Abstract:
A system for passive alarm propagation and suppression in a communication network is disclosed. The system includes a packet based network including one subset of network providing connectivity to other set(s) of network. The network includes a first edge node and a second edge node; a first customer node connecting to the first edge node and a second customer node connecting to the second edge node; and a replicated alarm suppression table (RAST) residing in the first provider edge node.

Description:
FIELD OF INVENTION  
       [0001]     The present invention generally relates to packet based networks, and more specifically, relates to passive alarm propagation and suppression in packet based networks.  
       BACKGROUND OF THE INVENTION  
       [0002]     An Alarm Indication Signal (AIS) is a signal transmitted in lieu of a normal signal to maintain transmission continuity, and indicate to a receiving terminal that there is a fault located somewhere along the transmission path, which could be source node, intermediate nodes, or any links along the path. An AIS has been used by Transport networks to indicate upstream alarms. When downstream nodes receive alarms from their upstream nodes, they can suppress secondary alarms which are caused by the upstream faults.  
         [0003]     AIS alarm propagation has been used in conventional transport networks for a long time. However, such approaches are not effective in a packet based network for propagating faults, especially in a connection-less oriented packet network, where each node can be connected to its peers via multiple connections. Such propagation used by circuit networks can flood a packet network if there are many upstream faults.  
         [0004]     IEEE802.1ag/D4.1 has proposed another form of AIS for provider edge nodes. This form multicasts an AIS signal to an entire administration domain, so that bridges can suppress alarms of losing its connectivity to their peers. However, there are issues with the proposed methods. IEEE802.1ag/D4.1 provides two possible ways to send AIS to affected nodes. A first method is to let a provider edge node send periodic AIS message to all the nodes in an administration domain. This method can introduce too many messages, flooding an administrative domain. The excessive messages can cause congestion and unnecessary traffic within the administration domain. A second method only sends one AIS message when a provider edge detects failure. Subsequently, an AIS “clear” message is sent when the provider node recovers from connectivity failure. In this case, even though the number of AIS messages in the administrative domain may be reduced, the AIS “clear” message may not be sent to newly added bridges when the provider node recovers from its connectivity failure, or nodes being created after the failure occur may not get a failure message.  
         [0005]     Therefore, there is a need for a system that effectively enables fault propagation and achieve alarm suppression, in a multipoint packet based network.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention discloses a versatile system, in a packet based network, that determines whether an AIS message is to be propagated or suppressed to a customer node.  
         [0007]     The present invention provides a Replicated Alarm Suppression Table (RAST), dynamically set up in a provider edge node of a packet based provider network. When a customer node detects a connectivity failure with its peers, the customer node may check the RAST to determine whether the failure is caused by the provider domain supporting the customer node to, in turn, determine whether an alarm report is to be suppressed or not, and to determine the actual cause of the connectivity failure.  
         [0008]     In one embodiment, a customer node notifies a provider edge node, and the provider edge node then checks the RAST to determine cause of the failure. If the failure is caused by a failed connectivity between its supporting provider edge nodes, then the customer node may suppress the customer node&#39;s secondary alarm report. If no failure is detected on the connectivity between its supporting provider edge nodes, then the customer node may report the connectivity fault to its peers indicating the connectivity fault is caused by its own administration domain.  
         [0009]     In another embodiment, a primary connection failure of a provider edge node may not necessarily affect a connectivity of a customer node to its peers. When multiple paths across a provider domain exist, a secondary connection may be found to overcome the primary connection failure. Thus there is no need for the provider edge to propagate its failure to its customer node.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:  
         [0011]      FIG. 1  depicts one embodiment of a replicated alarm suppression table corresponding to a packet based network, according to the present invention;  
         [0012]      FIG. 2  depicts one embodiment of a simplified packet based network that provides communication between edge nodes and customer nodes according to the present invention;  
         [0013]      FIG. 3  is flow diagram illustrating passive alarm propagation and suppression for a packet based network according to the present invention; and  
         [0014]      FIG. 4  depicts one embodiment of a simplified packet based network in which an alternative path across a provider domain for connections between customer sites according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The present invention is hereafter in relation to certain exemplary embodiments below. It is understood, however, that the embodiments below are not necessarily limitations to the present disclosure. Although only a few exemplary embodiments of this invention have been described in detail, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments. It is understood that modifications, changes and substitutions are intended in the foregoing disclosure, and in some instances some features of the invention will be employed without a corresponding use of other features.  
