Abstract:
A system and method for minimizing blocking in optical networks utilizes algorithms developed to reduce non-revenue generating OEO conversions as a result of blocking based on routing and wavelength and/or subband assignment. Demands are prioritized on a basis of optical reach, and regenerators required for overcoming optical reach limitations are strategically placed to overcome blocking.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to optical communications systems and particularly relates to bandwidth and/or regenerator assignment systems and methods for demand and resource management in optical communications systems.  
         BACKGROUND OF THE INVENTION  
         [0002]    For All Optical networks, the wavelength and/or subband (group of wavelengths) assignment for traffic from the source node to the destination node can involve blocking at intermediate nodes, especially when the number of nodes and the number of different demands for bandwidth from point to point in a network is very large. An example of blocking in an optical network  10  is described with reference to FIG. 1. Therein, a first demand  12  includes an optical signal route from origin node  14  through optical switching nodes  16  and  18  to destination node  20 . Also, a second demand  22  includes an optical signal route from origin node  24  through optical switching nodes  16 ,  18 , and  20 , to destination node  28 . Further, a third demand  30  includes an optical signal route from origin node  32  through optical switching node  18 , to destination node  20 . Blocking occurs at a link from nodes  18  to  20  if the demands  12 ,  22 , and  30  are all assigned with the same wavelength.  
           [0003]    Wavelength and/or subband blocking magnitudes depend on several factors. For example, blocking magnitudes depend on the number of intermediate nodes within the optical reach. The larger the number of intermediated switch sites within the optical reach, the more blocking needs to be resolved. However, this number is not something that can be limited unless an over-lay top tier network (with fewer switch sites) is created. Otherwise, the number of intermediate switch sites is totally dependent on the community-of-interest demands. Also, blocking magnitudes depend on the number of point to point demands in a network: The larger the number of different point to point demands, the more blocking occurs. Again, the number of point to point demands in a network cannot be limited unless an over-lay top tier network (with fewer switch sites) is created. Further, optical reach has an indirect effect on blocking magnitudes. Optical reach in itself does not have a direct effect on wavelength and/or subband blocking. However, in general, the longer the optical reach, the larger the number of intermediate switch sites within the optical reach, as above. The question arises—should optical reach be limited? The answer is no because the shorter optical reach would require more distance regenerators in a network. Still further, blocking magnitudes depend on system capacity. Generally, the larger the number of available wavelengths and/or subbands in a single system, the less the blocking. Again, the larger capacity of the systems would also help to reduce the number of systems needed to be deployed and thus reduce the overall cost.  
         SUMMARY OF THE INVENTION  
         [0004]    A system and method for minimizing blocking in optical networks utilizes algorithms developed to reduce non-revenue generating OEO conversions as a result of blocking based on routing and wavelength and/or subband assignment. First, demands having predetermined routes are prioritized based on a comparison of the optical reach of the system and lengths of the predetermined routes. Second, bandwidth is preferentially assigned to demands having routes with lengths not greater than the optical reach. Third regenerators required for overcoming optical reach limitations for demands having routes with lengths greater than the optical reach are strategically placed at blocked links to overcome blocking for those demands wherever possible. The system and method preferably accommodates a subband routing methodology by assigning wavelengths and subbands to demands based on demand priority and wavelength and subband availability.  
           [0005]    The system and method of the present invention is advantageous over previous solutions in that it assigns system resources to demands within the optical reach as much as possible, uses regenerators to overcome blocking for demands greater than the optical reach as much as possible, and then uses translators to overcome the residual blocking. This system and method efficiently conserves system resources, including bandwidth, regenerators, and translators, while reducing blocking in the network.  
           [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic block diagram of an optical communications system with blocking.  
         [0008]    [0008]FIG. 2 is a block diagram of a computer-implemented resource allocation system according to the present invention.  
         [0009]    [0009]FIG. 3 is a flow chart diagram depicting a method of prioritizing assignment of channels and/or subbands to demands according to the present invention.  
         [0010]    [0010]FIG. 4 is a flowchart diagram depicting a method of assigning channels and/or subbands for demands having a length not greater than the optical reach according to the present invention.  
         [0011]    [0011]FIG. 5 is a flowchart diagram depicting a method of assigning channels and or subbands with strategic regenerator placement for demands having a length greater than the optical reach according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    According to the present invention, demands for bandwith from point to point in an optical communications system are prioritized based on a comparison of optical reach of the network with lengths of routes of the demands. Bandwidth is preferentially assigned to demands having routes with lengths not greater than the optical reach, and regenerators required for overcoming optical reach limitations for demands having routes with lengths greater than the optical reach are strategically placed at blocked links to overcome blocking for those demands wherever possible.  
         [0013]    A resource allocation system  34  according to the present invention is described with reference to FIG. 2. Therein, an input module  36  is receptive of demands  38  for bandwidth from an origin node to a destination node of the network. The input module  36  is further receptive of optical network attributes  40 . Example optical network attributes include fiber types of the network, line hardware, systems/fiber, subbands per system, channels per subband, network node placement, network node interconnection, and scale of the network. Resource allocation system  34  further has a routing module  42  in communication with input module  36  and operable to route the demands on the network according to a shortest path (SP) and/or shortest cycle (SC) methodology. Hence, routed demands  44  are generated by routing module  42  and communicated to prioritization module  46 .  
