Transmitting apparatus

[0001] [Technical field to which the invention belongs] The present invention relates to a transmission device of a ring network, and in particular, a plurality of transmission devices are connected in a ring shape so as to be able to transmit in each of the up direction and the down direction, and a work band and a protection band are allocated in each direction to cause a transmission line failure. The present invention relates to a ring network transmission device that loops back and rescues a transmission signal using a protection band. [0002] [Conventional technology] Frame configuration Due to the increase in communication volume, SONET (Synchronous Optical Network), which uses optical communication capable of large-capacity transmission, has become widespread. In such a synchronous optical communication network SONET, user data is multiplex-transmitted according to the frame format of STS-N (N: integer). Figure 23 (A) is a frame configuration diagram of STS-1 at 51.84 Mbps, which has 9 x 90 (bytes / 125 μs) as a whole, 3 x 9 bytes of overhead OH, and 87 x 9 bytes of STS payload STS-. It consists of 1 SPE. 9 bytes in payload STS-1 SPE is path overhead POH, remaining 86 x 9 Packets of multiple low-order group channels (VT packets) are multiplexed in bytes. In the synchronous optical communication network SONET, in addition to the above STS-1, there are frame formats such as STS-3 (155.52 Mbps), STS-12 (622.08 Mbps), STS-48 (2.488 Gbps), ..., and optical transmission. It can be used as appropriate depending on the road. VT (Virtual Tributory) packets are VT1.5, VT2, VT3, There are types such as VT6. As shown in Fig. 23 (B), VT1.5 composes packets with 27 bytes (= 3 x 9 bytes), and the bit rate of one VT channel is 1.728 Mbps (= 27 x 8/125 Mbps). Figure 23 (C) is an explanatory diagram of the mapping of VT1.5 packets in the VT-structured STS-1 SPE. The first column is the path overhead POH, and the 30th and 59th columns are all "1" fixed staff (Fixed). In Stuff), the payload STS-1 SPE is divided into three regions R1 to R3 consisting of 28 columns. Rows 1 to 28 of each area are sequentially 1-1,2-1,3-1,4-1,5-1,6-1,7-1,1-2,2-2, ... 7 With a -4, the VT1.5 packets on channel 1 are placed in columns 2, 31, and 60, the VT1.5 packets on channel 2 are placed in columns 3, 32, and 61, and so on. The VT1.5 packets on channel 28 are placed in columns 29, 58, and 87. [0003] Ring configuration As a network configuration of the synchronous optical communication network SONET, a ring configuration in which transmission devices are connected in a ring shape is known from the viewpoint of ensuring reliability. According to the ring configuration, transmission can be continued via the alternative transmission line even if a transmission line failure occurs, and the reliability of transmission can be improved. FIG. 24 is a schematic configuration diagram of an ADM (Add / Drop Mux) transmission device that can be connected to a ring, and FIG. 25 is a ring configuration explanatory diagram. The ADM transmission device is a terminal device equipped with a MUX (multiplexer) function and an Add / Drop function, and has a cross-connect function and an add / drop function for the lower group side (tributary side). The line interface (LINE IF) 1a and 1b transmit high-order group signals (for example, OC-48: 2.488 Gbps optical signal) to the WEST side and EAST side optical transmission lines 8a, respectively.₁, 8b₁Demultiplexers (DMUX) 2a and 2b separate the high-order group signal into low-order group signals (for example, STS-1 electric signal) and cross-connect them. Part 3 cross-connects at the STS-1 level, multiplexers (MUX) 4a and 4b multiplex the cross-connected STS-1 signals into higher-order group signals, and line interfaces (LINE IF) 5a and 5b become the higher-order group signals. Optical transmission line 8a on the EAST side and WEST side by adding an overhead and converting it into an optical signal₂, 8b₂Send to. The signal direction input to the EAST side of the transmission device (node) and output from the WEST side is the EW direction (EAST WEST direction), and the signal direction input to the WEST side of the transmission device (node) and output from the EAST side. Is called the WE direction (WEST EAST direction). [0004] The cross-connect unit 3 switches the STS-1 signal inserted (added) from the tributary interface 6a, 6b .. via the MUX / DMUX 7a, 7b .. at the STS level and sends it in the WE direction or the EW direction. At the same time, the signal received from the transmission line from the WE direction or the EW direction is dropped on the tributary side, separated into low-order group signals of a predetermined speed via the MUX / DMUX 7a, 7b .., and the tributary interface 6a, 6b. .. Send to the tributary side. Both the WE and EW transmission lines have a work channel and a protection channel. channel) is assigned. For example, in the case of OC-48, of the 48 channels of STS-1, the 1st to 24th channels are active lines and the 25th to 48th channels are standby lines. Normally, the transmission device transmits a signal using the active channel, and when a failure occurs, a spare channel is used for relief. [0005] Protection in the event of a transmission line failure In the ring configuration, as shown in FIG. 25, the ADM devices 10a to 10d are connected in a ring shape, and if a failure occurs in a predetermined transmission line or the quality deteriorates, a signal is transmitted in a direction that does not pass through the transmission line. As a result, communication is continued and reliability and quality are ensured. Networks with multiple nodes connected in a ring are roughly classified into UPSR (Uni-directional Path Switched Ring) method and BLSR (Bi-directional Line Switched Ring) method. Compared to the UPSR method, the BLSR method has the advantage that the line capacity can be increased because the same channel can be used between different nodes (in a span). In the BLSR method, when a failure occurs at multiple locations and the ring transmission line is divided, a signal that cannot reach the target node is generated, and that signal is transmitted to another node by loopback for failure relief. May be done. In order to prevent such a misconnection, a squelch (squelch) is executed in which a path alarm indication signal (P-AIS) is inserted into a signal of a channel that cannot reach the target node and transmitted. [0006] FIG. 26 is an explanatory diagram of fault relief. In the UPSR method, as shown in (a), the EW direction side from the node (C) to the node (B) and the WE from the node (C) to the node (D). The same signal is transmitted in the direction by, for example, channel ch.1, and the node (A) selectively receives the signal of one channel ch.1 by the path switch PathSW. Therefore, for example, as shown in FIG. 26 (b), even if a failure occurs between the nodes (A) and (B), the node (A) is a channel via the node (D) by the path switch PathSW. Since the signal of ch.1 can be selectively received, the communication between the nodes (C) and (A) can be continued. [0007] Further, in the BLSR method, as shown in FIG. 26 (c), the node (C) sends a signal to the node (A) by, for example, the channel ch.1 in the EW direction, and the channel ch.1 in the WE direction. Sends a signal to node (D) by, and node (D) sends a signal to node (A) by channel ch.1 on the WE side (use of the same channel in another span). That is, using the same channel ch.1, communication between nodes (C)-(A), nodes (C)-(D), and nodes (D)-(A) becomes possible, which is compared with the UPSR method. The line capacity can be increased. As shown in Fig. 26 (d), this BLSR method uses APS (Automatic Protection) using K1 and K2 bytes when a failure occurs between nodes (A) and (B). It is relieved by the Switch) protocol. The signal sent from the node (C) to the channel ch.1 of the active line by this APS protocol is switched to the channel ch.25 of the backup line at the node (B) and turned back (loopback) to the node (A). By switching the standby line channel ch.25 to the active line channel ch.1, communication between channels (C) and (A) can be continued. Since the communication between the nodes (C)-(D) and the nodes (D)-(A) does not pass through the obstacle section, the communication is performed by the channel ch.1 respectively. [0008] FIGS. 27 to 30 are explanatory diagrams of the APS protocol, where WK indicates an active line and PT (diagonal line) indicates a spare line. Each node A to H is connected in a ring shape with different transmission lines in the WE direction and the EW direction, and a working line and a backup line are assigned to each transmission line. FIG. 27 shows the case where the nodes (A)-(E) communicate in both directions. In this state, if a failure occurs in the EW direction transmission line between the nodes (F) and (E) as shown in FIG. 28, the node (E) detects the failure and becomes a switching node, and the node of the opposite station ( For F), switching requests (SF-RING; Signal Falure Ring) 51 and 52 indicating a transmission line failure are sent to both the short path and the long path according to the APS protocol. The node (D), (C), (B), (A), (H), (G) that received the long path request 52 identifies the destination (F) of the request 52 and addresses it to its own node. If it recognizes that it is not, it will be in a full pass-through state and will pass through the backup line (protection channel). In