INTER-NETWORK CONNECTION SYSTEM

Abstract: An inter-network connection system between a main network (30) having a call setting processor (33) and a subnetwork (34) having a connection control unit with loopback means. In the case of communication within the subnetwork, the loopback means in the subnetwork is actuated by a first signal sent from the call setting processor in the main network, and a communication path for extension is set between the terminals of the subnetwork without passing through a switchboard SW (32) in the main network. In the case of communication between a terminal of the main network and a terminal of the subnetwork, operation of the loopback means of the subnetwork is stopped by a second signal sent from the call setting processor in the main network, and a communication path for line wire is set between the switchboard SW of the main network and the terminal of the subnetwork.

Description: [Technical Field] The present invention relates to a packet communication system for dividing data into digitalized blocks for transfer, and in particular to an inter-network connecting system between a main network which has an exchange function and a subnetwork which does not have an exchange function. For example, there is a public network as the main network, and there is, as the subnetwork, a customer station network connected to the public network. [Background Art] Conventionally, data communication networks have been developed based on a telephone exchange network, however, accompanied by the rapid expansion of the data processing field, various problems due to lack of functions in the communication systems have been pointed out. As a countermeasure to solve these problems, an idea of an integrated services digital network (ISDN) has been provided. The ISDN is being reconstructed from a conventional narrow band ISDN (64 Kbps) to a broad band ISDN (150 Gbps) in which various services such as a data communication network, facsimile network, voice network, various private line networks, picture communication network and so forth are integrated into one digital communication network. Due to the rapid development of the communication techniques such as the above-mentioned ISDN, the rapid development of data processing techniques by computers, and so forth, it has been desired to provide a data communication system in which various terminals and data instruments are combined, and in which data and resources can be efficiently utilized. In particular, to correspond to the demands for broad band and multimedia services, for a variety of communication configurations, and so forth, it has been desired to develop an economic, easy to expand, and efficient system in, not only the main network such as a public network, but also in a subnetwork when the subnetwork such as a customer station network is connected to the main network such as a public network. As a conventional subnetwork, a network connecting system is known which comprises a PBX having an exchange function and a call processing processor for controlling the PBX so it can be connected to a main network. In the conventional system, however, as described later in more detail with reference to the drawings, since a call process setting means is necessary in the subnetwork, if the subnetwork is used as a customer station network, it is suitable for a big company but there is a problem in economy for small companies or a standard home. As another conventional network connecting system, there is a system in which the exchange function which is necessary for the subnetwork (for example a customer station network) is provided in an exchange of a main network. In this conventional system, since the subnetwork itself does not have the exchange function, the cost can be made lower than the above-mentioned first conventional system. In this conventional system, however, as described later in more detail with reference to the drawings, even for data transfer between terminals in the subnetwork, a physical communication path is provided in a subscriber line between the subnetwork and the main network for folding the signal in the exchange in the main network so that there is a problem in that the traffic amount in the exchange is increased and the capacity of the exchange must be large. Also, in order to effectively accommodate a plurality of subscribers, when a subscriber network constitution in which a multiplexing line concentration unit is inserted between the subscriber lines is utilized, it is necessary to make the capacity of the feeder loop large and to provide an exchange function (remote exchange function) for suitable distribution of data from the feeder loop to respective subscribers. [Disclosure of the Invention] In view of the problems in the above-described conventional arts, the objects of the present invention are, in realizing an inter-network connecting system between a main network (for example, a large scale network (a basic LAN) or a public network) and a subnetwork (for example, a branch LAN or a customer station network), to provide expandability to enable the realization of various subnetwork constructions, to economize by reducing the initial cost so that the system can be introduced into an usual home, and to have efficiency so as to reduce the influence of the traffic in the subnetwork on the main network. US-A-4 792 800 discloses a network termination unit comprising a switching device for coupling two channels on a passive bus in one direction of transmission with two channels on the passive bus in the other direction to establish a loop-back connection for a local communication among the terminal equipment through the network termination unit. It further discloses that the switching device also couples the passive bus with the subscriber line to establish a connection for an external communication. Reference is also made to US-A-4 791 662, which basically describes a control unit with an exchange, the control unit being capable of processing a call. According to the invention, there is provided an inter-network connecting system comprising a main network having an exchange and a call setting processing processor for controlling said exchange, and a subnetwork, connected to said main network, having a plurality of terminals and a connection control unit comprising loopback means, wherein said call setting processing processor is arranged to give a calling terminal a first special signal so as to operate the loopback means in said connection control unit to set a physical communication path for an extension line between terminals in said subnetwork, when an extension line communication which is a communication in said subnetwork is to be carried out, said call setting processing processor is arranged to give a calling terminal a second special signal so as to stop the operation of the loopback means in said connection control unit to set a physical communication path for an outer line between the exchange and the terminal in said subnetwork, when an outer line communication which is a communication between said main network and a terminal in said subnetwork is to be carried out, said