(51) Int Cl.: H04L 12/24 ( ) H04L 12/26 ( )

Transcription

1 (19) (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION (4) Date of publication and mention of the grant of the patent: Bulletin 07/01 (1) Int Cl.: H04L 12/24 (06.01) H04L 12/26 (06.01) (21) Application number: (22) Date of filing: (4) System and method for transmission of operations, administration and maintenance packets between ATM and switching networks upon failures Vorrichtung und Verfahren zur Übertragung im Fehlerfall von OAM paketen zwischen ATM und geschalteten Netzwerken Appareil et procédé pour la transmission de paquets de OAM entre des réseaux ATM et des réseaux de commutation en cas d erreurs (84) Designated Contracting States: DE ES FR GB IT () Priority: US 7 (43) Date of publication of application: Bulletin 03/2 (73) Proprietor: Alcatel Canada Inc. Kanata, Ontario K2K 2E6 (CA) (72) Inventors: Puppa, Gary J. Orleans, Ontario K1E 2Y4 (CA) Park, Robin Jeffrey Kanata, Ontario K2K 3A8 (CA) Cameron, Brett Graham Ottawa, K2S 1E1 (CA) Susilo, Gatot Kanata, Ontario K2K 3A7 (CA) (74) Representative: Feray, Valérie et al Feray Lenne Conseil 39/41, avenue Aristide Briand Antony (FR) (6) References cited: ALCATEL: "ATM in the next generation network - ATM-MLPS mediation" ALCATEL TECHNICAL WHITE PAPER, XX, XX, 31 August 01 ( ), pages 1-16, XP "ATM-MPLS network interworking version 1.0 AF-AIC " ATM FORUM TECHNICAL COMMITTEE, XX, XX, vol. af-aic , August 01 (01-08), pages 1-23, XP KRASNODEMBSKI K ET AL: "END-TO-END QOS PROVISIONING ACROSS HETEROGENEOUS DOMAINS" PROCEEDINGS OF THE IEEE CONFERENCE 00 ON HIGH PERFORMANCE SWITCHING AND ROUTING. HEIDELBERG, GERMANY, JUNE, 26-29, 00, PROCEEDINGS OF THE IEEE CONFERENCE ON HIGH PERFORMANCE SWITCHING AND ROUTING, NEW YORK, NY: IEEE, US, 26 June 00 ( ), pages , XP ISBN: EP B1 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). Printed by Jouve, 7001 PARIS (FR)

2 Description 2 3 [0001] The invention relates to digital communication systems and more specifically to a network mode capable of providing asynchronous transfer mode traffic to a multi-protocol label switching (MPLS) link. [0002] MPLS is quickly gaining support in the communication industry as a high-speed core of many communication networks. Networks are being developed and deployed which interface ATM networks with MPLS networks. New network systems are being deployed which incorporate both MPLS and ATM network topologies. [0003] For each topology, there is a separate, operations, administration and maintenance (OAM) protocol for generating and transmitting OAM messages whether in cells, packets, frames or another format. [0004] An ATM-MPLS mediation system is outlined in document by Alcatel, entitled "ATM in the next generation network - ATM-MPLS mediation" published in Alcatel Technical White Paper, XX, XX, 31 August 01 ( ), pages 1-16, XP This document discusses standards for forward interoperability, and mentions an ATM/ MPLS mediation function capable of advertising the state of an LSP tunnel. Any non-recoverable failure in the MPLS core is notified to the ATM network, so that an alternative route can be applied. [000] ATM-MPLS internetworking is also discussed in the paper "ATM-MPLS network internetworking version 1.0 AF-AIC " ATM forum technical committee, XX, XX, vol. af-aic , August 01 (01-08), pages 1-23, XP This paper discusses ATM-MPLS-ATM management plane internetworking aspects, with an internetworking function capable of transferring ATM OAM information through the MPLS network by encapsulating ATM OAM cells in MPLS frames. [0006] Aspects concerning QoS provisioning across heterogeneous domains are discussed in a paper authored by Krasnodembski K et al. entitled "End-to-end QoS provisioning across heterogeneous domains", published in Proceedings of the IEEE conference 00 on high performance switching and routing, Heidelberg, Germany, June 26-29, 00, Proceedings of the IEEE conference on high performance switching an routing, New York, NY: IEEE, US, 26 June 00 ( ), pages , XP ISBN: The paper discusses an inter domain QoS router in the context of RSVP based domains and ATM domains. [0007] According to a first aspect, the invention relates to a method of notifying network nodes about a disruption in service, according to claim 1. [0008] According to a second aspect, the invention relates to asynchronous transfer mode/multi-protocol label switching (ATM/MPLS) edge switch according to claim 8. [0009] An object of the present invention is to provide a method for transmission of information relating to OAM packets between ATM and switching networks, such as MPLS networks, as they are generated and transmitted. [00] An embodiment provides a method of notifying a first communication network of a fault related to a second communication network, said first communication network being connected to said second communication network, said first communication network having a first OAM protocol adapted to monitor integrity of said first communication network, said second communication network having a second OAM protocol adapted to monitor integrity of said second communication network, said method comprising: detecting said fault related to said second communication network; generating a first OAM cell of said first OAM protocol indicating detection of said fault; transmitting said first OAM cell to said first communication network to indicate said fault to said first communication network. 4 0 [0011] Thus, a network element such as an edge switch provides a connection point for a first network such as an ATM network to a second network such as a MPLS network, monitors the integrity of a routing path in the second network connected to the edge switch and transmits fault information associated with the second network routing path to the first network. [0012] The first communication network may be connected with the second communication network at a network element. [0013] The first communication network may be an ATM network, the first OAM protocol may be an ATM OAM protocol, the second communication network may be a MPLS network and the second OAM protocol may be a MPLS OAM protocol. [0014] Detecting the fault may occur at the network element. [00] The network element may be adapted to receive connectivity verification cells from the second communication network. [0016] The fault related to the second communication network may be detected at the network element by recognition of expiry of a time interval in which a number of connectivity verification cells have not been received. [0017] The number of connectivity verification cells may be at least three. [0018] The first OAM cell may be an ATM AIS cell. [0019] In an embodiment, there is provided a network element for connecting a first communication network to a 2

3 2 3 4 second communication network is provided. The first communication network has a first communication protocol and a first OAM protocol for use in monitoring integrity of the first communication network. The second communication network has a second communication protocol and a second OAM protocol for use in monitoring integrity of the second communication network. The network element includes a first section adapted to provide communications for the network element with the first communication network and notify the network element of the fault in the first communication network. The first section detects the faults related to the first communication network. The network element also includes a second section adapted to provide communications for the network element with the second communication network, detect that the first section has notified the network element of the fault and notify the second communication network of the fault. [00] In other aspects of the invention, various combinations and subsets of the above aspects are provided. [0021] The foregoing and other aspects of the invention will become more apparent from the following description of specific embodiments thereof and the accompanying drawings which illustrate, by way of example only, the principles of the invention. In the drawings, where like clements feature like reference numerals (and wherein individual elements bear unique alphabetical suffixes): Figure 1 shows a block diagram of a communication network comprising two edge switches according to an embodiment of the invention which each link an ATM network to a Multi-Protocol Label Switching (MPLS) network; Figure 2 shows a block diagram of the tunnel in the MPLS network connecting the ATM/MPLS edge switches of Figure 1; Figure 3 shows a block diagram of an ATM cell and an ATM frame and their equivalent MPLS frame generated and manipulated by one edge switch of Figure 1; Figure 4 shows a block diagram illustrating points of failure in the ATM network, the ATM/MPLS edge switch and the MPLS network of Figure 1; Figure shows a block diagram illustrating the relationship between ATM OAM cells and MPLS OAM frames in the network of Figure 1; Figure 6 shows a block diagram showing the interworking of MPLS fault indications with ATM connection control in the ATM/MPLS edge switch of Figure 1; and Figure 7 shows a state diagram of a MPLS OAM state machine present in the ATM/MPLS edge switch of Figure 6. [0022] The description which follows, and the embodiments described therein, are provided by way of illustration of an example, or examples, of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. 1.0 Basic Features of System [0023] Briefly, the embodiment provides a system and method for transmission of information in OAM messages from a non-atm network. [0024] In the embodiment, an ATM/MPLS edge switch, provides a connection point for an ATM network to a MPLS network, monitors the integrity of a routing path in the MPLS network connected to the edge switch and transmits fault information received in MPLS OAM frames associated with the MPLS routing path to the connected ATM networks. [002] First a description of a network configuration which a network element associated with the embodiment is provided, followed by a description of components of the elements. Next, error OAM protocols received and processed by the network element for two different network protocols are described, and finally an interface system for the different OAM schemes for the two different networks is described. 2.0 System Configuration 0 [0026] Following is a description of a network having a switch associated with the embodiment. Referring to Figure 1, communications network 0 is shown, comprising a first ATM network 2(1), a second ATM network 2(2) and a multi-protocol label switched (MPLS) network 4. ATM networks 2 comprise a number of interconnected ATM switches 6 connected by communications links 8 which can each carry ATM traffic thereon. [0027] At the edge of ATM network 2(1), ATM edge switch 1(1) provides a connection for Customer Premise Equipment (CPE) 112(1) to ATM network 2(1) via link 116(1). Similarly, at an edge of ATM network 2(2), ATM edge switch 1(2) provides a link for CPE 112(2) to ATM network 2(2) via link 116(2). ATM edge switch 1(1) is shown having a connection to another ATM network 114. ATM edge switch 1(1) is connected to elements in ATM network 2(1). Similarly, ATM edge switch 1(2) is connected to elements in ATM network 2(2). 3