addition, the node (F) that received the short path request 51 becomes a switching node, sends a reverse request (RR-RING; Reverse Request Ring) to the short path, and receives it to the long path. Send the same request 53 (SF-RING) as the requested request 52. [0009] In the case of a transmission line failure, the bridge and switch are performed at the same time when the request from the long path is received. The bridge represents the state in which the same traffic is switched from the active channel to the spare channel and transmitted, and the switch represents the state in which the traffic from the spare channel is switched to the active channel and transmitted. Therefore, due to the occurrence of a failure between the nodes (F) and (E), the node (E) forms a bridge and sends a signal to the node (A) to the standby line PT as shown by the dotted line in FIG. Node (F) forms a switch and switches the spare line PT from node (F) to active line WK from node (F) as shown by the dotted line. The above is the signal relief from the node (E) to the node (A), but the signal from the node (A) to the node (E) can be rescued in the same manner. That is, as shown in FIG. 30, the node (F) forms a bridge that returns the signal from the active line WK from the node (A) to the node (E) to the spare line PT, and the node (E) forms this spare line. Switch from PT to active line. Therefore, the communication between the nodes (E) and (A) is continued. [0010] K1 and K2 used for the APS protocol are included in the section overhead SOH as shown in Fig. 31. The K1 byte consists of the 1st to 4th bit switching request and the 5th to 8th bit partner station ID (K1 byte destination node identification number), and the K2 byte is the 1st to 4th bit own station ID. (Identification number of request generating node), bit (S / L bit) indicating whether the 5th bit is a short path request ("0") or a long path request ("1"), and 6 to 8 It consists of the status of the bit. In the K1 byte switching request, "1011" indicates the above-mentioned SF-RING, "0001" indicates the above-mentioned RR-RING, and "0000" indicates no request. In addition, the status of K2 bytes indicates AIS (Alarm Indication Signal) by "111". [0011] Squelch Since the same channel can be used on multiple lines in a BLSR network, a miss connection will occur if a failure occurs at multiple locations. To prevent this erroneous connection, P-AIS (Path Alarm) is used for the line that causes the erroneous connection. Indication Signal) is inserted. This P-AIS insertion operation is called squelch. The squelch table is used for squelch execution, and its contents specify the Add / Drop node of each channel and is set in each node. As shown in Fig. 32 (A), the node has an EAST side and a WEST side. The direction in which the signal travels from the EAST side to the WEST side of the node is called the EW direction, and the direction in which the signal travels from the WEST side to the EAST side is called the WE direction. .. As shown in Fig. 32 (B), the squelch table describes (1) channel units, (2) Add / Drop nodes in the WE and EW directions on the EAST side and WEST side of the node, respectively. .. However, enter the Add node in the Source station name field of the squelch table, and the Drop node in the Destnation station name field. Therefore, assuming bidirectional communication between nodes (A)-(E), nodes (A)-(C), and nodes (C)-(E) as shown in FIG. 33, each node ( The squelch tables SQTL-A to SQTL-H of A) to (H) are as shown in the figure. In addition, node The squelch table is created using the node IDs (A) to (H). [0012] This squelch table is used to determine whether the signal of each channel can be rescued by loopback when a failure occurs at two or more points in the ring. As a result of judgment by the squelch table, the signal that cannot be rescued may be output from a wrong node different from the original node, and if there is a possibility of causing such a misconnection, squelch is executed. It is the switching node that performs the squelch, when two or more locations on the ring fail. However, squelch is not executed in the following cases. (1) If a failure occurs at both ends of the local node (isolated), (2) If there is no failure on either side of the local node (if it is not a switching node), (3) If the bridge or switch is not actually done Is. [0013] FIG. 34 describes the squelch determination process in the node (E) when a failure occurs simultaneously between the nodes (E)-(D) and between the nodes (F)-(G). If the squelch routing is not executed, the signal of channel ch.1 from node (A) to node (E) is returned to channel ch.25 of the backup line by the bridge function at node (G) and switched at node (D). Depending on the function, channel ch.25 of the standby line will be returned to channel ch.1 of the active line, and a erroneous connection will occur in which the signal from node (A) to node (E) is transmitted to node (D). Further, the signal of channel ch.1 from the node (E) to the node (C) is returned to the standby line channel ch.25 by the bridge function at the node (E), and the signal of the active line is returned by the switch function at the node (F). It will return to channel ch.1, and a erroneous connection will occur in which the signal from node (E) to node (C) is transmitted to the lower order group via node (E). [0014] Therefore, (1) when multiple failures occur, identify the location of the failure and (2) Find the node that the signal does not reach due to the failure (signal unreachable node) from the ring topology, (3) then refer to the squelch table, and check whether the node entered in the squelch table is the signal unreachable node. , (4) Squelch is executed if the node has not reached the signal. The ring topology is an array of node names constituting the ring network starting from the node of interest and arranging them in order in the clockwise direction. FIG. 34 shows the ring topology RTG of the node (E). From the failure location and ring topology RTG in Fig. 34, it is clear that the node that has not reached the signal from node (E) has node ID = 9,6,4,1,14,3. Check if the Source node and Destination node entered in the squelch table SQTL-E of node (E) match the signal unreachable node. As a result, the node (C) with node ID = 14 and the node (A) with node ID = 4 become signal unreachable nodes, so squelch is executed. That is, at the switching nodes (D), (E), (F), and (G), P-AIS is inserted into the channel signal after the bridge and the channel signal after the switch, respectively, and squelch is executed. [0015] Construction of ring topology FIG. 35 is an explanatory diagram of ring topology construction, and as shown in FIG. 35 (A), an identification number is assigned to each node in a system in which four nodes (A) to (D) are connected by a ring transmission line RL. Give. For example, it is assigned as node (A) ID = 15, node (B) ID = 3, node (C) ID = 7, and node (D) ID = 8. Next, as shown in Fig. 35 (B), (1) the node (A) that instructs the construction of the ring topology (ring map) has the number of inserted nodes as 1, and the ID of its own node = 15. Is added to the first column to send the ring topology frame RTGF, for example, clockwise. (2) Next, the node (B) sends a ring topology frame RTGF in which the number of inserted nodes is 2 and the own node ID is inserted next to the ID of the node (A). (3) Similarly, the node (C) sends a ring topology frame RTGF in which the number of inserted nodes is 3 and the own node ID is inserted next to the ID of the node (B), and (4) the node ( D) sets the number of inserted nodes to 4, and sends a ring topology frame RTGF that inserts its own node ID next to the ID of node (C). [0016] (5) Node (A) identifies that it has made a round because the first insertion node ID is its own node ID, and as shown in Fig. 35 (C), it is the end of the ring topology frame RTGF. Is sent with the END flag added to, and each node is notified of the completed ring topology frame. Each node that receives this ring topology frame constructs a ring topology with its own node at the head. For example, the ring topology for node (A) is "15,3,7,8", for node (B) it is "3,7,8,15", and for node (C) it is "7,8,15,3". , Node D is "8,15,3,7". By constructing this ring topology, it becomes easy to send the local node ID and the target node ID in K1 and K2 bytes by the APS protocol. [0017] [Problems to be Solved by the Invention] In the conventional ring network, the VT channel is fixedly assigned to the user. Therefore, even if communication becomes impossible due to the occurrence of multiple failures and squelch is executed on a predetermined channel by the BLSR method, the traffic of other channels flowing through the ring network is not affected. That is, even if squelch is executed on the node causing loopback due to a failure and P-AIS is inserted into the channel, the traffic of other channels is not affected. However, in a ring network in which the VT channel is fixedly assigned to the user as in the conventional example, if the user does not communicate, the bandwidth of the user channel (1.728 Mbps bandwidth in VT1.5) is unused and the bandwidth is effectively utilized. I can't plan. Therefore, a ring network has been proposed in which an arbitrary connection is dynamically set in a transmission line having a free band for communication. This ring network maps packets (IP packets, ATM cells, etc.) having various connection IDs