calling terminal is arranged to add a received first or second special signal from said call setting processing processor to data to be transmitted, and said connection control unit is arranged to judge whether the loopback means should be operated or not for each of said data in accordance with said first special signal or said second special signal, to set a physical communication path for said extension line communication and/or said outer line communication. It is preferable that the main network and the subnetwork be utilized to construct an integrated services digital network (ISDN). It is preferable that the first special signal and the second special signal are one or a plurality of fixed data groups, respectively. It is preferable that the connection control unit comprises a rewritable table, the first special signal and the second special signal are one or a plurality of fixed data groups, respectively; one or a plurality of data group corresponding to the first special signal and the second special signal are stored in the rewritable table, and the connection control unit compares the first special signal or the second special signal added to the data from the calling terminal with the contents of the table, whereby judgement is made as to whether the loopback function should be operated or not, to set a physical path. It is preferable that the call setting processing processor comprises means for rewriting the contents of the table in the connection control unit. It is also possible that the terminals comprise means for rewriting the contents of the table in the connection control unit. It is preferable that the connecting control unit comprises means for supervising traffic of the extension line communication and of the outer line communication; and the contents of the table are automatically changed in accordance with the amount of traffic in such a way that, the amount of data of the first special signal is increased when the amount of traffic of the extension line communication becomes larger than the amount of traffic of the outer line communication, and the amount of data of the second special signal is increased when the amount of traffic of the outer line communication becomes larger than the amount of traffic of the extension line communication. It is also preferable that a third signal is provided for simultaneously setting physical paths in the communication in the subnetwork and in the communication between the main network and the terminal of the subnetwork, whereby by the third signal, physical paths for the extension line communication and for the outer line communication can be simultaneously set. It is also possible that the data has a destination identification label therein, and the first special signal and the second special signal are logically provided in the destination identification label. It is preferable that the third special signal is logically provided in the destination identification label. It is preferable that the first special signal, the second special signal, and the third special signal are subjected to error correction. It is also possible that the destination identification label is subjected to error correction. It is possible that the connection control unit is provided with a buffer for storing data, and when an idle communication is found in the line from the main network, data is taken out from the buffer and transferred to the terminal. It is also possible that a buffer for storing data is provided on the line between the connection control unit and the main network, and when an idle communication is found in the loopback line, data is taken out from the buffer and transferred to the terminal. It is also possible that a first buffer and a second buffer for storing data are provided respectively in the loopback means in the connection control unit and on the line between the connection control unit and the main network so that data is alternately taken out from the first buffer and the second buffer and transferred to the terminal. It is also possible that the connection control unit comprises an empty buffer detecting unit for detecting which of the first buffer and the second buffer is empty, and, when either one of the buffers is empty, data are sequentially transferred from the other buffer to the terminal. It is also possible to comprise a buffer common to the loopback means in the connection control unit and the line of the connection control unit from the main network, and writing means for writing loopback data and data from the main network at high speed so that the data is transferred to the terminal in accordance with the writing sequence into the buffer. It is also possible that the loopback data and the data from the main network are provided with priority data, and the connection control unit transfers the data from the terminal and the data from the main network to the terminal in the sequence of priority in accordance with the priority data. It is preferable that the priority data indicates whether or not the extension line communication has a priority to the outer line communication. It is also possible that the priority data indicates a priority depending on the contents of the communication services. It is preferable that the connection control unit comprises a priority control unit for writing data and the priority data into the buffer, and the priority control unit transfers that data to the terminals in accordance with the priority data read from the buffer. It is preferable that the connection control unit comprises a plurality of buffers for storing different priority data, the data are stored in respective buffers based onthe priority data, and the data are transferred from respective buffers to the terminals in the order of the priority. It is also possible that the terminals construct a plurality of subnetworks, and the plurality of subnetworks are connected to the main network. [Brief Explanation of the Drawings] Figure 1 is a block diagram showing an example of a conventional inter-network connecting system, Fig. 2 is a block diagram showing another example of a conventional inter-network connecting system, Fig. 3 is a block diagram showing an inter-network connecting system according to a first embodiment of the present invention, Fig. 4 is a block diagram showing an example of the construction of the connection control unit (CC) in Fig. 3, Fig. 5A and Fig. 5B are block diagrams for explaining an example of the operation of the connection control unit shown in Fig. 4, Fig. 6 is a diagram showing an example of the construction of the table provided in the connection control unit according to another embodiment of the present invention, Fig. 7 is a diagram for explaining an example of changing the contents of the table shown in Fig. 6 in accordance with the amount of traffic, Fig. 8 is a block diagram for explaining a path when physical communication paths are provided simultaneously in the extension line and the outer line, according to another embodiment of the present invention, Fig. 9 is a diagram for explaining an example in which a code for setting a path in an extension line, in an outer