         [0016]     Referring to  FIG. 1 , a replicated alarm suppression table ( 130 ) corresponding to a packet based network ( 100 ) according to the present invention is depicted. Network ( 100 ) includes a provider network ( 110 ) and a plurality of customer sites, including Site ( 102 ), Site ( 104 ), Site ( 106 ), Site ( 108 ), Site ( 122 ), Site ( 124 ), Site ( 126 ), and Site ( 128 ). Provider network ( 110 ) includes a plurality of provider edge nodes, including Edge Node U, Edge Node V, Edge Node W, Edge Node X, Edge Node Y, and Edge Node Z, and a plurality of provider network internal nodes which are not shown in  FIG. 1 . Each customer site may include at least one customer node.  
         [0017]     A person of the ordinary skill in the art will understand, some terms in the present invention may be interpreted as follows: a domain which provides connectivity to other domains may be called a “Provider Network”; a “Provider Network” may or may not be a network by service providers; a simple provider network may be a physical link connecting two domains, or set of nodes; an edge node of a “Provider Network” may be called a provider edge node; a domain which gets part of its connectivity from another domain may be called a “Customer Network”; and nodes within the “customer Network” may be called customer nodes.  
         [0018]     As illustrated in  FIG. 1 , Site ( 102 ) includes Customer Node a, Site ( 104 ) includes Customer Node b, Site ( 106 ) includes Customer Node c, Site ( 108 ) includes Customer Node d, Site ( 122 ) includes Customer Node e, Site ( 124 ) includes Customer Node f, Site ( 126 ) includes Customer Node g, and Site ( 128 ) includes Customer Node h and Customer Node i. Provider network ( 110 ) connects to each customer site through connections between each provider edge node and each customer node.  FIG. 1  illustrates primary connections between each provider edge node and each customer node. Edge Node U connects to Customer Node a and Customer Node b, Edge Node V connects to Customer Node c, Edge Node W connects to Customer Node d, Edge Node X connects to Customer Node e, and Edge Node Z connects to Customer Node f, Customer Node g, Customer Node h, and Customer i.  
         [0019]     In order for a provider edge node to determine whether a provider connectivity fault is a cause of a particular customer connectivity failure, the provider edge node may need to have a table to keep track of supporting customers from other edge nodes.  FIG. 1  depicts a replicated alarm suppression table (RAST) ( 130 ). Table ( 130 ) corresponds to connectivity between each provider edge node and each customer node in Network ( 100 ). In Table ( 130 ), a column correlates Maintenance Domain Intermediate Point (MIP) according to IEEE802.1ag, including Edge Node U, Edge Node V, Edge Node W, Edge Node X, Edge Node Y, and Edge Node Z. Another column correlates Maintenance Association End Point (MEP) according to IEEE802.1ag, including Customer Node a, Customer Node b, Customer Node c, Customer Node d, Customer Node e, Customer Node f, Customer Node g, Customer Node h, and Customer Node i. As Table ( 130 ) illustrates, each MIP corresponds to each MEP according to primary connectivity between each provider edge node and each customer node in Network ( 100 ), that is, Edge Node U at MIP associates with Customer Node a and Customer Node b at MEP, Edge Node V at MIP associates with Customer Node c, Edge Node W at MIP associates with Customer Node d, Edge Node X at MIP associates with Customer Node e, and Edge Node Z at MIP associates with Customer Node f, Customer Node g, Customer Node h, and Customer Node i at MEP.  
         [0020]     In one embodiment, Table ( 130 ) may be established by each customer site registering to a provider edge node of nodes belonging to this customer site. Each edge node sends its own RAST to all other edge nodes in Network ( 100 ). Table ( 130 ) is dynamically set up correlating to each MIP/MEP, with a registration process by insertion or deletion of a connection between a provider edge node (e.g. Edge Node W) and a customer node (e.g. Customer Node d).  
         [0021]     As illustrated in  FIG. 1 , when connectivity between Edge Node W and Edge Node Z fails, using Table ( 130 ), Edge Node W may recognize that its connectivity loss to Edge Node Z is the cause of Customer Node d&#39;s connectivity loss to Node f/g/h/j. Furthermore, using Table ( 130 ), Customer Node d may obtain knowledge that Edge Node Z connects to Customer Node f, Customer Node g, Customer Node h, and Customer Node i. Then Customer Node d may not report secondary connection failures to the NMS. These secondary connection failures include connections between Customer Node d and Customer Node f, Customer Node d and Customer Node g, Customer Node d and Customer Node h, and Customer Node d and Customer Node i. This process suppresses an alarm report avoiding possible alarm signal flooding in Network ( 100 ).  
