Abstract:
According to an additional embodiment, a method may include communicatively coupling a first network element to a second network element via a first path of a first point-to-point network. The method may also include communicatively coupling the first network element to a third network element via a second path of the first-point-to-point network. The method may additionally include communicatively coupling the second network element to a fourth network element via a first path of a second point-to-point network. The method may further include communicatively coupling the third network element to the fourth network element via a second path of the second point-to-point network. The method may also include configuring the first path and the second path of the first point-to-point network as paths of a first linear protected switching connection and the first path and the second path of the second point-to-point network as paths of a second linear protected switching connection such that traffic associated with a service and communicated between the first network element and the fourth network element via the first path of the first point-to-point network and the first path of the second point-to-point network may be switched over to the second path of the first point-to-point network and the second path of the second point-to-point network in response to an event.

Description:
RELATED APPLICATION 
       [0001]    This application is related to copending Patent Application entitled “Method and System for Implementing Network Element-Level Redundancy,” application Ser. No. ______ (064731.0803), filed on the same date as the present application. 
         [0002]    This application is also related to copending Patent Application entitled “Method and System for Implementing Network Element-Level Redundancy,” application Ser. No. ______ (064731.0804), filed on the same date as the present application. 
         [0003]    This application is also related to copending Patent Application entitled “Method and System for Implementing Network Element-Level Redundancy,” application Ser. No. (064731.0806), filed on the same date as the present application. 
     
    
     TECHNICAL FIELD OF THE DISCLOSURE 
       [0004]    The present disclosure relates generally to networked communications and, more particularly, to a method and system for implementing network element-level redundancy. 
       BACKGROUND 
       [0005]    In telecommunications, information is often sent, received, and processed according to the Open System Interconnection Reference Model (OSI Reference Model or OSI Model). In its most basic form, the OSI Model divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers, which are also known respectively as Layer 7 (L7), Layer 6 (L6), Layer 5 (L5), Layer 4 (L4), Layer 3 (L3), Layer 2 (L 2),  and Layer 1 (L1). It is therefore often referred to as the OSI Seven Layer Model. 
         [0006]    Layer 2 is the layer which typically transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. Layer 2 provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in Layer 1. Examples of Layer 2 protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. Layer 2 data transfer may be handled by devices known as switches. 
         [0007]    To ensure high reliability and availability in communications networks, protection switching is often used. When implemented, protection switching typically provides a primary or “working” path for a network and a redundant or “protection” path for the network. Accordingly, each path may be monitored, and if a failure is detected on the working path, network traffic may be switched to the protection path. An example of protection switching may be Ethernet Linear Protection Switching (ELPS) as defined by the ITU G.8031 standard. 
         [0008]    While protection switching may provide redundancy for link or path failures, it does not provide redundancy in the event of a failure of a network element (e.g., a switch) redundantly-interfaced to a point-to-point network. Accordingly, this disclosure provides for such network-element level redundancy. 
       SUMMARY 
       [0009]    In accordance with the present disclosure, disadvantages and problems associated with creating redundancy in L2 networks may be reduced or eliminated. 
         [0010]    According to one embodiment, a method may include communicatively coupling a first network element to a second network element via a first path of a point-to-point connection. The method may also include communicatively coupling the first network element to a third network element via a second path of the point-to-point network. The method may further include configuring the first path and the second path as paths of a linear protected switching connection (LPSC) such that traffic associated with a service and communicated via one of the first path and the second path may be switched over to the other of the first path and the second path in response to an event. 
         [0011]    According to another embodiment, a method may include communicatively coupling a first network element to a second network element via a first link of a multi-chassis link aggregation group. The method may also include communicatively coupling the first network element to a third network element via a second link of the multi-chassis link aggregation group. The method may additionally include communicatively coupling the second network element to a fourth network element via a first path of a point-to-point network. The method may further include communicatively coupling the third network element to the fourth network element via a second path of the point-to-point network. The method may also include configuring the first path and the second path as paths of a linear protected switching connection such that traffic associated with a service and communicated between the first network element and the fourth network element via the first link and the first path may be switched over to the second link and the second path in response to an event. 
         [0012]    According to an additional embodiment, a method may include communicatively coupling a first network element to a second network element via a first path of a first point-to-point network. The method may also include communicatively coupling the first network element to a third network element via a second path of the first-point-to-point network. The method may additionally include communicatively coupling the second network element to a fourth network element via a first path of a second point-to-point network. The method may further include communicatively coupling the third network element to the fourth network element via a second path of the second point-to-point network. The method may also include configuring the first path and the second path of the first point-to-point network as paths of a first linear protected switching connection and the first path and the second path of the second point-to-point network as paths of a second linear protected switching connection such that traffic associated with a service and communicated between the first network element and the fourth network element via the first path of the first point-to-point network and the first path of the second point-to-point network may be switched over to the second path of the first point-to-point network and the second path of the second point-to-point network in response to an event. 