line, or in both lines is logically provided to a destination identification label, according to still another embodiment of the present invention, Fig. 10 is a diagram for explaining an example in which an error correction is conducted on a special signal or a destination identification label for setting a path in an extension line, in an outer line, or in both lines, according to still another embodiment of the pretend invention, Fig. 11 is a block diagram showing an example of the construction in which a buffer is provided in the connection control unit, according to still another embodiment of the present invention, Fig. 12 is a block diagram showing another example of the construction in which a buffer is provided in the connection control unit, according to still another embodiment of the present invention, Fig. 13 is a block diagram showing an example of the construction in which two buffers are provided in the connection control unit, according to still another embodiment of the present invention, Fig. 14 is a block diagram showing another example of the construction in which two buffers are provided in the connection control unit, according to still another embodiment of the present invention, Fig. 15 is a block diagram showing an example of the construction in which a common buffer is provided in the connection control unit, according to still another embodiment of the present invention, Fig. 16A is a diagram for explaining an example in which a priority signal is added to data, according to still another embodiment of the present invention, Fig. 16B is a diagram showing an example of the priority signal in Fig. 16A, Fig. 16C is a diagram showing another example of the priority signal in Fig. 16A, Fig. 17 is a block diagram showing a construction in which a priority control unit is provided in the connection control unit according to still another embodiment of the present invention, Fig. 18 is a diagram showing a construction of a buffer according to still another embodiment of the present invention, Fig. 19 is a block diagram showing a construction in which a buffer is provided for each priority in the connection control unit according to still another embodiment of the present invention, Fig. 20 is a block diagram showing a construction in which a plurality of subnetworks and a main network are connected, according to still another embodiment of the present invention, Fig. 21 is a block diagram showing an example in which a ring LAN is used as the subnetwork according to still another embodiment of the present invention, Fig. 22 is a block diagram showing an example in which a plurality of small subnetworks are provided in the subnetwork according to still another embodiment of the present invention, and Fig. 23 is a block diagram showing a construction of the connection control unit in Fig. 22. [Best Mode for Carrying Out the Invention] Throughout the specification, the same reference numbers represent the same parts, and the same numbers with appended characters represent modifications of the same parts. For better understanding of the present invention, conventional inter-network connecting systems are explained with reference to Fig. 1 and Fig. 2. Fig. 1 is a block diagram showing an example of a conventional inter-network connecting system. In the figure, a main network (for example, a trunk LAN) is provided with an exchange (SW) 1 for setting a physical path and a call setting processing processor (CP) 2 for carrying out a call setting processing by transmitting and receiving signals before setting the physical path. In the subnetwork (for example a branch line or a customer station network) also, a private branch exchange (PBX) 3 for setting a physical path and a call setting processing processor (CP s ) 4 for carrying out a call setting processing by transmitting and receiving signals before setting the physical path are provided. Each terminal (TE) 5 accommodated by the PBX 3 requires, when communication is to be carried out, a number of the opposite terminal, from the PBX 3 regardless of whether the opposite terminal is in the subnetwork or out of the subnetwork. The call setting processing processor (CP s ) 4 which receives the requirement supplies a logical identification number (LCN) for communication or a destination identification label (VCI), which is different depending on whether the opposite terminal is in the subnetwork or in the main network, to the call originating terminal and the opposite terminal. When the opposite terminal (TE) 5 receives this, the call setting process is completed, and thereafter, a physical path is set between the terminals. For example, when the requirement from the terminal 5 is data communication with another terminal in the subnetwork, the PBX 3, which received this requirement, gives a logical identification number LCN provided in the header of the received packet to the opposite terminal, as shown in the figure, and after a call setting processing shown in the figure by dotted line, a physical communication path P s between the terminals is set. When the request from the terminal 5 in the subnetwork is to effect data communication with a terminal in the main network, the CP s 4 connected to the PBX 3 provides the received logical identification number LCN' or the opposite terminal to the CP 2 in the main network, so that a physical path P M is set after a call setting processing between the terminal 5 and the PBX 3, and the CP 2 which received the logical identification number LCN' provides a logical identification number N'' of the calling origin to the CP s 4 in the subnetwork so that a physical path P' M is set between the main network and the subnetwork. As described above, as a connection requirement from a terminal, there are a method for directly designating the terminal number of the opposite terminal, a method for distributing a connection requirement from a terminal to all terminals by a broadcasting method and, by using a compatibility check function in each terminal, for designating a terminal which provided a response, and a method of mixing both methods. The conventional system in Fig. 1 has flexibility, however, since it requires a high-cost call setting processing processor (CP s ) 4 in the subnetwork such as a customer station network, it is suitable for a big company but there is a problem in economy for a small company or for a standard home. Figure 2 is a block diagram showing another example of a conventional inter-network connecting system. In the figure, an example is shown in which a subnetwork (customer station network and so forth) in an ISDN and a main network in a main network are connected. The main network comprises an exchange (SW) 21 and a call setting processing processor (CP) 22. The subnetwork comprises a network terminal (NT) 23 having no exchange function, a plurality of nodes (N₁ to N n ) 24, and terminals (TE) 25 respectively connected to these nodes. In this case, the exchange function of the subnetwork is provided in the exchange SW. In the transfer between a terminal in the subnetwork and the main network, a physical path P M is provided in a subscriber line between