JP2526483B2 - Cell switching system and device - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used in digital communications. In particular, the present invention relates to a cell switching technique in the asynchronous transfer mode.

[0002]

2. Description of the Related Art Asynchronous transfer mode (hereinafter referred to as ATM: Async) in which information is divided into fixed-length cell units, transmitted and received, and exchanged.
The cell switching method called rouous Tranfer Mode) is regarded as a promising method for realizing the next-generation broadband communication. In such a cell switching system, switching is performed for each cell based on the identifier written in the header area of each cell.

A conventional example will be described with reference to FIGS. 6 and 7. FIG. 6 is a block diagram of an output buffer type ATM switch. FIG. 7 is a block diagram of a conventional reception filter. Cells inputted from the input port 2 ₂₁ to 2 _2n are transmitted to the internal bus 21 through an input interface 2 ₄₁ to 2 _4n. Input port 2 to internal bus 21
The transmission right from ₂₁ to _22n is controlled by the switch controller 27. In this conventional example, the transmission right is _cyclically given to the input ports 2 ₂₁ to _{22 n} in a time division manner. The input interfaces 2 ₄₁ to 2 _4n of the input ports 2 _{21 to} 2 _2n are
A buffer for several cells is used internally to transmit cells to the internal bus 21 in accordance with a transmission right signal from the switch controller 27. The cells multiplexed on the internal bus 21 have output ports 2 ₃₁ to 2 3.
_The header section is checked by the _3n reception filters 2 ₅₁ to _{25 n} , and only the cells addressed to their own output ports 2 ₃₁ to _{23 n} are _fetched and received by the reception buffers 2 ₆₁ to _{26 n} .

As shown in FIG. 7, reception filters 2 ₅₁ to ₂₅ n
Then, all the incoming cells are temporarily stored in the register 31. The control circuit 36 determines a virtual path identifier (hereinafter, referred to as VPI: Virtual Path Identifier) or a virtual channel identifier (hereinafter, referred to as VCI: Virtual C) from the header information of the cell.
hannel Identifier) to retrieve the control memory 34
The data stored in the receiving buffers 2 ₆₁ to 2 of the next stage are checked through the gate 32 when the data is collated with the data stored in.
Transfer to _6n . If they do not match, the cell is discarded.

In the output buffer type switch,
The throughput of the internal buffer 21 is from the input port 2 ₂₁ to
Greater than 2 _2n total throughput. When all mbit / sec line speed of the input ports 2 ₂₁ to 2 _2n and the output port 2 ₃₁ to 2 _3n, where the throughput of the internal bus 21 is more n × mbit / sec. Therefore,
Viewed from the input port 2 ₂₁ to 2 _2n, be arrived if the cell is continuously, one cell input port 2 _21, 2 _22, ...,
One cell can always be sent to the internal bus 21 within the time of arriving at 2 _2n , so it is sufficient to prepare several cells as a timing adjustment buffer on the input port 2 ₂₁ to _22n side. is there. That is, no cells are discarded on the side of the input ports 2 ₂₁ to _{22 n} . After that, input ports 2 ₂₁ to 2
The cell arrival time interval when cells continuously arrive at _2n at the line speed is called one cell time.

On the other hand, on the side of the output ports 2 ₃₁ to _{23 n} , cell discard may occur due to congestion. For example, from a plurality of input ports 2 ₂₁ to _{22 n} at the same time to a specific output port 2 ₃₁ to
When a cell addressed to 2 _3n arrives, that is, a plurality of cells arrive at a specific output port 2 ₃₁ to 2 _3n within one cell time. In this case, the output from the reception buffers 2 ₆₁ to _{26 n.} Since there is only one cell within one cell time, there are more cells to enter, so cells gradually accumulate in the receive buffers 2 ₆₁ to _{26 n} , and eventually cells are discarded due to buffer overflow. Become.

Generally, the original information to be sent consists of a continuous burst of a plurality of relatively long packets.
In M, these pieces of information are divided into short fixed-length cells and sent. For example, if even one cell is discarded due to buffer congestion, the entire packet that contained that cell cannot be restored, and all cells constituting this packet will be retransmitted. Furthermore, if even one packet does not arrive, the entire original burst information cannot be restored, so that the desired transfer does not end until all the packets arrive safely (Japanese Patent Laid-Open No. 3-26038). Japanese Patent Laid-Open No. 3-82244 and Japanese Patent Laid-Open No. 3-17171
37, JP-A-3-128547).

