Abstract:
A multiplexing system for ISDN circuits. Multiplexers in the system include data terminals, voice interfaces having voice trunks, high speed digital circuits and ISDN circuits, together with a control channel interface which connects trunking circuits by controlling calls on the control channel. When an outgoing voice call originates, data information from data terminals voice is multiplexed with compressed information from a voice interface and transmitted to trunking circuits. When calls originate, the control channel controls calls and connects them with trunking circuits. When using ISDN circuits, after setting up a communication channel for the circuits, a CPU controls calls to multiplex ISDN circuits on the control channel. By this structure decreasing the multiplexing ratio due to voice multiplexing call control on ISDN circuits can be eliminated when linking multiplexers with communication channels having high speed digital circuits and ISDN circuits.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an ISDN circuit multiplexing system using a multiplexer in which high speed digital and ISDN circuits are installed, and specifically relates to an ISDN circuit multiplexing system in which incoming calls and call control connections are made through the aforementioned ISDN circuit. 
     Call control data on an ISDN circuit control channel (D-channel) include the call control data for only the channel on the ISDN circuit. No call control data are included for multiplexing ISDN circuit channels. Therefore, when one tries to dynamically use ISDN circuits by allocating a needed band width for outgoing calls from terminals, it is not possible to multiplex a plurality of outgoing calls for transmission (for example, to have a 64 Kbps band transmit four 16 Kbps of compressed voice data). When using a multiplexed ISDN circuit, one has had to install a dedicated control channel within the ISDN circuits independent from the control channel to control calls based on one&#39;s unique data; or one has had to allocate a fixed band for the fixed use of ISDN circuit communication channels. 
     In the related technology, when one attempts multiplexed use of ISDN circuits by manipulating calls from terminals, a special control channel must be installed, consequently increasing the number of pieces of equipment required for controlling control channels. In addition, an additional band for the aforementioned control channel is required within the ISDN circuits, decreasing operational efficiency; This also complicates multiplex processing with respect to send/receive data control in the control channel. 
     SUMMARY OF THE INVENTION 
     This invention intends to provide a multiplexing system for ISDN circuits in which call control by means of an ISDN circuit for the voice-grade multiplexed linking does not decrease the multiplex ratio when multiplexers are connected to a communication channel constituted with a high speed digital circuit and an ISDN circuit. 
     This invention pays an attention to the fact that there is a high speed digital circuit between multiplexers and makes the control channel of the aforementioned high speed digital circuit (Dp-channel) available for multiplexed linking by means of ISDN circuits. 
     In addition, call control data for transmitting outgoing calls coming from a terminal are dynamically sent/received by the control channel of a high speed digital circuit connecting multiplexers, upon setting up a ISDN circuit communication channel by means of said multiplexers. Also, the control data are constituted in the same manner as the call control data of trunk circuits; the data not related with communication channels are transmitted via a control channel of high speed digital circuits. 
     The above configuration for the dynamic use of ISDN circuits for outgoing calls coming from terminals eliminates the need for a special control channel, providing inexpensive and efficient multiplexed transmission on ISDN circuits. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing the trunking system of the multiplexer of this invention. 
     FIG. 2 is a diagram showing an embodiment of the allocating band width for high speed digital circuits as illustrated in FIG.  1 . 
     FIG. 3 is a diagram showing a communication routing for voice compression data via trunking circuits. 
     FIG. 4 is a diagram showing a call control sequence during call controlling at trunking circuits. 
     FIG. 5 is a diagram showing a communication routing for voice compression data using ISDN circuits. 
     FIG. 6 is a diagram showing a control sequence for transmitting voice compression data originated from ISDN circuits. 
     FIG. 7 is a diagram showing a control sequence for terminating communication on ISDN circuits. 
     FIG. 8 is a diagram showing a configuration of call setting messages during call control on high speed digital circuits. 
     FIG. 9 is a diagram showing a configuration of call setting messages during call control on ISDN circuits. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention is described referring to drawings hereafter. 
     FIG. 1 is a schematic configuration of a trunking system to which the circuit multiplexing system of this invention is applied. This trunking system is constituted with a plurality of multiplexers  10 , high speed digital circuits  20  which mutually connect these multiplexers  10 , and an ISDN network  25 , a back up for the high speed digital circuits. For the two end the multiplexers  10 , a plurality of voice terminals  31  such as telephones are connected via a switchboard (PBX)  30 , together with a plurality of data terminals  40 . 
