switching system into a 4-wire analog signal, and for connecting a 4-wire analog signal of the long distance subscriber line signal switching system into a 4-wire digital signal transferred to the digital switching system, and a second PCM equipment for converting the 4-wire analog signal of the first PCM equipment into a 2-wire signal, and for converting the analog signal of the long distance subscriber line signal switching system into a 4-wire analog signal transferred to the first PCM equipment.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for SIGNAL MATCHING APPARATUS FOR EXCHANGING SIGNALS BETWEEN AN ANALOG SWiTCHING SYSTEM AND A DIGITAL SWITCHING SYSTEM earlier filed in the Korean Industrial Property Office on Mar. 14 1997 and there duly assigned Ser. No. 8613/1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention concerns an apparatus for matching an analog switching system with a digital switching system to exchange signals between them. 
     2. Related Art 
     Generally, the analog switching system is a manual switching system installed in a rural network area which is not provided with means for utilizing the main network installed in an urban area. The analog switching system employs the long distance subscriber line signal handled by the rural network, and provides the long distance subscribers with calling service by making a connection with a central exchange which is installed in the urban area typically located over a few hundred kilometers from the analog switching system. 
     Typically, such analog switching systems require an analog-to-digital (A/D) converter, such as a PCM30-4 (A/D converter) in order to achieve a system which is harmonious with a digital switching system. However, since such systems are typically designed according to the signaling system known as R1, R2/CAS, such a system may not be employed in a rural network system as generally described above, and as described in more detail below. Therefore, there has been a requirement for a signal conversion system to process a 2-wire long-distance subscriber line signal so as to match the digital switching system with the analog switching system typically employed in a rural network system. 
     Thus, there is a need in the art to provide a signal matching system which matches a digital switching system with an analog switching system using a 2-wire long-distance subscriber line signal. 
     The following patents are considered to be representative of the prior art, and are burdened by the disadvantages set forth herein: U.S. Pat. No. 4,535,444 to Falzone et al, entitled Digital Switching Exchange For Telephone Systems, U.S. Pat. No. 5,657,358 to Panech et al, entitled Subscriber RF Telephone System For Providing Multiple Speech And/Or Data Signals Simultaneously Over Either A Single Or Plurality OfRF Channels, U.S. Pat. No. 5,687,194 to Paneth et al., entitled Subscriber RF Telephone System For Providing Multiple Speech And/Or Data Signals Simultaneously Over Either A Single Or A Plurality Of RF Channels, U.S. Pat. No. 5,325,422 to Ladd, entitled PBX Telephone Call Control System, U.S. Pat. No. 4,796,296 to Amada et al, entitled PCM Coder And Decoder Having Function Of Two-Wire/Four-Wire Conversion, U.S. Pat. No. 4,757,497 to Bejerle et al., entitled Local Area Voice/Data Communications And Switching System, and U.S. Pat. No. 4,309,766 to Lechner et al., entitled ArrangementFor Subscriber Circuits UtilizingDigital Time Division Multiplex Telecommunication Installations And Particularly For PCM Local 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a signal matching system which matches a digital switching system with an analog switching system using a 2-wire long distance subscriber line signal. 
     According to the present invention, a signal matching apparatus for exchanging signals between a digital switching system and a two-wire long distance subscriber line signal switching system comprises a first PCM equipment for converting the 4-wire E1 signal ofthe digital switching system into a 4-wire analog signal, and the 4-wire analog signal of the long distance subscriber line signal switching system into a 4-wire digital signal for transfer to the digital switching system, and a second PCM equipment for converting the 4-wire analog signal of the first PCM equipment into a 2-wire signal, and the analog signal of the long distance subscriber line signal switching system into a 4-wire analog signal for transfer to the first PCM equipment. 
