Switchboard having a dual switching system

Abstract: A switchboard system includes an input/output section (11), first and second switches (12a, 12b) each for acting an active side switch or a standby side switch, a signal processing section (13) for processing received cells, and a control section (14). The control section (14) switches active side ascending cell routes from the then active side switch (12a) to the then standby side switch (12b), transmits a plurality of specified cells through the active side switch (12a) to the signal processing section (13), and receives the specified cells through the active side switch (12a), and switches active side descending cell routes from the then active side switch (12a) to the then standby side switch (12b).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switchboard having a dual switching system for use in an ATM (Asynchronous Transfer Mode) switchboard. The present invention also relates to a method for controlling such a switchboard. 2. Description of the Prior Art In a circuit switching system including dual ATM switches as used in an ATM switchboard, a buffer is generally provided for a 156-Mbp line or a 622-Mbp line in order to prevent cell loss at the time of circuit switching between the dual ATM switches. The buffer generally stores ATM cells at the line terminal to prevent the ATM cells from flowing into a then-active side (ACT side) ATM switch during switching. In a small scale ATM switchboard wherein the circuit switching system should be more compact, the ATM switchboard can hardly be provided with a large number of buffers. As a result, cell loss problems are encountered at the time of the circuit switching. Japanese Patent Laid-Open Publication No. Hei. 7-264210 (first publication) describes a circuit switching system, which need not have a large number of buffers for the circuit switching system. Fig. 1 is a block diagram of the configuration of the conventional ATM switchboard described in the first publication. The ATM switchboard includes a distribution controller 142, a 0-system routing switch 41 0 , a 1-system routing switch 41 1 , a selecting controller 143, and a switching controller 100. A number of (m) input lines are connected to the distribution controller 142, and a number of (m) 0-system (ACT: active) lines and the same number of (m) 1-system (SBY: stand-by) lines are connected to the outputs of the distribution controller 142. All the 0-system lines on the output side of the distribution controller 142 are connected to the 0-system routing switch 41-0, and all the 1-system lines on the output side of the distribution controller 142 are connected to the 1-system routing switch 41-1. A number of (n) 0-system lines on the output side of the 0-system routing switch 41-0 and a number of (n) lines on the output side of the 1-system routing switch 41-1 are connected to the input of the selecting controller 143, the number of outputs of which is n. The ATM switchboard connects m input lines of the distribution controller 142 to the n output lines of the selecting controller 143, given m and n are integers, for transferring ATM cells from any of the m input lines 21 to any of the n output lines 22. In the description to follow for the operation of the ATM switchboard of Fig. 1, it is assumed that the 0-system lines are used in the initial stage between the distribution controller 142 and the selecting controller 143. More specifically, the distribution controller 142 and the 0-system routing switch 41-0 are connected together, and the 0-system routing switch 41-0 and the selecting controller 143 are connected together. The connection from the distribution controller 142 to the 0-system routing switch 41-0 is now to be switched to the 1-system routing switch 41-1. First, n × m specified cells used for the purpose of the switching are sent corresponding to the number (n) of the output lines to the m input lines of the 0-system routing switch 41-0. The switching controller 100 switches the output side between the routing switches after all the (m×n) specified cells supplied through the m input lines appear on the output side of the 0-system routing switch 41-0. More specifically, the connection from the 0-system routing switch 41-0 to the selecting controller 143 is switched to the connection from the 1-system routing switch 41-1 to the selecting controller 143. Thus, cell loss or line cutoff can be prevented by switching the cell routing switch at the time of switching between the 1-system and the 0-system. Other techniques for the circuit switching system are described in Japanese Patent Laid-Open Publications No. Hei. 6-303255 (second publication) and No. Hei. 11-261590 (third publication). In the description of the first publication, the switching operation takes place only when all the specified cells provided to the m input lines of the distribution controller 142 appear on the output side of the 0-system routing switch 41-0. Therefore, if part of the specified cells is lost for some reason during the cell transmission, the switching operation does not take place. This disadvantage is not solved either by the circuit switching systems or the ATM switch boards described in the second and third publications. EP 0 557 910 A2 discloses a switchboard system with an input section for receiving cells, a separate output section for outputting cells, first and second switches each for acting as an active side switch or a standby switch, and a controller for controlling switching. For switching from the active side ATM switch to the standby side ATM switch, delivery of ATM cells is switched to the standby side ATM switch for temporarily storing the ATM cells therein, while the active side ATM switch still keeps on transmitting the ATM cells until the active side ATM switch becomes empty. When the active side ATM switch detects empty, the standby side ATM switch is switched to start transmitting ATM cells from the now active side ATM switch. US 5 283 782 discloses a similar switchboard system. EP 0 385 429 A2, Rathgeb E. P. et al., "The MainStreetXpress Core Services Node - A Versatile ATM Switch Architecture for the Full Service Network", IEEE Journal on Selected Areas in Communications, Vol. 15, No. 5, 1997, p. 795-806, and JP 07 264210 A disclose further switching systems. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a circuit switching system for use in an ATM switchboard, which can prevent cell loss without having to provide a buffer at the line terminal near the distribution controller. The present invention solves this object by providing a switchboard system according to claim 1 and a method for controlling such a switchboard according to claim 6. In accordance with the present invention, the input/output section or the signal processing section need not have a buffer therein. Each of the first and second switches preferably has a buffer, which has a smaller circuit scale compared to the buffer which may otherwise be provided in the input/output section or the signal processing section. The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a conventional circuit switching system in an ATM switchboard. Fig. 2 is a block diagram of a circuit switching system for an ATM switchboard according to an embodiment of the present invention; Figs. 3 to 9 are block diagrams of the circuit switching system, showing the flow of cells during various stages of the switching operation; thereof; and Fig. 10 is a flow chart of the circuit switching system according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now the present invention will be more specifically described with reference to a circuit switching system in an ATM switchboard according to an embodiment thereof. Referring to Fig. 2, the circuit switching system in the ATM switchboard includes an input/output section 11, an ATM switch 12a disposed on the ACT side, an ATM switch 12b disposed on the SBY side, an ATM application processing section 13, and a control section 14. The ACT side and the SBY side are switched by the control section 14. A plurality of (m) input lines 101 and the same number of output lines 102 are connected to the external terminals of the input/output section 11, and m ACT side ascending signal lines 151 are connected from the input/output section 11 to the ACT side ATM switch 12a, whereas m SBY side ascending signal lines 171 are connected to the SBY side ATM switch 12b from the input/output section 11. In addition, m descending signal lines 152 are connected from the ATM switch 12a to the input/output section 11, whereas m descending signal lines 172 are connected from the ATM switch 12b to the input/output section 11. A plurality of (n) descending signal lines 161 and 181 of each of the ACT side and SBY side ATM switches 12a and 12b are connected to the inputs of the ATM application processing section 13. In addition, n ascending signal lines 162 and 182 of each of the ACT side and SBY side ATM switches 12a and 12b are connected to the outputs of the signal processing section 13. The control section 14 controls the input/output section 11, the ACT side ATM switch 12a, the SBY side ATM switch 12b, and the ATM application processing section 13. The ATM application processing section 13 operates for signal processing of the ATM cells such as voice/sound processing or packet processing. It is to be noted that although there is shown a single line for each of the signal paths in Fig. 2, the number of signal lines are such that the signal paths between input/output section 11 and each of the ATM switches include m ascending signal lines and m descending signal lines, and the signal paths between each of the ATM switches 12a and 12b and the ATM application processing section 13 include n ascending signal lines and n descending signal lines. The function of the ATM switchboard shown in Fig. 2 is different from that of the ATM switchboard shown in Fig. 1. More specifically, in the circuit ATM switchboard according to the present embodiment, the ATM cells transmitted through the m input lines 101 to the input/output section 11 are subjected to signal processing by the ATM application processing section 13, and are delivered through the input/output section 11 and the m output lines 102 after the signal processing. The internal route of the ATM switchboard is switched between the ATM switches 12a and 12b by the function of the circuit switching system. The operation of the present embodiment will be described with reference to Figs. 3 to 9 each representing the flow of cells at respective stages and to Fig. 10 illustrating the flowchart of the present embodiment. In this text, it is defined that the direction of the cell flow in which ATM cells are transmitted from the input/output section 11 or the ATM application processing section 13 to the ACT side ATM switch 12a is called "ascending" direction, and that the direction of the cell flow in which ATM cells are transmitted from the Act side ATM switch section 12a to the input/output section 11 or the ATM application section 13 is called "descending" direction. This also applies to the SBY side ATM switch 12b. Fig. 3 