Abstract:
A voice relaying apparatus includes a receiving section for receiving a cell from an asynchronous transfer mode (ATM) network, a plurality of cell assembling/disassembling units for assembling and disassembling the cells, and a transmitting section for transmitting the cells assembled by each of the plurality of cell assembling/disassembling units. Each of the plurality of cell assembling/disassembling units is composed of a cell disassembling section for disassembling the cell received by the receiving section, a detecting section for detecting whether or not the voice relaying apparatus is carrying out a relay switch operation, and a cell assembling section for assembling the cell disassembled by the cell disassembling section and then sending to the transmitting section, if the fact that the voice relaying apparatus is carrying out the relay switch operation is detected by the detecting section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a voice relaying apparatus and a voice relaying method in order to carry out a digital voice communication in an asynchronous transfer mode (ATM). 
     2. Description of the Related Art 
     Conventionally, a digital voice communication network for carrying out an inter-office communication in an asynchronous transfer mode is well known. In this digital voice communication network, a voice signal is relayed and switched in accordance with a procedure described below. At first, a cell received from a relay line is disassembled. As a consequently, a low-bit-rate coding voice signal is produced. This low-bit-rate coding voice signal is further decoded into a PCM voice signal of 64 kbps that can be treated within a digital switch and sent to the digital switch. The digital switch switches this PCM voice signal and outputs the switched PCM voice signal. The PCM voice signal outputted by the digital switch is again encoded into the low-bit-rate coding voice signal, and then assembled into the cell, and further sent to the relay line. 
     In the above-mentioned relaying and switching method, each time the relay switch operation is carried out by the digital switch, the processes are carried out, such as the disassembling of the cell, the decoding of the low-bit-rate coding voice signal, the encoding of the PCM voice signal and the assembling of the cell. This results in deterioration of quality of the voice sent and received through the digital voice communication network and also leads to increase of a transmission delay time of the voice. 
     As a first conventional technique to solve this problem, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 9-98169) discloses “VOICE RELAYING AND SWITCHING SYSTEM”. In this voice relaying and switching system, a cell received from a relay line is disassembled and converted into the low-bit-rate coding voice signal. Then, a predetermined synchronous signal is added to this low-bit-rate coding voice signal to thereby generate a pseudo digital voice signal, which is sent to a switch. If a digital voice signal switched by the switch includes the predetermined synchronous signal, only the low-bit-rate coding voice signal is extracted from the digital voice signal, and then assembled into the cell, and further sent to the relay line. 
     Accordingly, when a connection destination of the switch is the relay line, the process for decoding the low-bit-rate coding voice signal and the process for encoding the PCM voice signal can be omitted. As a result, this case can avoid the deterioration of call quality caused by these processes and the increase of transmission delay. However, in this voice relaying and switching system, because the digital voice signal must pass through the section for disassembling the cell, the switch and the section for assembling the cell at a speed of at least 64 kbps, the hardware which operate at high speed is required. 
     Also, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 10-4415) discloses “DATA TRANSMITTING APPARATUS”, as a second conventional technique. FIG. 1 shows the structure of this data transmitting apparatus. This data transmitting apparatus is provided with a switch (PBX)  704 , a transcoder  702  and an ATM multiplexer  701 . As the PBX  704 , a switch that can function as a relay station is employed. The ATM multiplexer  701  is composed of a cell assembling/disassembling device (CLAD)  715  for assembling the cell in accordance with data received from a transcoder  703  and a cell assembling/disassembling device (CLAD)  714  for assembling the cell in accordance with data received from another data transmitting apparatus and then transmitting to the transcoder  702 . 
     In this data transmitting apparatus, when the PBX  704  does not serve as the relay station, the transcoder  703  performs a band compression on the data received from the PBX  704 , and sends to the cell assembling/disassembling device  715 . Then, the transcoder  702  releases the band compression of the signal from the cell assembling/disassembling device  714 , and sends to the PBX  704 . However, when the PBX  704  serves as the relay station, the transcoder  703  does not perform the band compression on the data received from the PBX  704 , and sends to the cell assembling/disassembling device  715 . The transcoder  702  does not release the band compression of the data from the cell assembling/disassembling device  714 , and sends to the PBX  704 . Hence, when the PBX  704  serves as the relay station, the process for disassembling the cell and the process for assembling the cell can be omitted in the relay station to thereby avoid the deterioration of the call quality and the increase of the transmission delay caused by these processes, even in a case of a multiple-stage relay. 
