JP3540430B2 - ATM switch - Google Patents

Description

[0001]
[Industrial applications]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asynchronous transfer mode (ATM) switch which is suitable for two-way image communication such as digital telephone and video telephone and transfers video information having a large amount of information.
[0002]
[Prior art]
Conventionally, ATM exchanges are exchanges that transfer bidirectional image communications such as digital telephones and videophones to an ATM network and perform exchanges in an asynchronous transfer mode. Generally, an ATM switch is designed such that input and output terminals corresponding to upstream and downstream of the switch have the same capacity. In addition, traffic is designed to be averaged in the input and output directions for each input / output terminal. In other words, for the traffic applied to the input / output terminals of the ATM switch connected to the transmission line, a switch designed on the assumption that the bidirectional traffic volume is equal is used, and this is called a bidirectional balanced switch here.
[0003]
The video-on-demand (VOD) service is a service that distributes video programs such as video information at the request of subscribers, and is scheduled to be provided on ATM networks. The VOD system includes, as communication facilities, a server device that provides a video program in response to a request from a subscriber and an image terminal in a general subscriber's home. The subscriber operates the terminal device to send program selection information to the server device in the form of a control signal through the ATM network, and receives the video program image and audio signal sent from the server device by the terminal device, To play. The control signal transmitted to the up line by the subscriber's program selection operation is a burst signal of several 100 Kbps, and the video signal transmitted from the server device to the down line has an information amount of about 6 Mbps. As described above, the transmission information amount of the VOD service is more than 10 times the signal rate of the video phone at 500 Kbps, and is also biased toward the downlink.
[0004]
[Problems to be solved by the invention]
On the other hand, conventional ATM exchanges use two-way balanced switches that are designed for two-way communication such as digital telephones and videophones, and that are designed on the assumption that the input and output terminals have the same traffic volume. ATM cells arriving at any input terminal of such a bidirectional balanced switch are temporarily stored in an ATM cell storage buffer, then routed by the ATM cell header in the ATM switch element, and output to the target port. . At this time, the bidirectional balanced switch is designed on the assumption that cells are not concentrated on a specific output port.
[0005]
An ATM switch generally contains a large number of general subscriber terminals. When the VOD service is accommodated in such an ATM exchange network and the video information distribution service is performed, a significant unbalanced traffic occurs between the server device and the subscriber terminal device. When such a service is provided to a certain subscriber terminal, the connection between the server device of the ATM exchange and the subscriber terminal via a transmission line having a band necessary for distributing moving image information is established. In between, the transmission band from the subscriber terminal to the exchange is hardly used, though a wide band for moving images is always secured through the exchange. In other words, the traffic volume of the input / output terminals is extremely small in the up-link compared to the down-link, and becomes extremely unbalanced. Therefore, the line accommodation efficiency is low from the viewpoint of the whole exchange. Further, when an ATM switch having a large traffic volume per terminal is used, there is a disadvantage that the configuration becomes redundant.
[0006]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the drawbacks of the prior art and to provide an ATM exchange which efficiently accommodates communication equipment in which the amount of transmission information in the vertical direction is uneven.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an ATM switch according to the present invention comprises: first ATM switch means for transferring and routing cells in both directions in first and second directions of a transmission line; Second ATM switch means for transferring and routing in a second direction, and a first ATM for sending first information having a flow rate in both directions and receiving second information having a significantly higher flow rate in a second direction. A cell connected between the input / output port and the first and second ATM switch means for identifying first information and second information among cells of information arriving at the first input / output port, The first information is transferred to the first ATM switch, the second information is transferred to the second ATM switch, and the information received from the first and second ATM switch is output to the first input / output port. A first interface circuit means for transmitting the first and second information. Connected between the second input / output port from which the first information arrives and the first and second ATM switch means, and transfers the information arriving at the second input / output port to the first ATM switch means. And second interface circuit means for outputting information output from the first and second ATM switch means to the second input / output port.
