Abstract:
When a leased line is incorporated in a virtual private network forming a composite communication network together with a public network, a service control point searches a data base to see what private branch exchanger is the closest to a caller, and establishes a communication path including the leased line in the composite communication network so that high quality economical communication is offered between the subscribers.

Description:
FIELD OF THE INVENTION 
     This invention relates to a communication method and, more particularly, to a method for communicating through a leased line in a virtual private network and a leased line. 
     DESCRIPTION OF THE RELATED ART 
     VPN (Virtual Private Network) and IN (Intelligent Networks) are kinds of private communication service through a public network. Specified subscribers communicate with one another through the virtual private network or the intelligent networks. Exchangers are incorporated in those networks, and steer pieces of data between the specified subscribers. When a terminal calls another terminal, the exchangers establish a communication path in the virtual private network or the intelligent networks, and pieces of data are transferred through the communication path between the terminals. In the following description, both VPN and IN are simply referred to as “virtual private network”. 
     On the other hand, a leased line is exclusively used by a specific user, and an exchanger of the public network does not participate the communication between terminals of the specific user. The leased line achieves a high quality communication rather than the circuit switching service, and the communication through the leased line is more economical rather than the communication through the public network. 
     If the specified subscribers of the virtual private network have the leased line, the public network and the leased lines are theoretically available for the communication. In the following description, if a leased line is provided in parallel to a part of a virtual private network, the communication system is referred to as “composite communication network”. The present inventor searched documents already published for the composite communication network. The present inventor found Japanese Patent Publication of Unexamined Application Nos. 4-291595, 6-205137, 7-183945, 7-221838 and 8-195814. The present inventor checked the Japanese Patent Publication of Unexamined Applications to see how the leased line is used in the composite communication network. However, the leased line is not effectively used. 
     FIG. 1 illustrates a prior art composite communication network. The virtual private network is owned by a user group  1 , and a code (ggggg) is assigned to the user group  1 . Subscribers  1   a / 1   b / 1   c  belong to the user group  1 . The user group has a head office H 1  in a city X and a branch office B 1  in another city Y, and private branch exchangers  2   a / 2   b  are placed in the head office H 1  and the branch office B 1 , respectively. The subscribers  1   b  and  1   c  are in the head office H 1  and the branch office B 1 , and are connected to the private branch exchangers  2   a / 2   b,  respectively. The subscriber  1   a  is in yet another city Z. The communication between the head office H 1  and the branch office B 1  is so much that a leased line  3  is connected between the private branch exchangers  2   a  and  2   b.    
     The virtual private network is established in a public network  4 , and the public network  4  has exchangers  4   a / 4   b / 4   c.  The cities X/ Y/ Z are in the service areas of the exchangers  4   a / 4   b / 4   c,  respectively. The exchanger  4   c  serves as a service switching point, and is under the control of a service control point SCP. 
     When the subscriber  1   a  wants to communicate with the subscriber  1   c  through the virtual private network, the subscriber  1   a  requests the exchanger  4   c  to establish a communication path to the subscriber  1   c  in the virtual private network. The exchanger or the service switching point requests the service control point SCP to route the communication path from the subscriber  1   a  to the subscriber  1   c.  The service control point SCP takes the service area of the exchanger  4   b  into account, and routes the communication path  5  as “Exchanger 4c”—“Exchanger 4a”—“Exchanger 4b”—“PBX 2b”—“Subscriber 1c”. Even though the leased line  3  is connected between the private branch exchangers  2   a  and  2   b,  the leased line  3  is not used for the communication between the subscribers  1   a  and  1   c.    
     As described hereinbefore, the leased line provides a high quality communication, and is more economical rather than the public network. Therefore, the communication through the leased line  3  is desirable. However, the leased line  3  is not always used for the communication. 
     SUMMARY OF THE INVENTION 
     It is therefore an important object of the present invention to provide a method for a composite communication network which is a higher in quality and more economical than a virtual private network. 