shows the initial stage of the cell flow, wherein the ATM cells are transmitted through the ACT side signal lines 15 (151 and 152) and 16 (161 and 162) and the ACT side ATM switch 12a. In this stage, the ATM cells are transmitted between the input/output section 11 and the ACT side switch 12a and between the ACT side switch 12a and the ATM application processing section 13. In other words, the ATM switch section 12a is on the ACT side and the ATM switch 12b is on the SBY side literally as they are labeled. The circuit switching system operates for the switching processing based on the sequential numbers as described below. (1) The control section 14 initially sets the ACT side ATM switch 12a to pass specified cells along the signal path including all the devices connected in the circuit. (2) The control section 14 also initially sets the ATM application processing section 13 so that the ATM application processing section 13 returns the received specified cells to the ascending cell routes of the signal path in which the received cells have been transmitted through the descending cell route. (3) When the switching operation between the ATM switches is to be executed, the control section 14 switches the active ascending cell route from both the ascending signal lines 151 and 162 in Fig. 2 to the ascending signal lines 171 and 182 to the SBY side ATM switch 12b, in step S1 of Fig. 10. This stage is shown in Fig. 4. Thus, ATM cells output from both the input/output section 11 and the ATM application processing section 13 flow into the SBY side ATM switch 12b, with the ACT side switch 12a continuing to deliver own ATM cells in the descending direction. (4) The control section 14 instructs the SBY side ATM switch 12b to temporarily store the received ATM cells in a built-in buffer (not shown) of the SBY side ATM switch 12b in step S2 of Fig. 10. This stage is shown in Fig. 5. (5) The control section 14 then controls the input/output section 11 to transmit therethrough one or more of specified cell to the ATM application processing section 13 through each of the signal lines passing the ACT side ATM switch 12a in step S3 of Fig. 10. In this stage, although a single specified cell may be transmitted from the input/output section 11 through each of the signal lines, a plurality of prescribed cells are preferably sequentially transmitted. More specifically, the input/output section 11 transmits p ×m specified cells, for example, through the ACT side ATM switch so that each of m signal lines passes p specified cells, and each of n signal lines passes p ×m/n (integer) specified cells. The reason of transmitting a plurality of (p) specified cells through each of the m or n signal lines is that even if part of the plurality of specified cells is lost during the transmission, the remainder of the specified cells should be safely transmitted and then returned to the input/output section 11. (6) The ATM application processing section 13 returns the transmitted specified cells to the input/output section 11 through the ACT side ATM switch 12a as shown in Fig. 6. (7) If the input/output section 11 detects reception of the first one of the specified cells (or heading cell) through each of the m descending signal lines from the ATM application processing section 13 in S4 of Fig. 10, the input/output section 11 notifies the control section 14 of the fact of reception of the heading cell. Thus, the control section 14 judges that there is no ATM cell staying in the descending cell routes of the ACT side ATM switch 12a. This is because during the period between the departure of the heading cell from the input/output section 11 and its return to the input/output section 11 through the ACT side ATM switch 12a, ATM application processing section 13 and the ACT side ATM switch 2a, all the ATM cells staying in the built-in buffer of the ACT side ATM switch 12a must be discharged. It is to be noted that if the reception of the heading cell is not detected in S4 of Fig. 10, the control section 14 waits for control until the reception of any cell is detected. (8) The control section 14 then switches both the descending cell routes between the ATM switch 12a and the input/output section 11 and between the ATM application processing section 13 and the ATM switch 12a to the descending cell routes between the SBY side ATM switch 12b and the input/output section and between the ATM application processing section 13 and the ATM switch 12b, in S5 of in Fig. 10. This stage is shown in Fig. 7. (9) The control section 14 instructs the SBY side ATM switch 12b to start delivering own ATM cells that are temporarily stored in the built-in buffer of the SBY side ATM switch 12b, in step S6 of Fig. 9. This stage is shown in Fig. 8. (10) The control section 14 changes the label of the ATM switch 12a to indicate the SBY side and the label of the ATM switch 12b to indicated the ACT side, thereby updating the internal management information in the control section 14 in step S7 of Fig. 10. This stage is shown in Fig. 9. In the present embodiment, the ATM switches 12a and 12b have respective built-in buffers for temporarily storing ATM cells therein. In this regard, each of the input/output section 11 and the ATM application processing section 13 need not have a buffer for temporarily storing the ATM cells. It is to be noted that signal lines used in the switchboard of the present embodiment may be metallic wires or optical fibers. The ATM application processing section may function for any signal processing such as voice/sound processing or ATM cell processing.