4 2 3 [0028] MPLS network 4 comprises MPLS switches 118 which are connected together via communications links 1. At one edge of MPLS network 4, ATM/MPLS edge switch 122(1) provides an interface between ATM network 2(1) and MPLS network 4. At another edge of MPLS network 4, ATM/MPLS edge switch 122(2) provides an interface between ATM network 2(2) and MPLS network 4. [0029] Referring to Figure 2, ATM/MPLS edge switches 122 communicate with MPLS switches 118 in MPLS network 4 via communications links 124. Communications links 124 are two fibre optic cables carrying uni-directional data between an MPLS switch 118 and an ATM/MPLS edge switch 122. Communications links 1 are two fibre optic cables carrying uni-directional data between two MPLS switches 118. In communications link 124(1), communications carried from ATM/MPLS edge switch 122(1) to MPLS switch 118A, in the direction of ATM/MPLS edge switch 122(2), are carried on a cable 2; communications in the other direction are carried on a cable 212. Similarly communications links 1 and 124(2) have cables 2 in the direction of ATM/MPLS edge switch 122(2) and cables 212 in the direction of ATM/ MPLS edge switch 122(1). [00] MPLS switches 118 utilize dedicated and pre-arranged MPLS routing paths to carry traffic within MPLS network 4. These dedicated and pre-arranged MPLS routing paths or tunnels are composed of two uni-directional label switched paths (LSPs) 0 and 2 between ATM/MPLS edge switches 122(1) and 122(2). It will be appreciated that the term "tunnel" is interchangeable with the term "MPLS routing path". In tunnel 4, LSP 0 carries traffic from ATM/MPLS edge switch 122(1) to ATM/MPLS edge switch 122(2). Similarly, in tunnel 4, LSP 2 carries traffic from ATM/MPLS edge switch 122(2) to ATM/MPLS edge switch 122(1). 2.1 ATM and MPLS Format Conversion [0031] As ATM/MPLS edge switches 122 are at the edge of an ATM network and a MPLS network, each ATM/MPLS edge switch 122(1) must translate ATM cells and frames to MPLS frames and vice versa for traffic sent between ATM network 2 and MPLS network 4. Referring to Figure 3, aspects of the conversion of ATM cells and frames received from CPE 1(1) by ATM/MPLS edge switch 122(1) to MPLS frames, and vice versa are shown. [0032] As is known in the art ATM data may be either encapsulated into cells or frames. Cell 0 comprises 48 bytes of data in data field 2 and five bytes of header data in header field 4. The header field 4 includes data relating to error checks and destination information. Frequently, ATM cells 0 are used to encode voice calls in AAL 1/2/ signalling parameters. ATM frames are used to carry larger sizes of data. Exemplary ATM frame 6 comprises data field 8 which may have 6 Kbytes of data. Header field 3 is comparable to header field 4 used in ATM cell 0. When ATM traffic leaves ATM network 2 and is provided to MPLS 4, for each of the ATM cells 0 and the ATM frames 6, the data and header information must be transposed into a MPLS frame 312. [0033] MPLS frame 312 comprises data field 314, header field 316, first label field 318 and second label field 3. When transposing data of an ATM cell 0 or frame 6 to a MPLS frame 312, the respective ATM data field (either data field 2 or 8) is inserted into MPLS data field 314. Similarly, the contents of the respective ATM cell or frame header fields (either header field 4 or header field 3) is inserted into MPLS header field 316. Header field 316 may be a component of data field 314. The contents of first label 318 and second label 3 provide routing information for MPLS frame 312 through MPLS network 4. First label field 318 contains identification information relating to the MPLS routing path for the MPLS frame 6. Second label field 3 contains connection information relating to the particular internal ATM connection which is to be used by the ATM/MPLS edge switch 122 at the end of the routing path for a connection to the downstream ATM network Switch Description 4 0 [0034] Referring to Figure 4, ATM/MPLS edge switch 122 comprises an ATM card 0, a fabric card 2, an MLPS card 4, at least one ATM port 6, at least one MPLS port 8, two fabric ports 4 and 412, a control card (not shown in this figure) and two I/O cards (not shown). [003] ATM/MPLS edge switch 122 interfaces ATM network 2 with MPLS network 4. Therefore, it has an ATM (line) card 0 for interfacing with a connection to ATM network 2 and a MPLS (line) card 4 for interfacing with a connection to MPLS network 4. ATM network 2 connects to ATM card 0 of ATM/MPLS edge switch 122 via link 8(1) through ATM port 6 and an input/output (I/O) card (not shown). MPLS network 4 connects to MPLS card 4 via link 124(1) through MPLS port 8 and an I/O card (not shown). Inside ATM/MPLS edge switch 122, ATM card 0 can provide traffic to fabric card 2 through fabric port 4 and fabric card 2 can connect to MPLS card 4 through fabric port 412. [0036] In direction 4, ATM card 0 receives cells 0 and frames 6 transmitted from ATM network 2 and converts them into an internal format for processing by fabric card 2. For traffic destined for MPLS network 4, fabric card 2 forwards the traffic to the appropriate MPLS card 4. MPLS card 4 converts its received traffic into MPLS frames 312 as described earlier and transmits the MPLS frames 312 to MPLS network via link 124(1). 4

