Abstract:
There is provided a line redundant method for implementation of line switching in a switching matrix, including the bridge step of outputting a data signal to a plurality of redundant lines in the switching matrix, and the selector step of selecting only a data signal, of a plurality of data signals input from another switching matrix other than the switching matrix through the plurality of redundant lines, which is input through a redundant line required in the switching matrix, and not selecting the data signals input to the switching matrix through the lines other than the required redundant line. A line redundant system for implementing this method is also provided.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a selector, line redundant method, and line redundant system which realize line switching-in a switching matrix to recover from line troubles and the like and, more particularly, to a line redundant scheme which has a simple hardware arrangement and allows line switching on a port basis. 
         [0003]    2. Description of the Prior Art 
         [0004]    Recently, demands have arisen for an improvement in the reliability of an ATM (Asynchronous Transfer Mode) switching network with respect to line troubles. As a line redundant scheme in a case wherein ATM switching is realized on a SONET (Synchronous Optical Network) or SDH (Synchronous Digital Hierarchy) network, an APS (Automatic Protection Switching)-scheme is available, in which when a failure occurs in a Working route (Working Connection) the route is automatically switched to a protection route (Protection Connection) to continue the communication. As standards for this scheme, Bellcore (Bell Communications Research) standards, ANSI (American National Standards Institute) T1.105.01-1998, ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) G.783, and the like are defined. 
         [0005]    There are two types of switching control schemes in APS, namely a physical layer scheme using K1/K2 bytes on a SONET framer as control information for the opposite side and an ATM layer scheme using an OAM (Operation Administration and Maintenance) cell called an APS cell as control information for the opposite side. 
         [0006]    The physical layer scheme includes two types of schemes, namely a (1+1) scheme and (1:1) scheme. In this case, in the (1+1) scheme, on the transmission side, a data signal is copied, and the identical data signals are simultaneously sent out to the two connections, i.e., the working route and protection route. On the reception side, the data signal is normally received through the working route. When a trouble occurs on the working route, only the connection on the reception side is switched from the working route to the protection route, thereby continuing the communication of a main data signal. 
         [0007]    In the (1:1) scheme, on the transmission side, a main data signal and sub-data signal are respectively received through the working route and protection route. On the reception side, data signals from the two routes are normally received through the respective routes. When a trouble occurs on the working route, the connection is switched from the working route to the protection route on both the sides, i.e., the transmission side and reception side, thereby continuing the communication of the main data signal. 
         [0008]    Of the above two types of physical layer schemes, the (1+1) scheme to which the present invention is applied requires a bridge function of distributing a data signal sent to the working route on the transmission side to the protection route as well, a selector function of cutting off a data signal, of data signals input to a switch on the reception side, which is sent from the protection route, and a function of performing line switching control on a port on the opposite side by using K1/K2 bytes on a SONET frame. 
         [0009]    For example, a conventional arrangement for a line redundant system for realizing APS is disclosed in Japanese Unexamined Patent Application Publication (KOKAI) No. 9-275405. In an embodiment in this reference, the arrangement of a dual redundant system in an ATM switch is described. A selector (input cutoff circuit) and bridge (output-side distribution circuit) exist on a common switching fabric. 
         [0010]    The operation of this conventional system will be described below with reference to  FIGS. 1 ,  2 , and  3 . 
         [0011]      FIG. 1  shows an example of the overall arrangement of the system in a case wherein terminals  1  and  4  communicate with each other. The terminals  1  and  4  communicate with each other through ATM switching matrixes  2  and  3 . Dual transmission paths are set between the ATM switching matrixes  2  and  3  by APS based on the (1+1) scheme. Dotted lines  16  indicate the flows of data signals sent out from the terminal  1  to the terminal  4 . Note that in  FIG. 1 , an illustration of the flows of data signals from the terminal  4  to the terminal  1  is omitted. 
         [0012]      FIG. 2  shows the detailed arrangements of a common switching fabric  13   a,  0-system line accommodating section  30   a - 0 , and 1-system line accommodating section  40   a - 1  of the ATM switching matrix  2  shown in  FIG. 1 . Note that  FIG. 2  also shows the arrangement of a portion which receives data signals to be sent from the terminal  4  to the terminal  1 . 