         [0013]    According to a further embodiment, a method may include communicatively coupling a first network element to a second network element via a first path of a point-to-point network. The method may also include communicatively coupling the first network element to a third network element via a second path of the point-to-point network. The method may additionally include communicatively coupling the second network element and the third network element to a multipoint-to-multipoint network. The method may further include configuring the first path and the second path as paths of a linear protected switching connection such that traffic associated with a service and communicated between the first network element and the multipoint-to-multipoint network via one of the first path and the second path may be switched over to the other of the first path and the second path in response to an event. 
         [0014]    Certain embodiments of the disclosure may provide one or more technical advantages. A technical advantage may be that a network may provide network element-level redundancy for point-to-point Ethernet virtual channels across a network. 
         [0015]    Certain embodiments of the disclosure may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a more complete understanding of the present disclosure and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0017]      FIG. 1  illustrates a block diagram of an example network including protection switching among multiple network elements, in accordance with certain embodiments of the present disclosure; 
           [0018]      FIG. 2  illustrates a block diagram an example network element, in accordance with certain embodiments of the present disclosure; 
           [0019]      FIG. 3  illustrates a block diagram of an example network including protection switching among multiple network elements, wherein such multiple network elements are interfaced to a single link aggregation group, in accordance with certain embodiments of the present disclosure; 
           [0020]      FIG. 4  illustrates a block diagram of an example network including protection switching among multiple network elements interfaced between point-to-point network domains, in accordance with certain embodiments of the present disclosure; 
           [0021]      FIG. 5  illustrates a block diagram of another example network including protection switching among multiple network elements interfaced between point-to-point network domains, in accordance with certain embodiments of the present disclosure; and 
           [0022]      FIG. 6  illustrates a block diagram of an example network including protection switching among multiple network elements interfaced between a point-to-point network and a multipoint-to-multipoint network, in accordance with certain embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  illustrates a block diagram of an example network  100   a  including protection switching among multiple network elements  102  (e.g., network elements  102   b  and  102   c ), in accordance with certain embodiments of the present disclosure. As shown in  FIG. 1 , network  100   a  may include network element  102   a  communicatively coupled to network element  102   b  and network element  102   c  via point-to-point network  122 . 
         [0024]    Each network element  102  (e.g., network elements  102   a - 102   c ) in network  100   a  and network elements  102  described in  FIG. 3-6  (e.g., network elements  102   d - 102   s  of networks  100   b - 110   e ) may comprise any suitable system operable to transmit and receive traffic. As used herein, “traffic” means information transmitted, stored, or sorted in a network  100  (e.g., networks  100   a - 100   e ). Such traffic may comprise optical or electrical signals configured to encode audio, video, textual, and/or any other suitable data. The data may also be real-time or non-real-time. Traffic may be communicated via any suitable communications protocol, including, without limitation, the Open Systems Interconnection (OSI) standard and Internet Protocol (IP). Additionally, the traffic communicated in networks  100  may be structured in any appropriate manner including, but not limited to, being structured in frames, packets, or an unstructured bit stream. In the illustrated embodiment, each network element  102  may be operable to transmit traffic to one or more other network elements  102  and receive traffic from the one or more other network elements  102 . Network elements  102  will be discussed in more detail below with respect to  FIG. 2 . 
         [0025]    Point-to-point network  122  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   a  and network element  102   b,  and between network element  102   a  and network element  102   c.    
         [0026]    Network element  102   a  may communicate with network elements  102   b  and  102   c  using linear protected switching. Accordingly, network element  102   a  may be communicatively coupled to network elements  102   b  and  102   c  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118  and a protection path  120 . Network element  102   a  may be communicatively coupled to network element  102   b  via working path  118 , and may be communicatively coupled to network element  102   c  via protection path  120 . In certain embodiments, with respect to network element  102   a,  the linearly protected switching connection may be configured in accordance with the ITU G.8031 standard. In these and other embodiments, with respect to network elements  102   b  and  102   c,  the linear protected switching connection may be configured in connection with a modified multi-chassis version of the ITU G.8031 standard. In addition, network element  102   a  may be communicatively coupled to other network entities (e.g., other network elements) via link  126   a,  network element  102   b  may be communicatively coupled to other network entities via link  126   b,  and network element  102   c  may be communicatively coupled to other network entities via link  126   c.    
         [0027]    Network element  102   a  may be configured to perform linear protected switching between working path  118  and protection path  120 . For example, network element  102   a  may be configured to perform protection switching between paths  118  and  120  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In certain embodiments, network element  102   a  may be multi-homed such that network elements  102   b  and  102   c  appear as a single network element to network element  102   a.    
         [0028]    In addition, network elements  102   b  and  102   c  may be configured to implement protection switching between working path  118  and protection path  120 . For example, network elements  102   b  and  102   c  may be configured to perform protection switching between paths  118  and  120  in accordance with the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   b  and  102   c  may be communicatively coupled via a synchronization connection  124 . Via synchronization connection  124 , network elements  102   b  and  102   c  may communicate to each other such state information and switchover information. In certain embodiments, such communication via synchronization connection  124  may be in accordance with Inter-Control Center Communications Protocol (ICCP) or similar protocol. Synchronization connection  124  may include a direct link, a point-to-point connection over point-to-point network  122 , a dedicated management network, or any other suitable type of connection. In these and other embodiments, synchronization connection  124  may include redundancy (e.g., multiple physical links between network elements  102   b  and  102   c ) to provide high reliability and availability of communication between network elements  102   b  and  102   c.    
