Abstract:
To automate fiber connectivity management in optical systems, a dedicated low bit-rate communications channel unique to each fiber connection in an optical system is provided. The dedicated communications channel simplifies fiber connectivity management by supporting the exchange of port identification information from one optical component to another after which processing determines if the specific connection is a desired association. The dedicated communications channel supports optical interconnection surveillance for all card-to-card optical connections within a group of related cards or within an optical network link. Automating fiber connectivity management in this manner will enhance future products by simplifying the fiber connection validation process and ensuring that any specific connection between optical components is the required association. This will be particularly useful in complex optical environments with many interconnected devices and where troubleshooting faulty connections would be time-consuming and, therefore, very costly.

Description:
FIELD OF THE INVENTION 
     This invention relates to optical connectivity management and, more particularly, to a method and apparatus for verifying optical connections in an optical system. 
     BACKGROUND OF THE INVENTION 
     The demand for increased network capacity brought on largely by the advent of the information age has led to the introduction of high bit rate optical links employing a technology known as dense wavelength division multiplexing (DWDM). Carriers are always looking to maximize their network capacity and multiplex as many wavelength channels as possible onto a single optical fiber. 
     In the future, bandwidth-hungry carriers will continue to demand increased transport capabilities to handle the explosion in the volume of digital traffic. At the transport level, this will likely be accommodated through the use of DWDM with 100 or more wavelengths on a single optical fiber, and with each wavelength carrying a high bit rate channel. If a large number of such multi-wavelength fibers pass through a given network element node, the equipment at the node will be required to support such capacities. 
     Fiber optic network element nodes are presently configured for different networking topologies as required to achieve the cost containment, reliability and bandwidth management objectives of the specific application. Supported configurations include point-to-point terminals, survivable ring nodes, linear add/drop multiplexers (ADMs), optical hubs, regenerators and optical amplifiers. To function properly, individual pieces of equipment must be installed correctly and with correct optical interconnections between respective components. In addition, to address changing needs over time, equipment within a network element node may periodically need to be upgraded to a more advanced technology or reconfigured to support increased system capacity requirements. 
     Network element architecture support s a variety of network topologies using a common “bay/shelf” equipment layout as shown in FIG.  1 . As can be seen, a network element bay (node) is typically built from modular components: shelves and plug-in circuit packs that make it easy to deploy the required capacity and then expand later as needed. The desired topology can be physically mapped into a specific arrangement of circuit packs (or cards) within the shelves of a network element bay. This modular architecture makes it easy to configure each network element for the specific requirements of each deployment site without over-provisioning, while allowing easy upgrades and expansions as new capacity is needed and new capabilities are developed. Therefore, upgrades from one type of network element to another can be easily accomplished without the need for replacing entire bays or shelves. 
     Network element installations, upgrades and reconfigurations can generally be accomplished by the addition or re-arrangement of individual circuit packs. Upgrades in this manner are common to optical amplifier products, for example, and target an increase in optical power which translates (in most cases) to an increase in the number of wavelengths that a given system can accommodate. 
     Specifically, in the case of optical amplifier products, the number of wavelengths that can be supported by a family of amplifier circuit packs generally depends on the DWDM network topology. For example, at line terminating equipment (LTE) sites where wavelengths are usually added to or dropped from the main traffic flow, a simple and low cost approach of optical amplification is to use a dual amplifier configuration as shown in  FIG. 2   a . Here, an amplifier group consists of a dual amplifier card connected to a dual optical service channel (OSC) card. The dual nature of these circuit cards (or packs) arises because of the inherent bi-directional flow of traffic (data) in transmission networks. 
     In  FIG. 2   b  an upgraded configuration is shown wherein a booster amplifier has been added to each output of the dual amplifier to launch more optical power in order to effect an increase in the number of wavelengths the system can accommodate. In general, different power (i.e. different number of pump lasers) booster amplifiers may be used depending on the power requirements of the system. In order to facilitate such upgrades from a physical standpoint, space is typically left at the end of an amplifier group (e.g. Dual OSC circuit pack and Dual Amplifier circuit pack) in anticipation that the amplifier group will be upgraded with booster amplifiers. 
