Abstract:
The present invention provides an improved optical communication network ( 300 ) that utilizes an apparatus of optical channel protection. The apparatus for optical channel protection of the present invention including a transmitting end network switch ( 200 ), a first and a second receiving end network switch ( 201, 202 ), a plurality of wavelength tuneable transmitting end transponders ( 400, 401 . . . 405 ), a plurality of wavelength tuneable receiving end transponders ( 400′, 401′ . . . 405 ′), a transmitting end controller ( 10   a ) connected to a network monitoring and control system ( 100   a ) and a receiving end controller ( 10   b ) connected to said network monitoring and control system ( 100   a ). The present invention utilizes a method of optical channel protection that can be broadly categorized under optical multiplex switching.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority date of Malaysian Application No. PI 2012001582 filed Apr. 6, 2012, the contents of which are hereby incorporated by reference in their entirety. 
     The present invention relates to the field of optical channel protection in optical networks. More particularly the present invention relates to an improved broadband optical network that incorporates an optical channel protection apparatus that provides for broadband optical channel protection in broad band fibre optic communication networks. 
     BACKGROUND TO THE INVENTION 
     Many core and metro networks have already migrated to fibre optics. Fibre optics are also entering the access network arena, reaching the neighbour-hood, the premises, the business and the home. New packet technologies create new applications, driving demand for bandwidth and higher QoS (Quality of Service), including high network availability. 
     All this traffic is enabled by multiple optical resources, which are gathered together to construct a transport network. These resources include fibres, passive optical elements, CPE equipment (routers, switches, line cards), network equipment (transponders, DWDM multiplexers, optical amplifiers, regenerators), and more. However, it is enough for one of these heterogeneous resources to fail in order to bring the network down, as in the case of fibre cuts during road construction or equipment failure. Backup resources which can quickly take over upon such a failure are essential to guarantee high network availability. This is where optical channel protection comes into play to provide for the contingency of provisioning alternate paths for optical communication traffic data in the event the main data path becomes inoperable. 
     Protection of traffic in optical networks can generally be classified under two types. The first type of protection being a concept of line protection is a so-called Optical Multiplex Section (OMS) protection used preferably in a multi-channel multi-section ring networks. The ring network is formed by at least two concentric optical fibre rings capable of carrying data traffic in two opposite directions (clockwise and counter-clockwise) between network elements NE in the ring. The two concentric fibre rings usually serve as a main route and a protection route for all optical channels of the network, although sometimes the main and the protection routes are arranged within the same fibre. The OMS protection ensures in case of a fault of the traffic via a multiplex section on the main route and a protection route (say in a section between two specific network elements, that may include multiple optical channels), the protection route that can be used to redirect the required data traffic from the main route, and thus bring the traffic to its destination network element using the opposite direction. In this case, the redirected traffic must pass a longer distance than it would pass via the main route. The OMS protection is usually utilized in SDH and SONET, where it is respectively named MSSPRING (Multiplex Section Shared Protection Ring) and BLSR (Bi-Directional Line Shared Protection). 
     The second known type of traffic protection in optical networks is a so-called OCH protection (Optical Channel Protection). The OCH protection is intended for protecting a specific optical channel and by default can be implemented by providing simultaneous transmission of data traffic of that specific optical channel along both the main route and the protection route. In case of a fault in one of the routes, the other will safely bring the traffic to its destination point. 
     U.S. Pat. No. 7,840,133 B2 provides a technique for carrying out protection of data traffic in a multi-channel multi-section optical communications network by simultaneously using Optical Multiplexed Section (OMS) protection and Optical Channel (OCH) protection. The technique comprises selection of a working optical signal in an OCH protected optical channel, in case of a fault in a section of the network, by relying on an indication associated with OMS switching functionality that is required to overcome the mentioned fault. 
     US 2002/0180957 A1 discloses a hub structure for use in an optical network, the optical network comprising a ring structure carrying a bidirectional optical data signal and a plurality of hub structures arranged in-line within the ring structure, the optical data signal comprising primary and secondary path transmission signals having opposing transmission directions on the ring structure, the hub structure comprising a drop unit arranged, in a normal state, to drop and through connect a secondary receive path signal for further processing at the hub structure. 
