Patent Publication Number: US-2023164091-A1

Title: Spectrum-Aware Cross-Layer Optimization

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Greek Patent Application No. 20210100817 filed Nov. 22, 2021, the disclosure of which is hereby incorporated herein by reference. 
     BACKGROUND 
     Capacity planning is an ongoing process for network service providers. Such providers regularly need to allocate network resources to be able to successfully service communications that their networks are called upon to carry. Further, such providers often need to plan for adding network resources to meet anticipated increases in network demand To facilitate the process of resource allocation and resource addition, a provider may employ a network model. By employing a model, a network service provider may test plans for resource allocation and resource addition before the plans are implemented, thereby allowing the service provider to efficiently allocate resources and identify deficient plans using the model, and to avoid service interruptions that might occur due to implementation of a deficient plan. 
     BRIEF SUMMARY 
     It has been recognized that current network modeling suffers from the use of uniform models that are imprecise and can result in significant inaccuracies. More particularly, it has been recognized that the currently employed uniform models model networks at a level of abstraction that uses broad approximations for elements at lower levels of abstraction, and that the use of such broad approximations gives rise to significant imprecision in the resulting model and attendant inefficiencies in the allocation of network resources based on the model. 
     In view of the drawbacks associated with current network modeling techniques, the presently disclosed technology is provided. In the present technology, a network may be modeled at a relatively higher layer of abstraction, e.g., at a packet layer, without requiring the use of broad approximations for elements below the higher layer of abstraction, e.g., at a transport layer, by allowing for modeling of elements below the higher layer of abstraction, resulting in a more precise network model. The present technology may be said to provide a cross-layer optimization (XL optimization) technique of network modeling resource allocation, or a spectrum-aware XL optimization technique of network modeling and resource allocation. 
     In one aspect, the technology provides a method for allocating network resources to one or more signals that are to be conveyed over the network. The method includes calculating a transport capacity for a sublink of the network based on a spectral efficiency of at least one subpath included in the sublink; and allocating the sublink to at least one signal based on the calculated transport capacity. 
     In another aspect, the technology provides a network sublink. The sublink includes at least one subpath, the sublink being allocated to convey one or more signals on the network by performing an operation including calculating a transport capacity for the sublink based on a spectral efficiency of the at least one subpath and allocating the sublink to the one or more signals based on the calculated transport capacity. 
     In still another aspect, the technology provides a non-transitory computer-readable medium. The computer-readable medium having stored thereon a computer-readable program for performing a method for allocating network resources to convey one or more signals that are to be transmitted over the network, the method including calculating a transport capacity for at least one sublink of the network based on a spectral efficiency of at least one subpath included in the sublink; and allocating the sublink to at least one signal based on the calculated transport capacity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are not intended to be drawn to scale. Also, for purposes of clarity not every component may be labeled in every drawing. In the drawings: 
         FIG.  1    is a functional block diagram illustrating how a uniform model is used to model a network link. 
         FIG.  2    is a functional block diagram illustrating how a cross-layer optimization model of an embodiment may be used to model a network link. 
         FIGS.  3  and  4    are functional block diagrams illustrating how a cross-layer optimization model may be used to allocate a network resources to convey a signal over the network. 
         FIG.  5    is a flow chart depicting an operation of allocating network resources to convey a signal over the network. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of systems and methods are described herein. It should be understood that the words “example” and “exemplary” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as being an “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or features. In the following description, reference is made to the accompanying figures, which form a part thereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. 
     The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     In order to aid in understanding the example embodiments described herein, an example of the uniform network model of the related art is described first.  FIG.  1    is a functional block diagram illustrating how a uniform model  100  is used to model a network link  105 . As can be seen from the figure, the network link  105  is considered at two levels of abstraction, a higher level layer, e.g., packet layer  110 , and a lower level layer, e.g., a transport layer  115 . The link  105  refers to a communicative coupling between two end points, e.g., endpoints A and B, as seen in the context of the higher level layer  110 . A sublink  120  refers to a communicative coupling between the two endpoints, A and B, as seen in the context of the lower level layer  115 . The two endpoints A and B may refer to any two points between which one or more transmissions are sent. For instance, endpoint A may be a source and endpoint B may be a destination, endpoint A may be a destination while endpoint B may be a source, or endpoints A and B may exchange bi-directional communication. For purposes of brevity, the case of A being a source and B being a destination will be described with the understanding that the alternative cases will be readily understood in view of such description. 