     Similarly, a low cost implementation of a line amplifier (LA) site comprises the dual amplifier configuration of  FIG. 3   a.  At LA sites, there is no electrical regeneration of the optical signal and no wavelengths are added or dropped. As seen in  FIG. 3   b , booster amplifiers may again be used to increase the launch power and, hence, number of wavelengths that can be accommodated. Different levels (i.e. number of pumps) of booster amplifiers can be added depending on the new number of wavelengths to be supported. 
     Furthermore, to accommodate familiar network housekeeping techniques such as dispersion compensation, wavelength equalization or add/drop multiplexing, line amplifier sites usually offer some form of mid-stage access (MSA) capability. An example of a line amplifier arrangement exploiting this MSA capability is shown in  FIG. 3   c , where dispersion compensation modules (DCMs) have been added to the system of  FIG. 3   b.    
     It is apparent that next generation products must operate in a modular manner to support different network element topologies which offer scalability with respect to the number of wavelengths deployed. As seen, upgrades or re-arrangements necessarily result in the fiber connections between respective circuit cards having to be changed. Traditionally, installers (craftspeople) have been dispatched to manually configure the association between different cards (circuit packs) connected through fiber at a given network element node. However, the optical interconnect density at network element nodes is continually increasing and is, as a result, becoming more and more complex. Accordingly, the fiber connections in such systems are prone to installation errors. As systems get more and more complex to support ever-increasing network capacity requirements, the consequences of incorrect connections will be more severe and network management support will have to be increased. 
     Therefore, providing some form of optical interconnection surveillance for all card-to-card optical connections within a group of related cards or within an optical network link is gaining importance as optical connections are becoming more complex. A method to identify connections and/or missing connections and to verify that these are, in fact, desired associations will be essential to reducing installation time and performing system upgrades. Methods for providing surveillance, alarming, fault location determination, and easing maintenance are critical to the effective implementation and functioning of future systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method to automate fiber connectivity management in optical systems. The inventive method entails providing a dedicated low bit-rate communications channel unique to each fiber connection in an optical system. The purpose of this dedicated communications channel is to simplify fiber connection management by providing information to the system about a fiber connection between two respective cards, validating fiber connections in the system and ensuring that any specific connection between optical devices is the desired association. The dedicated communications channel of the invention supports optical interconnection surveillance for all card-to-card optical connections within a group of related cards or within an optical network link. 
     According to a first aspect of the invention, a port identification message generated at a first optical component is sent to a second optical component over a fiber connection using wavelength division multiplexing (WDM) techniques. Upon reception, the port identification message is sent to an agent along with information identifying the second optical component for processing. The agent checks this information against a predefined connection model to determine if the fiber connection is a desired association. 
     In another embodiment, an out-of-band arrangement may be employed wherein the port identification message generated at the first optical component is sent to the second optical component over a separate optical link parallel to the fiber connection. The port identification message and information identifying the second optical component are then processed to determine if the fiber connection is a desired association. 
     According to a third aspect of the invention, verification of a fiber connection may be achieved by applying a unique dither to an optical signal being transmitted over a fiber connection from a first optical component to a second optical component. The dither is detected at the second optical component and is sent to the agent for processing in order to determine the validity of the fiber connection. 
     Presently, interfaces between optically connected devices are configured manually and are, therefore, prone to installation errors. Providing fiber connectivity management according to the invention will enhance future products by simplifying the fiber connection validation process and ensuring that any specific connection between optical devices is, in fact, the required association. The invention is particularly useful in complex optical environments with many interconnected devices and where troubleshooting faulty connections is time-consuming and, therefore, very costly. 
     Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the physical layout of a typical network element bay. 
         FIG. 2   a  depicts the dual amplifier configuration commonly employed at a line terminating equipment (LTE) site. 
         FIG. 2   b  is an upgraded version of the system in  FIG. 2   a  using two additional booster amplifiers. 
         FIG. 3   a  illustrates the dual amplifier configuration commonly employed at a line amplifier site. 
         FIG. 3   b  is an upgraded version of the system in  FIG. 3   a  using two additional booster amplifiers. 
         FIG. 3   c  depicts the inclusion of mid-stage access (MSA) capability into the upgraded system of  FIG. 3   b  wherein the MSA component is a dispersion compensation module (DCM). 