[0008]
According to the present invention, the ATM switch further comprises: first ATM switch means for transferring and routing cells in the first direction of the transmission line and in a second direction opposite to the first direction, and A first information cell having a bi-directional flow rate is transferred bi-directionally in the first and second directions of the transmission line, and a second information cell having a significantly higher flow rate in the second direction is transferred to the second direction. The second ATM switch means for transferring and routing to the first ATM switch means, and the input / output terminal on the preceding stage in the first direction of the first ATM switch means to the input / output on the subsequent stage in the first direction of the second ATM switch means. The first connection path means connected to the terminal and the input / output terminal on the upstream side in the first direction of the second ATM switch means are connected to the input / output terminal on the downstream side in the first direction of the first ATM switch means. Second connection means for connecting, and second ATM switch means. Accommodates an input terminal for receiving the second information on the front side in the second direction, and an output terminal for outputting the second information on the rear side in the second direction, and the second ATM switch means is provided from the first direction. When receiving the cell of the first information, the cell is transferred to the first connection path means. When the cell of the information is received from the second direction, the first information and the second information of the cell are exchanged. Identifying and transferring the first information cell to the second connection means and the second information cell to the output terminal.
[0009]
[Action]
According to the invention, the first ATM switch means transfers and routes cells bidirectionally in the first and second directions. The second ATM switch means transfers and routes the cell in the second direction of the transmission line. When a cell of information arrives at the first input / output port, the first interface circuit means discriminates the first information from the second information, and transmits the first information to the first ATM switch means. Transferring the second information to the second ATM switch means; When receiving information from the first and second ATM switch means, the information is output to the first input / output port. When information arrives at the second input / output port, the second interface circuit means transfers the information to the first ATM switch means, and outputs the information output from the first and second ATM switch means to the second input / output port. Output to port.
[0010]
According to the invention also, the first ATM switch means routes the cells in both directions in the first and second directions of the transmission line. The second ATM switching means transfers cells of the first information bidirectionally in the first and second directions, and routes cells of the second information in the second direction. The second ATM switch means, when receiving the first information cell from the first direction, transfers this cell to the first connection path means, and when receiving the information cell from the second direction, this cell , The first information cell and the second information are identified, and the first information cell is transferred to the second connection path means, and the second information cell is transferred to the output terminal.
[0011]
【Example】
Next, an embodiment of the ATM exchange according to the present invention will be described in detail with reference to the accompanying drawings. In the embodiment shown in FIG. 1, the ATM switch 10 is a switch that divides and accommodates information into fixed-length cells, adds a destination label to the cells, and transfers the cells to the ATM network. In general, the size of the information flow in such an ATM exchange depends on the number of cell transfers per unit time. The ATM exchange 10 accommodates a number of VOD service terminals 11, terminal devices 13 such as video telephone terminals and digital telephone terminals, and trunk lines (not shown). Although a large number of these terminals 11 and 13 are actually accommodated, only two are shown in FIG.
[0012]
The embodiment also includes a video on demand (VOD) service function, and for this purpose, a server 12 for VOD service is also accommodated. The VOD service transmits the program selection information to the server 12 in the form of a control signal through the ATM exchange 10 by operating the VOD service terminal 11, and responds to this by transmitting the video and image signals of the video program transmitted from the server 12 to the VOD service. An image / audio distribution service in which the service terminal 11 receives and reproduces a video program on the terminal 11. The server 12 is a service device that receives program selection information from the VOD service terminal 11, and distributes video program images and / or audio signals in response to requests from subscribers based on the selection information. The video image from the server 12 has a bandwidth of 6 Mbps in this embodiment. In this embodiment, the VOD service terminal 11 installed in the subscriber's house sends the program selection control information 100 in the form of a burst signal of several hundred Kbps to the server 12, and receives the video image video information 101 from the server 12. I do. Therefore, the information transmitted to and received from the VOD service terminal 11 is more downlink information.
[0013]
The ATM switch 10 also houses a general voice and / or image terminal 13. When the general terminal 13 is a video telephone terminal, it transmits and receives bidirectional balanced information 102 of, for example, 500 Kbps, and when it is a digital telephone terminal, it transmits and receives bidirectional balanced information 102 of, for example, 64 Kbps. The information signals to and from these terminals 13 are premised on being balanced in both directions, but have a significantly smaller amount of information than the VOD service terminal 11.