     In accordance with one aspect of the present invention, there is provided a method for routing a communication path between a first subscriber and a second subscriber through a public network having service switching points and a service control point and a private network containing entry points and a leased line selectively connected between the entry points, and the method comprises the steps of transferring a first identification number and a second identification number respectively assigned to the first subscriber and second subscriber through at least one of the service switching points to the service control point, determining one of the entry points closest to the first subscriber and a routing number used in the private network, notifying the routing number to the one of the entry points through the public network for routing a communication sub-path passing through the leased line in the private network and establishing the communication path having the communication sub-path between the first subscriber and the second subscriber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the method will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic view showing the communication path established in the prior art composite communication network; 
     FIG. 2 is a schematic view showing a communication path established in a composite communication network through a method according to the present invention; 
     FIG. 3 is a flow chart showing the method according to the present invention; 
     FIG. 4 is a schematic view showing another communication path established in a composite communication network through a method according to the present invention; 
     FIG. 5 is a flow chart showing the method according to the present invention; 
     FIG. 6 is a schematic view showing a communication path established in a composite communication network through a method according to the present invention; and 
     FIG. 7 is a flow chart showing the method according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 2 illustrates a communication path established in a composite communication network through a method embodying the present invention. The composite communication network is similar to that shown in FIG. 1, and corresponding exchangers and corresponding lines are labeled with the same references as those of the prior art composite communication network. The private branch exchangers  2   a / 2   b,  house cables  8  and the leased line  10  form in combination a private network  9 . The public network  4  and the private network  9  as a whole constitute a composite communication network. 
     An extension number (YYY) is assigned to an extension of the subscriber  1   c,  and the subscribers  1   a / 1   c  have a telephone number “aaaaaaaa” and another telephone number “yyyyyyyy”. The exchangers  4   c / 4   a / 4   b  are respectively assigned area&#39;s identification numbers “A”, “B” and “C”, and the private branch exchangers  2   a / 2   b  are assigned area&#39;s identification numbers “X” and “Y”, respectively. The area&#39;s identification number “X” is represented by a telephone number “xxxxxxxx”. The cities X/Y/Z are in the service areas of the exchangers  4   a / 4   b /  4   c , respectively, and term “service area” means “nearest area from the aspect of routing”. 
     When the subscriber  1   a  wants to communicate with the subscriber  1   c,  a communication path  10  is established between the subscribers  1   a  and  1   c  in the composite communication network under the control of the service control point SCP, and the leased line  3  forms a part of the communication path  10 . 
     FIG. 3 illustrates a control sequence for establishing the communication path  10  in the composite communication network. A data base  11  is stored in the service control point SCP, and contains at least three tables DB 11   a,  DB 11   b  and DB 11   c.    
     The first table DB 11   a  defines relation between a caller&#39;s identification number, an identification number for a virtual private network group and a caller&#39;s area identification number. The caller&#39;s identification number is equal to the telephone number assigned to a subscriber  1   a / 1   b / 1   c.  When a caller&#39;s identification number is given, the first table DB 11   a  specifies the identification number of the virtual private network and the identification number of the caller&#39;s area. The identification number of the caller&#39;s area is indicative of the exchanger of the public network  4  to which the caller is connected. The second table DB 11   b  defines relation between the identification number of a virtual private network, an extension number, an identification number of a destination and an identification number of a destination area. The identification number of the destination is indicative of the telephone number of a subscriber to be connected to the caller, and the identification number of the destination area is indicative of the private branch exchanger  2   a / 2   b  to which the destination is connected. When the identification number of a virtual private network and the extension number are given, the second table DB 11   b  specifies the identification number of the destination and the identification number of a destination area from the identification number of the virtual private network and the extension number. The first table DB 11   a  gives the identification number of the virtual private network group to the service control point SCP, and the extension number is provided from the caller to the service control point SCP. 
     The third table DB 11   c  defines relation between the identification number of a virtual private network group, the identification number of the caller&#39;s area, the identification number of the destination area, an entry point number and a prefix. The entry point number is representative of the telephone number assigned to an appropriate private branch exchanger  2   a / 2   b  for entering into the leased line  3 . The prefix is combined with the extension number in order to determine a routing number for the private branch exchangers  2   a / 2   b.  When the identification number of the virtual private network group, the identification number of the caller&#39;s area and the identification number of the destination area are given, the third table DB 11   c  specifies the entry point number and the prefix. The first table DB 11   a  gives the identification number of the virtual private network group and the identification number of the caller&#39;s area to the service control point SCP, and the second table DB 11   b  gives the identification number of the destination area to the service control point SCP. 