         [0029]    In operation, paths  118  and  120  may provide connectivity for services between network element  102   a  and network elements  102   b  and  102   c.  For a particular service, one of paths  118 ,  120  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   a,    102   b,  and  102   c  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118  to protection path  120 ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0030]    In addition, during operation paths  118  and  120  may be configured in accordance with any suitable redundancy scheme. For example, a 1+1 protection scheme may be used in which traffic is replicated among paths  118  and  120  and an end point network element may determine which path to select. As another example, a 1:1 scheme may be used in which all traffic is communicated over a single path (e.g., working path  118 ) and is protection switched to the other (e.g., protection path  120 ) in response to an event. 
         [0031]    Protection switching from one path to another may occur in response to any suitable event. For example, failure of a path  118 ,  120  may cause a switchover to the other path. As another example, failure of a link  126   b  or  126   c  or other event upstream of network elements  102   b  and/or  102   c  may cause a switchover (e.g., failure of link  126   b  may cause a switchover from working path  118  to protection path  120 ). As an additional example, a switchover may occur automatically after a failure condition has been remedied (e.g., a wait to restore timer initiated after a failure on working path  118  may trigger a switchover from protection path  120  to working path  118 ). As a further example, a switchover may occur in response to a human-initiated action (e.g., a command to switchover issued by a network operator/administrator). All such events may be monitored by network elements  102   b  and  102   c  and all such monitoring may be synchronized between network elements  102   b  and  102   c  via synchronization connection  124 . In addition, switchovers may be initiated by network element  102   b  and/or network element  102   c  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   b  and  102   c  via synchronization connection  124 . 
         [0032]    A technical advantage of network  100   a  is that it provides for network element-level redundancy for point-to-point Ethernet virtual channels across a network. In addition, an access network element (e.g., network element  102   a ) need not be directly connected to network elements  102   b  and  102   c,  as would be the case with multiple chassis link aggregation. 
         [0033]      FIG. 2  illustrates a block diagram an example network element  102 , in accordance with certain embodiments of the present disclosure. Network element  102  of  FIG. 2  may be exemplary of the various network elements discussed elsewhere in this disclosure (e.g., network elements  102   a - 102   p ). Each network element  102  may be coupled to one or more other network elements  102  via one or more transmission media  12 . Each network element  102  may generally be configured to receive data from and/or transmit data to one or more other network elements  102 . In certain embodiments, network element  102  may comprise a switch configured to route data received by network element  102  to another device (e.g., another network element  102 ) coupled to network element  102 . 
         [0034]    As depicted in  FIG. 2 , each network element  102  may include a master control unit  103 , a switching element  104 , and one or more network interfaces  106  communicatively coupled to each of master control unit  103  and switching element  104 . 
         [0035]    Master control unit  103  may include any suitable system, apparatus, or device configured to manage network element  102 , including management of routing of data between ports  110 . As shown in  FIG. 2 , master control unit  103  may maintain a routing table, wherein such routing table may include any table, database, file, or other data structure configured to maintain information relating a particular ingress port  110  and/or link aggregation group (LAG)  112  to a corresponding egress port  110  and/or LAG  112 . 
         [0036]    Switching element  104  may be communicatively coupled to master control unit  103  and may include any suitable system, apparatus, or device configured to receive traffic via a port  110  and route such traffic to a particular network interface  106  and/or port  110  based on analyzing the contents of the data and/or based on a characteristic of a signal carrying the data (e.g., a wavelength and/or modulation of the signal). For example, in certain embodiments, a switching element  104  may include a switch fabric (SWF). 
         [0037]    Each network interface  106  may include any suitable system, apparatus, or device configured to serve as an interface between a network element  102  and a transmission medium  12 . Each network interface  106  may enable its associated network element  102  to communicate to other network elements  102  using any suitable transmission protocol and/or standard. Network interface  106  and its various components may be implemented using hardware, software, or any combination thereof. For example, in certain embodiments, one or more network interfaces  106  may include a network interface card. In the same or alternative embodiments, one or more network interfaces  106  may include a line card. 
         [0038]    As depicted in  FIG. 2 , each of network interfaces  106  may include one or more physical ports  110 . Each physical port  110  may include any system, device or apparatus configured to serve as a physical interface between a corresponding transmission medium  12  and network interface  106 . For example, a physical port may comprise an Ethernet port, an optical port, or any other suitable port. 
         [0039]    As shown in  FIG. 2 , two or more physical ports  110  of a particular network element  102 , their corresponding physical ports  110  of another network element  102 , and their corresponding transmission media  12  may be grouped into a link aggregation group (LAG)  112 . Although each LAG  112  in  FIG. 2  is depicted as including a particular number of member physical ports  110 , LAG  112  may include any suitable number of member physical ports  110 . LAG  112  may combine its member ports or member LAGs using link aggregation such that the member ports are represented as a single logical port to components of a network  100  (e.g., a network  100   a - 100   e ) external to LAG  112 . Although each LAG  112  in  FIG. 2  is depicted as including only ports  110  of a single network element  102 , a LAG  112  may in some embodiments include ports  110  of two or more network elements  102  (e.g., multi-chassis link aggregation). 