         [0013]      FIG. 3  is a block diagram showing the detailed arrangement of the ATM switching matrix  3  in APS operation. In this case, the internal arrangement of the ATM switching matrix  3  is the same as that of the ATM switching matrix  2 , and the letter added to the end of the reference numeral of each component is changed from a to b. The 0/1-system line accommodating sections  30   a - 0  and  40   a - 1  of the ATM switching matrix  2  are respectively connected to 0/1-system line accommodating sections  30   b - 0  and  40   b - 1  of the ATM switching matrix  3 . A selector  19   b  in  FIG. 3  exhibits a state after APS operation; the selector  19   b  selects an output from the 1-system line accommodating section  40   b - 1  and cuts off an output from the 0-system line accommodating section  30   b - 0 . 
         [0014]    As is obvious from  FIGS. 1 and 2 , the data signal transmitted from the terminal  1  is input to the ATM switching matrix  2  through a line accommodating section  12   a  and bridged (distributed) to the 0-system line accommodating section  30   a - 0  and 1-system line accommodating section  40   a - 1  by the common switching fabric  13   a.  The resultant signals are then output to a working route  14  and protection route  15 , respectively. 
         [0015]    As is obvious from  FIGS. 1 and 3 , the data signal input from the working route  14  to the ATM switching matrix  3  arrives at the terminal  4  through the 0-system line accommodating section  30   b - 0 , a common switching fabric  13   b,  and a line accommodating section  12   b.  On the other hand, the data signal input from the protection route  15  to the ATM switching matrix  3  is input to the common switching fabric  13   b  through the 1-system line accommodating section  40   b - 1 , but the output to the line accommodating section  12   b  is cut off by the selector ( 19   b  in  FIG. 3 ) in the common switching fabric  13   b.    
         [0016]    The detailed arrangement of a conventional APS scheme will be described with reference to  FIG. 2 . Assume that a general technique is used as a switching control function using K1/K2 bytes. A description about the detection of a trouble in the working route and the exchange of control information with opposite ports by using K1/K2 bytes after the detection will therefore be omitted. 
         [0017]    Referring to  FIG. 2 , the ATM switching matrix  2  is constituted by the common switching fabric  13   a,  the 0-system line accommodating section  30   a - 0 , the 1-system line accommodating section  40   a - 1 , and an OS (Operating System)  50   a . The line accommodating sections are comprised of transmission/input interfaces (to be referred to as line IFs hereinafter)  32   a  and  33   a  (Q-system side) and  42   a  and  43   a  (1-system side), output ports  34   a - 1  to  34   a -N (0-system side) and  44   a - 1  to  44   a -N (1-system side) for accommodating a plurality of lines (N lines for each line IF in  FIG. 2 ) , input ports  35   a - 1  to  35   a -N (0-system side) and  45   a - 1  to  45   a -N (1-system side), and line control sections  31   a  and  41   a  which perform APS control, together with the OS  50   a , by using opposite ports and K1/K2 bytes of SONET frames in APS operation. 
         [0018]    The output ports  34   a - 1  to  34   a -N and  44   a - 1  to  44   a -N and input ports  35   a - 1  to  35   a -N and  45   a - 1  to  45   a -N are constituted by an optical module (not shown) , a framer (not shown) for interfacing between a physical layer and an ATM layer, and the like. The respective pairs of 0/1-system transmission/input ports in the 0-system line accommodating section  30   a - 0  and 1-system line accommodating section  40   a - 1  are connected to switch IFs  17   a - 1  to  17   a -n to realize a redundant arrangement. 
         [0019]    For example, referring to  FIG. 2 , each of the pairs of output ports ( 34   a - 1  and  44   a - 1 ), . . . , ( 34   a -N and  44   a -N) and of input ports ( 35   a - 1  and  45   a - 1 ), . . . , ( 35   a -N and  45   a -N) has an APS redundant arrangement. 
         [0020]    The common switching fabric  13   a  is comprised of a switch core  16   a , switch IFs  17   a - 1  to  17   a -n, and switch control section  80   a . The switch core  16   a  has  2   n  interfaces on the transmission/reception side for the switch IFs  17   a - 1  to  17   a -n and switches ATM cells from the respective switch IFs. The switch IFs  17   a - 1  to  17   a -n connect the interfaces of the common switching fabric  13   a  to the 0/1-system line accommodating sections in pairs. The switch control section  80   a  controls the dual redundant arrangement in cooperation with the OS  50   a.    
         [0021]    A bridge  18   a  and selector  19   a  are accommodated in the switch IFs  17   a - 1  to  17   a -n. The bridge  18   a  has a function of simultaneously distributing a data signal from the switch core  16   a  to the 0-system line accommodating section  30   a - 0  to the 1-system line accommodating section  40   a - 1 . The selector  19   a  has a cutoff function of inhibiting an unselected data signal from being input to the switch core  16   a  by selecting one of the 0/1-system line accommodating section pair  30   a - 0  and  40   a - 1 . 
