Abstract:
A first route is associated with a first channel of two or more channels in a first dense wavelength division multiplex (DWDM) link. A second route is associated with a second channel of the two or more channels in the first dense wavelength division multiplex (DWDM) link. A third route is associated with a third channel of two or more channels in a second dense wavelength division multiplex (DWDM) link. The first route, the second route and the third route provide similar connections. The first DWDM link is different from the second DWDM link. The third route is preselected as an alternate diverse route for a connection through the first route.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to field of network communication. More specifically, the present invention is directed to a method and a system for providing diverse secondary route when using transmission media that support multiple channels. 
     BACKGROUND 
     Generally, network traffic for a connection between two nodes is carried on a transmission link. Additional links are used to support additional connections. The transmission media for each link may be fiber, copper, or other transmission media. For example, when optical link is used, new fiber lines are used to accommodate additional connections.  FIG. 1  is an exemplary illustration of multiple fiber connections between two switches. The eight ports in the switch  105  on the left side are connected to the eight ports in the switch  110  on the right side. While the approach of adding more connections and using more ports works, it is expensive. As the demand for bandwidth increase, there will not be any ports left to add new fiber connections. 
     Advance in network communication allows multiple connections or channels to be a single physical link. For example, Wavelength Division Multiplexing (WDM) is a technology that allows a single optical fiber to support multiple optical channels. WDM uses multiple lasers and transmits several wavelengths or colors of light (lamdas) simultaneously over a single optical fiber.  FIG. 2A  is an exemplary illustration of transmitting multiple signals using different wavelengths. Each wave length or channel travels within its unique color band, which is modulated by the data (text, voice, video, etc.). WDM systems (also referred to as DWDM systems) are capable of supporting multiple wavelengths. One wavelength is sufficient to transfer a 622 Mbit/s (OC-12), 2.5 Gbit/s (OC-48), 10 Gbit/s (OC-192), or 40 Gbit/s (OC-768) signal. 
       FIG. 2B  is an exemplary illustration of DWDM using a single fiber. DWDM is important because it enables a single optical fiber to carry many times the amount of network traffic it could not otherwise. Signals from the different ports of the switch  205  are transmitted at slightly different wavelengths of light. These signals are multiplexed so that they can travel together on one fiber  220 . At the other end of the fiber, the different wavelengths are separated, and the signals recovered by the switch  210 . Thus with DWDM, upgrade costs can be reduced. 
     With DWDM comes a challenge of figuring out how to manage all of these high capacity channels running in parallel in a single optical fiber. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method for computing a diverse route is disclosed. A first route is associated with a first channel of two or more channels in a first dense wavelength division multiplex (DWDM) link. A second route is associated with a second channel of the two or more channels in the first dense wavelength division multiplex (DWDM) link. A third route is associated with a third channel of two or more channels in a second dense wavelength division multiplex (DWDM) link. The first route, the second route and the third route provide similar connections. The first DWDM link is different from the second DWDM link. The third route is preselected as an alternate diverse route for a connection through the first route. 
     Other objects, features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example in the following drawings in which like references indicate similar elements. The following drawings disclose various embodiments of the present invention for purposes of illustration only and are not intended to limit the scope of the invention. 
         FIG. 1  is an exemplary illustration of multiple fiber connections between two switches. 
         FIG. 2A  is an exemplary illustration of transmitting multiple signals using different wavelengths 
         FIG. 2B  is an exemplary illustration of DWDM using a single fiber. 
         FIG. 3A  is an exemplary diagram illustrating a network topology with a single fiber physical link. 
         FIG. 3B  is an exemplary flow diagram illustrating a route lookup procedure for a diverse route. 
         FIG. 4  is an exemplary diagram illustrating a network topology with logical links. 
         FIG. 5  is an exemplary table illustrating a physical transport identifier information group using private network to network (PNNI) routing protocol. 
         FIG. 6  is an exemplary table illustrating a system capabilities information group using PNNI. 
         FIG. 7  is an exemplary table illustrating a horizontal link information group using PNNI. 
         FIGS. 8A &amp; 8B  illustrate an exemplary flow diagram for a route lookup procedure to pre-select a diverse route using physical link identifier. 
         FIG. 9  is an exemplary diagram illustrating a network topology with two diverse route fiber physical links. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment of the present invention, a method for computing diverse route in a network is disclosed. A fiber link may comprise multiple logical channels. A logical channel serves as a link between two nodes. Another logical channel connecting the same nodes using a different fiber link is preselected as a diverse alternate route. The two fiber links go through different DWDM equipments. 