     Assuming now that the subscriber  1   a  dials the extension number (YYY), the extension number (YYY) is supplied from the subscriber  1   a  to the exchanger  4   c.  As described hereinbefore, the exchanger  4   c  serves as a service switching point SSP, and transfers the extension code (YYY) and the caller identification number (aaaaaaaa) to the service control point SCP. 
     When the extension number (YYY) and the caller identification number (aaaaaaaa) arrive at the service control point SCP, the service control point SCP starts the control sequence shown in FIG.  3 . The service control point SCP firstly searches the first table DB 11   a  for the caller&#39;s identification number “aaaaaaaa”, and acquires a piece of data information representative of the identification number “A” of the caller&#39;s area and another piece of data information representative of the identification number “ggggg” of the virtual private network group to which the subscriber  1   a  belongs as by step SP 1 . The service control point SCP stores the pieces of data information in an internal memory (not shown). 
     Subsequently, the service control point SCP searches the second table DB 11   b  for the combination of the identification numbers “ggggg” and the extension number “YYY”, and acquires a piece of data information representative of the identification number “yyyyyyyy” of the destination and another piece of data information representative of the identification number “Y” of the destination as by step SP 2 . The service control point SCP stores the pieces of data information in the internal memory. 
     Subsequently, the service control point SCP checks to see whether or not an identification number of destination is found at step SP 2  as by step SP 3 . If the answer at step SP 3  is given negative, the service control point SCP establish a communication path between the subscribers in the virtual private network through the prior art communication method as by step SP 4 . 
     On the other hand, when the identification number of the destination was found at step SP 2 , the answer at step SP 3  is given affirmative. With the affirmative answer, the service control point SCP searches the third table DB 11   c  for the combination of the identification numbers “ggggg”, “A” and “Y”, and acquires a piece of the data information representative of the entry point number “xxxxxxxx” and another piece of data information representative of the prefix “GGGGG” as by step SP 5 . As described hereinbefore, the entry point number “xxxxxxxx” is indicative of the private branch exchanger  2   a  closest to the exchanger  4   c.    
     Subsequently, the service control point SCP combines the extension number “YYY” with the prefix “GGGGG”, and produces a routing number “GGGGGYYY” used in private network  9  as by step  5 P 6 . The entry point number “xxxxx” and the routing number “GGGGGYYY” are stored in the internal memory. 
     Subsequently, the service control point SCP notifies the entry point number “xxxxxxxx” and the routing number “GGGGGYYY” to the service switching point SSP or the exchanger  4   c,  and the exchanger  4   c  routes the communication path  10  through the private network  9  as by step SP 7 . Namely, the exchanger  4   c  connects the subscriber  1   a  through the exchanger  4   a  to the private branch exchanger  2   a,  and supplies the routing number “GGGGGYYY” to the private branch exchanger  2   a.  The private branch exchanger  2   a  routes the communication path  10  through the leased line  3  to the private branch exchanger  2   b,  and the private branch exchanger  2   b  specifies the extension “YYY”. Thus, the subscriber  1   a  is connected through the communication path  10  to the subscriber  1   c.    
     In the above description, the subscribers  1   a  and  1   c  belong to the virtual private network group (ggggg). Even if either subscriber  1   a / 1   c  is out of the virtual private network (ggggg), a communication path is also established through the leased line  3 . 
     As will be understood from the foregoing description, the method according to the present invention selects the private branch exchanger closest to the caller on the basis of the combination of the caller&#39;s area and the destination area. For this reason, the leased line  3  surely forms a part of the communication path  10 , and the communication path achieves high quality communication at low cost. 
     Second Embodiment 
     FIG. 4 illustrates another communication path  20  established in a composite communication network  21 . The composite communication network  21  includes a public network  22  and a private network  23 . The private network  23  is similar to the private network  9 , and references used for the first embodiment designate corresponding private branch exchangers, corresponding subscribers, corresponding house cables and corresponding leased line without detailed description. 