5 2 [0037] In direction 442, MPLS card 4 receives MPLS frames 312 transmitted from MPLS network 4 over link 124 (1) and converts them into an internal format for processing by fabric card 2. MPLS card 4 forwards the internal data to fabric card 2. For traffic destined for ATM network 2, fabric card 2 forwards its output to the appropriate ATM card 0. ATM card 0 converts the traffic into cells 0 or frames 6 as shown in Figure 3 and transmits them into ATM network 2 over link 8(1). [0038] In addition to providing a traffic interface for ATM/MPLS traffic ATM/MPLS edge switch 122 is capable of indicating a failure in MPLS network 4 to ATM network 2 by monitoring tunnel 4 and by messaging to ATM network 2 the arrival of MPLS OAM frames. 3.0 ATM and MPLS OAM [0039] Referring again to Figure 1, in an ATM network 2(1), when communications are sent from CPE 112(1), through an ATM network 2(1) to CPE 112(3), a routing path is established from CPE 112(1), through ATM edge switch 1(1), switches 6 in ATM network 2(1), ATM edge switch 1(3) and is received at CPE 112(3). Upon a failure of an element in this routing path, for example communications link 8, an ATM OAM cell is generated and transmitted over ATM network 2(1) to inform ATM edge switches 1(1) and 1(3) of the failure. In particular, an ATM OAM Alarm Indication Signal (AIS) cell is generated and transmitted in the downstream direction towards CPE 112(3). An ATM AIS cell is transmitted from ATM switch 6A in lieu of the data cells to maintain transmission continuity and to indicate to ATM edge switch 1(3) that there is a transmission interruption located either at the equipment originating the ATM AIS cell or upstream of that equipment When ATM edge switch 1(3) receives the ATM AIS cell, it generates and transmits an ATM OAM Remote Defect Indicator (RDI) cell over the same routing path towards CPE 112(1) which arrives at ATM edge switch 1(1). This informs both ATM edge switches 1(1) and 1(3) about the failure in the routing path. ATM edge switches 1(1) and 1(3) can then inform CPEs 112(1) and 112(3) of the failure. [00] Referring to Figure 2, in MPLS network 4 LSPs 0 and 2 may each carry specialized operation, administration and maintenance (OAM) MPLS frames. The MPLS OAM frames follow ITU Y.17 MPLS standards. There are three types of MPLS OAM frames used by the embodiment: 1) Connectivity verification (CV) frames; 2) Backward defect indicator (BDI) frames; and 3) Forward defect indicator (FDI) frames [0041] The type of MPLS OAM frame transmitted within an LSP 0 or 2 is identified via the header information and the second label field 3 in a MPLS frame 312. The first label field 318 contains the tunnel identification information related to the OAM destination. Presently, in the embodiment, a MPLS OAM frame is identified with a value defined by the MPLS standards bodies. Currently, the value is "". This value is placed in second label field 3. The contents of the data field 314 identify the type of MPLS OAM frame. [0042] In the embodiment for a given MPLS tunnel 4, MPLS OAM frames are sent therein to monitor the status of the tunnel 4. [0043] To monitor and test the integrity of tunnel 4, dedicated CV frames are transmitted from ATM/MPLS edge switch 122 at one end of tunnel 4 to the switch at the other end. At the downstream switch MPLS OAM frame(s) are received analysed. Depending on the results of the analysis, the downstream switch may generate a type of response MPLS OAM frame which is transmitted upstream to the originating switch along its the associated LSP. At the originating switch, MPLS OAM frame(s) are received and analysed. The MPLS OAM frame(s) received at the originating switch 122 will indicate the status of the entire tunnel 4. For the purposes of the example, upstream switch is ATM/MPLS edge switch 122(1) and downstream switch is ATM/MPLS edge switch 122(2) for tunnel 4. [0044] There are four cases of conditions in the LSPs 0, 2 or the receiving ATM/MPLS edge switch 122(2) and other downstream components beyond ATM/MPLS edge switch 122(2). In Case A, tunnel 4 has no transmission problems therein. ATM/MPLS edge switch 122(1) generates and transmits CV frames on LSP 0. The CV frames are received by ATM/MPLS edge switch 122(2) which generates other CV frames which are transmitted over LSP 2. These other CV frames are received at ATM/MPLS edge switch 122(1) and ATM/MPLS edge switch 122(1) can determine that tunnel 4 is fully operational by the receipt of the CV frames with no other MPLS OAM frames. [004] CV frames are generated by ATM/MPLS edge switches 122 every one second according to ITU Y.17 standards. Accordingly, after a certain transmission and frame processing delay, when tunnel 4 and its downstream components which affect tunnel 4 are fully operational, the CV frames received by ATM/MPLS edge switch 122 should arrive approximately once every second. It will be appreciated that other time intervals could be used for transmitting CV frames. [0046] In Case B, it is presumed that there is a failure in LSP 0. Accordingly, when ATM/MPLS edge switch 122(1) generates and transmits a CV frame onto LSP 0, ATM/MPLS edge switch 122(2) does not receive it. ATM/MPLS edge switch 122(2) generates a response MPLS BDI frame which indicates that a failure has occurred backwards in

6 LSP 0. The MPLS BDI frame is transmitted on LSP 2 and is received at ATM/MPLS edge switch 122(1). ATM/ MPLS edge switch 122(1) then can determine that tunnel 4 is not fully operational. [0047] In Case C, it is presumed that there is a failure in both LSP 0 and LSP 2. As with Case B, CV frame from ATM/MPLS edge switch 122(1) is not received by ATM/MPLS edge switch 122(2). In response ATM/MPLS edge switch 122(2) generates and transmits a MPLS BDI frame to ATM/MPLS edge switch 122(1). Further, ATM/MPLS edge switch 122(1) does not receive the MPLS BDI frame. Accordingly, ATM/MPLS edge switch 122(1) recognizes the absence of any response to the originally transmitted CV frame and determines that tunnel 4 is not fully operational. [0048] Case D is a variation of Case A. In a normal situation if tunnel 4 is fully operational, ATM/MPLS edge switch 122(1) and ATM/MPLS edge switch 122(2) will be able to transmit and receive CV frames therebetween. However, if ATM/MPLS edge switch 122(2) has an indication that downstream to it, there is a further failure which affects tunnel 4, ATM/MPLS edge switch 122(1) generates a MPLS FDI frame, which indicates that forward of ATM/MPLS edge switch 122(2) there is a further integrity problem associated with tunnel 4. The MPLS FDI frame is transmitted from ATM/MPLS edge switch 122(2) to ATM/MPLS edge switch 122(1) via LSP 2. The MPLS FDI frame is received by ATM/MPLS edge switch 122(1). ATM/MPLS edge switch 122(1) can then recognize the fault downstream of tunnel 4. This case may also be an extension of Case B if a fault in tunnel 4 causes ATM/MPLS edge switch 122(2) to not receive CV frames from ATM/MPLS edge switch 122(1). In this case, both a MPLS FDI frame and a BDI frame are transmitted from ATM/MPLS edge switch 122(2) to ATM/MPLS edge switch 122(1) via LSP 2. [0049] The Cases are summerized in the following Table A: 2 Case Frames received at ATM/IP edge switch 122 LSP 0 Status LSP 2 Status A CV Up Up B CV, BDI Down Up C None Unknown Down D 1 FDI Up Down D2 BDI, FDI Down Down [000] It will be appreciated that MPLS switches 118 may be configured to generate and transmit MPLS OAM frames such that the use of CV frames is not necessary to detect failures in tunnel 4. If MPLS switches 118 can detect a failure in LSP 0, an MPLS switch 118 may generate and transmit a MPLS FDI frame downstream along LSP 0, toward ATM/MPLS edge switch 122(2). Upon receiving the MPLS FDI frame, ATM/MPLS edge switch 122(2) generates and transmits a MPLS BDI frame over LSP 2 to ATM/MPLS edge switch 122(1). 3.1 Failures Resulting in Generation and Transmission of OAM Cells or Frames [001] Referring again to Figure 4, propagation of error information in a tunnel in MPLS network 4 to ATM network 2 by switch 122 is shown. [002] If tunnel 4 fails per Cases C, Case D1 and Case D2 indicating a fault in tunnel 4 in direction 442 (for example, due to a failure at point 436 in a cable leading towards ATM/MPLS edge switch 122), MPLS card 4 receives and interprets the corresponding error state. ATM/MPLS edge switch 122 processes the error state information and further generates ATM AIS cell which is transmitted from ATM card 0 (point 424) towards ATM network 2 in direction 442 on connections that were associated with tunnel 4. [003] If ATM/MPLS edge switch 122 receives MPLS BDI frames per Cases C and Case D2 indicating a fault in tunnel 4 in direction 4 (for example, due to a failure at point 436 in a cable leading away from ATM/MPLS edge switch 122), no ATM AIS cells are generated and transmitted to ATM network 2. Instead, ATM RDI cells will pass through LSP 2 to ATM network 2, as described below. [004] If there is a fault in MPLS port 8 or its I/O card (i.e. a failure at point 434), ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from ATM card 0 (point 424) towards ATM network 2 in direction 442 on ATM connections linked to MPLS card 4 and MPLS port 8. [00] If MPLS card 4 fails and there is no redundant MPLS card 4 (i.e. a failure at point 432), ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from ATM card 0 (point 424) towards ATM network 2 in direction 442 on ATM those connections linked to MPLS card 4. [006] If fabric port 412 fails (i.e. a failure at point 4), ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from ATM card 0 (at point 424) towards ATM network 2 in direction 442 on ATM connections linked to fabric port 412. Also, a MPLS FDI frame is generated and transmitted from the MPLS card 4 having a connection to the fabric port 412 in direction 4 to all connected tunnels 4. 6