     A multiplexer  10  comprises: a communication channel switch  11 , which forms a communication channel between trunk circuits  20  and  25  together with a variety of terminals  40 , switchboards  30  and the like; a CPU  12 ; memories  13  which store a variety of programming such as switching behavior control programming, configuration data, and various tables and the like; control channel interface circuits  14  (hereafter referred to as Dp-channels); 4WSS/SR digital interfaces, 4WSS/SR analog interfaces or 2MTTC digital interface circuits  15  for connecting multiplexers  10  with switchboards  30 ; voice compression trunks  16  for converting (compressing) 64 Kbps PCM voice signals into 32 Kbps, 16 Kbps or 8 Kbps and/or inversely converting (decompressing) to communicate via high speed digital circuits  20 ; data terminal interface circuits  17  which interface with data terminals  40  having V.24, X.21 or V.35 interfaces; and interface circuits for connecting high speed digital circuits  20  and ISDN circuits  25 . 
     Now, high speed digital circuits  20  are I-interfaced for connecting multiplexers  10  for communication. In addition, ISDN circuits  25  are used as back up in place of high speed digital circuits during outage or are used for accommodating the overflow from high speed digital circuits  20 . 
     Voice data from voice terminals  31  such as telephones linked with a switchboard are compressed by means of a voice compression trunk  16  in the multiplexer  10  and are connected with the voice terminals  31  in the facing station via high speed digital circuits  20 , thus connecting voice communication between facing stations. 
     FIG. 2 illustrates an embodiment for the use of band width within high speed digital circuits  20  used in this invention. The band width within high speed digital circuits  20  is, in general, constituted with: control channel (Dp channel) band width  21  between multiplexers  10  for communicating control data such as connecting calls and the like; fixed connection band width  22  for fixed connection of data terminals and the like on a normally connected basis; and on-demand band width  23  for obtaining a specific band width when demanded by outgoing calls and the like from terminals. 
     For example, when 1536 Kbps are allocated for the band width for the high speed digital circuit  20 , 8 Kbps are allocated for the band width for a control channel  21 , 768 Kbps are allocated for the band width for fixed connection  22 , and the remaining 760 Kbps are allocated for the band width for on demand  23 . 
     FIG. 3 illustrates a routing for connecting voice terminals  31  linked with a switchboard  30 , being compressed by means of a voice compression trunk  16  in the multiplexer  10  and connected with the voice terminals  31  linked with a switchboard  30  in the facing station. 
     For example, if outgoing calls occur at the voice terminals  31  installed in the multiplexer  10  on the left hand side, and numbers are dialed, then, the switchboard  30  drives the interface circuit  15  linked with the switchboard. The central processing unit (CPU)  12  detects the fact that the interface circuit  15  linked with the switchboard is driven and acquires the voice compressing trunk  16  for voice compression. 
     Now, the voice compression trunk  16  is given a port  50  for connecting voice data without compression and a port  51  for connecting compressed voice data, and the voice data are supplied to and put out from communication switch  11 . 
     The CPU  12 , after acquiring the voice compression trunk  16 , connects the interface circuit  15  linked with the switchboard  30  and the port  50  for voice data without compression via the communication switch  11 . In addition, because the CPU  12  connects voice compression signals via the high speed digital circuit  20 , the CPU  12  obtains a required band width (16 Kbps band width for the compression to 16 Kbps) from the on-demand band width  23  within the high speed digital circuit  20  via the voice compression port  51  of the voice compression trunk  16  and the communication switch  11 . At this time, the CPU controls the Dp channel interface circuit  14  via the control channel band width  21  to drive the facing station for the calls on demand and sends call control data. 
     In the facing station on the right hand side of the figure, the Dp channel interface circuit  14  receives the call control data and recognizes the fact that there are incoming calls that are on demand, then, acquires a voice compression trunk  16  and connects the voice compression port  51  of that trunk  16  at the specific band width on high speed digital circuits  20  via a communication channel switch  11 . In addition, the port  50  for voice data without compression of that trunk  16  is connected with the interface circuit  15  which interfaces the port  50  and a switchboard  30  via the communication channel switch  11  for driving the switchboard  30  to call and connect with the voice terminal  31 . 
     In this way, the multiplexers  10  are given functions for the effective use of the high speed digital circuits  20  such as notifying voice data with a small band width using voice compression technique and the on demand feature for obtaining a required band width on demand. 
     FIG. 4 illustrates the control sequence for call control messages exchanged on the Dp channel when connected on demand. The outgoing station sends a call setting message M 10  to the facing (incoming) station. This call setting message M 10  includes compression data for voice compression and the data for the applied band width within the high speed digital circuits  20  and the like. The incoming station that received the call setting message M 10  analyzes the contents of this call setting message M 10 ; if the contents are processable, the station returns the call setting reception message M 11 . In addition, sending the call message M 12  and reply message M 13  from the incoming station establishes communications. 
     Also, receiving the reply message M 13  at the outgoing station establishes communications. 
