Abstract:
A system that allows information of MPLS layers to be reported to PW layers by providing a function having a correlation between MPLS layers and PW layers. A PE uses MPLS (Multi-Protocol Label Switching) tunneling and label technology to map a communication service to MPLS, thereby providing bidirectional services on an end-to-end basis. a communication system comprising the PE to perform label assignment control for bidirectional services, the PE to transmit, after completion of assignment control, a message in which the LDP message used in assignment control is a payload and a tunnel-directed label (L 2 ) used by bidirectional services is a header and the PE to associate, on the basis of the received LDP message used in assignment control, a service-directed label (P 1 ) included in the LDP message with the received tunnel-directed label (L 2 ) in the part where the message is terminated.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International PCT Application No. PCT/JP2007/000322, filed on Mar. 28, 2007. 
    
    
     FIELD 
     The embodiments discussed herein are related to technology which provides a telecommunication service using MPLS (Multi Protocol Label Switching), and are specifically related to a communication system which provides redundancy. 
     BACKGROUND 
     Recently, MPLS has received a lot of attention as packet transmission technology. The IETF (Internet Engineering Task Force) is promoting specification study and standardization of PWE3 (Pseudo Wire Emulation Edge-to-Edge), which provides existing services (such as FR (Frame Relay), ATM, TDM, and Ethernet) on an end-to-end (point-to-point) basis utilizing MPLS as tunneling technology. From the standpoint of service integration, Pseudo Wire (PW) technology utilizing MPLS is expected to expand into carrier networks and will require further higher reliability in the future. 
       FIG. 1  illustrates a model diagram of PWE3 defined by IETF (RFC (Request For Comments) 3915, 3986).  FIG. 1  illustrates a PSN (Packet Switched Network)  1  in which a PSN tunnel  2  and Pseudo Wire PW are established between provider edges PE 1  and PE 2 . In the Pseudo Wire PW, PW 1  and PW 2  are established in correspondence with customer services, for example. The provider edge PE 1  is connected to a customer edge CE 1  outside the Pseudo Wire PW via an attachment circuit  3 , and the provider edge PE 2  is similarly connected to a customer edge CE 2  outside the Pseudo Wire PW via an attachment circuit  4 . 
     Here, an end-to-end service  5  (such as Ethernet, ATM, Frame Relay, TDM, and PPP/HDLC) is emulated using a packet network. As technology which provides virtual pipes (tunnels), MPLS and L2TP (Layer 2 Tunneling Protocol) are mainly used. 
     In carrier networks, high reliability must be ensured. As an example, it is important to construct efficiency-focused connection management technology, and a mechanism in which for example a single failure in a network does not become a load on end users is required. 
     ITU-T Recommendation Y.1731, which specifies carrier Ethernet OAM (Operation, Administration, and Maintenance) has realized a mechanism considering the above. The specific configuration is illustrated in  FIGS. 2A ,  2 B, and  2 C. In the Ethernet service illustrated in  FIGS. 2A and 2B  (i.e., a service to aggregate traffic between CE 1 -[1, 2, . . . , n] CE 2 -[1, 2, . . . , n] at PE 1  and PE 2 ), Y.1731 specifies that a provider layer OAM management domain be provided in a provider domain PE 1 -PE 2 , and also that a customer layer OAM management domain be provided in a CE domain, and this customer domain is set in a manner that overlays the provider domain.  FIG. 2B  illustrates a case in which this system has a hierarchical structure including a customer layer  21  and a provider layer  22 . 
     In this case, alarm forwarding when a single failure occurs in the provider management domain  22  between PE 1 -PE 2  is performed in a manner such that an apparatus at the failure end generates an AIS (Alarm Indication Signal), detects LOC (Loss of Continuity), and notifies PE 1  and PE 2  of the AIS. Receiving this notice triggers PE 1  and PE 2  to generate an AIS notice for the customer domain and deliver it to the end point. On receiving the AIS, an alarm inhibit function operates to inhibit LOC detection, and at the same time a failure in the service domain may be detected and recognized. 