7 2 [007] If fabric card 2 fails or is removed and there is no redundant fabric card 2 (i.e. a failure at point 428), ATM/ MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from ATM card 0 towards ATM network 2 in direction 442 on all connections associated with fabric card 2. Also, a MPLS FDI frame is generated and transmitted from MPLS card 4 (point 432) in direction 4 on all tunnels 4 that have tunnel monitoring enabled. [008] If fabric port 4 fails (i.e. a failure at point 426), ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from ATM card 0 towards ATM network 2 in direction 442 on ATM connections associated with fabric port 4. An ATM AIS cell is generated and transmitted from the MPLS card 4 (point 432) towards the MPLS network 4 in direction 4 on those connections from the ATM card 0 with the failed fabric port 4. ATM OAM cells are supported in MPLS network 4 using cell mode encapsulation by transparently passing ATM OAM cells through MPLS network 4. MPLS card 4 simply passes ATM OAM cells from ATM network 2 with data cells through MPLS tunnel 4 if the connection is configured to use cell mode encapsulation. No ATM AIS cells are transmitted for connections configured using frame mode encapsulation. These ATM AIS cells are then carried transparently across their corresponding MPLS tunnel 4 to the far-end ATM network 2. [009] If ATM card 0 of ATM/MPLS edge switch 122 fails and there is no redundant ATM card 0 (i.e. a failure at point 424), ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell which is transmitted from MPLS card 4 (point 432) towards MPLS network 4 in direction 4. This is done for all connections in direction 4 using cell mode encapsulation connected to the faulted ATM card 0. These ATM AIS cells are then carried transparently across their corresponding MPLS tunnel 4 to the far-end ATM network 2. [0060] If there is a fault in ATM port 6 or its I/O card (a failure at point 422), then ATM/MPLS edge switch 122 recognizes the fault and generates an ATM AIS cell from ATM card 0. ATM/MPLS edge switch 122 transmits the ATM AIS cell in direction 4, into ATM/MPLS edge switch 122 for connections associated with the failed ATM port 6 configured to use cell mode encapsulation. ATM/MPLS edge switch 122 passes these ATM OAM cells through MPLS tunnel 4. If the connection is configured to use frame mode encapsulation, then no ATM AIS cells are generated and transmitted. [0061] In the event of a failure in ATM network 2 (for example, a failure in communications link 8 at point 4), then an ATM AIS OAM cell is generated by a switch in ATM network 2 and transmitted in direction 4, towards ATM/ MPLS edge switch 122, on all ATM connections. ATM/MPLS edge switch 122 passes this ATM OAM cell transparently through MPLS tunnel 4 as a typical cell if the connection uses cell mode encapsulation. If the connection is configured to use frame mode encapsulation, then the ATM OAM cell is terminated at ATM card 0 of ATM/MPLS edge switch MPLS and ATM OAM Interworking [0062] Referring to Figure, the correlation of ATM OAM cells and MPLS OAM frames is illustrated in more detail. In network 0, CPE 112(1) transmits cells or frames to CPE 112(2), as described previously. If a fault 00 occurs in MPLS network 4, ATM/MPLS edge switch 122(2) detects the fault by either receiving MPLS FDI frames from MPLS switch 118 at point 02 or by failing to receive CV frames. The transmission of MPLS FDI frames, if any, is indicated by arrow extending between point 02 and point 04. [0063] ATM/MPLS edge switch 122(2) transmits MPLS BDI frames from MPLS card 4(2) (point 04) towards ATM/ MPLS edge switch 122(1). ATM/MPLS edge switch 122(2) also transmits ATM AIS cells from ATM card 0(2) (point 06) towards CPE 112(2). The transmission of ATM AIS cells is indicated by arrow 12 extending between point 06 and point. [0064] When the ATM AIS cells arrive at ATM edge switch 1(2), ATM edge switch 1(2) notifies CPE 112(2) and transmits ATM RDI cells towards CPE 112(1). These ATM RDI cells transmitted towards CPE 112(1) are transparently passed through MPLS network 4 over tunnel 4. The ATM RDI cells arrive at ATM edge switch 1(1) which informs CPE 112(1) of the fault. The transmission of ATM RDI cells is indicated by arrow 14 extending between point and point 22. [006] When the MPLS BDI frames arrive at ATM/MPLS edge switch 122(1), MPLS card 4(1) removes the MPLS BDI frames from the datastream at point 08. MPLS BDI frames do not continue to ATM edge switch 1(2) since ATM RDI cells are transmitted to ATM edge switch 1(2). The transmission of MPLS BDI frames is indicated by arrow 16 extending between point 04 and point 08. Therefore, MPLS OAM frames are transmitted only on MPLS network Tunnel Status and ATM Connection Control [0066] Referring to Figure 6, further detail of ATM/MPLS edge switch 122 is provided. ATM/MPLS edge switch 122 has an LSP management system 600 residing on a control card 602. ATM card 0 is illustrated having ATM connection control 614. MPLS card 4 of ATM/MPLS edge switch 122 is also illustrated having MPLS OAM state machine 604, OAM task 624 and Change FIFO 6. Change FIFO 6 is comprised of Change of State entries 6. 7

