JPH09107362A - Alarm cell insertion method and alarm cell generator - Google Patents

Abstract

(57) [Abstract] AOAM function in ATM switching technology
It is possible to suppress the probability of cell discard due to buffer overflow on the transmission path due to transmission of an alarm cell due to detection of a failure in the transmission path of the TM network cell, and to minimize the capacity of the cell buffer on the transmission path. To aim. When a fault occurring on a transmission path of a cell of an ATM network is detected, an alarm cell for each connection multiplexed on the transmission route is generated at a fault detection point on the transmission route. When transmitting to the downstream side of the transmission path, the cell slots on the transmission path are counted and the empty cell slot into which an alarm cell can be inserted is detected, and the alarm on the transmission path is detected based on the count value of the cell slot. The alarm cell is inserted into the detected empty cell slot so that the cell insertion interval becomes equal to or larger than the predetermined insertion interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to OAM (Operation and Maintenance) in ATM (Asynchronous Transfer Mode) switching technology, which is the core of B-ISDN (Broadband Integrated Services Digital Network) which is a next generation communication network. Regarding function.

In the ATM network, various kinds of information such as voice, moving images and data are divided into fixed-length packets called cells, and the cells are handled in an integrated manner in the network for communication. A cell communication path is called a connection, and a connection in the ATM layer is called an ATM connection. OAM function is AT
When an M connection failure is detected, the OAM cell (alarm cell) containing failure notification information is the same ATM as the user cell.
Although it is inserted on the connection, it is required that the user traffic performance is not degraded at that time.

2. Description of the Related Art FIG. 8 is a diagram showing a configuration example of an ATM exchange. In this example, the ATM exchange accommodates input lines A to D and output lines E to H. The cells arriving at the ATM exchange through the input lines A to D are input to the ATM switch via the input line interface units A to D corresponding to the respective input lines. The ATM switch allocates each cell to the output line interface section according to the destination. If the input line interface section outputs cells to the ATM switch in a burst (continuously densely), the cell buffer may overflow. Normally, the ATM connection should be made to prevent such a situation. Is set, there is little possibility that cell discard will occur in the ATM switch.

FIG. 9 is a diagram showing the concept of the configuration of the input line and the fault detection function for the input line. The ATM connection is composed of two stages, a VC (Virtual Channel) connection and a VP (Virtual Path) connection. VC connection is a terminal
A connection established between terminals, and a VP connection is a connection established between exchanges.
Normally, a plurality of VP connections are multiplexed on a physical layer connection (a physical transmission medium such as an optical fiber cable), and a plurality of VC connections are multiplexed on a VP connection.

The OAM function uses an alarm cell called an AIS (Alarm Indication Signal) cell to monitor the failure of the ATM connection. For example, when a VP relay device that relays a VP connection between exchanges detects an VP connection failure, it generates a VP-AIS cell and sends it to the downstream side. When the input line interface section of the exchange connected to the downstream side receives this VP-AIS cell, all Vs multiplexed in the VP connection are received.
A VC-AIS cell for C connection is generated and A
Output to TM switch. When an input line to a switch is disconnected, the corresponding input line interface section detects a physical layer failure and generates an alarm cell for all connections accommodated in the input line to generate ATM cells.
Output to the switch.

FIG. 10 shows an example of the configuration of an alarm cell generator normally considered for realizing the above OAM function in the input line interface section. This alarm cell generator comprises an alarm state management unit 1, an alarm cell generation unit 2, an alarm cell buffer 3, an empty cell slot detection unit 4, a selector 5 and a control interface unit 6. Alarm status management unit 1
Monitors the input highway (highway = multiplexed transmission line), and when it detects a physical layer failure or an ATM connection failure, instructs the alarm cell generation unit 2 to which connection an alarm cell should be generated. The alarm cell generation unit 2 generates an alarm cell according to an instruction from the alarm state management unit 1. The alarm cell buffer 3 temporarily stores the alarm cell generated by the alarm cell generator 2. The empty cell slot detection unit 4 detects an empty cell slot arriving from the input highway and notifies the selector 5 of the timing. If no alarm cell is stored in the alarm cell buffer 3, the selector 5 sends the cell arriving from the input highway to the output highway as it is. If the alarm cell is stored in the alarm cell buffer 3, the selector 5 stores an empty cell. The alarm cell is taken out from the alarm cell buffer 3 and inserted into the empty cell slot at the timing of the empty cell slot notified from the slot detector 4. The control interface section 6 interfaces between the alarm cell generator and a higher-level control device.