     Thus far there has yet to be disclosed an apparatus and method of cost effective optical channel protection for optical communication networks that enables switching between a primary data transmission path that serves as a main data transmission path and a secondary data transmission path that serves as an auxiliary data transmission path in the event the primary data transmission path experiences a fault. 
     SUMMARY OF THE INVENTION 
     The following presents a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. 
     The present invention provides an improved broadband optical network that incorporates an improved optical channel protection apparatus. The optical communication network comprising of:
         a transmitting end that includes:   a plurality of transmitting end CPEs (Customer Premise Equipment) that are configured to transmit a plurality of transmission data optical signals at distinct optical wavelengths;   a first plurality of transmitting end fibre optic links that serve as a primary data transmission path for the transmission data optical signals originating from the plurality of transmitting end CPEs;   a plurality of transmitting end non-tuneable transponders, each transponder being responsive to a particular wavelength of a transmission data optical signal of the plurality of transmission data optical signals, that corresponds to a transmission data optical signal originating from a corresponding CPE of the plurality of transmitting end CPEs;
           the plurality of transmitting end non-tuneable transponders serving to receive a plurality of transmission data optical signals originating from the plurality of transmitting end CPEs via the first plurality of transmitting end fibre optic links and transmit said plurality of transmission data optical signals to a transmitting end CWDM/DWDM optical multiplexer;   the transmitting end CWDM/DWDM optical multiplexer serving to wavelength multiplex the plurality of transmission data optical signals and route a resulting wavelength multiplexed optical signal to a receiving end of the optical communication network;   
           a main fibre link that serves as a propagation and transmission media that allows the transmission and propagation of a wavelength multiplexed transmission data fibre optic signal that represents plurality transmission data optical signals originating from the plurality of transmitting end CPEs;   a receiving end that comprises;   a receiving end CWDM/DWDM optical de-multiplexer that serves to wavelength de-multiplex and route the de-multiplexed transmission data optical signals to a corresponding receiving end CPE of a plurality of receiving end CPEs via a corresponding receiving end non-tuneable transponder of a plurality of receiving end non-tuneable transponders.       

     The improved broadband optical network of the present invention further incorporating an apparatus for optical channel protection that includes:
         a transmitting end network switch, that is optically interconnected at a receiving side to the plurality of transmitting end CPEs and optically interconnected at the transmitting side (i.e. output side) to the plurality of non-tuneable transmitting end transponders and a plurality of transmitting end wavelength tuneable transponders; said transmitting end network switch serving to route transmission data optical signals originating from any one of the plurality of transmitting end CPEs (Customer Premise Equipment) to any one of the plurality of transmitting end non-tuneable transponders and/or any one of the plurality of transmitting end tuneable transponders;   each of said transmitting end wavelength tuneable transponder corresponding to each non-tuneable transmitting end transponder of opposite symmetrical location in relation to the location of each of said transmitting end non-tuneable transponder;   a second plurality of fibre optic links at the transmitting end that serve as auxiliary data transmission paths for the transmission data optical signals originating from any one of the plurality of transmitting end CPEs&#39;, in the event that any one of the first plurality of fibre optic links, or any one of the plurality of transmitting end non-tuneable transponders that correspond to any one of the first plurality of CPE&#39;s experiences a fault;   each of said transmitting end wavelength tuneable transponder being optically linked to a corresponding transmitting end CPE of the plurality of transmitting end CPEs via the transmitting end network switch and one of the second plurality of fibre optic links that corresponds to the corresponding transmitting end CPE;   a 1×N optical coupler, that serves to couple transmission data optical signals originating from any one of the plurality of transmitting end wavelength tuneable transponders and transmit an optically coupled transmission data optical signal to a 1×2 optical coupler; the 1×2 optical coupler, serving to couple the optically coupled transmission data optical signal output from the 1×N optical coupler to a wavelength multiplexed transmission data optical signal, output by the transmitting end CWDM/DWDM optical multiplexer;   a first receiving end network switch that is optically interconnected to the receiving end CWDM/DWDM de-multiplexer at a receiving side (i.e. input side) and being optically interconnected to a plurality of receiving end wavelength tuneable transponders and the plurality of receiving end non-tuneable transponders at a transmitting side (i.e. output side);