         [0022]     Referring to  FIG. 2 , a simplified packet based provider network ( 200 ) that provides communication between provider edge nodes and customer nodes is illustrated. Customer node ( 231 ) represents one of the customer nodes on one side of Provider Network ( 200 ). Customer node ( 233 ) and Customer node ( 235 ) represent two customer nodes on the opposite side of Provider Network ( 200 ). Provide Edge Note ( 202 ) is connected to Customer node ( 231 ), and Provider Edge Node ( 204 ) is connected to Customer node ( 233 ) and Customer node ( 235 ). In addition, Provider Edge Node ( 202 ) is connected to Provider Edge Node ( 204 ). When connectivity between Provider Edge Node ( 202 ) and Provider Edge Node ( 204 ) fails, Customer node ( 231 ) may lose connectivity to both Customer node ( 233 ) and Customer node ( 235 ).  
         [0023]     Referring now to  FIG. 3 , a flow diagram illustrates a process of passive alarm propagation and suppression for a packet based network ( 300 ) according to the present invention. In connection with  FIG. 2 , the process starts when Customer node ( 231 ) loses connectivity with Customer node ( 235 ) at ( 302 ). In step ( 304 ), Customer node ( 231 ) inquires Provider Edge Node ( 202 ). When Network ( 300 ) receives such inquiry, a RAST in Provider Edge Node ( 202 ) is checked ( 306 ). A determination ( 310 ) is made as to whether a failed connectivity is caused by the connectivity loss between Provider Edge Node ( 202 ) and Provider Edge Node ( 204 ). If Determination ( 310 ) result indicates no failure occurred between Provider Edge Node ( 202 ) and Provider Edge Node ( 204 ), then Provider Edge Node ( 202 ) indicates provider network free of failure to Customer Node ( 233 ), which is associated with Provider Edge Node ( 202 ). If Determination ( 310 ) result indicates a connectivity failure occurred between Provider Edge Node ( 202 ) and Provider Edge Node ( 204 ) is the cause of connectivity loss between Customer Node ( 231 ) and ( 233 )/( 235 ), then Provider Edge Node ( 202 ) notifies Customer Node ( 231 ) at Step ( 322 ), and Customer Node ( 231 ) may suppress an secondary alarm report ( 324 ) on losing connectivity to, in this case, Customer Node ( 233 ).  
         [0024]     Referring to  FIG. 4 , a simplified packet based network ( 400 ) in which an alternative path across a provider network ( 410 ) for connections between customer sites is illustrated. In  FIG. 4 , Customer Node ( 431 ) represents one of the customer nodes on one side of Network ( 410 ). Customer Node ( 433 ), Customer Node ( 435 ), and Customer Node ( 437 ), represent customer nodes on the opposite side of Network ( 410 ). Customer Node ( 437 ) connects to both Customer Node ( 433 ) and Customer Node ( 435 ).  
         [0025]     Also illustrated in  FIG. 4 , Provider Edge Node ( 402 ), Provider Edge Node ( 404 ), Provider Edge Node ( 406 ), and Provider Edge Node ( 408 ) represent four provider edge nodes within Network ( 410 ), wherein Provider Edge Node ( 402 ) is connected to Provider Edge Node ( 404 ), and Provider Edge Node ( 406 ) is connected to Provider Edge Node ( 408 ). In addition, Customer Node ( 431 ) is connected to both Provider Edge Node ( 402 ) and Provider Edge Node ( 406 ). Customer Node ( 433 ) is connected to Provider Edge Node ( 408 ), and Customer Node ( 435 ) is connected to Provider Edge Node ( 404 ).  
         [0026]     When connectivity fails between Customer Node ( 431 ) and Customer Node ( 435 ) due to failed connectivity between Provider Edge Node ( 402 ) and Provider Edge Node ( 404 ), Customer Node ( 431 ) may lose a primary connection route to Customer Node ( 435 ) via connection between Provider Edge Node ( 402 ) and Provider Edge Node ( 404 ). However, Customer Node ( 431 ) may connect to Customer Node ( 435 ) via an alternative route.  
         [0027]     As illustrated in  FIG. 4 , the alternative route of connection between Customer Node ( 431 ) and Customer Node ( 431 ) may be through a route from Customer Node ( 431 ) to Provider Edge Node ( 406 ), to Provider Edge Node ( 408 ), to Customer Node ( 433 ), to Customer Node ( 437 ), and to Customer Node ( 435 ). In this case, Customer Node ( 431 ) may not need to report an alarm to NMS associated with Customer Node ( 431 ), thereby reducing alarm report overhead in Network ( 400 ).  
         [0028]     The previous description of the disclosed embodiments is provided to enable those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art and generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.