the subnetwork and the main network. In case of the transfer between terminals in the subnetwork, a physical communication path P S is also provided in a subscriber line between the subnetwork and the main network but folding is effected by the exchange (SW) 21. When the exchange function of the main network (public network) is utilized to realize the communication between terminals in the subnetwork (customer station network) in the above-mentioned way, the amount of traffic in the exchange (SW) 21 is increased so that there is a problem in that the capacity of the exchange (SW) 21 must be made large. Also, if a subscriber network construction is applied in which a multiplexing line concentration unit is inserted between subscriber lines in order to efficiently accommodate a plurality of subscribers, there is a problem in that the capacity of the feeder loop must be made large and an exchange function (remote exchange function) for suitably distributing data from the feeder loop to respective subscriber lines is necessary. Next, embodiments of the present invention are described. Figure 3 is a block diagram showing an inter-network connecting system according to a first embodiment of the present invention. In the figure, a main network 30 has an exchange (SW) 32 and a call setting processing processor (CP) 33. A subnetwork 31 has a plurality of terminals (or units, hereinafter simply referred to as terminals) (TE1 - TEn) 35 and a connection control unit (CC) 34 having a loopback function. Briefly explaining the operation, in the connection control unit (CC) 34, when a communication between terminals in the subnetwork 31 is effected, loopback is carried out in the subnetwork without providing a physical communication network. Therefore, a physical communication path for connecting the main network 30 and the subnetwork 31 is set only for the communication between a terminal in the subnetwork 31 and a terminal (not shown in the figure) accommodated to the main network. Namely, in the call setting processing, based onthe requirement from a calling terminal 35, the call setting processing processor (CP) 33 allocates to the calling terminal and to the opposite terminal, a destination identifying label VCI and a signal LB or TH for specifying whether or not a loopback is to be effected in the subnetwork. The calling terminal transmits a packet including the destination identifying label VCI, data (INFO), and a special signal (LB/TH) for distinguishing the loopback LB or the through signal TH. When the special signal in the packet transmitted form the calling terminal 5 to the connection control unit (CC) 34 is the loopback signal LB, the loopback function in the connection control unit (CC) 34 operates. As a result, the physical communication path is folded in the subnetwork and becomes a physical communication path P s for extension line, and it does not pass through the exchange (SW) 32 of the main network 30. When the special signal in the packet transmitted from the calling terminal 5 to the connection control unit (CC) 34 is the through signal TH, the loopback function of the connection control unit (CC) 34 is stopped so that the physical path for external lines is connected through the exchange (SW) 32 to the called terminal. The loopback signal LB and the through signal TH are added to the packet, which is to be transmitted to the calling terminal, by the call setting processing processor (CP) 33 at the time of call setting processing. The calling terminal which received the loopback signal and the through signal TH transmits a transmitting packet or cell including the loopback signal LB or the through signal TH to the connection control unit (CC) 34. In Fig. 3, in response to all communication requests from the terminals (TE1 to TEn) 35, the call setting processing processor (CP) 33 in the main network 30 judges the destination required to be connected, communication mode, and so forth to provide a specific destination identifying label VCI to the calling terminal. For example, a VCI used for communication in the subnetwork and a VCI used for communication from the subnetwork through the main network are defined as follows. Communication in the subnetwork: VCI#1=(1XXXXXX) Communication through the main network: VCI#0=(0XXXXXX) where X is arbitrary (0 to 1) A terminal for example (TE1) 35 receives a destination identification label VCI from the call setting processing processor (CP) 33 by the communication with the call setting processing processor (CP) 33, and provides it to the head of the blocked transmitting data, and transmits it. The connection control unit (CC) 34 carries out connection control by distinguishing the above-mentioned special bit in the destination identification label VCI. For example, when VCI=VCI#1, the connection control unit (CC) 34 folds the packet belonging to the VCI#1 from the T line to the R line (see Fig. 4). Also, when VCI=VCI#0, the connection control unit (CC) 34 delivers the packet belonging to the VCI#0 to the main network 30. By this construction, since the call setting process necessary for the communication between terminals in the subnetwork is carried out by the use of the call setting processing processor in the main network, the subnetwork does not require any unit (for example PBX) relating to a call setting process other than terminals so that an economical network can be constructed. Also, since the traffic by the communication in the subnetwork is folded b y the connection control unit (CC) 34, it never flows into the exchange (SW) 32 in the main network 30 so that the main network can be efficiently operated. Even though the call setting process is carried out by the call setting processing processor (CP) 33 connected to the exchange (SW) 32, the traffic of the call setting process is very small in comparison with the actual communication traffic, and the increased traffic of the call setting process by the communication in the subnetwork is only in the order of adding the special signal LB or TH for grouping the packet into interior and exterior of the subnetwork to the destination identification label VCI, which is negligible. It is preferable that the main network and the subnetwork construct an integrated services digital network (ISDN). Figure 4 is a block diagram showing an example of the construction of the connection control unit (CC) 34 shown in Fig. 3, comprising two selectors 41 and 42, and a loopback control unit 43 for receiving the special signals LB and TH from the terminals (TE1 - TEn). The loopback control unit 43 receives the special signal LB/TH from the calling terminal (TE1 - TEn) through the tip line T, and in accordance with this signal, controls the selectors 41 and 42. The selector 41 selects data from the exchange (SW) 32 or data from the selector 42 in accordance with the output of the loopback control unit 43. The selector 42 outputs data from the terminal (TE1 - TEn) 35 to the selector 41 or to the tip line T for outputting to the exchange (SW) 32. As an embodiment, when the special signal LB is "1", the loopback is carried out, and when the special signal LB is "0", the through operation is