         [0014]    Prioritization module  46  generates prioritized demands  48  with predetermined routes based on a comparison of lengths of demand routes and an optical reach of the network. Preferably, demands with routes having lengths not greater than the optical reach are generally given priority over demands with routes having lengths greater than the optical reach. Notably, the optical reach is fiber-dependent, such that it may vary for demands with different routes where more than one fiber type is present in the network. Preferably, prioritization module  46  is further operable to prioritize demands based on hop count of the demands and the magnitude of the bandwidth required by the demands. For example, a demand passing through seven switch nodes (and thereby having a hop count of eight), is preferably given priority over a demand with a hop count of four. Further, demands with the same hop count are preferably prioritized based on bandwidth requirement, such that demands with higher bandwidth requirements are given priority over demands with lower bandwidth requirements. Of further note, all other demands are preferably given priority over demands with a hop count of zero. Thus, these zero length demands are an exception in that they are preferably not given priority over demands with routes having lengths greater than the optical reach.  
         [0015]    Resource allocation system  34  further has a link requirements evaluation module  50  in communication with input module  36  and receptive of routed demands  44 . Link requirements evaluation module  48  is operable to compute minimum link requirements and maximum capabilities  52  based on the routed demands  44  and the optical network attributes  40 . For example, if each fiber can provide a maximum of two systems, each system can provide a maximum of four subbands, and each subband can provide a maximum of four channels (wavelengths), then if there are a total of sixty-five channels that must be routed through a link, then there must be at least three fibers, and thus six systems. Consequently, the link has a total of ninety-six channels organized into twenty-four subbands. The minimum requirements and maximum capabilities  52  are communicated, along with the prioritized demands  48 , to assignment module  54 .  
         [0016]    Assignment module  54  is operable to generate assigned bandwidth  56  by assigning bandwidth to demands based on their priority. Thus, bandwidth is first assigned to demands with routes having lengths not greater than the optical reach, and bandwidth is next assigned to demands with routes having lengths greater than the optical reach. Also, bandwidth is last assigned to demands with a hop count of zero. Further, prioritization based on hop counts and magnitude of bandwidth requirements is further observed in the assignment process. Preferably, assignment module  54  seeks to use all available unblocked channels on a link and/or, if possible, increase the number of fibers on a link before adding translators to remove blocking. Also, for demands with routes having lengths greater than the optical reach, assignment module  54  is operable to strategically position regenerators required to overcome optical reach limitations within the network to overcome blocking for those links. Thus, assignment module  54  is operable to generate assigned regenerator positions  58  for allocating regenerators in the network. This technique eliminates the need for a translator and thus avoids a costly OEO conversion.  
         [0017]    Further embodiments of resource allocation system  34  also exist. For example, routing module  42  may be eliminated where demands are pre-routed and communicated to input module  36 . Also, link requirements evaluation module  50  may also be eliminated by communicating pre-evaluated link requirements and maximum capabilities to input module  36 . Further, additional embodiments of resource allocation system  34  will be apparent to one skilled in the art from the preceding and subsequent disclosure, wherein the method of the present invention may be implemented in a variety of ways.  
         [0018]    The flowchart of FIG. 3 depicts a method for prioritizing demands according to the present invention. Starting at  60 , the method proceeds to step  62 , wherein all demands are routed on the shortest path or shortest cycle, such that each demand comprises a need for a specific amount of bandwidth from an origin network node to a destination network node through a predetermined route comprising an ordered set of optical switching nodes. As mentioned above, this step is optional because the demands could also be pre-routed and communicated to the present invention.  
         [0019]    With demands routed, the method then proceeds to step  64 , wherein the number of fibers/systems (Fi/Si) required per link is computed without blocking considerations, and the first fiber/system is lit up such that fi=1/si=1 (where fi is the number of systems/fibers used on link i, and si is the number of subbands used on link i). For example, consider the case where each fiber can provide a maximum of two systems, each system can provide a maximum of four subbands, and each subband can provide a maximum of four channels (wavelengths). If there are a total of sixty-five channels that must be routed through link i, then Fi must equal three and Si must equal six. The first fi and first si can be lit up (powered up and made available but not assigned) until fi≦Fi and si≦Si, but fi cannot exceed Fl and si cannot exceed Si. Similarly as with step  62 , step  54  is also optional as this information can be pre-computed and the fiber pre-lit. Thus, the information may be received and/or assumed.  