         [0022]    As is obvious from the detailed arrangement of the ATM switching matrix  3  in  FIG. 3 , the following problems arise when a plurality of output ports  34   b - 1  to  34   b -N and  44   b - 1  to  44   b -N and input ports  35   b - 1  to  35   b -N and  45   b - 1  to  45   b -N are accommodated on the plurality of line accommodating sections  30   b - 0  and  40   b - 1  a predetermined number of ports at a time, and a selector  19   b  (input cutoff circuit) exists in the switch IF  17   b - 1  in the common switching fabric  13   b.    
         [0023]    Even when only switching from the input port  35   b - 1  in the 0-system line accommodating section  30   b - 0  on the working route to the input port  45   b - 1  in the 1-system line accommodating section  40   b - 1  on the protection route is to be performed, since the selector  19   b  exists in the common switching fabric  13   b , switching cannot be done on a input port basis. Hence, switching is done on a line accommodating section basis. As a consequence, the remaining input ports  35   b - 2  (not shown) to  35   b -N in normal operation in the 0-system line accommodating section  30   b - 0  are also switched to the input orts  45   b - 2  (not shown) to  45   b -N in the 1-system line accommodating section  40   b - 1 . When such switching occurs, cell loss may occur in the input ports  35   b - 2  (not shown) to  35   b -N which are normally operated. 
         [0024]    In addition, since switching from the working route to the protection route is performed by the selector  19   b , selectors  19   b  must be provided for all the switch IFs  17   b - 1  to  17   b -n in the common switching fabric  13   b . Consequently, the internal hardware arrangement of the common switching fabric  13   b  is complicated. 
       SUMMARY OF THE INVENTION 
       [0025]    The present invention has been made in view of the foregoing circumstances in the prior art, and has for its object to provide a line redundant method which performs line switching based on the (1+1) APS scheme on a port basis by using a selector having a cutoff function of outputting/not outputting one data signal of a plurality of data signals input from a switching matrix, and a line redundant system for implementing the method. 
         [0026]    In order to achieve the above object, according to the first aspect of the present invention, there is provided a line redundant method, comprising: 
         [0027]    the bridge step of outputting a data signal to a plurality of redundant lines in a switching matrix; and 
         [0028]    the selector step of selecting only a data signal, of a plurality of data signals input from another switching matrix other than the switching matrix through the plurality of redundant lines, which is input through a redundant line required in the switching matrix, and not selecting the data signals input to the switching matrix through the lines other than the required redundant line. 
         [0029]    In the first aspect, the selector step is implemented by using a framer function for the data signal. 
         [0030]    In order to realize the above object, according to the second aspect of the present invention, there is provided a line redundant system, comprising: 
         [0031]    bridge means for simultaneously outputting data signals to a plurality of grouped line accommodating sections connected to a common switching fabric in a switching matrix, and selector means for outputting only a data signal, of data signals input from another switching matrix other than the switching matrix to a plurality of grouped input ports in the line accommodating sections, which is required in the common switching fabric from the input port to the common switching fabric, and cutting off the data signals from other input ports other than the input port. 
         [0032]    In the second aspect, the selector means is implemented by using a framer provided for the input port. 
         [0033]    With the above arrangement, when line switching is performed by the (1+1) APS scheme, the selector function of cutting off a data signal output from a line accommodating section in the protection route to the common switching fabric can be implemented on a port basis. This eliminates the necessity of switch the remaining input ports during normal operation in the same line accommodating section, and hence prevents the occurrence of cell loss due to switching. 
         [0034]    In addition, since each switch IF in the common switching fabric needs not have a selector, the hardware arrangement of the common switching fabric can be simplified as compared with the conventional schemes. 