         FIG. 4  is a high-level representation of the arrangement of optical amplifier products at a line terminating equipment (LTE) site. 
         FIG. 5  depicts an in-band arrangement according to the invention which provides optical connectivity management between an amplifier circuit pack and a dual OSC circuit pack. 
         FIG. 6  depicts an out-of-band arrangement according to the invention which provides optical connectivity management between an amplifier circuit pack and a dual OSC circuit pack. 
         FIG. 7  depicts an alternate in-band embodiment of the invention using dithering to provide optical connectivity management between an OSC circuit pack and an amplifier circuit pack. 
         FIG. 8  depicts an extension of the in-band dithering technique shown in  FIG. 7  to provide optical connectivity management between two amplifier products. 
         FIG. 9  illustrates a general in-band embodiment of the invention implemented between two circuit packs and using variable optical attenuators (VOAs) as the dithering mechanism. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When an optical system is decomposed into multiple subsystems, the fiber connections between those subsystems are prone to installation error. An installer (or craftsperson) will generally have to manually configure the association between two respective components (or circuit packs) connected through fiber e.g. the connection between an OSC card and an amplifier card. As systems get more and more complex and the interconnect density continues to increase, trouble-shooting faulty connections becomes a daunting task for the craftsperson. The present invention seeks to simplify fiber connection management within optical networks. 
     The present invention is desirable between all interconnected devices in an optical system. For example, a portion of an optical system employing optical amplifier products is shown in FIG.  4 . This is simply a high-level block representation of  FIG. 2   a , the typical arrangement at a line terminating equipment (LTE) site. Note that unidirectional traffic flow is assumed over a single fiber. 
     Considering the transmit (upper) path, a plurality of input optical wavelengths  400  are fed into a multiplexer  402 . The output of the multiplexer is propagated through a series of amplifiers  404  to boost the multiplexed signal. Mid-stage access (MSA) capability  406  may also be included as shown to accommodate common network practices such as dispersion compensation, wavelength equalization, and optical add/drop multiplexing. Furthermore, an OSC card  408  is connected via connections  420  to an amplifier  404  and provides operations, administration, maintenance and provisioning (OAM&amp;P) functionality to the optical network. Similarly, the return (lower) path, consists of a series of amplifiers  404  with midstage access capability  406 , terminating at a demultiplexer  410  which generates a plurality of output optical wavelengths  430 . 
     The present invention can be applied to all the optical fiber connections shown in FIG.  4 . Specifically, the amplifier-to-OSC-card connections  420 , the amplifier-to-multiplexer connection  426  or amplifier-to-demultiplexer connection  428  and the amplifier-to-midstage access (MSA) element connections  424  all require some type of mechanism for optical connectivity management. It should be noted that the amplifier-to-OSC-card connections  420  designate optical paths not carrying live traffic while the remainder of the connections define paths carrying live traffic. 
     The present invention pertains to a class of enhanced optical interconnection features which are intended to provide a dedicated low bit-rate communications channel associated with each fiber connection in an optical system. This is gaining importance as optical connections are becoming more and more complex. As will become apparent, the invention simplifies fiber connection management within optical networks. 
       FIG. 5  depicts an “in-band” implementation of the invention to verify a fiber connection between an amplifier circuit pack  502  and a dual optical service channel (OSC) circuit pack  530 . This arrangement corresponds to the amplifier-to-OSC card connections  420  of  FIG. 4 , for example. The amplifier circuit pack  502  comprises an optical amplifier  506 , such as an erbium-doped fiber amplifier (EDFA). The amplifier  506  is preceded on its input side by an OSC drop filter  504  which is connected to an optical port  518  located on the exterior of the amplifier circuit pack  502 . An OSC add filter  508  is located at the output end of the amplifier  506  and is connected to an optical port  524 . On the exterior of the amplifier circuit pack (or card)  502  is further located an input (line-in) optical connector  501  and an output (line-out) optical connector  503 . 
     The dual OSC circuit pack  530  contains an OSC transmitter (Tx)  542  and an OSC receiver (Rx)  536 . The OSC receiver  536  is connected to an optical port  520 . Similarly, the OSC transmitter  542  is connected to an optical port  526 . A processing agent  500  is also connected to both the amplifier circuit pack  502  and dual OSC circuit pack  530  via electrical backplane connections denoted by the dashed lines labeled ‘e’. 
