JP2007325182A - Atm cell transfer system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform line switching for maintaining normality of a communication very simply without a line load by switching to a sub line when a fault is generated in an operation line. <P>SOLUTION: A P-MP path to be used in a broadcast communication among opposing devices of one-to-many is linked among interfaces 13, 14, 15 each performed NNI setting in an ATM switch 11. In an ATM switch 12 for opposing via two transmission paths 21, 22 by the P-MP path, an interface 16 to be linked a P-P path with an interface 18 is performed NNI setting, while an interface 17 to be linked the P-P path with the interface 18 is performed UNI setting. Then the NNI setting is switched to the UNI setting while the UNI setting is switched to the NNI setting when a fault is generated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to control of a logical path in an ATM (Asynchrous Transfer Mode) cell transfer system, in particular, an ATM cell transfer system employing a P-MP (Point to Multi Point) system.

  The basic form of ATM communication is as shown in FIG. 4, which is a technique for transferring 53-byte ATM cells on a logical virtual path extending between physical transmission paths 21 and 22 and ATM switches 31 and 32. . Originally, ATM is characterized by high reliability by a QoS (Quality of Service) function. However, depending on the user application, there are cases where duplexing of ATM lines is required to add higher reliability. In FIG. 4, ATM lines are duplexed by transmission lines 21 and 22.

  Redundant communication path redundancy functions such as lines and virtual paths in such ATM exchanges, with dedicated hardware circuits and complex software control, function for monitoring line status, function for notifying failure detection, function for cooperating with the opposite device, This is realized by implementing four communication path switching operation functions. Based on this premise, various control methods have been proposed.

  For example, in the technique described in Patent Document 1, a pair table in which a standby virtual path is set in the interface unit with respect to the active virtual path of the own interface unit is provided, and an alarm cell reception identification indicating the occurrence of a failure in the active virtual path is provided. Sometimes, by referring to the pair table and updating the routing table in which the routing information is set and switching to the standby virtual path, the processing load when switching from the active virtual path to the standby virtual path can be reduced. We are trying to speed up.

  The technique described in Patent Document 2 gives connection information for each path in a database, and when a failure is detected, refers to this connection information and instructs the originating ATM switch to set a reroute. When it is completed, by updating the database, even if a failure occurs on either the active or standby line, temporary rerouting is not set and a bypass route is not always set. We try to maintain duplication.

  Although Patent Document 3 is not related to the redundant communication path redundancy function, Patent Document 3 describes a technique of using the GFC bit in the ATM cell format for multicast communication.

JP 2001-313654 A (2nd page-4th page, FIG. 1) JP 2000-059394 A (page 1 to page 3, FIG. 1) JP 2000-041041 A (page 4, FIG. 1)

  The line redundancy function of duplicating communication lines and automatically switching to a protection line in the event of an operational line failure has long been in need in the data communication market where high reliability is demanded, and is especially highly necessary in carriers. However, in the above-described conventional technologies for realizing this, the mechanism and operation are complicated, so the implementation of the line redundancy function has a large impact on the device development cost / delivery time, and the maintenance management is also complicated. If introduced, there are various problems such as the dedicated control signal compressing the line bandwidth.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ATM cell transfer system capable of switching a line to maintain a normality of communication by switching to a secondary line without a line load and in a very simple manner when a failure occurs in an operation line. Is to provide.

  The ATM cell transfer system according to the present invention provides an ATM which receives a path having the same VPI / VCI number by providing a P-MP path used for broadcast communication between one-to-multiple opposing devices between the one-to-one opposing devices. There are two or more interfaces and internal logical paths, one is set to NNI, the other is set to UNI, and ATM cells received on the UNI setting side are discarded.

  When the occurrence of a failure on the ATM line is recognized, the NNI setting interface is changed to UNI setting, and one UNI setting interface is changed to NNI setting.

  More specifically, in the ATM cell transfer system of the present invention, a P-MP path used for broadcast communication between one-to-multiple opposing devices is extended between the NNI setting input / output interfaces in the transmission side ATM switch. And the NNI setting for the input interface in which the P-P path is extended between the output-side interface and the reception-side ATM switch facing the transmission-side ATM switch via the two transmission paths of the P-MP path. And setting the input interface having a P-P path between the output interface and the UNI setting, and discarding the ATM cell received on the UNI setting side.