[0014]
In this embodiment, the ATM switch 10 has two ATM switches 18 and 19. The VOD service terminal 11 is accommodated in a line unit (VLU) 15. The line unit 15 assembles the uplink information 100 from the VOD service terminal 11 and the uplink and downlink information 102 for the general terminal 13 into a cell from the subscriber transmission line 16 and transfers this to the ATM switch 18 via the path 17, and This is an interface circuit that receives downstream information from the server 12 to the VOD service terminal 11, which is video information 101, from the other ATM switch 19 and transfers it to the transmission line 16. A header is added to each cell, and the header includes a flag indicating the communication or control information 100 or 102. The line unit 19 also has a function of disassembling the cell. FIG. 3 shows a configuration example of the line unit 19. As can be seen, the line unit 15 has a multiplexing circuit (MUX) 201 that multiplexes the signals coming from the two ATM switches 18 and 19 and sends out the multiplexed signal to the transmission line 16 to the VOD service terminal 11.
[0015]
The server 12 is housed in a trunk line unit (TLU) 21. The trunk line unit 21 separates downlink information 101, which is video information output from the server 12, and communication and control information 102 with a small flow rate into a cell and assembles them into a cell.The former is connected to one ATM switch 19, and the other is connected to the other ATM switch 19. This is an interface circuit for sending to the switch 18 and sending upstream information 100 from the other ATM switch 18 to the server 12. A header is added to each cell, and the header includes a flag indicating whether the information is video information 101 or communication or control information 102. The trunk line unit 21 also has a function of disassembling the cell. Trunk line unit 21 has, for example, a configuration shown in FIG. As can be seen from the figure, the trunk line unit 21 has a demultiplexing circuit (DEMUX) 202 for demultiplexing a signal coming from the server 12 and distributing it to two ATM switches 18 and 19.
[0016]
The ATM switch 19 is a one-way switch having a configuration as illustrated in FIG. In the one-way ATM switch 19, large-capacity ATM cell storage buffers 191 and 192 corresponding to video information 101 having a large amount of information are connected to an input port 203 and an output port 204 of an ATM switch element 193, respectively. The ATM switch element 193 is a one-way type switch that adds a label to an input cell coming from the input buffer 191, routes the label in the switch 193, and transfers it to the output buffer 192. Although a large number of input / output ports 203 and 204 are actually accommodated, only four ports are shown in FIG.
[0017]
The other ATM switch 18 is a bidirectional balanced ATM switch as in the related art. The bidirectional balanced ATM switch 18 is connected to a line unit (LU) 22 which is an interface circuit with the general terminal 13 and is connected to a terminal 13 such as a video telephone terminal or a digital telephone terminal connected via a subscriber transmission line 23. The ATM switch is a balanced ATM switch that transfers the information 102 from the VOD service terminal 11 to the server 12. As shown in FIG. 7, the ATM switch 18 comprises an ATM switch element 181 and a bidirectional ATM cell storage buffer 182 connected to its input port 205 and output port 206. ATM cells arriving at an arbitrary input terminal are temporarily stored in an ATM storage buffer 182, then routed according to the ATM cell header in the ATM switch element, stored in a storage buffer 182 from a target output port 206, and output to an output terminal. Is output. At this time, it is designed so that cells are not concentrated on a specific output port 206. Although a large number of input / output ports 205 and 206 are actually accommodated, only four ports are shown in FIG.
[0018]
The conventional ATM switching network does not have a switch corresponding to the one-way ATM switch 31, but has only the two-way balanced ATM switch 18. For this reason, when trying to accommodate the VOD service provided by the server 12 to the VOD service terminal 11, while the ATM switch 18 secures a large amount of input / output terminals in both directions, the server 12 actually transmits the VOD service terminal. Only in the direction toward 11, large-capacity information transfer is performed. For this reason, the number of terminals that can be accommodated in the ATM switch 18 decreases, and the line accommodating efficiency decreases when viewed from the whole exchange. In addition, the amount of traffic at the input / output terminals is extremely small on the up as compared to the down, and becomes extremely unbalanced.