     Returning to  FIG.  1   , in the depicted example the link  105  corresponds to a path between router  125   a  and router  125   b  (corresponding to A and B) of routers  125 , whereas the sublink  120  corresponds to a path that runs through a plurality of transport network elements  130 , two owned-line systems  135   a  and  135   b,  and one leased-line system  140 . The owned-line systems  135   a  and  135   b  are line systems that are owned by the entity that allocates the network resources, e.g., the network service provider. The leased line system  140  is not owned by the entity that allocates the network resources and is, for example, leased by the entity that allocates the network resources. 
     In allocating resources according to model  100 , a signal to be conveyed over the network being modeled may be said to define a link in the higher level layer  110 . For example, if it is desired to transmit a signal that conveys information at a rate of 300 Gigabits per second (Gbps), the signal may be said to be carried by link  105 , with link  105  being able to support the transmission of data between routers  125   a  and  125   b  at a rate of 300 Gbps. Then, once link  105  is defined on the higher level layer  110 , an operation is performed to determine network elements of the lower level layer  115  that can provide a 300 Gbps communicative coupling between points A and B. In the example, the elements of the lower level layer  115  that satisfy the requirement of link  105  are referred to collectively as sublink  120 . Thus, in the example of  FIG.  1   , the sublink  120  is able to support the transmission of data between router  125   a  and  125   b  at a rate of 300 Gbps, and network elements  130 ,  135   a,    135   b,  and  140  support the allocation of such communication. That is, in the network to which uniform model  100  is applied, network elements  130 ,  135   a,    135   b,  and  140  may be used to transmit a 300 Gbps signal from point A to point B. 
     Notably, in the  FIG.  1    example each of the owned-line systems  135  and the leased-line system  140  are abstracted as couplings that can support a given communication rate. More specifically, the owned-line systems  135   a  and  135   b  and the leased line system  140  are each assigned a transport capacity value, e.g., a Gbps value, and such value is the only parameter considered when determining whether or not to allocate the systems  135   a,    135   b,  and  140  to service the signal transmitted from point A to point B. However, the real-world systems  135   a,    135   b,  and  140 —in actuality rather than as modeled—are not limited to the single values assigned to them in the  FIG.  1    model. The real-world transmission rates that systems  135   a,    135   b,  and  140  can support will vary according to many factors, and therefore using a single default value to model each of systems  135   a,    135   b,  and  140  introduces a large error margin and leads to significant imprecision in the allocation of systems  135   a,    135   b,  and  140 . For instance, if the default value of transport capacity for owned-line system  135   a  is higher than the actual transport capacity for owned-line system  135   a,  owned-line system  135   a  might be allocated for a signal that the owned-line system  135   a  cannot support, resulting in an erroneous allocation plan that may fail if implemented. Further, if the default value of transport capacity for owned-line system  135   a  is lower than the actual transport capacity for owned-line system  135   a,  owned-line system  135   a  may not be allocated for a signal that the system can support, resulting in an allocation plan that under-utilizes owned-line system  135   a.    
     In order to avoid the inefficiencies associated with the uniform modeling of  FIG.  1   , a spectrum aware XL optimization technique of network modeling is provided. An example of such modeling is described in connection with  FIG.  2   . 
       FIG.  2    is a functional block diagram illustrating how a spectrum aware XL optimization model  200  of an embodiment may be used to model a network link. As can be seen from the figure, a signal on link  105  of the higher level layer  110  of the network may be allocated network resources corresponding to a sublink  205  on the lower level layer  115  of the network  115 . The link  105  refers to a communicative coupling between two end points, e.g., endpoints A and B, as seen in the context of the higher level layer  110 , and the sublink  205  refers to a communicative coupling between the two endpoints, A and B, as seen in the context of the lower level layer  115 . In the depicted example, the link  105  corresponds to a path between routers  125   a  and  125   b,  whereas the sublink  205  corresponds to a path that runs through a plurality of transport network elements  210 , two owned-line systems  215   a  and  215   b,  and one leased line system  220 . The owned-line systems  215   a  and  215   b  are line systems that are owned by the entity that allocates the network resources, e.g., the network service provider. The leased-line system  220  is not owned by the entity that allocates the network resources and is, for example, leased by the entity that allocates the network resources. 