     The OSC drop filter  504  in the amplifier circuit pack  502  extracts an OSC signal from incoming optical traffic and directs the OSC signal to optical port  518  for transmission to the OSC receiver  536  of the dual OSC circuit pack  530 . On the other hand, the OSC add filter  508  combines an OSC signal received at optical port  524  of the amplifier circuit pack  502  with outgoing optical traffic to be transmitted through output port  503 . 
     The amplifier circuit pack  502  is connected to the dual OSC circuit pack  530  via an optical fiber link  522  which connects port  518  to port  520  and an optical fiber link  528  which connects port  524  to port  526 . Optical fiber link  522  completes the connection from the OSC drop filter  504  to the OSC receiver  536  while optical fiber link  528  completes the connection from the OSC transmitter  542  to the OSC add filter  508 . 
     To facilitate optical connectivity management according to this first embodiment of the invention, the amplifier circuit pack  502  is further equipped with a 1310 nm transmitter (Tx)  510  and an associated WDM coupler  512  as well as with a WDM filter  514  and an associated receiver (Rx)  516 . Likewise, the dual OSC circuit pack  530  has a 1310 nm transmitter (Tx)  538  with an associated WDM coupler  540  and a WDM filter  532  with an associated receiver (Rx)  534 . 
     At the amplifier circuit pack  502 , the WDM coupler  512  combines the output from its respective 1310 nm transmitter  510  with the OSC signal which is dropped at OSC drop filter  504  to optical port  518 . At the dual OSC circuit pack  530 , the WDM filter  532  extracts the 1310 nm portion of the combined signal transmitted from port  518  to port  520 , and delivers it to the 1310 nm receiver  534  for detection. The same methodology applies to the 1310 nm transmitter  538  with associated WDM coupler  540  on the dual OSC circuit pack  530  and the WDM filter  514  with associated 1310 nm receiver  516  on the amplifier circuit pack  502 . 
     The present invention seeks to identify the physical connections made between various optical components and to verify that these are, in fact, desired associations. For example, in relation to  FIG. 5 , the goal is to provide a method to determine if the fiber connections  522 ,  528  of port  518  to port  520  and port  524  to port  526 , respectively, are valid based on some predetermined model of the network element. 
     The optical connectivity management process is initiated with user input of a pre-provisioned or inferred connection expectation to the processing agent  500  (process B). The pre-provisioned or inferred connection expectation is determined by the application specific requirement of the network element. In either case, sufficient information is provided to the agent to construct a predefined connection model that may be stored in non-volatile memory. For example, the pre-provisioned connection expectation may take the form of a table mapping a desired topology to required connections as a function of card type, card location, port identification (ID), card slot location and network element ID. 
     The processing agent  500  manages optical connectivity for the entire network element and is preferably implemented by some form of control software with the necessary processor complex (i.e. cpu, memory, non-volatile memory, communications ports and other necessary hardware). The agent  500  may be resident on one or more circuit packs and their associated processor complex, as the design may require. The agent  500  establishes the ‘personality’ of the network element based on user input of the pre-provisioned or inferred connection expectation. Furthermore, the agent  500  processes information received from the individual circuit packs (to determine the validity of each fiber connection) and indicates the results remotely and locally via a user-output interface on a connection-by-connection basis. 
     Taking the connection of port  526  to  524  as an example, a port identification (ID) message for port  526  is generated by the 1310 nm transmitter (Tx)  538  on the dual OSC circuit pack  530  (process C). The port ID message contains at least the following information: the type of card, card location, port identification, card slot location and network element (NE) identification. With the use of the WDM coupler  540 , the port ID message is transmitted together with the standard OSC signal along the fiber connection  528  from port  526  on the dual OSC card  530  to port  524  on the amplifier card  502 . 