to the payload of a POS (Packet over Sonet or Packet over SDH) frame and transmits them. [0018] However, the proposed ring network has a problem that useless traffic flows in the ring in the event of multiple failures. FIG. 36 is an explanatory diagram of problems of such a ring network, (A) is a route explanatory diagram of packets (assumed to be ATM cells) of a ring network in which a failure has not occurred, and (B) is between nodes FG and DE. It is an explanatory diagram of the P-AIS route when a failure occurs, and the dotted line is the route through which P-AIS flows. Now, consider the case where P-AIS is inserted by executing squelch on node G that is causing loopback in the same way as the BLSR method in conventional Sonet (SDH). [0019] The ATM cell inserted from node A passes through node H and loops back at node G, but P-AIS is inserted due to multiple ring failures and communication continues (dotted line display). However, if squelch is executed on the loopback node G, a normal ATM cell will flow in the section from the insert node to the ring (node A) to the node that causes the loopback (node G) (solid line). display). Since this ATM cell is discarded at the loopback node by squelch, useless traffic TRF will flow in the ring. The packet communication network by POS is characterized in that when the bandwidth is free, the bandwidth is allocated to the connection request by the best F auto type service, and the bandwidth can be effectively used by this. For this reason, it is necessary to avoid sending useless data as much as possible. [0020] From the above, an object of the present invention is to prevent unnecessary traffic (packets) from flowing in the ring network during squelch execution. Another object of the present invention is that when the insert transmission device stops sending a packet to the ring network and executes squelch, an irreparable failure occurs for the lower group side source of the packet. Is to be able to notify. Another object of the present invention is to enable each transmission device to determine that a failure has occurred at a plurality of points in the network. Another object of the present invention is to make it possible to identify the drop transmission device for each connection, thereby easily determining that communication between the insert transmission device and the drop transmission device has become impossible for each connection and squelch. Is to be able to do. Another object of the present invention is to enable squelch to be performed in a point-to-multipoint drop connection in which the same packet is transmitted from one insert transmission device to a plurality of drop transmission devices. Another object of the present invention is to enable squelch to be executed in a multipoint-to-point insert connection in which packets are transmitted from a plurality of insert transmission devices to one drop transmission device using the same connection ID. Is. [0021] [0021] [Means for solving problems]<u style="single">In the present invention, a plurality of transmission devices are connected in a ring shape so as to be able to transmit in each of the upstream and downstream directions, a work band and a protection band are allocated in each direction, and a transmission signal is transmitted using the protection band in the event of a transmission line failure. It is a transmission device in a network that loops back and relieves, and it is a failure occurrence detection means that detects that a failure has occurred at multiple points on the transmission line and also finds a signal unreachable range that the signal does not reach due to multiple points of failure. Communication between the insert transmission device that incorporates the packet input from the next group side into the higher order group signal and sends it to the transmission line and the drop transmission device that takes out the packet from the higher order group signal and sends it to the lower order group side cannot be relieved due to a transmission line failure. An unresolvable detection means that detects whether or not it has become possible based on whether or not the drop transmission device exists in the signal unreachable range. The packet transmission stop means to stop, the connection in the direction of inserting the packet into the transmission line and the connection in the direction of taking out the packet from the transmission line and transmitting the packet are set as a pair, and when the rescue impossible state is reached, the paired connection is set. It is provided with a failure notification means for sending a failure notification packet to a packet source on the lower order group side via the channel.</u><u style="single">In a point-to-multipoint drop connection that transmits the same packet from one insert transmission device to multiple drop transmission devices, when the same connection ID is used in different spans of the network, the transmission device moves in the packet transmission direction. A means for holding the device ID of the drop transmission device farthest from the insert transmission device is provided, and the unresolvable detection means of the insert transmission device is such that the farthest end drop transmission device of the held packet does not have the signal. When it is within the reach, it is judged that the rescue is impossible.</u><u style="single">In a point-to-multipoint drop connection that transmits the same packet from one insert transmission device to multiple drop transmission devices, if the same connection ID is not used in different spans of the network, the transmission device will move in the packet transmission direction. A means for holding the device ID of the drop transmission device closest to the insert transmission device is provided, and the unresolvable detection means of the insert transmission device is such that the latest end drop transmission device of the held packet has not reached the signal. When it is in the range, it is judged that it cannot be rescued.</u>[0025] BEST MODE FOR CARRYING OUT THE INVENTION (A) Transmission device configuration (a) Overall configuration FIG. 1 is a configuration diagram of the transmission device of the present invention, 51.₁~51₄Is the input side ring interface part (ring IF part) of the higher order group to which the transmission line is connected, 52 is the ATM switch part, 53₁~53₄Is the output side ring IF section of the higher order group to which the transmission line is connected, 54 is the monitoring control section, 55₁~ 55n is the low-order group input side low-speed IF section (tributary IF section), 56₁~ 56n is the low-speed IF section whose output is in the low-order group. The BLSR system of the ring network includes (1) 2 Fiber-BLSR system and (2) 4-Fiber BLSR system, and the transmission device in Fig. 1 shows the case of 4-Fiber BLSR system. [0026] As shown in Fig. 2 (A), the 2-Fiber BLSR method uses one transmission line (fiber) in each of the WE and EW directions, and each transmission line has a working line and a spare line (extra or extra). The band of protection) is allocated, and when a failure occurs in one transmission line, it loops back and transmits a signal through the spare band of the other transmission line. [0027] As shown in Fig. 2 (B), the 4 Fiber-BLSR method uses two transmission lines (fibers) in the WE direction and EW direction, respectively, and the current transmission lines ULWI and ULWO are on the input / output side in the WE direction. , The spare transmission lines ULSI and ULSO are provided, and the current transmission lines DLWI, DLWO and the spare transmission lines DLSI and DLSO are provided on the input / output side in the EW direction. In the 4 Fiber-BLSR method, the current and spare fibers are housed in different fibers. It is different from the BLSR method. In 2 Fiber, the active bandwidth (work bandwidth) is halved and protected, so the traffic to secure the bandwidth must be accommodated in 1/2 or less of the total. 4-Fiber can loop back all traffic using protective fiber. [0028] (b) Input side ring IF section Input side ring IF section 51₁~51₄Each has the same configuration, and includes a K1 / K2 reception processing unit 61, an input side VRT (Virtual Routing Table) 62, and a reception data processing unit 63. The K1 / K2 reception processing unit 61 receives the frame signal of Sonnet or SDH (hereinafter referred to as Sonet), performs photoelectric conversion, separates the ATM cell and the overhead from the Sonet frame, and K1 / K2 included in the section overhead. Input K2 bytes to the monitoring control unit 54. FIG. 3 is a configuration diagram of a Sonet frame used for the ring network of the present invention, and shows the format of OC-3. However, Fig. 3 is an example, and OC-48, OC96, .. etc. are actually used. SONET OC-3 (STS-3) frames consist of 9x270 bytes, the first 9x9 bytes are Section Overhead SOH, and the rest are Path Overhead (Path). Overhead) POH and payload (payload) PL. As shown in FIG. 31, the section overhead SOH contains various control bytes such as K1 / K2 bytes, and the payload PL is mapped to the ATM cell CL. [0029] The input side VRT62 corresponds to the VPI / VCI (connection ID) included in the header of the ATM cell, and as shown in Fig. 4 (A), 1 in-device connection identifier (device CID), 2 enable. (enable) Holds data, 3 routine tag (output port number), etc. The enable data is "1" when the use of VPI / VCI is