Abstract:
A gateway unit for mutually connecting subscriber network, public switched telephone network (PSTN) and packet communication network, comprising subscriber network interface connected to subscriber network, PSTN interface connected to line exchange network, exchange unit exchange-connecting communication path among subscriber network, PSTN and packet communication network, control unit controlling connecting state of communication path at exchange unit, signal conversion unit converting form of signal transmitted and received between exchange unit and packet communication network into forms suitable for communication protocol of packet communication network and communication protocol of subscriber network, respectively, switching unit for route-controlling to transmit signal which is output from signal conversion unit toward destination in packet communication network, and information communication unit mediating information communications among subscriber network interface, PSTN interface, control unit, signal conversion unit and switching unit by using general-purpose local area network (LAN).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-017060, filed Jan. 25, 2005, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gateway unit used for connecting, for example, a public switched telephone network (PSTN) and an Internet protocol (IP) network with each other. 
     2. Description of the Related Art 
     In recent years, an information communication service including voice and data communication has become diversified. Resulting form this background, the number of carriers to newly enter a communication service field has increased and the intensity of service competition among carriers has increased. Such new carriers are called new common carriers (NCCs) and provide a variety of services by using a technique such as a voice over Internet protocol (VoIP). The VoIP is a technique to integrate a voice network and a data network by packetizing and transferring digital voice data. 
     In many cases, the NCCs are loaned facilities such as exchangers at a predetermined charge from a specific carrier already having a subscriber line. Many of the NCCs construct their own exchange networks such as IP networks by their own funds. The NCCs form communication systems by adding a PSTN of the specific carrier. These facilities are utilized in a compound manner for providing services to public users. 
     A gateway unit is used for connecting different communication networks such as the PSTN and the IP network with each other. This kind of gateway unit has an IP conversion unit for converting voice data and binary data into an IP packet and a packet switching unit for switching the IP packet. An example of this kind of gateway unit is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-205831. This document discloses a button telephone main apparatus as an example of the gateway unit. This document also discloses a system formed by a bus topology. The information communication in the bus topology becomes half double communication. 
     By the way, an internal control system in this kind of gateway unit is often a unique system at every gateway unit vender and a low-speed transmission system such as serial transmission. The low speed of a data transmission speed inside the gateway unit causes the performance of processing to notify, for example, failure information to an external network managing device to deteriorate. In this case, the gateway unit makes the response of the network management slow in speed. In many cases, the gateway unit and a network management device to manage it are connected through the IP. Thereby, the adaptation of the unique system for the internal control system requires protocol conversion processing and makes the response of the network management further slow in speed. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a gateway unit for mutually connecting a subscriber network, a public switched telephone network (PSTN) and a packet communication network, comprising a subscriber network interface connected to the subscriber network; a PSTN interface connected to the line exchange network; an exchange unit for exchange-connecting a communication path among the subscriber network, the PSTN and the packet communication network; a control unit for controlling a connecting state of the communication path at the exchange unit; a signal conversion unit for converting a form of a signal transmitted and received between the exchange unit and the packet communication network into forms suitable for a communication protocol of the packet communication network and a communication protocol of the subscriber network, respectively; a switching unit for route-controlling to transmit a signal which is output from the signal conversion unit toward a destination in the packet communication network; and an information communication unit mediating information communications among the subscriber network interface, the PSTN interface, the control unit, the signal conversion unit and the switching unit by using a general-purpose local area network (LAN). 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a system view showing an embodiment of a communication system regarding the present invention; 
         FIG. 2  is a system block diagram showing an existing voice communication system; 
         FIG. 3  is a functional block diagram showing an embodiment of a gateway unit  1  in  FIG. 1 ; 
         FIG. 4  is a functional block diagram showing main configurations of a subscriber line interface  11  and a PSTN interface  12  in  FIG. 3 ; 
         FIG. 5  is a functional block diagram showing a main configuration of an exchange unit  100  in  FIG. 3 ; 
         FIG. 6  is a functional block diagram showing a main configuration of an IP conversion unit  14  in  FIG. 3 ; and 
         FIG. 7  is a detail view of the gateway unit  1  in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is the system view showing the embodiment of the communication system regarding the present invention. In  FIG. 1 , a plurality of subscriber lines  114  of a subscriber network SN are housed in a gateway unit  1  at first. The gateway unit  1  is connected to an IP network DN. The IP network DN is a packet communication network and is formed as a unique network of a new common carrier (NCC) or the like. The Internet may be connected as the IP network DN. 