     At the amplifier circuit pack  502 , the port ID message is extracted from the OSC signal via the WDM filter  514  and 1310 nm receiver (Rx)  516  (process D). This information, along with information identifying port  524 , must then provided to the processing agent  500  in order to completely specify the optical connection between the two ports under consideration. Specifically, a composite message is formulated at the amplifier circuit pack  502  that includes self-identity information (card, port, slot etc.) and the connection information (port ID message) received by it. This composite message is sent to the processing agent  500  via the backplane connection ‘e’ (process E). The optical connection specified by the composite message is checked against the connection model stored in the agent  500  (either locally or remotely), and the connection can be confirmed as correct. In cases where the hardware supports the appropriate communication path, an incorrect connection can be identified and alarmed via a user-output interface. In any event, a lack of confirmation that the connection is correct when it is made will indicate that a connection attempt is incorrect. In this manner, verification for each fiber connection is performed on a connection-by-connection basis. Additionally, once a valid:fiber connection is made, the information may be passed to a connection assist tool which builds a connection map of the network element. 
     The same methodology can be applied to verify the connection between port  518  and port  520 . However, in this instance, to be consistent with the direction of transmission of the OSC signal, the 1310 nm transmitter (Tx)  510  is located on the amplifier circuit pack  502  and its associated 1310 nm receiver (Rx)  534  on the dual OSC circuit pack  530 . 
     The user-output interface allude to above may comprise any suitable indication means visible to a user (or craftsperson) for confirming a correct connection or alarming of a misconnection. For example, small and inexpensive LEDs may be located at each port of a given circuit pack. Using appropriate electronics, the LEDs can be made to light up in different ways in order to provide one or more types of user feedback. For example, an LED can be made to remain in a blinking state as long as a connection to its respective port is invalid or missing; once a valid port connection is made, the LED can be made to turn off signifying a valid fiber connection. As anyone skilled in the art will appreciate, this is just one of many possible indication scheme, and has been included merely for illustrative purposes. Many other possibilities or variations may exist. 
       FIG. 6  depicts an “out-of-band” implementation of the present invention for verifying the fiber connections between an amplifier circuit pack  602  and a dual OSC circuit pack  630  as in the previous example. Therefore, the basic configuration closely resembles that of FIG.  5 . The dual OSC circuit pack  630  comprises an OSC transmitter (Tx)  644  and an OSC receiver (Rx)  646 . The amplifier circuit pack  602  comprises an OSC drop filter  604  preceding an optical amplifier  606  and an OSC add filter  608  located after the amplifier  606 . 
     To complete the connection of the OSC transmitter  644  to the OSC add filter  608 , a fiber connection  626  connects a port  636  on the dual OSC circuit pack to a port  620  on the amplifier circuit pack  602 . Similarly, a fiber connection  624  connects a port  616  on the amplifier circuit pack  602  to a port  634  on the dual OSC circuit pack  630  to complete the connection of the OSC drop filter  604  to the OSC receiver  646 . The goal in this implementation is to again verify that proper port-to-port connections are established i.e. port  616  on the amplifier circuit pack  602  is connected to port  634  on the dual OSC circuit pack  630  and port  636  on the dual OSC circuit pack  630  is connected to port  620  on the amplifier circuit pack  602 . In this implementation, however, transmission of a port ID message from one circuit pack to another will be supported over a separate physical link parallel to each fiber connection in the system. 
     Taking the fiber connection  626  as an example, a 1310 nm transmitter (Tx) or receiver (Rx)  642  is provided at the dual OSC circuit pack  630  and is connected to an optical port  638 . An associated 1310 nm receiver (Rx) or transmitter (Tx)  612  is provided at the amplifier circuit pack  602  and is connected to an optical port  618 . Transmission of the port ID message from one circuit pack to the other is supported over a separate optical link  628  running parallel to the fiber connection  626 . The optical link  628  connects the optical port  618  to port  638 . Using a keyed dual fiber interconnect system (i.e. with two optical fibers packaged in one jacket), the parallel fiber link  628  can be made invisible to the user. Two examples of systems having keyed optical connector types suitable for establishing the paired fiber connections according to this specific implementation are the MT-RJ and SCDC interconnect systems. These two interconnect systems are but two examples of how the paired fiber connection may be realized in this implementation, and those skilled in the art will appreciate that various other methods are possible. Finally, a similar arrangement exists for the fiber connection  624  with a separate optical link  622  running parallel to it connecting a port  614  on the amplifier circuit pack  602  to a port  632  on the dual OSC circuit pack  630 . 
