Abstract:
A method is provided for protection switching in an optical network. The method may include establishing a baseline power level for a channel. The method may further include receiving a signal associated with the channel via each of a first path of the optical network and a second path of the optical network. The method may also include monitoring a power intensity of the signal received via the first path. The method may additionally include protection switching from the signal received via the first path to the signal received via the second path in response to a determination that the baseline power level exceeds the power intensity of the signal received via the first path by a predetermined threshold.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/254,354 entitled “Baseline-Based Optical Signal Error Detection” filed Oct. 23, 2009, the contents of which is hereby incorporated by reference in its entirety. 
         [0002]    This application also claims the benefit of U.S. provisional application No. 61/254,364 entitled “Elastic Baseline-Based Optical Signal Error Detection” filed Oct. 23, 2009, the contents of which is hereby incorporated by reference in its entirety. 
         [0003]    This application is related to copending Patent Application entitled “Method and System for Protection Switching,” application Ser. No. ______ (064731.0766), filed on the same date as the present application. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0004]    The present invention relates generally to optical networks and, more particularly, to a method and system for protection switching in an optical system. 
       BACKGROUND 
       [0005]    Telecommunications systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of communicating the signals over long distances with very low loss. Optical networks often employ redundancies to maximize performance and availability. Such redundancies may include optical unidirectional path switched ring (OUPSR). With OUPSR, an optical signal may be transmitted via two or more optical paths between the same source and destination node. An OUPSR device at the destination may include a photodetector per each path to monitor signals received from the two or more paths. Based on such received signals, the OUPSR device may select one of the signals to be forwarded to a transponder or receiver at the destination node. For example, the OUPSR may determine, based on the photodetector monitoring, whether one of the paths has experienced a loss of signal or “loss of light.” If a particular path experiences a loss of light, then the OUPSR may select another path to forward to the transponder or receiver. Such selection may be referred to as a “protection switch.” 
         [0006]    In order to accurately detect loss of light, photodetectors must often be of high quality and carefully calibrated. Such calibration adds complexity, time, and cost to the manufacturing process. If high-quality and carefully-calibrated photodetectors are not used, noise introduced into an optical system may cause operational problems in OUPSR. For example, amplified spontaneous emission (ASE) noise may be introduced into an optical network. In certain cases, ASE may further increase in networks including cascaded intermediate line amplifiers (ILAs). In the presence of noise, an OUPSR photodetector may detect light induced by noise even if a failure exists in a particular path, and thus, may not initiate a protection switch. Thus, OUSPR photodetectors must be extremely accurate in order to differentiate between noise and actual signal power. 
       SUMMARY 
       [0007]    In accordance with a particular embodiment of the present disclosure, a method is provided for protection switching in an optical network. The method may include establishing a baseline power level for a channel. The method may further include receiving a signal associated with the channel via each of a first path of the optical network and a second path of the optical network. The method may also include monitoring a power intensity of the signal received via the first path. The method may additionally include protection switching from the signal received via the first path to the signal received via the second path in response to a determination that the baseline power level exceeds the power intensity of the signal received via the first path by a predetermined threshold. 
         [0008]    Technical advantages of one or more embodiments of the present invention may provide methods and systems for calibrating a baseline power level in connection with a protection switching device, and establishing a threshold in connection with such baseline power level such that the expected noise in an optical network path is substantially less than a relative loss of light power level equal to the calibrated baseline power level minus the established threshold. Accordingly, a measurement of intensity of a signal received via the path at a power level below the relative loss of light power level may indicate a “true” loss of signal, despite the presence of noise with an intensity that may otherwise indicate a valid signal. 
         [0009]    Embodiments of the present invention may thus allow for an economically efficient protection switching system that may not require high-quality and carefully-calibrated photodetectors to correctly account for noise. 
