Patent Publication Number: US-6662308-B1

Title: Dual-homing select architecture

Description:
FIELD OF THE INVENTION 
     The present invention relates to data telecommunication networks. More particularly, the present invention relates to a network survivability scheme for use in a data telecommunication network. 
     BACKGROUND OF THE INVENTION 
     Traditionally, data telecommunication networks have been designed to carry traffic with “best effort” characteristics. In a system using best efforts, in the event of a failure the system will attempt to reroute data signals, but will discard the data if the attempt at rerouting is not successful. The explosive growth of the Internet and the increasing importance of the information exchanged over it leads to the need for highly reliable data networks. To reliably manage larger quantities of information, superior survivability schemes for managing the flow of data need to be implemented. A survivability scheme provides a network with a procedure for rerouting data being conveyed over the network in the event of a failure in the network. 
     Routers are devices for managing the flow of data over a network. Currently, routers are responsible for communicating with other routers and choosing between multiple paths when sending data over the network to routers located in other parts of the network. In choosing between multiple paths, a router will select the most efficient path (based on some measurement, e.g., distance, cost, . . . ) between two locations (referred to hereafter as a network node, or simply node) and will automatically reroute data in the event of system failures. Generally, a data network consists of multiple nodes and a transport network. An individual node represents the router hardware and software for directing the data, and a transport network represents the physical paths available to transmit data between nodes. Presently, if a failure occurs in one node, an indication of the failure is communicated to other network nodes so that the routers in these nodes become aware that a failure has occurred and can reroute the affected data appropriately. 
     One method for providing network reliability is by implementing dual-homing architecture in the nodes and connecting the nodes over a shared protection transport network. An example of this arrangement is depicted in FIG.  1 . To facilitate discussion the edge routers  1 - 2  in node  1  will be referred to as source edge routers and the edge routers  3 - 4  in node  2  will be referred to as destination edge routers. Each edge router  1 - 4  can act as a source or destination edge router depending on the direction the data is flowing. In a dualhoming architecture system, the traffic from a source edge router  1  is directed or “homed” to two diverse core routers A and B so that the failure of a single core router can be tolerated. This scheme allows core router B to manage the data from edge router  1  if core router A fails and vice versa. If the path between edge router  1  and core router B is assigned as the primary path P and core router B fails, a secondary path S between edge router  1  and core router A could be used. 
     Likewise, a dual-homing architecture is implemented in node  2 . In node  2 , destination edge router  4  is homed to core routers C and D. If the path between edge router  4  and core router D is designated as the primary path P and the path between edge router  4  and core router C is designated as the secondary path S, a failure in core router D would have to be detected by edge router  4  so that edge router  4  would use the secondary path data. 
     Given the dual-homing approach between edge and core routers, the role of the transport network can be to either provide two diverse optical-pipes (primary and secondary) between each pair of core routers or enable sharing of protection capacity in order to recover from any transport network failure (e.g. link failure). FIG. 2 illustrates the network architecture where the transport network is just providing diverse optical pipes. (Note that unshared protection is provided between the pair of source-destination edge routers, implying that the protection-switching function is only required at the edge routers). This architecture can be realized by providing either (1+1) or (1:1) protection of edge-to-edge primary paths. In (1+1) architecture, the traffic is simultaneously fed into both primary and secondary paths. This enables the destination edge router to identify a failure by simply monitoring primary as well as secondary paths. In (1:1) architecture, under the no failure condition, the traffic is only fed into the primary paths, and when a failure occurs the traffic is switched to the secondary path for all the affected primary paths. This enables the system to use the protection capacity (secondary paths) for carrying preemptable traffic under normal conditions, but at the cost of complex signaling mechanisms that will considerably increase the restoration time. A third option is to split the traffic and use two diverse paths in a load sharing mode. Here, there is really no concept of primary and secondary paths. Each path becomes a back-up for the other. Each path is provisioned with enough capacity to handle traffic for both. Like (1:1) architecture, this approach also requires signaling to move the traffic from one path to the other. 