  Then, when the occurrence of a failure on the ATM line is recognized in the NNI setting input interface of the receiving side ATM switch, the NNI setting is switched to the UNI setting and the UNI setting is switched to the NNI setting by a command from the receiving side ATM switch.

  The first effect of the present invention is that, unlike other redundant functions represented by APS, there is no need to exchange control signals exclusively for confirmation and notification of redundancy status between interfaces, and an ATM switch that detects the occurrence of a failure on the receiving side. By switching the UNI / NNI interface setting simply by sending a command from the ATM to the ATM interface, the main line can be switched to the sub line, so that no extra load is imposed on the communication line by the control signal.

  The second effect of the present invention is that the redundant switching function is realized by using the PFC path standardized by the ATM Forum and the GFC bit difference of the UNI / NNI cell format. This means that no hardware is required, and the line can be easily switched with only the software function.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the invention will be described in detail below with reference to the drawings. First, a general description of ATM cell transfer will be started.

[ATM cell transfer]
ATM cell transfer is performed by extending a virtual logical path: VPI (Virtual Path Identifier) and a virtual logical channel: VCI (Virtual Connection Identifier), each of which is assigned a unique number between ATM interfaces, and passing the ATM cell therethrough. A VPI / VCI number is set in the header portion of the ATM cell, and the ATM transfer apparatus (hereinafter referred to as “ATM switch”) determines the VPI / VCI number in the ATM cell header and the VPI / VCI of the extended path. The cell can be transferred to the destination line by comparing the VCI numbers and sending the ATM cell to the matching path.

  If there is no path corresponding to the VPI / VCI number set in the header of the received ATM cell, the ATM switch determines that there is no destination and discards the received ATM cell. There are two types of paths, a one-to-one P-P (Point to Point) path and a one-to-multiple P-MP (Point to Multi-Point) path. The P-MP path is originally intended for a broadcast function for transferring the same information to a plurality of destinations, and a plurality of paths having the same VPI / VCI number are established. The cell is copied and transmitted to all paths having the VCI number. In the present invention, this P-MP path is used for redundancy control.

  FIG. 4 is a diagram showing a basic ATM cell transfer system. In the ATM switch 31, a P-MP path of VPI / VCI = 1/32 is established between the interface 33, the interface 34, and the interface 35. The ATM switch 32 facing the ATM switch 31 via the transmission lines 21 and 22 has a PP path of VPI / VCI = 1/32 between the interface 36 facing the interface 34 and the interface 38. A PP path of VPI / VCI = 2/32 is established between the interface 37 and the interface 39 facing the interface 35.

  Upon receiving the ATM cell from the interface 33, the ATM switch 31 confirms that the VPI / VCI number in the ATM cell header is 1/32 and copies and transfers this ATM cell to the P-MP path with VPI / VCI = 1/32. Then, the data is transmitted from the interface 34 and the interface 35. The ATM cell is received by the interface 36 and the interface 37 of the ATM switch 32, and the VPI / VCI number of the header is confirmed.

  Since the interface 36 has the same 1/32 PP path as the header, the received ATM cell is transferred to the path and transmitted from the interface 38. On the other hand, since the interface 37 has only 2/32 P-P paths having different VPI / VCI numbers, the ATM switch 32 determines that there is no transfer destination and discards the received ATM cell.

[Description of configuration]
By the way, as is well known, there are two types of ATM cells: a user-network interface (UNI) cell format and a network-network interface (NNI) cell format, and an ATM switch also has an interface suitable for each UNI / NNI. Exists. Therefore, normally, the interface setting of the opposing ATM switch is the same, and the UNI cell is transmitted / received via the UNI interface and the NNI cell is transmitted / received via the NNI interface.

  5A is a format diagram of the UNI cell, and FIG. 5B is a format diagram of the NNI cell. There is one difference between the UNI cell format and the NNI cell format. That is, the GFC bit in the UNI cell format does not exist in the NNI cell format, and the VPI bit is assigned to that portion. Therefore, the UNI cell format has 8 VPI bits and 16 VCI bits, whereas the NNI cell format has 12 VPI bits and 16 VCI bits.