[0008]

When the discard occurs due to the congestion of the receive buffer, the conventional cell switch randomly discards the cells overflowing from the receive buffer. For example, if the discarded cells are 10 cells and all the discarded 10 cells are cells included in the same packet, only one packet should be retransmitted. However, if the discarded cells are contained in different packets, 10 packets must be retransmitted after all. Furthermore, if all the 10 packets to be retransmitted are part of different information bursts, the transfer will not be completed until the retransmission of each packet is successfully completed for all the information bursts. When a plurality of retransmissions occur at the same time in this manner, congestion is further assisted, and eventually there is a possibility that no information transfer will be completed satisfactorily.

To prevent this, it is necessary to selectively discard or pass cells. In order to improve the overall throughput, it is important to identify each packet or each burst and to preferentially treat a specific packet or cells included in a specific burst.

Conventionally, a priority control method has been considered as a countermeasure against buffer congestion. This is to provide an area in which the priority identifier can be set in the header of each cell, and to discard the low priority cell at the time of congestion. But this control
If the low priority cells are discarded and congestion still occurs after the low priority cells are discarded, the high priority cells are not randomly identified and are discarded randomly. Will end up.

The present invention has been made against such a background. When congestion occurs in the reception buffer, some cells of the related burst information are prevented from being discarded and the utilization efficiency is high. An object is to provide a cell switching system and device.

[0012]

The first aspect of the present invention is to:
It is a cell switching system provided with a plurality of ATM terminal devices and a cell switch for switching and connecting cells transmitted and received by the terminal devices.

Here, the feature of the present invention resides in that, when the terminal device transmits a series of packets composed of a plurality of cells of continuous information, the header information of the cell is included in the header of the series of packets. And a means for giving an identifier indicating the middle and the end, and the cell exchange is in a state where the means for detecting the identifier indicating the start, the middle and the end and the cell passing amount becomes large and needs to be discarded. At this time, the series of packets is preferentially given from the detection of the identifier indicating the head to the detection of the identifier indicating the end by the detecting means in accordance with the control mode signal of the exchange method inputted from the outside. And means for processing. The preferential processing means is preferably provided in the reception filter of the cell exchange. Further, it is preferable that the means for preferentially processing include means for setting a control mode flag according to a control mode signal and means for setting a burst passing flag while the series of packets are passing.

A second aspect of the present invention is an apparatus used in this cell exchange system.

[0015]

When the receiving buffer becomes congested, only cells belonging to a specific burst are taken into the buffer and all other cells are discarded to prevent the specific burst information from being discarded. That is, when the cell assembling device on the terminal device side transmits a cell, a burst identifier indicating the start, middle and end of a series of bursts is written in the header area of each cell together with the connection identifier.

The cell exchange is provided with the burst identifier discriminating means before the receiving buffer of each outgoing line of the switch, and if the burst identifier discriminating means receives a cell in which the burst start identifier is set, then the cell switching device is operated thereafter. Until a cell having the same connection identifier as this cell and a burst end identifier is set, cells other than the cell having the same connection identifier as the burst start identifier are discarded.

As a result, even if congestion occurs in the reception buffer, cells belonging to a particular burst are always avoided from being discarded, so that the utilization efficiency of the cell exchange is improved as compared with the conventional cell exchange in which cells are randomly discarded.

The idea of the present invention is that it is advantageous in traffic control not to partially discard a plurality of cells that make up a series of packets when one piece of information is meaningful for the series of packets. Is based on. Since the administrator of the communication network cannot enter the contents of the information, it is desirable to previously specify in the network a terminal device that can display that a series of packets is being transmitted.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram of an embodiment of the present invention. FIG. 2 is a block diagram of the reception filter.

The present invention, a plurality of terminal devices ATM 1 ₁₁ ~
1 _2n and a cell exchange 2 that exchanges and connects cells transmitted and received by the terminal devices ₁₁ 1 to _12n .