     Since (1+1) and (1:1) architectures use unshared protection, the amount of protection capacity must be large enough to carry the total network traffic (along secondary paths that are disjoint to the primary paths). If the total network traffic is T, then, from some real network design exercises, we know that additional capacity required for unshared protection is about  2 T. This required protection capacity can be reduced if the transport network is able to provide shared protection for any failure in the transport network domain. FIG. 3 illustrates such an architecture. In this FIG., p( 1 ), p( 2 ), and p( 3 ) (depicted by solid lines) represent optical pipes carrying primary traffic between nodes consisting of core routers (A and B) and (C and D), (E and F) and (C and D), and (G and H) and (C and D). The optical pipes reserved for carrying protection traffic (in case of a failure) are depicted by dotted lines. Note that the optical pipe p( 4 ) can be shared for any failure affecting optical pipes p( 1 ), p( 2 ), and p( 3 ), thus requiring less capacity than the unshared protection case. It is well known in the art that for some real networks that, compared to unshared protection, shared protection can save protection capacity on the order of 20% to 40%. Given the significant savings in protection capacity, high cost of long-haul optics, and availability of shared protection capability in today&#39;s transport networks, using shared protection in the transport network is an attractive option. However, it is still necessary to consider the recovery from a router failure in a node when shared protection is used in the transport network. 
     Like traditional multi-layer survivability schemes, transport network failures can be recovered by the shared protection transport network, and router failures can be recovered by using Internet Protocol—Multi Protocol Level Switching (IP-mpLS). However such nested multi-layer survivability schemes have major drawbacks. For example, they require that transport networks be provisioned for both the primary and protection paths of the nodes. This means that in addition to the transport network failure protection (provided by the transport network), the architecture is providing (1:1) protection for failures in the nodes. Depending on the availability of the network and type of services, the nodes may be required to protect only a fraction of the traffic, which in an extreme case is 100%. Such an architecture simplifies operation and management of the network by recovering node and transport network failures locally but results in substantially more capacity costs in the transport layer. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a network architecture for combining a dual-homing approach in the nodes with a shared protection transport network. The network architecture removes the need for signaling between nodes over the transport network in the event of a router failure in one of the nodes. The network architecture incorporates select functions into the nodes for managing the data flow between individual edge routers and their connection through core routers to the transport network. 
     The select function determines whether failures have occurred in core routers within the node containing the select function and provides switching so that a single accurate data path is sent to the transport network. The select function eliminates the need for sending multiple data paths (e.g., a primary data path and a secondary data path to provide backup for the primary data path) and signaling (e.g., to indicate which path should be used) from the node over the transport network to other nodes. The select function allows the individual nodes to recover independently without signaling other nodes over the transport network, thereby eliminating the need for complex signaling mechanisms. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a prior art network architecture. 
     FIG. 2 is a block diagram of a prior art network architecture depicting an unshared protection scheme in the transport layer. 
     FIG. 3 is a block diagram of a prior art network architecture depicting a shared protection scheme in the transport layer. 
     FIG. 4 is a block diagram of a network architecture in accordance with the present invention. 
     FIG. 5 is a block diagram of the selector for outgoing data in FIG. 4 in accordance with the present invention. 
     FIG. 6 is a block diagram of the selector for incoming data in FIG. 4 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4 discloses a network architecture  40  in accordance with the present invention. 
     The system comprises a first node  42 , a transport region  44 , and a second node  46 . Each of the nodes  42  and  46 , and the transport region  44  are capable of independently recovering from a network failure without requiring complex signaling between the nodes  42  and  46  over the transport region  44 . The present invention removes the need for error signaling between individual nodes  42  and  46  over the transport region  44  in the event of a failure in one of the nodes  42  and  46 , thus eliminating complex signaling mechanisms. First node  42  and second node  46  form a nodal system. A nodal system comprises more than one node with each node couplable to every other node within the system. In accordance with the present invention, failures within an individual node are detected and recovered within that node, and are not communicated between the individual nodes in the nodal system. In a preferred embodiment, the individual nodes of the nodal system are couplable through a transport region  44 . 
     In the preferred embodiment, illustrated in FIG. 4, first node  42  comprises edge routers  42 A and  42 B, core routers  42 C and  42 D, and select function  42 E; and second node  46  comprises edge routers  46 A and  46 B, core routers  46 C and  46 D, and select function  46 E. Transport region  44  comprises a transport network. Transport networks are well known and are currently capable of independently detecting and recovering from any single failure in the transport region  44 . Therefore, the specific manner in which independent recovery is accomplished in the transport region  44  is not central to the invention and is thus not described in detail herein. 
     To achieve independent recovery in each of the nodes  42  and  46 , select functions  42 E and  46 E are introduced. Select functions  42 E and  46 E manage failures within their respective nodes  42  and  46 . While first node  42  is discussed below, the explanation is equally applicable to second node  46 . In the preferred embodiment, the select function  42 E performs different operations on the outgoing traffic (traffic that is going from the edge routers  42 A,B to the transport region  44 ) and the incoming traffic (traffic that is being received by the edge routers  42 A,B from the transport region  44 ). 