         [0040]      FIG. 3  illustrates a block diagram of an example network  100   b  including protection switching among multiple network elements (e.g., network elements  102   e  and  102   f ), wherein such multiple network elements are interfaced to a single multi-chassis link aggregation group (e.g., LAG  112 ), in accordance with certain embodiments of the present disclosure. As shown in  FIG. 3 , network  100   b  may include network element  102   d  communicatively coupled to network element  102   e  and network element  102   f  via a multi-chassis LAG  112 , and network element  102   g  communicatively coupled to network element  102   e  and network element  102   f  via point-to-point network  122 . 
         [0041]    As described above, each of network elements  102   d - 102   g  may comprise any suitable system operable to transmit and receive traffic. Point-to-point network  122  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   e  and network element  102   g,  and between network element  102   f  and network element  102   g.  Point-to-point network  122  depicted in  FIG. 3  may be similar to point-to-point network  122  depicted in  FIG. 1 . 
         [0042]    Network element  102   d  may be multi-homed via LAG  112  to network elements  102   e  and  102   f  such that network elements  102   e  and  102   f  appear as a single network element to network element  102   d.    
         [0043]    Network element  102   g  may communicate with network elements  102   e  and  102   f  using linear protected switching. Accordingly, network element  102   g  may be communicatively coupled to network elements  102   e  and  102   f  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118  and a protection path  120  and may be similar to the linearly protected switching connection described above with respect to  FIG. 1 . Network element  102   g  may be configured to perform linear protected switching between working path  118  and protection path  120 . For example, network element  102   g  may be configured to perform protection switching between paths  118  and  120  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0044]    In addition, network elements  102   e  and  102   f  may be configured to implement protection switching between working path  118  and protection path  120 . For example, network elements  102   e  and  102   f  may be configured to perform protection switching between paths  118  and  120  in accordance with a modified multi-chassis version of the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   e  and  102   f  may be communicatively coupled via a synchronization connection  124 . Via synchronization connection  124 , network elements  102   e  and  102   f  may communicate to each other such state information and switchover information. Synchronization connection  124  depicted in  FIG. 3  may be similar to synchronization connection  124  depicted in  FIG. 1 . 
         [0045]    In operation, paths  118  and  120  may provide connectivity for services between network element  102   g  and network elements  102   e  and  102   f  (and ultimately, connectivity for services between network elements  102   d  and  102   g ). For a particular service, one of paths  118 ,  120  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   e,    102   f,  and  102   g  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118  to protection path  120 ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0046]    Similarly, for a particular service, one of member links  128   a  and  128   b  of LAG  112  may be designated as active and the other as standby, such that traffic for such service is communicated over such active link. In the event of a failure or other event, one or more of network elements  102   d,    102   e,  and  102   f  may cause traffic associated from the service to be switched from the active link to the standby link (e.g., from link  128   a  to link  128   b ). 
         [0047]    In addition, during operation paths  118  and  120  and links  128  may be configured in accordance with any suitable redundancy scheme. For example, a 1+1 protection scheme may be used in which traffic is replicated among paths  118  and  120  and links  128  and an end point network element may determine which path/link combination to select. As another example, a 1:1 scheme may be used in which all traffic is communicated over a single path/link combination (e.g., working path  118  and link  128   a ) and is protection switched to the other (e.g., protection path  120  and link  128   b ) in response to an event. 
         [0048]    Protection switching from one path/link combination to another may occur in response to any suitable event. For example, failure of either of a path  118 ,  120  or a link  128  in a path/link combination may cause a switchover to the other path/link combination (e.g., a failure in either of path  118  or link  128   a  may cause switchover to the combination of path  120  and link  128   b ). As an additional example, a switchover may occur automatically after a failure condition has been remedied (e.g., a wait to restore timer initiated after a failure on working path  118  may trigger a switchover from protection path  120  to working path  118 , and a switchover from link  128   b  to link  128   a ). As a further example, a switchover may occur in response to a human-initiated action (e.g., a command to switchover issued by a network operator/administrator). All such events may be monitored by network elements  102   e  and  102   f  and all such monitoring may be synchronized between network elements  102   e  and  102   f  via synchronization connection  124 . In addition, switchovers may be initiated by network element  102   e  and/or network element  102   f  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   e  and  102   f  via synchronization connection  124 . 
         [0049]    A technical advantage of network  100   b  is that it provides for network element-level redundancy for point-to-point Ethernet virtual channels across a network that is interoperable with multi-chassis link aggregation. 