Here, a feature of the present invention is that when the terminal devices ₁₁ 1 to _12n transmit a series of packets composed of a plurality of cells of continuous information, a series of packets is added to the header information of the cells. Of the packet is provided with a burst identifier assigning circuit 1 as means for assigning the identifiers indicating the beginning, middle and end of the packet, and the cell exchange 2 detects the identifier indicating the beginning, middle and end, and the cell passage amount is large. When it becomes necessary to dispose of it,
Means for preferentially processing a series of packets from the detection of the identifier indicating the beginning to the detection of the identifier indicating the end by the detecting means in accordance with the control mode signal of the exchange method inputted from the outside. It is provided with the reception filters 2 _{51 to} 25 _n including and.

The reception filters 2 ₅₁ to ₂₅ n include a register 31 for temporarily accumulating incoming cells, as shown in FIG.
The control memory 34 in which the header information of this cell and the destination information corresponding to this header information are stored, and the header information of the cell accumulated in the register 31 and the destination information stored in this control memory 34 are collated. The control circuit 33 and the register 31 according to the comparison result by the control circuit 33.
The control circuit 33 includes a gate 32 for sending out the cells stored in the control circuit 33, and the control circuit 33 serves as a means for switching the control mode according to the control mode signal, and the VPI and VPI of the cell in which the identifiers indicating the beginning and the end are detected. VC
A selection register 35 for temporarily storing I, and a burst passing flag 3 indicating that the series of packets is passing.
Including 7 and.

Next, the operation of the embodiment of the present invention will be described. As described above, the reception filters 2 ₅₁ to _{25 n} include the register 31, the gate 32, the control circuit 33, and the control memory 3.
4 and a selection register 35. The control circuit 33 has two status flags inside. One is a flag for identifying a mode in which exclusive control is performed and a mode in which exclusive control is not performed. Switching between these modes is performed at the time of initial setting or when the control unit 28 sets the congestion state of the reception buffers 2 ₆₁ to 26 _n. Monitor and control. Hereinafter, it will be referred to as the control mode flag 36. The other flag is a flag for distinguishing between the passing burst state and other states, and is hereinafter referred to as a burst passing flag 37. The control memory 34 is an associative memory having a function of collating the data stored in the memory with the input data. When the same data as the input bit string is stored in the memory, the control result is compared. The output "1" is output, and otherwise, "0" is output as the collation result. In the control memory 34 of the present invention, all the connection identifiers VPI / VCI to be received by the corresponding output ports 2 ₃₁ to _{23 n} are stored. VPI / VCI is written when the connection is set.

Next, the structure of the cell used in the embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a diagram showing a cell format used in the exclusive control method of the embodiment of the present invention. FIG. 4 is a diagram showing a packet state according to the embodiment of the present invention. VPI / VCI is a connection identifier and is always added to each cell for cell routing and connection identification. The next burst identifier area is a newly introduced area for the present invention, in which a burst start, burst end, and no instruction is given by the burst identifier assigning circuit 1 of the terminal devices ₁₁ 1 to _12n shown in FIG. One of the three identifiers is written. The burst start identifier is written in the first cell of the burst to which the exclusive control of the present invention is applied, and the burst end identifier is similarly written in the last cell of the burst to which the exclusive control method of the present invention is applied. A non-designated identifier is written in all cells other than the first and last cells of the burst and the cells to which the exclusive control of the present invention is not applied even in the first or last cells. Each identifier is associated with a number, which is 1: start of burst, 2: end of burst, and 0: no instruction. This burst identifier may be attached to either a packet unit or a burst composed of a plurality of packets. FIG. 4A shows an example in the case of attaching in units of packets, and FIG. 4B shows an example in which a burst consisting of 3 packets is attached as a target. It should be noted that a method of assigning an identifier such as a cell at the beginning of a packet, a cell in the middle of a packet, and a cell at the end of a packet for each packet has been defined by standardization, but as described above, the burst identifier of the present invention is used. Differ in that there is an undirected identifier.