           said receiving end first network switch serving to receive a plurality of optically wavelength division de-multiplexed transmission data optical signals originating from the receiving end CWDM/DWDM optical de-multiplexer and routing the received optically wavelength division multiplexed transmission data optical signals to the corresponding receiving end non-tuneable transponders of the plurality of non-tuneable receiving end transponders and/or corresponding receiving end wavelength tuneable transponders of a plurality receiving end wavelength tuneable transponders;   each receiving end wavelength tuneable transponder of the plurality of receiving end wavelength tuneable transponders corresponding to each receiving end non-tuneable transponder of the plurality of receiving end non-tuneable transponders of opposite symmetrical location in relation to the location of said each receiving end wavelength tuneable transponder;   
           a second receiving end network switch that is optically interconnected to a plurality of the plurality of receiving non tuneable transponders and the plurality of receiving end wavelength tuneable transponders at a receiving side (i.e. input side) and a plurality of receiving end CPEs at the transmitting side (i.e. output side); said second network switch serving to receive and route optical signals of predefined wavelengths originating from any one of the plurality receiving end non-tuneable transponders and/or any one of the receiving end wavelength tuneable transponders to a corresponding receiving end CPE;   a transmitting end controller that serves to control the routing of optical signals by the transmitting end network switch;   a receiving end controller that serves to control the routing of optical signals by the first and second receiving end network switches respectively; and   a network monitoring and control system that coordinates and arbitrates the operation of the transmitting end controller and the receiving end controller       

     It should be noted that the plurality of transmitting end non-tuneable transponders and the plurality of transmitting end wavelength tuneable transponders serve to convert transmission data optical signals transmitted by the plurality of transmitting end CPEs from 1310 nm or 1500 nm optical signals into the ITU-T DWDM (Dense Wavelength Division Multiplexing) or ITU-T CWDM (Coarse Wavelength Division Multiplexing) transmission format, before relaying aforementioned transmission data optical signals to the subsequent stage of the transmitting end of the broadband optical communication network of the present invention and hence the receiving end via the main fibre link of the broadband optical communication network of the present invention. Conversely, at the receiving end, the plurality of receiving end non-tuneable transponders and the plurality of receiving end wavelength tuneable transponders serve to the de-multiplexed transmission data optical signals, received via the output lines of the receiving end CWDM/DWDM optical de-multiplexer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an exemplary optical communication network comprising of a transmitting end, a fibre link and a receiving end which incorporates a first preferable embodiment of the apparatus for optical channel protection of the present invention; 
         FIG. 2  is a diagram attempting to illustrate the operation of the exemplary embodiment of the broadband optical communication network of the present invention as illustrated in  FIG. 1  during normal operation; and 
         FIG. 3  is a diagram attempting to illustrate the operation of the exemplary embodiment of the broadband optical communication network of the present invention as illustrated in  FIG. 1  during the case when a fault is detected both at the transmitting and receiving ends. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of an exemplary embodiment and is not intended to represent the only form in which the embodiment may be constructed and/or utilized. The description sets forth the functions and the sequence for constructing the exemplary embodiment. However, it is to be understood that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the scope of this disclosure. 
     It should be noted, that description set forth in the following passages, with reference to  FIGS. 1 to 3 , only describe a preferable embodiment of the broadband optical communication network  350  of the present invention. 
     The present invention provides an improved broadband optical network  350  that incorporates an improved optical channel protection apparatus. 
     A preferable embodiment of the improved broadband optical network  350  of the present invention will now be described with reference to  FIG. 1 . Before proceeding further, it should be noted that the preferable embodiment of the improved optical communication network  350  of the present invention as described herein, is an improved broadband optical communication network  350  due to incorporation of an improved optical channel protection apparatus. 