         [0050]      FIG. 4  illustrates a block diagram of an example network  100   c  including protection switching among multiple network elements  102   i  and  102   j  interfaced between point-to-point network domains  122   a  and  122   b,  in accordance with certain embodiments of the present disclosure. As shown in  FIG. 4 , network  100   c  may include network element  102   h  communicatively coupled to network element  102   i  and network element  102   j  via point-to-point network  122   a,  and network element  102   k  communicatively coupled to network element  102   i  and network element  102   j  via point-to-point network  122   b.    
         [0051]    As described above, each of network elements  102   h - 102   k  may comprise any suitable system operable to transmit and receive traffic. Point-to-point network  122   a  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   h  and network element  102   i,  and between network element  102   h  and network element  102   j.  Point-to-point network  122   b  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   k  and network element  102   i,  and between network element  102   k  and network element  102   j.  Point-to-point networks  122   a  and  122   b  depicted in  FIG. 4  may be similar to point-to-point networks  122  depicted in  FIGS. 1 and 3 . 
         [0052]    Network element  102   h  may be multi-homed such that network elements  102   i  and  102   j  appear as a single network element to network element  102   h.    
         [0053]    Network element  102   h  may communicate with network elements  102   i  and  102   j  using linear protected switching. Accordingly, network element  102   h  may be communicatively coupled to network elements  102   i  and  102   j  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118   a  and a protection path  120   a  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 and 3 . Network element  102   h  may be configured to perform linear protected switching between working path  118   a  and protection path  120   a.  For example, network element  102   h  may be configured to perform protection switching between paths  118   a  and  120   a  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0054]    Furthermore, network element  102   k  may communicate with network elements  102   i  and  102   j  using linear protected switching. Accordingly, network element  102   k  may be communicatively coupled to network elements  102   i  and  102   j  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118   b  and a protection path  120   b  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 and 3 . Network element  102   k  may be configured to perform linear protected switching between working path  118   b  and protection path  120   b.  For example, network element  102   k  may be configured to perform protection switching between paths  118   b  and  120   b  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0055]    In addition, network elements  102   i  and  102   j  may be configured to implement protection switching between working path  118   a  and protection path  120   a  and protection switching between working path  118   b  and protection path  120   b.  For example, network elements  102   i  and  102   j  may be configured to perform protection switching between paths  118   a  and  120   a  and between paths  118   b  and  120   b  in accordance with a modified multi-chassis version of the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   i  and  102   j  may be communicatively coupled via a synchronization connection  124 . Via synchronization connection  124 , network elements  102   i  and  102   j  may communicate to each other such state information and switchover information. Synchronization connection  124  depicted in  FIG. 4  may be similar to synchronization connections  124  depicted in  FIGS. 1 and 3 . 
         [0056]    In operation, paths  118   a  and  120   a  may provide connectivity for services between network element  102   h  and network elements  102   i  and  102   j  (and ultimately, connectivity for services between network elements  102   h  and  102   k ). For a particular service, one of paths  118   a,    120   a  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   h,    102   i,  and  102   j  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118   a  to protection path  120   a ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0057]    Similarly, paths  118   b  and  120   b  may provide connectivity for services between network element  102   k  and network elements  102   i  and  102   j  (and ultimately, connectivity for services between network elements  102   h  and  102   k ). For a particular service, one of paths  118   b,    120   b  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   k,    102   i,  and  102   j  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118   b  to protection path  120   b ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0058]    In addition, during operation paths  118   a,    118   b,    120   a  and  120   b  may be configured in accordance with any suitable redundancy scheme. For example, a 1+1 protection scheme may be used in which traffic is replicated among paths  118  and  120   a,  and an end point network element may determine which paths to select. As another example, a 1:1 scheme may be used in which all traffic is communicated over a single pair of paths (e.g., working paths  118   a  and  118   b ) and is protection switched to the other pair of paths (e.g., protection paths  120   a  and  120   b ) in response to an event. 
         [0059]    Protection switching from one pair of paths to another may occur in response to any suitable event. For example, failure of any path  118   a,    118   b,    120   a,  or  120   b  may cause a switchover in both point-to-point networks  122   a  and  122   b  (e.g., a failure in either of path  118   a  or path  118   b  may cause switchover to path  120   a  and  120   b ). As an additional example, a switchover may occur automatically after a failure condition has been remedied (e.g., a wait to restore timer initiated after a failure on working path  118   a  or  118   b  may trigger a switchover from protection path  120   b  to working path  118   b,  and a switchover from protection path  120   a  to working path  118   a ). As a further example, a switchover may occur in response to a human-initiated action (e.g., a command to switchover issued by a network operator/administrator). All such events may be monitored by network elements  102   i  and  102   j  and all such monitoring may be synchronized between network elements  102   i  and  102   j  via synchronization connection  124 . In addition, switchovers may be initiated by network element  102   i  and/or network element  102   j  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   i  and  102   j  via synchronization connection  124 . 
         [0060]    A technical advantage of network  100   c  is that it provides a redundant solution to two L2 network domains that provide point-to-point L2 services. 