8 [0067] Briefly, OAM task 624 communicates with LSP management system 600 to inform it of changes of state of MPLS OAM state machine 604. From this information, LSP management system 600 determines whether tunnel 4 is available for ATM connections and whether ATM AIS cells should be transmitted into ATM network 2, communicating this information to ATM connection control 614. Accordingly, the embodiment provides an interface allowing MPLS tunnel status information to be provided to ATM nodes. [0068] As noted earlier, MPLS network 4 transmits MPLS OAM frames, either CV, FDI or BDI frames, to ATM/ MPLS edge switch 122. MPLS OAM frames arrive at OAM state machine 604 in MPLS card 4, shown by arrow 606. There is one MPLS OAM state machine 604 for each tunnel 4 and each failure state, either CV, FDI or BDI failure. [0069] Referring to Figure 7, MPLS OAM state machine 604 is shown for one tunnel 4 and one failure state. A MPLS OAM state machine 604 for CV failures will transition from Unknown state 702 to OK state 704 if connectivity verification of the tunnel is successful. Connectivity verification may be successful upon receipt of a consecutive number of CV frames. MPLS OAM state machine 604 for CV failures will transition from Unknown state 702 to Defect state 706 if connectivity verification fails. [0070] In performing connectivity verification, CV frames should be received by MPLS OAM state machine 604 for CV failures periodically, about once every second. However, after a period of time has elapsed without receiving a CV frame, MPLS OAM state machine 604 for CV failures moves to Defect state 706. This time period may be configurable. A debounce mechanism is provided for CV frames by setting the period of time after which a CV failure is declared to a time longer than one second. In the embodiment, the time period is three seconds. [0071] For MPLS OAM state machine 604 for BDI failures, when in Unknown state 702 or OK state 704 and it receives a BDI frame, MPLS OAM state machine 604 moves to Defect state 706. The same is true for MPLS OAM state machine 604 for FDI failures, moving from Unknown state 702 to Defect state 706 when it receives a FDI frame. [0072] While in Defect state 706, the defect can be cleared. For MPLS OAM state machine 604 for CV failures, the defect is cleared when the MPLS OAM state machine 604 receives a series of consecutive CV frames. The number of CV frames may be configurable. In the embodiment, the default number of CV frames needed to clear a CV failure is 3. For MPLS OAM state machine 604 for BDI failures, the defect is cleared when the MPLS OAM state machine 604 does not receive a further BDI frame within a defined period of time. The defined period of time may be varied by the MPLS OAM state machine 604. In the embodiment, the default defined period is three seconds. A defect in MPLS OAM state machine 604 for FDI failures is similarly cleared. Upon the clearing of a defect, MPLS OAM state machine 604 moves to OK state 704. [0073] In OK state 704, transitions are made to Defect state 706 upon the absence of receipt of a number of CV frames or the receipt of either a BDI or FDI frame, as described above. [0074] Referring back to Figure 6, when a MPLS OAM state machine 604 for tunnel 4 indicates a change of state to Defect state 706, it generates and enqueues a Change of State entry 6 on Change FIFO 6, indicated by arrow 622. The entry 6 contains information about the destination LSP and MPLS OAM status information. OAM task 624 periodically monitors FIFO 6 for new entries. Upon detection of a new entry therein, OAM task 624 transmits an indication of the failure state of either or both of LSPs 0 and 2 in tunnel 4 to LSP management system 600, indicated by arrow 608. [007] If tunnel 4 is in a state indicating that LSP 0 is "down" (see table A), LSP management system 600 broadcasts this to ATM connection control 614 in ATM cards 0 and LSP 0 cannot be used. This broadcast is indicated by arrows 6 and 612. ATM connection control 614 in each ATM card 0 receives this message and stops transmitting data over a failed LSP 0. [0076] When a MPLS OAM state machine 604 is informed by arriving MPLS OAM frames or lack thereof that LSP 0 which was "down" is now "up", it transitions to OK state 704 and writes a change of state entry 6 to Change FIFO 6, indicated by arrow 622. OAM task 624 reads this change of state from Change FIFO 6, indicated by arrow 626, and indicates the change to LSP management system 600, shown by arrow 608. LSP management system 600 broadcasts this to ATM connection control 614 in ATM cards 0 and LSP 0 can now be used to transmit data. This broadcast is indicated by arrows 6 and 612. ATM connection control 614 in each ATM card 0 receives this message and can again transmit data over LSP 0. [0077] If the information from Change of State entry 6 provided to LSP management system 600 indicates that LSP 2 is "down", LSP management system 600 broadcasts this to ATM connection control 614 in ATM cards 0. This broadcast is indicated by arrows 6 and 612. For each ATM connection connected over a failed LSP 2, ATM connection control 614 starts inserting ATM AIS cells into ATM network 2, indicated by arrow 616. The ATM AIS cell contains a code identifying it as an ATM AIS cell. The ATM cell header contains the virtual path identifier (VPI) and virtual connection identifier (VCI) that uniquely specifies the individual ATM connection. [0078] When a MPLS OAM state machine 604 is informed by arriving MPLS OAM frames or lack thereof that LSP 2 which was "down" is now "up", it transitions to OK state 704 and writes a change of state entry 6 to Change FIFO 6, indicated by arrow 622. OAM task 624 reads this change of state from Change FIFO 6, indicated by arrow 626, and indicates the change to LSP management system 600, shown by arrow 608. LSP management system 600 broad- 8

9 casts this to ATM connection control 614 in ATM cards 0. This broadcast is indicated by arrows 6 and 612. For each ATM connection connected over a recovered LSP 2, ATM connection control 614 stops inserting ATM AIS cells into ATM network 2 and transmits the normal data cells received, indicated by arrow 616. [0079] The system and method of interworking MPLS OAM frames with ATM OAM cells informs ATM networks 2 of failures in MPLS network 4 providing information that can be used to route around failures in network 0. ATM networks 2 can be instructed by LSP management system 600 to avoid transmitting data on failed tunnels 4, as is described above, providing a more reliable network 0. [0080] It is noted that those skilled in the art will appreciate that various modifications of detail may be made to the present embodiment, all of which would come within the scope of the invention. Claims 1. A method of notifying network nodes about a disruption in service, for an asynchronous transfer mode, ATM, network (2) carrying an ATM connection in a label switched path, LSP, (0) over a core multi-protocol label switching, MPLS, network (4), comprising the steps of: 2 (i) providing an ATM/MPLS edge switch (122(1)) at the interface between the ATM network and the MPLS network; (ii) establishing a routing path traversing a first segment (2(1)) of the ATM network, over the edge switch to the MPLS network, and towards a second segment (2(2)) of the ATM network; (iii) monitoring the routing path at the edge switch and generating an alarm signal upon detection of a fault affecting the LSP; and (iv) transmitting said alarm signal to the ATM network, whereby step (iii) comprises: 3 providing at said edge switch a failure state indication for a detected fault by monitoring said routing path at said ATM network, at said MPLS network and between the ingress and the egress ports of said ATM/MPLS edge switch; and based on said failure state indication, generating the alarm signal, wherein the alarm signal is an ATM OAM alarm indication signal, AIS, packet, and whereby step (iv) comprises broadcasting said alarm signal to nodes of the ATM network which are affected by the detected fault directly towards said first segment and/or towards said second segment through said label switched path depending whether the detected fault has occurred on said routing path at said ATM network, at said MPLS network, or between the ingress and the egress ports of said edge switch The method of claim 1, wherein step (iii) comprises: monitoring from a MPLS network interface (4) on said edge switch (122) the status of the LSP using MPLS OAM packets received from the MPLS network (4); and detecting the fault (436) and generating the failure state indication at the MPLS network interface (4), wherein the failure state indication indicates a failure in said LSP across the MPLS network, and wherein in step (iv), said alarm signal is broadcast to affected nodes towards said first segment. 3. The method of claim 1, wherein step (iii) comprises: 0 monitoring from a MPLS network interface (4) on said edge switch (122) operation of said egress port (8) using physical interface circuitry; and detecting the fault (434) and generating the failure state indication at the MPLS network interface (4), wherein the failure state indication indicates a failure at said egress port of said edge switch, and wherein in step (iv), said alarm signal is broadcast to affected nodes towards said first segment. 4. The method of any one of claims 1 to 3, wherein step (iii) comprises: 9

10 monitoring from said edge switch (122), operation of a MPLS network interface (4) using a controller provided on the edge switch; detecting the fault (432) at said MPLS network interface and generating the failure state indication demonstrating a failure at said MPLS network interface and transmitting said failure state indication to an ATM network interface (0) on said edge switch; and at the ATM network interface, generating said alarm signal, and wherein in step (iv), said alarm signal is broadcast to affected nodes towards said first segment. 2. The method of any one of claims 1 to 4, wherein step (iii) comprises: monitoring the routing path between a MPLS network interface (4) and an ATM network interface (0) at said edge switch using a controller provided on said edge switch; detecting the fault (426, 428, 4) within the edge switch and generating a failure indication demonstrating a failure on said routing path between the ATM network interface and the MPLS network interface; wherein in step (iv), said alarm signal is broadcast to affected nodes towards said first segment and wherein based on said failure state indication, said method further comprises a step of generating at said MPLS network interface a MPLS OAM forward defect indication, FDI, packet. 6. The method of any one of claims 1 to, wherein step (iii) comprises: monitoring operation of an ATM interface at said edge switch from a controller on said edge switch; detecting the fault (424) at said ATM network interface and generating a failure state indication demonstrating a failure on said routing path at the ATM network interface; and generating said alarm signal at said MPLS network interface, and wherein in step (iv), said alarm signal is broadcast to affected nodes towards said second segment. 7. The method of any one of claims 1 to 6, wherein step (iii) comprises: 3 4 monitoring from an ATM network interface operation of said routing path at said ingress port (6) on said edge switch; detecting the fault (422) at said ingress port and generating a failure state indication demonstrating a failure on said ingress port; transmitting said failure state indication to a MPLS network interface (4) on said edge switch; and generating said alarm signal at said MPLS network interface, and wherein in step (iv), said alarm signal is broadcast to affected nodes towards said second segment. 8. An asynchronous transfer mode/multi-protocol label switching, ATM/MPLS, edge switch (122) for notifying network nodes about a disruption in service, for an asynchronous transfer mode, ATM, network (2) carrying an ATM connection in a label switched path, LSP, (0) over a core multi-protocol label switching, MPLS, network (4), said ATM/MPLS edge switch (122(1)) being provided at the interface between the ATM network and the MPLS network, and configured to monitor a routing path traversing a first segment (2(1)) of the ATM network, over the edge switch to the MPLS network, and towards a second segment (2(2)) of the ATM network, so that an alarm signal can be generated upon detection of a fault affecting the LSP and transmitted to said ATM network, wherein said ATM/MPLS edge switch comprises: 0 means for monitoring said routing path at said ATM network, at said MPLS network and between the ingress and the egress ports of said ATM/MPLS edge switch and for providing a failure state indication for a detected fault ; and means for broadcasting, based on said failure state indication, said alarm signal, wherein the alarm signal is an ATM OAM alarm indication signal, AIS, packet, to nodes of the ATM network which are affected by the detected fault directly towards said first segment and/or towards said second segment through said label switched path depending whether the detected fault has occurred on said routing path at said ATM network, at said MPLS network, or between the ingress and the egress ports of said edge switch. 9. The edge switch of claim 8, characterized in that the edge switch comprises: a MPLS interface (4) for monitoring operation of the LSP, and generating a failure state indication if the fault