     The present invention will now be described more specifically with reference to the drawings attached only by way of example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a block diagram illustrating the construction of an analog 2-wire long distance subscriber line network; 
     FIG. 2 is a block diagram illustrating the connection of the analog 2-wire-long-distance subscriber line switching system and the digital switching system according to the present invention; 
     FIG. 3 is a diagram illustrating the steps of processing the signal when the digital switching system calls a subscriber of the analog switching system according to the present invention; 
     FIG. 4 is a graph illustrating the waveform of the signal transmitted from the digital switching system according to the present invention; 
     FIG. 5 is a diagram illustrating the steps of processing the signal when the analog switching system calls a subscriber of the digital switching system according to the present invention; and 
     FIG. 6 is a graph illustrating the waveform ofthe signal transmitted from the analog switching system according to the present invention 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 illustrating the construction of the analog 2-wire long distance subscriber line network, the hook-off signal initiated by a subscriber of the analog switching system  10  is transmitted to the transmission input/output device (TIO)  12  of the manual switching station, which converts the hook-off signal into a seizure signal transferred through amplifiers  14 ,  16  to the input/output transmission device  18  of the analog switching station. The amplifiers  14 ,  16  serve to amplify the signals according to the distance to be traversed. The analog switching transmission input/output device  18  converts the seizure signal into the corresponding hook-off signal transferred to the central exchange  20 , which transmits the dial tone through the occupied line to the analog switching transmission input/output device  18 . 
     Then, the analog switching transmission input/output transmission device  18  converts the dial tone into a corresponding seizure acknowledgment signal (Seizure Ack) which is transferred through the amplifiers  14 ,  16  to the manual switching transmission input/output device  12 , which in turn converts the seizure acknowledgment signal into a dial tone which is transferred to the calling subscriber of the manual switching system  10 . Thereafter, the calling subscriber dials the desired number, and that digital data is delivered through the manual switching, transmission input/output device  12  and the analog switching transmission input/output device  18  to the central exchange (ATC),  20 . The ATC  20  analyzes the digital data so as to connect the calling subscriber with the receiving subscriber. If the receiving subscriber is free, the ATC  20  transfers the ring-back tone to the analog switching transmission input/output device  18 , which in tum converts the ring-back tone into the receiving subscriber&#39;s free-state signal which is transferred through the amplifiers  14 ,  16  to the manual switching transmission input/output device  12 . Finally, the manual switching transmission input/output device  12  converts the receiving subscriber&#39;s free-state signal into a ring-back tone signal which is transferred to the calling subscriber, thus forming the communication path. This is a typical rural network switching system which is much used in the rural networks of Russia. 
     The analog switching system requires a PCM 30-4 A/D converter in order to achieve a system which cooperates with the digital switching system. However, since such system is designed according to the well-known signaling system R1, R2/CAS, it may not be employed in the rural network system shown in FIG.  1 . Hence, there has been required a signaling conversion system to process the 2-wire long distance subscriber line signal so as to match the digital switching system with the analog switching system typically used in the rural network system. 
     Referring to FIG. 2, there is provided a long signal control processor  100 , which converts the E1 signal of the digital switching system into a line/register signal required by the analog switching system so as to match with the 2-wire long distance subscriber line signal, and which analyzes the received line/register signal. CDTI 102  converts the line register signal into a 4-wire E1 digital signal when the subscriber of the digital switching system  110  calls the 2-wire long distance subscriber line. 
     The first PCM equipment  104  in PCM stage  112  consists of a PCM-30-4 and converts the line/register 4-wire digital signal of the CDTI  102  into the 4-wire analog signal transferred to the 4-wire/2-wire converter  106 , and the analog signal ofthe analog switching system into the digital signal transferred to the digital switching system  110 . The second PCM equipment  106  converts the analog 4-wire signal into the 2-wire signal transferred to the manual switching station input/output transmission device  12 , and the 2-wire signal of the manual switching station input/output transmission device  12  into the 4-wire signal transferred to the first PCM equipment  104 . The manual switching station input/output transmission device  12  converts the hook-off signal into a seizure signal transferred through the amplifiers  14   a  and  16   a  to the analog switching station input/output transmission device  18 , which in turn converts the seizure signal into the hook-off signal transferred to the central exchange  20 . The exchange  20  transfers the dial tone to the corresponding occupied line and to the analog switching station input/output transmission device  18 . In addition, the exchange  20  analyzes the dial digital signal to connect with the receiving subscriber. 