carried out. Fig. 5A is a diagram showing a connection configuration of the selector when the special signal LB received by the loopback control unit 43 is "1". In this case, the loopback control unit 43 gives the selectors 41 and 42 the loopback signal. The selector 42 supplies a packet received from the calling terminal through the tip line T to the input of the selector 41 in accordance with the loopback signal. In accordance with this loopback signal, the selector 41 does not select data on the ring line R from the exchange SW but selects and outputs data from the selector 42. As a result, a physical path in the subnetwork is set so that communication can be realized without passing through the exchange SW. Fig. 5B is a diagram showing a connection configuration of the selector when the special signal received by the loopback control unit 43 is "0". In this case, the loopback control unit 43 gives the selectors 41 and 42 the through signal. The selector 42 supplies a packet received from the calling terminal through the tip line T to the ring line R at the side of the exchange SW in accordance with the loopback signal. In accordance with this through signal, the selector 41 selects and outputs data from the exchange SW through the ring line R but does not select data from the selector 42. As a result, a physical path P M between the subnetwork and the main network is set so that communication becomes possible. According to another embodiment of the present invention, instead of representing the loopback signal and the through signal by one bit added to the outer of the destination identification label as described above, it may be logically allocated within the destination identifying label. This embodiment is shown in Fig. 6. Fig. 6 is a diagram showing the contents of a table provided in the connection control unit (CC) 34 and in the call setting processing processor (CP) 33. In the figure, as a plurality of loopback signals LB, 0-20 (decimal expression) are stored in the table 60. As an example, LB=0 to LB=5 are signals for effecting loopback, and LB=6 to LB=20 are signals for effecting through communication. The loopback signals 0-20 are the destination identifying labels themselves in this embodiment. Therefore, when the destination identifying label in the packet transmitted from a calling terminal in the subnetwork is one of 0-5, loopback is effected to carry out an extension communication. When the destination identifying label is one of 6-20, through communication with an outer line is carried out. The contents of the table 60 can be rewritten by the control by the call setting processing processor (CP) 33, the control by a terminal having a function to supervise traffic, or the control by the connection control unit (CC) 34. In Fig. 6, the destination identification label for loopback and the destination identification label for through communication are fixedly provided. However, instead of this, according to another embodiment of the present invention, the destination identification label for loopback may be changed in accordance with traffic. Fig. 7 show this. In left diagram in Fig. 7, in order to decrease the number of calls of the loopback when the traffic of the outer line (the number of channels) is increased, only LB=0, LB=1 and LB=3 are the destination identification labels for loopback, and LB=4 to LB=20 are all the destination identification labels for through communication for outer lines. In right diagram in Fig. 7, in order to increase the number of calls of the loopback when the traffic of the extension line (the number of channels) is increased, LB=0 to LB=7 are the destination labels for through communication for the outer lines. Fig. 8 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In this embodiment, in addition to the above-mentioned LB and TH signals, a both-way signal BT for setting physical paths in both the extension line and the outer line simultaneously is used. When a loopback control unit 43a receives the both-way signal BT=1, it gives the selector 42a the both-way signal and gives the selector 41a the loopback signal. As a result, the selector 42a sends a packet from a calling terminal in the subnetwork to both the tip line T of the exchange side and to the input of the selector 41a, and the selector 41a receives the loopback signal so as to selectively send the output signal from the selector 42a to the ring line R of the subnetwork side. In this way, physical paths are simultaneously set for the terminal in the subnetwork and for the terminal in the main network so that the same data can be transmitted in a broadcasting configuration. Fig. 9 is a diagram showing a data format according to an embodiment of the present invention. In the figure, a packet consists of a VCI in a header part and data in a data part. The destination identification label VCI consists of 7 bits. When its top bit is "1", it is the loopback signal LB so that the connection control unit (CC) performs a loopback control in which data belonging to LB in the T line is delivered to the TE side. When the top bit of the destination identification label is "0", it is the through signal TH so that the connection control unit (CC) performs a through control in which data belonging to the TH in the T line is delivered to the exchange side SW. Fig. 10 is a diagram showing a data format according to another embodiment of the present invention. In the figure, the loopback signal LB is not logically included in the destination identification label VCI but is provided separately from the destination identification label VCI, and further, the loopback signal LB is provided with a CRC code for effecting error correction. The CRC code may be provided in the through signal TH or in the destination identification label VCI. Fig. 11 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, the connection control unit (CC) 34b comprises, in addition to the selectors 41b and 42b and the loopback control unit 43b, a buffer 44 and an idle communication detecting unit 45. The buffer 44 is provided in the loopback path between the selector 42b and the selector 41b, and stores packets output from the selector 41b for loopback. When the idle communication detecting part 45 detects an idle communication in the line 1 ○ from the main network, it controls the selector 41b so as to selectively output the output 2 ○ of the buffer 44 to the R line of the subnetwork side. Thus, only when an idle communication is produced in the line from the main network, is the loopback carried out so that the line is efficiently utilized. This is effective when the traffic of the outer line is large. Fig. 12 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, the buffer 44 is provided between the R line from the main network and the input of the selector 41b, for storing the packets from the main network. The idle communication detecting unit 45, when detects an idle communication in the loopback 2 ○ from the selector 42b, controls the selector 41b to selectively output the packet 1 ○ in the buffer 44 to the R line of the subnetwork side. Thus, the packet from the main network can be transferred to the