[0019]
In the operating state, the line unit 15 receives various information 100 and 102 from the VOD service terminal 11 on the transmission line 16. When the line unit 15 receives the VOD service program selection information 100 transmitted from the VOD service terminal 11 and the information 102 such as call setting and call information for the general terminal 13, the line unit 15 identifies them, and among them, The information 102 is distributed to the path 17, and the information 102 passes from the line unit 22 to the telephone terminal 13 on the transmission path 23 through the balanced ATM switch 18. The VOD service selection information 100 from the VOD service terminal 11 is also transferred to the balanced ATM switch 18, which is transmitted from the trunk line unit 21 to the server 12 through the balanced ATM switch 18. On the other hand, when the trunk line unit 21 receives the video information 101 of the VOD service from the server 12, it identifies it and distributes it to the one-way ATM switch 19, and the one-way ATM switch 19 The video information 101 is routed to the VOD service terminal 11 via the line unit 15. In addition, the general terminal 13 such as a videophone or a digital telephone on the subscriber transmission line 23 performs two-way communication via the balanced ATM switch 18.
[0020]
As described above, in the present embodiment, the one-way ATM switch 19 is introduced, and the switching from the server 12 to the VOD service terminal 11 is integrated in the switch 19. The input and output terminals of the ATM switch 19 in the direction from the server 12 to the VOD service terminal 11 secure the capacity required for moving image information transmission, and the input and output terminals from the VOD service terminal 11 to the server 12 The input and output terminals have the necessary capacity for signal transmission. In this way, the necessary capacity can be set for the input and output terminals in the up direction and the down direction, respectively, so that efficient operation can be achieved.
[0021]
FIG. 2 shows an ATM switch 30 according to another embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate similar elements. The ATM switch 30 of this embodiment is significantly different from the embodiment of FIG. 1 in that a bidirectional unbalanced ATM switch 31 is provided instead of the one-way ATM switch 19 in the embodiment shown in FIG. The bidirectional unbalanced ATM switch 31 accommodates the VOD service terminal 11 via the transmission line 16 by the line unit 32 and is connected to the server 12 via the trunk line unit 33. The line unit 32 has a function of assembling information from the transmission path 16 into cells, adding a header thereto, and decomposing the cells. The trunk line unit 33 has a function of assembling information from the server 12 into a cell, adding a header corresponding to the information type to the cell, and decomposing the cell. The ATM switch 31 is also connected to the two-way balanced ATM switch 18 via crossing paths 34 and 35, and via the latter to the general terminal 13 such as a videophone or digital telephone.
[0022]
Although the unbalanced ATM switch 31 is a bidirectional switch, it is an unbalanced switch in which the traffic flow handled by the switch is set to be large in the downward direction. The input / output terminals of the ATM switch 31 are necessary for transmitting moving image information and control information in the direction from the server 12 to the subscriber terminal 11 when setting up a call between the VOD service terminal 11 and the server 12. It has a large capacity. This capacity is larger than the capacity of the input / output terminals for information sent from the subscriber to the balanced ATM switch 18, such as control information sent from the subscriber terminal 11 to the server 12. The ATM switch 31 has a function of switching moving image information sent from the server 12 to the VOD service terminal 11, and a function of separating a control signal and moving image information. Whether the signal is a control signal or moving image information is displayed as an identification flag in the header of the cell. The unbalanced ATM switch 31 switches the separated control information to the path 34 to the balanced ATM switch 18 according to the header.
[0023]
More specifically, as shown in FIG. 6, the unbalanced ATM switch 31 has an ATM switch element 317. The switch element 317 is composed of an input port 220 and an output port 221 having a large input / output capacity indicated by a thick line in FIG. have. Cell buffers 313 and 314 are connected to the input port 220 and the output port 221 respectively. One cell buffer 313 accommodates an input / output terminal 311 connected directly to the trunk line unit 33 and an input / output terminal 311 connected to the other cell buffer 314 so as to directly enter and exit the line unit 32. The output terminal 312 is housed. The input / output terminal 311 is an unbalanced input / output terminal including a signal line 311a having a large input / output capacity indicated by a bold line and a signal line 311b having a small capacity indicated by a thin line. Similarly, the other input / output terminal 312 is an unbalanced input / output terminal including a signal line 312a having a large input / output capacity and a signal line 312b having a small capacity.
