Abstract:
Vulnerability of an optical network to channel impairments or the like, is addressed by utilizing real-time monitoring and control of prescribed optical channel impairments. The impairments are compensated for by employing an optimization process in the optical network such that the optical signals from the source or sources of the impairments are controllably adjusted at any particular node in the network. The optical signals are attenuated more or less at the source node of the associated optical channel in order to optimize performance of the corresponding optical channel in the network. A variable optical attenuator (VOA) is used at the λ laser source of optical channel having the impairment to obtain the attenuation. The optical signal impairment is measured at a receiving node and the source node of the associated optical channel is determined. Then, a control message is transmitted to the identified source node indicating that a VOA associated with the corresponding optical channel λ laser source is to be adjusted to insert more or less attenuation as the case may be. This process is iterated until the corresponding optical channel yields optimum performance for the impairment being measured. A VOA in a remote node associated with the λ laser source of the associated optical channel is first adjusted. Then, a VOA in the local node associated with the optical channel being monitored is adjusted to further optimize the prescribed metric of the optical channel being monitored. This adjustment is iterated until the performance of the associated channel is optimized.

Description:
TECHNICAL FIELD 
     This invention relates to optical transmission systems and, more particularly, to performance optimization of optical channels in optical transmission systems. 
     BACKGROUND OF THE INVENTION 
     Optical transmission systems and, especially, those employing Wavelength Division Multiplexing (WDM) are desirable because they provide extremely wide bandwidths for communications channels. Each communications channel in the WDM transmission system carries a plurality of optical channels, i.e., wavelengths, on a single optical fiber and single optical repeater. However, there is a trade off between providing wider bandwidth communications channels, with their lower cost of transport, and their vulnerability to channel impairments or the like that corrupt the quality of transmission. Therefore, the ability of an optical transmission system, for example, those employing WDM, to minimize the effects of channel impairments and other signal corrupting mechanisms on the optical communications services is extremely important. 
     SUMMARY OF THE INVENTION 
     Vulnerability of an optical network to channel impairments or the like, is addressed by utilizing real-time monitoring and control of one or more prescribed optical channel impairments. The one or more impairments are compensated for by employing an optimization process in the optical network such that the optical signals from the source or sources of the impairments are controllably adjusted at any particular node in the network. In a specific embodiment of the invention, the optical signals are attenuated more or less at the source node of the associated optical channel, e.g., wavelength λ, in order to optimize performance of the corresponding optical channel in the network. This is realized by employing a variable optical attenuator at the λ laser source of optical channel having the impairment. 
     More specifically, in a particular embodiment of the invention, the optical signal impairment is measured at a receiving node and the source node of the associated optical channel is determined. Then, a control message is transmitted to the identified source node indicating that a variable optical attenuator associated with the corresponding optical channel light source, e.g., λ laser source, is to be adjusted to insert more or less attenuation as the case may be. This measurement and adjustment process is iterated until the corresponding optical channel yields optimum performance for the impairment being measured. In this embodiment of the invention, the control messages are transmitted in an optical supervisory channel. 
     In another embodiment of the invention, a VOA in a remote node associated with the λ laser source of the associated optical channel is first adjusted. Thereafter, if necessary, a VOA in the local node associated with the optical channel being monitored is adjusted to further optimize the prescribed metric of the optical channel being monitored. This adjustment of the local VOA is iterated until the performance of the associated channel is optimized. 
     In still another embodiment of the invention, either a VOA in a remote node associated the λ laser source of the associated optical channel adjusted or a VOA at a local node associated with the received prescribed optical channel is adjusted or both VOAs are adjusted depending on an evaluation of the prescribed metric of the prescribed optical channel to optimize the prescribed metric of the prescribed optical channel. 
     In yet another embodiment of the invention a VOA in a remote node associated the λ laser source of the associated optical channel adjusted and a VOA at a local node associated with the received prescribed optical channel are substantially simultaneously adjusted to optimize the prescribed metric of the prescribed optical channel. 