         [0010]    It will be understood that the various embodiments of the present invention may include some, all, or none of the enumerated technical advantages. In addition, other technical advantages of the present invention may be readily apparent to one skilled in the art from the figures, description and claims included herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a block diagram illustrating an example optical network, in accordance with certain embodiments of the present disclosure; 
           [0013]      FIGS. 2A-2C  are each flow charts illustrating a finite state machine in accordance with certain embodiments of the present disclosure; 
           [0014]      FIG. 3  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector, demonstrating an application of a baseline power level and a threshold established by the state machine depicted in  FIG. 2A , in accordance with certain embodiments of the present disclosure; 
           [0015]      FIG. 4  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector, demonstrating an application of a baseline power level and a threshold established by the state machine depicted in  FIG. 2B , in accordance with certain embodiments of the present disclosure; and 
           [0016]      FIG. 5  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector, demonstrating an application of a baseline power level and a threshold established by the state machine depicted in  FIG. 2C , in accordance with certain embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  illustrates an example optical network  10 . Optical network  10  may include one or more optical fibers  28  operable to transport one or more optical signals communicated by components of the optical network  10 . The components of optical network  10 , coupled together by optical fiber  28 , may include nodes  12   a  and  12   b  and one or more optical add/drop multiplexers (OADMs)  32 . Although the optical network  10  is shown as a point-to-point optical network with terminal nodes, the optical network  10  may also be configured as a ring optical network, a mesh optical network, or any other suitable optical network or combination of optical networks, and may include any number of nodes intermediate to nodes  12   a  and  12   b.  The optical network  10  may be used in a short-haul metropolitan network, a long-haul inter-city network, or any other suitable network or combination of networks. 
         [0018]    A node  12  and/or OADM  32  may represent a Label Switching Router (LSR). One or more label switched paths (LSPs) including a sequence of nodes  12  and OADMs  32  may be established for routing packets throughout optical network  10 . For example, traffic may travel from source node  12   a,  through zero, one, or more intermediate OADMs  32 , to destination node  12   b.    
         [0019]    Node  12   a  may include transmitters  14 , a multiplexer  18 , an amplifier  26 , and a splitter  24 . Transmitters  14  may include any transmitter or other suitable device operable to transmit optical signals. Each transmitter  14  may be configured to receive information transmit a modulated optical signal at a certain wavelength. In optical networking, a wavelength of light is also referred to as a channel. Each transmitter  14  may also be configured to transmit this optically encoded information on the associated wavelength. The multiplexer  18  may include any multiplexer or combination of multiplexers or other devices operable to combine different channels into one signal. Multiplexer  18  may be configured to receive and combine the disparate channels transmitted by transmitters  14  into an optical signal for communication along fibers  28 . 
         [0020]    Amplifier  26  of node  12   a  may be used to amplify the multi-channeled signal. Amplifier  26  may be positioned before and/or after certain lengths of fiber  28 . Amplifier  26  may comprise an optical repeater that amplifies the optical signal. This amplification may be performed without opto-electrical or electro-optical conversion. In particular embodiments, amplifier  26  may comprise an optical fiber doped with a rare-earth element. When a signal passes through the fiber, external energy may be applied to excite the atoms of the doped portion of the optical fiber, which increases the intensity of the optical signal. As an example, amplifier  26  may comprise an erbium-doped fiber amplifier (EDFA). However, any other suitable amplifier  26  may be used. 
         [0021]    Splitter  24  may represent an optical coupler or any other suitable optical component operable to split an optical signal into multiple copies of the optical signal and transmit the copies to other components within network  10 . In the illustrated embodiment, splitter  24  may receive a signal from amplifier  26  of node  12   a  and split the received traffic into two copies. One copy may be transmitted via path  42   a,  while the other copy may be transmitted over  42   b,  in order to provide redundancy protection for the signal, as described in greater detail below. 
         [0022]    The process of communicating information at multiple channels of a single optical signal is referred to in optics as wavelength division multiplexing (WDM). Dense wavelength division multiplexing (DWDM) refers to the multiplexing of a larger (denser) number of wavelengths, usually greater than forty, into a fiber. WDM, DWDM, or other multi-wavelength transmission techniques are employed in optical networks to increase the aggregate bandwidth per optical fiber. Without WDM or DWDM, the bandwidth in networks would be limited to the bit rate of solely one wavelength. With more bandwidth, optical networks are capable of transmitting greater amounts of information. Referring back to  FIG. 1 , node  12   a  in optical network  10  may be configured to transmit and multiplex disparate channels using WDM, DWDM, or some other suitable multi-channel multiplexing technique, and to amplify the multi-channel signal. 