       FIG. 2C  illustrates a case in which there is no hierarchical structure. While a failure in the service domain may be detected by not receiving a CC (Connectivity Check) transmitted from the customer device, receiving no CC may be detected in principle with a time-out of a timer having a length several times longer than a transmission interval. Therefore the detection time is estimated to be much longer than that in  FIG. 2B . While reducing the detection time may be achieved by speeding up (shortening) the CC cycle, in that case, not only might bandwidth in the provider be suppressed, but also processing at PEs may be burdened with a load. 
     As described above, layer management in a packet network is important to achieving flexible connection management for each customer. Considering the above, it is necessary to construct layers such those as illustrated in  FIG. 3  in PW/MPLS also, and based on that, a mechanism for providing OAM, connection management, and failure notification is required. Specifically, the service layer  31  corresponds to the customer layer  21 , and the Pseudo Wire (PW) layer  32  and the MPLS layers  33  and  34  correspond to the provider layer  22 . Packets consisting of L 2  and OAM (FDI, etc.), and packets consisting of L 1 , P 1 , and OAM (BDI, etc.) are bidirectionally transmitted from PE 2  to PE 1 , and from PE 1  to PE 2 , respectively. When a failure is reported/detected in the MPLS layer  34 , escalation to the PW layer  32  and the service layer  31  is required. In other words, since each layer is independent of the others, it is necessary to perform LOC detection by timing out for each PW unit at PE 1 . Even in the case of a failure in the MPLS LSP (Label Switching Path), there is no mechanism to notify the PW layer  32  of an alarm, and as a result, a failure is detected by Loss Detection (timer-dependent) which may be not only time-consuming, but also complicated since one-to-one processing is performed for each PW. 
     In addition, it is necessary to insert flags equivalent to RDI (Remote Defect Indication) on the opposite part. Unlike what is illustrated in  FIGS. 2B and 2C , the MPLS layers  33  and  34  existing under the PW layer  32  have two unidirectional paths. Therefore it is necessary to assume a unidirectional failure and thus that RDI is a necessary function. Consequently, this optional function to insert the RDI is further required. In the MPLS layers  33  and  34 , communication is performed through tunnels  35  and  36 . 
     Considering the above, processing for each PW becomes complicated as in  FIG. 2B  in the PW/MPLS above. And as was described in the beginning, it is desirable that PE 1  be notified of a failure on the basis of a single failure occurring below the MPLS layer, and then RDI may be generated. However, this has not been achieved satisfactorily with the current framework. Specifically, escalation to the PW layer  32  and the service layer  31  cannot be achieved when a failure is notified/detected in the MPLS layers  33  and  34 . 
     This situation is illustrated more specifically in  FIG. 4 . OAM, which is equivalent to AIS occurring in a lower layer of PW (ITU-T Y.1711 FDI, for example), is received at PE 1 . PE 1  needs to extract labels P 1 - 1 ˜P 1 - n  to identify opposite customer services with L 2  or LSP 2  (MPLS label) to identify this AIS equivalent OAM. 
     However, the current framework of signaling (label distribution) is independent for each layer (MPLS, PW). Practically, RSVP-TE defined in RFC3209 or LDP (Label Distribution Protocol) defined in RFC3036 are used in MPLS, and LDP defined in RFC4447 (RFC3036) is used in PW. These are performed in independent procedures based on IP (Internet Protocol). In other words, there is a possibility that a signal for signaling or a label mapping message may not be transmitted on the MPLS tunnel in a configuration of PW, and thus the opposite labels of the tunnel-directed label L 2  or the customer service identification labels P 1 - 1 ˜P 1 - n  may not be extracted. 
     While patent document 1 discloses alarm forwarding in a network, it is different from embodiments of the present invention in that a wavelength is used in a unidirectional link.
     Patent Document 1: Japanese Laid-open Patent Publication No. 2004-312152   

     SUMMARY 
     An embodiment of the present invention provides a management system of labels and paths applied to a communication apparatus using PW (Pseudo Wire) technology on the basis of MPLS. It allows an LOC function from the lower layers (below MPLS) to be reported (escalated) to PW by providing a function having a correlation between MPLS (layers) and PW (layers), and is characterized by its efficient failure notification. Practically, such function is achieved by extending PW signaling. 