     In this embodiment, connectivity management is again initiated by a user input of a pre-provisioned connection expectation to a processing agent  600  (process B). In this case, however, a port ID message identifying a port  636  or  620  of the fiber connection  626  is sent via the 1310 nm transmitter (Tx)  642  or  612  along the separate optical link  628  and is received at the associated 1310 nm receiver (Rx)  612  or  642 . This information along with self-identity information (port, card, slot etc.) of the port  620  or  636  corresponding to the receiver (Rx)  612  or  642  is then sent to the agent  600  via a backplane connection ‘e’ (process E). The agent  600  processes the information and notifies the user of the result i.e. the information is checked against the connection model and the connection is either confirmed or alarmed as incorrect (process F). Suitable indication means, such as the one described for the implementation of  FIG. 5 , may again be employed to indicate the status of a particular connection to a user. Furthermore, once a valid port connection is made, the information may then be passed to a connection assist tool which builds a connection map of the network element. 
     Note that in this embodiment, because connectivity management for each fiber connection is implemented over a separate optical link, the direction of transmission of the port ID message is immaterial i.e. information for a given port can be generated and transmitted from either circuit pack to the other. All that is simply required is that a 1310 nm transmitter (Tx) be provided at one end of an optical link and that an associated receiver (Rx) be provided at the other end. For example, with regards to the optical link  628  in  FIG. 6 , the dual OSC circuit pack  630  may contain the transmitter (Tx)  642  with an associated receiver (Rx)  612  located on the amplifier circuit pack  602 . The converse also may also hold. The same applies to the optical link  622  between port  632  and port  614 . 
     Those skilled in the art will appreciate that the separate physical link associated with each fiber connection in a system according to this embodiment of the invention need not necessarily be of an optical nature. For example, a combined optical/electrical implementation may be employed wherein a separate electrical link (e.g. twisted pair copper) is uniquely associated with each fiber connection. In this case, the 1310 nm transmitters and receivers would be replaced by their electrical counterparts. 
       FIG. 7  depicts an alternate “in-band” implementation of the invention applied to a connection between the Tx module of an OSC card  702  and the corresponding receiving portion of an amplifier card  706 . The OSC card  702  now includes a dither controller  704  which is connected to an optical transmit (Tx) port  710  located on the exterior of the OSC card  702 . The OSC transmit (Tx) port  710  provides connectivity to other optical components. The amplifier card  706  includes a tap coupler  707  feeding a photodiode  708  which, in turn, is connected to a dither detector  712 . The amplifier card  706  also includes an input (line-in) port  701 , an output (line-out) port  703  and an optical port  714 . The optical port  714  provides connectivity to other optical components. Therefore, the OSC card  702  is connected to the amplifier card  706  via a fiber connection  718  which connects the transmit (Tx) port  710  on the OSC card  702  to the optical port  714  on the amplifier card  706 . Finally, a processing agent  700  is provided as in the previous implementations and, as before, is connected to both cards  702 ,  706  via electrical backplane connections denoted by the dashed lines labeled ‘e’. 
     As in the previous implementations, the goal here is to verify that the fiber connection  718  between the OSC transmit (Tx) port  710  and the optical port  714  on the amplifier card  706  is a desired association. However, in this alternate “in-band” realization, optical connectivity management is implemented by modifying the active underlying transmission between optical components (or cards) without impacting the performance as described below. 
     Referring to  FIG. 7 , optical connectivity management is initiated with user input of a pre-provisioned or inferred connection expectation to the processing agent  700  (process B). In response, the processing agent  700  sends a message via its electrical backplane connection ‘e’ (process C) to the OSC card  702  directing the dither controller  704  to add a small dither signal to the optical signal (e.g. OSC signal) generated at the OSC transmitter (not shown). Dithering implies low-level (1-10%) modulation of an optical signal. The technique of dithering an optical signal is well known in the art and, as such, will not be described in any detail. In any case, a unique dither code (or specific modulation format) is applied to the optical signal generated at the OSC transmitter. This may be accomplished, for example, with the use of a low loss, low attenuation, polarization-independent attenuation device. 
