Abstract:
A method and apparatus for optical performance monitoring that provides for multi-rate and multi-protocol monitoring includes, identifying a protocol associated with each of a plurality of communication signals using respective data rates extracted therefrom, determining, for each of the plurality of communication signals, a respective bit-error rate (BER), and generating an alarm indicative of BER excursions beyond a protocol appropriate BER threshold level

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of optical communications and, more specifically, to signal monitoring.  
         BACKGROUND OF THE INVENTION  
         [0002]    There is a growing trend toward all-optical re-configurable networks promising higher levels of data-rate and protocol transparency. However, in order to maintain these higher performance levels, signal quality monitoring must be provided at the optical layer. In such systems measurement of optical parameters is critical as it provides vital information regarding the performance of the system. Such information can then be used for diagnosis and repair of an optical network or for performance of optimization actions. One standard measurement of signal quality in optical systems has been the bit error rate (BER) of a system. The BER of a system is affected by two forms of signal degradation, noise and distortion. The measurement of such parameters must be accurate, have a wide range, and be performed in a timely manner so as to provide the necessary information in the shortest amount of time for the appropriate actions.  
           [0003]    Some techniques used for monitoring optical signal quality include spectral analyzing and sampling. The conventional approach to analyzing the optical parameters of a spectrally dependent system is to use an optical spectrum analyzer. These systems are generally based on an optical tool known as a monochromater. Monochromater-based optical spectrum analyzers are typically slow, large in size for most embedded and field applications, and tend to drift with time, giving poor absolute accuracy. The sampling method on the other hand, is the only method that accounts for both noise and distortion and thus comes closest to BER measurement. Unfortunately, previous implementations of sampling methods have been very complicated, slow, and are limited to a single data rate and a single protocol.  
         SUMMARY OF THE INVENTION  
         [0004]    The invention advantageously provides a method and apparatus for optical performance monitoring that provides for multi-rate and multi-protocol monitoring.  
           [0005]    In an embodiment of the invention, a method for multi-protocol and multi-rate optical performance monitoring includes, identifying a protocol associated with each of a plurality of communication signals using respective data rates extracted therefrom, determining, for each of the plurality of communication signals, a respective bit-error rate (BER), and generating an alarm indicative of BER excursions beyond a protocol appropriate BER threshold level.  
           [0006]    In another embodiment of the invention an apparatus for multi-protocol and multi-rate optical signal performance monitoring includes, a plurality of multi-protocol processors (MPPs), for identifying a protocol associated with each of a plurality of communication signals using respective data rates extracted therefrom, and for determining, for each of the plurality of communication signals, a respective bit-error rate (BER), and a controller, for generating an alarm indicative of BER excursions beyond a protocol appropriate threshold level appropriate to the associated protocol. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 depicts a high-level block diagram of a typical central office network node;  
         [0009]    [0009]FIG. 2 depicts a high-level block diagram of an embodiment of an optical performance monitoring module suitable for use in the system  100  of FIG. 1;  
         [0010]    [0010]FIG. 3 depicts a high-level block diagram of an embodiment of a micro-controller suitable for use in the optical performance monitoring module of FIG. 2; and  
         [0011]    [0011]FIG. 4 depicts a flow diagram of a method for multi-protocol and multi-rate optical performance monitoring.  
         [0012]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    The invention advantageously provides a method and apparatus for optical performance monitoring that provides for multi-rate and multi-protocol monitoring.  
         [0014]    [0014]FIG. 1 depicts a high-level block diagram of a typical central office network node  100 . The central office network node  100  of FIG. 1 includes a demultiplexer  150 , a plurality of optical signal taps  110   1 - 110   N  (collectively signal taps  110 ), an optical performance monitoring module (OPMM)  130 , a communications bus  140 , an optical cross connect (OXC) switch  120 , and a demultiplexer  160 . An optical signal is applied to the demultiplexer  150  and is thereby separated into a plurality of wavelengths λ 1 -λ N  (collectively optical signals λ). The optical signals λ are sampled using the optical taps  110 , and the outputs of the optical taps  110  are applied to individual channels of the OPMM  130 . The optical signals λ are subsequently applied as inputs to the OXC switch  120 . Within the OPMM  130 , the sampled optical signals λ are conditioned, as will be explained below, and the bit error rate (BER) information for each of the optical signals λ is extracted in individual channels of the OPMM  130 . Based on the BER information extracted, a micro-controller, or other control device, generates alarms adapted for use as indicators of malfunctions or as control signals to initiate corrective actions to correct for errors in the optical signals evidenced by the BER information obtained. Although the micro-controller of FIG. 2 is depicted as being incorporated within the OPMM  130 , the micro-controller can be advantageously employed as a separate component or as a part of other components in a system. Additionally, the photodetectors can be integrated with the TIA/PA, and the CDR can be combined with the DESER on the same chip. In the central office network node  100  of FIG. 1, the alarms or control signals are applied to the OXC  120  via the communications bus  140 . The output signals from the OXC  120  are recombined by the multiplexer  160 .  