         [0035]    The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative examples. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0036]      FIG. 1  is a block diagram showing the overall arrangement of a conventional line redundant system to explain a conventional line redundant scheme for ATM switching matrixes and the system therefor; 
           [0037]      FIG. 2  is a block diagram showing the detailed arrangement of an ATM switching matrix  2  at the time of APS operation in the arrangement shown in  FIG. 1 ; 
           [0038]      FIG. 3  is a block diagram showing the detailed arrangement of an ATM switching matrix  3  at the time of APS operation in the arrangement shown in  FIG. 1 ; 
           [0039]      FIG. 4  is a block diagram showing the overall arrangement of a line redundant system to explain a line redundant scheme for ATM switching matrixes and the system therefor according to an embodiment of the present invention; 
           [0040]      FIG. 5  is a block diagram showing the detailed arrangement of an ATM switching matrix  102  at the time of APS operation in the arrangement shown in  FIG. 4 ; 
           [0041]      FIG. 6  is a block diagram showing the detailed arrangement of an ATM switching matrix  103  at the time of APS operation in the arrangement shown in  FIG. 4 ; 
           [0042]      FIG. 7  is a block diagram showing an example of path setting on the transmission side of an APS line; and 
           [0043]      FIG. 8  is a block diagram showing an example of path setting on the reception side of the APS line. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0044]    A preferred embodiment of the present invention will be described below with reference to  FIGS. 4 to 8 . 
         [0045]      FIG. 4  shows an example of the overall arrangement of a system in a case wherein terminals  101  and  104  communicate with each other. Note that in the present invention, as in the prior art, a description about the detection of a trouble in the working route and the exchange of control information with opposite ports by using K1/K2 bytes after the detection, which are general techniques, will be omitted. 
         [0046]      FIG. 5  shows the detailed arrangements a common switching fabric  113   a , 0-system line accommodating section  130   a - 0 , and 1-system line accommodating section  140   a - 1  in APS operation in an ATM switching matrix  102  in  FIG. 4 . The ATM switching matrix  102  is constituted by the common switching fabric  113   a , the 0-system line accommodating section  130   a - 0 , the 1-system line accommodating section  140   a - 1 , and an OS  150   a  for controlling the ATM switching matrix  102 . Each line accommodating section accommodates a plurality of lines (N lines for each line IF in  FIG. 5 ). The common switching fabric  113   a  is comprised of switch IFs  117   a - 1  to  117   a -n each of which accommodates one pair of 0-system line accommodating section  130   a - 0  and 1-system line accommodating section  140   a - 1 , a switch core  116   a  for analyzing the header information of a data signal and distributing the information to each line accommodating section, and a switch control section  180   a . Each switch IF accommodates a bridge  118   a  which simultaneously distributes data from the switch core  116   a  to the 0-system line accommodating section  130   a - 0  to the 1-system line accommodating section  140   a - 1 . Note that the operation of the bridge  118   a  is the same as that of the bridge  18   a  in the prior art, and hence a description thereof will be omitted. 
         [0047]      FIG. 6  shows the detailed arrangements of a common switching fabric  113   b , 0-system line accommodating section  130   b - 0 , and 1-system line accommodating section  140   b - 1  in APS operation in the ATM switching matrix  103  in  FIG. 4 . The arrangement of the embodiment of the present invention shown in  FIG. 6  differs from that of the prior art shown in  FIG. 3  in that a selector function is implemented, at the time of switching, for the data signals respectively input from the ATM switching matrix  102  and ATM switching matrix  2  to an ATM switching matrix  103  and ATM switching matrix  3  through a protection route  115  and protection route  15 . 
         [0048]    In the prior art shown in  FIG. 3 , the selector function is implemented on the common switching fabric  13   b  side in the ATM switching matrix  3 . In contrast, in the embodiment of the present invention shown in  FIG. 6 , the selector function is implemented at input ports  135   b - 1  to  135   b -N in the 0-system line accommodating section  130   b - 0  and input ports  145   b - 1  to  145   b -N in the 1-system line accommodating section  140   b - 1 . 
         [0049]    For example, the following are the details of the selector function in a case wherein after a trouble occurs in a working route  114 , the data signal received by the 0-system input port  135   b - 1  through the working route  114  is cut off, and the data signal received by the 1-system input port  145   b - 1  through the protection route  115  is switched to be output to the common switching fabric  113   b  side. 
         [0050]    The switching control function using K1/K2 bytes, an OS  150   b  for controlling the ATM switching matrix  103 , and a line control section for a 0-system line control section  131   b  and 1-system line control section  141   b  cooperate with each other to determine a specific one of the 0-system input port  135   b - 1  and 1-system input port  145   b - 1  from which a data signal should be output. When the occurrence of a trouble in the working route  114  is detected, the OS  150   b  and the line control section cooperate with each other to generate control signals so as to cut off the data signal output from the input port  135   b - 1  through the 0-system line control section  131   b  and output a data signal from the input port  145   b - 1  through the 1-system line control section  141   b.    