     Moreover, Japanese Laid-Open Patent Disclosure (JP-A-Heisei 9-55753) discloses “METHOD FOR RELAYING AND SWITCHING COMPRESSED VOICE IN ATM”, as a third conventional technique. In this method for relaying and switching a compressed voice in ATM, it is detected whether or not a cell (digital compression voice data) received from an ATM network is relayed and switched by a digital switch, when it is relayed and switched by the digital switch and again transmitted to the ATM network. When a cell (digital compression voice data) is received from the ATM network, such a check is done that whether or not a relay switch operation is accomplished by the digital switch. Then, if such a fact that the relay switch operation is accomplished is detected, the cell is passed without the compression and expansion of the voice data and the assembling and disassembling of the cell. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has an object to provide a voice relaying apparatus and a voice relaying method capable of further reducing a delay time when a voice signal is switched. 
     In order to achieve the above-mentioned object, a voice relaying apparatus according to a first aspect of the present invention includes a cell disassembling section to disassemble the cell received from a network and a detecting section to detect whether or not the voice relaying apparatus is carrying out a relay switch operation. The voice relaying apparatus assembles the cell disassembled by the cell disassembling section if the detecting section detects that the voice relaying apparatus is carrying out the relay switch operation and transmutes the assembled cell to the network. 
     Also, in order to achieve the above-mentioned similar object, a voice relaying apparatus according to a second aspect of the present invention comprises a receiving section for receiving a cell from an asynchronous transfer mode (ATM) network, a plurality of cell assembling/disassembling units for disassembling and assembling the cells and a transmitting section for transmitting the cell assembled by each of the plurality of cell assembling/disassembling units. Each of the plurality of cell assembling/disassembling units is composed of a cell disassembling section to disassemble the cell received by the receiving section, a detecting section to detect whether or not the voice relaying apparatus is carrying out a relay switch operation, a controller to select the cell disassembled by the cell disassembling section if the detecting section detects that the voice relaying apparatus is carrying out the relay switch operation and a cell assembling section to assemble the cell which is selected by the controller, and to supply the assembled cell to the transmitting section. 
     Accordingly, if the relay switch operation is being carried out, the low-bit-rate coding voice signal obtained by disassembling the received cell is not decoded into the PCM voice signal. In addition, the signal before the pass to the switch is immediately transferred to the relay destination. As a consequently, it is possible to omit the time when data is reciprocated between this voice relaying apparatus and the switch to thereby reduce the delay time when the voice signal is switched. 
     Moreover, in order to correspond to an actual ATM network needing the discrimination between target destinations (relay destinations) if there are three or more target destination nodes, the voice relaying apparatus according to the present invention can further comprise a unit for reporting the relay destination. Furthermore, it can have the configuration of transferring the cell to the relay destination by changing a destination address in accordance with information of reporting the relay destination. 
     Moreover, in order to achieve the above-mentioned similar object, a voice relaying method according to a third embodiment of the present invention is provided with the steps of disassembling a cell received from an asynchronous transfer mode (ATM) network, detecting whether or not a relay switch operation is being carried out, selecting the disassembled cell if such a fact that the relay switch operation is being carried out is detected and assembling the selected cell and transmitting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more better understanding of the present invention may be achieved by reading a detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an explanatory diagram for explaining a conventional technique; 
     FIG. 2 is a schematic block diagram for indicating a configuration of a voice relaying and switching system to which a voice relaying apparatus according to an embodiment of the present invention is applied; 
     FIG. 3 is an explanatory diagram for conceptually showing a positioning of a voice relaying and switching system including the voice relaying apparatus according to the present invention in an ATM network system; 
     FIG. 4 shows an address table used by a multiplexer/demultiplexer to assign a received cell to any one of first to third cell assembling and disassembling units; 
     FIG. 5 shows an address table used to generate a destination address in an address indicator when a call is made between a station “A” and a station “B”; 
     FIG. 6 shows an address table used to generate a destination address in one address indicator when a call is made between the station “A” and a station “C”; and 
     FIG. 7 shows an address table used to generate a destination addresses in another address indicator when the call is made between the station “A” and the station “C”. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A voice relaying apparatus according to an embodiment of the present invention will be described in detail below with reference to the attached drawings. FIG. 2 illustratively shows a structure of a voice relaying and switching system to which the voice relaying apparatus according to an embodiment of the present invention is applied. This voice relaying and switching system is provided with a voice relaying unit  1  and a digital switch (hereafter, referred to as “PBX”)  2 . In addition, FIG. 2 includes a block diagram showing a structure of the voice relaying unit  1  and a block diagram showing a structure of cell assembling/disassembling units  10 ,  20  and  30  within this voice relaying unit  1 . 