     Aforementioned improved broadband optical communication network  350  broadly comprising of a transmitting end  200   a  optically interconnected to a receiving end  200   b  by a main fibre link  700 . Broad-band optical communication in the improved broadband optical communication of the network  350  of the present invention being a consequence of the utilization wavelength division multiplexing and de-multiplexing to increase the information carrying capacity of the main fibre link  700 . 
     The transmitting end  200   a  of the broadband optical communication network  350  of the present invention, comprising of the following:
         a plurality of transmitting end CPEs (Customer Premise Equipment)  100 ,  101  . . .  105  that are configured to transmit a plurality of transmission data optical signals at distinct optical wavelengths;   a transmitting end network switch  200 , that is optically interconnected at a receiving side to the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  and optically interconnected at the transmitting side (i.e. output side) to a plurality of non-tuneable transmitting end transponders  300 ,  301 , . . . ,  305  and a plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . . ,  405  via a first and second plurality of transmitting end fibre optic links  801 ,  802  respectively.   a transmitting end CWDM/DWDM optical multiplexer  500  that is optically interconnected at its input side (i.e. receiving side) to the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  and optically interconnected at its output side (i.e. transmitting side) to a 1×2 optical coupler  601 ; and   a 1×N optical coupler  600  that is optically interconnected at its input side to the plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . . ,  405  and optically interconnected at its output side to the 1×2 optical coupler  601 .       

     The output of the 1×2 optical coupler  601  being optically interconnected to the main fiber link  700 , to consequently enable transmission of a wavelength division multiplexed transmission data optical signal to the receiving end  200   b  of the broadband optical communication network  350  of the present invention. 
     The receiving end  200   b  of the broadband optical communication network  300  of the present invention comprising of the following components:
         a receiving end CWDM/DWDM optical de-multiplexer  501  that is optically interconnected at its input to the main fibre link  700  to consequently enable reception of the wavelength division multiplexed transmission data optical signal from the transmitting end  200   a;      a receiving end first network switch  201  that is optically interconnected at a receiving side to a plurality of output lines of the CWDM/DWDM optical de-multiplexer  501  and optically interconnected at its transmitting side to a plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ and a plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′, . . . ,  405 ′;   a receiving end second network switch  202  that is optically interconnected to at its receiving side to the plurality of receiving end non-tuneable transponders  300 ′,  301 ′ . . . ,  305 ′ and a plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′, . . . ,  405 ′ and optically interconnected at its transmitting side to a plurality of receiving end CPEs  100 ′  101 ′, . . . ,  105 ′.       

     The optical switching and routing of optical signals by the transmitting end network switch  200  being controlled by a transmitting end controller  10   a  and likewise the optical switching and routing of optical signals of the first and second receiving end network switches  201 ,  202  being controlled by a receiving end controller  10   b . Both the controllers  10   a ,  10   b  being, electrically/optically interconnected to a network monitoring and control system  100   a  that coordinates and arbitrates the operations of said transmitting end and receiving end controllers  10   a ,  10   b.    
     It should be noted that, each of the plurality of non-tuneable transmitting end transponders  300 ,  301 , . . . ,  305  and each of the plurality of non-tuneable receiving end transponders  300 ′,  301 ′, . . . ,  305 ′, are responsive to predefined wavelengths of transmission data optical signals originating from corresponding transmitting end CPEs. Particularly, transponders  300  and  300 ′ are responsive to a transmission data optical signal transmitted at a first wavelength by a first CPE  100 ; transponders  301  and  301 ′ are responsive to a transmission data optical signal transmitted at a second wavelength by a second CPE  101 ; and transponders  305  and  305 ′ are responsive to a transmission data optical signal transmitted at a third wavelength by a third CPE  105 . 