     For outgoing traffic, in accordance with the preferred embodiment, a data signal from an edge router, such as edge router  42 A, is simultaneously fed to a primary core router, such as core router  42 C, and a secondary core router, such as core router  42 D, to create a primary data signal and a secondary data signal, respectively. The select function  42 E will then check the path containing the primary core router  42 C to detect the presence of a failure in the path. For outgoing signals, the select function  42 E selects and passes either the primary data signal or the secondary data signal to the transport region  44 . In the absence of a failure in the path containing the primary core router  42 C, the primary data signal is passed to the transport region  44 . If a failure is detected in the path containing the primary core router  42 C, the select function  42 E selects and passes the secondary data signal to the transport region  44 . This configuration removes the need for signaling from a first node  42  to a second node  46  over the transport region  44  to recover from a primary core router  42 C failure in the first node for outgoing traffic. Therefore, an indication of a failure within a node does not need to be externally communicated by that node. 
     For incoming traffic, in accordance with the preferred embodiment, a data signal from the transport region  44  is simultaneously fed by the select function  42 E to primary core router  42 C and secondary core router  42 D to create a primary data signal and a secondary data signal, respectively. The select function  42 E will then check the path containing the primary core router  42 C to detect the presence of a failure in the path. For incoming signals, the select function  42 E directs an edge router, such as edge router  42 A, to selects either the primary data signal or the secondary data signal. In the absence of a failure in the path containing the primary core router  42 C, the primary data signal is used by the edge router  42 A. If a failure is detected in the path containing the primary core router  42 C, the select function  42 E directs the edge router  42 A to use the secondary data signal. This configuration removes the need for signaling from the first node  42  to the second node  46  over the transport region  44  to recover from a primary core router  42 C failure in the first node  42  for incoming traffic. Therefore, an indication of a failure within a node does not need to be externally communicated by that node. 
     With the capabilities of the select function  42 E and dual feeding between the edge router  42 A and the core routers  42 C-D, the present invention provides a system architecture  40  in which the failure of a single core router  42 C or  42 D can be recovered locally without any recovery signaling between nodes over the transport region  44 . Recovery signaling is not required between the nodes because the select function  42 E checks for local core router failures and allows a single signal to pass. Since only a single signal is being passed from the local node, non-local nodes do not have to choose between a primary data signal and a secondary data signal, thus eliminating the need for node recovery signaling to pass over the transport region  44 . This frees the transport network from failure related communications between the nodes. 
     FIGS. 5 and 6, setting forth block diagrams  300  and  400 , respectively, illustrate one implementation of the select functions  42 E and  46 E of FIG. 4 in block diagram form for traffic flowing into the transport region  44  from node  42  and for traffic flowing from the transport region  44  into node  46 , respectively, in accordance with the preferred embodiment. Select function  42 E is implemented through selector/detector  305  and select function  46 E is implemented through selector/detector  405 . It will be readily apparent to those skilled in the art that the select functions  42 E and  46 E can be implemented in other manners without departing from the spirit of the present invention. 
     In block diagram  300 , for traffic flowing from edge router  42 A into the transport region  44  through selector/detector  305 , the selector/detector  305  comprises two detectors  310  and  330 , and a selector  350 . Data signals from edge router  42 A are dual fed to a primary signal path P and a secondary signal path S which each carry a data signal equivalent to the data signal from edge router  42 A. The primary signal is homed to primary core router  42 C and the secondary signal is homed to secondary core router  42 D. 
     The detector  310  checks the primary core router  42 C for external and internal failures. The detector  310  checks for external primary core router  42 C failures by checking the input interface  332  of primary core router  42 C for irregularities, in a known manner, such as for a loss of signal (LOS). Internal failures are identified by “pinging” the primary core router  42 C at a diagnosis port  336 , also in a known manner, to detect failures in the primary core route  42 C. Pinging involves sending a diagnosis signal to the diagnosis port  336  of the primary core router  42 C, receiving a signal from the primary core router  42 C in response to the diagnosis signal, and comparing the response to an expected result. The detector  330  checks for external primary core router  42 C failures by checking the output interface  338  of primary core router  42 C for irregularities, in a known matter, such as for a loss of signal (LOS). Alternatively, pinging could be implemented in the core routers  42 C,D with the detector  310  monitoring the core routers  42 C,D for an indication of an internal failure. Detectors capable of identifying external and internal core router failures, such at detectors  310  and  330 , are known in the art and are thus not described in detail herein. 