     A technical advantage of the invention is that the transmission performance of the one or more optical channels is optimizes in substantially real time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 illustrates, in simplified block form, details of an optical ring transmission system; 
     FIG. 2 illustrates, in simplified block diagram form, details of an optical node, including an embodiment of the invention, that may be employed in the system of FIG. 1; 
     FIG. 3 shows, in simplified block diagram form details of a terminal equipment unit that may be employed in the optical nodes of FIG.  2  and FIG. 6; 
     FIG. 4 shows, in simplified block diagram form details of another terminal equipment unit that may be employed in the optical nodes of FIG.  2  and FIG. 6; 
     FIG. 5 is a flow chart illustrating the steps used in implementing optical channel optimization in the embodiment of the invention employing the optical node of FIG. 2; 
     FIG. 6 illustrates, in simplified block diagram form, details of another optical node, including an embodiment of the invention, that may be employed in the system of FIG. 1; 
     FIG. 7 is a flow chart illustrating the steps used in implementing one process for optical channel optimization in the embodiment of the invention employing the optical node of FIG. 6; 
     FIG. 8 is a flow chart illustrating the steps used in implementing another process for optical channel optimization in the embodiment of the invention employing the optical node of FIG. 6; and 
     FIG. 9 is a flow chart illustrating the steps used in implementing yet another process for optical channel optimization in the embodiment of the invention employing the optical node of FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows, in simplified form, bi-directional optical transmission system  100 , which is connected in a ring configuration. For brevity and clarity of exposition optical transmission system  100  is shown as including only optical nodes  101  through  104 , each incorporating an embodiment of the invention. Optical nodes  101  through  104  are interconnected by bi-directional optical transmission medium  105 , which for brevity and clarity of exposition, in this example, transport active service transmission capacity. In this example, optical transmission medium  105  is comprised of optical fibers  106  and  107 . It should be noted that bidirectional optical transmission system  100  typically would employ either a two (2) optical fiber or a four (4) optical fiber system. In a preferred embodiment of the invention, transmission medium  105  includes two (2) optical fibers, fiber  106  and fiber  107  that are employed for transporting optical channels, i.e., wavelengths, and also protection optical channels. The optical transmission system  100  could transport, for example, 8, 16, 32, 40, 80, etc. communications channels, i.e., wavelengths. It should also be noted that in either the two (2) optical fiber arrangement or the four (4) optical fiber arrangement a separate so-called telemetry, e.g., supervisory, channel could be employed as a maintenance channel, in addition to the communications channels. Thus, in an eight (8) channel system, nine (9) channels are transported, in a 16 channel system, 17 channels are transported and so on. The supervisory channel provides maintenance support of the optical network including optical nodes  102  through  104 , as well as, optimization information for use in nodes  101  though  104  to optimize transmission over the optical wavelengths in optical transmission system  100 . Use of the supervisory channel in transporting the optimization information in order to optimize of the optical wavelengths in optical transmission system  100  is described below. Additionally, the maintenance information, as well as, he optimization information could be transported in-band in the channel overhead. Indeed, so long as the desired information is appropriating supplied it does not really matter what medium is employed to transport it, in-band, out-of-band, telemetry channel, supervisory channel, channel overhead, or the like. Two (2) and four (4) optical fiber transmission systems are known. 
     FIG. 2 illustrates, in simplified block diagram form, details of individual ones of optical nodes  101 - 104 , each including an embodiment of the invention, that may be employed in the system of FIG.  1 . At the outset it is noted that for simplicity and clarity of exposition this embodiment will be described in terms of one optical channel, i.e., wavelength, for each direction of transmission. However, it will be apparent that the invention is equally applicable to a plurality of optical channels, i.e., wavelengths, being received and transmitted to and from the optical node. Specifically, an optical signal received from the east via optical fiber  106  is supplied to optical demultiplexer (DMUX)  201 . The received optical signal is a wave division multiplexed (WDM) optical signal and typically includes a set of N wavelengths (λs), wherein N=0, 1, . . . N, and an optical supervisory channel. Such WDM optical signals including an optical supervisory channel are well known in the art. A demultiplexed λ of the received optical signal from DEMUX  201  is supplied via optical path  202  to terminal equipment  203 , while the demultiplexed optical supervisory channel is supplied via optical path  204  to controller  205 . A multiplexed optical signal to be supplied as an output to the east is supplied from optical multiplexer (MUX)  209  to east bound optical fiber  107 . Similarly, an optical signal received from the west via optical fiber  107  is supplied to optical demultiplexer (DMUX)  206 . Again, the received optical signal is a wave division multiplexed (WDM) optical signal and typically includes a set of N wavelengths (λs), wherein N=0, 1, . . . and an optical supervisory channel. A demultiplexed x of the received optical signal is supplied from DMUX  206  via optical path  207  to terminal equipment  203 , while the demultiplexed optical supervisory channel is supplied via optical path  208  to controller  205 . A multiplexed optical signal to be supplied as an output to the west is supplied from optical multiplexer (MUX)  210  to west bound optical fiber  106 . 
