JP3002726B1 - Variable speed digital switching system - Google Patents

Abstract

A variable rate digital switching system suitable for handling moving picture traffic is provided. SOLUTION: Incoming line and outgoing line TDM arranged in a grid pattern
A cross point buffer is provided at each grid point of the bus, and each of the cross point buffers checks the frame header of the input TDM frame on the incoming TDM bus and buffers only the data of the time slot addressed to the outgoing TDM bus to which it belongs. Ring and transfer the contents of the frame header to the scheduler, which schedules how to allocate time slots in the output TDM frame to each crosspoint buffer based on the contents of the frame header.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital switching system, and more particularly to a variable speed digital switching system for processing variable speed traffic such as video traffic.

[0002]

2. Description of the Related Art As a conventional digital switching system, T
The DM system and the ATM system are widely used. TD
The S switch (space switch), which is an M-type switch,
A switch that arranges time-division gates between incoming and outgoing lines and opens and closes the time-division gates at a high speed, thereby exchanging incoming and outgoing lines in units of time slots while multiplexing. FIG. 1 is a diagram illustrating the principle of the S switch. The S-switch is composed of a time-division gate and a control memory for controlling the opening and closing thereof, and information in each time slot of the incoming line corresponds to a desired destination through the time-division gate specified in the control memory. Move to the time slot on the outgoing line. At this time, the time position of the time slot is preserved, and the time position of the incoming / outgoing line becomes the same. The control memory is prepared for each outgoing line, and stores which incoming line gate is opened and information is passed through for each time slot.

[0003] A cross point buffer, which is an ATM type exchange, is a system in which a buffer is arranged at the intersection of an input port and an output port. FIG. 2 is a diagram illustrating the principle of the cross point buffer. The operation will be described with reference to FIG. 2 using buffers ij located in the input row i and the output row j. The buffer ij looks at the header of the ATM cell input from the input port i by the action of the address filter, and inputs only the buffer whose destination is j to the buffer ij. When the cells to be transmitted are stored in the buffer, a transmission request is issued to the output control circuit of the output row j. When the request is accepted, the cells are transmitted to the output port j.

[0004] The TDM exchange has an advantage that once connection setup is completed, delay guarantee and loss rate guarantee can be reliably performed without performing special control such as flow control and congestion control. Currently, it is mainly used for voice communication with severe delay conditions.

[0005]

However, the TDM exchange has the following problems. The first problem is that the increase in capacity of the TDM exchange depends on the speed limit of the TDM bus and the speed limit of the RAM. Further, as the speed of the TDM bus increases and as the number of inputs increases, the input time slot increases. Because it is difficult to establish synchronization of
It is difficult to increase the capacity to Gbps or more.

The second problem is that the TDM switch is originally a means for efficiently switching traffic of the same speed, so that the TDM switch operates efficiently in a situation where traffics having various required speeds coexist. Without
The time slot delay increases, ie, it is difficult to handle multi-rate traffic.

A third problem is that in order to handle variable speed in the current TDM network, it is necessary to request a time slot at the maximum speed of the traffic, and the transmission efficiency becomes very poor. It is difficult to handle speed traffic efficiently.

[0008] Traffic with severe delay conditions includes video traffic in addition to the voice traffic described above.
MPEG2 is a typical moving picture encoding method, but encoding with this method usually generates variable-rate traffic. FIG. 3 shows an example of the MPEG2 stream. Assuming that the average use bandwidth of this traffic is about 1 Mbps and the maximum use bandwidth is about 5 Mbps, when using the conventional TDM switching method, the connection must be set at about 5 Mbps, which is the maximum use bandwidth. However,
Since the average use bandwidth of this traffic is about 1 Mbps, a transmission bandwidth of about 4 Mbps is wasted. Therefore, when attempting to handle moving image traffic using a TDM switch, it is important to solve the third problem among the three problems of the existing TDM switching system, in particular.

