Abstract:
A method of hunting for a communication channel in a communication system where a plurality of communication lines each have a plurality of communication channels includes the steps of maintaining a record of current channel statuses of the communication channels with respect to all the communication lines, and distributing busy channels evenly among the communication lines by selecting a communication channel based on the record of channel statuses and assigning the selected communication channel to a call.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a method of hunting for a communication channel and a device operating based on the method, and particularly relates to a method of hunting for a communication channel and a device operating based on the method where the method hunts for a PCM communication channel in a communication system comprised of a plurality of PCM communication lines. 
     2. Description of the Related Art 
     FIG. 1 is an illustrative drawing showing a network access device and a switch in a communication system. FIG. 2 is an illustrative drawing showing two switches in a communication system. 
     In FIG.  1  and FIG. 2, a switch  10  includes PCM-communication-line control devices  11 , a network switch  12 , subscriber circuits  13 , a signal processing device  15 , a central controller  16 , a main memory  17 , and a bus  18 . 
     In FIG. 1, each of the PCM-communication-line control devices  11  is connected to a network access device  21  via a PCM communication line  20 . In FIG. 2, each of the PCM-communication-line control devices  11  is connected to another switch  22 . The subscriber circuits  13  are directly connected to subscriber terminals  14 . Each PCM communication line  20  has a capacity for  30  different communication channels, for example. In the configuration of FIG. 1, the network access device  21  transmits a call-transmission signal or a call-disconnection signal to the switch  10  via a PCM communication line  20  when such a signal is received from a subscriber terminal connected to the network access device  21 . The switch  10  attends to control of the call. 
     Under the control of the central controller  16 , the network switch  12  switches communication lines. The signal processing device  15  receives a call-transmission signal or a call-disconnection signal from a subscriber terminal  14  or from the network access device  21 , and searches for or hunts for an available channel in a PCM communication line  20 . If a channel is available, the signal processing device  15  allocates the channel to the communication channel of a subscriber who initiated the call. If all the channels are busy in a given PCM communication line  20 , a search is conducted with respect to another PCM communication line  20 . Then, an available channel that is found is allocated to the communication channel of the subscriber who initiated the call. 
     When a subscriber initiates a call, there may be a communication channel in a PCM communication line  20  where the communication channel was selected on a previous occasion in response to the subscriber&#39;s previous call. In such a case, a search for an available channel is started from a channel next following the previously selected communication channel in this PCM communication line  20 . If an available channel is found, the signal processing device  15  allocates the channel to the communication channel of the subscriber who initiated the call. If all the channels are busy in a given PCM communication line  20 , a search is conducted with respect to another PCM communication line  20 . Then, an available channel that is found is allocated to the communication channel of a subscriber who initiated the call. 
     For the purpose of hunting for a channel in an environment where a plurality of PCM communication lines are provided, typically, channel statuses as to whether the channels are available are controlled separately for each PCM communication line. When a subscriber initiates a call, a search for an available channel is conducted in a PCM communication line. If an available channel is found, the channel is allocated to the communication channel of the subscriber who initiated the call. If all the channels are busy in this PCM communication line, a search is conducted in another PCM communication line. When an available channel is found, the channel is allocated to the communication channel of a subscriber who initiated the call. Alternately, an initial search for an available channel may be started from a channel next following a previously selected channel that was chosen for a previous call. 
     In such a channel hunt method as described above, a channel of a second PCM communication line is allocated in response to a call when all the channels of the first PCM communication line are busy or all the channels next following the previously selected channel in the first PCM communication line are busy. Because of this, a PCM communication line which is currently allocated to calling subscribers tends to have more busy channels than other PCM communication lines. If this PCM communication line suffers failure, many numbers of calls are terminated. 
     Further, when a PCM communication line is to be shut down for the maintenance purpose, shutting down is not performed until all the channels become non-busy. It takes time to shut down a PCM communication line that is allocated to calling subscribers since such a line has a larger number of busy channels than other lines. 