  FIG. 6 is a diagram for explaining the operation when an ATM cell in the NNI cell format is received by the UNI interface. Due to the format differences as described above, the upper 4 bits of the VPI bit in the NNI cell format are recognized as GFC bits in the UNI cell format, and as shown in FIG. The VPI number is recognized differently from when it is received by the interface.

  That is, as in the example of FIG. 6, when the UNI interface receives an NNI format ATM cell with VPI = 1055 (0100 0001 1111), it is recognized as VPI = 31 (0001 1111) because the upper 4 bits are not recognized. The

  The present invention applies the fact that ATM cells in NNI format broadcast on the P-MP path of the NNI interface are discarded at the UNI interface and are normally received and transferred only at the NNI interface. A path is used for a redundant line, and a change in UNI / NNI interface setting is used as a redundant line switching operation.

  FIG. 1 is a block diagram showing the configuration of the ATM cell transfer system of the present invention. This basic configuration is the same as in FIG. 4, but the reference numbers for the thirties in FIG. 4 have been changed to the teens. Further, the interfaces 34 to 37 in FIG. 4 are imaged corresponding to the same type of cell format, but in FIG. 1, the interfaces 14 to 16 are compatible with the NNI cell format, and the interface 17 is in the UNI cell format.

  The ATM switch 12 has a function of automatically changing the UNI / NNI settings of both interfaces accommodating the main line / sub line when a line failure is detected on the main line, thereby realizing the switching of the redundant line. Is done. That is, the interface 16 that accommodates the main line is switched from NNI setting to UNI setting, and the interface 17 that accommodates the secondary line is switched from UNI setting to NNI setting.

  FIG. 2 is a detailed view of the interfaces 16 and 17 and the ATM switch 12. The interfaces 16 and 17 have the same configuration, and are signal receiving units 16-1 and 17-1 that receive signals from the transmission paths 21 and 22, and termination processing units 16-2 and 17- that terminate the received signals. 2, failure detection units 16-3 and 17-3 that check the normality of signals and detect failures, and OAM processing units 16-4 and 17-4 that execute maintenance operation functions related to ATM.

  The ATM switch 12 includes a broadcast transfer processing unit 12-1 for transferring an ATM cell from the termination processing unit 16-2 or the termination processing unit 17-2 to the interface 18, an OAM processing unit 16-4, or an OAM processing unit. CPU 12-2 that processes maintenance operation information from 17-4 and transmits an interface setting change command to termination processing unit 16-2 and termination processing unit 17-2, and termination processing unit 16 according to instructions from the maintenance person -2 and a U / I control unit 12-3 that transmits an interface setting change command to the termination processing unit 17-2.

[Description of operation]
In FIG. 1, the transmission line 21 is used as a main line (operation line) and the transmission line 22 is used as a sub line (protection line) out of two transmission lines through the P-MP path. Both the interface 14 and the interface 15 of the ATM switch 11 facing the ATM switch 12 are set to the NNI interface, and the ATM cells transmitted from the interface 14 are also in the NNI format. The VPI / VCI number of the P-MP path and ATM cell header is 1055/32. On the other hand, in the ATM switch 12, the interface 16 accommodating the main line is an NNI interface, and the interface 17 accommodating the sub line is a UNI interface.

  In the ATM switch 12, a P-P path is established between the interface 16 and the interface 17 and the interface 18 serving as the destination, and the VPI / VCI number is 1055/32 here as well. Since the interface 16 is an NNI interface, the received NNI cell reads the VPI number in the header correctly as 1055 and transfers it to the interface 18 via the 1055/32 PP path. In FIG. 2, the route is from the signal receiving unit 16-1 and the termination processing unit 16-2 via the broadcast transfer processing unit 12-1.

  On the other hand, since the interface 17 is a UNI interface, the VPI number in the NNI cell header is read as 31 as described above. However, since there is no path of VPI / VCI = 31/32 in the interface 17, the received NNI cell is discarded. In FIG. 2, the NNI cell received by the signal processing unit 17-1 is discarded by the termination processing unit 17-2. In this way, since only the main line is valid and cells received from the sub line are discarded, the collision of the same cell in the ATM switch 12 does not occur.