     The subscriber network SN includes a subscriber terminal  5 , a base station CS  1  of a mobile phone system, a radio terminal PS  1 , etc. The subscriber terminal  5  and the base station CS  1  are connected to the gateway unit  1  via subscriber lines  114 . The subscriber lines  114  are access lines assigned for each of a plurality of subscriber terminals  5  and radio terminal PS  1 . 
     The gateway unit  1  transmits a signal (a digital data signal such as voice data and video and image data) generated from the subscriber network SN to the IP network DN. The gateway unit  1  transmits a signal addressed to a terminal in the subscriber network SN from the IP network DN into the subscriber network SN to arrive at the terminal. Thereby, the gateway unit  1  can arbitrarily set an interactive communication path between a subscriber terminal  7  belonging to the IP network DN and the subscriber terminal  5 , or the radio terminal PS  1  belonging to the subscriber network SN. Further, in the system in  FIG. 1 , network monitoring equipment ME is provided with the IP network DN. The monitoring equipment ME transmits and receives a variety of items of information to and from the gateway unit  1  via the IP network DN and mainly manages an operation state of the gateway unit  1 . 
       FIG. 2  is the system block diagram showing the existing voice communication system. In  FIG. 2 , the subscriber terminal  5  is housed in an exchanger  3  of a line exchange network XN via the subscriber line  114 . The exchanger  3  is a facility belonging to the line exchange network XN. In the case of combination of the systems in  FIG. 1  and  FIG. 2 , the gate way unit  1  is disposed on a subscriber terminal side rather than the exchanger  3 . Therefore, a network-network interface (NNI) between the subscriber network SN and the line exchange network XN becomes a connecting point between the gateway  1  and the exchanger  3 . That is, the gateway unit  1  is arranged on the subscriber network SN side rather than the NNI between the subscriber network SN and the line exchange network XN. Communication protocols of the subscriber network SN, the line exchange network XN and the IP network DN are different with one another. 
       FIG. 3  is the functional block diagram of the first embodiment in  FIG. 1 . In  FIG. 3 , the gateway unit  1  has a control unit  16  and a subscriber line interface  11  and a PSTN interface  12 . The subscriber line interface  11  controls interface processing of the subscriber line  114  and the PSTN interface  12  controls interface processing of the subscriber line  115 . 
     The subscriber line interface  11  houses the subscriber terminal  5  and the radio base station CS  1  via the subscriber line  114  to provide an exchange station side interface of an integrated service digital network (ISDN). The PSTN interface  12  is connected to a subscriber line  115  to provide a terminal side interface of the ISDN. A communication quantity of the subscriber line  115  is designed in advance on the basis of demand estimation of traffic. 
     The control unit  16  has the exchange unit  100 . The exchange unit  100  exchanges and controls the communication paths among each subscriber line  114  and the IP network DN, respectively. 
     Further, the gateway unit  1  has an IP conversion unit  14  and a packet switch  15 . The IP switching unit  14  is disposed between the control unit  16  and the IP network DN to convert protocols among networks. That is, the IP conversion unit  14  converts a time division multiplex signal supplied via other communication network (line exchange network XN, etc.) into an IP packet to input it to the packet switch  15 . The IP packet is routed in accordance with a destination IP address to be transmitted to the IP network DN through a LAN cable  117 . The IP conversion unit  14  converts the IP packet which is input through the LAN cable  117  and the packet switch  15  from the IP network DN into the time division multiplexing signal. 