     The call control messages in this call control process are sent/received between the Dp channel interface circuits  14  using the control channel band width  21  within the high speed digital circuits  20 . 
     FIG. 5 illustrates the connection route established when voice data from the voice terminals  31  linked with the switchboard  30  are compressed by means of the multiplexer  10 , and transmitted to voice terminals  31  linked with the switchboard  30  in the facing station using an ISDN network  25 . Here described is the connection system to meet the situation in which the voice terminals  31  are calling the voice terminals  31  in the facing station but all the high speed digital circuits  20  are busy and, therefore, not available, then, the voice data automatically take a detour using the ISDN network  25 . 
     First of all, when the voice terminals  31  in the outgoing station call the voice terminals in the facing (incoming) station and dial their numbers, the CPU  12  acquires the voice compression trunk  16 , as illustrated in the aforementioned FIG. 3, and obtains the needed band width from the on-demand band width  23  within the high speed digital circuits  20 . When all the on-demand band widths are busy and the required band width is not available at the time, the CPU  12  drives the ISDN circuits  25  to set up a communication channel  26  with the facing station. This ISDN communication channel  26  is used in place of the high speed digital circuits  20 . 
     An ISDN communication channel is set up by allocating a 64 Kbps band width (B-channel) following the general D-channel control data. In addition, when the ISDN communication channel  26  is set up, it is controlled in the same way as the on-demand band width  23  within the high speed digital circuits  20 . Therefore, the actual call control data control the D-channel interface circuits  14  and send/receive call control signals via the control channel band width  21  within the high speed digital circuits  20 . 
     The status of the communication channel switch  11  is the same as it is for connecting the high speed digital circuits  20 . With this processing, when 64 Kbps (B-channel) are allocated for the ISDN network  25  band width, four calls can be communicated in a single B-channel if the voices are compressed to 16 Kbps. 
     FIG. 6 illustrates the call control sequence when compressed voice data is outgoing from ISDN circuits. The operation of this invention is described hereafter referring to the flow chart and control data send/receive sequence illustrated in FIG.  6 . 
     To begin with, upon recognizing outgoing calls from voice terminals  31 , the CPU  12  determines whether or not all the high speed digital circuits  20  are busy (S 10 ). When there is a vacancy, it connects calls using the high speed digital circuits  20  and controls them using the Dp-channel illustrated in FIG. 4 (S 11 ). 
     At the step S 10 , when all the high speed digital circuits  20  are busy, the CPU takes a detour using the ISDN network  25  and sends ISDN calls (S 12 ). 
     When ISDN calls are sent, the CPU determines whether or not the voice signals should be compressed (S 13 ). When the voice signals are not to be compressed, the CPU controls the calls in the normal way; when the voice signals are to be compressed, the CPU determines whether or not the communication channel  26  needs to be set up within the ISDN circuit network  25  with respect to the targeted station (S 14 ). 
     At the Step  14 , when the result of the judgment is that the communication channel  26  has to be set up, the CPU determines whether or not there is a needed band width remaining within the allocated band width (S 15 ). When there is a needed band width remaining within the allocated band width, there is no need to set up a new communication channel  26  within the ISDN network  25 . Then, the CPU waives the process for setting up a communication channel and controls compressed voice calls (S 18 ). 
     When judgment at the step S 14  is that the communication channel  26  is not set up and judgment at the step S 15  is that there is insufficient band width remaining, the CPU determines that there is a need for setting up a communication channel  26 , and then, drives the ISDN network  25  to set up the communication channel  26  (S 16 ). 
     Setting up the communication channel begins with transmitting the call control data (message) on the ISDN network  25 . First, the outgoing station sends a call setting message M 21 . This call setting message M 21  includes the data showing the call was set to detour using the ISDN network  25  because all the high speed digital circuits  20  were busy. 
     The incoming station, which received the aforementioned call setting message  21 , analyzes the call setting message and recognizes that the incoming message took a detour using the ISDN network  25 , and executes the process required for processing incoming calls (S 17 ) to set up a communication channel  26  within the ISDN network  25 . As soon as calls are processed, the incoming station sends a call setting reception message M 22 , which indicates that the incoming station received the call setting message M 21  which was normally processed, and sends the reply message M 23  which indicates that the incoming station has set up the communication channel  26 . 
     The outgoing station recognizes that the communication channel  26  is set up by receiving this reply message M 23 . The communication channel  26  is set up between multiplexers according to the above process and control data control sequence. 
     Note that the call control data and its sequence for the D-channel required for setting up the ISDN network  25  follow the call control data and its control sequence determined for controlling ISDN circuits. 