An object of the present invention is to solve the above-mentioned problems of the conventional TDM switching system and to provide a variable speed digital switching system suitable for handling traffic with strict delay conditions, particularly moving picture traffic. .

[0010]

SUMMARY OF THE INVENTION Accordingly, a variable rate digital switching system according to the present invention includes a plurality of incoming lines TD each.
The M bus and the outgoing TDM bus are arranged in a grid,
A cross point buffer is provided at each grid point of the DM bus,
A crosspoint buffer belonging to each outgoing TDM bus is connected to a respective scheduler, and each of the crosspoint buffers examines the frame header of the input TDM frame on the incoming TDM bus and sends a message to the outgoing TDM bus to which Only the data of the time slot is buffered and the content of the frame header is transferred to the scheduler. The scheduler determines how the time slot in the output TDM frame is stored in each crosspoint buffer based on the content of the frame header. Performing scheduling on whether to allocate, and each crosspoint buffer sequentially puts the buffered data in its assigned time slot of the output TDM frame according to the scheduling; And characterized in that the output from the serial outgoing line TDM bus.

In one embodiment of the variable speed digital switching system according to the present invention, a plurality of incoming TDM buses and outgoing TDM buses are arranged in a grid, and a cross point buffer is provided at each grid point of the TDM bus. A crosspoint buffer belonging to the outgoing TDM bus is connected to each scheduler, each content analyzer is connected to each scheduler, and each of the crosspoint buffers examines a frame header of an input TDM frame on the incoming TDM bus. Buffering only the data of the time slot addressed to the outgoing TDM bus to which it belongs, and transferring the contents of the frame header to the content analyzer. The content analyzer checks the frame header, and checks the outgoing line to which it belongs. Each crosspoint buffer on the TDM bus The contents of the stored data are determined, and the information is notified to the scheduler. The scheduler determines the time slot in the output TDM frame based on this information and the amount of data stored in each crosspoint buffer. In such a manner as to allocate the data to each cross point buffer, and sequentially input the data buffered in the time slot allocated to itself in the output TDM frame according to the scheduling. Output from the outgoing line TDM bus. In this way, the TDM
By combining an S-switch as a type of exchange and a cross-point buffer type switch as a type of ATM exchange, even if the number of inputs is increased to increase the capacity, the timing of slight input between time slots can be reduced. Since the displacement can be absorbed by the buffer, the capacity can be easily increased as compared with the conventional TDM switching system. Also,
In the case of handling variable speed traffic, for example, if the connection setting is set to the average use band, if the data to be transmitted to one input is smaller than this average use band, this transmission band may be used by other inputs. If the data to be transmitted by a certain input is larger than the average used bandwidth, the transmission can be performed by borrowing a vacant transmission band of another input, so that the variable rate traffic can be handled efficiently. Furthermore, even when dealing with multi-rate traffic, it is advantageous because the delay of time slots can be suppressed.

According to another embodiment of the present invention, the scheduling is a maximum queuing system in which time slots are allocated to the crosspoint buffers on the outgoing line in order from the crosspoint buffer having the longest queue length. It is characterized by the following. In this way, time slot loss due to buffer overflow can be minimized.

According to still another embodiment of the present invention, the scheduling is performed by a minimum queuing method for allocating time slots to the crosspoint buffers on the outgoing line in order from the crosspoint buffer having the shortest queue length. It is characterized by having done. If you do this,
The average buffering delay of the time slot can be minimized.

According to still another embodiment of the present invention, the scheduling is performed by allocating a time slot to the cross point buffer on the outgoing line based on a round robin method. In this way, the maximum delay time of the time slot can be guaranteed.

According to still another embodiment of the present invention, the scheduling is performed by randomly allocating a time slot to the cross point buffer on the outgoing line. In this way, the scheduling process can be simplified.

According to still another embodiment of the present invention, the time slot length of the TDM frame is 16 kilobits, and the frame period is a divisor of the image frame period of the input image signal.