     In  FIG. 3 , the number of housed lines of the subscriber lines  114  housed in the subscriber line interface  11  and the number of housed lines of the subscriber lines  115  housed in the PSTN interface  12  is equal with each other. Or the number of the housed lines of the subscriber lines  114  housed in the subscriber line interface  11  is made larger than that of the subscriber lines  115  housed in the PSTN interface  12 . This manner has an advantage in system design. The number of the housed lines has the same meaning as the communication capacity. 
     The control unit  16  controls the gateway unit  1 . That is, the control unit  16  requires to the interfaces  11  and  12  so that they control the subscriber lines  114  and  115 . The control unit  16  notifies failure data detected by the interfaces  11  and  12  to the network monitoring equipment ME if necessary. 
     The control unit  16  of the gateway unit  1  is connected to the monitoring equipment ME via the IP network DN. The monitoring equipment ME acquires a variety of items of information from the control unit  16  to comprehensively manage it. According to this processing, the monitoring equipment ME can remotely monitor and manage the gateway unit  1 . 
     In  FIG. 3 , the control unit  16  is connected to the IP network DN through the IP conversion unit  14  and the packet switch  15 . The interfaces  11  and  12  and the control unit  16  have dedicated central processing units (CPUs) and memories (not shown), respectively, to be operated by computing processing of the CPUs, based on the programs stored in each memory. 
       FIG. 4  is the functional block diagram showing main configurations of the interfaces  11  and  12  in  FIG. 3 . In  FIG. 4 , the subscriber lines  114  and  115  are connected to a basic interface processing unit  111 . The processing unit  111  operates on the basis of an internal clock given via a clock distribution line CL to terminate a switch station side interface (U interface) of the ISDN. That is, the processing unit  111  converts a signal in an ISDN format including B1 and B2 channels and a D channel into the time division multiplexing signal in which, for example, a plurality of time slots are byte-interleaved. This time division multiplexing signal is supplied to the exchange unit  100  through a PCM-highway interface (PCM-HW I/F)  112  to be an interface to the exchange unit  100 . The B1 and B2 channels are used for transmission of voice data and link access procedure balanced (LAPB) data which is digitally coded. The D channel is used for transmission of a call control signal, a D channel packet, etc. 
     In addition, in  FIG. 4 , the subscriber line interface  11  has a CPU  113 , a read only memory (ROM)  214 , a random access memory (RAM)  215 , a high level data link controller (HDLC)  116 , a LAN I/F  217  and a bus line  118 . 
     Each part in the subscriber line interface  11  is connected with one another via the bus line  118 . The CPU  113  integrally executes a variety of kinds of control relating to operations of the subscriber line interface  11 . The HDLC  116  processes the call control signal included in the D channel. The LAN interface  217  is connected to a relay  218  through an internal bus  19 . The relay  218  connects the internal bus  19  of a zero system or a one system to the LAN I/F  217  in response to a system switching signal. 
       FIG. 5  is a functional block diagram showing a main configuration of the control unit  16  in  FIG. 3 . The control unit  16  is doubled to the zero system control unit  16   a  and the one system control unit  16   b  as described later. In  FIG. 5 , a line exchange switch (TSW)  13  corresponds to the exchange unit  100  in  FIG. 3 . The TSW  13  is connected to the subscriber line interface  11 , the PSTN interface  12  and the IP conversion unit  14  via a time division multiplexing bus  110 . The TSW  13  interchanges time slots on the bus  110  in accordance with line connection setting. Thereby, communication paths among the interfaces  11  and  12  and the IP conversion unit  14  are switched and connected. 
     The control unit  16  integrally executes a variety of kinds of control relating to operations of the gateway unit  1  by the processing of the CPU  161  based on the control program stored in the ROM  162  and the RAM  163 . In particular, the control unit  16  controls connection states of the communication paths at the TSW  13  on the basis of the communication quantity of the time division multiplexing bus  110  connecting the PSTN interface  12  and the exchange unit  100  and the communication quantity of the subscriber line  115 . 
     A clock unit  17  selects an arbitrary subscriber line  115  as a master clock from the PSTN interface  12 . The selected master clock is connected to the clock unit  17  via a clock supply line DL to supply the master clock to the clock unit  17 . The clock unit  17  generates an internal clock synchronizing with a network clock from the master clock. The internal clock is distributed and supplied to each part of the gateway unit  1  via the clock distribution line CL. Thereby, the gateway unit  1  operates in synchronization with the network clock. 