[0006]

When an ATM switch distributes cells arriving from each input line to each output line, cell discard does not occur even if cells are simultaneously distributed from a plurality of input lines to one output line. As described above, a cell buffer corresponding to the output line is provided in the ATM switch.
As described above, the ATM connection is normally set so that the cell buffer does not overflow in the ATM switch, so that there is little possibility that cells will burst from the input line to the input line interface section. However, when a failure of the VP connection or a physical layer failure is detected in the input line interface unit, an alarm cell for the connection multiplexed on the input line is generated and inserted into the empty cell slot. Cells may be output in bursts from the ATM switch to the ATM switch.

FIG. 11 shows the input line interface section A to A.
It is the figure which showed the example of the burst output of the cell to a TM switch. VC with VCI (virtual channel identifier) = 1 to 10
When the failure of the VP connection in which the connections are multiplexed is detected, the input line interface unit is set to VCI =
Generate alarm cells for 1-10. If empty cell slots successively arrive at that time, alarm cells are continuously output from the input line interface unit to the ATM switch as shown in the figure. In such a case, cell discard may occur in the ATM switch.

FIG. 12 is a diagram showing an example in which cell discard occurs in the ATM switch. As shown, A,
When cells are input to the ATM switch from the three input line interface units B and C and these cells are stored in the cell buffer for the output line interface unit D, the input line side of the input line interface unit A If a failure occurs in the alarm line and the alarm cells are burst-outputted from the input line interface section A to the ATM switch as shown in FIG. 11, the cell buffer capacity is exceeded and cell discard occurs. In such a state, normal cells from the input line interfaces B and C cannot enter the cell buffer in the ATM switch, which increases the cell discard rate of normal ATM connections. In order to avoid such an adverse effect on user traffic, the cell buffer capacity may be increased, but this causes a problem of increasing the hardware scale.

FIG. 13 is a diagram showing another example in which a cell buffer overflows due to the generation of an alarm cell. Cells are transmitted at high speed from the upstream side exchange A to the downstream side exchange B, and the exchange B is connected to an output line interface section for performing speed conversion from high speed to low speed. The output line interface section absorbs the speed difference by a cell buffer for speed conversion provided inside. Normally, when low-speed conversion is performed on the transmission path in this way, cells should be transmitted with a sufficient cell interval so that the cell buffer for speed conversion does not overflow and cell discard does not occur during low-speed conversion. There is. In FIG. 13, when the alarm cell generated by the input line interface section of the exchange A upon detecting a failure of the input line is burst-inserted into the empty cell slot,
Even if the switch A does not exceed the cell buffer capacity in the ATM switch and cell discard does not occur, the interval between the cells to be transmitted on the line from the switch A to the switch B becomes narrow. There is a possibility that the cell buffer for speed conversion in some parts overflows and cell discard occurs.

Further, when the alarm cell is inserted, it is necessary to wait for an empty cell slot to arrive from the input line. Therefore, the alarm cell is generated as shown in the configuration example of the alarm cell generator of FIG. After that, it must be stored in the alarm cell buffer for waiting until it can be inserted (until an empty cell slot arrives). However, as the number of connections to be monitored increases, the capacity of the alarm cell buffer also needs to be increased, which is one of the factors that increase the hardware scale.

The present invention has been made in view of the above problems, and there is a possibility that a cell is discarded due to a buffer overflow on the transmission path due to the sending of an alarm cell upon detection of a failure in the transmission path of the cell of the ATM network. It is intended to suppress the cell buffer and minimize the capacity of the cell buffer on the transmission path.

[0012]

According to the present invention, in order to solve the above-mentioned problems, when a fault occurring on a transmission route of a cell of an ATM network is detected, a fault detection point on the transmission route is detected. A method of inserting an alarm cell for generating an alarm cell for each connection multiplexed on the transmission path and transmitting the alarm cell to the downstream side of the transmission path, counting cell slots on the transmission path and issuing an alarm. An empty cell slot into which a cell can be inserted is detected, and an alarm cell is inserted in the detected empty cell slot so that the alarm cell insertion interval on the transmission path becomes equal to or more than a predetermined insertion interval based on the count value of the cell slot. A method of inserting an alarm cell for inserting a cell is provided.