     In allocating resources according to model  200 , a signal to be conveyed over the network being modeled may be said to be carried by a link in the higher level layer  110 . For example, if it is desired to transmit a signal that conveys information at a rate of 300 Gigabits per second (Gbps), the signal may be said to be carried by link  105 , with link  105  being able to support the transmission of data between points A and B at a rate of 300 Gbps. Then, once the signal is defined on link  105  of the higher level layer  110 , an operation is performed to determine network elements of the lower level layer  115  that can provide a 300 Gbps communicative coupling between routers  125   a  and  125   b.  In the example, the elements of the lower level layer  115  that satisfy the requirement of link  105  are referred to collectively as sublink  205 . Thus, in the example of  FIG.  2   , the sublink  205  is able to support the transmission of data between points A and B at a rate of 300 Gbps, and network elements  210 ,  215   a,    215   b,  and  220  may support the allocation of such communication. That is, in the network to which XL model  200  is applied, network elements  210 ,  215   a,    215   b,  and  220  may be used to transmit a 300 Gbps signal from point A to point B. In this regard, it should be noted that in general each of the network elements  210 ,  215   a,    215   b,  and  220  are not exclusively used for transmitting the illustrative 300 Gbps signal, or any other signal, and may be used to transmit multiple signals including the 300 Gbps. Nevertheless, it is also possible that any one or more of network elements  210 ,  215   a,    215   b,  and  220  are exclusively used for transmitting the illustrative 300 Gbps signal. 
     A difference between the modeling of  FIG.  1    and the modeling of  FIG.  2    is the manner in which the owned-line systems are modeled. In  FIG.  1   , the owned-line systems  135   a  and  135   b  are abstracted as couplings that can support given a communication rate, e.g., communication rate expressed in Gbps, whereas in  FIG.  2   , each of the owned-line systems  215   a  and  215   b  are abstracted as couplings that provide a bandwidth capacity, e.g., bandwidth capacity expressed in GHz. Further, in the  FIG.  2    model a transmission capacity for each of the owned-line systems  215   a  and  215   b  is determined according to the bandwidth capacity of the system and a spectral efficiency for a signal, e.g., an optical signal, deployed across the system, the spectral efficiency being dependent on one or more factors including at least parameters of the owned-line system and the spectral efficiency being expressed as the rate at which information can be transmitted per unit of bandwidth, e.g., as bits per second per hertz (bps/Hz). Moreover, a transmission capacity for the two owned-line systems  215   a  and  215   b,  when considered together as a subpath  207 , is determined according to the bandwidth capacity of the subpath  207  and a spectral efficiency for a signal, e.g., an optical signal deployed across the subpath  207 , the spectral efficiency being dependent on one or more factors including at least parameters of the subpath  207 , and the spectral efficiency being expressed as the rate at which information can be transmitted per unit of bandwidth, e.g., as bits per second per hertz (bps/Hz). Thus, for example, if the subpath  207  has a bandwidth capacity of 150 GHz and the spectral efficiency of an optical signal across the subpath is 2 bps/Hz, the transport capacity of the subpath  207  for the optical signal is 150 GHz×2 bps/Hz, or 300 Gbps. 
     The spectral efficiency for a given optical signal may depend on one or more of the signal modulation, the signal protocol, the technology type of transponders used to relay the signal, the length of lines traversed by the signal, and the type of lines traversed by the signal, although these enumerated factors are merely illustrative and are not presented as an exhaustive list of factors that may affect the spectral efficiency. Moreover, it is noted that the spectral efficiency may be dictated by the minimum signal-to-noise ratio required to successfully transmit the signal over the line system as spectral efficiency may be traded off against signal-to-noise ratio (SNR). For example, higher order modulation formats, that yield higher spectral efficiency, suffer from higher degradation of the SNR, and therefore to meet a minimum SNR requirement it may be necessary to employ a lower order modulation that yields a lower spectral efficiency. 