subnetwork only when an idle communication is produced in the loopback, so that this is effective when the traffic of the extension line is large. Fig. 13 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, two buffers 44a and 44b are provided. The buffer 44a is arranged between the R line from the main network and the input 1 ○ of the selector 41d. The buffer 44b is arranged between the output for loopback of the selector 42d and the input 2 ○ for loopback of the selector 41d. The selector control unit 45 controls the selector 41d in such a way as to alternately select the output of the buffer 44a and the output of the buffer 44b to incorporate it into the selector 41d. The loopback control unit 43d and the selector 42d operate in the same way as the corresponding loopback control unit and selector in Fig. 4, Fig. 5A, Fig. 5B, or Fig. 8. This embodiment is preferably applied to a case where the from length of a packet is constant. Fig. 14 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, instead of the selector control unit 45 in Fig. 13, an empty buffer detecting unit 46 is provided. The empty buffer detecting unit 46 controls a selector 41e in such a way that, when either of the buffers 44a and 44b is empty, the packet from the other buffer is incorporated into the selector 41e. By this, since the output of the empty buffer in the buffers 44a and 44b is not selected by the selector 41e, the packet can be transferred efficiently. Fig. 15 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, a first speed converting unit 47a is provided between the R line of the main network side and the first input of the selector 41f, a second speed converting unit 47b is provided between the loopback output of the selector 41f and the second input of the selector 41f, and a buffer 44f is provided between the output of the selector 41f and the R line of the subnetwork side. Accordingly, the buffer 44f is a common buffer for the loopback function and for the line from the main network. In Fig. 15, the loopback control unit 43f controls only the selector 42f in accordance with the special signal LB from the T line of the subnetwork so that, in case of loopback, packets from the T line of the subnetwork are transmitted to the speed converting unit 47b, and in case of through communication, they are transmitted to the T line of the main network. The packets from the main network are converted into high speed data by the speed converting unit 47a, selected by the selector 41f, and written in the buffer 44f at high speed. The loopback packets output from the selector 42f are also converted into high speed data by the speed converting unit 47b, selected by the selector 41f, and written at high speed into the buffer 44f. According to the sequence of writing into the buffer 44f, the packets are transferred to the terminal in the subnetwork. The selector control unit 45f controls the selector 41f so as to alternately select the outputs of the speed converting units 47a and 47b. Thus, after obtaining high speed data by speed conversion of packets, they are stored in the buffer, and they are transferred in accordance with the storing sequence, whereby the transfer of data can be effected at high speed. Fig. 16A to 16C are diagrams showing a packet format in which a priority is added to the packet according to an embodiment of the present invention. In Fig. 16A, the packet is provided with a priority signal PR, other than data, the destination identification label, and the special signal LB for indicating whether it is for loopback or not. As shown in Fig. 16B, when PR="1" for example, outer lines have the priority to be processed, and when PR="0", extension lines have the priority to be processed. Also, as shown in Fig. 16C, as a priority signal, the priority may be determined in accordance with the contents of the service. Namely, for example, when PR="2", this means a signaling for a call setting having the highest priority; when PR="1", this means sound or video data having the second priority order; and when PR="0", this means data having the lowest priority. Fig. 17 is a block diagram showing the construction of the connection control part (CC) provided with a priority control unit 48. In this case, a loopback control unit 43g controls only a selector 42g in accordance with the special signal LB from the T line of the subnetwork side in the same way as in Fig. 15, so that in case of loopback, a packet from the T line of the subnetwork side is transmitted to a buffer 44g, and in case of the through communication, it is transmitted to the T line of the main network. The priority control unit 48 reads priority signals in the packets input to the buffer 44g, and outputs them sequentially from the buffer 44g in order from the higher priority. Fig. 18 is a diagram showing an example of the contents of the buffer 44g shown in Fig. 17. As shown in the figure, the buffer 44g stores, fore each packet, data and a priority signal PR. In this case, the data includes data shown in Fig. 9 and the destination identification label, or data shown in Fig. 10, the destination identification label VCI, the special signal LB, the error correction code CRC, and so forth. Fig. 19 is a block diagram showing the construction of the connection control unit (CC) according to still another embodiment of the present invention. In the figure, a buffer is provided for each priority, and data of packets are stored into respective buffers in accordance with the priorities. Namely, data of PR="1" is stored in a buffer 44h, and data of PR="0" is stored in a buffer 441h. The priority control unit 48h controls a selector 41h based on the priority signal stored in the buffer, and selects the output of the buffer 44h or 441h in the order of priorities to transmit to a terminal in the subnetwork. In this case also, the loopback control unit 43h controls only the selector 42h in accordance with the special signal LB from the T line of the subnetwork side so that, in the case of the loopback, the packet from the T line of the subnetwork side is transmitted to the buffers 44h and 441h, and in the case of the through communication, it is transmitted to the T line of the main network. Fig. 20 is a block diagram showing still another embodiment of the present invention. In the figure, a subnetwork 201 consists of a master subnetwork 202 and a plurality of slave subnetworks #1-#m. Each subnetwork comprises a connection control unit (CC2) 230 and a plurality of nodes #1-#n. To each node, a terminal which is not shown in the figure is connected. Each slave subnetwork may be considered as being replaced by each terminal shown in Fig. 3. The master subnetwork 202 comprises a connection control unit (CC1) 220 having an exchange function and a call setting processing processor (CP) 221. As the call setting processing processor (CC1) 220, a PBX is used. In this case, the master subnetwork (PBX) has the same function as the main network (public network) in the embodiment shown in Fig. 3. Even in a customer station network, if it is large scale, it may have a plurality of subnetworks as above. The construction of the main network 200 is the