Further, in the present invention, as a first mode of the alarm cell generating device provided on the transmission path of the cell of the ATM network, as shown in FIG. 1, a fault occurring on the upstream side of the transmission path 200 is detected. A fault detection unit 101 and a warning cell generation unit 102 that generates a warning cell for each connection multiplexed on the transmission path 200 in which the fault is detected.
An alarm cell buffer 103 for temporarily accumulating the generated alarm cell, and a transmission path 200 in which the failure is detected.
Counting the upper cell slots and detecting an empty cell slot in which an alarm cell can be inserted, and based on the count value of the cell slot, the alarm cell insertion interval on the transmission path 200 is equal to or more than a predetermined insertion interval, Alarm cell buffer 103
There is provided an alarm cell generation device 100 including an alarm cell insertion unit 104 which takes out an alarm cell from the cell and inserts it into the detected empty cell slot.

The alarm cell generator 100 of the first embodiment described above.
Will be described. When the failure detection unit 101 receives a warning cell flowing from the upstream side of the transmission path 200 of the cell or detects a failure of the transmission path 200 by detecting a physical layer failure, the failure detection unit 101 notifies the warning cell generation unit 102 of the failure. Notify the failure. The alarm cell generation unit 102 generates an alarm cell for each connection multiplexed on the transmission path 200 and sequentially outputs the alarm cell to the alarm cell buffer.
The alarm cell buffer 103 temporarily stores the alarm cell input from the alarm cell generation unit 102. The alarm cell insertion unit 104 detects the arrival timing of an empty cell slot into which an alarm cell can be inserted while counting the number of cell slots arriving on the transmission path 200. If the alarm cell buffer 103 stores alarm cells, the alarm cell inserting unit 104 takes out the alarm cell from the alarm cell buffer 103 and inserts it into the empty cell slot when the empty cell slot arrives. At this time, the alarm cell insertion interval is set to be a predetermined insertion interval or more based on the count value of the arrival cell slot. In other words, the alarm cell buffer 10
Even if empty cell slots continuously arrive when a plurality of alarm cells are stored in No. 3, alarm cells are not continuously inserted.

Further, the alarm cell generation device 100, when the alarm cell generation amount exceeds the alarm cell buffer capacity and the alarm cell buffer 103 overflows because the empty slot into which the alarm cell can be inserted does not arrive when the failure is detected, A notification process (notification to a network maintenance person, a host controller, etc.) about the occurrence of overflow can be performed.

Further, according to the present invention, as a second mode of the alarm cell generator provided on the transmission path of the cell of the ATM network, a failure detection unit for detecting a failure occurring on the upstream side of the transmission path, and an alarm cell. An alarm cell generator that generates an alarm cell for each connection multiplexed on the transmission path in which the fault is detected according to the generation instruction, and counts the cell slot on the transmission path in which the fault is detected. An empty cell slot into which an alarm cell can be inserted is detected, and an alarm cell is generated by the alarm cell generation unit so that the alarm cell insertion interval on the transmission path becomes equal to or more than a predetermined insertion interval based on the count value of the cell slot. There is provided an alarm cell generation device including an alarm cell insertion unit for issuing a generation instruction to generate an alarm cell and inserting the alarm cell into the detected empty cell slot.

The operation of the alarm cell generator of the second embodiment will be described. Similar to the first embodiment, the fault detection unit monitors the cell transmission path and notifies the alarm cell generation unit when a fault is detected, and the alarm cell insertion unit arrives on the transmission route. While counting the cell slots, the arrival timing of an empty cell slot into which an alarm cell can be inserted is detected. When the alarm cell insertion unit detects the arrival of an empty cell slot when the alarm cell insertion interval determined based on the cell slot count value is already equal to or more than the predetermined interval, the alarm cell generation unit issues an alarm. Issue a cell generation instruction.
If the alarm cell generation unit notifies the failure of the transmission path by the failure detection unit, each connection multiplexed on the transmission path is received each time an alarm cell generation instruction is received from the alarm cell insertion unit. Alarm cells are sequentially generated and sent to the alarm cell insertion unit. The alarm cell insertion unit inserts the alarm cell transmitted from the alarm cell generation unit into the detected empty cell slot in response to the alarm cell generation instruction.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram showing a configuration example of the input line interface section of the ATM switch in the embodiment of the present invention. The optical signal input to the input line interface section through the input line of the optical fiber cable is converted into an electric signal by the optical / electrical conversion device. Input data at this stage is SDH
The cells are packed in a frame (1 frame 125 μS). The SDH termination device takes out a cell from the SDH frame and generates a cell frame signal indicating the beginning of the cell. FIG. 3 is a diagram showing the relationship between the cell flow and the cell frame signal. One cell is a 53-byte frame consisting of a header part and a payload part (a part where user information is stored), and the cell frame signal represents the timing of the head position of the header part of the cell with a pulse. The cells and cell frame signals output by the SDH termination device are passed to various cell processing devices (including an alarm cell generation device) in the subsequent stage.