11 affects the routing path across the MPLS network or at said egress port of the routing path on said edge switch; an ATM interface (0) for generating and transmitting said ATM OAM alarm indication signal, AIS, packet of receipt of said failure state indication; and a controller (602) for monitoring operation of the routing path within the edge switch, and operation of said ATM and MPLS interfaces, wherein the MPLS interface (4) is configured to transmit said ATM OAM AIS packet transparently over the LSP when the fault affects said ingress port of the routing path on said edge switch, and to generate and transmit a MPLS OAM forward defect indication, FDI, packet over said LSP when the fault affects the routing path between the ATM network interface and the MPLS network interface.. The edge switch of claim 9, wherein the MPLS network interface comprises: a MPLS operations, administration and maintenance, OAM, state machine (604) for each LSP tunnel originating at said edge switch for receiving a MPLS OAM frame indicating a change of state of operation of the routing path carried in a LSP tunnel across the MPLS network; and an OAM task (624) for placing the change of state signals from all MPLS OAM state machines in a queue (7) and for informing the LSP management system of each changes of state in order. 11. The edge switch of claim, wherein the ATM network interface further comprises means for transmitting said ATM OAM alarm indication signal, AIS, to a node in the first segment of the ATM network affected by the fault, if the fault is at the MPLS network interface or in the MPLS network. 2 Patentansprüche 1. Verfahren zum Melden einer Dienstunterbrechung an Knoten für ein Netz (2) mit asynchronem Übertragungsmodus, ATM, das eine ATM-Verbindung in einem kennsatzgeschalteten Pfad, LSP (0) über ein Netz (4) mit Kennsatzschaltung für mehrere Protokolle, MPLS, im Kern, das die Schritte umfasst: (i) Bereitstellen eines ATM/MPLS-Rand-Umschalters (122(1)) an der Schnittstelle zwischen dem ATM-Netz und dem MPLS-Netz; (ii)aufbauen eines Leitweges, der ein erstes Segment (2(1)) des ATM-Netzes durchquert, über den Randschalter zum MPLS-Netz und zu einem zweiten Segment (2(2)) des ATM-Netzes; (iii)überwachen des Leitweges am Rand-Umschalter und Erzeugen eines Alarmsignals bei Erfassung eines Fehlers, der den LSP beeinträchtigt; und (iv)übertragen des Alarmsignals zum ATM-Netz, wodurch der Schritt (iii) umfasst: Bereitstellen einer Fehlerzustandsangabe an dem Rand-Umschalter für einen erfassten Fehler durch das Überwachen des Leitweges beim ATM-Netz, beim MPLS-Netz und zwischen den Eingangs- und Ausgangsanschlüssen des ATM/MPLS-Ra nd-umschalters; und, basierend auf der Fehlerzustandsangabe, Erezeugen des Alarmsignals, wobei das Alarmsignal ein Paket für ein ATM-OAM-Alarmangabesignal, AIS, ist, und wodurch der Schritt (iv) das Rundsenden des Alarmsignals zu den Knoten des ATM-Netzes, die von dem erfassten Fehler betroffen sind, direkt zu dem ersten Segment und/oder zu dem zweiten Segment über den kennsatzgeschalteten Pfad, abhängig davon, ob der erfasste Fehler auf dem Leitweg beim ATM-Netz, beim MPLS-Netz oder zwischen den Eingangsund Ausgangsanschlüssen des Rand-Umschalters aufgetreten ist. 2. Verfahren nach Anspruch 1, bei dem der Schritt (iii) umfasst: - Überwachen des Status des LSP unter Verwendung von MPLS-OAM-Paketen, die vom MPLS-Netz (4) her empfangen wurden, von einer MPLS-Netz-Schnittstelle (4) am Rand-Umschalter (122) aus; und - Erfassen des Fehlers (436) und Erzeugen der Fehlerzustandsangabe an der MPLS-Netz-Schnittstelle (4), wobei die Fehlerzustandsangabe einen Fehler in dem LSP über das MPLS-Netz angibt, und wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum ersten Segment hin rundgesendet wird. 11