     The first aspect of the present invention provides a communication system which is a transmission system using MPLS (Multi Protocol Label Switching) tunneling and label technology to map a communication service to the MPLS and to provide bidirectional services on an end-to-end basis. The communication system is characterized by including a means to perform label assignment control for the bidirectional services; a means to transmit, after completion of the assignment control, a message in which an LDP message used in the assignment control is a payload and a tunnel-directed label (L 2 ) used by the bidirectional services is a header; and a means to associate, on the basis of the received LDP message used in the assignment control, a service-directed label (P 1 ) included in the corresponding LDP message with the received tunnel-directed label (L 2 ), in the part where the message is terminated. 
     This allows the customer service label P 1  from the first edge to the second edge to be associated with the customer service label P 2  from the second edge to the first edge in MPLS bidirectional communication system. Therefore, the tunnel label L 2  in a certain direction in the MPLS layer may be escalated to the customer service identification label P 2  in the certain direction in the PW service layer, to the customer service label P 1  in the opposite direction, and to the tunnel label L 1  in the opposite direction. 
     The second aspect of the present invention provides a communication system to perform the bidirectional communication services of the first aspect, and is characterized in that the means to associate includes a means to analyze the message to determine the presence of a message having the same Forwarding Equivalence Class (FEC) or the same forwarding attribute in the label assignment; and a means to look up labels (P 1 - 1 ˜P 1 - n ) transmitted from the first end to the second end which identify the customer service, and to detect corresponding labels (P 2 - 1 ˜P 2 - n ) transmitted from the second end to the first end which identify the customer service. 
     The third aspect of the present invention provides a communication system according to the first aspect of the present invention, and is characterized in that the header of the message includes a specific label for control management. 
     The fourth aspect of the present invention provides a communication system according to the first aspect of the present invention, and is characterized in that the header of the message includes a specific data field for control management. 
     The fifth aspect of the present invention provides a communication system according to the first aspect of the present invention, and is characterized in that the header of the message includes IP and UDP. 
     The sixth aspect of the present invention provides a communication system according to any of the first to fifth aspects of the present invention, and is characterized in that, when receiving a failure notification message in which a tunnel-directed label used by a service is a header, a service-directed label in the opposite direction is obtained, and a payload associated with the obtained service-directed label reflects that a service using a tunnel to which the received failure notification message belongs is in a disconnection state. 
     This allows correspondence between labels L 2  and P 1 - n , for example to transmit data including the label L 2  and OAM (FDI, etc.) from the provider edge PE 2  to the provider edge PE 1 , and to transmit data including the label L 1 , label P 1 - n , and OAM (RDI, etc.) from the edge PE 1  to the second edge PE 2  for failure notification. In other words, if a failure occurs in a path toward one provider edge PE 1 , a packet having the label L 2  and the customer service identification label P 2  as management codes followed by management data is transmitted to notify PE 1  of the failure. Then PE 1  may transmit data having the label L 1  and the customer service identification label P 1  as management information to the other provider edge PE 2  through a path without a failure. 
     The seventh aspect of the present invention provides a communication system according to any of the first to fifth aspects of the present invention, and is characterized in that, when receiving a failure notification message in which a tunnel-directed label used by a service is a header, a corresponding service-directed label or a service identification is obtained from the header, and the user is notified of a disconnection state of the service. 
     The eighth aspect of the present invention provides a communication system according to any of the first to fifth aspects of the present invention; it is a failure notification system at an MPLS path endpoint and a connecting point in a transmission system. The transmission system connects paths in tandem formed by mapping to MPLS and provides bidirectional services on an end-to-end basis. The communication system is characterized in that when the MPLS path endpoint and the connecting point receive the failure notification message in which a tunnel-directed label used by a customer service is a header, a service-directed label in the forward direction is obtained from the header, and a disconnection state of the service is reflected in a payload associated with the obtained service-directed label. 