     User unit  211  receives detected received signals from terminal equipment  203  and supplies signals to be transported over the optical network to terminal equipment  203 . Details of terminal equipment  203  are shown in FIGS. 3 and 4 and described below. Terminal equipment also supplies versions of the received optical signals to monitor  212 . Monitor  212  includes apparatus for obtaining measures of prescribed signal transmission metrics, for example, bit-error-rate (BER), signal-to-noise ratio, cross talk, or the like. Arrangements for obtaining measurement of such metrics are well known in the art. For example, cross talk may be evaluated by employing an optical spectrum analyzer to observe a desired optical channel, i.e., wavelength, and an adjacent optical channel, i.e., wavelength. The results of these measurements are supplied from monitor  212  to controller  205  where they are included in a control message to be included in a supervisory channel for transmission to a node including the source of the corresponding optical channel that is being monitored. The optical supervisory channel including the resulting control message is supplied via path  213  to MUX  209  where it is multiplexed with other optical channels to be supplied to east bound optical fiber  107 . Similarly, the optical supervisory channel including the resulting control message is supplied via path  214  to MUX  210  where it is multiplexed with other optical channels to be supplied to west bound optical fiber  106 . The supervisory channel including the control message of the optical channel being monitored is demultiplexed at a node including the source of the optical channel. Utilizing the instant node for purposes of explanation, the incoming WDM optical signal including an optical supervisory channel from the east is demultiplexed in DEMUX  201  and the control message is supplied via path  204  to controller  205 . Similarly, an incoming optical WDM optical signal including an optical supervisory channel from the west is demultiplexed in DEMUX  206  and the control message is supplied via path  208  to controller  205 . In response to the supplied control messages controller  205  supplies corresponding control messages to each of variable optical attenuators  215  and  216 . Variable optical attenuators  215  and  216  are adjusted accordingly and, consequently, optical channels signals supplied from terminal equipment  203  are attenuated more or less as indicated by the supplied control messages. A corresponding adjusted optical channel is supplied from VOA  215  to multiplexer (MUX)  210  to be multiplexed with the optical supervisory channel including the VOA control message from controller  205  for transmission in the west bound direction over optical fiber  106 . Similarly, a corresponding adjusted optical channel is supplied from VOA  216  to multiplexer (MUX)  209  to be multiplexed with the optical supervisory channel including the VOA control message from controller  205  for transmission in the east bound direction over optical fiber  107 . 
     The above described performance optimization process of monitoring a particular optical channel, generating a VOA control message, transmitting the control message, in this example, over the optical supervisory channel to a source node including the source of the optical channel being monitored, and adjusting the VOA at the source node is iterated until the performance of the optical channel being monitored has been optimized. Indeed, the transmission performance of the one or more optical channels is thereby optimized in substantially real time. This performance optimization process for the embodiment shown in FIG. 2 is shown in FIG.  5  and described below. 