[0017]

FIG. 4 is a diagram illustrating the principle of an embodiment of a variable rate digital switching system according to the present invention. The switch 1 according to the present system includes input and output TDM buses 2 ₁ , 2 ₂ ,. . . , 2 _i and 3 _1, 3 _2,. . . , 3 _j and cross point buffers 4 _1,1 , 4 _1,2 ,... Provided at each grid point of the incoming and outgoing TDM buses. . . , 4 _{i, j} and content analyzers 5 ₁ , 5 ₂ ,. . . , 5 _j and schedulers 6 ₁ ,
62 _,. . . , 6 _j .

FIG. 5 shows an example of the format of a TDM frame used in the variable rate digital switching system shown in FIG. Usually, the time slot length of a TDM frame is 1o
Although the length of the TDM frame is about 125 μs, the use of a larger time slot length is more efficient and the capacity can be easily increased when handling moving picture traffic. In particular, in many video signal encoding schemes such as MPEG2, the frame period is 33 ms, so that, for example, the time slot length is 16 kbit, the TDM
3.3 ms frame period (622.08 Mb transmission speed)
ps), it is a divisor of the frame period used in these encoding methods, and the video frame and the TDM
It becomes possible to associate frames. By this association, control for optimizing the moving image quality can be performed in the exchange, and the network quality is the same as compared with the conventional exchange system (TDM exchange system, ATM exchange system, packet exchange system, etc.). Even
There is also an advantage that the moving image quality can be improved.

Returning now to FIG. 4, the operation of the variable speed digital switching system according to the present invention will be described as an example. When transmitting a TDM frame as shown in FIG. 5, the incoming and outgoing TDM buses 2 ₁ , 2 ₂ ,. . . , 2 _i and 3 ₁ ,
32 _,. . . , 3 _j at a transmission speed of 155 Mbps to 50
A high-speed TDM bus of about Gbps is used.

The incoming TDM buses 2 ₁ , 2 ₂ ,. . . , 2 _i
5 receives an input TDM frame as shown in FIG. 5, each of the crosspoint buffers on the incoming TDM bus checks the header of the input TDM frame, and the outgoing TDM bus to which it belongs belongs to the destination TDM bus. Only the data of the time slot is buffered, and the TDM frame header is transferred to the content analyzer connected to the outgoing TDM bus to which the TDM frame belongs. The content analyzer examines the TDM frame header and determines the content of data buffered in each crosspoint buffer on the outgoing TDM bus to which the content analyzer belongs, for example, MPEG.
In the case of data, the type of picture (I picture, P picture or B picture) is determined, and the information is notified to the scheduler. Based on this information and the amount of data stored in each crosspoint buffer, the scheduler assigns a time slot in the output TDM frame to each crosspoint buffer on the outgoing TDM bus to which it belongs. Scheduling. Each of the crosspoint buffers sequentially puts the buffered data in a time slot assigned to itself in the output TDM frame according to the scheduling, and outputs the data from the outgoing TDM bus.

As a scheduling method for allocating a time slot in the output TDM frame to each cross point buffer, for example, there is the following method. The first scheduling method is a maximum queuing method in which time slots are sequentially allocated to the crosspoint buffers on the outgoing line from the crosspoint buffer having the longest queue length. The advantage of this method is that
Time slot loss due to buffer overflow can be minimized.

The second scheduling method is a minimum queuing method in which time slots are sequentially allocated to the crosspoint buffers on the outgoing line from the crosspoint buffer having the shortest queue length. The advantage of this scheme is that the average buffering delay of the time slot can be minimized.

The third scheduling method is a method of allocating a time slot to the cross point buffer on the outgoing line based on a round robin method.
The advantage of this scheme is that the maximum delay time of the time slot can be guaranteed.

The third scheduling method is a method of randomly allocating a time slot to the cross point buffer on the outgoing line. The advantage of this method is that
That is, the scheduling process can be simplified.