     Regarding calculations of transport capacity based on bandwidth capacity and spectral efficiency, it should be noted that such calculations are not limited to calculating a single transport capacity based on a single bandwidth capacity and a single spectral efficiency. One possible alternative is calculating a range of transport capacities based on a bandwidth capacity and a spectral efficiency, with the spectral efficiency being specified as a range of spectral efficiencies to account for a margin of error In any event, transport capacities may be calculated based on bandwidth capacities and spectral efficiencies of the required optical signals, with the bandwidth capacities and the spectral efficiencies being computed for optical signals across specific owned-line systems. 
     Referring back to  FIG.  2   , it should be noted that an important distinction between the owned-line systems  215   a  and  215   b  and the leased-line system  220  lies in the information available to the network service provider. The service provider has ready access to the information necessary to calculate spectral efficiencies for a given signal, e.g., an optical signal, that traverses the owned-line systems  215   a  and  215   b  because the provider owns the owned-line systems  215   a  and  215   b.  By contrast, the service provider does not have ready access to the information necessary to calculate the spectral efficiency for a given signal, e.g., an optical signal traverses the leased-line system  220  because the provider does not own the leased-line system  220 . Accordingly, since the service provider has ready access to the information necessary to calculate spectral efficiencies for the owned-line systems  215   a  and  215   b,  it is possible for the provider to calculate spectral efficiencies for the owned-line systems  215   a  and  215   b  and, in turn, calculate the transport capacities of the owned-line systems  215   a  and  215   b  based on the spectral efficiencies. Whereas, since the service provider does not have ready access to the information necessary to calculate the spectral efficiency of the leased-line system  220 , it is not possible for the service provider to calculate the transport capacity of the leased-line system  220 . Rather the service provider must use a default value for the transport capacity of the leased-line system  220 . Such default value is generally a broad approximation of the transport capacity of the leased-line system  220 , which may be provided by the owner of the leased-line system  220  or may be specified in the lease agreement. 
     For example, a service provider can deploy an optical signal that spans one or multiple owned-line systems, e.g., owned-line systems  215   a  and  215   b,  which will determine the spectral efficiency of the optical signal and the total transport capacity that the owned-line systems can support. That is, the transport capacity of an owned-line system is not assigned a pre-defined Gbps as the Gbps of the system depends on the optical signals deployed on the system. By contrast, the service provider can only deploy an optical signal on a leased-line system, e.g., leased line system  220 , without examining spectral efficiency, thereby defining a unique spectral efficiency for the signal across the leased-line system and a unique transport capacity for the leased-line system. Accordingly, it is possible to abstract the leased-line system transport capacity as a Gbps default value. Such default value is generally a broad approximation of the transport capacity of the leased-line system, and may be provided by the owner of the leased-line system or may be specified in the lease agreement. 
     Another feature of the spectrum-aware XL optimization of the present technology is the ability to allocate contiguous spectrum. To describe the contiguous spectrum aspect, reference is made to  FIGS.  3  and  4   . 
       FIGS.  3  and  4    are functional block diagrams illustrating how a spectrum-aware XL optimization model  300  of an embodiment may be used to select network elements for carrying a signal while considering the availability of contiguous spectrum between such elements. 
     Referring to  FIG.  3   , the network model  300  is considered at two levels of abstraction, a higher level layer, e.g., packet layer  110 , and a lower level layer, e.g., a transport layer  115 . A link  305  refers to a communicative coupling between two end points, e.g., endpoints C and E, as seen in the context of the higher level layer  110 . A sublink  310  refers to a communicative coupling between the two endpoints, C and E, as seen in the context of the lower level layer  115 . In the depicted example, the link  305  corresponds to a direct communicative coupling between routers  315   c  and  315   e  of routers  315 , whereas the sublink  310  corresponds to a path through multiple transport network elements  320 , three owned-line systems  325   a,    325   b,  and  325   c,  and one leased-line system  330 . The three owned-line systems  325   a,    325   b,  and  325   c  are line systems that are owned by the entity that allocates the network resources, e.g., the network service provider. The leased-line system  330  is not owned by the entity that allocates the network resources and is, for example, leased by the entity that allocates the network resources. 