     FIG. 3 shows, in simplified block diagram form details of a terminal equipment unit  203  that may be employed in the optical nodes of FIG.  2  and FIG.  6 . Specifically, shown are detectors  301  and  303  that are supplied optical signals from user unit  211 . These optical signals are a prescribed wavelength employed by user unit  211 . Detectors  301  and  303  convert the optical signals from user unit  211  into electric signals. The electrical signals from detectors  301  and  303 , in turn are supplied to drive lasers  302  and  304 , respectively, to yield appropriately modulated optical signals at the optical channel wave length λ v that are supplied via paths  217  and  218  to VOA  215  and VOA  216 , respectively. Also shown, are detectors  303  and  304  that detect optical signals supplied via paths  207  and  208 , respectively, at the optical channel λ to yield electrical versions thereof. These detected electrical signals from detectors  303  and  304  are supplied to drive lasers  306  and  308 , respectively, and are also supplied via path  220  to monitor  212 . The optical signal outputs from lasers  306  and  308  are at a prescribed wavelength expected by user unit  211  and are supplied to user unit  211  and via path  219  to monitor  212 . 
     FIG. 4 shows, in simplified block diagram form details of another terminal equipment unit  203  that may be employed in the optical nodes of FIG.  2  and FIG.  6 . Equipment elements that are the same as those shown and described above in relationship to FIG. 3 have been similarly numbered and will not be described in detail again. The differences being the equipment arrangement shown in FIG.  3  and that shown in FIG. 4 is that the optical channel signals supplied via paths  202  and  207  are supplied directly via path  220  to monitor  212 , and the electrical signal outputs from detectors  305  and  307  are not shown as being supplied to monitor  212 . This allows for monitoring the optical channel signals directly in optical form. This may be done, in one example, by employing an optical spectrum analyzer or other optical metric measuring equipment. It should be noted, however, that the electrical signal outputs form detectors  305  and  307  may also be supplied to monitor  212  in other implementations. 
     FIG. 5 is a flow chart illustrating the steps used in implementing optical channel optimization in the embodiment of the invention employing the optical node of FIG.  2 . Specifically, the performance monitoring process of the optical channels is started in step  501 . If should be noted that the monitoring process may be initiated by a user via user unit  211  (FIG. 1) supplying an appropriate initiation signal to controller  205  or automatically in response to detection of some performance metric being outside acceptable criteria, for example, some characteristic limit or threshold value, that could include upper and lower limits, or the like. Step  502  initializes to an optical channel, i.e., wavelength, to be performance monitored, i.e., evaluated. In this example, the wavelength is set to λ=1. Thereafter, step  503  evaluates a prescribed performance metric of the wavelength. As indicated, the metric being evaluated may be bit-error-rate (BER), signal-to-noise (S/N) ratio, cross talk or the like. It is noted that if the predetermined metric being evaluated is cross talk that an optical spectrum analyzer may be advantageously employed in monitor  212  (FIG.  2 ), and terminal equipment  203  as shown in FIG. 3 would be employed to supply the incoming optical channels, i.e., wavelengths λ, to monitor  212 . By way of an example, cross talk is measured by employing an optical spectrum analyzer (OSA), which yields a measurement of the average power spectrum of an incoming optical channel. The spectral region of interest is selected by the MUX and DEMUX filters at the remote node at which the optical originated. These filters have a finite bandwidth, chosen to encompass the entire spectral range that carries the optical channel being evaluated. It is these filters that allow transmission of the undesired cross talk that is manifested by a perturbation in the measured optical spectrum. Usually, the largest contributors of cross talk are caused by optical channel sources adjacent to the optical source for the optical channel under evaluation. However, it is possible that other, nearby optical sources may also contribute cross talk. In such an instance, the measured spectral region can be widened to capture such nearby optical sources. Then, control is passed to step  504  that tests to determine whether the predetermined metric is within acceptable criteria. If the test result in step  504  is YES, control is transferred to step  505 . If the test result in step  504  is NO, step  506  determines the source node including the optical channel, i.e., λ laser source, being monitored. This is readily realized by employing a map, typically stored in controller  205  (FIG.  2 ), of the originating and terminating nodes of the optical channel, i.e., wavelength λ, or optical channels, i.e., wavelengths λ N , being evaluated. Step  507  causes a message to be sent to the determined source node, in this example, via a control message in an optical supervisory channel, in order to adjust a VOA associated with the λ laser source. Then, step  508  determines whether the associated VOA has been adjusted. This may be realized by the node including the λ laser source sending an acknowledge message via the optical supervisory channel to the node that is monitoring the performance of the optical channel. If the test result in step  508  is NO, control is returned to step  507  and steps  507  and  508  are iterated until step  508  yields a YES result and an acknowledgment that the associated VOA has been adjusted. Upon step  508  yielding a YES result, step  509  evaluates the predetermined metric being monitored. Then, step  510  tests to determine whether the metric is within acceptable criteria. If the test result in step  510  is NO, control is returned to step  507  and appropriate ones of steps  507  through  510  are iterated until step  510  yields a YES result. Upon step  510  yielding a YES result, control is also transferred to step  505 . Step  505  tests to determine if the λ=N, i.e., whether the last λ in a set has been evaluated. If the test result in step  505  is NO, step  511  sets λ=λ+1 and control is returned to step  503 . Thereafter, appropriate ones of steps  503  through  511  are iterated until step  505  yields a YES result. Then, the process is ended in step  512 . In this manner the optimization process effectively optimizes the one or more optical channels in essentially real time. 