         [0023]    As discussed above, the amount of information that can be transmitted over an optical network varies directly with the number of optical channels coded with information and multiplexed into one signal. Therefore, an optical signal employing WDM may carry more information than an optical signal carrying information over solely one channel. An optical signal employing DWDM may carry even more information. 
         [0024]    After the multi-channel signal is transmitted from node  12   a,  the signal may travel over one or more paths  42  (e.g., paths  42   a  and  42   b ) to node  12   b.  Each path  42  may include one or more OADMs  32 , one or more amplifiers  26 , and one or more fibers  28  coupling such OADMs  32  and amplifiers  26 . 
         [0025]    An OADM  32  may include any multiplexer or combination of multiplexers or other devices operable to combine different channels into one signal. An OADM  32  may be operable to receive and combine the disparate channels transmitted across optical network  10  into an optical signal for communication along fibers  28 . In addition, an OADMs  32  comprise an add/drop module, which may include any device or combination of devices operable to add and/or drop optical signals from fibers  28 . An OADM  32  may be coupled to an amplifier  26  which may be used to amplify a WDM and/or DWDM signal as it travels through the optical network  10 . After a signal passes through an OADM  32 , the signal may travel along fibers  28  directly to a destination, or the signal may be passed through one or more additional OADMs  32  before reaching a destination. 
         [0026]    Similar to amplifier  26  of node  12   a,  other amplifiers  26  or optical network  10  may be used to amplify the multi-channeled signal communicated by OADMs  32 . Amplifiers  26  may be positioned before and/or after certain lengths of fiber  28 . Amplifiers  26  may comprise an optical repeater that amplifies the optical signal. This amplification may be performed without opto-electrical or electro-optical conversion. In particular embodiments, amplifiers  26  may comprise an optical fiber doped with a rare-earth element. When a signal passes through the fiber, external energy may be applied to excite the atoms of the doped portion of the optical fiber, which increases the intensity of the optical signal. As an example, amplifiers  26  may comprise an erbium-doped fiber amplifier (EDFA). However, any other suitable amplifiers  26  may be used. 
         [0027]    An optical fiber  28  may include, as appropriate, a single, unidirectional fiber; a single, bi-directional fiber; or a plurality of uni- or bi-directional fibers. Although this description focuses, for the sake of simplicity, on an embodiment of the optical network  10  that supports unidirectional traffic, the present invention further contemplates a bi-directional system that includes appropriately modified embodiments of the components described below to support the transmission of information in opposite directions along the optical network  10 . Furthermore, as is discussed in more detail below, the fibers  28  may be high chromatic dispersion fibers (as an example only, standard single mode fiber (SSMF) or non-dispersion shifted fiber (NDSF)), low chromatic dispersion fibers (as an example only, non zero-dispersion-shifted fiber (NZ-DSF), such as E-LEAF fiber), or any other suitable fiber types. 
         [0028]    Node  12   b  may be configured to receive signals transmitted over optical network  10 . For example, as shown in  FIG. 1 , a portion of the multi-channel signal through path  42   a  may be dropped to node  12   b  by OADM  32   a,  and a portion of the multi-channel signal through path  42   b  may be dropped to node  12   b  by OADM  32   b.  Node  12   b  may include an OUPSR device  80  and a receiver  22 . OUPSR device  80  may include a selector  82  and a switch  84 . OUPSR device  80  may be configured to receive at least a portion of the multi-channel signal from each of path  42   a  and  42   b  and, on a channel-by-channel basis, selects which of the two signals to pass to receiver  82 . Such selection may be made on any suitable criteria, including bit error rate and/or power levels of the individual signals. 