permitted, and "0" when the use is not permitted. The reception data processing unit 63 converts the VPI / VCI of the cell header into the device CID, adds a routine tag to the cell, and outputs the data to the ATM switch 52. [0030] (c) Output side ring IF section Output side ring IF part 53₁~53₄Each has the same configuration, and includes an output side VRT65, a transmission data processing unit 66, and a K1 / K2 transmission processing unit 67. As shown in Fig. 5 (B), the output side VRT65 stores the VPI / VCI (connection ID) corresponding to the device CID, and the transmission data processing unit 66 stores the device CID of the cell input from the switch 52 as the output side VRT65. Converted to VPI / VCI by reference, the K1 / K2 transmission processing unit 67 creates an overhead containing K1 / K2 bytes according to the instruction from the monitoring control unit 54, maps the ATM cell to the payload of the Sonet frame, and then maps the ATM cell to the payload. The frame signal is lightning-converted and sent to the transmission line. [0031] (d) Input side low speed IF section Input side low speed IF section (tributary IF section) 55₁Each of ~ 55n has a received data processing unit 71 and an uplink VRT72, respectively. The uplink VRT72 corresponds to the VPI / VCI (connection ID) included in the header of the ATM cell input from the tributary side, and as shown in Fig. 5, 1 In-device connection identifier (device CID), 2 Holds enable data, 3 routine tag (output port number), 4 squelch table information, etc. The enable data is "1" when the use of VPI / VCI is permitted, and "0" when the use is not permitted. The squelch table information indicates the identifier (destination node ID: Dest Node ID) of the drop transmission device that drops the ATM cell input from the tributary side, and is used when determining whether or not to execute the squelch. [0032] The received data processing unit 71 converts the VPI / VCI of the cell header into the device CID, adds a routine tag to the cell, outputs it to the ATM switch 52, and executes squelch in hardware using the squelch table information. Judge whether or not. FIG. 7 is a hardware configuration diagram for determining whether or not to execute squelch. The monitoring control unit 54 is the ring IF unit 51.₁,51₃When it is detected that a failure has occurred at multiple points in the ring network by referring to the K1 / K2 bytes to be input, the unreachable range data including the node ID that identifies the node that cannot communicate is output. The storage unit 71a of the reception data processing unit 71 stores this unreachable range data, and the register 71b reads and stores the destination node ID corresponding to the VPI / VCI of the ATM cell input from the tributary side from the uplink VRT72 and stores it. The 71c also stores enable data. The comparison unit 71d compares the destination node ID with the node ID included in the unreachable range data, and checks whether the destination node (drop transmission device) is a node within the unreachable range. [0033] The node ID that matches the destination node ID is not included in the unreachable range data, that is, the insert transmission device of interest can communicate with the drop transmission device (the output of comparison unit 71d is "0"). If the enable data is "1", the ANDGate 71e outputs a high-level read enable signal REN. As a result, the received data processing unit 71 changes the VPI / VCI of the ATM cell input from the tributary side to the device CID, adds a routine tag to the header, and inputs it to the switch unit 52. [0034] On the other hand, if the node ID that matches the destination node ID is included in the unreachable range data, that is, if the insert transmission device of interest cannot communicate with the drop transmission device (the output of the comparison unit 71d is "". 1 "), the read enable signal REN is not output assuming that an irreparable failure has occurred. As a result, the received data processing unit 71 does not output the ATM cell input from the tributary side to the switch, that is, does not send it to the transmission line (squelch execution). Further, the device CID notification unit 71f notifies the monitoring control unit 54 of the device CID according to the VPI / VCI executed by the squelch. The monitoring control unit 54 stores this notified device CID and periodically inputs it to the low-speed IF unit 56 on the output side. When the device CID is input from the monitoring control unit 54, the low-speed IF unit 56 obtains the VPI / VCI corresponding to the device CID paired from the downlink VRT75, and obtains the OAM cell (P-AIS) of the VPI / VCI. Create it, send it to the tributary side, and notify the downstream terminal. [0035] (e) Output side low speed IF section Output side low speed IF section 56₁Each of ~ 56n has the same configuration, and has a downlink VRT75 and a transmission data processing unit 76. As shown in Fig. 6, the downlink VRT75 stores the VPI / VCI of the ATM cell to be sent to the tributary side in correspondence with the device CID. The relationship between this device CID and VPI / VCI is as follows: Output side low speed IF section 56₁Input side low speed IF section 55 corresponding to ~ 56n₁The relationship between the VPI / VCI stored in the upstream VRT72 of ~ 55n and the device CID is simply arranged in reverse. That is, the connection settings are set as a pair for uplink / downlink. The transmission data processing unit 76 refers to the downlink VRT75, converts the device CID of the ATM cell input from the switch 52 into VPI / VCI, and sends it to the tributary side. Further, the transmission data processing unit 76 periodically receives the device CID corresponding to the VPI / VCI that executed the squelch from the monitoring control unit 54, obtains the VPI / VCI corresponding to the device CID from the downlink VRT75, and obtains the VPI. Create an OAM cell (P-AIS) with / VCI and notify the terminal on the tributary side. [0036] (B) First Example of Squelch Execution (a) First Example 8 and 9 are explanatory views of the first embodiment in which squelch is executed by the insert transmission device (insert node), and a ring network is configured by nodes A to H. During normal operation, communication is performed between each node as shown by the solid line in Fig. 8. In such a case, as shown in FIG. 9, when a multiple failure occurs between the node DE and the node FG and a connection that cannot communicate occurs, in the first embodiment, the squelch processing for the connection is performed by the insertion node A of the connection. , E. That is, it stops sending the packet of the connection to the transmission line. This prevents unnecessary cells that cannot communicate from flowing in the ring and effectively utilizes the bandwidth. [0037] In the BLSR method in the conventional Sonet (SHD), squelch is executed by inserting P-AIS into the connection that may be erroneously connected at the loopback node as described in Fig. 36 (B). However, such a method causes unnecessary traffic to flow and wastes bandwidth. Therefore, in the present invention, squelch is executed by performing an operation of stopping cell transmission at the insert node at the entrance of the ring for a connection that may be erroneously connected, thereby eliminating the generation of unnecessary traffic in the ring. Effectively utilize the bandwidth in the ring. [0038] (b) Modification example As shown in Fig. 36 (B), in the conventional BLSR method in Sonet (SDH), P-AIS is inserted at the loopback node, and this P-AIS is also transmitted downstream (direction from the ring). As a result, it is communicated that the downstream device has a failure. Even in the POS ring transmission method, it is necessary to send a network failure notification signal downstream to the connection in the squelch state. However, if the transmission of the ATM cell is stopped at the entrance to the ring for the connection in the squelch state as in the first embodiment of FIG. 9, is the drop node at the exit of the ring simply in the state where there is no ATM cell? , It is not possible to determine whether the ATM cell is not coming by squelch, and it is not possible to identify the occurrence of a failure. To solve this problem, set the connection settings as an uplink / downlink pair. [0039] Normally, the connection setting is always set in the uplink / downlink pair, so as shown in Fig. 10, data is stored in the insert node for the uplink connection (direction to insert into the ring) for which squelch is determined to be necessary due to the occurrence of multiple failures. The output to the ring is stopped, and for the paired downlink connection (direction from the ring), the insert node performs processing to send a failure notification signal such as P-AIS to the lower-order group side downstream direction. Achieves squelch in the downstream direction. [0040] (c) Processing flow FIG. 11 is a squelch execution processing flow of the first embodiment. The monitoring control unit 54 is the ring IF unit 51.