         [0061]      FIG. 5  illustrates a block diagram of another example network  100   d  including protection switching among multiple network elements (e.g., network elements  102   m  and  102   n ) interfaced between point-to-point network domains, in accordance with certain embodiments of the present disclosure. As shown in  FIG. 5 , network  100   d  may include network element  102   l  communicatively coupled to network element  102   m  and network element  102   n  via point-to-point network  122   c,  and network elements  102   o  and  102   p  communicatively coupled to network element  102   m  and network element  102   n  via point-to-point network  122   d.    
         [0062]    As described above, each of network elements  102   l - 102   p  may comprise any suitable system operable to transmit and receive traffic. Point-to-point network  122   c  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   l  and network element  102   m,  and between network element  102   l  and network element  102   n.  Point-to-point network  122   b  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   m  and network element  102   o,  between network element  102   m  and network element  102   p,  between network element  102   n  and network element  102   o,  and between network element  102   n  and network element  102   p.  Point-to-point network  122   c  and  122   d  depicted in  FIG. 5  may be similar to point-to-point networks  122  depicted in  FIGS. 1 and 3  and/or point-to-point networks  122   a  and/or  112   b  depicted in  FIG. 4 . 
         [0063]    Network element  102   l  may be multi-homed such that network elements  102   m  and  102   n  appear as a single network element to network element  102   l.  Network elements  102   m  and  102   n  may be multi-homed such that network elements  102   o  and  102   p  appear as a single network element to each of network elements  102   m  and  102   n.  Network elements  102   o  and  102   p  may be multi-homed such that network elements  102   m  and  102   n  appear as a single network element to each of network elements  102   o  and  102   p.    
         [0064]    Network element  102   l  may communicate with network elements  102   m  and  102   n  using linear protected switching. Accordingly, network element  102   l  may be communicatively coupled to network elements  102   m  and  102   n  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118   c  and a protection path  120   c  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 ,  3  and  4 . Network element  102   l  may be configured to perform linear protected switching between working path  118   c  and protection path  120   c.  For example, network element  102   l  may be configured to perform protection switching between paths  118   c  and  120   c  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0065]    Furthermore, network element  102   m  may communicate with network elements  102   o  and  102   p  using linear protected switching. Accordingly, network element  102   m  may be communicatively coupled to network elements  102   o  and  102   p  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118   d  and a protection path  120   d  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 ,  3  and  4 . Network element  102   m  may be configured to perform linear protected switching between working path  118   d  and protection path  120   d.  For example, network element  102   m  may be configured to perform protection switching between paths  118   d  and  120   d  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0066]    In addition, network element  102   n  may communicate with network elements  102   o  and  102   p  using linear protected switching. Accordingly, network element  102   n  may be communicatively coupled to network elements  102   o  and  102   p  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118   e  and a protection path  120   e  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 ,  3  and  4 . Network element  102   n  may be configured to perform linear protected switching between working path  118   e  and protection path  120   e.  For example, network element  102   n  may be configured to perform protection switching between paths  118   e  and  120   e  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0067]    In addition, network elements  102   m  and  102   n  may be configured to implement protection switching between working path  118   c  and protection path  120   c.  For example, network elements  102   m  and  102   n  may be configured to perform protection switching between paths  118   c  and  120   c  in accordance with a modified multi-chassis version of the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   m  and  102   n  may be communicatively coupled via a synchronization connection  124   a.  Via synchronization connection  124   a,  network elements  102   m  and  102   n  may communicate to each other such state information and switchover information. Synchronization connection  124   a  depicted in  FIG. 5  may be similar to synchronization connections  124  depicted in  FIGS. 1 ,  3  and  4 . 
         [0068]    Similarly, network elements  102   o  and  102   p  may be configured to implement protection switching between working path  118   d  and protection path  120   d  and protection switching between working path  118   e  and protection path  120   e.  For example, network elements  102   o  and  102   p  may be configured to perform protection switching between paths  118   d  and  120   d  and between paths  118   e  and  120   e  in accordance with a modified multi-chassis version of the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   o  and  102   p  may be communicatively coupled via a synchronization connection  124   b.  Via synchronization connection  124   b,  network elements  102   o  and  102   p  may communicate to each other such state information and switchover information. Synchronization connection  124   b  depicted in  FIG. 5  may be similar to synchronization connection  124   a  and/or synchronization connections  124  depicted in  FIGS. 1 ,  3  and  4 . 
         [0069]    In operation, paths  118   c  and  120   c  may provide connectivity for services between network element  102   l  and network elements  102   m  and  102   n  (and ultimately, connectivity for services between network elements  102   l  and  102   o  and between network elements  102   l  and  102   p ). For a particular service, one of paths  118   c,    120   c  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   l,    102   m,  and  102   n  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118   c  to protection path  120   c ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0070]    Similarly, paths  118   d  and  120   d  may provide connectivity for services between network element  102   m  and network elements  102   o  and  102   p  (and ultimately, connectivity for services between network elements  102   l  and  102   o  and between network elements  102   l  and  102   p ). For a particular service, one of paths  118   d,    120   d  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   m,    102   o,  and  102   p  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118   d  to protection path  120   d ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0071]    Moreover, paths  118   e  and  120   e  may provide connectivity for services between network element  102   n  and network elements  102   o  and  102   p  (and ultimately, connectivity for services between network elements  102   l  and  102   o  and between network elements  102   l  and  102   p ). For a particular service, one of paths  118   e,    120   e  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   n,    102   o,  and  102   p  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118   e  to protection path  120   e ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0072]    In addition, during operation, each set of paths  118   c  and  120   c,    118   d  and  120   d,  and  118   e  and  120   e,  may be configured in accordance with any suitable redundancy scheme. For example, a 1+1 protection scheme may be used in which traffic is replicated among paths making up a linearly protected switching connection, and an end point network element may determine which paths to select. As another example, a 1:1 scheme may be used in which all traffic is communicated over one path of a linearly protected switching connection and is protection switched to the other path of the linearly protected switching connection in response to an event. 
