Abstract:
A method for transmitting data in a layer two network having layer three routing capabilities includes transmitting, via a physical loopback, the data from a layer two switching component of a multi service platform to a layer three switching component of the multi service platform. The data specifies an initial routing path for the data that identifies a first layer two switch, and the method includes determining a new routing path for the data, the new routing path identifying a second layer two switch different than the first layer two switch. The method also includes updating the data to specify the new routing path, and transmitting, via the physical loopback, the data that specifies the new routing path from the layer three switching component to the layer two switching component.

Description:
CROSS REFERENCE TO PARENT APPLICATION 
     This application is a continuation of pending U.S. patent application Ser. No. 10/718,529, filed Nov. 24, 2003, which is expressly incorporated herein by reference in its entirety. 
    
    
     CROSS REFERENCE TO RELATED APPLICATION 
     The present application is related to a U.S. patent application Ser. No. 10/704,715, filed on Nov. 12, 2003, now U.S. Pat. No. 7,450,592, issued Nov. 11, 2008, in the names of K. LIU et al., the disclosure of which is expressly incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of communications. More particularly, the present invention relates to improving reliability when adding layer three routing to layer two networks. 
     2. Background Information 
       FIG. 1  illustrates an example of today&#39;s networking environment in which layer two networks are provided with layer three routing. In today&#39;s networking environment, a customer edge device  10  connects to a layer two switch  12 , such as an ATM switch or a frame relay switch. The switches  12  are interconnected with interoffice trunks  14 . The connection  16  between the switch and the customer edge device  10  can be any known interface. 
     In an asynchronous transfer mode (ATM) example, a permanent virtual connection (PVC)  18  is configured from the ATM switch port connecting to the customer edge device  10  to a trunk  15  terminating at the far end of the switch  12 . The trunk  15  is similar to the other trunks  14  shown, except, the trunk  15  is partitioned. The partitioning is required to separate a user-network interface (UNI) e.g., an Internet protocol (IP) interface, from the standard layer two trunk group. At least one partition is required for the standard ATM trunks, and another partition is required for each IP interface that is defined. Complex provisioning and associated administrative burden are required to partition the trunk  15 . 
     The IP interface across the trunk  15  is defined between the switch  12  and a platform  20 , such as an Alcatel 7670 RSP (routing switch platform), available from Compagnie Financiere Alcatel of France. The defined IP interface on the ATM trunk  15  uses standard ATM encapsulation. The defined IP interface must also specify a virtual path identifier/virtual channel identifier (VPI/VCI) of the PVC connection  18 , associated with the IP service, to the customer edge device  10 . 
     The platform  20  includes layer two switching capabilities and layer three switching capabilities. In today&#39;s multi service platforms  20 , the layer two portion is independent from and isolated from the layer three portion. Typically, a layer three port  22  of the multi service platform  20  terminates the UNI connection  15 . 
     A problem associated with the current configuration is that when the UNI connection  15  (either the link or a port) fails, the layer two network will not re-route a circuit to the multi service platform  20  because the layer two network only extends to the connection  15 . In other words, the PVC  18  terminates on the layer two switch  12 , and not on the platform  20 . Thus, no layer two protection is available for the trunk  15  between the switch  12  and the platform  20 . If the trunk  15  fails, all customers using the link  15  would be out of service. 
     Current solutions addressing the single point of failure problem include dual homing from a customer site  10  to two different platforms  20 . In this case, when one connection fails, the other connection can maintain connectivity. This approach, however, consumes too many network resources by requiring both paths to be permanently maintained, adding significant complexity to the provisioning and maintenance procedures for this service. 
     Another solution reduces the length of the connection between the switch  12  and the platform  20  by deploying the switches  12  and platforms  20  within the same central office. Thus, the connection  15  becomes an intra-central office connection. This solution, however, increases the overall switch deployment cost and is still subject to a single point of failure. 