same as the main network 30 in Fig. 3. In this way, even when each terminal in Fig. 3 is replaced by a slave subnetwork to form layered networks, all of the before described embodiments of the present invention can be applied. Namely, each slave subnetwork requires, when it calls, from the master subnetwork 202, the destination identification label VCI. If the destination is in the subnetwork, the call setting processing processor (CP) 221 in the master subnetwork provides the destination identification label VCI to the calling terminal and to the called terminal. To the destination identification label VCI, the before-mentioned special signal LB, TH or BT is added. Only when the destination is in the outer line, is the call setting process carried out by signalling with the call setting processing processor (CP) 211 in the main network. The connection control unit (CC2) 230 in each slave subnetwork carries out the loopback or through operation in accordance with the special signal from the terminal in the same way as the before-mentioned embodiments. Fig. 21 is a block diagram showing still another embodiment of the presetn invention. In Fig. 21, a subnetwork 31a is formed by a ring LAN, and 36 is a network terminal (NT). In this case also, the call setting process in the communication in the subentwork or in the communication between the subnetwork and the main network is carried out by the call setting processing processor (CO) 33 in the main network 30 in the same way as the before-described embodiments. Similar to the before-described embodiments, when the special signal LB provided to the calling terminal is "1", the communication is effected in the ring LAN; and when the above-mentioned special signal LB is "0", a physical communication path is set between the main network 30 and the subnetwork 31a. Further, since the communication in the subnetwork and the communication through the main network are carried out by the same call setting processing processor, the communication is possible by the same protocol. Therefore, no gateway for converting the protocol is necessary between the subnetwork 31a and the main network 30. Fig. 22 is a block diagram showing still another embodiment of the present invention, in which the system is expanded to have a plurality of subnetworks. Namely, even when a subnetwork 31b is constructed by a plurality of small subnetworks 31-1 and 31-2, the same operation as in all of the embodiments described above is possible. Fig. 23 is a block diagram showing the construction of the connection control unit (CC) 34b in Fig. 22. In the figure, the connection control unit (CC) 34b is further provided with a multiplexer (MUX) 231 for switching the small subnetworks and a distributor (DIST) 232. In the above embodiments, explanations were given in which the special signal for the connection control is provided in the packet separately from the VCI, or is logically included in the destination identification label. The present invention, however, is not restricted to this but, for example, it may be the first bit in the logical identification number in the header of the packet or it may be provided at any other place in the packet. [Possibility of Utilization in Industry] As described above, according to the present invention, by merely providing a physical path setting function in a subnetwork, various flexible multipoint communications can be realized and the construction of a network having superior expandability becomes possible. Further, there is no need to comprise a call setting processing function in the subnetwork so that an economic network can be constructed. Still further, the traffic due to the communication in the subnetwork does not flow into the exchange of the main network so that the exchange in the main network can be operated efficiently. Still further, since the call setting process is carried out between a terminal in the subnetwork and the exchange in the main network, and since the other units in the subnetwork do not relate to the call setting process, the scale of each unit (NT, CC and so forth) can be greatly reduced. Still further, the communication can be carried out by the same protocol regardless of the configuration of the communication such as the communication in the subnetwork, inter-subnetwork communication, communication through the main network, and so forth.

Claims: An inter-network connecting system comprising: a main network (30) having an exchange (32) and a call setting processing processor (33) for controlling said exchange; and a subnetwork, connected to said main network, having a plurality of terminals (35) and a connection control unit (34) comprising loopback means; wherein said call setting processing processor (33) is arranged to give a calling terminal a first special signal (LB) so as to operate the loopback means in said connection control unit (34) to set a physical communication path (P S ) for an extension line between terminals (35) in said subnetwork, when an extension line communication which is a communication in said subnetwork is to be carried out; said call setting processing processor (33) is arranged to give a calling terminal a second special signal (TH) so as to stop the operation of the loopback means in said connection control unit (34) to set a physical communication path (P M ) for an outer line between the exchange (32) and the terminal (35) in said subnetwork, when an outer line communication which is a communication between said main network (30) and a terminal (35) in said subnetwork is to be carried out; said calling terminal is arranged to add a received first or second special signal from said call setting processing processor (33) to data to be transmitted; and said connection control unit (34) is arranged to judge whether the loopback means should be operated or not for each of said data in accordance with said first special signal or said second special signal, to set a physical communication path for said extension line communication and/or said outer line communication. An inter-network connecting system as claimed in claim 1, wherein said main network (30) and said subnetwork construct an integrated services digital network (ISDN). An inter-network connecting system as claimed in claim 1, wherein said first special signal and said second special signal are one or a plurality of fixed data groups for expanding to destination identification, respectively. An inter-network connecting system as claimed in claim 1, wherein: said connection control unit (34) comprises a rewritable table (60); said first special signal and said second special signal are one or a plurality of fixed data groups for expanding to destination identification, respectively; and said connection control unit (34) is arranged to compare said first special signal or said second special signal added to the data from said calling terminal with the contents of said table (60), whereby judgement is made as to whether the loopback function should be operated or not, to set a physical path. An inter-network connecting system as claimed in claim 4, wherein said call setting processing processor (33) comprises