         [0073]    Protection switching from one path to another may occur in response to any suitable event. For example, failure of any path of in a linearly protected switching connection may cause a switchover to the other path of the linearly protected switching connection (e.g., a failure in path  118   c  may cause switchover to path  120   c,  a failure in path  118   d  may cause switchover to path  120   d,  and a failure in path  118   e  may cause switchover to path  120   e ). Advantageously, in network  100   d  a failure in one path may cause a switchover only in the linear protected switching connection including such path without leading to switchover of other linear protected switching connections, thus minimizing disruption. For example, a failure of path  118   d  causing a switchover to path  120   d  may have no effect on the protection switching status of paths  118   c  and  120   c.  In addition, a failure of path  118   c  causing a switchover to path  120   c  may cause traffic to be switched from the linear protected switching connection including paths  118   d  and  120   d  to the linear protected switching connection including paths  118   e  and  120   e,  but may have no effect on the protection switching statuses of the linear protected switching connection including paths  118   d,    120   d,    118   e,  and  120   e.    
         [0074]    As an additional example, a switchover may occur automatically after a failure condition has been remedied (e.g., a wait to restore timer initiated after a failure on working path  118   c  may trigger a switchover from protection path  120   c  to working path  118   c ). As a further example, a switchover may occur in response to a human-initiated action (e.g., a command to switchover issued by a network operator/administrator). 
         [0075]    All such events for the linear protected switching connection including paths  118   c  and  120   c  may be monitored by network elements  102   m  and  102   n  and all such monitoring may be synchronized between network elements  102   m  and  102   n  via synchronization connection  124   a.  In addition, switchovers for the linear protected switching connection including paths  118   c  and  120   c  may be initiated by network element  102   m  and/or network element  102   n  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   m  and  102   n  via synchronization connection  124   a.    
         [0076]    All such events for the linear protected switching connection including paths  118   d  and  120   d  and the linear protecting switching connection including paths  118   e  and  120   e  may be monitored by network elements  102   o  and  102   p  and all such monitoring may be synchronized between network elements  102   o  and  102   p  via synchronization connection  124   b.  In addition, switchovers for the linear protected switching connection including paths  118   d  and  120   d  and the linear protected switching connection including paths  118   e  and  120   e  may be initiated by network element  102   o  and/or network element  102   p  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   o  and  102   p  via synchronization connection  124   b.    
         [0077]    A technical advantage of network  100   d  is that it provides a redundant solution to two L2 network domains that provide point-to-point L2 services using multiple levels of redundancy. 
         [0078]      FIG. 6  illustrates a block diagram of an example network  110   e  including protection switching among multiple network elements (e.g., network elements  102   r  and  102   s ) interfaced between a point-to-point network  122  and a multipoint-to-multipoint network  130 , in accordance with certain embodiments of the present disclosure. As shown in  FIG. 6 , network  100   d  may include network element  102   q  communicatively coupled to network element  102   r  and network element  102   s  via point-to-point network  122 , with network elements  102   r  and  102   s  communicatively coupled to multipoint-to-multipoint network  130 . 
         [0079]    As described above, each of network elements  102   q - 102   s  may comprise any suitable system operable to transmit and receive traffic. Point-to-point network  122  may be any network of one or more network elements (e.g., routers and switches) suitable to provide one or more point-to-point paths between network element  102   q  and network element  102   r,  and between network element  102   q  and network element  102   s.  Point-to-point network  122  depicted in  FIG. 6  may be similar to point-to-point networks  122  depicted in  FIGS. 1 and 3  and point-to-point networks  122   a  and  122   b  depicted in  FIGS. 4 and 5 . 
         [0080]    Multipoint-to-multipoint network  130  may include a bridged network or similar network that uses flooding (e.g., broadcasting) and examination of source addresses in received packet headers to locate unknown devices in a network. Once a device has been located, its location may recorded in a table referenced by a unique address (e.g., Media Access Control (MAC) address) or the device so as to preclude the need for further broadcasting. 
         [0081]    Network element  102   q  may be multi-homed such that network elements  102   r  and  102   s  appear as a single network element to network element  102   q.    