     Thus, a solution is needed to address the single point of failure problem and the complexity of provisioning problem without increasing consumption of network resources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described in the detailed description that follows, by reference to the noted drawings by way of non-limiting examples of embodiments of the present invention, in which like reference numerals represent similar parts throughout several views of the drawings, and in which: 
         FIG. 1  is a diagram showing a prior art networking environment; and 
         FIG. 2  is a diagram showing a networking environment, according to an aspect of the present invention; 
         FIG. 3A  is a diagram showing a line card; 
         FIG. 3B  is a diagram showing a line card having one additional loopback; and 
         FIG. 3C  is a diagram showing two line cards. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention relates to increasing reliability of interconnected layer two and layer three networks. The increased reliability is achieved by providing a physical loopback between layer two and layer three switching components within a multi service platform. 
     In view of the above, the present invention through one or more of its various aspects and/or embodiments is presented to accomplish one or more objectives and advantages, such as those noted below. 
     According to an aspect of the present invention, a multi service platform includes a layer two switching component, a layer three switching component, and a physical loopback. The physical loopback connects the layer two switching component and the layer three switching component. The layer two capabilities and layer three capabilities are, therefore, integrated together. The physical loopback may be a fiber jumper cable. 
     In one embodiment, the layer two switching component and the layer three switching component are on a line card. Both ends of the loopback may terminate on the line card. At least one additional physical loopback may be provided, connecting to another layer three switching component on the line card. Thus, redundancy for the layer three functionality is provided on the line card. At least one additional line card may include another layer two switching component and another layer three switching component. Thus, the at least one additional line card provides redundancy. The additional line card(s) may include at least one additional physical loopback terminating on the additional line card(s). 
     According to another aspect of the present invention, a network includes multiple layer two switches, and at least one platform. The platform includes a layer two switching component, a layer three switching component and a physical loopback between the layer two switching component and the layer three switching component. The network also includes at least one connection between one of the layer two switches, which communicates with a customer edge device, and the layer two switching component of the platform. Thus, a failure of the connection, which extends to the platform, is protected by layer two network failure restoration. 
     The layer two network switches may be ATM switches. Moreover, the connection(s) may be a permanent virtual connection (PVC). Further, the layer two switching component of the platform may be an ATM switch, and the layer three switching component of the platform may be an IP router. 
     In yet another aspect, a method is provided for routing traffic across a layer two network having layer three routing capabilities. The method includes routing traffic from a customer across the layer two network to a layer two switching component in a platform, and routing traffic from the layer two switching component across a physical loopback to a layer three switching component in the platform. The method also includes determining, at the layer three switching component, where to route the traffic, returning the traffic to the layer two switching component, and forwarding the traffic to a destination based upon the determined route. In one embodiment, the layer two network is an ATM network. 
     The various aspects and embodiments of the present invention are described in detail below. 
     The present invention improves reliability of layer two networks having layer three routing by extending the layer two network to a layer two switching component of a multi service platform. Thus, if an interface between the layer two switch and the layer two switching component of the multi service platform fails, the layer two network failure recovery scheme re-routes the circuit to the layer two portion of the multi service platform. 
     Referring now to  FIG. 2 , an embodiment of the present invention is shown. The multi service platform  20  includes a physical loopback  30  which connects the layer two switching component  24  of the platform  20  and a layer three switching component  22  of the platform  20 . In one embodiment, the loopback  30  is an OC3 or OC12 fiber jumper cable. The cable may be approximately two feet long. Of course the loopback  30  is not limited to this length and is also not limited to the OC3 or OC12 throughput values. The layer two and layer three portions  22 ,  24  may be provided on a line card, e.g., an Alcatel MR8, within the platform  20 . 
     In one embodiment, the layer two network is an ATM network, and the layer three network is an IP network, although any other type of layer two and layer three networks can be provided, for example, ethernet, frame relay and multiprotocol label switching (MPLS). In the ATM/IP embodiment, the multi service platform  20  includes an ATM switch as the layer two portion  24  and an IP router as the layer three portion  22 . 