     Upon initial reading of the description of a preferable embodiment of the broadband optical communication network  350  of the present invention, as presented above, it may not be evident to the reader that the above said improved broadband optical communication network  350  incorporates an optical channel protection apparatus. More particularly the optical channel protection apparatus of the present invention comprises of the following components of the broadband optical communication network  350 :
     1. The transmitting end network switch  200  that is optically interconnected to the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  at its receiving side (i.e. input side) and is further optically interconnected to the plurality of first fibre optic links  801  and the plurality of second fibre optic links  802  and hence is optically interconnected to the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  and the plurality of wavelength tuneable transponders  400 ,  401 , . . . ,  405 ;   2. The plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . . ,  405 , that are optically interconnected to the plurality of second fibre optic links  802  at a receiving side (i.e. input side);   3. The 1×N optical coupler  600  that is optically interconnected to a transmitting side (i.e output side) of the plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . . ,  405 ;   4. The 1×2 optical coupler  601  that is optically interconnected to the output of the transmitting end CWDM/DWDM optical multiplexer  500  and the transmitting side (i.e. output side) of the 1×N optical coupler  600 ;   5. The first receiving end network switch  201  that is optically interconnected at its receiving side to the plurality of output lines of the receiving end CWDM/DWDM optical de-multiplexer  501  and is further optically interconnected at its transmitting side to the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ and the plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′ . . . ,  405 ′;   6. The plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′, . . . ,  405 ′ that are optically interconnected to the receiving side of the second receiving end network switch  202 ;   7. The second receiving end network switch  202  that is optically interconnected at its receiving side to the transmitting sides (i.e. output sides) of the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ and the plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′, . . . ,  405 ′;   8. The transmitting end controller  10   a  that serves to control the optical switching and routing of the transmitting end network switch; and   9. The receiving end controller  10   b  that serves to control the optical switching and routing of the first  201  and second  202  receiving end network switches; and   10. The network monitoring and control system  100   a  that serves to coordinate and arbitrate the operations of both the transmitting end controller  10   a  and the receiving end controller  10   b.      

     It should be noted that the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  and the plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . . ,  405  serve to convert transmission data optical signals transmitted by the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  from 1310 nm or 1500 nm optical signals into the ITU-T DWDM (Dense Wavelength Division Multiplexing) or ITU-T CWDM (Coarse Wavelength Division Multiplexing) transmission format, before relaying aforementioned transmission data optical signals to the subsequent stage of the transmitting end  200   a  of the broadband optical communication network  350  of the present invention and hence the receiving end  200   b  via the main fiber link  700  of the broadband optical communication network  350  of the present invention. Conversely, at the receiving end  200   b , the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ and the plurality of receiving end wavelength tuneable transponders  400 ′,  401 ′, . . . ,  405 ′ serve to the de-multiplexed transmission data optical signals, received via the output lines of the receiving end CWDM/DWDM optical de-multiplexer  501  from 1310 nm or 1500 nm optical signals into optical signals with the ITU-T DWDM/CWDM transmission format. 
     The operation of the broadband optical communication network  300  of the present invention will now be described with reference to  FIGS. 2 to 5 . 
     With reference to  FIG. 2 , during normal operation, when none of the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  and the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ experience a fault will now be described. 