     Accordingly, there is a need for a channel hunt method and a device based on such a method which can reduce the number of calls to be terminated at the time of failure of a PCM communication line, and can shorten a time period required for shutting down a PCM communication line. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of the present invention to provide a channel hunt method and a device based on such a method which can satisfy the need described above. 
     It is another and more specific object of the present invention to provide a channel hunt method and a device based on such a method which can reduce the number of calls to be terminated at the time of failure of a PCM communication line, and can shorten a time period required for shutting down a PCM communication line. 
     In order to achieve the above objects according to the present invention, a method of hunting for a communication channel in a communication system where a plurality of communication lines each have a plurality of communication channels includes the steps of maintaining a record of current channel statuses of the communication channels with respect to all the communication lines, and distributing busy channels evenly among the communication lines by selecting a communication channel based on the record of channel statuses and assigning the selected communication channel to a call. 
     The method as described above distributes busy channels evenly among the communication lines, so that concentration of busy channels in a particular communication line can be avoided. This reduces the number of calls that are to be terminated at a time of communication-line failure, and shortens a time period required for closing a communication line. 
     In order to distribute busy channels evenly among the communication lines, according to one aspect of the present invention, the communication channels have channel numbers assigned thereto, and the communication lines have line numbers assigned thereto, wherein the step of distributing the busy channels includes the steps of searching through the record for an available channel having a search channel number by checking the communication lines in an ascending order of the line numbers, repeating the search by successively incrementing the search channel number from a smallest channel number to a largest channel number until the available channel is found, and assigning the available channel to the call. 
     According to the present invention, there are at least three other variations of the communication-channel-hunt method that achieves even distribution of busy lines. These three variations and the particular variation that was described above may be provided as one set, and a selection may be made among the four variations to perform a search of a desired type to look for a communication channel in a desired manner. 
     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an illustrative drawing showing a network access device and a switch in a communication system; 
     FIG. 2 is an illustrative drawing showing two switches in a communication system; 
     FIG. 3 is an illustrative drawing showing a configuration of a communication system to which the present invention is applied; 
     FIG. 4 is a block diagram of a switch according to an embodiment of the present invention; 
     FIG. 5 is an illustrative drawing showing a channel-status-control table; 
     FIG. 6 is an illustrative drawing showing a busy-channel-count-control table; 
     FIG. 7 is an illustrative drawing showing a pattern-control table; 
     FIG. 8 is a flowchart of a process of hunting for a communication channel which is performed by a central control device of FIG. 4; 
     FIG. 9 is a flowchart of a communication-channel-hunt method of a first pattern according to the embodiment of the present invention; 
     FIG. 10 is a flowchart of a communication-channel-hunt method of a second pattern according to the embodiment of the present invention; 
     FIG. 11 is a flowchart of a communication-channel-hunt method of a third pattern according to the embodiment of the present invention; 
     FIG. 12 is a flowchart of a communication-channel-hunt method of a fourth pattern according to the embodiment of the present invention; and 
     FIG. 13 is a flowchart of a process of changing a pattern that indicates a communication-channel-hunt method in the pattern-control table of FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 3 is an illustrative drawing showing a configuration of a communication system to which the present invention is applied. 
     In FIG. 3, a switch  30  is connected to a network access device  41  via PCM communication lines  40   1  through  40   M , and, also, is connected to another switch  43  via PCM communication lines  42   N  through  42   X . The switch  30  has a plurality of subscriber terminals  34  directly connected thereto. The network access device  41  also has a plurality of subscriber terminals  45  directly connected thereto. Further, the switch  43  is directly connected to subscriber terminals  46 . An input/output device  39  is provided for the switch  30 . 
     Each of the PCM communication lines  40   1  through  40   M  and the PCM communication lines  42   N  through  42   X  has  30  communication channels, for example. The network access device  41  sends a call-transmission signal or a call-disconnection signal to the switch  30  via a PCM communication line when receiving such a signal from one of the subscriber terminals  45  connected to the network access device  41 . The switch  30  attends to control of the call. 
     FIG. 4 is a block diagram of a switch according to an embodiment of the present invention. 