         [0051]    That is, in the present invention, when the data signal bridged on the transmission side is input and a trouble occurs in the working route, line switching control is performed such that the data signal output from the 0-system input port of the pair of 0- and 1-system input ports is cut off, and the 1-system input port whose output has been cut off is allowed to output a data signal. In this manner, the selector function is implemented. 
         [0052]    The above selector function can be implemented by, for example, SONET framers that are originally provided for the input ports  135   b - 1  to  135   b -N and  145   b - 1  to  145   b -N. 
         [0053]    A SONET framer has a determination function of determining whether or not to output a data signal from the SONET framer as well as a function of assembling ATM cells into a SONET frame. The selector function can therefore be implemented by using the determination function. 
         [0054]    Note that not only SONET framers but also many commercially available framers have the function of inhibiting an input data signal from being output to the common switching fabric side. Therefore, in units other than ATM switching matrixes incorporating SONET framers, the data signals input to various framers can be cut off (selected) for each port in a line accommodating section before the outputting of the signals to the common switching fabric side by using the same function of the framers in the ports. 
         [0055]    The arrangement of the present invention eliminates the necessity of the selectors  19   b  (see  FIG. 3 ) respectively arranged in the switch IFs  17   b - 1  to  17   b -n on the common switching fabric  13   b , and can simplify the hardware arrangement of the common switching fabric  113   b  as indicated by a switch IF  117   b - 1  in  FIG. 6 . Note that the use of this function has no influence on the remaining ports accommodated in the same system. 
         [0056]    As described above, when it is necessary to perform line switching from the input port  135   b - 1  in the working route in the 0-system line accommodating section  130   b - 0  to the input port  145   b - 1  in the protection route in the 1-system line accommodating section  140   b - 1 , only the corresponding ports can be switched. That is, since the remaining input ports  135   b - 2  (not shown) to  135   b -N during normal operation in the 0-system line accommodating section  130   b - 0  in which the reception circuit port  135   b - 1  is accommodated are not forcibly switched to the reception circuit ports  145   b - 2  (not shown) to  145   b -N in the 1-system line accommodating section  140   b - 1 , cell loss does not easily occur in lines input to the input ports  135   b - 2  (not shown) to  135   b -N during normal operation. 
         [0057]    To allow data signals to pass through the ATM switching matrixes  102  and  103 , path setting must be done in advance. This path setting is performed such that 0- and 1-system line accommodating sections are paired. 
         [0058]      FIG. 7  shows an example of path setting on the transmission side of an APS line. As is obvious from  FIG. 7 , a path is established from a input port  155   a  of a line accommodating section  112   a  to a output port  134   a - 1  of the 0-system line accommodating section  130   a - 0 . On the transmission side, a switch IF (not shown) in the common switching fabric  113   a  bridges (distributes) a data signal from the 0-system side to output it to the 1-system line accommodating section  140   a - 1  as well. Even if, therefore, the 0-system line accommodating section  130   a - 0  is extracted, path setting for a switch core (not shown) in the common switching fabric  113   a  is performed with respect to the 0-system line accommodating section  130   a - 0 . That is, in the 0-system line accommodating section  130   a - 0 , path setting is performed from the switch core to the output port  134   a - 1 . In addition, in the 1-system line accommodating section  140   a - 1  to which the data signal from the 0-system side is bridged, path setting is also performed for a input port  144   a - 1  from the switch core (not shown). 
         [0059]      FIG. 8  shows an example of path setting on the reception side of an APS line. As is obvious from  FIG. 8 , a path is established from the input port  135   b - 1  of the 0-system line accommodating section  130   b - 0  to a output port  154   b  of a line accommodating section  112   b . At the same time, a path is established from the input port  145   b - 1  of the 1-system line accommodating section  140   b - 1 , which pairs up with the above port, to the output port  154   b  of the line accommodating section  112   b.    
         [0060]    As described above, path setting is always performed on both the transmission and reception sides of line accommodating section pairs. Note that when one of an APS line accommodating section pair is extracted, and the other is inserted, the OS that controls the ATM switching matrix performs path setting for the inserted line accommodating section again by using path setting for a line accommodating section that is not extracted. 
         [0061]    In the above description, an ATM switching matrix is used as a switching matrix, and an ATM cell is used as a data signal. However, the switching matrix and data signal are not limited to those described above as long as they comply with the APS specifications. For example, the present invention can also be applied to a line redundant scheme in an IP over SONET system which directly transmits IP packets through a SONET network.