FIG. 4 is a diagram showing the configuration of an alarm cell generator as an embodiment of the present invention. The device of this embodiment is obtained by adding an insertion interval control unit 7 to the alarm cell generator of FIG. 10 shown as an example of the prior art. Insertion interval control unit 7
Is a functional portion that counts the cell slots arriving from the input highway and controls the alarm cell insertion interval based on the cell slot count value and the arrival timing of the empty cell slot notified from the empty cell slot detection unit 4. Is. In other words, if the alarm cells are stored in the alarm cell buffer 3, the insertion interval control unit 7 controls the selective switching of the selector 4 so that the alarm cell insertion interval becomes equal to or larger than the predetermined number of cell slots.

FIG. 5 shows an example of inserting an alarm cell. The cell slot numbers in the figure are numbers given for convenience of explanation. In this example, when the number of alarm cell insertion interval cell slots is set to “3”, that is, alarm cells are inserted at least every 3 cell slots (at least 2 cell slots are provided between alarm cells). This is the case. When a plurality of alarm cells are stored in the alarm cell buffer 3 of the alarm cell generator and an alarm cell is inserted in the empty cell slot of the cell slot number 1, the empty cells of the cell slot numbers 2 and 3 will continue thereafter. Although the slots arrive consecutively, the alarm cell is not inserted because the interval of two cell slots after cell slot number 1 is not yet open. When an empty cell with cell slot number 4 arrives,
Since there is an interval of two cell slots between the cell slot number 1 and the cell slot number 4, the alarm cell is inserted in the empty cell slot of the cell slot number 4. Further, the cell slot number 7 which arrives after the space of 2 cell slots after the cell slot number 4 is not an empty cell slot, so that the alarm cell cannot be inserted. Therefore, the alarm cell is inserted in the cell slot number 8 which is the first empty cell slot that arrives after the cell slot number 7.

In the alarm cell insertion example of FIG. 5, all the cell slots including the cell slot in which the user cell is inserted are counted when counting the alarm cell insertion intervals, but only the empty cell slots are counted. A counting method may be used. In that case, the alarm cell is inserted into the cell slot number 4 in FIG. 5, and then the next alarm cell is inserted into the empty cell slot of the cell slot number 10. It is also possible to determine the control condition of the alarm cell insertion interval other than the above according to the situation.

The alarm cell insertion interval should be determined in consideration of conditions such as the cell buffer capacity on the downstream side of the cell transmission path. However, when the insertion interval is set as a fixed value in advance, It is possible to arbitrarily set and change from the control console through the control interface unit 6.

When the arrival of the empty cell slot is very small compared with the capacity of the alarm cell buffer 3, the generated alarm cell exceeds the buffer capacity of the alarm cell buffer 3 and causes a buffer overflow. there is a possibility. In this case, the fact that the alarm cell has not been inserted normally due to the alarm cell buffer overflow is notified to the network maintainer or a higher-level device through the control interface unit 6.

FIG. 6 is a diagram showing a configuration example of the insertion interval control unit 7. The insertion interval controller 7 includes a counter 71 and an AND gate 72. The counter 71 counts the number of cell slots by the pulse of the cell frame signal, and outputs a carry-out (“H” level) after counting a predetermined number (alarm cell insertion interval cell slot number) from the previous alarm cell insertion. The AND gate 72 outputs the logical product of the empty cell slot detection signal (“H” at the time of detection) from the empty cell slot detection unit 4 and the carry-out signal of the counter 71, and the output is the selector switching signal of the selector 5. used. When the selector switching signal is "L", the selector 5 selects the input highway side and sends the arriving cell slot to the output highway as it is, but when the selector switching signal becomes "H", it switches to the alarm cell buffer 3 side. During that time, an alarm cell is inserted into an empty cell slot.

The counter 71 is reset when the alarm cell insertion into the empty cell slot is completed. This reset can be performed by, for example, appropriately delaying the output signal of the AND gate 72 and inputting it to the reset terminal of the counter 71. When the counter 71 is reset, the carry-out output stops (becomes "L").
At the same time, the control interface unit 6 causes the counter 71 to
Input the initial value of the counter to the initial value load terminal of. The counter initial value is a value such that a carry-out is output when the counter 71 counts a predetermined number (alarm cell insertion interval cell slot number) after the initial value is set.

FIG. 7 is a diagram showing the configuration of an alarm cell generator as another embodiment of the present invention. The device of this embodiment differs from the device of FIG. 4 in that the alarm cell buffer is not provided. In the apparatus of this embodiment, the insertion interval control unit 7
Issues an alarm cell generation instruction to the alarm cell generation unit 2 and sends the selector 5 to the alarm cell generation unit 2 side when a predetermined insertion interval or more is vacant after the alarm cell inserted last time and an empty cell slot arrives. Switch to. Further, the alarm cell generation unit 2 generates an alarm cell when the alarm state management unit 1 notifies the failure and the insertion interval control unit 7 receives an alarm cell generation instruction. In this case, when the alarm cell generation unit 2 receives the alarm cell generation instruction, it generates one alarm cell and outputs it to the selector 5, and waits for the next alarm cell generation instruction. That is, in the apparatus of this embodiment, an alarm cell is generated and inserted each time an empty slot that satisfies the alarm cell insertion condition arrives. With such a configuration of the alarm cell generator, the alarm cell buffer is not needed, so that the effect of reducing the hardware scale can be obtained.

According to the ITU-T recommendation, alarm cells are to be sent at a rate of 1 cell per second per connection. In the case of the apparatus of the embodiment shown in FIG. 4, the alarm cell to be transmitted is created in advance and stored in the alarm cell buffer 3, and when an empty cell slot arrives, the alarm cell is taken out from the buffer and transmitted. Therefore, the above standards can be sufficiently satisfied. On the other hand, in the case of the apparatus of the embodiment of FIG. 7, since the alarm cell is generated after the empty cell slot arrives, the timing of alarm cell transmission is slightly delayed as compared with the apparatus of the embodiment of FIG. 4, but it is also within the allowable range. There is no problem because it is a delay.

In each of the above-mentioned embodiments, the alarm cell generator is provided in the input line interface section. However, when it is considered to surely suppress the cell buffer discard in the ATM switch connected to the downstream side, the alarm cell generator is installed. It is also possible to provide in the output line interface section and control the alarm cell insertion interval on the output line. However, such a configuration is not practical and has little merit for the following reasons.

Even if the alarm cell generator is provided in the output line interface unit, it is necessary to detect the failure of the input line in the input line interface unit. However, since the connection number on the input line interface and the connection number on the output line interface are different, a mechanism is required to convert the connection numbers for all the faulty connections and notify the output line interface section. .

Since only one alarm cell is inserted per connection per second, the alarm cell transmission band is very small compared to the normal user cell transmission band. Therefore, unless the cell buffer in the ATM switch is full due to burst insertion of alarm cells in the input line interface, the cells sent from the output line will be in burst state more than normal cell flow. There is little chance of becoming Therefore, if you control the alarm cell insertion interval in the input line interface,
It does not adversely affect the exchanges connected to the downstream side. Also, if the ATM switch is equipped with a VC shaper (a function that provides a buffer for each VC connection and sends cells on the VC connection at fixed time intervals), the cells are output in bursts from the output line. There is no problem so there is no problem.

[0031]

As described above, according to the present invention, upon detection of a fault on the transmission path of a cell, alarm cells are multiply generated for the connections multiplexed on the transmission path. However, the probability that cell discard will occur due to overflow of the cell buffer installed on the downstream side of the transmission path can be suppressed, so that there is an effect of suppressing deterioration of user traffic performance of other normal connections. If the possibility of overflow of the cell buffer is reduced, the capacity of the cell buffer conventionally provided can be reduced, so that the effect of reducing the hardware scale can be obtained. Further, according to the present invention, it is possible to omit the alarm cell buffer in the configuration of the alarm cell generator which is usually considered, which also contributes to the reduction of the hardware scale.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the principle according to the present invention.