         [0015]    [0015]FIG. 2 depicts a high-level block diagram of an embodiment of an OPMM suitable for use in the central office network node  100  of FIG. 1. The OPMM  130  includes a plurality of input channels, dependent on the number of signals to be processed. The OPMM  130  of FIG. 2 includes a plurality of wideband photodetectors (PD)  215   1 - 215   N  (collectively PD  215 ), a plurality of combination low noise wideband transimpedance/limiting post amplifiers (TIA/PA)  220   1 - 220   N  (collectively TIA/PA  220 ), a plurality of wideband adaptive clock and data recovery (CDR) circuits  230   1 - 230   N  (collectively CDR circuits  230 ), a plurality of deserializers (DESER)  240   1 - 240   N  (collectively DESER  240 ), a plurality of multi-protocol processors (MPP)  250   1 - 250   N  (collectively MPP  250 ), and a micro-controller  260 . Although some of the components of the OPMM  130  are depicted as specific devices, other devices performing substantially the same function as the illustrated devices can be substituted for the corresponding devices illustrated. For example, the photodetectors can be integrated on the same chip as the TIA/PA or wideband phototransistors can be used in place of the photodetectors, and bandpass filters with gain can be used in place of the TIA/PA. It should be noted that any specific device used must provide a band wide enough to accommodate the desired multi-protocol and multi-rate optical channel performance monitoring.  
         [0016]    Each of the optical signals λ applied to the OPMM  130  are converted to electrical signals by a respective wideband PD  215 . Each of the electrical signals is also then amplified by a respective TIA/PA  220  and applied as an input to a corresponding CDR circuit  230 . The CDR circuits  230  automatically lock to the incoming data rate to extract clock rates and thereby synchronize the data of each of the respective electrical signals. The CDR circuits  230  have a short lock time, preferably a few milliseconds, for application in high rate optical systems and are optionally programmable. Each of the CDR circuits  230  provides the data rate information to a respective MPP  250 . The DESER  240  shown in FIG. 2 are optional and are used to interface between the CDR circuits  230  and the respective MPP  250  to convert serial high-speed data into lower speed parallel data (e.g., one OC-48 bit signal converted into four, OC-12 bit signals) if necessary.  
         [0017]    The MPP  250  identify the data protocol by comparing the rate information provided by the CDR circuits  230  to a stored data rate protocol table as depicted in Table 1, which follows:  
                             TABLE 1                       Data Rate in Mb/s   Corresponding Protocol                                51.84   SONET (OC-1)       155.52   SONET (OC-3)       200   ESCON       622.08   SONET (OC-12)       1062   Fibre Channel (FC)       1250   Gigabit Ethernet (GbE)       2125   2 × Fibre Channel       2,488.32   SONET (OC-48)       9,953.28   SONET (OC-192)       10,000   10 × Gigabit Ethernet (GbE)       10,664.23   SONET (OC-192) w/FEC                  
 
         [0018]    Table 1 is provided merely for exemplary purposes and it would be appreciated by those skilled in the art that the present invention can be advantageously employed implementing various other protocols. In situations wherein the rates are very close (e.g., OC192 and 10 GbE), a method based on network statistics is used. In this case, the CDR assumes the most probable protocol first (e.g. OC192), followed by the next until the correct protocol is identified by the MPP  250 .  
         [0019]    Once the protocol is successfully identified, the MPP  250  identify the overhead error bits or BER for each conditioned optical signal from the corresponding CDR circuit  230  or DESER  240  by comparing the data rate of the input, conditioned optical signal to the identified protocol in the stored data rate protocol table. The MPP  250  then communicates the BER information to the micro-controller  260  via the control bus  270 . The micro-controller  260  receives the BER information identified by each of the MPP  250  for each conditioned optical signal and compares the identified BER to stored thresholds maintained in a memory of the micro-controller  260 . The stored thresholds indicate the acceptable maximums and minimums of BER for particular protocols and, if any of the identified BER from the MPP  250  for each conditioned optical signal do not conform to those stored threshold levels, the micro-controller  260  generates an alarm for the appropriate channel(s).  
         [0020]    The alarms are communicated via the plurality of output channels  140   1 - 140   N  (collectively output channels  140 ). The alarms generated by the micro-controller  260  can manifest in the form of an alarm to a user or service provider to indicate the need for repair or a control signal to activate automatic protection switching (i.e., trigger an OXC to switch to an alternate signal channel for further transmission). Additionally, the control signal could be used to optimize system components through feedback circuit (e.g., apply a feedback signal to adjust a tunable/programmable network element settings such as a dispersion compensation module, or optical amplifier). Even further, the control signal generated by the micro-controller  260  could simply be fed to a channel monitor for ultimate display on a display unit. The aforementioned applications of the control signal from the micro-controller  260  are only exemplary and can be used singly or in any combination. Other and various applications for the control signal can be imagined by those skilled in the art and should be considered as included in the present invention.  