     The ninth aspect of the present invention provides a communication system according to any of the first to fifth aspects of the present invention, and is characterized in that, when the means to associate, on the basis of the received message used in the assignment control, associates the service-directed label included in the corresponding message with the received tunnel-directed label, if it is determined that all service-directed labels included in the corresponding message are present in a single tunnel which holds an opposite service, then the tunnel is notified that a service using a tunnel to which the received failure notification message belongs is in a disconnection state. 
     The tenth aspect of the present invention provides a communication system which is used in a transmission system to use MPLS (Multi Protocol Label Switching) tunneling and label technology to map a communication service to the MPLS and to provide bidirectional services on an end-to-end basis. The communication system is characterized by including a means to perform label assignment control for the bidirectional services; a means to receive, after completion of the assignment control, a message in which a message used in the assignment control is a payload and a tunnel-directed label used by the bidirectional services is a header; and a means to associate, on the basis of the received message used in the assignment control, a service-directed label included in the corresponding message with the received tunnel-directed label. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a model diagram of PW based on RFC3915 in the prior art; 
         FIG. 2A  illustrates a prior art and an OAM structure adopted in Y.1731; 
         FIG. 2B  illustrates a prior art and an OAM structure adopted in Y.1731; 
         FIG. 2C  illustrates a prior art and an OAM structure adopted in Y.1731; 
         FIG. 3  illustrates a problem and is a schematic diagram of the operation in the conventional alarm processing in the case of using PW (Pseudo Wire) technology based on MPLS; 
         FIG. 4  is a schematic diagram illustrating the problem more specifically; 
         FIG. 5  is a diagram to illustrate a first example of the present invention; 
         FIG. 6A  is a schematic diagram illustrating a processing of an embodiment of the present invention; 
         FIG. 6B  is a schematic diagram illustrating a processing of an embodiment of the present invention; 
         FIG. 6C  is a schematic diagram illustrating a processing of an embodiment of the present invention; 
         FIG. 7  is an apparatus block diagram of the first example of the present invention; 
         FIG. 8  is an apparatus block diagram of the first example of the present invention; 
         FIG. 9  is a diagram illustrating operations in the first example of the present invention with reference to  FIGS. 6A ,  6 B,  6 C, and  7 ; 
         FIG. 10A  is a schematic diagram of the second example of the present invention; 
         FIG. 10B  is a schematic diagram of the second example of the present invention; 
         FIG. 10C  is a schematic diagram of the third example of the present invention; 
         FIG. 11  is an apparatus block diagram of the third example of the present invention; and 
         FIG. 12  is a schematic diagram of the fourth example of the present invention; 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Example 1 
     An example of the present invention is illustrated in  FIGS. 5 and 6 .  FIG. 5  illustrates that assignment of PW labels is determined based on RFC4447. In PW layer  51 , an LDP message  52  to request P 1  is transmitted from PE 2  to PE 1 , and in the opposite direction, an LDP message  53  to request P 2  is transmitted from PE 1  to PE 2 . In this way, PW signaling is established. At this time, the LDP message following the IP header has a common element in signaling in both directions except for only a requested label, such as an IP address in  FIG. 5 . 
     As illustrated in  FIG. 6A , once PW signaling is established, PE 2  directs the P 2 -mapped LDP message directly toward a tunnel # 2  (PE 2 -&gt;PE 1 ) and transmits a control message having this LDP message as a PDU (Protocol Data Unit). At a receiving end, or at PE 1 , correlation between L 2  and P 2  may be obtained in a control processing unit within an apparatus. As described in detail below, correspondence between P 2  and P 1  may be obtained in the signaling stage according to a method of an embodiment of the present invention, and practically correlation between L 2  and P 1  is obtained in the map information in IP-based signaling. Here, a format of the LDP message includes the following:
 
PW FEC TLV (common in both directions)+label mapping message TLV (P1 or P2)
 
     where FEC: Forwarding Equivalence Class; and TLV: Type, Length, and Value 
     Forwarding Equivalence Class (FEC) refers to a group of IP packets to be transmitted in the same manner, for example such as in the case of transmitting the same paths in the same forwarding processing. A label identifies the FEC. Specifically, FEC represents a message having the same forwarding attribute in label assignment. Correspondence between P 1  and P 2  is obtained on the basis of the LDP massage stored in PE 1  and the LDP message transmitted from PE 2  to PE 1 . This correspondence is illustrated in  FIG. 6B  and in the relationship between input (tunnel label) and output (PW) in  FIG. 6C . 