     At first, FIG. 3 conceptually shows the positioning of the voice relaying and switching system including the voice relaying apparatus according to the present invention in an ATM network system. Communication nodes (stations) “A”, “B” and “C” are installed in this ATM network system. The voice relaying and switching system shown in FIG. 2 is installed in each node. Respective virtual channels VC are created through the ATM network between the station “A” and the station “B” and between the station “B” and station “C”. Hereafter, this embodiment is described assuming that this virtual channel VC is present. It should be noted that FIG. 2 shows the voice relaying and switching system installed in the station “B” but the similar voice relaying and switching systems are also installed in the station “A” and the station “C”. 
     The structure of the voice relaying unit  1  according to the embodiment of the present invention will be described below with reference to FIG.  2 . The voice relaying unit  1  is provided with a first line interface section (LINE CARD)  11 , a first multiplexing/de-multiplexing section (MUX/DEMUX)  12 , a first cell assembling/disassembling unit (CLAD)  10 , a second cell assembling/disassembling unit (CLAD)  20 , a third cell assembling/disassembling unit (CLAD)  30 , a second multiplexing/de-multiplexing section (MUX/DEMUX)  13  and a second line interface section (LINE CARD)  14 . 
     The first line interface section  11  is composed of an interface circuit for connecting this voice relaying unit  1  to the ATM network. 
     The first multiplexing/de-multiplexing section  12  de-multiplexes a cell received from the ATM network into a signaling cell containing signaling data or a signaling signal and a voice cell containing voice data or a voice signal, and then sends to any of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30 . Also, the first multiplexing/de-multiplexing section  12  multiplexes the signaling cell and the voice cell from any of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30 , and then transmits to the ATM network. 
     Each of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30  disassembles the signaling cell and the voice cell from the first multiplexing/de-multiplexing section  12 . Also, each of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30  assembles internally generated or externally supplied signals into the signaling cell and the voice cell to be sent to the first multiplexing/de-multiplexing section  12 . These detailed descriptions will be discussed in later. 
     The second multiplexing/de-multiplexing section  13  multiplexes the signal from any of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30 , and then sends to the second line interface section  14 . Moreover, the second multiplexing/de-multiplexing section  13  de-multiplexes the multiplexed signal from the second line interface section  14 , and then sends to any of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30 . 
     The second line interface section  14  is composed of an interface circuit for connecting this voice relaying unit  1  to the PBX  2 . 
     Now, the structures of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30  will be described. It should be note that since the structures of the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30  are identical to that of the first cell assembling/disassembling unit  30 , only the configuration of the first cell assembling/disassembling unit  10  will be described. This first cell assembling/disassembling unit is provided with a cell disassembling section  16 , an identification signal adding section  17 , a control section  18  and a cell assembling section  19 . 
     The cell disassembling section  16  is composed of a first cell disassembling section (CLD)  101  and a second cell disassembling section (CLD)  102 . The first cell disassembling section  101  extracts a first signaling signal  113  from a signaling cell supplied from the first multiplexing/de-multiplexing section  12 , and sends the first signaling signal  113  to the second multiplexing/de-multiplexing section  13 . Also, the second cell disassembling section  102  extracts a first voice signal  114 , which is a low-bit-rate coding voice signal, from a voice cell supplied from the first multiplexing/de-multiplexing section  12 , and sends the first voice signal  114  to the identification signal adding section  17  and the control section  18 . 
