(1) Field of the Invention
The present invention relates to a connection oriented mode communication system suitable for use in, for example, a communication technology of an ATM (Asynchronous Transfer Mode) communication system in which a virtual communication path (virtual connection) is established and communication is effected by means of the communication path. The present invention also relates to a node apparatus for use in such connection oriented mode communication system and a connection setting method.
(2) Description of Related Art
FIG. 25 is a block diagram showing one example of an existing ATM network. In an ATM network 100 shown in FIG. 25, for example, a plurality of ATM nodes 101A to 101E such as an ATM switch (ATM-SW) are unitarily subjected to management of topology (network arrangement) information of the ATM network 100, whereby a network management system (NMS) 102 can manage call processing control such as call setting control including an establishment of PVC (Permanent Virtual Connection) or the like for each of the ATM nodes (hereinafter sometimes referred to as simply node) 101A to 101E.
As shown in FIG. 25, the ATM node 101A and the ATM node 101D are arranged to accommodate subscriber's terminals 103A and 103D, respectively. Conversely, the ATM nodes 101B, 101C and 101E are arranged to serve as a relaying node for relaying signals between the nodes 101A and 101D.
While in FIG. 25 the ATM nodes 101A to 101E are connected to one another sequentially through a single physical connection line 104, actually the ATM nodes 101A to 101E are connected to one another in a mesh-manner through a proper number of the physical connection lines 104. Also, the number of nodes constituting the ATM network 100 is not limited to the number of nodes appearing in FIG. 25.
Now, in the above-described existing ATM network 100, it is assumed that, as for example shown with a broken line 105 in FIG. 26, the subscriber's terminals 103A and 103D are connected through a PVC [virtual (communication) connection] of a physical link which is established so as to include the ATM nodes 101A, 101B, 101C and 101D.
In this case, according to the arrangement of the existing ATM network 100, for example, the NMS 102 generates Connection (PVC) Setting Request 106 to each of the ATM nodes 101A, 101B, 101C and 101D, and each of the ATM nodes 101A, 101B, 101C and 101D builds a set of assignments of connection effective in the apparatus (hereinafter referred to as intra-unit connection) which indicates a transfer route of a received signal extending through the virtual connection on the input-and-output sides and the apparatus itself. Thus, a communication connection by way of the ATM nodes 101A to 101D is established.
As is widely known, according to the ATM communication arrangement, the connection of the above-described type is specified by a virtual path identifier (hereinafter referred to as VPI) and a virtual channel identifier (hereinafter referred to as VCI) which are attached within a header of an ATM cell (hereinafter sometimes referred to as simply “cell”) Then, each of the ATM nodes 101A to 101D builds a set of assignments (assignment table) specifying the correspondence between the target of reception VPI/VCI designated by the above-mentioned Connection Setting Request 101 generated from the NMS 102, and the destination of the conversion of the VPI/VCI within the apparatus, ICID (Internal Channel IDentifier) and a tag (TAG) for carrying out routing within the apparatus. Thereafter, each of the ATM nodes 101A to 101D makes a setting effective in the apparatus for the specified received cell based on the assignment table. In this way, a desired connection setting is accomplished.
The PVC setting operation carried out in the ATM nodes 101A to 101D (also 101E) will hereinafter be described in more detail. In the following description, every ATM node 101A to 101D is not discriminated from one another and hence each ATM node 101A to 101D is simply denoted as ATM node 101 so long as it is not specifically noted.
FIG. 26 is a block diagram showing in detail the arrangement of the ATM node 101. As shown in FIG. 26, the ATM node 101 includes, for example, an ATM switching unit 110, a plurality of network individual units 112, multiplexing-demultiplexing units (common units) 113 of which number corresponds to the number of the network individual units 112 actually provided in the ATM node 101, a central controller (CC) 141 and a main memory (MM) 142.
The network individual unit 112 is connected with at least one physical line 104 (hereinafter sometimes referred to as simply “line 104”), whereby the network individual unit 112 serves as an interface unit between the network including the line 104 and the ATM node 101. Thus, the network individual unit 112 is selected so that its type matches with the type of accommodating network.