12 3. Verfahren nach Anspruch 1, bei dem der Schritt (iii) umfasst: - Überwachen des Betriebs des Ausgangsanschlusses (8) unter Verwendung einer physikalischen Schnittstellenschaltung von einer MPLS-Netz-Schnittstelle (4) am Rand-Umschalter (122) aus; und - Erfassen des Fehlers (434) und Erzeugen der Fehlerzustandsangabe an der MPLS-Netz-Schnittstelle (4), wobei die Fehlerzustandsangabe einen Fehler an dem Ausgangsanschluss des Rand-Umschalters angibt, und wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum ersten Segment hin rundgesendet wird Verfahren nach einem der Ansprüche 1 bis 3, bei dem Schritt (iii) umfasst: Überwachen des Betriebs einer MPLS- Netz-Schnittstelle (4) unter Verwendung einer auf dem Rand-Umschalter bereitgestellten Steuerung vom Rand- Umschalter (122) aus; Erfassen des Fehlers (432) an der MPLS-Netz-Schnittstelle und Erzeugen der Fehlerzustandsangabe, die einen Fehler an der MPLS-Netz-Schnittstelle zeigt, und Übertragen der Fehlerzustandsangabe zu einer ATM-Netz-Schnittstelle (0) auf dem Rand-Umschalter; und Erzeugen des Alarmsignals an der ATM-Netz-Schnittstelle, und wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum ersten Segment hin rundgesendet wird.. Verfahren nach einem der Ansprüche 1 bis 4, bei dem Schritt (iii) umfasst: - Überwachen des Leitweges zwischen einer MPLS-Netz-Schnittstelle (4) und einer ATM-Netz-Schnittstelle (0) am Rand-Umschalter unter Verwendung einer auf dem Rand-Umschalter bereitgestellten Steuerung; - Erfassen des Fehlers (426, 428, 4) im Rand-Umschalter und Erzeugen einer Fehlerangabe, die einen Fehler auf dem Leitweg zwischen der ATM-Netz-Schnittstelle und der MPLS-Netz-Schnittstelle zeigt; wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum ersten Segment hin rundgesendet wird, und wobei - auf Basis der Fehlerzustandsangabe das Verfahren ferner einen Schritt des Erzeugens eines Pakets für eine MPLS-OAM-Weiterleitungsfehlerangabe, FDI, umfasst. 6. Verfahren nach einem der Ansprüche 1 bis, bei dem Schritt (iii) umfasst: Überwachen des Betriebs einer ATM- Schnittstelle am Rand-Umschalter von einer Steuerung auf dem Rand-Umschalter aus; Erfassen des Fehlers (424) an der ATM-Netz-Schnittstelle und Erzeugen einer Fehlerzustandsangabe, die einen Fehler auf dem Leitweg an der ATM-Netz-Schnittstelle zeigt; und Erzeugen des Alarmsignals an der MPLS-Netz-Schnittstelle, und wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum zweiten Segment hin rundgesendet wird. 7. Verfahren nach einem der Ansprüche 1 bis 6, bei dem Schritt (iii) umfasst: Überwachen des Betriebs des Leitweges am Eingangsanschluss (6) auf dem Rand-Umschalter von einer ATM-Netz-Schnittstelle aus; Erfassen des Fehlers (422) am Eingangsanschluss und Erzeugen einer Fehlerzustandsangabe, die einen Fehler auf dem Eingangsanschluss zeigt; Übertragen der Fehlerzustandsangabe zu einer MPLS-Netz-Schnittstelle (4) auf dem Rand-Umschalter; und Erzeugen des Alarmsignals an der MPLS-Netz-Schnittstelle, und wobei in Schritt (iv) das Alarmsignal zu betroffenen Knoten zum zweiten Segment hin rundgesendet wird. 8. Rand-Umschalter (122) für asynchronen Übertragungsmodus/Kennsatzumschaltung für mehrere Protokolle, ATM/ MPLS, zum Melden einer Unterbrechung des Dienstes an Netzknoten für ein Netz (2) mit asynchronem Übertragungsmodus, ATM, das eine ATM-Verbindung in einem Pfad mit Kennsatzumschaltung, ISP, (0) über ein Netz (4) mit Kennsatzumschaltung für mehrere Protokolle, MPLS, im Kern trägt, wobei der ATM/MPLS-Rand-Umschalter (122(1) an der Schnittstelle zwischen dem ATM-Netz und dem MPLS-Netz bereitgestellt und so konfiguriert ist, dass er einen schwächer werdenden Pfad, der ein erstes Segment (2(1)) des ATM-Netzes durchquert, über den Rand-Umschalter zum MPLS-Netz und zu einem zweiten Segment (2(2)) des ATM-Netzes hin überwacht, so dass bei Erfassung eines Fehlers, das den LSP betrifft, ein Alarmsignal erzeugt und zum ATM-Netz übertragen werden kann, wobei der ATM/MPLS-Rand-Umschalter umfasst: eine Einrichtung zum Überwachen des Leitwegs beim ATM-Netz, beim MPLS-Netz und zwischen den Eingangsund Ausgangsanschlüssen des ATM/MPLS-Ra nd-umschalters und zum Bereitstellen einer Fehlerzustandsangabe für einen erfassten Fehler; 12

13 und eine Einrichtung zum Rundsenden des Alarmsignals, basierend auf der Fehlerzustandsanzeige, wobei das Alarmsignal ein Paket für ein ATM-OAM-Alarmanzeigesignal, AIS, ist, zu Knoten des ATM-Netzes, die von dem erfassten Fehler betroffen sind, direkt zu dem ersten Segment und/oder zu dem zweiten Segment über den kennsatzgeschalteten Pfad, abhängig davon, ob der erfasste Fehler auf dem Leitweg beim ATM-Netz, beim MPLS-Netz oder zwischen den Eingangs- und Ausgangsanschlüssen des Rand-Umschalters aufgetreten ist. 9. Rand-Umschalter nach Anspruch 8, dadurch gekennzeichnet, dass der Rand-Umschalter umfasst: eine MPLS-Schnittstelle (4) zum Überwachen des Betriebs des LSP und Erzeugen einer Fehlerzustandsangabe, wenn der Fehler den Leitweg über das MPLS-Netz betrifft, oder am Ausgangsanschluss des Leitweges auf dem Rand-Umschalter; eine ATM-Schnittstelle (0) zum Erzeugen und Übertragen des Pakets des Alarmangabesignals, AIS, für ATM-OAM, für den Empfang der Fehlerzustandsangabe; und Steuerung (602) zum Überwachen des Betriebs des Leitweges im Rand-Umschalter, und des Betriebs der ATM-und MPLS-Schnittstellen, wobei die MPLS-Schnittstelle (4) so konfiguriert ist, dass sie das ATM-OAM-AIS-Paket transparent über den LSP überträgt, wenn der Fehler den Eingangsanschluss des Leitweges auf dem Rand-Umschalter betrifft, und ein Paket für eine MPLS-OAM-Weiterleitungsfehlerangabe, MI, erzeugt und über den LSP überträgt, wenn der Fehler den Leitweg zwischen der ATM-Netz-Schnittstelle und der MPLS-Netz-Schnittstelle betrifft.. Rand-Umschalter nach Anspruch 1, bei dem die MPLS-Netz-Schnittstelle umfasst: 2 eine Maschine (604) für den Betriebs-, Verwaltungs- und Wartungs-, OAM-, Zustand bei MPLS für jeden LSP- Tunnel, der am Rand-Umschalter beginnt, zum Empfangen eines MPLS-OAM-Rahmens, der eine Änderungen des Betriebszustandes des in einem LSP-Tunnel über das MPLS-Netz getragenen Leitweges angibt; und eine OAM-Aufgabe (624) zum Anordnen der Änderung von Zustandssignalen von allen MPLS-OAM-Zustandsmaschinen in einer Warteschlange (7) und zum Informieren des LSP-Verwaltungssystems der Reihe nach über die Zustandsänderungen. 11. Rand-Umschalter nach Anspruch, bei dem die ATM-Netz-Schnittstelle ferner umfasst: eine Einrichtung zum Übertragen des ATM-OAM-Alarmangabesignals, AIS, zu einem Knoten im ersten Segment des ATM-Netzes, der von dem Fehler betroffen ist, wenn sich der Fehler an der MPLS-Netz-Schnittstelle oder im MPLS-Netz befindet. 3 Revendications 1. Procédé de notification à des noeuds de réseau d une interruption de service, pour un réseau à mode de transfert asynchrone, ATM, (2) transportant une connexion ATM dans un chemin à commutation par étiquette, LSP, (0) sur un réseau fédérateur à commutation multiprotocole par étiquette, MPLS (4), comprenant les étapes consistant à: 4 0 (i) disposer un commutateur de périphérie ATM/MPLS (122(1)) à l interface entre le réseau ATM et le réseau MPLS ; (ii) établir un chemin de routage traversant un premier segment (2(1)) du réseau ATM, sur le commutateur de périphérie vers le réseau MPLS, et vers un deuxième segment (2(2)) du réseau ATM ; (iii) surveiller le chemin de routage au niveau du commutateur de périphérie et générer un signal d alarme lors de la détection d une anomalie affectant le LSP ; et (iv) transmettre ledit signal d alarme au réseau ATM, dans lequel l étape (iii) comprend les étapes consistant à : fournir audit commutateur de périphérie une indication d état d anomalie pour une anomalie détectée par surveillance dudit chemin de routage au niveau dudit réseau ATM, au niveau dudit réseau MPLS et entre les ports d entrée et de sortie dudit commutateur de périphérie ATM/MPLS ; et sur la base de ladite indication d état d anomalie, générer le signal d alarme, dans lequel le signal d alarme est un paquet de signal d indication d alarme, AIS, OAM ATM, et dans lequel l étape (iv) comprend la diffusion dudit signal d alarme aux noeuds du réseau ATM qui sont affectés par l anomalie détectée directement vers 13