[0024]
One of the input ports 220 of the ATM switch element 317 is connected to the output 222 of a multiplexer (MUX) 315, and the input of the multiplexer 315 is connected to a signal line having a small output capacity from the cell buffers 314 and 318. Have been. The multiplexer 315 has a signal multiplexing function of multiplexing signals having a small output capacity from the cell buffers 314 and 318 and outputting the multiplexed signal to the input port 222 of the ATM switch element 317. In addition, one of the output ports 221 of the ATM switch element 317 is connected to the input 223 of the demultiplexing circuit (DEMUX) 316, and the output thereof is a signal line having a small output capacity to the cell buffers 313 and 318. It is connected. The demultiplexing circuit 316 has a demultiplexing function of demultiplexing the multiplexed signal at the output port 223 of the switch element 317 and distributing it to the cell buffers 313 and 318. The cell buffer 318 is a buffer to which the connection lines 34 and 35 to the two-way balanced ATM switch 18 are connected and temporarily stores information exchanged with the ATM switch 18.
[0025]
The cell including the video information 101 of the VOD service with a large information flow transmitted from the server 12 is input from the input / output terminal 311a to the cell buffer 313 and enters the switch element 317 with a large flow capacity. The video information 101 is routed by the switch element 317, enters the cell buffer 314 from its output terminal 221 and is output from this to the input / output terminal 312 with a large flow rate. On the other hand, the information 100 of program selection from the VOD service terminal 11 and the information 102 of call setting and call information for general terminals 13 such as videophones and digital phones have a low information flow rate. The signal is input from the unit 32 to the cell buffer 314, multiplexed by the multiplexer 315, and input to the input port 222 of the switch element 317. Similarly, information on a switch connection line of the NO.7 system or the like having a small information flow rate is also input to the cell buffer 318 and multiplexed by the multiplexer 315. These cells of information 100 and 102 are routed in switch element 317 and switched to corresponding output ports 221 and 223. The information 100 and 102 with a small information flow output from the output port 223 of the switch element 317 are separated by the demultiplexing circuit 316 and distributed to the cell buffers 313 and 318, respectively, and output to the output terminals 311b and 34 with the small information flow. Is done.
[0026]
Returning to FIG. 2, when the VOD service terminal 11 sends out information 100 on program selection of the VOD service and information 102 on the general terminal 13 such as call setting and call information from the subscriber transmission line 16, the line unit 32 The data is received, assembled into cells, and input to the ATM switch 31. ATM switch 31 routes this to path 34 according to its header. The information 100 or 102 input to the ATM switch 18 from the path 34 is routed to the line unit 22 from the ATM switch 18 and transmitted to the general terminal 13 from the transmission path 23. Further, the program selection information 100 of the VOD service is routed from the ATM switch 18 to the path 35, and is input to the unbalanced ATM switch 31 again. The unbalanced ATM switch 31 routes the cells of the control information 100 to the trunk line unit 33, whereby the control information 100 reaches the server 12. On the other hand, the video information 101 of the VOD service from the server 12 is assembled into cells by the trunk line unit 33, and is then input to the ATM switch 31. The ATM switch 31 routes this to the route to the line unit 32 according to its header. Thereby, the video information 101 reaches the VOD service terminal 11. In addition, the general terminal 13 such as a videophone or a digital telephone on the subscriber transmission line 23 performs two-way communication via the balanced ATM switch 18. This is similar to the embodiment shown in FIG.
[0027]
The embodiment described with reference to FIG. 2 has a configuration in which moving image information and control information are separated in the bidirectional unbalanced switch 31. Therefore, it is not necessary to provide the line interface portions 32 and 33 with an information separating function. This has the effect of using existing equipment more effectively than in the embodiment described with reference to FIG.