     The dithered optical signal exits the OSC card  702  at the transmit (Tx) port  710  and is transmitted to optical port  714  of the amplifier card  706  over the fiber connection  718 . for tapping off a portion of the received OSC signal and a photodiode  708  connected to a dither detector  712 . At the amplifier card  706 , a portion of the dithered optical signal is tapped off to the photodiode  708  which feeds into the dither detector  712  (process D). After detection, the dither information is sent to the processing agent  700  via an electrical backplane connection ‘e’ (process E). As in the previous embodiments, the agent  700  processes the information and, using suitable indication means, notifies the user of the result. 
     The dithering technique performs optical interconnection surveillance by verifying whether a connection is valid or invalid on a connection-by-connection basis. Specifically, the processing agent  700  sends a message to the dither controller  704  of the OSC card  702  to add a small dither to the optical signal generated at the OSC transmitter. At the amplifier card  706 , information extracted by the dither detector  712  is sent back to the agent  700  for processing. If the information from the dither detector  712  matches with the dither pattern (or code) for that particular connection in the stored connection model, then the fiber connection is confirmed as valid. 
     The processing agent  700  is linked to both a user-input interface (for receiving the pre-provisioned or inferred connection expectation) and a user-output interface (for verifying connections to a user). If a connection is determined to be valid (i.e. it is a desired association), the processing agent  700  effects suitable indication means on the user-output interface to inform the user that a correct connection has been made. However, if a particular connection is invalid or missing, then the processing agent effects the user-output interface to indicate that the intended connection has not yet been completed. 
     In the implementation shown in  FIG. 7 , the dithered optical signal is left alone and there is no attempt to cancel or remove the dither from the optical signal received at downstream equipment e.g. the amplifier card  706 . In such circumstances, the dither may be handled via standard techniques such as equipment correlation or orthogonal signaling. For example, each piece of downstream equipment may detect the dither and a system agent may then correlate the presence of the signal at each downstream device with the path followed by that carrier. In the case of orthogonal signaling, the dither codes can be made sufficiently different to allow unique and unambiguous detection through electrical filtering or digital signal processing with little or no cross talk from other signals. The detection process may either employ time-domain pattern matching (correlation) techniques or frequency-domain techniques such as filtering. Alternatively, the dither may be cancelled from the optical signal received at downstream equipment using destructive interference with the aid of a low loss, low-attenuation device as described in the embodiments that follow. 
       FIG. 8  depicts an additional “in-band” implementation of the invention employing the dithering technique to provide connectivity management between two amplifier products. Again, the idea here is to modify the active underlying transmission without significantly impacting performance. 
     A first amplification module  802  is comprised of a dither controller  804  whose output feeds a pump controller  806  of a respective optical amplifier  808 . The output of the amplifier  808  is tapped off to a photodiode  810  which provides feedback to the dither controller  804 . A second amplification module  818  is comprised of a photodiode  822  which feeds a dither detector  824 . The dither detector  824  is further connected to a dither controller  826  whose output feeds a pump controller  830  of an optical amplifier  832 . An output port  814  of amplification module  802  is connected to an input port  816  of amplification module  818  via a fiber connection  812 . As in all previous examples, both optical components of interest are connected via electrical backplane connections ‘e’ to a processing agent  800 . 
     The implementation presented in  FIG. 8  begins with user input of a pre-provisioned or inferred connection expectation to the agent  800  (process B). The agent  800  sends a message via its backplane connection ‘e’ to the dither controller  804  of amplification module  802  to dither the pump controller (laser)  806 . This generates a dithered optical signal at the output of the source amplifier  808  (i.e. the underlying traffic is dithered). The photodiode  822  of the receiving amplification module  818  passes the received dithered. optical signal to the dither detector  824  (process D) which then extracts the applied dither and sends this information to the agent  800  via the electrical backplane connection ‘e’ (process E). The agent  800  processes the information and notifies the user of the result. 
     The amplification module  818  further comprises the dither controller  826  which provides a cancellation signal to the pump controller  830  of the optical amplifier  832 . The dither is then cancelled from the received optical signal using destructive interference. 
     Finally, a generic example of using the dithering technique to provide connectivity management between arbitrary optical components is illustrated in FIG.  9 . In this embodiment, an existing laser signal or amplifier output  901  is dithered using a variable optical attenuator (VOA)  908  in a first circuit pack  902  and then detected and removed by a VOA  932  in a downstream circuit pack  918 . VOAs are standard devices known in the art used for attenuating the intensity of an optical signal in response to a control signal. 