     FIG. 6 illustrates, in simplified block diagram form, details of another optical node, including an embodiment of the invention, that may be employed in the system of FIG.  1 . The elements of the optical node of FIG. 6 that are identical to those of the optical node of FIG. 2 have been similarly numbered and will not be described again. The differences between the optical node of FIG.  2  and the optical node of FIG. 6 are the use of so-called local VOA  601  and so-called local VOA  602  in the incoming optical paths  202  and  207 , respectively. VOA  601  and VOA  602  are controlled in response to appropriate control messages from controller  205 . 
     FIG. 7 is a flow chart illustrating the steps used in one process for implementing optical channel optimization in the embodiment of the invention employing the optical node of FIG.  6 . Specifically, the performance monitoring process of the optical channels is started in step  701 . If should be noted that the monitoring process may be initiated by a user via user unit  211  (FIG. 1) supplying an appropriate initiation signal to controller  205  or automatically in response to detection of some performance metric being outside acceptable criteria. Step  702  initializes to an optical channel, i.e., wavelength, to be performance monitored, i.e., evaluated. In this example the wavelength is set to λ=1. Thereafter, step  703  evaluates a prescribed performance metric of the wavelength, as described above in relationship to FIG.  5 . Step  704  tests to determine whether the predetermined metric is within acceptable criteria. If the test result in step  704  is YES, control is transferred to step  705 . If the test result in step  704  is NO, step  706  determines the source node including the optical channel, i.e., λ laser source, being monitored, as described above in relationship to FIG.  5 . Step  707  causes a message to be sent to the determined source node, in this example, via a control message in an optical supervisory channel, in order to adjust a VOA associated with the λ laser source at a remote node. Then, step  708  determines whether the associated VOA has been adjusted. This may be realized by the node including the λ laser source sending an acknowledge message via the optical supervisory channel to the node that is monitoring the performance of the optical channel. If the test result in step  708  is NO, control is returned to step  707  and steps  707  and  708  are iterated until step  708  yields a YES result and an acknowledgment that the associated remote VOA has been adjusted. It should be noted that the adjustment of the remote VOA should significantly optimize the predetermined metric being monitored. Upon step  708  yielding a YES result, step  709  evaluates the predetermined metric being monitored. Then, step  710  tests to determine whether the predetermined metric is within acceptable criteria. If the test result in step  710  is NO, control is returned is passed to step  711  which causes a control message to be sent to a local VOA, for example, VOA  601 , associated with the k source being monitored. Then, step  712  tests to determine if the local VOA has been adjusted. If the test result in step  712  is NO, control is returned to step  711  and steps  711  and  712  are iterated until step  712  yields a YES result. Thereafter, control is returned to step  709  and steps  709  through  712  are iterated until step  710  yields a YES result. Upon step  710  yielding a YES result, control is also transferred to step  705 . Step  705  tests to determine if the λ=N, i.e., whether last λ in a set has been evaluated. If the test result in step  705  is NO, step  713  sets λ=λ+1 and control is returned to step  703 . Thereafter, appropriate ones of steps  703  through  713  are iterated until step  705  yields a YES result. Then, the process is ended in step  714 . 