     Under normal operation, at the transmitting end  200   a , a plurality transmission data optical signals  900 ,  901 , . . . ,  905  originating from the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  respectively are received by the transmitting end network switch  200 . Said transmitting end network switch  200 , subsequently transmits said plurality of transmission data optical signals  900 ,  901 , . . . ,  905  originating from the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  to the corresponding plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  upon receipt of a control signal from the transmitting end controller  10   a . The plurality of transmitting end transponders  300 ,  301 , . . . ,  305  respectively receiving aforementioned respective transmission data optical signals  900 ,  901 , . . . ,  905  via the first plurality transmitting end of fibre links  801 , converting the aforementioned transmission data optical signals  900 ,  901 , . . . ,  905  from 1310 nm or 1500 nm optical signals to ITU-T CWDM or DWDM transmission format transmission data optical signals  900 ,  901 , . . . ,  905  and transmitting these signals  900 ,  901 , . . . ,  905  to the transmitting end CWDM/DWDM optical multiplexer  500 . Said transmitting end CWDM/DWDM optical multiplexer  500 , upon receipt of the plurality of transmission data optical signals  900 ,  901 , . . . ,  905  originating from the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105 , subsequently wavelength multiplexes said transmission data optical signals  900 ,  901 , . . . ,  905  to consequently produce and transmit a wavelength division multiplexed transmission data optical signal  1000  to the 1×2 optical coupler  601 . The 1×2 optical coupler  601  serving to optically couple the wavelength division multiplexed transmission data optical signal  1000  with a transmission data optical signal  900 ,  901 , . . . ,  905  originating from the output of the 1×N optical coupler  600 . Since, under normal operation, with no faults occurring in the plurality of first fibre links  201  and plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305 , there will not be any transmission data optical signal  900 ,  901 , . . . ,  905  originating from any one of the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105  that will routed and transmitted by the transmitting end network switch  200  to any one of the plurality of transmitting end wavelength tuneable transponders  400 ,  401 , . . .  405  and hence no transmission data optical signal  900 ,  901 , . . . ,  905  will be fed to the 1×N optical coupler  600 , resulting in the 1×N optical coupler  600  output being without an optical signal output. Consequently, the result of the optical coupling, by the 1×2 optical coupler  601  of the wavelength multiplexed transmission data optical signal  1000  with the output of the 1×N optical coupler  600  yields nothing but the wavelength multiplexed transmission data optical signal  1000 . Said 1×2 optical coupler  601 , subsequently transmits said wavelength multiplexed transmission data optical signal  1000  to the receiving end  200   b  of the broad-band optical communication network  350  of the present invention via the main fibre link  700 . 
     Upon receipt of the wavelength multiplexed transmission data optical signal  1000  by the receiving end  200   b  of the broad-band optical communication network  350  of the present invention, the receiving end CWDM/DWDM optical de-multiplexer  501 , de-multiplexes the received wavelength division multiplexed transmission data optical signal  1000  into its individual wavelength constituents, namely the transmission data optical signals  900 ,  901 , . . . ,  905  that respectively correspond to transmission data optical signals originating from the first transmitting end CPE  100 , the second transmitting end CPE  101 , . . . , and the final transmitting end CPE  105 . Consequently aforementioned transmission data optical signals  900 ,  901 , . . . ,  905  become available at the transmitting side (output side) output lines of the receiving end CWDM/DWDM de-multiplexer  501  and subsequently propagate to the first receiving end network switch  201 . Since, under the condition of the normal operation, where none of the none of the fibre links interconnecting the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305  at the transmitting end  200   a  and none of the fibre links interconnecting the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ at the receiving end  200   b  experience a fault, the resulting wavelength de-multiplexed transmission data optical signals  900 ,  901 , . . . ,  905 , being routed by the first receiving end network switch  201  due to execution of control instructions received by the receiving end controller  10   b , to the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′. The plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ serving convert aforementioned de-multiplexed transmission data optical signals  900 ,  901 , . . . ,  905  from ITU-T CWDM or DWDM transmission format to 1310 nm or 1500 nm optical signals and to relay said plurality of wavelength de-multiplexed transmission data optical signal  900 ,  901 , . . . ,  905  to a second receiving end network switch  202 . The second receiving end network switch  202 , under the control of the receiving end controller  10   b , route aforementioned wavelength de-multiplexed transmission data optical signals  900 ,  901 , . . . ,  905  to the respective receiving end CPE  100 ′,  101 ′, . . . ,  105 ′ of the plurality of receiving end CPEs  100 ′,  101 ′, . . . ,  105 ′. More particularly, transmission data optical signal  900 , having a first wavelength is routed to CPE  100 ′, transmission data optical signal  901 , having a second wavelength is routed to CPE  101 ′ and transmission data optical signal  905 , having a third wavelength is routed to CPE  105 ′. 