       FIG. 3A  is an exemplary diagram illustrating a network topology with a single fiber physical link. Nodes  305 ,  310 ,  315  are connected to nodes  320 ,  325 ,  330  through the DWDM network using a single fiber link  300  (also referred to as a DWDM link). The nodes  335 ,  340  represent customer premise equipments (CPE). DWDM multiplexes multiple channels into a single DWDM link  300 . Each channel is represented as a different wavelength over the DWDM link  300 . The network views each channel as a separate logical link. For example, using a route look up procedure, there are two distinct routes from the CPE  335  to the CPE  340 . The first route includes the following route segments: CPE  335  to node  305 , node  305  to node  310 , node  310  to node  320 , node  320  to node  330 , and node  330  to CPE  340 . The second route includes the following route segments: CPE  335  to node  305 , node  305  to node  315 , node  315  to node  325 , node  325  to node  330 , and node  330  to CPE  340 . The first route in the above example may be considered as a primary route or primary link between CPE  335  and CPE  340 . Typically, the second route may be selected as an alternate route between CPE  335  and CPE  340 . 
       FIG. 3B  is an exemplary flow diagram illustrating a route lookup procedure for a diverse route. The route look up procedure starts at block  350 . At block  355 , a node advertising a called address is retrieved from an address table. At block  360 , a determination is made to see if the above node is in a routing table. If not, another node is retrieved from the address table. Otherwise, a determination is made to see if a route is available for the node, as shown in block  365 . When there is no route, as shown in block  375 , the route lookup procedure ends at block  390 . 
     When there is a route, the route is selected for the connection. In some situations, there may be a requirement that when an alternate route is to be used, it must be completely diverse from a current route. For example, the I.630 protocol requires that a backup route be completely diverse from a primary route. A route is completely diverse from another route when there is no common route segments between the two routes. At block  380 , a determination is made to see if the selected route is a diverse route as compared to a current route (i.e., the failing route). When the selected route is not a diverse route, the route lookup procedure moves to block  365  to see if another route can be selected. When the selected route is a diverse route, that route is used to re-establish the connection. The route lookup procedure ends at block  390 . It should be noted that the diverse route may be selected when the primary route is established (e.g., during call setup or immediately after call setup). 
       FIG. 4  is an exemplary diagram illustrating a network topology with logical links.  FIG. 4  illustrates two logical links in the DWDM link  300  of  FIG. 3A . For example, the first or current route uses the logical link  400  through nodes  405 ,  410 ,  420 ,  430  between CPE  335  and CPE  340 . The second or alternate route uses the logical link  402  through nodes  405 ,  415 ,  425 ,  430  between CPE  335  and CPE  340 . The first route and the second route described above are considered by routing protocols (e.g., Private Network-to-Network Interface (PNNI)) as diverse routes since they have no common route segment. As such, the second route using the logical link  402  can be selected as the diverse route for the first route. 
     However, this approach does not work when the logical link  400  and the logical link  402  share the same DWDM link. When the DWDM link is disconnected, both the logical link  400  and the logical link  402  are disconnected. As such, although the second route is a diverse route, it would be erroneous to choose the second route as the secondary or alternate route. Choosing the wrong second route would introduce additional delay and traffic loss before the connection between the CPE  435  and the CPE  440  is re-established. 
     In one embodiment, a physical link identifier is used to indicate the physical link that the logical link is associated with. By performing a physical link identifier comparison, the error of selecting a diverse second route that has the same common DWDM link as the first route can be prevented. This physical link identifier may be implemented in a routing protocol that is used with DWDM link. The physical link identifier is used during the route selection procedure to pre-select a diverse route. When the physical link identifiers of the primary route and the potential diverse route are different, the potential diverse route is selected. When the physical link identifiers of the primary route and the potential diverse route are similar, as in the case when a common DWDM link is used, the potential diverse route is not selected. 
     The routing protocol mentioned above may be, for example, the PNNI (Private Network-to-Network Interface) protocol. In this case, the physical link identifier may be implemented in the PNNI message or packet. There are different types of PNNI packets (e.g., hello, PTSP, PTSE, Database summary). A “packet type” field in a header of the PNNI packet identifies the packet type. With each packet type, there are information groups. For example, in the PTSE (Protocol Topology State Elements) packet type, the information groups include PTSE, nodal state parameters, nodal information group, outgoing resource availability, horizontal links, system capabilities, etc. 