         [0021]    [0021]FIG. 3 depicts a high-level block diagram of an embodiment of a micro-controller suitable for use in the OPMM  130  of FIG. 2. The micro-controller  260  of FIG. 3 comprises a processor  310  as well as a memory  320  for storing the algorithms and control programs. The processor  310  cooperates with conventional support circuitry  330  such as power supplies, clock circuits, cache memory and the like as well as circuits that assist in executing the software routines stored in the memory  320 . As such, it is contemplated that some of the process steps discussed herein as software processes may be implemented within hardware, for example, as circuitry that cooperates with the processor  310  to perform various steps. The micro-controller  260  also contains input-output circuitry  340  that forms an interface between the various functional elements communicating with the micro-controller  260 . For example, in the embodiment of FIG. 2, the micro-controller  160  communicates with the MPP  250  and the CDR circuits  230  via the control bus  270  and dispatches the generated alarms via output channels  140 .  
         [0022]    Although the micro-controller  260  of FIG. 3 is depicted as a general-purpose computer that is programmed to perform various control functions in accordance with the present invention, the invention can be implemented in hardware, for example, as an application specified integrated circuit (ASIC). As such, the process steps described herein are intended to be broadly interpreted as being equivalently performed by software, hardware, or a combination thereof.  
         [0023]    [0023]FIG. 4 depicts a flow diagram of one embodiment of a method  400  for achieving multi-protocol and multi-rate optical performance monitoring. The method  400  processes the signals tapped from an optical signal source by identifying the protocol of the optical signals, extracting error information, and producing an alarm in response to any extracted error information, the alarm adapted to indicate an error within an optical signal. Although the method  400  will be described within the context of generating an alarm in response to error information, it will be appreciated by those skilled in the art that the subject invention may be advantageously employed in various methods wherein, for example, an alarm generated in response to error information is not only used to indicate an error with an optical signal, but also to initiate corrective actions within a system.  
         [0024]    The method  400  is entered at step  402 , when an optical signal from a tap  110  is applied as an input to an OPMM  130 .  
         [0025]    At step  404 , the optical signal from the tap coupled as an input to the OPMM is converted to an electrical signal by a photodetector  215 .  
         [0026]    At step  406 , the electrical signal converted by the photodetector is amplified by a combination low noise, wideband, transimpedance/limiting post amplifier  220 .  
         [0027]    At step  408 , the amplified electrical signal is applied as an input to a CDR circuit  230 . The CDR circuit automatically locks to the incoming data rate to extract clock rates and synchronizes the data. The CDR circuit then provides the data rate information to a MPP  250  or, optionally, to a DESER  240 .  
         [0028]    At step  408 - 2 , the data rate information from the CDR is optionally input to a DESER  240 . The DESER  240  converts serial high-speed data into lower speed parallel data if necessary, before the data rate information is processed by the MPP  250 .  
         [0029]    At step  410 , a MPP  250  identifies the data protocol by comparing the rate information provided by the CDR circuit  230  to a stored data rate protocol table as depicted in Table 1 above or as described above, by using network statistics and protocol probability. As mentioned, Table 1 is provided merely for exemplary purposes and it would be appreciated by those skilled in the art that the present invention can be advantageously employed implementing various other protocols.  
         [0030]    At step  412 , the MPP  250  identifies the overhead error bits (BER) by comparing the data rate of the input, conditioned optical signal to the identified protocol in the stored data rate protocol table. The MPP  250  then communicates the BER information to a micro-controller.  
         [0031]    At step  414 , the micro-controller  260  receives the BER information identified by the MPP  250  and compares the identified BER to stored thresholds maintained in a memory of the micro-controller  260 . The stored thresholds indicate the acceptable maximums and minimums of BER for particular protocols, and if any of the identified BER from the MPP  250  do not conform to those stored threshold levels, the micro-controller  260  generates an alarm for the appropriate channels. The alarm can subsequently be sent to a user or service provider to indicate the error or indicate a need for service or repair.  
         [0032]    The above-described method  400  of FIG. 4 provides a general methodology according to the subject invention. As previously noted, although the method  400  of FIG. 4 is described within the context of generating an alarm in response to error information, it will be appreciated by those skilled in the art that the subject invention may be advantageously employed in methods wherein the control signal generated in response to error information is not only used to generate an alarm, but also to initiate corrective actions within a system.  
         [0033]    While the forgoing is directed to specific embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. As such, the appropriate scope of the invention is to be determined according to the claims, which follow.