     Now reference is made to  FIGS. 6A ,  6 B, and  6 C for more detailed explanation. First, the LDP message from PE 2  (label message to request PW FEC and P 1 ) is stored at point “a” in the PW layer ( FIG. 6A ) when PW is established. Next, the following processing is executed at point “b” ( FIG. 6A ) after PW is established. Here, (0) to (3) described below correspond to the same reference numbers in  FIGS. 6B and 6C . 
     (0) if PE 1  maps P 1  when PW is established as described above, it is already known that the destination is PE 2 , and thus it is recognized that L 1  is to be mapped in front of P 1 . In other words, once P 1 - 1 ˜P 1 - n  are known, an L 1  equivalent to the corresponding LSP (Label Switched Path) may be referable. 
     (1) PW FEC TLV of the LDP message (with P 1  map request) which is input on the basis of IP is decoded. Because they have this LDP message in common, the message which requested P 1  in the signaling stage from PE 2  to PE 1  is associated with the received message which requested P 2 , and thus correspondence between P 1  and P 2  is obtained. 
     (2) Correspondence between L 2  (with control message ID) and P 2  is obtained. In other words, “L 2  (label) or LSP 2 +PW label belonging to LSP 2 ” is received. 
     (3) Therefore, with reference to L 2 , P 1  and thus L 1  is associated with L 2 . Specifically, with reference to the received (input) LDP message which is input on the basis of IP, correspondence between P 1  stored in PE 1  and the received (input) L 2 -labeled P 2  is obtained on the basis of having the same LDP message. Consequently, correspondence between P 2  and P 1 , and thus correspondence between L 2  and P 1  (output), are obtained. 
     A control message may be achieved, for example by using an OAM label of Y.1711 as a header and assigning this message as PDU. Although Y.1711 does not specify this function, such processing may be executed with a function type. 
     A control message may also be transmitted with an OAM header and an IP/UDP header assigned. In this case, termination may be achieved by setting IP=127.0.0.0 in IP control. The header has a packet structure which includes L 2 , OAM and an LDP message in this order. 
     As another example, an LDP message may also be mapped as a control message directed to PW transmission from PE 1  to PE 2 . Practically, a PW Associated Channel Header is assigned as a control word which identifies a VCCV message in a PWE3 VCCV draft (draft-ietf-pwe3-vccv-**.txt). An effect similar to OAM may be obtained also by using this header, and alarm forwarding illustrated in  FIG. 4  may be allowed. The header has a packet structure which includes L 2 , P 2 , CW (control word) and an LDP message in this order. 
     An apparatus configuration to implement this operation is illustrated in  FIG. 7 . Configuration of PE 1  is explained as an example. In  FIG. 7 , data LSP 2  received from PE 2  is terminated at the control packet header extracting and terminating unit  72  via the label processing terminating unit  71 , and then LDP message analysis is performed at the control signal analysis unit  73 . Next, an alarm notification message is generated at the control signal generating unit  75  with reference to the PW-tunnel mapping table generating/management unit  74 , and the alarm notification message is transmitted as LSP 1  to PE 2  via the label processing unit  76 . Further, a signal from the attachment circuit  79  of CE 1  transmits output to the control signal analysis unit  73  via the service header processing unit  77  and the control packet extracting and terminating unit  78 . The service header processing unit  77  and the control packet extracting and terminating unit  78  also transmits output as a main signal to the label processing unit  76 . Output from the control signal generating unit  75  and a main signal from the control packet header extracting and terminating unit  72  are transmitted to the attachment circuit  80  via the service header processing unit  79 . 