     Also depicted in  FIG.  3    is a link  335  that corresponds to a direct communicative coupling between routers  315   c  and  315   d  of routers  315 , and a sublink  340  that corresponds to link  335 . The link  335  and sublink  340  refer to a communicative coupling between the endpoint C and an endpoint D, with endpoint D being intermediate between endpoints C and E. 
     In allocating resources according to model  300 , a signal to be conveyed over the network being modeled may be said to be carried by a link in the higher level layer  110 . For example, if it is desired to transmit a signal that conveys information at a rate of 300 Gigabits per second (Gbps), the signal may be said to be carried by link  305 , with link  305  being able to support the transmission of data between points C and E at a rate of 300 Gbps. Then, once the signal is defined as carried by link  305  on the higher level layer  110 , an operation is performed to determine network elements of the lower level layer  115  that can provide a 300 Gbps communicative coupling between points C and E. In the example, the elements of the lower level layer  115  that satisfy the requirement of link  305  are referred to collectively as sublink  310 . Thus, in the example of  FIG.  3   , the sublink  310  is able to support the transmission of data between points C and E at a rate of 300 Gbps, and network elements  320 ,  325   a,    325   b,    330 , and  325   c  may support the allocation of such communication. That is, in the network to which uniform model  300  is applied, network elements  320 ,  325   a,    325   b,    330 , and  325   c  may be allocated for transmitting a 300 Gbps signal from point C to point E. 
     Like the modeling described in  FIG.  2   , the modeling of  FIG.  3    abstracts leased-line system as a couplings that can support a given communication rate, e.g., expressed in Gbps, and abstracts owned-line systems as couplings that provide a bandwidth capacity, e.g., expressed in GHz, with the transport capacities for each of the owned-line systems determined according to a spectral efficiency for the owned-line system and a given signal. Moreover, in the  FIG.  2    and  FIG.  3    models, when multiple owned-line systems are directly coupled, e.g., as in the case of owned-line systems  325   a  and  325   b,  the coupled owned-line systems define a subpath, e.g., subpath  355  of  FIG.  3   , and the spectral efficiency for an optical signal traversing the owned-line systems is a characteristic of the subpath. 
     A difference between the modeling of  FIG.  2    and the modeling of  FIG.  3    is that in the  FIG.  3    modeling the available frequencies for each owned-line system are specified. By specifying the available frequencies for the owned-line systems, allocations can account for the existence or absence of frequencies that are continuously available between owned-line systems. That is, using the  FIG.  3    model, coupling a first owned-line system to a second owned-line system is favored over coupling the first owned-line system to a third owned-line system when both couplings would satisfy signal requirements but the first and second owned-line system have contiguous available frequencies and the first and third owned-line system do not have contiguous available frequencies. Such allocation is advantageous in that it can avoid the recoloring necessary to couple owned-line systems that do not have contiguous frequencies when there exists an alternative coupling of owned-line systems that do have contiguous frequencies. Indeed, in optical networks for example, such recoloring requires costly optical-to-electrical-to-optical (OEO) operations. 
     The contiguous spectrum aspect of the present technology is illustrated in  FIG.  3    in the context of optical channels. The optical channels considered in the figure are 50 GHz wide. As can be seen from the figure, owned-line systems  325   a  and  325   b  are each configured to carry optical channels 50 GHz wide and each of the owned-line systems  325   a  and  325   b  have available frequencies corresponding to three optical channels  345 . That is, owned-line system  325   a  carries three optical channels of 50 GHz width each and centered respectively at a first carrier frequency (f 1 ), a second carrier frequency (f 2 ), and a third carrier frequency (f 3 ); and owned-line system  325   b  carries the same three optical channels of 50 GHz width each and centered respectively at f 1 , f 2 , and f 3 . Also, in each of owned-line systems  325   a  and  325   b,  the spectral efficiency for each channel is determined to be 2 bps/Hz, and thus the transport capacity for each channel in each owned-line system is 100 Gbps (50 GHz×2 bps/Hz). Accordingly, the three optical channels  345  have combined transport capacity of 300 Gbps, sufficient to carry the signal traversing link  305 , and are therefore allocated to carry the signal. To complete the coupling of point C to point E, the leased-line system  330 , having a transport capacity of at least 300 Gbps, and the owned-lined system  325   c  are allocated. Regarding the owned-line system  325   c,  the system is configured to carry optical channels 50 GHz wide, but the spectral efficiency of the channels is determined to be 4 bps/Hz, and thus each optical channel of owned-line system  325   c  has a transport capacity of 200 Gbps (50 GHz×4 bps/Hz). Accordingly, two optical channels  350  of owned-line system  325   c  are allocated to the signal of link  335  as the two optical channels  350  have an aggregate transport capacity of 400 Gbps, which satisfies the 300 Gbps requirement of the signal, albeit with excess capacity. Moreover, contiguous available frequencies are not considered with respect to owned-line system  325   c  because owned-line system  325   c  is not to be couple to another owned-line system. 