₁,51₃Based on the K1 / K2 bytes input from the K1 / K2 reception processing unit 61 of the above, it is checked whether or not a failure has occurred at multiple points in the ring network (step 101). If no failure occurs at a plurality of locations, the received data processing unit 63 converts the VPI / VCI of the input cell into the device CID, adds a routine tag and inputs it to the switch 52, and inputs the switch to the output side ring IF. It is sent to the transmission line through the unit (step 102). On the other hand, if it is found from K1 / K2 bytes that a failure has occurred at multiple points in the network, the monitoring and control unit 54 refers to the built-in ring topology to find a node from which the signal has not been reached from its own node. The unreachable range data is input to the received data processing unit 71 of the low-speed IF unit (step 103). [0041] As described in FIG. 7, the received data processing unit 71 checks whether the node ID of the drop node dropped by the ATM cell input from the tributary side matches the node ID included in the unreachable range data. That is, it checks whether squelch is required for the cell input from the tributary side (step 104). If it is not necessary to execute the squelch, that is, if the insert node and the drop node are not separated due to a failure and communication is possible, the process of step 102 is performed. On the other hand, if it is necessary to execute squelch, the received data processing unit 71 stops inputting the corresponding ATM cell input from the tributary side to the ATM switch 52, and prevents the cell from being sent to the transmission line (step). 105). Further, the received data processing unit 71 obtains the device CID corresponding to the VPI / VCI of the corresponding cell from the uplink VRT 72 and notifies the monitoring control unit 54. The monitoring control unit 54 stores the notified device CID, and periodically inputs the device CID to the low-speed IF unit 56 on the output side. The low-speed IF unit 56 obtains the VPI / VCI corresponding to the device CID paired from the downlink VRT75 each time the device CID is input from the monitoring control unit 54, and obtains the OAM cell (P-AIS) of the VPI / VCI. It is created and sent to the tributary side, and notified to the terminals downstream on the lower group side (step 106). Periodic transmission of the OAM cell (P-AIS) in step 106 continues until the failure is recovered. [0042] (d) Multiple failure detection processing In the first embodiment, the squelch is executed at the insert node, so it is necessary for all the nodes to recognize the location of the failure. Therefore, the intermediate node (node with no failure in the connection transmission lines on both sides) monitors the APS bytes (K1 / K2) flowing in both directions of WE and EW to determine where the failure has occurred. .. · Single point of failure detection at intermediate nodes When a failure occurs between node FE in Fig. 12 (A), node E uses APS bytes (K1 / K2 bytes) for node F to notify SF-R of a long path (S / L bit = "1"). While doing (APS: SF-R / F / E / L), short path (S / L bit = "0") SF-R notification (SF-R / F / E / S / RDI). When node F receives a short RDI notification from node E, it sends a long SF-R notification to node E (APS: SF-R / E / F / L). The middle node (A ~ D, G ~ H) monitors ASP bytes in both directions of EW and WE, and if the source ID of one APS byte and the destination ID of the other APS byte match in both directions, it is single. Judge as a failure. [0043] -Multiple failure detection at intermediate nodes When a single failure occurs in Fig. 12 (A) and a failure occurs between nodes AB as shown in Fig. 12 (B), node B sends a long-path SF-R notification in APS bytes (SF-R / A / B / L), short path SF-R notification (SF-R / A / B / S / RDI). When node A receives an RDI notification from node B with a short path, it sends SF-R notification to node B with a long path (APS: SF-R / B / A / L). As a result, when viewed from the intermediate node G, SF-R / B / A / L is received counterclockwise, and SF-R / E / F / L is received clockwise. Therefore, since the source ID of one APS byte and the destination ID of the other APS byte do not match, it is judged as a multiple failure. The farthest node seen from node G is the source ID (node A and node F) of the received APS byte. After this farthest node, it is judged that the signal has not reached the range from node G. [0044] · Single / multiple fault detection on faulty adjacent nodes The above is the case of detecting the occurrence of a single / multiple failure in the intermediate node, but the detection of a single / multiple failure in the node (adjacent node with a failure) in which a failure occurs in one of the connection transmission lines is as follows. Will be done. That is, referring to the single point of failure in FIG. 12 (A), the failure adjacent nodes E and F both receive the SF-R notification addressed to themselves with a long path (S / L bit = "1") in APS bytes. Further, referring to the multiple failures in FIG. 12 (B), the failure adjacent nodes E and F both receive the SF-R notification of APS bytes and long path not addressed to themselves. Therefore, a single point of failure / multiple points of failure is detected depending on whether or not the long-pass SF-R notification is addressed to oneself. [0045] FIGS. 13 to 15 are multiple failure (multiple failure) occurrence detection processing flows. The monitoring control unit 54 of the node of interest checks whether a transmission line failure has occurred (step 201), and if it detects the occurrence of a failure, it transmits short-path and long-path SF-Rs to adjacent nodes that sandwich the failure point (step 201). 202). Then, when the monitoring control unit 54 of the node of interest receives the SF-R notification from another node (step 203), it checks whether the SF-R notification is the SF-R notification addressed to its own node (step 204). If it is not addressed to the local node, it is determined that multiple failures have occurred (step 205), and if it is addressed to the local node, it is checked whether it is a long-path SF-R notification or a short-path SF-R notification (step 206). If it is a long path (S / L bit = "1"), it is determined that there is a single failure (step 207), and if it is a short path (S / L bit = "0"), a failure occurs in both transmission lines. It is determined that the isolation rate failure has occurred (step 208). [0046] If no failure is detected in step 201, it is checked whether a short path SF-R notification has been received (step 211). If the short-pass SF-R notification has been received, the long-pass SF-R is sent to the short-pass SF-R source (step 212). Then, if SF-R is received from another node (step 213), it is checked whether the SF-R notification is an SF-R notification addressed to the own node (step 214). If it is not addressed to the local node, it is determined that multiple failures have occurred (step 215), and if it is addressed to the local node, it is checked whether it is a long-path SF-R notification or a short-path SF-R notification (step 216). If it is a long path, it is determined that it is a single point of failure (step 217), and if it is a short path, it is determined that it is an isolate rate failure in which a failure occurs in both transmission lines (step 218). [0047] If the short-pass SF-R notification has not been received in step 211, it is checked whether the long-pass SF-R notification in the EW direction and the WE direction has been received (step 221). If it is not received, it is determined that no failure has occurred (step 222). However, if a long-pass SF-R notification in the EW and WE directions is received, it is checked whether the insert node of one SF-R notification and the drop node of the other SF-R match (step 223). If they match, it is determined that a single failure has occurred (step 224), and if they do not match, it is determined that multiple failures have occurred. For example, node E in FIG. 12B detects the occurrence of multiple failures in steps 201 to 208 above, node F detects the occurrence of multiple failures in steps 211 to 218, and intermediate nodes G and H in steps 221 to 225. Detect a failure. [0048] (C) Second Example of Squelch Execution Point-to-multipoint connection is a communication mode in which the same packet is simultaneously transmitted from one node A to many nodes G, F, E, and C as shown by the communication path PTMC in Fig. 16, and it is necessary to set a connection for each destination. Effective use of bandwidth can be achieved. Further, the multi-two-point connection is a form in which packets are transmitted from a large number of nodes to one node using the same connection ID as shown in the communication path MTPC in FIG. 16, and has an advantage that the connection ID can be saved. [0049] (a) Point-to-multipoint connection -When using the same connection ID in different spans POS (Packet over In ring transmission by Sonet), when point-to-multipoint connection is set and the same connection ID (VPI / VCI for ATM cell, IP address for IP packet) is used in different spans, mistakes occur due to multiple failures. A connection may occur. For example, in FIG. 17, a packet looped back at node F is looped back at node B and merges with another connection, resulting in a misconnection. When such multiple failures occur, conventional Sonet (SDH) performs squelch processing by inserting P-AIS at the loopback node F, but when squelch is executed at the loopback node in the ring network by POS as well. Useless traffic will flow in the ring. [0050] Therefore, in the present invention, the squelch processing for the point-to-multipoint connection is performed by the insert node that inserts the packet into the ring to prevent unnecessary