     The identification signal adding section  17  is composed of a decoder (DEC)  103 , a signal generator (GEN)  105  and a multiplexer (MUX)  104 . The decoder  103  decodes the first voice signal  114  from the second cell disassembling section  102  to thereby generate a first PCM voice signal  115  of 64 kbps. The generated first PCM voice signal  115  is send to the multiplexer  104 . The signal generator  105  generates a synchronous signal  116 , and sends to the multiplexer  104 . This synchronous signal  116  is used as a CLAD identification signal indicative of the first cell assembling/disassembling unit  10 . The multiplexer  104  multiplexes the first PCM voice signal  115  from the decoder  103  and the synchronous signal  116  from the signal generator  105 , and sends the multiplexed signal to the second multiplexing/de-multiplexing section  13 . 
     The control section  18  is composed of a coder (COD)  111 , a detector (DET)  108 , a controller (CNT)  107 , a selector (SEL)  110  and an address indicator (ADR)  106 . 
     The coder  111  converts a second PCM voice signal  118  of 64 kbps from the second multiplexing/de-multiplexing section  13 , into a low-bit-rate coding voice signal, and sends it to the selector  110  as a second voice signal  119 . The detector  108  detects a synchronous signal included in the second PCM voice signal  118 , and generates a detection signal  112  representative of the detection result. This detection signal  112  is sent to the controller  107  and the address indicator  106 . 
     The controller  107  generates a control signal  121  in accordance with a detection signal  120  from the detector  108 , and sends the control signal  21  to the selector  110 . This control signal  121  is such a signal that the selector  110  select the second voice signal  119  from the coder  111  if the detection signal  120  indicates that the synchronous signal is not detected, and the selector  110  select the first voice signal  114  from the cell disassembling section  102  if the detection signal  120  indicates that the synchronous signal is detected. Therefor, the selector  110  selects any one of the first voice signal  114  from the second cell disassembling section  102  and the second voice signal  119  from the coder  111 , in accordance with the control signal  121  from the controller  107 , and then sends the selected signal to the cell assembling section  19 . The address indicator  106  generates an address indication signal  122  for indicating an address of a transmission destination, in accordance with the detection signal  120  from the detector  108 . This address indication signal  122  is sent to the cell assembling section  19 . 
     The cell assembling section  19  is composed of a first cell assembling section (CLA)  112  and a second cell assembling section (CLA)  109 . The first cell assembling section  112  assembles a second signaling signal  117  supplied from the second multiplexer/demultiplexer  13  into a signaling cell. The second cell assembling section  109  assembles the first voice signal  114  or the second voice signal  119  sent through the selector  110 , into a voice cell. At this time, an address indicated by the address indication signal  122  from the address indicator  106  is set to the voice cell as a transmission destination address. 
     Next, the operations of the voice relaying apparatus having the above-mentioned structure will be described below with reference to FIGS. 2 to  4 . Hereafter, a first case in which a call is made between the station “A” and the station “B” and a second case in which the relay switch operation is carried out in the station “B” to make a call between the station “A” and the station “C” are described. 
     In the first case, if a voice signal is transmitted from the station “A” to the station “B”, the operation is as follows. At first, when the station “B” receives a cell sent through the ATM network from the station “A”, the first line interface section  11  supplies the received cell to the first multiplexer/demultiplexer  12 . Then, the first multiplexer/demultiplexer  12  de-multiplexes the received cell into a signaling cell and a voice cell. The first multiplexer/demultiplexer  12  also assigns the de-multiplexed signaling cell and voice cell to any of the first cell assembling/disassembling unit  10 , the second cell assembling/disassembling unit  20  and the third cell assembling/disassembling unit  30 , in accordance with a destination address noted in the received cell. This assignment is carried out in accordance with an address table shown in FIG.  4 . 
     For example, if the destination address of the signaling cell from the station “A” is “bs 1 ”, the received signaling cell is sent to the first cell disassembling section  101  of the first cell assembling/disassembling unit  10 . In this case, since the destination address of the voice cell from the station “A” is “bv 1 ”, the received voice cell is sent to the second cell disassembling section  102  of the first cell assembling/disassembling unit  10 . 