Claims: A switchboard system comprising: an integrally formed input/output section (11) for receiving/transmitting cells, said input/output section (11) having a plurality of (m) external input terminals connected to m external input lines (101), m external output terminals connected to m external output lines (102), m internal input terminals and m internal output terminals; first and second switches (12a, 12b) each for acting as an active side switch or a standby side switch, each of said first and second switches (12a, 12b) having m first ascending terminals, a plurality of n first descending terminals, n second ascending terminals, and m second descending terminals, said m first ascending terminals being coupled to said m internal output terminals through m first ascending lines (151, 171), said m second descending terminals being connected to said m internal input terminals through m first descending lines (152, 172), said m first ascending terminals being coupled to n first descending terminals by switching, said n second ascending terminals being coupled to said m second descending terminals by switching; an ATM application signal processing section (13) separate from said input/output section (11) for signal processing, such as voice/sound processing or packet processing, of received ATM cells, and for returning the processed ATM cells to said input/output section (11) and to said output lines (102) thereof, said signal processing section (13) having n signal input terminals connected to said n first descending terminals of each of said first and second switches (12a, 12b) through n second descending lines (161, 181), and n signal output terminals connected to said n second ascending terminals of each of said first and second switches (12a, 12b) through n second ascending lines (162, 182); and a control section (14) for controlling switching between said first switch (12a) and said second switch (12b), wherein said control section (14) is configured to consecutively perform the following controlling during said switching functions: said control section (14) being adapted to the switch being active side ascending cell routes from said first and second ascending lines (151, 162) of a then active side switch (12a) to said first and second ascending lines (171, 182) of the then standby side switch (12b), said input/output section (11) being adapted to transmit a plurality of specified cells through at least said first ascending lines (151) and said second descending lines (161) of said active side switch (12a) to said signal processing section (13), and to receive said specified cells through at least said second ascending lines (162) and said first descending lines (152) of said active side switch (12a), and said control section (14) being adapted to switch active side descending cell routes from said first and being second descending lines (152, 161) of said then active side switch (12a) to said first and second descending lines (172, 182) of said then standby side switch (12b), each of given m and n being an integer. The switchboard system as defined in claim 1, wherein said control section (14) being adapted to switch said active side descending cell routes after said input/output section (11) having received a heading cell among said specified cells. The switchboard system as defined in claim 1, wherein said second switch (12b) includes a buffer for temporarily storing cells during said switching. The switchboard system as defined in claim 3, said second switch (12b) being adapted to deliver said cells stored in said buffer through said first and second descending lines (172, 181) after said control section (14) having switched said active side descending cell routes. The switchboard system as defined in claim 3, wherein said signal processing section (13) being adapted to ATM processing. A method for controlling switching in a switchboard system having an integrally formed input/output section (11) for receiving/transmitting cells, first and second switches (12a, 12b) each for acting as an active side switch or a standby side switch to transmit cells to/from said input/output section (11), an ATM application signal processing section (13) separate from said input/output section (11) for signal processing, such as voice/sound processing or packet processing, of received ATM cells, and for returning the processed ATM cells to said input/output section (11), said method comprising the consecutive steps of: switching active side ascending cell routes from first and second ascending lines (151, 162) of a then active side switch (12a) to first and second ascending lines (171, 182) of the then standby side switch (12b); transmitting a plurality of specified cells through said active side switch (12a) to said signal processing section (13) and receiving said specified cells through said active side switch (12a), and switching active side descending cell routes from first and second descending lines (152, 161) of said then active side switch (12a) to first and second descending lines (172, 181) of said then standby side switch (12b). The method as defined in claim 6, wherein said switching of active side descending cell routes is effected after a heading one of said specified cells is received by said input/output section (11). The method as defined in claim 6, wherein said second switch (12b) stores cells in a buffer after said switching of active side ascending cell routes. The method as defined in claim 8, wherein said second switch (12b) delivers said cells stored in said buffer after said switching active side descending cell routes. The method as defined in claim 6, further comprising the steps of updating control information to exchange a label between said active side switch (12a) and said standby side switch (12b).

Inventors: OWADA JUNICHI, OWADA, JUNICHI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 2001
Main classification: H04L12
IPC codes: H04L1, H04L12