packets from flowing in the ring and effectively utilize the bandwidth in the ring. That is, when multiple failures occur, the insert node of the point-to-multipoint connection determined to require squelch performs an operation of stopping packet output to the ring to execute squelch. In the example of Figure 17, squelch is performed on insert node A. Specific methods of squelch execution in the case of using the same connection ID in different spans in point-to-multipoint connection, insert a squelch table information of the uplink VRT72 of Figure 5 to set the node ID of the farthest end drop node from Tonodo Is. In the point-to-multipoint connection example shown in Fig. 16, the node ID of the farthest drop node C is set in the squelch table information field of the upstream VRT72 of insert node A. In this way, if a failure occurs between the insert node A and the farthest drop node C, and another failure occurs anywhere, the insert node A sends a multicast packet to the transmission line. Stop (execute squelch). This eliminates the need to individually set the squelch for the number of drops in a point-to-multipoint drop connection. [0051] -When the same connection ID is not used in different spans In ring transmission by POS (Packet over Sonet), if the same connection ID is not used in different spans, there is no possibility of misconnection. For example, figure Packets looped back at node F at 18 are not looped back at node B, so no misconnection occurs. In other words, during multiple failures, there is no need for squelch if both insert nodes A and drop nodes G, F of the point-to-multipoint connection are present in the fragmented ring. Therefore, in the present invention, when the same connection ID is not used in different spans in the point-to-multipoint connection, when the drop node closest to the insert node (latest drop node) exists in the signal unreachable range in the packet transmission direction. When it is determined that the rescue is impossible, the insert node A stops sending the multicast packet to the transmission line (execution of squelch). Specifically, the node ID of the latest drop node is set from the insert node as the squelch table information of the upstream VRT72 in FIG. In the example of FIG. 16, the node ID of the latest drop node G is set in the squelch table information field of the upstream VRT72 of the insert node A. In this way, only when a failure occurs between the insert node A and the farthest drop node G and another failure occurs elsewhere and communication becomes impossible, multicast is performed on the insert node A. Stop sending packets to the transmission line (squelch execution). [0052] As described above, the insert node can continue to communicate with the drop node existing between the insert node and the failure point. As a result, as shown in FIG. 18, squelch is not performed even at the time of multiple failures between the nodes BC and between the nodes E and F, and the connection between the nodes AGF is maintained. By using this method, it is not necessary to individually (as many as the number of drops) squelch settings for point-to-multipoint drop connections. [0053] -Point-to-multipoint squelch execution processing flow FIG. 19 is a point-to-multipoint squelch execution processing flow. Set the drop node ID of the multicast packet in the squelch table information field of the upstream VTR72 of the insert node (step 301). Specifically, it checks whether the same connection ID is allowed to be used in different spans of the ring network (step 301a). If the same connection ID is allowed to be used in different spans, set the farthest drop node ID of the point-to-multipoint connection in the squelch table information field of the uplink VTR72 (step 301b). However, if the same connection ID is not allowed to be used in different spans, the most recent drop node ID of the point-to-multipoint connection is set in the squelch table information field of the uplink VTR72 (step 301c). [0054] In such a state, the monitoring control unit 54 checks whether a failure has occurred at a plurality of locations in the ring network based on the K1 / K2 bytes input from the K1 / K2 reception processing unit 61 of the ring IF unit 51 (step 302). If no failure occurs at a plurality of locations, the received data processing unit 63 converts the VPI / VCI of the input cell into the device CID, adds a routine tag and inputs it to the switch 52, and inputs the switch to the output side ring IF. It is sent to the transmission line through the unit (step 303). On the other hand, if it is found from K1 / K2 bytes that a failure has occurred at multiple points in the network, the monitoring and control unit 54 refers to the built-in ring topology to find a node from which the signal has not been reached from its own node. The unreachable range data is input to the received data processing unit 71 of the low-speed IF unit (step 304). As described in FIG. 7, the received data processing unit 71 checks whether the drop node ID corresponding to the VPI / VCI of the cell input from the tributary side matches the node ID included in the unreachable range data. For example, if the cell input from the tributary side is a multicast cell, squelch is required by checking whether the drop node ID corresponding to the VPI / VCI of the multicast cell matches the node ID included in the unreachable range data. Check for existence (step 305). [0055] If it is not necessary to execute squelch, that is, if the insert node of the point-to-multipoint connection and the nearest drop node or the farthest drop node are not separated due to a failure and communication is possible, the process of step 303. I do. On the other hand, if squelch execution is required, the received data processing unit 71 stops inputting the multicast cell input from the tributary side to the ATM switch 52 to prevent the cell from being sent to the transmission line (step 306). .. In addition, the received data processing unit 71 obtains the device CID corresponding to the VPI / VCI of the corresponding multicast cell from the uplink VRT72 and notifies the monitoring control unit 54. The monitoring control unit 54 stores the notified device CID, and periodically inputs the device CID to the low-speed IF unit 56 on the output side. Each time the device CID is input, the low-speed IF unit 56 obtains the VPI / VCI corresponding to the device CID paired from the downlink VRT75, creates an OAM cell (P-AIS) of the VPI / VCI, and tributary. It is sent to the side and notified to the downstream terminal (step 307). Periodic transmission of the OAM cell (P-AIS) in step 307 is continued until the failure is recovered. [0056] (b) Multi-point two-point connection -When using the same connection ID in different spans When a multipoint to point connection is set in ring transmission by POS and the same connection ID is used in different spans, a misconnection may occur due to multiple failures. In FIG. 20, a packet looped back at node B is looped back at node F and merges with another connection to cause a misconnection. When such multiple failures occur, in the conventional Sonet (SDH), squelch processing is performed by inserting P-AIS at the loopback node, but when squelch is executed at the loopback node in the ring network by POS as well. Useless traffic will flow in the ring. [0057] Therefore, in the present invention, the bandwidth in the ring is effectively utilized by performing the squelch processing for the multipoint to point connection at each insert node that inserts the packet into the ring. That is, when multiple failures occur, each insert node of the multipoint-to-point connection determined to require squelch executes squelch by performing an operation of stopping packet output to the ring. In the example of FIG. 20, squelch is executed on nodes F, G, nodes C, E, and node A. [0058] [0058] -When the same connection ID is not used in different spans In ring transmission by POS (Packet over Sonet), if the same connection ID is not used in different spans, there is no possibility of misconnection. For example, in Figure 21, packets looped back at node B are not looped back at node F and no misconnection occurs. In other words, during multiple failures, there is no need for squelch if both insert and drop nodes are present in the multipoint to point connection within the fragmented ring. However, when the insert node is separated from the drop node for the multipoint two-point connection at the time of multiple failures (nodes D and E in FIG. 21), the output of the packet to the ring is stopped at the insert nodes D and E. (Squelch execution), effectively use the bandwidth in the ring. [0059] Therefore, in the present invention, when the same connection ID is not used in different spans in the multipoint-to-point connection, the drop node ID is set as the squelch table information of the upstream VRT72 of each insert node. In this way, due to multiple failures, squelch is executed for the insert node separated from the drop node, and squelch is not executed for the insert node that is not separated from the drop node. When a failure occurs between nodes BC and EF in FIG. 21, insert nodes C and E execute squelch, but insert nodes F and G do not execute squelch and the connection is maintained. [0060] Pair setting A connection squelched for a multipoint connection needs to send a failure notification signal such as P-AIS to the downstream (direction from the ring). However, if