If the physical line 104 is arranged to accommodate an ordinary ATM network in which ATM cells are mapped on a predetermined signal frame such as a SDH (Synchronous Digital Hierarchy), SONET (Synchronous Optical Network) or the like to accomplish signal transmission (i.e., in a CRS (Cell Relay Service)), it is necessary to provide an interface for each accommodated ATM network 104. For this reason, the network individual unit 112 adapted to the CRS such as one having a network interface (IF) unit 111 for each accommodated ATM network 104 is used.
Conversely, if the physical network 104 accommodates a communication lines in which signal transmission is effected by a temporal frame [in a CES (Circuit Emulation Service)], the actually mounted network individual unit 112 is one adapted to the CES having a function for mapping the ATM cells on the above frame [e.g., AAL1 (ATM Adaptation layer 1) terminating function].
If the network individual unit 112 is the CES type, the signal frame transmitted through a single physical line 104 is subjected to a time division multiplex processing. Further, while in the example illustrated in FIG. 26 all of the network individual units 112 have a network IF unit 111 in order for coping with the CRS, all of the network individual units 112 may be arranged to cope with the CES. Also, the network individual units 112 to the CRS and the network individual units 112 adapted to the CES may be provided in a coexisting fashion in the arrangement of the ATM node.
Whichever the arrangement adapted to the CRS or one adapted to the CES the network individual unit 112 employs, the network individual units 112 is provided with fundamental functions requiring the minimum necessity for setting the virtual connection. That is, the network individual units 112 is provided with a VPI/VCI-ICID converting function that an (input) VPI/VCI attached to the header of the up-link input ATM cell transmitted from the physical network 104 is converted into an input internal channel identifier (I-ICID: Input-ICID) inherent to the node 101 itself, and that an I=ICID of a down-link input cell transmitted from the ATM switch unit 110 is inversely converted into a (output) VPI/VCI.
The multiplexing-demultiplexing unit 113 will hereinafter be described. The multiplexing-demultiplexing unit 113 accommodates the network individual units of which number corresponds to the network transmission rate which is capable of being dealt by the unit itself. The multiplexing-demultiplexing unit 113 is also a unit for carrying out multiplexing and demultiplexing on an ATM cell which is transmitted and received between the network individual unit 112 and the ATM switch unit 114. For example, if the allowable network transmission rate of the ATM switch unit 110 is about 2.4 Gbps and the network individual unit 112 is arranged to cope with a signal of about 155 Mbps level [e.g., a signal based on the SONET of OC (Optical Carrier level)−3], the multiplexing-demultiplexing unit 113 can accommodate 16 channels at maximum. If the network individual unit 112 is arranged to cope with a signal of about 622 Mbps level (e.g., a signal of OC-12), the multiplexing-demultiplexing unit 113 can accommodate four channels at maximum.
The multiplexing-demultiplexing unit 113 includes an assignment table (conversion table) (not shown) which designates an assignment relation (combination information) effective between the I-ICID given by the central controller 141 upon setting a call (virtual connection) and a tag and O-ICID (output-ICID: Output internal channel identifier). The multiplexing-demultiplexing unit 113 attaches a tag corresponding to the I-ICID of the input cell from the network individual unit 112 to the cell based on the assignment relation. The multiplexing-demultiplexing unit 113 also has a function to convert the corresponding I-ICID into an O-ICID, delete tag-information of the input cell from the ATM switch unit 110, and convert the O-ICID into the I-ICID.
The ATM switch unit 110 also has a function of switching on the cell in accordance with the tag attached to the cell from each of the multiplexing-demultiplexing units 113, thus supplying the cell to a predetermined multiplexing-demultiplexing unit 113. For example, the ATM switch unit 110 repeats selection of one out of two choices, “1” or “0” at every bit of the tag, whereby ATM switch unit 110 carries out switching operation independently.
The central controller 141 is a unit for communicating with respective components 110 to 113 through a bus line 115 so that these components 110 to 113 are intensively controlled. Thus, various setting necessary for call control processing can be achieved. For example, the central controller 141 assigns the VPI/VCI to a call as a target of PVC setting in accordance with the contents of PVC Setting Request 106 from the NMS 102. Then, the central controller 141 converts the VPI/VCI into the internal channel identifier (ICID) which specifies the component address within the node itself (e.g., input/output port number of the multiplexing-demultiplexing unit 113 or the like) that the input cell shall undergo (i.e., connection settled within the component). Thereafter, the central controller 141 determines the tag based on the internal channel identifier.