In the above embodiment, the content analyzer examines the frame header, and the scheduler performs scheduling based on the information. However, the content analyzer is omitted, and the scheduler performs scheduling directly from the contents of the frame header. It is also possible to configure.

[0026]

According to the present invention, the problem of the conventional TDM switching system can be solved by combining the S switch, which is a kind of TDM switch, and the crosspoint buffer type switch, which is a kind of ATM switch, A variable rate digital switching system suitable for handling traffic with severe delay conditions, particularly video traffic, is provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of an S switch.

FIG. 2 is a diagram illustrating the principle of a cross point buffer switch.

FIG. 3 is a graph showing an example of an MPEG2 stream.

FIG. 4 is a diagram illustrating the principle of an embodiment of a variable rate digital switching system according to the present invention.

FIG. 5 is a diagram showing an example of a format of a TDM frame.

[Explanation of symbols]

1 switch 2 ₁ to 2 _i incoming TDM bus 3 ₁ to 3 ₂ outgoing lines TDM bus 4 _1,1 ~4 _{i, j} crosspoint buffer 5 ₁ to 5 _j Content Analyzer 6 ₁ to 6 _j scheduler

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04Q 11/00 H04L 12/28

Claims (7)

(57) [Claims] 1. A plurality of incoming TDM buses and outgoing T
A DM bus is arranged in a grid, a cross point buffer is provided at each grid point of the TDM bus, and a cross point buffer belonging to each outgoing TDM bus is connected to each scheduler. It examines the frame header of the input TDM frame on the TDM bus, buffers only the time slot data addressed to the outgoing TDM bus to which it belongs, and transfers the contents of the frame header to the scheduler. Scheduling how to allocate a time slot in an output TDM frame to each crosspoint buffer based on the contents of a frame header, wherein each of the crosspoint buffers determines the position of the output TDM frame according to the scheduling. Assigned time slots will sequentially put the data is buffered, variable speed digital switching system and outputs from said outgoing line TDM bus. 2. A plurality of incoming TDM buses and outgoing T each.
A DM bus is arranged in a grid, a cross point buffer is provided at each grid point of the TDM bus, a cross point buffer belonging to each outgoing TDM bus is connected to each scheduler, and each content analyzer is connected to each scheduler. Each of the cross point buffers checks the frame header of the input TDM frame on the incoming TDM bus, buffers only the time slot data destined for the outgoing TDM bus to which the cross point buffer belongs, and the contents of the frame header. To the content analyzer, the content analyzer examines the frame header, determines the content of data stored in each crosspoint buffer on the outgoing TDM bus to which the content analyzer belongs, and notifies the scheduler of the information. And the scheduler uses this information Based on the amount of data stored in the crosspoint buffer, the output TD
Scheduling how to allocate time slots in M frames to each crosspoint buffer, wherein each of said crosspoint buffers is buffered in its assigned time slot of said output TDM frame according to said scheduling. Wherein said data is sequentially input and output from said outgoing TDM bus. 3. The variable rate digital switching system according to claim 1, wherein the scheduling is performed by allocating time slots to the cross point buffers on the outgoing line in order from the cross point buffer having the longest queue length. A variable rate digital switching system characterized by a maximum queuing system. 4. The variable rate digital switching system according to claim 1, wherein said scheduling allocates time slots to the cross point buffers on the outgoing line in order from the cross point buffer having the shortest queue length. A variable speed digital switching system characterized by a minimum queuing system. 5. The variable rate digital switching system according to claim 1, wherein the scheduling is performed by allocating a time slot to a cross point buffer on the outgoing line based on a round robin system. Variable speed digital exchange system. 6. The variable rate digital switching system according to claim 1, wherein said scheduling is performed by randomly allocating a time slot to a cross point buffer on said outgoing line. Digital switching system. 7. The variable rate digital switching system according to claim 1, wherein a time slot length of said TDM frame is 16 kilobits, and a frame period is a divisor of an image frame period of an input image signal. A variable speed digital exchange system characterized by the following.