     The public network  22  includes exchangers  22   a / 22   b / 22   c / 22   d , a service control point SCP and at least one subscriber  23 . A telephone number “dddddddd” is assigned to the subscriber  23 . Each of the exchangers  22   a / 22   b / 22   c / 22   d  serves as a service switching point, and is communicable with the service control point SCP. Identification numbers “A”, “B”, “C” and “D” are respectively assigned to the exchangers  22   a,    22   b,    22   c  and  22   d,  and the private branch exchangers  2   a / 2   b  also have identification numbers “X”, and “Y”, respectively. 
     FIG. 5 illustrates another control sequence embodying the present invention. The data base  11  has a fourth table DB 11   d  instead of the second table DB 11   b,  and the service control point SCP executes a job called as “Off Net Zone”. 
     Assuming now that the subscriber  1   a  dials the telephone number “dddddddd”, the communication path  20  is established in the composite communication network  21 , and the leased line  3  forms a part of the communication path  20  as follows. The exchanger  22   a  supplies the telephone number of the subscriber  1   a  or the identification number of the caller “aaaaaaaa” and the telephone number “dddddddd” of the destination  23  to the service control point SCP. 
     The service control point SCP starts the control sequence shown in FIG.  5 . The service control point SCP searches the first table DB 11   a  for the identification. number “aaaaaaaa” of the subscriber  1   a,  and specifies the identification number “ggggg” of the virtual private network and the identification number of callers area “A” as by step SP 11 . 
     Subsequently, the service control point SCP checks to see whether or not an identification number of caller&#39;s area is found at step SP 11  as by step SP 12 . If the answer at step SP 12  is given negative, the service control point SCP determines the communication through the prior art method, and a communication path is established in the public network  22  as by step SP 13   
     On the other hand, when the identification number of caller&#39;s area was found at step SP 11 , the answer at step  5 P 12  is given affirmative, and the service control point SCP starts the job called as “Off Net Zone”, because the telephone number “dddddddd” is not registered in the first table DB 11   a.  In detail, the service control point SCP searches the fourth table DB 11   d  for the combination of the identification number “ggggg” and the telephone number “dddddddd”, and decides the destination area to be “D” as by step SP 14 . 
     Subsequently, the service control point SCP searches the third table DB 11   c  for the combination of the identification number “ggggg”, the area identification numbers “A” and “D”, and decides the entry point number and the prefix to be “xxxxxxxx” and “HHHHH” as by step SP 15 . 
     Subsequently, the service control point SCP produces a routing number “HHHHHdddddddd” for the private network  23  as by step SP 16 , and supplies the entry point number “xxxxxxxx” and the routing number to the service switching point  22   c.  The routing number “HHHHdddddddd” is maintained in the private network  23 . The subscriber  1   a  is connected through the exchangers  22   a  and  22   b  to the private branch exchanger  2   a,  and the private branch exchanger  2   a  further connects it through the leased line  3  to the private branch exchanger  2   b.  The private branch exchanger  2   b  is connected through the exchangers  22   c / 22   d  to the subscriber  23 . Thus, the subscriber  1   a  is connected through the communication path  20  to the subscriber  23 , and the leased line  3  is effectively used in the communication. 
     Third Embodiment 
     FIG. 6 illustrates a communication path  30  established in a composite communication network  31 . The composite communication network  31  includes a public network  32  and a private network  33 . Exchangers  32   a / 32   b / 32   c,  a service control point  32   d  and a subscriber  32   e  are incorporated in the public network  32 , and the exchanger  32   a  serves as a service switching point SSP for the subscriber  32   e.  A telephone number “eeeeeeee” is assigned to the subscriber  32   e.    