     The operation of an example of the present invention is described more specifically with reference to  FIGS. 6 ,  7 ,  8 , and  9 .  FIG. 8  illustrates a flow of associating between services. In step S 1 , PW signaling (LDP) is performed on the basis of the existing RFC4447 so as to establish PW. This result is confirmed at both PEs. In step S 2 , PE (hereinafter PE 2 , with reference to  FIGS. 6A ,  6 B, and  6 C) transmits to PE 1  the control packet (OAM) for LSP 2 * in which a payload consisting of a PW-directed label mapping message received by PE and the associated PW FEC TLV (e.g., the flow corresponds: control signal generating (not shown in FIG.  7 )-&gt;label processing  71  in  FIG. 7 ). While PE 2  is considered in  FIG. 6A , the same applies to PE 1 . Alternatively, the received PW (or those which belongs to the label) may transmit a control packet directed to PE 1  (IP) instead of the above-described control packet for LSP 2 . 
     In step S 3 , PE 1  receives the control packet. In step S 4 , a field* to identify the tunnel label and control packet for LSP 2  is determined (corresponding to the flow in  FIG. 7 : label processing-&gt;control packet terminating). Then the control signal or the payload is passed to the control signal analysis unit for processing. At this time, the control signal analysis unit is also notified that the control signal is directed to LSP 2 . The above-described determination of the field may be performed by determining the following:
 
IP address for “LSP2-&gt;PW or PE1”+control packet.
 
     In step S 5 , FEC analysis is performed. In step S 6 , it is determined whether or not the same FEC is present in the PW-tunnel mapping table generating/management ( FIG. 6B ). If the result is No, the operation is terminated. If the result is Yes, in step S 7 , the label mapping message transmitted from PE 1  to PE 2  is looked up and a PW label is determined. Specifically, labels P 1   i˜n  to identify the customer transmitted from PE 1  to PE 2  are looked up, and are mapped to the customer identification labels P 2   j - n  received by PE 1 . In step S 8 , label information of opposite PW may be obtained in LSP 2 . 
       FIG. 9  illustrates a flow of failure detection. In step S 10 , an alarm about the failure in LSP 2  is given. Specifically, FDI is received at PE 1 . The alarm is passed to the control signal analysis unit  73  via the label processing unit  71  and the control packet terminating unit  72  in  FIG. 7 . In step S 11 , with reference to the LSP information, opposite PW information (label information) is obtained from the PW-tunnel mapping table ( FIG. 7 ) as described in  FIGS. 6A ,  6 B, and  6 C. In step S 12 , a BDI message corresponding to the obtained PW label (PW) is generated at the control signal generating unit  75  ( FIG. 7 ). In step S 13 , the BDI message is transmitted to PE 2  for each PW unit. 
     Example 2 
     In  FIG. 6A , the direction of alarm forwarding is that of opposite PW, or a transmission direction outgoing from PE which receives the failure notice. However, in practice, a so-called attachment circuit (AC)  80  is present outside PW (between PE-CE) as described in  FIG. 10A . An alarm forwarding using OAM (AIS, etc.) toward the CE part in this direction may also be possible. In  FIG. 7 , analysis is performed at the control signal analysis unit  73 , and the processing result is passed to the generating unit  75 . Finally, the result is reported outside via the service (AC) header processing unit  78  and the attachment circuit  80 . 
     Example 3 
     While embodiments of the present invention consider the case in which PW is established over one domain between PEs, if a multi-domain/multi-carrier system is considered, the case in which PW is connected in tandem between several domains is considered so that an end-to-end service is provided as described in  FIG. 10B . 
     This embodiment of the present invention may also be applicable. When an LSP failure notice from PE 1  is received at PE 2 , as illustrated in the embodiments of the present invention, alarm forwarding in PW 1  between PE 2  and PE 1  as well as alarm forwarding in PW 2  between PE 2  and PE 3  may be achieved. Specifically, when a failure is detected between PE 1  and PE 2 , the data is transmitted to PE 2  as FDI (LSP 1 ), and is further transmitted from PE 2  to PE 3  as FDI/AIS via Pseudo Wire PW 2 . In addition, as for PE 1 , the failure information is transmitted from PE 2  to PE 1  as in the first embodiment of the present invention. 