     In addition, in  FIG. 5 , the control unit  16  has a LAN I/F  164  and a bus line  165 . Each part in the control unit  16  are connected with one another via the bus line  165 . The LAN I/Fs  164  are provided in two systems, one is connected to LAN switches  200  and  201  sides (described later) via the internal bus  19 , the other is connected to a packet switch  15  side via an outer bus  190 . Providing the LAN I/Fs  164  in two systems, enables to limit accessing between the general-purpose LAN and the IP network DN. Further, the control unit  16  has a series state controller  169 . The controller  169  controls redundant switching between an active system (zero system) and a stand-by system (one system). 
       FIG. 6  is the functional block diagram showing the main configuration of the IP conversion unit  14 . In  FIG. 6 , the time division multiplexing data transferred from the exchange unit  100  via the time division multiplexing bus  110  is interface-processed by means of the PCM-HW I/F  142 , after that, fed to a digital signal processor (DSP)  141 . The DSP  141  packetizes the voice data. 
     The HDLC  146  processes the LAPB control signal to packetize it. The packet data generated from the DSP  141  and the HDLC  146  are output to the packet switch  15  from a packet I/F  148  via a serial bus  216 . The CPU  143  integrally executes each kinds of control relating to operations of the IP conversion unit  14  on the basis of the control program stored in a ROM  144  and a RAM  145 . A LAN I/F  147  transmits and receives a variety of signals to and from the control unit  16  via the internal bus  19 . The LAN I/F  147  is connected to a relay  149  via the internal bus  19 . The relay  149  connects the internal bus  19  of the zero system or the one system to the LAN I/F  147  in response to the system switching signal. 
       FIG. 7  is the detail view of the gateway unit  1  in  FIG. 1 . In  FIG. 7 , any of the subscriber line interfaces  11  and  12  and the IP conversion unit  14  is mounted on the gateway unit  1 , as a dedicated interface unit, respectively. 
     Line collecting unit  20  has a plurality of LAN switches (LAN-SWs)  180  and  181 . The LAN-SWs  180  and  181  are counterpart with each other, and one operates as a redundant system of the other. The LAN-SW  180  is set as the zero system (active system) and the LAN-SW  181  is set as one system (stand-by system). Each interface unit I/F  18  is connected to the LAN-SWs  180  and  181  through a common communication interface, respectively and operation-controlled by a control packet supplied from either LAN-SW  180  or  181 . Further, all LAN-SWs  180  are connected to a LAN-SW  200  via the zero system internal bus and all LAN-SWs  181  are connected to a LAN-SW  201  via the one system internal bus. The LAN-SWs  180 ,  181 ,  200  and  201  may be either switch of a layer  2  or a layer  3 . 
     The LAN-SWs  180 ,  181 ,  200  and  201  autonomously notify their own state (failure state or statistics information) to the control unit  16 . The control unit  16  integrally controls the LAN-SWs  180 ,  181 ,  200  and  201  on the basis of this notification information to determine whether communications between each interface unit I/F  18  and the control unit  16 . 
     The control unit  16  has a zero system control unit  16   a , a one system control unit  16   b  and a system switching control unit  16   c . The control unit  16   a  is connected to the LAN-SW  200  and the one system control unit  16   b  is connected to the LAN-SW  201 . The control unit  16   c  outputs system switching signal to each interface unit I/F  18  to switch-operate relays  218  (shown in  FIG. 4) and 149  (shown in  FIG. 6 ). The control units  16   a  and  16   b  are connected with each other to periodically transmit and receive information related to operation control of each interface unit I/F  18 . 
     The control units  16   a  and  16   b  are connected to the packet switch  15 , respectively. The packet switch  15  is connected to the IP network DN through a LAN cable. Thereby, the control units  16   a  and  16   b  can information-communicate with the network management equipment ME. 
     The control unit  16   a  has a function to reset the LAN-SW  180  by supplying a reset signal thereto. The control unit  16   b  has a function to reset the LAN-SW  181  by supplying a reset signal thereto. Any reset processing can be achieved by means of hardware. 