     With reference to  FIG. 3 , the operation of the broadband optical communication network  350  of the present invention when there is a fault in any one of the fiber links interconnecting the plurality of transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305 , any one of the transmitting end non-tuneable transponders  300 ,  301 , . . . ,  305 , any one of the fiber links interconnecting the plurality of receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′ and any one of the receiving end non-tuneable transponders  300 ′,  301 ′, . . . ,  305 ′. 
     More particularly, with reference to  FIG. 3 , the operation of the broadband optical communication network  350  of the present invention when one transmission path at the transmitting end  200   a , i.e. the transmission path that includes the transmitting end non-tuneable transponder  300  and the fibre links that interconnect to said transmitting end non-tuneable transponder  300  and one transmission path at the receiving end  200   b , i.e. the transmission path that includes the receiving end non-tuneable transponder  305 ′ and the fibre links that interconnect to said receiving end non-tuneable transponder  305 ′ both experience a fault, will now be described. 
     At, the transmitting end  200   a , since the transmission data optical signal transmission path which includes the transmitting end non-tuneable transponder  300  and the fibre link interconnecting said transmitting end non-tuneable transponder  300  which includes one of the fibre links of the first plurality of transmitting end fibre links  801  experiences a fault, the transmission data optical signal  900  having a first wavelength emitted by the first transmitting end CPE  100  and that is destined for the first non-tuneable transmitting end transponder  300 , is instead instructed by the transmitting end controller  10   a , to route aforementioned transmission data optical signal  900 , to the corresponding transmitting end wavelength tuneable transponder  400 , i.e. the wavelength tuneable transponder  400  that is symmetrically opposite in location to the faulty first non-tuneable transmitting end transponder  300 . The above sequence of events effected upon detection of a fault and after tuning of the transmitting end wavelength tuneable transponder  400  by said transmitting end controller  10   a . The transmitting end controller  10   a , tunes aforementioned wavelength tuneable transponder  400  to be responsive to the wavelength of the first transmission data optical signal  900  emitted by the transmitting end CPE  100 , by way of control signals transmitted to the transmitting end network switch  200  and executed by the transmitting end network switch  200 . 
     Subsequent to the tuning of aforementioned transmitting end wavelength tuneable transponder  400  to be responsive to a transmission data optical signal having a first wavelength emitted by the first CPE  100  of the plurality of transmitting end CPEs  100 ,  101 , . . . ,  105 , aforementioned first transmission data optical signal  900  is routed by the transmitting end network switch  200  to aforementioned transmitting end wavelength tuneable transponder  400 . Said transmitting end wavelength tuneable transponder  400 , converting the received transmission data optical signal  900  from a 1310 nm or 1500 nm optical signal into an optical signal with the ITU-T CWDM or DWDM transmission format transmission data optical signal. The transmission data optical signal  900  is then fed to one of the input lines of the 1×N optical coupler  600 . Since the remaining normal transmission paths that include the remaining transmitting end non-tuneable transponders  301 , . . . ,  305  and the fibre links that interconnect to them do not experience a fault, the remaining transmission data optical signals  901 , . . . ,  905  originating from transmitting end CPEs  101 , . . . ,  105  are not transmitted to the other transmitting end wavelength tuneable transponders  401 , . . . ,  405  via the second plurality of transmitting end fibre links  802 , consequently resulting in the output of the 1×N coupler being the transmission data optical signal  900 . The output of the 1×N coupler  600 , which in this case is the transmission data optical signal  900  subsequently, propagates to one of the input lines of the 1×2 coupler  601 . 