     The first cell disassembling section  101  extracts the first signaling signal  113  from the received signaling cell, and sends the first signaling signal  113  to the second multiplexer/demultiplexer  13 . The second cell disassembling section  102  extracts the first voice signal  114 , which is the low-bit-rate coding voice signal, from the received voice cell, and sends the first voice signal  114  to the decoder  103  and the selector  110 . 
     The decoder  103  decodes the received first voice signal  114  to thereby generate the first PCM voice signal  115 . Then, the generated first PCM voice signal  115  is send to the multiplexer  104 . On the other hand, the signal generator  105  generates the synchronous signal  116  used as the CLAD identification signal. 
     The multiplexer  104  inserts the synchronous signal  116  from the generator  105  into the first PCM voice signal  115  from the decoder  103 . In this inserting operation, for example, a particular voice signal is determined for each several bytes of the first PCM voice signal  115 , and then the synchronous signal  116  is inserted into LSB (Least Significant Bit) of this particular voice signal. If the synchronous signal  116  is inserted into the first PCM voice signal  115  in this manner, even when it is decoded into an analog signal by the decoder of the PBX  2 , the original voice signal can be reproduced without any actual trouble. 
     On the other hand, if a voice signal is transmitted from the station “B” to the station “A”, the operation is as follows. Here, let us consider that a voice signal from the PBX  2  is de-multiplexed by the second multiplexer/demultiplexer  13 , and is sent to the first cell assembling/disassembling unit  10 . In this case, the second signaling signal  117  from the second multiplexer/demultiplexer  13  is inputted to the first cell assembling section  112 . The first cell assembling section  112  assembles this second signaling signal  117  into a cell, and further sets “as 1 ” indicative of a port  1  of the station “A” as the destination address, and sends to the first multiplexer/demultiplexer  12 . 
     Also, the second PCM voice signal  118  from the second multiplexer/demultiplexer  13  is sent to the coder  111  and the detector  108 . The coder  111  converts this second PCM voice signal  118  into the low-bit-rate coding voice signal, and sends the low-bit-rate coding voice signal to the selector  110  as the second voice signal  119 . 
     The detector  108  detects whether or not the synchronous signal is contained in the second PCM voice signal  118 . In this case, the station “B” is under controlling the call between the station “A” and the station “B”, and is not under controlling the relay switch operation. Thus, the second PCM voice signal  118  is a signal encoded by a coder (not shown) in the PBX  2 . Hence, the second PCM voice signal does not contain the synchronous signal. As a result, the detector  108  supplies the detection signal  120  indicating that the synchronous signal is not detected to the controller  107  and the address indicator  106 . 
     The controller  107 , since the detection signal  120  from the detector  108  indicates that the synchronous signal is not detected, selects the second voice signal  119  from the coder  111 , and then sends the selected second voice signal  119  to the second cell assembling section  109 . 
     Simultaneously with the above-mentioned selecting operation, the address indicator  106  generates the address indication signal  122  in response to the detection signal  120  from the detector  108 . The address indication signal  122  is generated in accordance with, for example, an address table shown in FIG.  5 . The generate address indication signal  122  is send to the second cell assembling section  109 . The second cell assembling section  109  assembles the second voice signal  119  supplied via the selector  110 , into a voice cell. Then, the second cell assembling section  109  sets the destination address of the voice cell to “av 1 ” indicative of the port  1  of the station “A” in accordance with the address indication signal  122  from the address indicator  106 , and then supplies to the first multiplexer/demultiplexer  12 . 
     The second multiplexer/demultiplexer  12  multiplexes the signaling cell containing the second signaling signal  117  from the first cell assembling/disassembling unit  10  and the voice cell containing the second voice signal  119 , and sends the multiplexed cells through the first line interface section  11  to the ATM network. In the ATM network, the multiplexed cells are transferred to the station “A” in accordance with the destination address of each cell. In the station “A”, the multiplexed cells are distributed to the port  1 , and then decoded into each signaling signal and voice signal. These signaling signal and voice signal are supplied to the PBX. The above-mentioned operations enable the call to be made between the station “A” and the station “B”. 