the data is stopped at the entrance to the ring, the drop node at the exit of the ring will not receive the failure notification. To solve this problem, the connection setting is solved by setting a point-to-multipoint drop connection as a pair for a multipoint-to-point insert connection. For connections that are determined to require squelch when multiple failures occur, packets are stopped for upstream connections (direction of insertion into the ring), and for downlink connections set in pairs (direction of exit from the ring). Performs processing to send a failure notification signal such as P-AIS. [0061] -Multipoint-to-point squelch execution processing flow FIG. 22 is a multipoint-to-point squelch execution processing flow. Set the drop node ID in the squelch table information field of the uplink VTR 72 of each insert node in the multipoint to point connection (step 401). Specifically, it checks whether the same connection ID is allowed to be used in different spans of the ring network (step 401a). If the same connection ID is allowed to be used in different spans, set the squelch execution flag in the squelch table information field of the uplink VTR72 according to the packet of the multipoint to point connection (step 401b). As a result, in the case of a multipoint to point connection, squelch is executed unconditionally if multiple failures occur. However, if the use of the same connection ID is not allowed in different spans, the drop node ID is set in the squelch table information field of the uplink VTR72 according to the packet of the multipoint to point connection (step 401c). [0062] In such a state, the monitoring control unit 54 checks whether a failure has occurred at a plurality of locations in the ring network based on the K1 / K2 bytes input from the K1 / K2 reception processing unit 61 of the ring IF unit 51 (step 402). If no failure occurs at multiple locations, the received data processing unit 63 converts the VPI / VCI of the input cell to the device CID, adds a routing tag and inputs it to the switch 52, and inputs the switch to the output side ring IF. It is sent to the transmission line via the unit (step 403). [0063] On the other hand, if it is found from K1 / K2 bytes that a failure has occurred at multiple points in the network, the monitoring control unit 54 refers to the built-in ring topology and finds a node from which the signal has not been reached from its own node. The unreachable range data is input to the received data processing unit 71 of the low-speed IF unit (step 404). The received data processing unit 71 reads the squelch table information corresponding to the VPI / VCI of the cell input from the tributary side from the uplink VRT72, and checks whether the squelch table information is the squelch execution flag. If it is a drop node ID instead of the squelch execution flag, as described in FIG. 7, it is checked whether the drop node ID matches the node ID included in the unreachable range data. If the squelch table information is the drop node ID instead of the squelch execution flag and this drop node ID is not included in the unreachable range data, the process of step 403 is performed. That is, if the insert node and the drop node of the multipoint to point connection are not separated due to a failure and communication is possible, the process of step 403 is performed. [0064] On the other hand, if (1) the squelch table information is the squelch execution flag, or (2) the squelch table information is the drop node ID instead of the squelch execution flag, and this drop node ID is included in the unreachable range data. For example, squelch execution is required, and the data processing unit 71 stops inputting the cell input from the tributary side to the ATM switch 52 to prevent the cell from being sent to the transmission line (step 406). Further, the received data processing unit 71 obtains the device CID corresponding to the VPI / VCI of the corresponding cell from the uplink VRT and notifies the monitoring control unit 54. The monitoring control unit 54 stores the notified device CID, and periodically inputs the device CID to the low-speed IF unit 56 on the output side. Each time the device CID is input, the low-speed IF unit 56 obtains the VPI / VCI corresponding to the device CID paired from the downlink VRT75, creates an OAM cell (P-AIS) of the VPI / VCI, and tributary. It is sent to the side and notified to the downstream terminal (step 407). Periodic transmission of the OAM cell (P-AIS) in step 407 is continued until the failure is recovered. Although the case where an ATM cell is mainly used as a packet has been described above, it goes without saying that the present invention can be applied to a transmission device that uses an IP packet or other packets. [0065] Additional notes (Appendix 1) Multiple transmission devices are connected in a ring shape so that they can be transmitted in each of the upstream and downstream directions, and the work band and protection band are allocated in each direction, and the transmission signal is transmitted using the protection band in the event of a transmission line failure. In a network that loops back and rescues Communication between the insert transmission device that incorporates the packet input from the lower-order group side into the higher-order group signal and sends it to the transmission line and the drop transmission device that extracts the packet from the higher-order group signal and sends it to the lower-order group side is relieved due to a transmission line failure. A means of detecting if it has become impossible, A packet transmission stop means for stopping the transmission of the packet to the transmission line when the relief becomes impossible. A ring-shaped network transmission device characterized by being equipped with. [0066] (Appendix 2) Further, it is provided with a failure occurrence detecting means for detecting that a failure has occurred at a plurality of points on the transmission line and for finding a signal unreachable range in which a signal does not reach due to a failure at a plurality of points. The unrecoverable detection means of the insert transmission device determines that the drop transmission device is unrecoverable when the drop transmission device is present in the signal unreachable range. The transmission device according to Appendix 1, which is characterized in that. (Appendix 3) An uplink connection and a downlink connection are set as a pair, and when the uplink connection becomes unrecoverable, a failure notification is sent to the packet source on the lower-order group side via the paired connection. Failure notification means for sending packets, The transmission device according to Appendix 1 or Appendix 2, characterized in that the device is provided with. [0067] (Appendix 4) The first transmission device that detects the failure of one of the upstream and downstream transmission lines is the first packet that notifies the failure occurrence to the second transmission device that sandwiches the failure occurrence point in that direction (Appendix 4). A second packet (long packet) is transmitted, a second packet (short packet) for notifying the occurrence of a failure is transmitted to the second transmission device in the second direction, and the first packet is received. In a network in which the transmission device transmits a third packet (long packet) for notifying the occurrence of a failure to the first transmission device, the failure occurrence detection means has multiple failures based on the destination of the long packet received from another node. Judge as occurrence, The transmission device according to Appendix 3, which is characterized in that. [0068] (Appendix 5) A table that holds the device ID of the device and the device ID of the packet drop transmission device is provided in correspondence with the packet connection ID. The unresolvable detection means of the insert transmission device obtains a drop transmission device for packets input from the lower order group side from the table due to the occurrence of a failure at a plurality of locations, and the drop transmission device exists in the signal unreachable range. When it is judged that relief is impossible, The transmission device described in Appendix 2, which is characterized in that. (Appendix 6) In a point-to-multipoint drop connection in which the same packet is transmitted from one insert transmission device to a plurality of drop transmission devices, when a communication remedy becomes impossible due to a transmission line failure, the insert transmission device changes. Stop sending the packet to the transmission line, The transmission device according to Appendix 1, which is characterized in that. [0069] (Appendix 7) In a point-to-multipoint drop connection in which the same packet is transmitted from one insert transmission device to multiple drop transmission devices, the device ID of the drop transmission device farthest from the insert transmission device in the packet transmission direction is set. Keep it on the table The unresolvable detection means of the insert transmission device obtains the farthest end drop transmission device of the packet from the table due to the occurrence of a failure at a plurality of locations, and cannot be relieved when the drop transmission device is in the signal unreachable range. Judge that it has become The transmission device according to Appendix 5, which is