     In the ATM/IP embodiment, the ATM network terminates on the ATM switching component  24  in the platform  20 . That is, a PVC  18  connects all the way to the ATM port  24 . Although a PVC is described in this example, any other type of ATM connection, e.g., a switched virtual connection (SVC) can be used. The physical loopback  30  connects the IP component  22  and the ATM component  24 . Thus, the ATM network includes the ATM switch  24  on the platform  20  and accordingly protects against ATM trunk  14  failures for all trunks terminating on the switch with its failure restoration. 
     The physical loopback  30  thus becomes the only unprotected link. The failure probability of the link  30  is low, however, because the link is so short. Moreover, the reliability is further enhanced by the extension of the layer two network recovery scheme. 
     When data arrives at the ATM port  24  from the PVC  18 , the cells are forwarded to the IP interface  22 . The IP interface then performs an IP look-up to determine the destination of the traffic. The traffic is then returned to the ATM component  24  and ultimately to its destination  32  via, e.g., another PVC  34 . 
     Referring now to  FIG. 3A , the platform of an exemplary embodiment includes a line card  40  including a layer two switching component  24  and a layer three switching component  22 . The platform also includes a loopback  30  having both ends of the loopback terminate on the line card  40 . 
     Referring now to  FIG. 3B , the platform of an exemplary embodiment includes a line card  40  having at least one additional physical loopback  30  connecting to another layer three switching component  22  on the line card  40 , wherein redundancy for the layer three functionality is provided on the line card  40 . 
     Referring now to  FIG. 3C , the platform of an exemplary embodiment includes at least one additional line card  40 ′ comprising at least one additional layer two switching component  24 ′ and at least one additional layer three switching component  22 ′, wherein the at least one additional line card  40 ′ provides redundancy. 
     In one embodiment, both ends of the loopback  30  are on the same line card. Thus, the IP functionality is isolated to a single card, permitting protection with line card redundancy. In a further embodiment, redundant physical loopbacks are provided. That is, each card can be provided with a physical loopback  30 . Line card redundancy could also be implemented on a single line card for each platform to provide redundancy for the layer three functionality. Redundancy on line cards terminating layer two trunks is less critical because layer two re-routing occurs if these cards fail. 
     An advantage of the present invention is that all UNIs can be provisioned to the same layer two switching component  24 . Then, the loopback  30  can extend from the port  24  to the IP interface  22 . Accordingly, end-to-end ATM connections can be provided. In other words, the ATM trunks  14  remain as pure ATM connections, obviating the need to partition the trunks  14  to provide separate IP interfaces. Consequently, existing CACing and bandwidth engineering methods can still be used. Moreover, simplified provisioning and better ATM bandwidth utilization occur. 
     Thus, the present invention provides a physical loopback connection between layer two and layer three switching components of a multi service platform thereby improving end to end reliability. It is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the invention in its aspects. Although the invention has been described with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed; rather, the invention extends to all functionally equivalent structures, methods, and uses such as are within the scope of the appended claims. 
     In accordance with various embodiments of the present invention, the methods described herein are intended for operation as software programs running on a computer processor. Dedicated hardware implementations including, but not limited to, application specific integrated circuits, programmable logic arrays and other hardware devices can likewise be constructed to implement the methods described herein. Furthermore, alternative software implementations including, but not limited to, distributed processing or component/object distributed processing, parallel processing, or virtual machine processing can also be constructed to implement the methods described herein. 
     It should also be noted that the software implementations of the present invention as described herein are optionally stored on a tangible storage medium, such as: a magnetic medium such as a disk or tape; a magneto-optical or optical medium such as a disk; or a solid state medium such as a memory card or other package that houses one or more read-only (non-volatile) memories, random access memories, or other re-writable (volatile) memories. Accordingly, the invention is considered to include a tangible storage medium or distribution medium, as listed herein and including art-recognized equivalents and successor media, in which the software implementations herein are stored. 
     Although the present specification describes components and functions implemented in the embodiments with reference to particular standards and protocols, the invention is not limited to such standards and protocols. Each of the standards for layer two and layer three transmission represent examples of the state of the art. Such standards are periodically superseded by faster or more efficient equivalents having essentially the same functions. Accordingly, replacement standards and protocols having the same functions are considered equivalents.