     The first circuit pack  902  includes a dither controller  904  connected to a VOA controller  906  which, in turn, supplies a control signal to the VOA  908 . As is standard, the attenuation of the VOA  908  is controlled using embedded tap couplers  903 ,  905  and PIN diode detectors  909 ,  910  located both before and after the VOA  908 . Similarly, the downstream circuit pack  918  includes a dither detector  924  which is connected to a dither controller  926 . The dither controller  926  provides a dither cancellation signal to a VOA controller  930  which supplies a control signal to the VOA  932 . The attenuation of the VOA  932  is controlled using embedded tap couplers  920 ,  921  and PIN diode detectors  922 ,  923  located both before and after the VOA  932 . The circuit packs  902 ,  918  are connected via an optical fiber  912  which connects a port  914  on the first circuit pack  902  to a port  916  on the downstream circuit pack  918 . 
     Connectivity management for this embodiment is initiated in the same manner as before with user input of a pre-provisioned or inferred connection expectation to an agent  900 . The agent  900  then sends a message via a backplane connection ‘e’ to the dither controller  904  of the first circuit pack  902 . In this case, however, the dither is added by modulating an attenuation control signal from the VOA controller  906  with a small signal from the dither controller  904 . The amplitude of this dither may be maintained as a fixed percentage of the average output power, as measured at the output tap  905 . 
     At the downstream circuit pack  918 , the tap coupler  920  provides a portion of the optical signal received from the first circuit pack  902  to the PIN diode  922  for detection. The dither which was applied at the first circuit pack  902  is then extracted by the dither detector  924  and sent to the agent via an electrical backplane connection ‘e’. The agent  900  processes the information and notifies the user of the result (i.e. connection verification). 
     Using the inverse of the signal extracted by the dither detector  924 , a dither cancellation signal may be generated by the dither controller  926  and applied to the VOA controller  930  to effect the removal of the dither at the VOA  930  using destructive interference. Furthermore, dither cancellation may be confirmed by the dither controller  926  operating at the output tap of the VOA  932 . Note that the dither amplitude for the cancellation signal can be controlled as a fixed percentage of the average input power, and its effectiveness confirmed via the output tap. 
     Regardless of the chosen method of implementation, the present invention is highly desirable between all interconnected devices in an optical system. The primary purpose of the dedicated communications channel is to identify the connection made and verify that this is, in fact, a desired association. The invention is capable of identifying connections that either conform to or deviate from a pre-defined connection model. The invention is also capable of identifying any connection and/or missing connection which differs from user input of a pre-provisioned expectation (interconnect rules for a given software release). 
     In an ideal implementation, the invention will provide a bi-directional channel directly associated with each optical fiber connection made in a system. In this way, the optical association between optically interconnected devices may be easily established. If a unidirectional implementation is chosen, the optical component that receives the interconnect message (port ID message) is required to open a software data channel to the ‘sending’ component to establish full association between the two components under consideration. Whatever the case may be, the invention provides sufficient information to a processing agent in order that it may fully resolve a fiber connection. The agent must communicate with both the smart connect message sender and receiver to confirm the desired connection has been established. 
     Optical connectivity management provided for in the manner of the present invention offers numerous advantages. The invention provides a platform to construct a complete network model (based on verifiable connections), which has many applications in surveillance, alarming, fault location, reducing installation time, easing maintenance, and in-field system upgrades. 
     For example, the invention facilitates the efficient installation or upgrade of an optical network. However, as optical connections are becoming more and more complex, the fiber connections between components are prone to installation and upgrade errors as installers usually have to manually configure the association between two circuit cards. The present invention provides a mechanism to validate optical connections from end-to-end and to verify that these, in fact, are the desired associations. 
     Furthermore, the invention provides a simple mechanism to locate faults within an optical network. This affords a simple procedure for the craftsperson where troubleshooting faulty connections would otherwise be very time-consuming and therefore costly. Therefore, the connection model that has been established can be a very effective system-lineup-and-test (SLAT) and maintenance tool. 
     While preferred embodiments of the invention have been described and illustrated, it will be apparent to one skilled in the art that numerous modifications, variations and adaptations may be made without departing from the scope of the invention as defined in the claims appended hereto.