     In addition, as soon as the setting up of the communication channel  26  for the ISDN network  25  is completed according to the aforementioned process, or the communication channel  26  within the ISDN network  25  is already set up, and there is a needed band width remaining within the allocated band width at step S 15 , the CPU  12  executes the call control process for transmitting the voice compression data to this communication channel  26  (S 18 ). This call control is executed when data are transmitted on the Dp-channel which is the control channel within the high speed digital circuits  20 . 
     First, the outgoing station sends the call setting message M 30 . This call setting message M 30  is constituted in the same manner as the call setting message M 10  used for controlling calls on the high speed digital circuits but includes data that has no relation with the high speed digital circuits  20 . The incoming station that receives this call setting* message M 30  recognizes that it is a message addressed to itself and executes the incoming process (S 19 ) by executing the same process as the call control message process for the high speed digital circuits  20 . 
     After that, the same process as the call control process for the high speed digital circuits  20  is executed as illustrated in FIG. 4; then, the call setting reception* message M 31 , call* message M 32  and reply* message M 33  are sent to be connected with the communication channel switch  11  linked with the ISDN network  25  (S 20 ). 
     The outgoing station that received the reply* message M 33  connects the ISDN network  25  and the communication channel switch  11  (S 21 ) to establish a communicating status using the ISDN network  25 . 
     These XXX* messages are the same as the XXX messages used for call control for the high speed digital circuits  20 ; the communication channel  26  in the ISDN network  25  is controlled in the same way as the high speed digital circuits  20 . 
     FIG. 7 illustrates the control sequence when communications are completed. The actions at the time of completing a call are described referring to the flow chart and the send/receive sequence illustrated in FIG.  7 . 
     First, when the outgoing station detects that a call is completed, then it sends a disconnection* message M 40  to complete the communication over the ISDN network  25  in the same manner as it did for setting up a call using the Dp channel of the high speed digital circuits  20 . 
     The incoming station that received this disconnection* message  40  executes the call completing process (S 40 ) and sends the release* message M 41 . 
     The outgoing station that received this release* message M 41  sends the release complete* message M 42 . The fact that the incoming station receives this release complete* message releases the communication status over the ISDN network  25 . 
     These sequential messages are transmitted via the Dp channel  21  of the high speed digital circuits  20 . 
     When this release sequence is completed, the outgoing station determines whether or not the aforementioned communication channel  26  of the ISDN network  25  is engaged with another call (S 41 ). 
     At this step, S 41 , if the communication channel  26  is engaged with another call, the following process is waived to complete the sequence of processing. 
     On the other hand, if all communications in the aforementioned communication channel  26  are completed and the channel is available, the release process for the aforementioned communication channel  26  is executed (S 42 ). At this time, a disconnection message M 50  is sent to the D-channel within the ISDN network  25 . 
     The incoming station that received this disconnection message M 50 , releases the aforementioned communication channel  26  (S 43 ) to send the release message M 51 . 
     In addition, the communication channel  26  within the ISDN network  25  is released by the outgoing station receiving the release message M 51  and sending the release completion message M 52 . 
     This sequential message transmission is carried out on the D-channel in the ISDN network  25 . 
     FIG. 8 illustrates the configuration of the call setting message M 10  transmitted on the Dp-channel when controlling calls on the high speed digital circuits  20  and constructed with the message type  70  and data element  71 . Now, the message type  70  includes the data showing that it is the call setting message; the data element  71  includes the data needed to control calls with voice compression data and applicable band width and the like. 
     FIG. 9 illustrates the configuration of the call setting* message M 30  transmitted on the Dp channel within the high speed digital circuits  20  for multiplexed transmission made available by call controlling on the communication channel  26  within the ISDN network  25 . These message are constructed with the band width setting message M 10 , type M 80  message indicating that this is a call control signal for the ISDN network  25 , incoming station data M 81  indicating the destination of the signal, and the outgoing station data M 82  indicating the sender of the signal such that these messages are sent/received between multiplexers installed on the communication channel  26  of the ISDN network  25 . Actual call control data are the same as the call setting messages used for the high speed digital circuits  10 . 
     Call control between the two stations is described above, however, the same process is possible among multiple stations. The call control messages for the ISDN network  25 , when each multiplexer recognizes the message type M 80  and when the incoming station data M 81  is not addressed to oneself, relays to the destination such that messages are sent/received in series. 
     In addition, voice compression transmission is described, however, calls departing from data terminals can transmit multiplexed data on ISDN circuits through the same processing. 
     As such, this invention can efficiently and dynamically multiplexes transmission on ISDN circuits. 
     As described, this invention realizes the dynamic, efficient, multiplexed transmission on ISDN circuits. In addition, when taking a detour using ISDN circuits when all the high speed digital circuits are busy, compressed information transmitted through a trunk circuit can be automatically transmitted in the same format, providing an increased operational efficiency to ISDN circuits.