     The switch  30  of FIG. 4 includes PCM-communication-line control devices  31 , a network switch  32 , subscriber circuits  33 , a signal processing device  35 , a central control device  36 , a main memory  37 , and a bus  38 . 
     Each of the PCM-communication-line control devices  31  is connected to the network access device  41  and the switch  43  via the PCM communication lines  40   1  through  40   M  and the PCM communication lines  42   N  through  42   X , respectively. The subscriber circuits  33  are directly connected to the subscriber terminals  34 . The network switch  32  operates under the control of the central control device  36  to attend to switching of lines. The main memory  37  stores therein control programs for the central control device  36  and switch control information for the network switch  32 . 
     When one of the subscriber terminals  34  transmits a call or disconnects a call or when a call-transmission signal or a call-disconnection signal is received from one of the subscriber terminals  45  via the network access device  41 , the signal processing device  35  searches for an available channel as will be described later in detail. The signal processing device  35  allocates an obtained available channel to the communication channel of a subscriber who transmitted the call. The input/output device  39  provides a means of input/output control between the switch  30  and a maintenance worker. The switch  43  has basically the same configuration as the switch  30 . 
     The network switch  32  attends to line switching under the control of the central control device  36 . The signal processing device  35  receives a call-transmission signal or a call-disconnection signal from a subscriber terminal  34  or from the network access device  41 , and searches for or hunts for an available channel in any given PCM communication line. If a channel is available, the signal processing device  35  allocates the channel to the communication channel of a subscriber who initiated the call. If all the channels are busy in the given PCM communication line, a search is conducted with respect to another PCM communication line. Then, an available channel that is found is allocated to the communication channel of the subscriber who transmitted the call. 
     In the present invention, data tables are stored in the main memory  37 . 
     FIG. 5 is an illustrative drawing showing a channel-status-control table. This table includes table entries arranged in matrix having PCM-communication-line numbers  1  through X as rows and channel numbers  1  through  30  as columns. Here, the PCM-communication-line numbers  1  through X correspond to the PCM communication lines  40   1  through  40   M  and  42   N  through  42   X , respectively. Further, the channel numbers range from 1 to 30 because one PCM communication line has 30 channels in this example. Each of the table entries includes two bits, the lower bit indicating an available/busy status and the upper bit indicating whether the channel is a previously selected communication channel. 
     FIG. 6 is an illustrative drawing showing a busy-channel-count-control table. This table includes the number of busy channels (i.e., channels engaged in ongoing communication) with respect to each of the PCM communication lines corresponding to the PCM-communication-line numbers  1  through X. 
     FIG. 7 is an illustrative drawing showing a pattern-control table. This table includes a pattern indicator that indicates one of four different patterns corresponding to four different hunt methods. 
     FIG. 8 is a flowchart of a process of hunting for a communication channel which is performed by the central control device  36 . 
     The process of FIG. 8 is carried out when one of the subscriber terminals  34  connected to the switch  30  or one of the subscriber terminals  45  connected to the network access device  41  sends a call-transmission signal or a call-disconnection signal. 
     At a step S 10 , a received signal is analyzed. If the signal relates to call transmission, the procedure goes to a step S 12 . 
     At the step S 12 , the pattern-control table of FIG. 7 is consulted to look up a type of a channel hunt method. 
     At a step S 14 , a check is made as to which one of the patterns  1  through  4  corresponds to the type found in the pattern-control table. If the pattern  1  is selected, the procedure goes to a step S 16  to attend to a communication-channel-hunt method of the pattern  1 . If the pattern  2  is selected, the procedure goes to a step S 18  to attend to a communication-channel-hunt method of the pattern  2 . If the pattern  3  is selected, the procedure goes to a step S 20  to attend to a communication-channel-hunt method of the pattern  3 . If the pattern  4  is selected, the procedure goes to a step S 22  to attend to a communication-channel-hunt method of the pattern  4 . Thereafter, at a step S 24 , a call-connection process using the obtained communication channel is performed. This ends the procedure. 
     If the check at the step S 10  finds that the received signal relates to call disconnection (i.e., call termination), the procedure goes to a step S 26 . 