  FIG. 3 is a diagram for explaining the operation when a line failure occurs in the ATM cell transfer system of the present invention. When a failure occurs in the transmission line 21 which is the main line, the CPU 12-2 of the ATM switch 12 sends an AIS signal (Alarm Indication Signal) or LOS (Loss of Signal) from the OAM processing unit 16-4 of the interface 16. Recognize the line fault condition by receiving. First, an interface setting change command for changing the interface 16 from the NNI setting to the UNI setting is transmitted to the termination processing unit 16-2. Subsequently, an interface setting change command for changing the interface 17 from the UNI setting to the NNI setting is transmitted to the termination processing unit 17-2.

  The termination processing units 16-2 and 17-2 change the interface according to the interface setting change command. This change order has the purpose of avoiding the collision of the same cell in the ATM switch 12, and only when the both interfaces are set to UNI, the cell cannot be received from the ATM switch 12, but the setting is changed. Since the time is much shorter than the influence time of failure occurrence and the failure detection processing time, it can be ignored.

  When the setting change is completed, as shown in FIG. 3, the ATM cell received from the transmission line 22 by the interface 17 changed to the NNI setting is recognized as VPI / VCI number = 1055/32 and is normally in the P-P path of 1055/32. Transferred. Therefore, thereafter, the transmission line 22 is used as the main line (operation line).

  On the other hand, the ATM cell transmitted through the transmission path 21 in which the failure has occurred does not reach the ATM switch 12 due to the failure, or even if it has arrived, it is recognized as VPI = 31 by the interface 16 changed to the UNI setting. Discarded as none. Even if the received ATM cell header is not normal and missing due to a failure and VPI = 31 is not recognized, there is no VPI number 1055 in the UNI cell format having only 8 bits of VPI area. There is no possibility that an error is erroneously read into 1055 and erroneously transferred, and the discarding process is not affected at all.

  In the above description, the main purpose is automatic recovery by switching the line when a failure occurs, but the maintenance administrator inputs a command to the ATM switch to switch the UNI / NNI interface setting by the U / I control unit 12-3. Etc. As a result, it is possible to use the maintenance function so that the constructed network can be operated without affecting communication at the time of construction such as line accommodation change.

The block diagram which shows the structure of the ATM cell transfer system of this invention Detailed view of interfaces 16 and 17 and ATM switch 12 in FIG. A diagram showing the configuration change of the ATM cell transfer system when a failure occurs in the main line It is a figure which shows basic ATM cell transfer. The figure for demonstrating the format of a UNI cell and a NNI cell The figure for demonstrating operation | movement when the ATM cell of a NNI cell format is received by the UNI interface.

Explanation of symbols

11,12 ATM switch 13-18 interface 21,22 transmission line
12-1 Broadcast transfer control unit
12-2 CPU
12-3 U / I controller
16-1, 17-1 Signal receiver
16-2, 17-2 Termination section
16-3, 17-3 Fault detection unit
16-4, 17-4 OAM processing section

Claims (4)

  Two or more ATM interfaces and two or more internal logical paths that receive paths of the same VPI / VCI number are provided by providing P-MP paths used for broadcast communication between one-to-multiple opposing devices between one-to-one opposing devices. An ATM cell transfer system characterized in that one is set to NNI and the other is set to UNI, and ATM cells received on the UNI setting side are discarded.   2. The ATM cell transfer system according to claim 1, wherein when an occurrence of a fault on the ATM line is recognized, the NNI setting interface is changed to UNI setting and one UNI setting interface is changed to NNI setting. A P-MP path used for broadcast communication between one-to-multiple opposing devices is established between the NNI-set input / output interfaces in the transmission-side ATM switch;
In the receiving-side ATM switch facing the transmitting-side ATM switch via the two transmission paths using the P-MP path, the input interface in which the PP path is extended to the output interface is set to NNI, and the output An input interface in which a P-P path is established with the interface is set to UNI setting,
An ATM cell transfer system, wherein an ATM cell received on the UNI setting side is discarded. When a failure on the ATM line is recognized in the NNI setting input interface of the receiving side ATM switch, the NNI setting is switched to the UNI setting and the UNI setting is switched to the NNI setting by a command from the receiving side ATM switch. 4. The ATM cell transfer system according to claim 3, wherein

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