characterized in that. (Appendix 8) When the same connection ID is not used in different spans of the network in a point-to-multipoint drop connection in which the same packet is transmitted from one insert transmission device to multiple drop transmission devices. The unresolvable detection means of the insert transmission device is characterized in that it determines that the drop transmission device closest to the insert transmission device in the packet transmission direction is in the signal unreachable range and is determined to be unrecoverable. The transmission device described in Appendix 6. [0070] (Appendix 9) In a point-to-multipoint drop connection in which the same packet is transmitted from one insert transmission device to multiple drop transmission devices, if the same connection ID is not used in different spans of the network, the packet transmission direction Hold the device ID of the drop transmission device closest to the insert transmission device in the table. The unresolvable detection means of the insert transmission device obtains the latest end drop transmission device of the packet from the table due to the occurrence of a failure at a plurality of locations, and cannot be rescued when the drop transmission device is in the signal unreachable range. Judging that The transmission device according to Appendix 5, which is characterized in that. (Appendix 10) In a multipoint-to-point insert connection that transmits packets from multiple insert transmission devices to one drop transmission device using the same connection ID, communication became impossible due to multiple transmission line failures. When each insert transmission device stops sending the packet to the transmission line, The transmission device according to Appendix 1, which is characterized in that. [0071] (Appendix 11) In a multipoint-to-point insert connection that transmits packets from multiple insert transmission devices to one drop transmission device using the same connection ID, the same connection ID is used in different spans of the network. When not in use, the unrecoverable detection means of each insert transmission device determines that the drop transmission device is unrecoverable when it is in the signal unreachable range. The transmission device according to Appendix 1, which is characterized in that. (Appendix 12) In a multipoint-to-point insert connection in which packets are transmitted from multiple insert transmission devices to one drop transmission device using the same connection ID, the same connection ID is used in different spans of the network. If not used The drop transmission device ID is stored in the table of each insert transmission device. The unresolvable detection means of each insert transmission device obtains a multipoint-to-point drop transmission device from the table when a failure occurs at a plurality of locations, and cannot be relieved when the drop transmission device is within the signal unreachable range. The transmission device according to Appendix 5, wherein the transmission device is determined to have become. [0072] (Appendix 13) A multipoint-to-point insert connection and a point-to-multipoint drop connection are managed as a pair, and when a predetermined insert connection becomes unrecoverable, a failure notification packet is inserted into the paired drop connection. Failure notification means, The transmission device according to Appendix 6, which is characterized by being equipped with. [0073] [Effect of the invention] As described above, according to the present invention, when the insert node and the drop node are separated due to a transmission line failure and communication of a predetermined packet becomes impossible, the packet is stopped to be sent to the ring network, so that the squelch is executed. Useless traffic (packets) does not flow in the ring network, wasteful use of bandwidth is eliminated, and effective use of bandwidth can be achieved. Further, according to the present invention, when an upstream connection and a downstream connection are set as a pair and the upstream connection becomes unresolvable due to a transmission line failure and squelch is executed, the pair's downstream connection is set. Since the occurrence of the irreparable failure is notified to the packet transmission terminal on the lower group side via the system, the packet transmission terminal on the lower group side can stop the transmission of the packet thereafter. [0074] Further, according to the present invention, since the drop node ID of the packet is held together with the in-device ID corresponding to the connection ID in the table for converting the connection ID of the packet into the in-device ID, the insert node cannot be relieved. The possible detection means can easily find the drop node of the packet input from the lower order group side from the table when a failure occurs at a plurality of places, thereby checking whether the drop node exists in the signal unreachable range. It is possible to easily recognize whether or not the rescue is impossible. In addition, the squelch can be determined by hardware processing, which enables high-speed processing without imposing a burden on software. Further, according to the present invention, squelch can be executed in a point-to-multipoint drop connection in which the same packet is transmitted from one insert node to a plurality of drop nodes. Further, according to the present invention, squelch can be executed in a multipoint-to-point insert connection in which packets are transmitted from a plurality of insert nodes to one drop node using the same connection ID. [0075] Further, according to the present invention, a multipoint-to-point insert connection and a point-to-multipoint drop connection are set as a pair, and a predetermined insert connection becomes unresolvable due to a transmission line failure and squelch is executed. At that time, since the occurrence of the unresolvable failure is notified to the packet transmission terminal on the lower group side via the drop connection of the pair, the packet transmission terminal on the lower order group side stops transmitting the packet thereafter. be able to. [Simple explanation of drawings] FIG. 1 is a configuration diagram of a transmission device of the present invention. FIG. 2 is an explanatory diagram of 2 FIBER-BLSR method and 4 FIBER-BLSR method. FIG. 3 is an explanatory diagram of SONET OC-3 frame format. FIG. 4 is an explanatory diagram of an input side / output side VRT (Virtual Routing Table). FIG. 5 is an explanatory diagram of an upstream VRT. FIG. 6 is an explanatory diagram of a downlink VRT. FIG. 7 is a squelch execution discriminating circuit. FIG. 8 is an explanatory diagram of a communication path in a normal state. FIG. 9 is an explanatory diagram when squelch is executed at the insert node. FIG. 10 is an explanatory diagram of a failure notification method in the downstream direction. FIG. 11 is a squelch execution processing flow. FIG. 12 is an explanatory diagram of a failure detection principle at an intermediate node. FIG. 13 is a multiple failure occurrence detection processing flow (No. 1). FIG. 14 is a multiple failure occurrence detection processing flow (No. 2). FIG. 15 is a multiple failure occurrence detection processing flow (No. 3). FIG. 16 is an explanatory diagram of a multipoint connection. FIG. 17 is a point-to-multipoint connection explanatory diagram (with connection ID reuse). FIG. 18 is a point-to-multipoint connection explanatory diagram (no connection ID reuse). FIG. 19 is a point-to-multipoint connection squelch execution processing flow. FIG. 20 is an explanatory diagram of a multi-point to point connection (with reuse of connection ID). FIG. 21 is an explanatory diagram of a multi-point to point connection (no connection ID reuse). FIG. 22 is a squelch execution processing flow of a multipoint to point connection. FIG. 23 is an explanatory diagram of the STS-1 frame format. FIG. 24 is a schematic configuration diagram of an ADM transmission device. FIG. 25 is a ring configuration diagram. FIG. 26 is an explanatory diagram for relieving a disability. FIG. 27 is a first explanatory diagram of the APS protocol. FIG. 28 is a second explanatory diagram of the APS protocol. FIG. 29 is a third explanatory diagram of the APS protocol. FIG. 30 is a fourth explanatory diagram of the APS protocol. FIG. 31 is an explanatory diagram of K1 / K2 bytes. FIG. 32 is an explanatory diagram of a squelch table. FIG. 33 is an explanatory diagram of a squelch table of each node of the ring network. FIG. 34 is an explanatory diagram of a squelch determination process when a failure occurs. FIG. 35 is an explanatory diagram of ring topology construction. FIG. 36 is an explanatory diagram of problems of a ring network by POS. [Explanation of symbols] 51₁~51₄ Input side ring interface part (ring IF part) of higher order group 52 ... ATM switch section 53₁~53₄ Output side ring IF part of higher order group 54 ... Monitoring and control unit 55₁~ 55n Low-order group input side low-speed IF section (tributary IF) 56₁~ 56n Low-speed IF section with low-order output 61 ... K1 / K2 reception processing unit 62 ... Input side VRT (Virtual Routing Table) 63 ... Received data processing unit 65 ... Output side VRT 66 ... Received data processing unit 67 K1 / K2 transmission processing unit 71 ... Received data processing unit 72 ... Upstream VRT 75 ... Down VRT 76 ... Transmission data processing unit