     As described in  FIG. 10C , the input into the L 1  label or LSP 1  corresponds to the output from P 1 - 1  through P 1 - n . Data having the same message as that of the input data is looked up at PE 2 , and is transmitted from PE 2  to PE 3  with reference to the control codes of P 3 - 1  through P 3 - n  and the control code of L 3 . Therefore, in this case, an example is given in which a failure occurs in LSP 1  established between PE 1  and PE 2 , and this failure is reported to PE 2 . 
     In PE 2 , a failure in LSP 1  is recognized on the basis of the received label (L 1 ). At this time, as described in the embodiments of the present invention, information of labels of upper PWs (P 1 - 1 ˜P 1 - n ) may be identified from information of L 1 . In order to switch PW labels, PE 2  has switching information from P 1  to P 3  already in the setup stage. Therefore, when a failure occurs in LSP 1 , PE 3  and thus CE may be notified of the failure via PW 2 . The same message as that transmitted from the failure to PE 2  is transmitted to PE 3 . 
       FIG. 11  illustrates a configuration diagram of the implementation. Specifically, an apparatus having the same configuration as that illustrated in  FIG. 7  is provided at PE 2 . The data to identify the upper PW with reference to the LSP 1  failure is received from PE 1 . Label processing and control packet header extraction are performed, and analysis of the LDP message of this data is performed in the control signal analysis unit  73 . Data having the same LDP message is detected from the PW-tunnel mapping table. Then an alarm belonging to PW (P 3 - 1 ˜P 3 - n ) on PE 3  is generated at the control signal generating unit. After adding an alarm notification message and performing label processing, the alarm is transmitted to the third edge PE 3 . 
     The only difference from  FIG. 7  is that IFs (interfaces) on both parts are PWs (MPLS). Also, the case in the opposite direction, for example the case in which PE 1  receives the LSP failure notice from PE 2 , may be achieved with the embodiments of the present invention. 
     Example 4 
     The embodiments of the present invention, for example in the case illustrated in  FIG. 6A , provide a means to identify PW (unidirectional) associated with LSP 2  and to provide an alarm forwarding mechanism toward the opposite PW. Therefore, a layer which transmits in the opposite direction is a PW layer, i.e., a service individual unit. However, if all counterparts of the PWs associated with LSP 2  belong to a single LSP (LSP 1 ), alarm forwarding traffic may be reduced. 
     In this processing, a mechanism is required which confirms that all counterparts of the PWs associated with LSP 2  belong to L 1 . A method to achieve such a mechanism is illustrated in  FIG. 12 . In PE 1 , as illustrated in  FIG. 12 , information of P 1 - 1 ˜P 1 - n  is obtained from information of LSP 2  or L 2 . Correlation between P 1 - i  and LSP to be transmitted has already been obtained, because signaling is performed on the same node, and in transmission of a main signal, P 1 - i  is mapped and then a tunnel label is mapped. 
     Under this condition, once it is found that P 1 - 1 ˜P 1 - n  are mapped to a single LSP, PE 1  transmits a message equivalent to a BDI (Backward Defect Indicator) in the equivalent LSP layer, instead of an RDI, which is transmitted in the PW layer. 
     On the receiving part, PE 2 , alarm forwarding processing is performed on the basis of L 1 . The processing illustrated in  FIGS. 6A and 6B  is also performed at PE 2 . 
     As described above, the embodiments of the present invention provide a management system of labels and paths applied to a communication apparatus using PW (Pseudo Wire) technology on the basis of MPLS. This allows an LOC function from the lower layers (below MPLS) to be reported (escalated) to PW by providing a function having a correlation between MPLS layers and PW layers, and is characterized by its efficient failure notification. 
     Consequently, an alarm inhibition function may be achieved and high-efficiency failure notification may be allowed, and thus management efficiency may be increased.