         [0029]    OUPSR device  80  may include a selector  82  and a switch  84 . Selector  82  may include a photodetector  86  (e.g., photodetectors  86   a  and  86   b ) associated with each path  42 . A photodetector  86  may be any system, device or apparatus configured to detect an intensity of light and convert such detected intensity into an electrical signal indicative of such intensity. Such electrical signals from photodetectors  86  may be communicated to decision module  88 . Based on analysis of the electrical signals from photodetectors  86 , decision module  88  may determine, on a channel-by-channel basis, whether to pass the signal dropped from path  42   a  or the signal dropped from path  42   b.  A signal indicative of such determination may be communicated from decision module  88  to switch  84 , and switch  84  may pass either the signal from path  42   a  or the signal from path  42   b  to receiver  22  based on the signal received from decision module  88 . For example, decision module  88  may be configured such that the signal received from path  42   a  is passed to receiver  22  unless the intensity of signal received via path  42   a  falls below a particular threshold relative to a baseline power level (thus indicating a loss of light condition), in which case switch  84  may protection switch such that the signal received via path  42   b  is passed to receiver  22 . In addition, as described in greater detail below with respect to  FIGS. 2-5 , decision module  88  may dynamically vary the baseline power level and threshold. 
         [0030]    Receiver  22  may include any receiver or other suitable device operable to receive an optical signal. Receiver  22  may be configured to receive one or more channels of an optical signal carrying encoded information and demodulate the information into an electrical signal. 
         [0031]      FIG. 2A  is a flow chart illustrating a finite state machine  200   a  in accordance with certain embodiments of the present disclosure. State machine  200   a  may be maintained by decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10 . State machine  200   a  may begin at state  202  in response to a determination and/or instruction to provision OUPSR for a particular channel. If, while in state  202 , OUPSR device determines that a “clean” condition exists with respect to the channel over one or more paths  42 , state machine  200   a  may proceed to state  204 . A clean condition may exist where one or more parameters associated with the particular channel indicate that communication via one or more of paths  42  is available. For example, a clean condition may exist when OUPSR device  80  is present, a signal is detected on the channel by OUPSR device  80 , and Alarm Indication Signal-Optical (AIS-O)=0 and Unequipped/Unvprovisioned (UNEQ)=0 for all paths  42  coupled to OUPSR device  80 . 
         [0032]    At state  204  decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may continue to poll for the continued existence of the clean condition for a predetermined amount of time (e.g., 3 poll cycles of OUPSR device  80 ). If the clean condition exists for the predetermined amount of time, state machine  200   a  may proceed to state  206 . If the clean condition fails to exist during the predetermined amount of time (e.g, OUPSR device  80  is removed, failure to detect signal on the channel by OUPSR device  80 , AIS-O=1, and/or UNEQ=1), state machine  200   a  may again proceed to state  204 . 
         [0033]    At state  206 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may apply and store an initial baseline power level and initial threshold for one or more of photodetectors  86 . Thus, state  206  may be thought of as a self-calibration phase of OUPSR device  80 . In some embodiments, the initial baseline power level may be approximately equal to the intensity of light detected by a photodetector  86  during state  204 . In the same or alternative embodiments, the initial threshold may be equal to a predetermined value (e.g., 5 dBm). After the initial baseline power and initial threshold are applied and stored, state machine  200   a  may proceed to state  208 . 
         [0034]    At step  208 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may maintain the initial baseline power level and/or initial threshold until the clean condition ceases to exist (in which case state machine  200   a  may proceed again to step  202 ) and/or OUPSR is deprovisioned for the particular channel (in which case state machine  200   a  may cease).  FIG. 3  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector  86 , demonstrating an application of a baseline power level and a threshold established by state machine  200   a  depicted in  FIG. 2A , in accordance with certain embodiments of the present disclosure. For the purposes of exposition of  FIG. 3 , it is assumed that the initial baseline power level is established at a value of −10 dBm and the initial threshold is −5 dBm. While OUPSR is provisioned, a photodetector  86  (e.g., photodetector  86   a ) may monitor the intensity of light received via a path  42  (e.g., path  42   a ). If, at any time while OUPSR is provisioned, the intensity of light received by the photodetector  86  has decreased below the baseline power level by more than the threshold, decision module  88  (or another component of OUPSR device  80 ) may cause a protection switch on switch  84 . The power level at which the protection switch may occur may be considered a relative loss of light (LOL) power level, wherein such relative LOL power level may be greater than the amount of noise expected to be detected at the photodetector  86 , but still low enough relative to the baseline power level to indicate that a protection switch is appropriate. Thus, a loss of light condition and an accompanying protection switch may be triggered when an actual detected power level has decreased below the relative LOL power level, rather than being triggered as a result of absolute loss of light, allowing for effective operation in noisy conditions. 