     Selector  350  controls the flow of the primary data signal P and the secondary data signal S into the transport region  44 . In the absence of failures detected by detectors  310  and  330 , selector  350  is set to pass the primary data signal P from the primary core router  42 C to the transport region  44 . If, however, detectors  310  and/or  330  identify a primary core router  42 C failure, detectors  310  and/or  330  will communicate the presence of a failure to selector  350  through interface  320  and/or  340 . Upon receiving a signal indicating a primary core router  42 C failure, selector  350  will switch from passing the primary data signal P out of the primary core router  42 C to passing the secondary data signal S out of the secondary core router  42 D into the transport region  44 . Selector  350  comprises a switch for switching from a primary data signal P to a secondary data signal S with the switch controlled by a signal from the detectors  310  and/or  330 . Selector  350  may also comprise other components for terminating and converting the data signals. For example, the selector  350  may terminate optical signals and convert optical signals to electrical signals. Selectors capable of controlling primary and secondary data signals based on an input, such as selector  350 , are known in the art and are thus not described in detail herein. 
     In block diagram  400 , for traffic flowing from the transport region  44  into edge router  46 A through selector/detector  405 , the selector/detector  405  comprises a splitter  403 , two detectors  410  and  430 , and a selector  450 . Splitter  403  receives a new data signal from transport region  44  and creates a primary signal P and a secondary signal S which are each equivalent to the received signal. The primary signal P is passed to primary core router  46 C and the secondary signal S is passed to secondary core router  46 D. Splitters capable of creating two data signals from a single data signal, such as splitter  403 , are known in the art and are thus not described in detail herein. 
     The detector  410  checks the primary core router  46 C for external and internal failures. The detector  410  checks for external primary core router  46 C failures by checking the input interface  432  of primary core router  46 C for irregularities, in a known manner, such as for a loss of signal (LOS). Internal failures are identified by “pinging” the primary core router  46 C at a diagnosis port  436 , also in a known manner, to detect failures in the primary core route  46 C. Pinging involves sending a diagnosis signal to the diagnosis port  436  of the primary core router  46 C, receiving a signal from the primary core router  46 C in response to the diagnosis signal, and comparing the response to an expected result. Alternatively, pinging could be implemented in the core routers  46 C,D with the detector  410  monitoring the core routers  46 C,D for an indication of an internal failure. The detector  430  checks for external primary core router  46 C failures by checking the output interface  438  of primary core router  46 C for irregularities, in a known matter, such as for a loss of signal (LOS). Detectors  410  and  430  are similar to detectors  310  and  330 , and do not require further description. 
     Selector  450  passes a primary data path P and a secondary data path S to edge router  46 A, and directs whether edge router  46 A should use the primary data signal P or the secondary data signal S. In the absence of failures detected by detectors  410  and  430 , selector  450  will direct edge router  46 A to use the primary data signal P from the primary core router  46 C. If, however, detectors  410  and/or  430  identify a primary core router  46 C failure, detectors  410  and/or  430  will communicate the presence of a failure to selector  450  through interface  420  and/or  440 . Upon receiving a signal indicating a primary core router  46 C failure, selector  450  will switch from directing edge router  46 A to use the primary data signal P out of the primary core router  46 C to using the secondary data signal S out of the secondary core router  46 D. Selector  450  comprises an indicator for generating a signal informing edge router  46 A of which path to use based on a signal from the detectors  410  and/or  430 . Selector  450  may also comprise other components for terminating and converting the data signals. For example, the selector  450  may terminate electrical signals and convert electrical signals to optical signals. Selectors capable of generating an output based on an input, such as selector  450 , are known in the art and are thus not described in detail herein. 
     The select functions  42 E and  46 E of FIG. 4 can be implemented in any well known manner, for example, through hardware using discrete components or integrated circuits, or a combination of software running on a processor and hardware (e.g., APS, Standard 1+1 Protection, OSPF, MPLS, . . . ). Additionally, the description and illustrations of the architecture incorporating the select function only illustrates the case when a primary path and its protection path are homed to two core routers physically located in the same geographical area. However, this is not a limitation of the select function. The primary and secondary paths may be homed to core routers physically located in diverse geographical areas. In such a case the select function can be distributed across two transport network elements (one to which the primary path is homed and the other to which the secondary path is homed) using embedded transport network signaling. 
     Having thus described a few particular embodiments of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements as are made obvious by this disclosure are intended to be part of this description though not expressly stated herein, and are intended to be within the spirit and scope of the invention. For example, the number of regions, paths, and routers were chosen to facilitate discussion. Many more regions, paths, and routers could be used without departing from the spirit of the present invention. Accordingly, the foregoing description is by way of example only, and not limiting. The invention is limited only as defined in the following claims and equivalents thereto.