     Also shown in  FIG.  3    is an example of elements in the lower level layer  115  supporting multiple signal allocations. As can be seen from the figure, owned-line systems  325   a  and  325   b  and leased line system  330  support both the signal carried on link  305  and the signal carried on link  335 . Regarding the signal carried on link  335 , a sublink  340  refers to a communicative coupling between the two endpoints, C and D, as seen in the context of the lower level layer  115 . The sublink  340  has a transport capacity of 300 Gbps, while the owned-line system  325   c  has a transport capacity of 400 Gbps. Additionally, the sublink  340  may be modeled as including subpath  355  and subpath  360 . The subpath  355  includes owned-line system  325   a  and owned-line system  325   b,  and has a transport capacity of 300 Gbps (100 Gbps for each one of the three optical channels). The subpath  360  includes leased-line system  360 , and has a transport capacity of 300 Gbps. 
       FIG.  4    shows the subpaths included in the network allocation for the signal carried on sublink  310  of  FIG.  3   . As can be seen from  FIG.  4   , sublink  310  is allocated to carry the signal and includes transport network elements  320 , owned line systems  325   a - c,  and leased line system  330 . As can be further seen from  FIG.  4   , the sublink  310  includes three subpaths, subpath  355 , subpath  360 , and subpath  365 . The subpaths  355  and  360  each have transport capacity of 300 Gbps, whereas the subpath  365  has a transport capacity of 400 Gbps because of the allocation of the two optical channels  350 . Nevertheless, the sublink  310  has an allocated transport capacity of 300 Gbps since the allocated transport capacity of the sublink  310  is set to the minimum allocated transport capacity of the subpaths  355 ,  360 , and  365  included in the sublink  310 . 
     Turning now to  FIG.  5   , the figure shows a flow chart depicting an operation of allocating network resources to convey a signal over the network. As can be seen from the figure, upon receipt of a request to convey a signal between two endpoints coupled by the network (step  505 ), a calculation is performed to calculate a transport capacity for a network sublink coupling the two endpoints, the transport capacity being calculated based on a spectral efficiency of at least one subpath included in the sublink (step  510 ). Next, if a subpath includes two or more owned-line systems that are coupled to each other, a determination is made as to an amount of contiguous available spectrum across the two or more owned-line systems (step  515 ), with the understanding that the amount of contiguous available spectrum may be zero. Then, a decision is made, based on the transport capacity and the amount of contiguous available spectrum as to whether or not to allocate the sublink to the signal (step  520 ). Notably, step  515  is optional, as it is required only for subpaths across owned-line systems and is not required for subpaths across leased-line systems. If the operation is performed without step  515 , step  520  is modified so that the decision as to whether or not to allocate the sublink to the signal is based on the transport capacity but not the amount of contiguous available spectrum. 
     Embodiments of the present technology include, but are not restricted to, the following. 
     (1) A method for allocating network resources to carry one or more signals that are to be conveyed over the network, including calculating a transport capacity for a sublink of the network based on a spectral efficiency of at least one subpath included in the sublink; and allocating the sublink to at least one signal based on the calculated transport capacity. 
     (2) The method according to (1), wherein the step of calculating includes calculating a transport capacity for the sublink of the network based on respective spectral efficiencies for two or more subpaths included in the sublink. 
     (3) The method according to (1), wherein the step of calculating further includes determining an amount of contiguous available spectrum across the subpath. 