         [0035]      FIG. 2B  is a flow chart illustrating a finite state machine  200   b  in accordance with certain embodiments of the present disclosure. State machine  200   b  may be maintained by decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10 . As shown in  FIG. 2B , states  202 ,  204 , and  206  of state machine  200   b  may be similar or identical to states  202 ,  204 , and  206  of state machine  200   a  depicted in  FIG. 2A . In addition, state  208  of state machine  200   b  may be similar to state  208  of state machine  200   a,  except that when state machine  200   b  reaches state  208 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may continuously monitor power at a photodetector  86  (e.g., photodetector  86 ) to detect an average power intensity for each particular channel of interest. Such average power level may be calculated using any suitable number of previously detected power levels for a particular channel. For example, the average power level may be a moving average power level based on a predetermined number of recent detected power levels (e.g., the five most recent detected power levels for the particular channel). If the average power level is greater than the then-present baseline power level, state machine  200   b  may proceed to step  212 . 
         [0036]    At state  212 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may modify the baseline power level based on the detected average power level (e.g., may re-establish the baseline power level to be approximately equal to the detected average power level). After the baseline power level has been modified, state machine  202   b  may proceed again to state  208 . 
         [0037]      FIG. 4  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector  86 , demonstrating an application of a baseline power level and a threshold established by state machine  200   b  depicted in  FIG. 2B , in accordance with certain embodiments of the present disclosure. As shown in  FIG. 4 , the intensity of light received by a photodetector  86  (e.g., photodetector  86   a ) on a particular channel may increase after OUPSR has been provisioned for numerous reasons (e.g., an increase in noise taking place after optical network  10  has been set up and OUPSR has been provisioned). Accordingly, the baseline power level established in accordance with state machine  200   b  may also increase over time to account for the increase in detected light intensity. Because the established threshold is not varied in accordance with state machine  200   b,  the relative LOL level will also increase each time the baseline power level is increased, such that the difference between the relative LOL level and the baseline power level is always approximately equal to the value of the established threshold. In accordance with state machine  200   b,  if, at any time while OUPSR is provisioned, the intensity of light received by the photodetector  86  has decreased below the dynamically changing baseline power level by more than the threshold (e.g., below the dynamically changing relative LOL level), decision module  88  (or another component of OUPSR device  80 ) may cause a protection switch on switch  84 . Thus, a method in accordance with state machine  200   b  allows for variance in established baseline and relative LOL levels to account for when increased noise is coupled into optical network  10 . 
         [0038]      FIG. 2C  is a flow chart illustrating a finite state machine  200   c  in accordance with certain embodiments of the present disclosure. State machine  200   c  may be maintained by decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10 . As shown in  FIG. 2C , states  202 ,  204 , and  206  of state machine  200   c  may be similar or identical to states  202 ,  204 , and  206  of state machine  200   a  depicted in  FIG. 2A  and/or states  202 ,  204 , and  206  of state machine  200   b  depicted in  FIG. 2B . In addition, state  208  of state machine  200   c  may be similar to state  208  of state machine  200   a  and/or state  208  of state machine  200   b,  except that when state machine  200   c  reaches state  208 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may continuously monitor power at a photodetector  86  (e.g., photodetector  86 ) to detect an average power intensity for each particular channel of interest. Such average power level may be calculated using any suitable number of previously detected power levels for a particular channel. For example, the average power level may be a moving average power level based on a predetermined number of recent detected power levels (e.g., the five most recent detected power levels for the particular channel). If the average power level is greater than the then-present baseline power level, state machine  200   c  may proceed to step  210 . 