     Next, the second case in which the relay switch operation is carried out in the station “B” to make a call between the station “A” and the station “C” will be described below. In this second case, since the virtual channel VC is not present between the station “A” and the station “C”, the station “A” and the station “C” are connected to each other through the relay switch operation in the station “B”. A call path in this second case is composed of a first call path from the station “A” to the station “B” and a second call path from the station “B” to the station “C”. After the establishment of both the first call path and the second call path, the PBX  2  in the station “B” connects these two call paths to each other. This enables the call to be made between the station “A” and the station “C”. Each of the operation in the first call path and the operation in the second call path is identical to the above-mentioned operation (the operation between the station “A” and the station “B”). 
     Here, the process carried out in the PBX  2  for connecting the two call paths is described in detail with reference to FIGS. 2 and 3. For the convenience of description, let us suppose that the first cell assembling/disassembling unit  10  in the station “B” is used to connect with the station “A”, and the second cell assembling/disassembling unit  20  in the station “B” is used to connect with the station “C”, respectively. 
     The PBX  2  sends a signal including the first PCM voice signal  115  to which the synchronous signal  116  is added, derived from the first cell assembling/disassembling unit  10 , namely, the call path from the station “A” to the call path to the station “C”, namely, the second cell assembling/disassembling unit  20 . On the contrary, the PBX  2  sends a signal including the first PCM voice signal  215  to which a synchronous signal  216  is added, derived from the second cell assembling/disassembling unit  20 , namely, the call path from the station “C”, to the call path to the station “A”, namely, the first cell assembling/disassembling unit  10 . Accordingly, the detector  108  of the first cell assembling/disassembling unit  10  detects the synchronous signal  216  generated in the second cell assembling/disassembling unit  20 . Also, a detector  208  of the second cell assembling/disassembling unit  20  detects the synchronous signal  116  generated in the first cell assembling/disassembling unit  10 . 
     Next, the controller  107  generates such a control signal  121  that the selector  110  selects the first voice signal  114  from the second cell disassembling section  102 , in accordance with the detection signal  120  from the detector  108 . The selector  110  selects the voice signal in accordance with this control signal  121 . Similarly, a controller  207  generates such a control signal  221  that a selector  210  selects a first voice signal  214  from a second cell disassembling section  202 , in accordance with a detection signal  220  from a detector  208 . The selector  210  selects the voice signal in accordance with this control signal  221 . Also, the address indicator  106  generates the address indication signal  122 , in accordance with the detection signal  120  from the detector  108 . Similarly, an address indicator  206  generates an address indication signal  222 , in accordance with a detection signal  220  from the detector  208 . 
     The address indicator  106  generates “av 2 ” as the address indication signal  122 , in accordance with an address table shown in FIG.  6 . Then, the second cell assembling section  109  sends the voice cell in which the destination address is changed in accordance with the address indication signal  122 , through the first multiplexer/demultiplexer  12  and the first line interface section  11  to the ATM network. Accordingly, the voice signal (the first voice signal  114 ) from the first cell assembling/disassembling unit  10  is sent to the station “C”. 
     Similarly, the address indicator  206  generates “av 1 ” as the address indication signal  222 , in accordance with an address table shown in FIG.  7 . Then, the second cell assembling section  209  sends the voice cell in which the destination address is changed in accordance with the address indication signal  222 , through the first multiplexer/demultiplexer  12  and the first line interface section  11  to the ATM network. Accordingly, the voice signal (the first voice signal  214 ) from the second cell assembling/disassembling unit  20  is sent to the station “A”. 
     The voice signal from this first cell assembling/disassembling unit  10  is originally the voice signal from the station “A”, and the voice signal from the second cell assembling/disassembling unit  20  is the voice signal from the station “C”. Accordingly, the call path is accomplished between the station “A” and the station “C”. At this time, the first voice signal  114  and the first voice signal  214 , which are the low-bit-rate coding voice signals, are not decoded into the PCM voice signals. Moreover, the signal before supplying to the PBX can be immediately transferred to the relay destination. 
     The voice relaying apparatus and the voice relaying method according to the present invention, when the relay switch operation is carried out in the ATM network, the low-bit-rate coding voice signal is not decoded into the PCM voice signal. Moreover, the signal before supplying to the PBX is immediately transferred to the relay destination. Consequently, the time of the reciprocation between the voice relaying apparatus and the PBX can be shortened and the delay time can be decreased.