Next, the operation of the control circuit 33 will be described with reference to FIG. FIG. 5 is a flowchart showing the operation of the control circuit 33. In FIG. 6 shown in the conventional example, the internal bus 2
All the cells flowing over 1 are registered once in the register 31 shown in FIG.
Then, the control circuit 33 reads the VPI / VCI area and the burst identifier area in the header information of the cell received by the register 31 (S0). If the control mode flag is set to the mode in which exclusive control is not performed (S1), the read VPI / VCI is set to the control memory 34.
To obtain a collation output (S12). When the collation result is "1" (S13), the reception cell is a cell addressed to the output port 2 ₃₁ , 2 ₃₂ , ... _{23 3n which the} reception filter 2 ₅₁ , 2 ₅₂ , ..., _25n handles. Because there is a gate 32
Open and transfer to the reception buffers 2 ₆₁ , 2 ₆₂ , ..., _{26 n} of the next stage (S14). If the collation result is "0" (S13), the received cell is discarded (S15).
This operation is similar to that of a normal ATM switch.

Next, when the control mode flag is set to the exclusive control mode (S1), the burst passing flag is always reset to "0" (S2). Control circuit 3
3 retrieves the read burst identifier area (S3), and if the burst start identifier cannot be detected (S4), discards the received cell (S15). When the burst start identifier can be detected (S4), the read VPI / VCI is input to the control memory 34 (S5), and the collation result is "0".
If so (S6), the received cell is discarded (S15). If the comparison result is "1" (S6), the gate 32 is opened and this reception cell is set to the reception buffers 2 ₆₁ , 2 ₆₂ , ..., 2 in the next stage.
Transfer to _6n , set the burst passing flag to "1" (S7), and read VP into the selection register 35.
The I / VCI is set (S8). After that, while the burst passing flag is set to "1", the control circuit reads the VPI / VCI area and the burst identifier area from the received cell and sets the read VPI / VCI in the selection register. / VCI (S9). If they match (S10), the received cell is transferred to the next-stage reception buffers 2 ₆₁ , 2 ₆₂ , ..., _{26 n} (S16, S17).
However, the burst identifier read at this time is determined, and when this burst identifier is the burst end identifier (S11), the burst passing flag is further reset to "0" (S18). When the read VPI / VCI does not match the VPI / VCI set in the selection register (S10), this reception cell is discarded (S1).
9).

[0027]

As described above, according to the present invention,
When congestion occurs in the reception buffer, it is possible to prevent a part of cells of the related burst information from being discarded, and it is possible to realize a cell exchange method with high utilization efficiency. That is, when congestion occurs, cells belonging to a particular burst are reliably switched. This facilitates management because bidirectional multicast communication can be performed with only one identifier regardless of the number of lines in the group in terms of hardware.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2 is a block configuration diagram of a reception filter.

FIG. 3 is a diagram showing a cell format used in the exclusive control method.

FIG. 4 is a diagram showing a packet state according to the embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the control circuit.

FIG. 6 is a block configuration diagram of an output buffer type ATM switch.

FIG. 7 is a block diagram of a conventional reception filter.

[Explanation of symbols]

1 burst identifier assigning circuit 1 ₁₁ to _12n terminal device 2 cell switch 2 ₂₁ to 2 _2n input port 2 ₄₁ to 2 _4n input interface 2 ₅₁ to _25n reception filter 2 ₆₁ to 2 _6n reception buffer 2 ₃₁ to _23n output port 21 Internal Bus 27 Switch Control Section 31 Register 32 Gates 33, 36 Control Circuit 34 Control Memory 35 Selection Register 37 Burst Passing Flag

Claims (4)

(57) [Claims] 1. A plurality of terminal devices in an asynchronous transfer mode,
In a cell switching system including a cell switch that exchanges and connects cells transmitted and received by this terminal device, the terminal device, when transmitting a series of packets composed of a plurality of cells consisting of continuous information, The header information is provided with means for giving an identifier indicating the beginning, middle, and end of a series of packets, and the cell exchange detects the identifier for indicating the beginning, middle, and end, and discards due to a large cell passage amount. When a state in which the above is required is reached, in accordance with a control mode signal of the exchange method input from the outside, the detecting means detects the identifier indicating the beginning until the identifier indicating the end is detected. A cell exchange method characterized by comprising means for preferentially processing a series of packets. 2. The cell switching system according to claim 1, wherein the preferential processing means is provided in a reception filter of the cell switching system. 3. The means for preferentially processing sets a control mode flag according to a control mode signal,
3. The cell switching system according to claim 2, further comprising means for setting a burst transit flag during passage of the series of packets. 4. A device used in the cell switching system according to claim 1.