     In  FIG. 7 , the LAN-SWs  180  and  181  notify status signals indicating their own statuses to the control units  16   a  and  16   b  in response to polling requests, etc., respectively. The control unit  16  recognizes a driving state of the line collecting unit  20  to supply the control signal based on the recognition result to the control unit  16   c . The control unit  16   c  outputs a system switching signal to switch the zero system and one system in the line collecting unit  20  by switch-controlling relays  218 ,  149  on the basis of the driving states of the LAN-SWs  180  and  181 . 
     The zero system control unit  16   a  always performs health check of each interface unit I/F  18 . As a result, if all interface units  18  under a certain LAN-SW become into failure states, the gateway unit  1  determines that the LAN-SWs are in abnormality, brings the control unit  16   a  into the stand-by system and brings the control unit  16   b  into the active system so as to operate them. The system switching control unit  16   c  varies the state of the system switching signal to switch between the zero system and the one system. 
     According to above-stated configuration, any interface unit I/F  18  is connected to the control unit  16  via the LAN. Thereby, among each interface unit I/F  18  and the control unit  16 , for example, information communication in accordance with general-purpose LAN protocol based on the CSMA/CD can be achieved. 
     Accordingly, the gateway unit  1  can freely improve a data transfer speed and shorten times needed to acquire information and a variety of kinds of control. The gateway unit  1  can freely increase or decrease the number of wiring between LAN-SWs  200  and  180  (or LAN-SWs  201  and  181 ) in response to the number of lines housed in each interface unit I/F  18  and enhance its expandability. 
     According to above-mentioned configuration, the internal control paths from the control unit  16  to each interface unit I/F  18  are become redundant into the zero system and the one system, then, the LAN-SWs  180  and  181  and the control units  16   a  and  16   b  are connected to each interface unit I/F  18 , respectively. Thereby, for example, in the state of operating of the zero system, even when a failure occurs in either the zero system control unit  16   a  or the LAN-SW  180 , or in the internal bus  19 , the gateway unit  1  can prevent the stop of the system and continue operations by stopping the zero system to switch the operations to the one system. 
     This embodiment can reset the LAN-SWs  180  and  181 . In the case of the LAN-SWs  180  and  181  are layer  2  switches, a media access control (MAC) learning table occurs an abnormality at switching of redundancies to make a control communication to be sometimes interrupted. 
     Therefore, the gateway unit  1  can quickly re-start the control communication by resetting the LAN-SWs  180  and  181  at system-switching. Accordingly, the gateway unit  1  can be prevented from becoming instable as the control communication is disabled in a period of aging time and as the transmission and reception of the notification information between the interface units I/F  18  and the processing of detection of the failures are disabled. 
     The gateway unit  1  can synchronize information owned by both control units  16   a  and  16   b  by periodically transmitting and receiving the control information by means of the control units  16   a  and  16   b  by using the LAN-SWs  200  and  201 . Thereby, for example, even if a redundancy switching has occurred from the state of operation of the zero system, information in a time interval until the system switches to the one system can be shared between the control units  16   a  and  16   b . Accordingly, for example, even if the redundancy switching has occurred from the state of operating of the zero system, the gateway unit  1  can continue the operation without generating time-lag resulted from re-loading data at switching the redundancies. 
     Moreover, in the embodiment, an internal communication in the gateway unit  1  is achieved through the LAN, so that the affinity between the gateway unit  1  and the IP network DN can be further enhanced. That is, the gateway unit  1  only needs such a processing to the extent to convert an address of a packet header of the internal data so as to transmit information to the IP network DN. Thereby, the gateway unit  1  can further shorten the time necessary to data transmission without having to perform a complicated processing such as a protocol conversion. 
     As described above, according to the present invention, it becomes possible to provide a gateway unit for accelerate a speed of information transmission therein to improve processing performance. Further, it is eliminated for a control information packet to go around the LAN and malfunctions in control can be prevented by proving relays in each interface unit I/F  18 , respectively. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.