[0028]
【The invention's effect】
As described above, according to the present invention, the number of cells per input / output terminal can be increased in accordance with the coexistence of heterogeneous communications such as conventional telephones in which the two-way information flow is balanced and VOD services in which the one-way information flow is extremely large. The configuration is a combination of a two-way balanced switch with a small transfer amount and a one-way or two-way unbalanced switch with a large cell transfer amount. As a result, the redundancy of various elements such as buffers and switch elements in the ATM switch configuration can be minimized, and the ATM switch can be configured efficiently.
[0029]
When introducing a VOD service to a conventional balanced ATM switch that handles videophones and digital phones, it can be handled by adding a one-way or two-way unbalanced switch to the conventional two-way balanced switch.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a relay system of an embodiment of an ATM exchange according to the present invention.
FIG. 2 is a relay system diagram of another embodiment of the ATM exchange according to the present invention.
FIG. 3 is a diagram showing a configuration example of a line unit in the embodiment shown in FIG. 1;
FIG. 4 is a diagram showing a configuration example of a trunk line unit in the embodiment.
FIG. 5 is a block diagram showing a configuration example of a one-way type ATM switch in the embodiment shown in FIG. 1;
FIG. 6 is a block diagram showing a configuration example of a bidirectional unbalanced ATM switch in the embodiment shown in FIG. 2;
FIG. 7 is a block diagram of a balanced ATM switch in these embodiments.
[Explanation of symbols]
10,30 ATM switch
11 VOD service terminal
12 servers
13 General terminal
15, 22, 32 line units
16, 23 Subscriber transmission line
18 Bidirectional balanced ATM switch
19 One-way ATM switch
21, 33 Trunk line unit
31 Bidirectional unbalanced ATM switch

Claims (5)

First ATM switch means for transferring and routing cells bidirectionally in the first and second directions of the transmission path;
Second ATM switch means for transferring and routing cells in a second direction of the transmission path;
A connection between a first input / output port and first and second ATM switch means for transmitting first information having a flow rate in both directions and receiving second information having a remarkably high flow rate in a second direction. The first information and the second information are identified from the cells of the information arriving at the first input / output port, and the first information is transmitted to the first ATM switch means, and the second information is transmitted to the first ATM switch. First interface circuit means for transferring to the second ATM switch means and outputting information received from the first ATM switch means to the first input / output port;
Information which is connected between a second input / output port from which the first and second information is transmitted and from which the first information arrives, and first and second ATM switch means, and which arrives at the second input / output port And second interface circuit means for outputting information output from the first and second ATM switch means to a second input / output port. switch. First ATM switch means for transferring and routing cells bidirectionally in a first direction of the transmission path and in a second direction opposite to the first direction;
A first information cell having a bi-directional flow rate is transferred bi-directionally in the first and second directions of the transmission line, and a second information cell having a significantly higher flow rate in the second direction is transferred to the second direction. Second ATM switch means for forwarding and routing to
First connection path means for connecting the input / output terminal on the upstream side in the first direction of the first ATM switch means to the input / output terminal on the downstream side in the first direction of the second ATM switch means;
Second connection path means for connecting the input / output terminal on the upstream side in the first direction of the second ATM switch means to the input / output terminal on the downstream side in the first direction of the first ATM switch means;
The second ATM switch means accommodates an input terminal for receiving the second information at a preceding stage in the second direction and an output terminal for outputting the second information at a subsequent stage in the second direction,
The second ATM switch means, when receiving the first information cell from the first direction, transfers the cell to the first connection path means, and receives the first information cell from the second direction, and receives the first information cell from the second direction. Identifying the first information and the second information, and transferring the cell of the first information to the second connection path means and the cell of the second information to the output terminal. ATM switch. 3. The ATM switch according to claim 2, wherein the first ATM switch means that the cell received from the first connection path means is sent to the second connection path means, and the cell received from the second connection path means is received by the first ATM switch means. An ATM exchange for transferring to a first connection path means. 3. The ATM exchange according to claim 1, wherein the first information includes a signal requesting a video program distribution service, and the second information includes an image of the video program distribution service distributed in response to the signal. ATM exchange characterized by including information. 3. The ATM exchange according to claim 1, wherein said exchange accommodates a terminal which handles first information, and transfers a first information between said terminal and said first ATM switch means. An ATM exchange characterized by including an interface means.

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