means for rewriting the contents of said table (60) in said connection control unit (34). An inter-network connecting system as claimed in claim 4, wherein said terminals (35) comprise means for rewriting the contents of said table (60) in said connection control unit (34). An inter-network connecting system as claimed in claim 4, wherein: said connection control unit (34) comprises means for supervising traffic of said extension line communication and of said outer line communication and for automatically changing the contents of said table (60) in accordance with the amount of traffic in such way that the amount of data of said first special signal is increased when the amount of traffic of said extension line communication becomes larger than the amount of traffic of said outer line communication, and the amount of data of said second special signal is increased when the amount of traffic of said outer line communication becomes larger than the amount of traffic of said extension line communication. An inter-network connecting system as claimed in claim 1, wherein each calling terminal is operable to transmit a third signal (BT) for simultaneously setting physical paths in the communication in said subnetwork and in the communication between said main network and the calling terminal of said subnetwork; whereby by said third signal, physical paths for said extension line communication and for said outer line communication can be simultaneously set. An inter-network connecting system as claimed in claim 1 or 8, wherein said connection control unit (34a) is responsive to a destination identification label (VCI) in said data, said destination identification label including a logic signal representing said first special signal or said second special signal. An inter-network connecting system as claimed in claim 9 as appended to claim 8, wherein said connection control unit (34a) is responsive to said third special signal, which is logically provided in said destination identification label. An inter-network connecting system as claimed in claim 1, wherein means are provided for subjecting said first special signal and said second special signal to error correction. An inter-network connecting system as claimed in claim 8, wherein means are provided for subjecting said third special signal to error correction. An inter-network connecting system as claimed in claim 10, wherein means are provided for subjecting said destination identification label to error correction. An inter-network connecting system as claimed in claim 1, wherein said connection control unit (34b) is provided with a buffer (44) for storing data, said buffer being so arranged that, in use of said inter-network connecting system, when an idle condition is found in the line from said main network (30), data is taken out from said buffer (44) and transferred to said terminal (35). An inter-network connecting system as claimed in claim 1, wherein a buffer (44) for storing data is provided on the line between said connection control unit (34b) and said main network (30), said buffer (44) being so arranged that in use of the inter-network connecting system, when an idle condition is found in said loopback means, data is taken out from said buffer (44) and transferred to said terminal. An inter-network connecting system as claimed in claim 1, wherein a first buffer (44b) and a second buffer (44a) for storing data are provided respectively in the loopback means in said connection control unit (34b) and on the line between said connection control unit (34b) and said main network (30). An inter-network connecting system as claimed in claim 16, wherein the connection control unit (34d) includes means (41d) for alternately taking out data from said first buffer and said second buffer and for transferring this data to said terminal (35). An inter-network connecting system as claimed in claim 16, wherein said connection control unit (34e) comprises an empty buffer detecting unit (46) for detecting which of said first buffer (44b) and said second buffer (44a) is empty, and, when either one of the buffers is empty, to control sequential transfer of data from the other buffer to said terminal (35). An inter-network connecting system as claimed in claim 1 comprising: a buffer (44f) common to said loopback means in said connection control unit (34f) and the line of said connection control unit (34f) from the main network (30); and writing means (47b) for writing loopback data and data from said main network at high speed, for causing this data to be transferred to said terminal (35) in accordance with the writing sequence into said buffer (44f). An inter-network connecting system as claimed in claim 19, wherein: said connection control unit (34) is arranged to transfer the data from said terminal (35) and the data from said main network (30) to said terminal (35) in a sequence of priority in accordance with priority data with which said loopback data and the data from said main network are provided. An inter-network connecting system as claimed in claim 19, wherein: said connection control unit (34) is arranged to transfer the data from said terminal (35) and the data from said main network (30) to said terminal (35) in a sequence of priority in accordance with priority data with which said loopback data and the data from said main network are provided, said priority data indicating whether or not the extension line communication has priority over the outer line communication. An inter-network connecting system as claimed in claim 19, wherein: said connection control unit (34) is arranged to transfer the data from said terminal (35) and the data from said main network (30) to said terminal (35) in a sequence of priority in accordance with priority data with which said loopback data and the data from said main network are provided, said priority data indicating a priority depending on the contents of the communication services. An inter-network connecting system as claimed in claim 22, wherein said connection control unit (34g) comprises a priority control unit (48) for writing said data and said priority data into said buffer (44g), said priority control unit (34g) being arranged to transfer said data to said terminals (35) in accordance with the priority data read from said buffer (44g). An inter-network connecting system as claimed in claim 20, wherein said connection control unit (34h) comprises a plurality of buffers (44h, 441h) for storing different priority data, said buffers being arranged to store said data, respectively, based on said priority data and for transferring data from respective buffers to said terminals (35) in the order of the priority. An inter-network connecting system as claimed in any one of claims 1 to 24, wherein said terminals form a plurality of subnetworks(31-1, 31-2), and said plurality of subnetworks are connected to said main network (30).

Inventors: AMEMIYA SHIGEO, IGUCHI KAZUO, TAKEO HIROSHI, TEZUKA KOJI, AMEMIYA, SHIGEO, IGUCHI, KAZUO, TAKEO, HIROSHI, TEZUKA, KOJI, TEZUKA, KOJI, FUJITSU DAI-12 NAKAHARA-RYO
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H04Q5
IPC codes: H04Q11, H04M3