     The subscribers  33   a / 33   b  are connected through house cables  33   c  to private branch exchangers  33   d / 33   e , and a leased line  34  is connected between the private branch exchangers  33   d  and  33   e.  Hatching lines are indicative of a virtual private network  35 , and identification number (ggggg) is assigned to the virtual private network  35 . The subscriber  32   a  is not incorporated in the virtual private network  35 . A subscriber, who is not incorporated in the virtual private network  35 , has to dial an access code “JJJJJ” in order to communicate a subscriber incorporated in the virtual private network  35 . An extension number “YYY” is assigned to the subscriber  33   b,  and a telephone number “xxxxxxxx” is assigned to the private branch exchanger  33   d.    
     FIG. 7 illustrates a control sequence for communicating through the composite communication network  31 . The service control point  32   d  has a data base  36 , and four tables DB 36   a /DB 36   b /DB 36   c /DB 36   d  form parts of the data base  36 . The first table DB 36   a  defines relation between the access code and an identification number of virtual private network, and the second table DB 36   b  defines relation between the combination of the identification number of virtual private network and an extension number and a combination of a telephone number of a destination and an identification number of the destination area. The third table defines relation between a combination of an identification number of the virtual private network and a caller&#39;s telephone number and an identification number of caller&#39;s area, and the fourth table defines relation between the identification number of virtual private network, the identification number of caller&#39;s area and the identification number of destination area and a combination of an entry point number and a prefix. 
     Assuming now that the subscriber  32   e  dials the access code “JJJJ” and the extension number “YYY”, the access code “JJJJ” and the extension number “YYY” are transferred through the exchanger  32   a  to the service control point  32   d,  and the service control point starts the control sequence shown in FIG.  7 . 
     The service control point  32   d  searches the first table DB 36   a  for the access code, and specifies the identification number “ggggg” of the virtual private network  35  as by step SP 21 . The identification number “ggggg” is temporarily stored in an internal data storage (not shown) of the service control point  32   d.  The service control point  32   d  further searches the second table DB 36   b  for the combination of the identification number “ggggg” and the extension number “YYY”, and decides the telephone number of the subscriber  33   b  and the identification number of the destination area to be “yyyyyyyy” and “Y” as by step SP 22 . The telephone number “yyyyyyyy” and the identification number “Y” are stored in the internal data storage. 
     Subsequently, the service control point  32   d  checks to see whether or not an identification number of the destination is found at step SP 22  as by step SP 23 . If the answer is given negative, the service control point  32   d  establishes a communication path between the subscribers through the prior art method as by step SP 24 . 
     When the identification number of the destination was found at step SP 22 , the answer at step SP 23  is given affirmative, and the service control point  32   d  carries out the job called as “Off-Net Zone”. The service control point  32   d  searches the third table DB 36   c  for the combination of the identification number “ggggg” and the telephone number “eeeeeeee”, and decides the identification number of the caller&#39;s area to be “E” as by step SP 25 . The identification number “E” of caller&#39;s area is temporarily stored in the internal data storage. 
     Subsequently, the service control point searches the fourth table DB 36   d  for the combination of the identification numbers “ggggg”, “E” and “Y”, and decides the entry point and the prefix to be “xxxxxxxx” and “GGGGG” as by step SP 26 . The entry point number is representative of the private branch exchanger closest to the subscriber  32   e.    
     Subsequently, the service control point  32   d  combines the extension number “YYY” with the prefix “GGGGG”, and produces a routing number “GGGGGYYY” as by step SP 27 . The service control point  32 d supplies the routing number “GGGGGYYY” and the entry point number “xxxxxxxx” to the exchanger  32   a,  and the communication path  30  is established in the composite communication network  30  as by step SP 28 . In detail, the exchanger  32   a  connects the subscriber  32   e  through the exchanger  32   b  to the private branch exchanger  33   d.  The private branch exchanger  33   d  is connected through the leased line  34  to the private branch exchanger  33   e,  and the private branch exchanger  33   e  converts the extension number “YYY” to the telephone number “yyyyyyyy” assigned to the subscriber  33   b,  and the subscriber  32   e  is connected through the communication path  30  to the subscriber  33   b.    
     As will be appreciated from the foregoing description, the service control point has the table for the private branch exchanger closest to the caller, and the communication path is established through the leased line between the subscribers. As a result, high-quality communication is established in the composite communication network through the leased line. 
     Although particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention.