JPH11289332A - Switching method and device for buffer memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure non-break changeover for a buffer memory. SOLUTION: When there is a switching of a buffer unit from an active system to a reserve system, the amount of information accumulated in each component memory (a buffer memory) in an active system buffer unit is investigated and, information read-out is allowed regarding the component memory of the reserve system, corresponding to the component memory of the active system, where the accumulated amount of information is below a first set value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for switching a buffer memory, for example, an ATM (Asynchrono).
us Transfer Mode (Asynchronous Transfer Mode) Among components of a communication system such as a communication system, a device having a buffer memory for shaping, such as a switch, a multiplexer, a terminal, and the like, can be applied.

[0002]

2. Description of the Related Art In general, in a communication system including an information processing system and a switching system, an active system and a standby system having exactly the same configuration for each function are provided in order to improve reliability such that the operation of the system is not stopped even when a failure occurs. And a double redundant configuration is prepared. If the active system device that is actually performing its function breaks down, the switching process is immediately performed, and the function is realized by the standby system device.

[0003] In addition to the failure, the process of switching to the standby system is also performed in the case of maintenance or the like.

In these switching processes, it is required that communication be switched without interruption for a moment, that is, non-instantaneous interruption switching. The hitless switching in the ATM transmission means that no ATM cell is lost before and after the switching process, and the order of the ATM cells is not changed for each connection.

[0005] In particular, in the case of maintenance, etc., complete instantaneous interruption switching is required.

At normal times, ATM cells flow into the active system of the conventional ATM communication device and are sequentially output, but no ATM cells flow into the standby system.

At the time of the switching process, the flow of the ATM cells into the working system is first stopped, and the A
The TM cell flows in. In the current system, a new ATM
The number of stored cells is decreasing because the ATM cells that have been stored until then are only discharged as the cells no longer flow. Conversely, in the standby system, the number of ATM cells to be stored increases since only the flow-in and no flow-out occurs.

[0008] The ATM stored in the active device
When all the cells have flowed out, the ATM cells have started to flow out of the standby system, the standby system has become the active system, and the current active system has been subjected to the failure repair processing by the program or has been manually operated. Replaced with a new package.

[0009]

However, the inflow, accumulation and outflow of ATM cells in the above-mentioned active and standby systems are performed on a connection basis, and the A
Since the TM cell transmission speed is determined by the network in consideration of conditions such as traffic density, it is diversified at the same time. If there is a connection with a low transmission speed, it takes time until the ATM cells stored in the active device at the time of the switching process are exhausted, and during that time, in the standby device, cells may overflow in order from the connection with the high transmission speed. . If cells are lost due to overflow, the above-mentioned instantaneous interruption switching cannot be achieved.

[0010]

In order to solve this problem, a plurality of buffer units having a plurality of element memories operating as independent buffer memories are arranged in parallel, and the buffer units used are used as buffer memories. A method for switching from an active system to a standby system not used as a buffer memory has the following configuration.

That is, in the first invention, (1)
The transmitted information is read after being written into each element memory of the active buffer unit. (2) When switching is started, first, the information is transferred to each element memory in the active buffer unit. (3) Then, the amount of information stored in each element memory in the working buffer unit is checked to determine the amount of information (4). The reading of information is permitted for the standby element memory corresponding to the active element memory in which the amount of stored information has become equal to or less than the first set value.

In addition, a plurality of buffer units having a plurality of element memories operating as independent buffer memories are arranged in parallel, and the buffer units to be used are not used as buffer memories from the current system used as the buffer memory. An apparatus for switching to a standby system has the following configuration.

That is, in the second invention, (1) means for transmitting information to the active buffer unit before switching, and transmitting information to the standby buffer unit when switching is started; (2) means for checking the amount of information stored in each element memory in the active buffer unit; and (3) the amount of information stored is
The spare element memory corresponding to the active element memory having a value equal to or less than the set value of the standby system is provided with means for permitting reading of information.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Embodiment One embodiment of the present invention will be described below with reference to an example in which a buffer memory switching method and apparatus according to the present invention is applied to an ATM exchange.

In ATM communication, traffic control is indispensable in order to maintain communication quality. In this embodiment, an ATM switch having a shaping function for performing this traffic control is used to realize instantaneous interruption switching.

(A-1) Configuration of the Embodiment FIG. 1 shows a memory switching device 10 according to the embodiment. The memory switching device 10 is provided, for example, as an interface between a switch unit and an NIC (Network Interface Card) unit in an ATM exchange, and performs shaping between an ATM terminal or the like connected to the NIC unit and the switch unit. Used for

In FIG. 1, the input switching unit 11 is
A of all connections transmitted via 1A
This is a circuit that collectively transmits TM cells to one of the transmission lines 11B and 11C.

The transmission line 11B is an FI for active shaping.
This is a transmission path connected to the input terminal of the FO 12 and for transmitting an ATM cell from the input switching unit 11 to the working type FIFO 12.

Similarly, the transmission line 11C is connected to the input terminal of the standby system FIFO 13 and the ATM is transferred from the input switching unit 11 to the standby system FIFO 13.
This is a transmission path for transmitting cells.

The combination of the active-system shaping FIFO 12 and the output control unit 14 at the subsequent stage is one shaping device. The shaping device is the input A
By temporarily storing the TM cells in the buffer memory and controlling the timing of reading and outputting, the cell interval between the output and transmitted ATM cells is maintained, and the operation is performed so that the transmission speed does not exceed a certain speed instantaneously. Device.

The working type shaping FIFO 12 is
A plurality of buffer memories of an IFO (First In First Out), that is, a first-in first-out type, are provided in parallel. Here, the number is 2048, but may be more or less. For example, the number may be 4096.

Since each of the 2048 element FIFOs corresponds to one connection, the maximum number of connections that can be established via the memory switching device 10 is 2048. These 2048 element FIFOs
Have different identification numbers.

The output control unit 14 monitors the number of ATM cells stored in these element FIFOs, that is, the queue length (the number of queues), and controls the output (reading) timing of the ATM cells from the element FIFOs. This is a part that performs shaping for each connection with a different transmission speed.

The queue length identification unit 16 connected to the output control unit 14 starts the memory switching process from the shaping FIFOs 12 to 13 and then starts the active system shaping FIFO.
This is a part for identifying whether or not the queue length of each element FIFO in the IFO 12 is zero.

The standby-system shaping FIFO 13 and the output control unit 15 are provided with the active-system shaping FIFO 13, respectively.
The FO 12 has the same configuration and the same function as the output control unit 14. 2048 element FIFs in the standby system 13
Although different identification numbers are assigned to O, it is assumed that these element FIFOs are associated with the element FIFOs in the active system 12 on an one-to-one basis by identification numbers. The pair of elementary FIFOs of the active system and the standby system having a corresponding relationship become buffer memories of the same connection before and after a switching process described later.

The arrival flag 17 connected to the output control unit 15 is in a state indicating that the first ATM cell has arrived after the start of the switching process to each element FIFO in the spare shaping FIFO 13 after the start of the switching process. It is a register.

The output control units 15 and 14 are connected by control buses 18 and 19 for exchanging control signals during the switching process.

A transmission line 14A connected to the output terminal of the output control unit 14 is a transmission line for transmitting ATM cells for each connection, and is connected to the selection unit 20.

Similarly, a transmission line 15A connected to the output terminal of the output control unit 15 is a transmission line for transmitting ATM cells for each connection, and is connected to the selection unit 20.

The selecting section 20 is a section for multiplexing the ATM cells read from the active system 12 and / or the standby system 13 and transmitting the multiplexed ATM cells from the transmission line 20A.

Hereinafter, the operation of the present embodiment having such a configuration will be described.

(A-2) Operation of the Embodiment Normally, the ATM cells of all the established connections are supplied from the transmission line 11A to the input switching unit 11, and all of the ATM cells are connected to the active system via the transmission line 11B. It is sent to the shaping FIFO 12. At this time, the transmission paths of the ATM cells of all the connections are the transmission path 11A,
The order of the input switching unit 11, the transmission path 11B, the working-system shaping FIFO 12, the output control unit 14, the transmission path 14A, the selection unit 20, and the transmission path 20A.

In the working type FIFO 12 for shaping,
These ATM cells are stored in separate element FIFOs for each connection.
O, and are read out to the output selection unit 14 so as not to exceed a transmission rate that differs for each connection, and then carried to the selection unit 20 via the transmission path 14A,
0 multiplexes the cells of each of these connections and
Send from 0A. In this state, the transmission lines 11C, 15
No cell is transmitted A.

When a process for switching the memory used from the active system 12 to the standby system 13 is performed for the occurrence of a failure in the active system shaping FIFO 12 or the output control unit 14, or for maintenance, the input switching unit 11 immediately starts operating. The transmission path 11C is selected.

As a result, the ATM cells of all the connections transmitted on the transmission line 11A after the start of the memory switching process are supplied to the backup shaping FIFO 13 via the transmission line 11C.

Therefore, after the start of the switching process, the queue length of each element FIFO used in the active-system shaping FIFO 12 is reduced each time the output control unit 14 reads the ATM cell. The speed of this reduction depends on the transmission speed of the connection.

On the other hand, in the spare-system shaping FIFO 13 by the switching process, the ATM cell starts to be stored in the element FIFO corresponding to the established connection.

Attention is paid to one connection that is continuously extended before and after the switching process. Before the switching process, the ATM cells of this connection are stored in one element FIFO in the active-system shaping FIFO 12.
When the switching process is started, the data is started to be stored in a certain element FIFO in the standby-system shaping FIFO 13.

The queue length of the element FIFO of the standby system 13 is extended at a speed corresponding to the transmission speed of the connection. However, in order for the cell order of the connection to be maintained before and after the switching process, The corresponding element FI of the active system 12
Unless the queue length of the FO becomes 0, the standby system 13
ATM cells cannot be read from the element FIFO. On the other hand, in order not to lose the cells, each element FIFO of the standby system 13 in which cells are accumulated after the start of the switching process.
So no cell must overflow.

Therefore, the output control unit 15, which monitors the state of the arrival flag 17, sets the corresponding
When the first cell arrives at O, 2048 element FIs
The identification number for identifying the element FIFO from the FO is transmitted to the output control unit 14 via the control bus 19,
Make an inquiry.

The output control unit 14 receiving this identification number
The queue length identification unit 16 detects whether or not the queue length of the element FIFO of the identification number corresponding to the identification number in the active system 12 is 0, and this detection result is
At 8, it is sent to the output control unit 15.

If the queue length is 0, the output control unit 15 sends the ATM from the element FIFO in the standby system 13 to the ATM.
The cell is read out and transmitted to the transmission line 15A.

When the queue length is not 0, the cell is not read from the element FIFO in the standby system 13 until the queue length becomes 0. In this way, the order of the cells of the connection can be maintained before and after the switching process. If the connection is the same, the cell transmission speed is the same before and after the start of the switching process.
Immediately, the corresponding element FI of the standby system 13
If cells are read from the FO, the cells do not overflow in the standby system 13.

Such processing is performed by using the element F of another identification number.
Since the IFOs are also performed independently of each other, in the transient state from the start to the end of the switching process, even if the ATM cells of the connection with the higher transmission rate are transmitted through the transmission line 15A, the connection of the connection with the lower transmission rate is not possible. AT
A situation may arise in which the M cell is still being transmitted on the transmission line 14A.

The FIFO 12 for active shaping
When the queue lengths of all the element FIFOs are 0, the switching process ends. At this time, no cells are transmitted on the transmission path 14A, and the transmission paths of the ATM cells of all connections are the transmission path 11A, the input switching unit 11, the transmission path 1
1C, the standby system FIFO 13, the output control unit 15, the transmission path 15A, the selection unit 20, and the transmission path 20A. Thus, the FIFO 12 for the active shaping is used.
Can be replaced for maintenance.

Before and after the switching process, the selector 20 recognizes the ATM cell of each connection transmitted on the transmission line 14A and / or the transmission line 15A as to which transmission line the cell has been transmitted. The signals are multiplexed without being output from the transmission line 20A. The cell transmitted on the transmission line 20A is different from the cell transmitted on the transmission line 11A,
No cell has been lost, and the order of cells in each connection remains unchanged.

The first ATM cell of the connection established immediately after the start of the switching process is the element FI of the protection system 13.
Even when the cell reaches the FO, the output control unit 15 can recognize that the cell may be read by performing the above inquiry.

(A-3) Effects of Embodiment As described above, according to this embodiment, even if a plurality of connections having different transmission speeds are established, the cell order for each connection can be maintained without losing one cell. It is possible to switch the shaping FIFO from the active system to the standby system while maintaining the above condition, that is, without instantaneous interruption.

(B) Other Embodiments In the above description, after the queue length of the element FIFO of the active system 12 becomes 0, the corresponding element FI of the standby system 13
Although the ATM cells are read from the FO, actually, it takes time to exchange and operate signals between the output control units 14 and 15 and so on, as long as the cell order in each connection is maintained. A predetermined value larger than 0 may be set as the queue length, and when the number of stored ATM cells falls below this value, reading of cells from the element FIFO of the standby system 13 may be started. .

In the above description, the inquiry is made when the first one cell arrives for each element FIFO. However, the inquiry timing is set within a range where cell overflow does not occur, such as when the first few cells arrive. May be slower. After the switching process is completed, the exchange of the control signal between the output control units 14 and 15 becomes unnecessary, so that the processing operation in the output control units 14 and 15 can be simplified while preventing the overflow.

Further, the inquiry may be omitted. In this case, the output control unit 14 that has detected that the switching process has been started determines the identification number of the element FIFO in the active system 12 whose queue length has become equal to or less than a predetermined value since that time. It is preferable to notify the output control unit 15 by the following. This is more efficient when the number of connections established during the switching process is large.

In the above description, the number of FIFOs for shaping is two for the active system and the standby system. However, three or more FIFOs may be juxtaposed. This is because, after the switching process, a new standby-system shaping FIFO for the active-system shaping FIFO 13 may be required immediately.

Further, in the above-described embodiment, the present invention is applied to an ATM.
The case where the present invention is applied to an exchange has been described as an example.
The present invention can also be applied to ATM communication devices other than the M switch, for example, ATM multiplexers and ATM terminals.

Further, the scope of application of the present invention is not limited to the ATM. A plurality of buffer units having a plurality of element memories operating as independent buffer memories are arranged in parallel, and the buffer units to be used are used as buffer memories. A method and apparatus for switching from a working system to a spare system not used as a buffer memory.
Widely applicable.

[0055]

As described above, according to the first and second aspects of the present invention, when the buffer memory is switched from the active system to the standby system, the order in which the transmitted information is written to each element memory without losing the transmitted information. , It is possible to realize instantaneous interruption switching.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a memory switching device according to an embodiment.

[Explanation of symbols]

10: memory switching device, 11: input switching unit, 11A, 1
1B, 11C, 14A, 15A, 20A ... transmission line, 12
.. Active FIFO for shaping, 13. FIFO for standby shaping, 14, 15... Output control unit, 16... Queue length identification unit, 17... Arrival flag.

Claims (6)

[Claims] 1. A plurality of buffer units each having a plurality of element memories operating as independent buffer memories are arranged side by side, and a buffer unit to be used is not used as a buffer memory from an active system used as a buffer memory. In the method of switching to the standby system, normally, the transmitted information is read out after being written to each element memory of the active system buffer unit, and when the switching is started, first, the information in the active system buffer unit is first stored in the active system buffer unit. Then, the writing of information to each element memory is stopped, and information is written to each element memory in the standby buffer unit. Then, the amount of information stored in each element memory in the working buffer unit is checked. Corresponding to the active element memory in which the amount of stored information is less than the first set value. The component memory of the standby system is switching method of a buffer memory and permits reading of information. 2. The switching method according to claim 1, wherein after the switching is started, the amount of information stored in all the element memories of the active system becomes equal to or less than a first set value. In the period up to, a standby element memory in which an amount of information equal to or more than the second set value is written is detected, and only the element memory corresponding to the standby element memory among the active element memories is determined. A method of switching a buffer memory, comprising: checking whether the amount of the stored information has become equal to or less than a first set value. 3. The buffer memory switching method according to claim 1, wherein said information is an ATM cell. 4. A plurality of buffer units each having a plurality of element memories operating as independent buffer memories are arranged in parallel, and a buffer unit to be used is not used as a buffer memory from a current system used as a buffer memory. Means for transmitting information to the active buffer unit before switching, and transmitting information to the standby buffer unit when switching is started; and Means for examining the amount of information stored in each element memory; and information on the standby element memory corresponding to the active element memory in which the amount of stored information is less than or equal to the first set value. Means for permitting reading of a buffer memory. 5. The buffer memory switching device according to claim 4, wherein after the switching is started, the amount of information stored in all the elementary memories of the active system becomes equal to or less than a first set value. Means for detecting a spare element memory in which information of an amount equal to or greater than the second set value is written during the period up to, and only the element memory corresponding to the spare element memory among the active element memories. Means for checking whether the amount of the stored information has become equal to or less than a first set value. 6. The buffer memory switching device according to claim 4, wherein said information is an ATM cell.