     At the step S 26 , a PCM-communication-line number and a channel number are obtained from the communication channel to be disconnected. 
     At a step S 28 , a table entry corresponding to the PCM-communication-line number and the channel number obtained at the step S 26  is searched for in the channel-status-control table of FIG. 5, and the table entry is updated by setting zero to the lower bit of the entry so as to indicate an available status of the channel. 
     At a step S 30 , the number of busy channels in the busy-channel-count-control table is accessed by using the PCM-communication-line number, and is decreased by one. 
     At a step S 32 , a call-disconnection process is performed. This ends the procedure. 
     FIG. 9 is a flowchart of a communication-channel-hunt method of the pattern  1  according to the embodiment of the present invention. 
     At a step S 40 , a channel number CHNO is set to 1. 
     At a step S 41 , a PCM-communication-line number PCMNO is set to 1. 
     At a step S 42 , a table entry is searched for in the channel-status-control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 44 , the table entry found at the step S 42  is checked to find if the lower bit of the table entry is zero indicating an available status of the channel. If the channel is available, the procedure goes to a step S 46 . 
     At the step S 46 , the channel corresponding to the channel number CHNO and the PCM-communication-line number PCMNO is selected as a communication channel to be used. This ends the procedure. 
     If the check at the step S 44  finds that the channel is not available, the procedure goes to a step S 48 . 
     At the step S 48 , the PCM-communication-line number PCMNO is increased by one. 
     At a step S 50 , a check is made as to whether the PCM-communication-line number PCMNO is no larger than the maximum number X of the channel-status-control table. If the PCM-communication-line number PCMNO is smaller than or equal to X, the procedure goes back to the step S 42 . If the PCM-communication-line number PCMNO is larger than X, the procedure goes to a step S 52 , at which the channel number CHNO is incremented by one. Then, the procedure goes back to the step S 41 . 
     In this method, a search for an available channel is made from the PCM-communication-line number  1  to the PCM-communication-line number X by checking if the channel of the channel number  1  is available. If an available channel is found, the channel is selected as a communication channel to be used. If no channel having the channel number  1  is available in any one of the PCM communication lines, a search for an available channel is made again from the PCM-communication-line number  1  to the PCM-communication-line number X by checking if the channel of the channel number  2  is available. A search is repeated by incrementing the channel number until an available channel is found. This type of search insures that the number of busy channels in a given PCM communication line tends to be close to one averaged out over the PCM communication lines. 
     FIG. 10 is a flowchart of a communication-channel-hunt method of the pattern  2  according to the embodiment of the present invention. 
     At a step S 60 , a channel number CHNO is set to 1. 
     At a step S 61 , a PCM-communication-line number PCMNO is set to 1. 
     At a step S 62 , a table entry is searched for in the channel-status-control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 64 , the table entry found at the step S 62  is checked to find if the upper bit of the table entry is “1” indicating that the channel is a previously selected communication channel. If the channel is a previously selected communication channel, the procedure goes to a step S 66 . 
     At the step S 66 , the upper bit of the table entry is changed to zero to indicate that the channel is not a previously selected communication channel. 
     At a step S 67 , the PCM-communication-line number PCMN 0  is incremented by one. Then, the procedure goes to a step S 73 . 
     If the step S 64  finds that the channel is not a previously selected communication channel, the procedure goes to a step S 68 . 
     At the step S 68 , the PCM-communication-line number PCMNO is increased by one. 
     At a step S 70 , a check is made as to whether the PCM-communication-line number PCMNO is no larger than the maximum number X of the channel-status-control table. If the PCM-communication-line number PCMNO is smaller than or equal to X, the procedure goes back to the step S 62 . If the PCM-communication-line number PCMNO is larger than X, the procedure goes to a step S 72 , at which the channel number CHNO is incremented by one. Then, the procedure goes back to the step S 61 . 
     At the step S 73  following the step S 67 , a table entry is searched for in the channel-status-control control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 74 , the table entry found at the step S 73  is checked to find if the lower bit of the table entry is zero indicating an available status of the channel. If the channel is available, the procedure goes to a step S 76 . 