14 ledit premier segment et/ou vers ledit deuxième segment par l intermédiaire dudit chemin à commutation par étiquette suivant que l anomalie détectée s est produite sur ledit chemin de routage au niveau dudit réseau ATM, au niveau dudit réseau MPLS, ou entre les ports d entrée et de sortie dudit commutateur de périphérie Procédé selon la revendication 1, dans lequel l étape (iii) comprend les étapes consistant à : surveiller depuis une interface réseau MPLS (4) sur ledit commutateur de périphérie (122) l état du LSP en utilisant des paquets OAM MPLS reçus depuis le réseau MPLS (4) ; et détecter l anomalie (436) et générer l indication d état d anomalie au niveau de l interface réseau MPLS (4), dans lequel l indication d état d anomalie indique une anomalie dans ledit LSP à travers le réseau MPLS, et dans lequel dans l étape (iv), ledit signal d alarme est diffusé aux noeuds affectés vers ledit premier segment. 3. Procédé selon la revendication 1, dans lequel l étape (iii) comprend les étapes consistant à : surveiller depuis une interface réseau MPLS (4) sur ledit commutateur de périphérie (122) le fonctionnement dudit port de sortie (8) en utilisant un circuit d interface physique ; et détecter l anomalie (434) et générer l indication d état d anomalie au niveau de l interface réseau MPLS (4), dans lequel l indication d état d anomalie indique une anomalie au niveau dudit port de sortie dudit commutateur de périphérie, et dans lequel dans l étape (iv), ledit signal d alarme est diffusé aux noeuds affectés vers ledit premier segment. 4. Procédé selon l une quelconque des revendications 1 à 3, dans lequel l étape (iii) comprend les étapes consistant à : surveiller depuis ledit commutateur de périphérie (122), le fonctionnement d une interface réseau MPLS (4) en utilisant un contrôleur disposé sur le commutateur de périphérie ; détecter l anomalie (432) au niveau de ladite interface réseau MPLS et générer l indication d état d anomalie signalant une anomalie au niveau de ladite interface réseau MPLS et transmettre ladite indication d état d anomalie à une interface réseau ATM (0) sur ledit commutateur de périphérie ; et au niveau de l interface réseau ATM, générer ledit signal d alarme, et dans lequel dans l étape (iv), ledit signal d alarme est diffusé aux noeuds affectés vers ledit premier segment.. Procédé selon l une quelconque des revendications 1 à 4, dans lequel l étape (iii) comprend les étapes consistant à : surveiller le chemin de routage entre une interface réseau MPLS (4) et une interface réseau ATM (0) au niveau dudit commutateur de périphérie en utilisant un contrôleur disposé sur ledit commutateur de périphérie ; détecter l anomalie (426, 428, 4) dans le commutateur de périphérie et générer une indication d anomalie signalant une anomalie sur ledit chemin de routage entre l interface réseau ATM et l interface réseau MPLS ; dans lequel dans l étape (iv), ledit signal d alarme est diffusé aux noeuds affectés vers ledit premier segment et dans lequel sur la base de ladite indication d état d anomalie, ledit procédé comprend en outre une étape consistant à générer au niveau de ladite interface réseau MPLS un paquet d indication de défaut avant, FDI, OAM MPLS. 6. Procédé selon l une quelconque des revendications 1 à, dans lequel l étape (iii) comprend les étapes consistant à : surveiller le fonctionnement d une interface ATM au niveau dudit commutateur de périphérie depuis un contrôleur sur ledit commutateur de périphérie ; détecter l anomalie (424) au niveau de ladite interface réseau ATM et générer une indication d état d anomalie signalant une anomalie sur ledit chemin de routage au niveau de l interface réseau ATM ; et générer ledit signal d alarme au niveau de ladite interface réseau MPLS, et dans lequel dans l étape (iv), ledit signal d alarme est diffusé aux noeuds affectés vers ledit deuxième segment. 7. Procédé selon l une quelconque des revendications 1 à 6, dans lequel l étape (iii) comprend les étapes consistant à : surveiller depuis une interface réseau ATM le fonctionnement dudit chemin de routage au niveau dudit port d entrée (6) sur ledit commutateur de périphérie ; 14

15 détecter l anomalie (422) au niveau dudit port d entrée et générer une indication d état d anomalie signalant une anomalie sur ledit port d entrée ; transmettre ladite indication d état d anomalie à une interface réseau MPLS (4) sur ledit commutateur de périphérie ; et générer ledit signal d alarme au niveau de ladite interface réseau MPLS, et dans lequel dans l étape (iv) ledit signal d alarme est diffusé aux noeuds affectés vers ledit deuxième segment. 8. Commutateur de périphérie à mode de transfert asynchrone/commutation multiprotocole par étiquette, ATM/MPLS (122) pour notifier à des noeuds de réseau une interruption de service, pour un réseau à mode de transfert asynchrone, ATM (2) transportant une connexion ATM dans un chemin à commutation par étiquette, LSP (0) sur un réseau fédérateur à commutation multiprotocole par étiquette, MPLS (4), ledit commutateur de périphérie ATM/MPLS (122(1)) étant disposé à l interface entre le réseau ATM et le réseau MPLS, et configuré pour surveiller un chemin de routage traversant un premier segment (2(1)) du réseau ATM, sur le commutateur de périphérie vers le réseau MPLS, et vers un deuxième segment (2(2)) du réseau ATM, de sorte qu un signal d alarme puisse être généré lors de la détection d une anomalie affectant le LSP et transmis audit réseau ATM, dans lequel ledit commutateur de périphérie ATM/MPLS comprend : 2 des moyens pour surveiller ledit chemin de routage au niveau dudit réseau ATM, au niveau dudit réseau MPLS et entre les ports d entrée et de sortie dudit commutateur de périphérie ATM/MPLS et pour fournir une indication d état d anomalie pour une anomalie détectée ; et des moyens pour diffuser, sur la base de ladite indication d état d anomalie, ledit signal d alarme dans lequel le signal d alarme est un paquet de signal d indication d alarme, AIS, OAM ATM, aux noeuds du réseau ATM qui sont affectés par l anomalie détectée directement vers ledit premier segment et/ou vers ledit deuxième segment par l intermédiaire dudit chemin à commutation par étiquette suivant que l anomalie détectée s est produite sur ledit chemin de routage au niveau dudit réseau ATM, au niveau dudit réseau MPLS, ou entre les ports d entrée et de sortie dudit commutateur de périphérie Commutateur de périphérie selon la revendication 8, caractérisé en ce que le commutateur de périphérie comprend : une interface MPLS (4) pour surveiller le fonctionnement du LSP, et générer une indication d état d anomalie si l anomalie affecte le chemin de routage à travers le réseau MPLS ou au niveau dudit port de sortie du chemin de routage sur ledit commutateur de périphérie ; une interface ATM (0) pour générer et transmettre ledit paquet de signal d indication d alarme, AIS, OAM ATM de réception de ladite indication d état d anomalie ; et un contrôleur (602) pour surveiller le fonctionnement du chemin de routage dans le commutateur de périphérie, et le fonctionnement desdites interfaces ATM et MPLS, dans lequel l interface MPLS (4) est configurée pour transmettre ledit paquet AIS OAM ATM de manière transparente sur le LSP lorsque l anomalie affecte ledit port d entrée du chemin de routage sur ledit commutateur de périphérie, et pour générer et transmettre un paquet d indication d anomalie avant, FDI, OAM MPLS sur ledit LSP lorsque l anomalie affecte le chemin de routage entre l interface réseau ATM et l interface réseau MPLS Commutateur de périphérie selon la revendication 9, dans lequel l interface réseau MPLS comprend : une machine d état d opérations, administration et maintenance, OAM, MPLS (604) pour chaque tunnel LSP partant dudit commutateur de périphérie pour recevoir une trame OAM MPLS indiquant un changement d état de fonctionnement du chemin de routage transporté dans un tunnel LSP à travers le réseau MPLS ; et une tâche OAM (624) pour placer les signaux de changement d état provenant de toutes les machins d état OAM MPLS dans une file d attente (7) et pour informer le système de gestion de LSP de chaque changement d état dans l ordre. 11. Commutateur de périphérie selon la revendication, dans lequel l interface réseau ATM comprend en outre des moyens pour transmettre ledit signal d indication d alarme, AIS, OAM ATM à un noeud dans le premier segment du réseau ATM affecté par l anomalie, si l anomalie est à l interface réseau MPLS ou dans le réseau MPLS.

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