     (4) The method according to (1), wherein the sublink and the at least one subpath reside in a transport layer of the network, and the sublink corresponds to a higher level link that resides in a packet layer of the network. 
     (5) The method according to (1), wherein the sublink and the at least one subpath reside in the L 1  layer of the open systems interconnection (OSI) model of the network, and the sublink corresponds to higher level link that resides in L 3  layer of the OSI model of the network. 
     (6) The method according to (1), wherein the sublink includes at least one subpath owned by an entity that allocates the network resources and at least one subpath not owned by the entity that allocates the network resources, and wherein the step of calculating includes calculating a transport capacity for the sublink of the network based on a spectral efficiency of the at least one subpath owned by the entity that allocates the network resources and on a default transport capacity of the at least one subpath not owned by the entity that allocates the network resources. 
     (7) The method according to (1), wherein the step of calculating includes calculating a range of transport capacities for the sublink of the network based on a spectral efficiency of at least one subpath included in the sublink, and wherein the step of allocating includes allocating the sublink to the at least one signal based on the calculated range of transport capacities. 
     (8) The method according to (1), wherein the transport capacity is calculated in terms of bits per second (bps), and the spectral efficiency is calculated in terms of bits per second per hertz (bps/Hz). 
     (9) The method according to (1), wherein the spectral efficiency is calculated based on at least one or more of a physical characteristic of a transmission line included in the subpath, a transmission protocol implemented on the subpath, or a signal modulation implemented on the subpath. 
     (10) The method according to (1), wherein the spectral efficiency is calculated based on at least a minimum signal-to-noise ratio required for successfully transmitting a signal on the subpath. 
     (11) The method according to (1), wherein the sublink is configured to convey optical signals. 
     (12) The method according to (1), wherein the at least one subpath is configured to convey optical signals. 
     (13) A network sublink including at least one subpath, the sublink being allocated to convey one or more signals on the network by performing an operation including calculating a transport capacity for the sublink based on a spectral efficiency of the at least one subpath and allocating the sublink to the one or more signals based on the calculated transport capacity. 
     (14) The network sublink according to (13), wherein calculating a transport capacity for the sublink includes calculating a transport capacity for the sublink based on respective spectral efficiencies for two or more subpaths included in the sublink. 
     (15) The network sublink according to (13), wherein calculating a transport capacity further includes determining an amount of contiguous available spectrum across the subpath. 
     (16) The network sublink according to (13), wherein the sublink includes at least one subpath owned by an entity that allocates the network resources and at least one subpath not owned by the entity that allocates the network resources, and wherein calculating includes calculating a transport capacity for the sublink based on a spectral efficiency of the at least one subpath owned by the entity that allocates the network resources and on a default transport capacity of the at least one subpath not owned by the entity that allocates the network resources. 
     (17) The network sublink according to (13), wherein calculating a transport capacity for the sublink includes calculating a range of transport capacities for the sublink based on a spectral efficiency of at least one subpath included in the sublink, and wherein allocating the sublink to the one or more signals includes allocating the sublink to the one or more signals based on the calculated range of transport capacities. 
     (18) The network sublink according to (13), wherein the spectral efficiency is calculated based on at least one or more of a physical characteristic of a transmission line included in the subpath, a transmission protocol implemented on the subpath, or a signal modulation implemented on the subpath. 
     (19) The network sublink according to (13), wherein the spectral efficiency is calculated based on at least a minimum signal-to-noise ratio required for successfully transmitting a signal on the subpath. 
     (20) A non-transitory computer-readable medium having stored thereon a computer-readable program for performing a method for allocating network resources to convey one or more signals that are to be transmitted over the network, the method including calculating a transport capacity for at least one sublink of the network based on a spectral efficiency of at least one subpath included in the sublink; and allocating the sublink to at least one signal based on the calculated transport capacity. 
     Unless otherwise stated, the foregoing alternative examples are not mutually exclusive, but may be implemented in various combinations to achieve unique advantages. As these and other variations and combinations of the features discussed above can be utilized without departing from the subject matter defined by the claims, the foregoing description should be taken by way of illustration rather than by way of limitation of the subject matter defined by the claims.