         [0020]    With demands routed and Fi/Si per link computed, the method proceeds to step  66 , wherein the demands are prioritized based on optical reach (OR) by sorting the demands into three lists. For example, demands with a hop of zero (thus guaranteed to be less than the optical reach) are sorted into a list  68 . Also, demands with routes having lengths≦OR are sorted into a list  70 . Further, demands with routes having lengths&gt;OR are sorted into a list  72 . The list  70  is given priority over the list  72 , which in turn has priority over list  68 . With the demands prioritized based on optical reach, further prioritization takes place as needed. For example, lists  70  and  72  are further sorted in hop decreasing order at steps  74  and  76 . Further, demands with the same hop count in lists  70  and  72  are sorted in bandwidth decreasing order at steps  78  and  80 . Thus, by giving priority to demands with larger bandwidth requirements, then blocking of demands with smaller bandwidth requirements can be overcome, if necessary, with a smaller number of translators than would be required for demands with larger bandwidth requirements. This bandwidth size prioritization is another strategy in reducing non-revenue generating OEO conversions. Channels and/or subbands are-assigned to demands of list  70  first as at  82 . Assignment as at  84  of channels and/or subbands to demands of list  72  only occurs after assignment to demands of list  70  has completed as at  86  and  88 . Similarly, assignment as at  90  of channels and/or subbands to demands of list  68  only occurs after assignment to demands of list  72  has completed as at  92  and  94 . Once assignment of list  68  has been completed as at  96 , the method ends at  98 .  
         [0021]    A method according to the present invention for accomplishing assignment of list  70  is illustrated in FIG. 4. Therein, step  82  (FIG. 3) is further detailed as a sub-method. The method of FIG. 4 begins at  100  and proceeds to step  102 , wherein the available channels and/or subbands for the next demand in the list are found. Depending on whether blocking exists as at  104 , the method proceeds to  106 , wherein the blocking links are determined, or step  108 , wherein the channel(s) and/or subband(s) are assigned to the demand and made unavailable. After blocking links are determined at step  106 , then it is determined whether the set of available channels and/or subbands can be increased as at  110 . If so, the set is increased and related variables incremented at step  112 , and the method returns to step  102 . If the set cannot be increased, then the method proceeds to  104  where it is determined if blocking can be removed by reassigning one or more of the assigned channels or subbands of assigned demands. If so, the method proceeds to step  116  wherein the applicable demands are appropriately reassigned new channels and/or subbands. From there, the method proceeds to step  108  wherein the assigned channels and/or subbands are made unavailable. If however, the answer to the test at  114  is no, then the method proceeds to step  118 , wherein translators are used to overcome the blocking at the blocked links. The method proceeds from step  118  to step  108 , and from there the method ends at  120 .  
         [0022]    A method according to the present invention for accomplishing assignment of list  72  (FIG. 3) is illustrated in FIG. 5. Therein, step  84  (FIG. 3)is further detailed as a sub-method. The method of FIG. 5 begins at  122  and proceeds to step  124 , wherein the available channels and/or subbands for the next demand in the list are found. Depending on whether blocking exists as at  126 , the method proceeds to step  128 , wherein the blocking links are determined, or step  130 , wherein distance regenerators required to extend the optical reach are placed where required. In the case where there is no blocking, the regenerators are places anywhere along the route of the demand that will efficiently regenerate the optical signal beyond the optical reach to the destination node. Then, the method proceeds to step  132 , wherein the channel(s) and/or subband(s) are assigned to the demand and made unavailable. Where blocking exists, then after blocking links are determined at step  128 , it is determined whether the number of regenerators required to regenerate the optical signal beyond the optical reach to the destination node is greater than or equal to the number of blocking links as at  134 . For example, if the length of the demand route twice, but not thrice, exceeds the optical reach, then two regenerators are required. If there are two blocking links, then these regenerators can be placed at the blocking links to both regenerate the optical signal and overcome blocking at step  130 . The case may arise where a blocking link is at the beginning or end of a demand route such that placement there of the regenerator will not sufficiently extend the optical signal beyond the optical reach, and in this case an additional translator may be required. Nevertheless, the odds are that most regenerators required for a blocked demand can be strategically placed in the network to overcome blocking for a link, thereby decreasing the number of costly regenerators otherwise required.  
         [0023]    In the case where there are not enough regenerators to match the number of blocked links, it is preferred to check whether the set of available channels and/or subbands can be increased as at  136 . If so, the set is increased and related variables incremented at step  138 , and the method returns to step  124 . If the set cannot be increased, then the method proceeds to  140  where it is determined if blocking can be removed by reassigning one or more of the assigned channels or subbands of assigned demands. If so, the method proceeds to step  142 , wherein the applicable demands are appropriately reassigned new channels and/or subbands. From there, the method proceeds to step  132  wherein the assigned channels and/or subbands are made unavailable. If however, the answer to the test at  140  is no, then the method proceeds to step  144 , wherein translators are used to overcome the blocking of the blocked links. The method proceeds from step  144  to step  132 , and from there the method ends at  146 .  
         [0024]    Notably, the test at  134  may incorporate criteria to assess whether the regenerators can be successfully placed to both overcome blocking and serve their function as regenerators. Thus, the method can still attempt to increase the set of available channels and/or subbands before adding any additional OEO conversions. Similarly, where the number of regenerators is less than the number of blocked links and the set of available channels and/or subbands cannot be increased, then the method at step  144  can still strategically place the regenerators to overcome blocking and then add translators only as needed.  
         [0025]    While the invention has been described in its presently preferred form, it will be understood that the invention is capable of modification without departing from the spirit and scope of the invention as set forth in the appended claims.