     In one embodiment, when the PNNI routing protocol is used, the physical link identifier is specified in a physical transport identifier information group.  FIG. 5  is an exemplary table illustrating the physical transport identifier information group. The physical transport identifier  505  (e.g., the physical link identifier) is the identifier of the transport mechanism.  FIG. 6  is an exemplary table illustrating a system capabilities information group. The system capability information group includes a system capabilities information field  605  which can be used to carry system specific information such as, for example, the physical link identifier. The system capabilities information group in  FIG. 6  can be used to propagate the physical link identifier by adding the information group to any PTSE. 
       FIG. 7  is an exemplary table illustrating a horizontal link information group. In one embodiment, the system capabilities information field  705  includes information in the physical transport identifier information group. A horizontal link is a link between two logical nodes that belong to the same peer group. Using the horizontal link information group, the information about the physical link identifier can be propagated to peer nodes. For example, when the DWDM link (i.e., fiber link) is configured for a logical link  400  in  FIG. 4 , the fiber id is used to update the physical link identifier field. Thus, the physical link identifier is embedded in the horizontal link information group. This physical link identifier is used to pre-select the diverse alternate route. 
     Although the above discussion uses PNNI as the exemplary routing protocol, one skilled in the art would recognize that the physical link identifier technique may be implemented with other routing protocols to determine diverse routes when DWDM is used. 
       FIGS. 8A &amp; 8B  illustrate an exemplary flow diagram for a route lookup procedure to pre-select a diverse route using physical link identifier. The route lookup procedure starts at block  805 . This route lookup procedure performs the same operations from block  810  to block  845  as the route lookup procedure illustrated in  FIG. 3B . However, from block  845 , instead of selecting the route as the diverse route, a physical link identifier of the selected route is compared with a physical link identifier of the current route, as shown in block  850 . When the two physical link identifiers are the same, this indicates that they share the same DWDM link. In this situation, the selected route cannot be used even though it is a diverse route. The route lookup procedure moves to block  855 , which leads to block  820  to see if another route is available. When the comparison in block  850  indicates that the two physical link identifiers are different, this indicates that the two route use different fiber links and therefore the selected route is truly a diverse route. At block  860 , the route is selected as the alternate route. This selection is made because the route goes through different DWDM equipments. The route lookup procedure ends at block  865 . It would be appreciated to note that the alternate diverse route is preselected to 
     minimize delay when the primary route fails. 
       FIG. 9  is an exemplary diagram illustrating a network topology with two diverse route fiber physical links. The first route from CPE  935  to CPE  940  through the nodes  905 ,  910 ,  920  and  930  uses a fiber physical link  900 . The second route from CPE  935  to CPE  940  through the nodes  905 ,  915 ,  925  and  930  uses a different fiber link  902 . Even though the fiber physical link  900  may have multiple logical links connecting nodes  910  and  920 , using the physical link identifier technique above, none of these logical links will be pre-selected as the secondary or alternate diverse route. Instead, the second route using the fiber physical link  902  will be pre-selected as the alternate diverse route. This eliminates down time. 
     The method described above can be stored in the memory of a computer system as a set of instructions (i.e., software). The set of instructions may reside, completely or at least partially, within the main memory and/or within the processor to be executed. In addition, the set of instructions to perform the methods described above could alternatively be stored on other forms of machine-readable media. For the purposes of this specification, the term “machine-readable media” shall be taken to include any media which is capable of storing or embodying a sequence of instructions for execution by the machine and that cause the machine to perform any one of the methodologies of the present invention. The term “machine readable media” shall accordingly be taken to include, but not limited to, optical and magnetic disks. 
     Alternatively, the logic to perform the methods as discussed above, could be implemented in additional computer and/or machine readable media, such as, for example, discrete hardware components as large-scale integrated circuits (LSI&#39;s), application-specific integrated circuits (ASIC&#39;s), firmware such as electrically erasable programmable read-only memory (EEPROM&#39;s), and electrical, optical, acoustical and other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), etc. 
     Although the above discussion refers to fiber link and DWDM, it would be apparent to one skilled in the art that the method of the present invention can also be used with other transmission media such as, for example, copper, etc., that is capable of supporting multiple logical channels. 
     From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustration only and are not intended to limit the scope of the invention. Those of ordinary skill in the art will recognize that the invention may be embodied in other specific forms without departing from its spirit or essential characteristics. References to details of particular embodiments are not intended to limit the scope of the claims.