     Thus, it is seen that in the embodiment of FIG. 6, an adjustment of the remote VOA associated with the λ laser source being monitored is first made. Thereafter, if necessary, a local VOA associated with the λ laser source being monitored is adjusted until the predetermined metric being monitored is optimized. In this manner the optimization process effectively optimizes the one or more optical channels in essentially real time. 
     It should be noted that although in the process described in FIG. 7, the remote VOA is adjusted first and the local VOA is adjusted therefore, it will be apparent that the local VOA could equally be adjusted first and the remote VOA thereafter. Indeed, any desired adjustment scheme could be employed. For example, adjustments could alternate between the local and remote VOAs. 
     FIG. 8 is a flow chart illustrating the steps used in another process for implementing optical channel optimization in the embodiment of the invention employing the optical node of FIG.  6 . Specifically, the performance monitoring process of the optical channels is started in step  801 . If should be noted that the monitoring process may be initiated by a user via user unit  211  (FIG. 1) supplying an appropriate initiation signal to controller  205  or automatically in response to detection of some performance metric being outside acceptable criteria. Step  802  initializes to an optical channel, i.e., wavelength, to be performance monitored, i.e., evaluated. In this example the wavelength is set to λ=1. Thereafter, step  803  evaluates a prescribed performance metric of the wavelength, as described above in relationship to FIG.  5 . Step  804  tests to determine whether the predetermined metric is within acceptable criteria. If the test result in step  804  is YES, control is transferred to step  805 . If the test result in step  804  is NO, step  806  determines it the metric being monitored is substantially acceptable. That is, step  806  determines whether or not the metric is within a prescribed boundary for the metric being monitored. In effect, this step  806  determines, in effect, whether a significant or, merely, a finer adjustment is required to optimize the optical channel. If the test result in step  806  is YES only a trimming up type adjust may be required and control is transferred to step  812 . If the test result in step  806  is NO, a more significant adjustment may be required and control is transferred to step  807 . Step  807  determines the source node including the optical channel, i.e., λ laser source, being monitored, as described above in relationship to FIG.  5 . Step  808  causes a message to be sent to the determined source node, in this example, via a control message in an optical supervisory channel, in order to adjust a VOA associated with the λ laser source at a remote node. Then, step  809  determines whether the associated VOA has been adjusted. This may be realized by the node including the λ laser source sending an acknowledge message via the optical supervisory channel to the node that is monitoring the performance of the optical channel. If the test result in step  809  is NO, control is returned to step  808  and steps  808  and  809  are iterated until step  809  yields a YES result and an acknowledgment that the associated remote VOA has been adjusted. It should be noted that the adjustment of the remote VOA should significantly optimize the prescribed metric being monitored. Upon step  809  yielding a YES result, step  810  evaluates the prescribed metric being monitored. Then, step  811  tests to determine whether the prescribed metric is within acceptable criteria. If the test result in step  811  is NO, control is returned is passed to step  812  which causes a control message to be sent to a local VOA, for example, VOA  601 , associated with the λ source being monitored. Then, step  813  tests to determine if the local VOA has been adjusted. If the test result in step  813  is NO, control is returned to step  812  and steps  813  and  813  are iterated until step  813  yields a YES result. Thereafter, control is returned to step  810  and steps  810  through  813  are iterated until step  811  yields a YES result. Upon step  811  yielding a YES result, control is also transferred to step  805 . Step  805  tests to determine if the λ=N, i.e., whether last λ in a set has been evaluated. If the test result in step  805  is NO, step  814  sets λ=λ+1 and control is returned to step  803 . Thereafter, appropriate ones of steps  803  through  814  are iterated until step  805  yields a YES result. Then, the process is ended in step  815 . 