The main memory 142 is a unit for storing therein data, program (software, firmware) or the like which are necessary for the central controller 141 to operate.
In the above-described ATM node, the PVC (virtual connection) is set in the following manner. That is, when the central controller 141 receives Connection Setting Request 106 from the NMS 102, the above-described ATM node assigns the VPI/VCI (VPI/VCI effective within the component) to the received VPI/VCI as the connection setting target designated by Connection Setting Request 106. Also, the central controller 141 converts the VPI/VCI effective within the component into the I-ICID and further determines the above-described tag and O-ICID so as to correspond to the I-ICID.
The determined assignment relation (combination information) is sent to the corresponding cell input-side multiplexing-demultiplexing unit 113 and cell output-side multiplexing-demultiplexing unit 113, respectively. Each of the cell input-side multiplexing-demultiplexing unit 113 and cell output-side multiplexing-demultiplexing unit 113 holds the combination information as a piece of data of a table-style (assignment table). At this time, the central controller 141 sends data indicative of the assignment relation between the VPI/VCI and the I-ICID and data indicative of a reserved band (band reported by the user) to the network individual unit 112 on the input side (output side).
When the above combination information is supplied from the central controller 141 to the network individual unit 112, the network individual unit 112 holds the combination information as a set of table style data (assignment table), whereby the network individual unit 112 carries out VPI/VCI-ICID conversion setting for the PVC setting target and reserves a band reported by the user.
With the above setting operation, the input cell is converted in its (input) VPI/VCI into the I-ICID by the network individual unit 112, and the converted I-ICID is transmitted to an input port of the multiplexing-demultiplexing unit 113 which is designated by the I-ICID. The multiplexing-demultiplexing unit 113 refers to the I-ICID of the input cell, attaches the tag information corresponding to the I-ICID to the input cell, and converts the I-ICID into O-ICID.
In this way, the input cell is subjected to an automatic switching operation in the ATM switching unit 110 depending on the above tag information, and sent to the corresponding multiplexing-demultiplexing unit 113 on the output side. When the input cell is received by the multiplexing-demultiplexing unit 113 from the ATM switching unit 110, the multiplexing-demultiplexing unit 113 deletes the tag attached to the input cell, specifies an output port for the cell based on the O-ICID, and converts the O-ICID into an I-ICID. Then, the multiplexing-demultiplexing unit 113 outputs the cell to the network individual unit 112 through the corresponding port. Thereafter, the network individual unit 112 converts the I-ICID of the input cell into a corresponding VPI/VCI.
As described above, the ATM 101 makes the network individual unit 112 and the multiplexing-demultiplexing unit 113 hold the data indicative of the assignment relation (table) in accordance with PVC Setting Request 106 supplied from the NMS 102, whereby a transmission route for the cell within the self node 101 (virtual connection; e.g., a broken line 116 in FIG. 26) is established and the cell can be transmitted by way of the virtual connection.
If the virtual connection is established through each of the ATM nodes 101A to 101D in the above-described manner in accordance with PVC Setting Request 106 supplied from the NMS 102, then the PVC (Virtual Connection) setting is accomplished by way of the ATM nodes 101A to 101D.
According to the above-described arrangement of the conventional ATM network 100, however, when an engineer or the like wants to carry out inspection for maintenance or move the facility of the network 104 in which the connection including a plurality of nodes 101 is set, the engineer shall once break the service connection set in the network 104 (currently working connection) and then establish another connection (detouring connection). Thus, the network system cannot help but interrupting the service provided by means of the currently working connection.
In order to avoid such interruption in connection service, for example, there can be considered one solution that the physical network 104 is made redundant between the adjacent nodes 101 so that a desirable connection can be selected upon necessity, as is represented by the APS (Automatic Protection Switching) technology of SDH or SONET. However, according to the technology, to make the physical network 104 redundant is effected at unit of connection between adjacent nodes 101. Therefore, it is impossible to provide a plurality of connection choices including a plurality of nodes 101.