     The matching operation is described specifically with reference to FIGS. 2 to  6  as follows: 
     Firstly, describing the case that the subscriber of the digital switching system  110  calls the subscriber of the long distance subscriber line signal switching system in reference to FIG. 3, the digital switching system  110  maintains a “0” signal as shown by interval B of FIG. 4, and converts the hook-off signal generated by the subscriber CG of the digital switching system  1   10  into a seizure signal applied to the first PCM equipment  104 , which in turn converts the seizure signal into the digital signal transferred to the second PCM equipment  106 . The second PCM equipment  106  converts the digital seizure signal into a 2-wire hook-off signal transferred to the manual switching station input/output transmission device  12 , which in turn converts the hook-off signal into a seizure signal transferred through the amplifiers  14   a  and  16   a  to the analog switching station input/output transmission device  18 . In this case, the amplifiers  14   a  and  16   a  amplify the signal according to the transmission distance. 
     The analog switching station input/output transmission device  18  converts the seizure signal into the hook-off signal transferred to the central exchange  20  installed in the urban area. The exchange  20  transmits the dial tone through the corresponding occupied line to the analog switching station input/output transmission device  18 , which in turn converts the dial tone into the seizure acknowledgment signal Seizure Ack transferred through the amplifiers  14   a  and  16   a  to the manual switching station input/output transmission device  12 . 
     The manual switching station input/output transmission device  12  converts the seizure acknowledgment signal into the dial tone transferred through the second PCM equipment  106  and the first PCM equipment  104  to the digital switching system  110 , which in turn transfers the dial tone to the calling subscriber. Then, the call subscriber dials the desired number, from which the digital switching system  110  transfers the dial pulses as shown by interval C of FIG. 4 to the first and second PCM equipments  104  and  106 , which transfer the dialed digital data through the manual switching station transmission input/output device  12  to the analog switching station input/output transmission device  18  to the ATC  20 . The ATC  20  analyzes the digital signal to connect the calling subscriber CG with the receiving subscriber CD. In this case, the digital switching system  110  maintains “0” as shown by interval D of FIG. 4, recognizing the communication state. Finishing the communication, the digital switching system  110  maintains “1” as shown by interval E of FIG. 4, recognizing the idle state. Thus, when the subscriber of the digital switching system  110  calls the analog switching system, the digital switching system  110  always recognizes the states of the first and second PCM equipments  104  and  106  consisting of PCM-30-4 as “1”. 
     Secondly, referring to FIG. 5, describing the case that the subscriber of the long distance subscriber line signal switching system (exchange  20 ) calls the subscriber of the digital switching system  110 , the exchange  20  transfers the dialed ring signal from the subscriber CD of the exchange  20  to the corresponding occupied line and the ring-back tone to the calling subscriber CD. The ring signal is transferred to the analog switching station input/output transmission device  18 , which in turn delivers the ring signal through the amplifiers  14   a  and  16   a  to the manual switching station input/output transmission device  12 . 
     The manual switching station input/output transmission device  12  applies the ring signal to the second PCM equipment  106 . Then, the first and second PCM equipments  104  and  106 , respectively, convert the ring signal into a digital ring signal whose value is “0” for 1.5 seconds and “1” for 4 seconds as shown in FIG. 6, and transfers it to the digital switching system  110 , which in turn converts the digital ring signal into the ring signal sound of 25 Hz transferred to the receiving subscriber CG. In response to the ring signal sound, if the receiving subscriber CG picks up the transmitter/receiver off the hook, the digital switching system  110  transfers the answering signal (ANSWER AIG) to the first PCM equipment  104 . 
     The first and second PCM equipments  104  and  106 , respectively, convert the answering signal into the hook-off signal transferred to the manual switching station input/output transmission device  12 , which in turn converts the hook-off signal into the seizure signal transferred through the amplifiers  14 a and  16 a to the analog switching station input/output transmission device  18 . The analog switching station input/output transmission device  18  converts the seizure signal into a hook-off signal transferred to the central exchange  20 , which in turn connects the calling subscriber CD with the receiving subscriber CG of the digital switching system  110 . Receiving the hook-off signal, the digital switching system  110  maintains “0” state as shown in FIG. 6, and then takes on a “1” state after recognizing the connection of the communication line through the first PCM equipment  104 . 
     Thus, the PCM-30-4 A/D converter is effectively employed to match the signal of the digital switching system with that of the 2-wire long distance subscriber line signal analog switching system, so that the cost of developing the signal converter, as well as additional equipment, can be avoided. 
     It should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present invention, but rather that the present invention is not limited to the specific embodiments described in this specification except as defined in the appended claims.