     At the step S 76 , the channel corresponding to the channel number CHNO and the PCM-communication-line number PCMNO is selected as a communication channel to be used. This ends the procedure. 
     If the check at the step S 74  finds that the channel is not available, the procedure goes to a step S 78 . 
     At the step S 78 , the PCM-communication-line number PCMNO is increased by one. 
     At a step S 80 , a check is made as to whether the PCM-communication-line number PCMNO is no larger than the maximum number X of the channel-status-control table. If the PCM-communication-line number PCMNO is smaller than or equal to X, the procedure goes back to the step S 73 . If the PCM-communication-line number PCMNO is larger than X, the procedure goes to a step S 82 , at which the channel number CHNO is incremented by one. Then, the procedure goes to a step S 71 , at which the PCM-communication-line number PCMNO is set to 1. After this, the procedure goes to the step S 73 , and repeat the step S 73  and the following steps. 
     In this method, a check is made from the PCM-communication-line number  1  to the PCM-communication-line number X as to whether the channel having the channel number  1  is a previously selected channel. If no channel having the channel number  1  is a previously selected channel in any one of the PCM communication lines, a check is made as to whether the channel having the channel number  2  is a previously selected channel where the check is made from the PCM-communication-line number  1  to the PCM-communication-line number X. When a previously selected communication channel is found, a check is made as to if there is an available channel in PCM communication lines following in number the PCM communication line having the previously selected communication channel. If no channel having the current channel number is available in any one of the PCM communication lines, a check is made with respect to the channel having the next following channel number where the check proceeds from the PCM-communication-line number  1  to the PCM-communication-line number X. This process continues until an available channel is found. When an available channel is found, it is selected as a communication channel to be used. 
     In this method, a search for an available channel is directed to channels following the previously selected communication channel in terms of PCM-communication-line numbers and channel numbers. Thus, the number of busy channels tends to be averaged over the PCM communication lines  40   1  through  40   M  and  42   N  through  42   X , and it is possible to avoid a situation where busy channels are mostly found among channels having relatively small channel numbers. 
     FIG. 11 is a flowchart of a communication-channel-hunt method of the pattern  3  according to the embodiment of the present invention. 
     At a step S 90 , a PCM-communication-line number of a PCM communication line having the smallest number of busy channels is obtained by searching in the busy-channel-count-control table of FIG. 6, and is set in a PCM-communication-line number PCMNO. 
     At a step S 91 , a channel number CHNO is set to 1. 
     At a step S 92 , a table entry is searched for in the channel-status-control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 94 , the table entry found at the step S 92  is checked to find if the lower bit of the table entry is zero indicating an available status of the channel. If the channel is available, the procedure goes to a step S 96 . 
     At the step S 96 , the channel corresponding to the channel number CHNO and the PCM-communication-line number PCMNO is selected as a communication channel to be used. This ends the procedure. 
     If the check at the step S 94  finds that the channel is not available, the procedure goes to a step S 98 . 
     At the step S 98 , the channel number CHNO is increased by one. 
     At a step S 99 , a check is made as to whether the channel number CHNO is no smaller than the maximum number K (=30). If the channel number CHNO is larger than or equal to K, the procedure goes back to the step S 91 . If the channel number CHNO is smaller than K, the procedure goes back to the step S 92 . 
     In this method, a PCM communication line having the smallest number of busy channels is first selected from the PCM communication lines having the PCM-communication-line numbers  1  through X, and a search for an available channel is made from the channel number  1  and upwards. If an available channel is found, the channel is selected as a communication channel to be used. This type of search insures that the number of busy channels in a given PCM communication line tends to be close to one averaged out over the PCM communication lines. 
     FIG. 12 is a flowchart of a communication-channel-hunt method of the pattern  4  according to the embodiment of the present invention. 
     At a step S 100 , a PCM-communication-line number of a PCM communication line having the smallest number of busy channels is obtained by searching in the busy-channel-count-control table of FIG. 6, and is set in a PCM-communication-line number PCMNO. 