         [0039]    At state  210 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may modify the threshold based on the detected average power level. For example, the new threshold value may be increased by an amount approximately equal to the difference between the average power level and the then-present baseline power level, such that:
       New threshold value=Present Baseline Power Level−Average Power Level+Present Threshold Value       
 
         [0041]    To ensure that a suitable difference exists between the threshold value and the baseline power level, the calculated new threshold value may be compared to a predetermined minimum value. In some embodiments, the predetermined minimum value may be zero, to ensure that that threshold is not negative. If it is determined that the calculated new threshold value is greater than the predetermined minimum value, the threshold may be re-established with the calculated new threshold value, and state machine  200   c  may proceed again to state  208 . If it is determined that the calculated new threshold value is not greater than the predetermined minimum value, state machine  200   c  may proceed to state  212 , where the baseline power level and threshold may be modified as described below. 
         [0042]    State  212  of state machine  200   c  may be similar to state  212  of state machine  200   b,  except that, in addition to modifying the baseline power level based on the detected average power level, decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may also modify the threshold value. For example, at state  212 , decision module  88 , another component of OUPSR device  80 , or any other suitable component of optical network  10  may modify the baseline power level based on the detected average power level (e.g., may re-establish the baseline power level to be approximately equal to the detected average power level) and also modify the threshold such that it is approximately equal to the initial threshold established at step  206 . After the baseline power level and the threshold have been modified, state machine  202   c  may proceed again to state  208 . 
         [0043]      FIG. 5  illustrates an example graph of intensity of a light signal associated with a particular channel as detected by a photodetector  86 , demonstrating an application of a baseline power level and a threshold established by state machine  200   c  depicted in  FIG. 2C , in accordance with certain embodiments of the present disclosure. As shown in  FIG. 5 , the intensity of light received by a photodetector  86  (e.g., photodetector  86   a ) on a particular channel may increase after OUPSR has been provisioned for numerous reasons (e.g., an increase in noise taking place after optical network  10  has been set up and OUPSR has been provisioned). Accordingly, the threshold established in accordance with state machine  200   c  may also decrease over time to account for the increase in detected light intensity. In addition, if an increase in the detected light intensity would otherwise cause a decrease of the threshold below a predetermined minimum value (e.g., zero), the baseline power level established in accordance with state machine  200   c  may also increase to account for the increase in detected light intensity, and the associated threshold may be re-established to approximately its initial value to account for the changing in the baseline power level. Accordingly, due to the varying threshold and baseline power level, the relative LOL level will also increase as the detected power level increases. In accordance with state machine  200   c,  if, at any time while OUPSR is provisioned, the intensity of light received by the photodetector  86  has decreased below the dynamically changing relative LOL level, decision module  88  (or another component of OUPSR device  80 ) may cause a protection switch on switch  84 . Thus, a method in accordance with state machine  200   c  allows for variance in established baseline, threshold, and relative LOL levels to account for when increased noise is coupled into optical network  10 . In addition, the method of state machine  200   c  may, as compared with state machine  200   b,  reduce the frequency at which the baseline power level is re-established, which may improve performance over the method of state machine  200   b.    
         [0044]    A component of optical network  10  may include an interface, logic, memory, and/or other suitable element. An interface receives input, sends output, processes the input and/or output, and/or performs other suitable operation. An interface may comprise hardware and/or software. 
         [0045]    Logic performs the operations of the component, for example, executes instructions to generate output from input. Logic may include hardware, software, and/or other logic. Logic may be encoded in one or more tangible computer readable storage media and may perform operations when executed by a computer. Certain logic, such as a processor, may manage the operation of a component. Examples of a processor include one or more computers, one or more microprocessors, one or more applications, and/or other logic. 
         [0046]    A memory stores information. A memory may comprise one or more tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), and/or other computer-readable medium. 
         [0047]    Modifications, additions, or omissions may be made to optical network  10  without departing from the scope of the invention. The components of optical network  10  may be integrated or separated. Moreover, the operations of optical network  10  may be performed by more, fewer, or other components. Additionally, operations of optical network  10  may be performed using any suitable logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
         [0048]    Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.