     Thus, it is seen that in the embodiment of FIG. 6, the process illustrated in FIG. 8 may cause an adjustment to be first made of the remote VOA associated with the λ laser source being monitored and thereafter, if necessary, a local VOA associated with the λ laser source being monitored is adjusted until the prescribed metric being monitored is optimized. Alternatively, under certain condition it may only be necessary to adjust only one of the VOAs, for example, only the local VOA may be adjusted or only the remote VOA may be adjusted. In this manner the optimization process effectively optimizes the one or more optical channels in essentially real time. 
     FIG. 9 is a flow chart illustrating the steps used in yet another process for implementing optical channel optimization in the embodiment of the invention employing the optical node of FIG.  6 . Specifically, the performance monitoring process of the optical channels is started in step  901 . If should be noted that the monitoring process may be initiated by a user via user unit  211  (FIG. 1) supplying an appropriate initiation signal to controller  205  or automatically in response to detection of some performance metric being outside acceptable criteria. Step  902  initializes to an optical channel, i.e., wavelength, to be performance monitored, i.e., evaluated. In this example the wavelength is set to λ=1. Thereafter, step  903  evaluates a prescribed performance metric of the wavelength, as described above in relationship to FIG.  5 . Step  904  tests to determine whether the prescribed metric is within acceptable criteria. If the test result in step  904  is YES, control is transferred to step  905 . If the test result in step  904  is NO, step  906  determines the source node including the optical channel, i.e., λ laser source, being monitored, as described above in relationship to FIG.  5 . Step  907  causes a message to be sent to the determined source node, in this example, via a control message in an optical supervisory channel, in order to adjust a VOA associated with the λ laser source at a remote nod and a message to be sent to adjust a local VOA associated with the optical channel being monitored. Thus, it is seen that in this embodiment the remote VOA and the local VOA are adjusted simultaneously. Then, step  908  determines whether the associated VOAs have been adjusted. This may be realized by the node including the λ laser source sending an acknowledge message via the optical supervisory channel to the node that is monitoring the performance of the optical channel. The node including the local VOA makes its own determination if the local VOA has been adjusted. If the test result in step  908  is NO, control is returned to step  907  and steps  907  and  908  are iterated until step  908  yields a YES result and acknowledgments that the associated VOAs have been adjusted. It should be noted that the adjustment of the remote VOA should significantly optimize the prescribed metric being monitored. Upon step  908  yielding a YES result, step  909  evaluates the prescribed metric being monitored. Then, step  910  tests to determine whether the prescribed metric is within acceptable criteria. If the test result in step  910  is NO, control is returned is returned to step  907  and steps  907  through  910  are iterated until step  910  yields a YES result. Upon step  910  yielding a YES result, control is also transferred to step  905 . Step  905  tests to determine if the λ=N, i.e., whether last λ in a set has been evaluated. If the test result in step  05  is NO, step  911  sets λ=λ+1 and control is returned to step  903 . Thereafter, appropriate ones of steps  903  through  911  are iterated until step  905  yields a YES result. Then, the process is ended in step  912 . 
     Thus, it is seen that in the embodiment of FIG. 6, via the process illustrated in FIG. 9, both the remote VOA and local VOA are adjusted simultaneously. In this manner the optimization process effectively optimizes the one or more optical channels in essentially real time. 
     It should be further noted, that if the simultaneous adjustment of both the remote VOA and local VOA does not yield a desired optimization of the optical channel one or more of the processes described above in relationship with FIGS. 5,  7  and  8  made be utilized, as desired. For example, after the simultaneous adjustment of the remote and local VOAs, if it were desirable only to further adjust the remote VOA, steps  507  through  510  of FIG. 5 could be used. Similarly, if it were desirable only to further adjust the local VOA, steps  709  through  712  of FIG. 7 could be used. Finally, if it were desirable to further adjust the remote VOA, the local VOA or both VOAs, steps  806  though  813  of FIG. 8 could be used. 
     The above-described embodiments are, of course, merely illustrative of the principles of the invention. Indeed, numerous other methods or apparatus may be devised by those skilled in the art without departing from the spirit and scope of the invention. For example, the particular order that the local and remote VOAs associated with a particular optical channel are adjusted may vary from application to application.