     At a step S 101 , a channel number CHNO is set to 1. 
     At a step S 102 , a table entry is searched for in the channel-status-control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 104 , the table entry found at the step S 102  is checked to find if the upper bit of the table entry is “1” indicating that the channel is a previously selected communication channel. If the channel is a previously selected communication channel, the procedure goes to a step S 106 . 
     At the step S 106 , the upper bit of the table entry is changed to zero to indicate that the channel is not a previously selected communication channel. 
     At a step S 108 , the channel number CHNO is incremented by one. Then, the procedure goes to a step S 112 . 
     If the step S 104  finds that the channel is not a previously selected communication channel, the procedure goes to a step S 110 . 
     At the step S 110 , the channel number CHNO is increased by one. 
     At a step S 111 , a check is made as to whether the channel number CHNO is no smaller than the maximum number K (K=30). If the channel number CHNO is larger than or equal to K, the procedure goes back to the step S 101 . If the channel number CHNO is smaller than K, the procedure goes back to the step S 102 . 
     At the step S 112  following the step S 108 , a table entry is searched for in the channel-status-control table of FIG. 5 by using the channel number CHNO and the PCM-communication-line number PCMNO. 
     At a step S 114 , the table entry found at the step S 112  is checked to find if the lower bit of the table entry is zero indicating an available status of the channel. If the channel is available, the procedure goes to a step S 116 . 
     At the step S 116 , the channel corresponding to the channel number CHNO and the PCM-communication-line number PCMNO is selected as a communication channel to be used. This ends the procedure. 
     If the check at the step S 114  finds that the channel is not available, the procedure goes to a step S 118 . 
     At the step S 118 , the channel number CHNO is increased by one. 
     At a step S 120 , a check is made as to whether the channel number CHNO is no smaller than the maximum number K (K=30). If the channel number CHNO is larger than or equal to K, the procedure goes to a step S 121 , at which the channel number CHNO is set to 1, followed by going back to the step S 112 . If the channel number CHNO is smaller than K, the procedure goes back directly to the step S 112 . 
     In this method, a PCM communication line having the smallest number of busy channels is first selected from the PCM communication lines having the PCM-communication-line numbers  1  through X, and a search for a previously selected communication channel is made from the channel number  1  and upwards in the selected PCM communication line. If a previously selected communication channel is found, a search for an available channel is made in the selected PCM communication line by checking the channels following in number the previously selected communication channel. When an available channel is found, it is selected as a communication channel to be used. 
     In this method, a search for an available channel is directed to channels following the previously selected communication channel in the PCM communication line having the smallest number of busy channels, resulting in averaging out of the numbers of busy channels over the PCM communication lines  40   1  through  40   M  and  42   N  through  42   X . Further, the present invention makes it possible to avoid a situation where busy channels are found mostly among channels having relatively small channel numbers. 
     In this manner, the present invention avoids undesirable concentration of busy channels in a particular one of the PCM communication lines, and achieves even distribution of busy channels. The present invention thus can reduce the number of calls that are terminated at a time of PCM-communication-line failure, and, also, can reduce a time period required for closing a PCM communication line for the purpose of maintenance or the like. 
     FIG. 13 is a flowchart of a process of changing a pattern that indicates a communication-channel-hunt method in the pattern-control table. This process is performed by a maintenance worker who enters a command via the input/output device  39  to indicate one of the patterns  1  through  4 . 
     At a step S 200 , the entered command is analyzed to identify an indicated pattern number. 
     At a step S 202 , the pattern number indicated by the entered command is stored in the pattern-control table of FIG.  7 . This ends the procedure. 
     Use of the process described above makes it possible to select a desired communication-channel-hunt method. 
     As previously described, the process of FIG. 8, which includes therein the processes of FIG.  9  through FIG. 12, is performed by the central control device  36 , which is a central processing unit. In this regard, the central control device  36  encompasses various means that perform particular functions required for implementing the present invention. 
     Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 11-177173 filed on Jun. 23, 1999, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.