     Since the remaining normal transmission paths that include the remaining transmitting end non-tuneable transponders  301 , . . . ,  305  and the fibre links that interconnect to them do not experience a fault, the remaining transmission data optical signals  901 , . . . ,  905  originating from transmitting end CPEs  101 , . . . ,  105  are transmitted with the respective fibre links of the plurality of first transmitting end fibre links  801  to aforementioned remaining transmitting end non-tuneable transponders  301 , . . . ,  305 . Aforementioned remaining transmitting end non-tuneable transponders  301 , . . . ,  305  converting the received transmission data optical signals  901 , . . . ,  905  from the 1310 or 1500 nm optical signals to ITU-T CWDM or DWDM transmission format transmission data optical signals  901 , . . . ,  905 . Aforementioned remaining transmission data optical signals  901 , . . . ,  905  subsequently being relayed by the aforementioned remaining transmitting end non-tuneable transponders  301 , . . . ,  305  to the transmitting end CWDM/DWDM multiplexer  500  which wavelength multiplexes aforementioned remaining transmission data optical signal  901 , . . . ,  905  resulting in a wavelength division multiplexed transmission data optical signal  1000  at the output of the transmitting end CWDM/DWDM optical multiplexer  500  that subsequently propagates to another one of the two input lines of the 1×2 optical coupler  601  (the other input line receiving the transmission data optical signal  900  via the 1×N optical coupler  600 ). 
     The resulting output of the 1×2 optical coupler  601  due to the coupling of the wavelength multiplexed transmission data optical signal  1000  from the output of the transmitting end CWDM/DWDM multiplexer  500  and the coupling of the transmission data optical signal  900  from the output of the transmitting end 1×N optical coupler  600  is a composite optical signal  1001 , subsequently launches into the main fibre link  700 . 
     Upon receipt of the composite optical signal  1001  at the receiving end  200   b  of the broadband optical communication network  350  of the present invention, aforementioned composite optical signal  1001  is wavelength de-multiplexed by the receiving end CWDM/DWDM wavelength de-multiplexer  501  into is constituent transmission data optical signals  900 ,  901 , . . . ,  905 . Since, as has been mentioned in passages preceding this passage, that in the description of the operation of the broadband optical communication network  350  of the present invention, the receiving end non-tuneable transponder  305 ′ and the fibre links interconnecting to it experiences a fault, the plurality of transmission data optical signal  900 ,  901 , . . . ,  905  that result from the optical de-multiplexing of the composite optical signal  1001 , are respectively received and routed by the first receiving end network switch  201  to the receiving end non-tuneable transponder  300 ′, the receiving end non-tuneable transponder  301 ′ and the receiving wavelength tuneable transponder  405 ′. More particularly transmission data optical signal  900  is routed to the receiving end non-tuneable transponder  300 ′, transmission data optical signal  901  is routed to the receiving end non-tuneable transponder  301 ′ and the transmission data optical signal  905  is routed to the receiving end wavelength tuneable transponder  405 ′. The receiving end first network switch  201  transmitting and receiving control instructions from the receiving end controller  10   b  with relation to the detection of a fault in the receiving end non-tuneable transponder  305 ′ and the fibre links interconnecting to it and subsequently tuning the receiving end wavelength tuneable transponder  405 ′ to be responsive to the same wavelength transmission data optical signal (i.e. transmission data optical signal  905 ) as the receiving end non-tuneable transponder  305 ′. 
     Upon reception of the plurality of transmission data optical signals  900 ,  901 , . . . ,  905  by the receiving end non-tuneable transponder  300 ′, the receiving end non-tuneable transponder  301 ′ and the receiving end wavelength tuneable transponder  305 ′ respectively. Aforementioned transmission data optical signals  900 ,  901 , . . . ,  905  are converted from the ITU-T CWDM/DWDM frame format to 1310 nm or 1500 nm transmission data optical signals  900 ,  901 , . . . ,  905  and transmitted to the respective input lines at the receiving side (i.e. input side) of the second receiving end network switch  202 . Aforementioned second receiving network switch  202  under the control of the receiving end controller  10   b , subsequently routes aforementioned converted transmission data optical signal  900 ,  901 , . . . ,  905  originating respectively from said receiving end non-tuneable transponder  300 ′, receiving non-tuneable transponder  301 ′ and receiving end wavelength tuneable transponder  400 ′ to the corresponding receiving end CPE  100 ′,  101 ′, . . . ,  105 ′ of the plurality of receiving end CPEs  100 ′,  101 ′, . . . ,  105 ′.