         [0082]    Network element  102   q  may communicate with network elements  102   r  and  102   s  using linear protected switching. Accordingly, network element  102   q  may be communicatively coupled to network elements  102   r  and  102   s  through a linearly protected switching connection. The linearly protected switching connection may comprise a working path  118  and a protection path  120  and may be similar to the linearly protected switching connections described above with respect to  FIGS. 1 ,  3 ,  4 , and  5 . Network element  102   q  may be configured to perform linear protected switching between working path  118  and protection path  120 . For example, network element  102   q  may be configured to perform protection switching between paths  118  and  120  in accordance with the G.8031 standard and may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. 
         [0083]    In addition, network elements  102   r  and  102   s  may be configured to implement protection switching between working path  118  and protection path  120 . For example, network elements  102   r  and  102   s  may be configured to perform protection switching between paths  118  and  120  in accordance with a modified multi-chassis version of the G.8031 standard and each may thus maintain a G.8031 state machine for maintaining state information and switchover information for protection switching. In addition, network elements  102   r  and  102   s  may be communicatively coupled via a synchronization connection  124 . Via synchronization connection  124 , network elements  102   r  and  102   s  may communicate to each other such state information and switchover information. Synchronization connection  124  depicted in  FIG. 6  may be similar to synchronization connections  124  depicted in  FIGS. 1 ,  3  and  4  and synchronizations connections  124   a  and  124   b  depicted in  FIG. 5 . 
         [0084]    In operation, paths  118  and  120  may provide connectivity for services between network element  102   q  and network elements  102   r  and  102   s  (and ultimately, connectivity for services between network element  102   q  and multipoint-to-multipoint network  130 ). For a particular service, one of paths  118 ,  120  may be designated as active, such that traffic for such service is communicated over such active path. In the event of a failure or other event, one or more of network elements  102   q,    102   r,  and  102   s  may cause a protection switch of the service from the active path to the other path (e.g., from working path  118  to protection path  120 ). In certain embodiments, such protection switching may be implemented in accordance with the G.8031 standard. 
         [0085]    In addition, during operation paths  118  and  120  may be configured in accordance with any suitable redundancy scheme. For example, a 1+1 protection scheme may be used in which traffic is replicated among paths  118  and  120  and an end point network element may determine which path to select. As another example, a 1:1 scheme may be used in which all traffic is communicated over a single path (e.g., working path  118 ) and is protection switched to the other path (e.g., protection path  120 ) in response to an event. 
         [0086]    Protection switching from one path to another may occur in response to any suitable event. For example, failure of path  118  may cause a switchover in to path  120 . As an additional example, a switchover may occur automatically after a failure condition has been remedied (e.g., a wait to restore timer initiated after a failure on working path  118  may trigger a switchover from protection path  120  to working path  118 ). As a further example, a switchover may occur in response to a human-initiated action (e.g., a command to switchover issued by a network operator/administrator). All such events may be monitored by network elements  102   r  and  102   s  and all such monitoring may be synchronized between network elements  102   r  and  102   s  via synchronization connection  124 . In addition, switchovers may be initiated by network element  102   r  and/or network element  102   s  in response to such monitored events, and such initiation of such switchovers may also be synchronized between network elements  102   r  and  102   s  via synchronization connection  124 . 
         [0087]    To support multipoint-to-multipoint technologies (e.g., bridging) in multipoint-to-multipoint network  130 , network elements  102   r  and  102   s  may be configured to record unique addresses (e.g., MAC addresses) and locations of devices of multipoint-to-multipoint network  130 . In addition, the record of unique addresses and locations of devices may be synchronized between network elements  102   r  and  102   s  via synchronization connection  124 , so as to aid in re-convergence of multipoint-to-multipoint network  130  after switchover from one path  118 ,  120  to the other. 
         [0088]    A technical advantage of network  100   e  is that it provides a redundant solution to two L2 network domains (a point-to-point network and a multipoint-to-multipoint network) that provide L2 services. 
         [0089]    A component of a network  100  (e.g., a network  100   a - 100   e ) may include an interface, logic, memory, and/or other suitable element. An interface receives input, sends output, processes the input and/or output, and/or performs other suitable operation. An interface may comprise hardware and/or software. 
         [0090]    Logic performs the operations of the component, for example, executes instructions to generate output from input. Logic may include hardware, software, and/or other logic. Logic may be encoded in one or more tangible computer readable storage media and may perform operations when executed by a computer. Certain logic, such as a processor, may manage the operation of a component. Examples of a processor include one or more computers, one or more microprocessors, one or more applications, and/or other logic. 
         [0091]    A memory stores information. A memory may comprise one or more tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), and/or other computer-readable medium. 
         [0092]    Modifications, additions, or omissions may be made to networks  100  without departing from the scope of the invention. The components of networks  100  may be integrated or separated. Moreover, the operations of networks  100  may be performed by more, fewer, or other components. Additionally, operations of networks  100  may be performed using any suitable logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
         [0093]    Certain embodiments of the invention may provide one or more technical advantages. A technical advantage of one embodiment may be that alarm indication signals that typically originate from maintenance end points may be transmitted in the event that equipment upon which the maintenance end points have experienced a fault, thus reducing the occurrence of unnecessary alarms. 
         [0094]    Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure, as defined by the following claims.