FIG. 2 is a diagram showing a configuration example of an input line interface section in an ATM exchange.

FIG. 3 is a diagram showing a relationship between a cell flow and a cell frame signal.

FIG. 4 is a diagram showing a configuration of an alarm cell generator as an embodiment of the present invention.

FIG. 5 is a diagram showing an example of inserting an alarm cell in an alarm cell generator.

FIG. 6 is a diagram showing a configuration example of an insertion interval control unit in the alarm cell generator.

FIG. 7 is a diagram showing a configuration of an alarm cell generator according to another embodiment of the present invention.

FIG. 8 is a diagram showing a configuration example of an ATM exchange.

FIG. 9 is a diagram showing a concept of a configuration of an input line of an ATM exchange and a failure detection function for the input line.

FIG. 10 is a diagram showing a configuration example of an alarm cell generator that is usually considered.

FIG. 11 is a diagram showing an example of burst output of an alarm cell from an input line interface section to an ATM switch.

FIG. 12 is a diagram showing an example in which cell discard occurs due to buffer overflow in an ATM switch of an ATM switch.

FIG. 13 is a diagram showing an example in which cell discard occurs due to buffer overflow in an ATM switch on the downstream side of a cell transmission path.

[Explanation of symbols]

 1 Alarm state management unit 2 Alarm cell generation unit 3 Alarm cell buffer 4 Empty cell slot detection unit 5 Selector 6 Control interface unit 7 Insertion interval control unit 71 Counter 72 AND gate 100 Alarm cell generator 101 Fault detection unit 102 Alarm cell generation unit 103 alarm cell buffer 104 alarm cell insertion unit 200 cell transmission path

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryuichi Takechi 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, E ▲ Yu, Hiroshi 1015, Kamitadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Stock In-house (72) Inventor Yasushi Takagi 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph Telephone Co., Ltd. (72) Inventor Jun Itoda 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo In the company

Claims (4)

[Claims] 1. When an error occurring on a transmission path of a cell of an ATM network is detected, an alarm cell for each connection multiplexed on the transmission path is generated at a failure detection point on the transmission path. A method of inserting an alarm cell when transmitting to the downstream side of the transmission path by counting the number of cell slots on the transmission path and detecting an empty cell slot into which an alarm cell can be inserted, and counting the cell slot. Based on the above, an alarm cell insertion method for inserting an alarm cell into the detected empty cell slot so that the alarm cell insertion interval on the transmission path becomes equal to or greater than a predetermined insertion interval. 2. An alarm cell generator provided on a transmission path of a cell of an ATM network, comprising a failure detection unit for detecting a failure occurring on the upstream side of the transmission path, and a transmission path on which the failure is detected. Alarm cell generation unit that generates an alarm cell for each connection that is multiplexed in the above, an alarm cell buffer that temporarily stores the generated alarm cell, and a cell slot on the transmission path in which the fault is detected. An empty cell slot in which an alarm cell can be inserted is detected, and based on the count value of the cell slot, the alarm cell insertion interval on the transmission path is equal to or more than a predetermined insertion interval,
An alarm cell generating device, comprising: an alarm cell insertion unit that takes out an alarm cell from the alarm cell buffer and inserts it into the detected empty cell slot. 3. An alarm cell generator provided on a transmission path of a cell of an ATM network, comprising: a failure detection unit for detecting a failure occurring on the upstream side of the transmission path; An alarm cell generation unit that generates an alarm cell for each connection multiplexed on the transmission path in which a failure is detected, and a cell slot on the transmission path in which the failure is detected and an empty space in which an alarm cell can be inserted A cell slot is detected, and based on the count value of the cell slot, the alarm cell insertion interval on the transmission path is equal to or longer than a predetermined insertion interval,
An alarm cell generation device, comprising: an alarm cell generation instruction to the alarm cell generation unit to generate an alarm cell; and an alarm cell insertion unit that inserts the alarm cell into the detected empty cell slot. 4. When an alarm cell buffer overflows due to an alarm cell generation amount exceeding an alarm cell buffer capacity because an empty slot into which an alarm cell can be inserted does not arrive at the time of detecting a failure, notification processing for the overflow occurrence is performed. The alarm cell generator according to claim 2.