Patent Publication Number: US-7903968-B2

Title: Optical network transmission channel failover switching device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to optical networking technology, and more particularly, to an optical network transmission channel failover switching device which is designed for use with an optical network, such as a local area network used for linking Internet to the clients or a telephone network, for the purpose of providing the optical network with a transmission channel failover switching function. 
     2. Description of Related Art 
     Optical networking is a communication technology that utilizes optical fibers and laser beams for data transmission between computers, telephones and other electronic devices. Optical networks can be used to transmit signals either in analog or digital forms. Since laser beams are much higher in frequency than electrical and radio signals, optical networking is far more reliable and has far greater transmission capacity than traditional cable and radio communications. 
     PON (Passive Optical Network) systems are a widely employed technology for data communication between the Internet and local area networks that are used for connection to private users and small business entities. In practice, a PON system typically utilizes just one single strand of optical fiber for two-way transmission of optical signals to and from the client sites. One drawback to the traditional single-fiber two-way PON systems, however, is that when the single fiber is damaged or fractured, the data communication to the client sites is entirely disconnected. One solution to this problem is to provide two channels (i.e., two strands of fibers) in the optical transmission path: a primary channel and a secondary channel, where the primary channel is initially set to be responsible for optical transmission while the secondary channel is set to standby mode, such that in the event of a failure to the primary channel (such as when fractured), the failed primary channel can be failover switched to the backup channel. 
     To achieve the above-mentioned failover purpose, it is needed to develop an optical transmission channel failover switching device capable of switching the primary channel over to the backup channel in the event of a failure to the primary channel. Presently, one solution is to utilize two one-to-two (1×2) optical switches in an optical auto switch (OAS) to provide the desired failover switching function. One drawback to this solution, however, is that it lacks the capability of monitoring the backup channel to check whether the backup channel is in good usable condition when the primary channel fails. As a consequence, if the backup channel is also in unusable condition when the primary channel fails, it will cause the entire optical network system to shut down, resulting in degraded serviceability and security to network services. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of this invention to provide an optical network transmission channel failover switching device which is capable of providing a backup channel monitoring capability for failover switching of the primary channel. 
     The optical network transmission channel failover switching device according to the invention is designed for use with an optical network, such as a local area network used for linking to the Internet or a telephone network, for the purpose of providing the optical network with a transmission channel failover switching function. 
     In architecture, the optical network transmission channel failover switching device according to the invention comprises: (A) an equipment-side interface, which includes an input port and an output port; (B) a channel-side interface, which includes a first transmission port, a second transmission port, a first reception port, and a second reception port; (C) a first optical switching module, which includes a first connecting port, a second connecting port, a third connecting port, and a fourth connecting port, and which is capable of providing a two-to-two optical switching function for selectively connecting the first connecting port and the second connecting port to the third connecting port and the fourth connecting port; wherein the first connecting port is connected to the input port of the equipment-side interface, the second connecting port is used for monitoring beam reception and routing, the third connecting port is connected via the first transmission port of the channel-side interface to the primary channel of the optical fiber, and the fourth connecting port is connected via the second transmission port of the channel-side interface to the backup channel of the optical fiber; (D) a second optical switching module, which includes a first connecting port, a second connecting port, and a third connecting port, and is capable of providing a one-to-two optical switching function for connecting the first connecting port selectively to either one the second connecting port and the third connecting port; and wherein the first connecting port is connected to the output port of the equipment-side interface, the second connecting port is used for connection via the first input port of the channel-side interface to the primary channel of the optical fiber, and the third connecting port is used for connection via the second reception port of the channel-side interface to the backup channel of the optical fiber; (E) a monitoring beam generating module, which is capable of generating a monitoring beam and emitting the monitoring beam to the second connecting port of the first optical switching module for injection via the first optical switching module into the backup channel of the optical fiber; (F) a first optical sensing module, which is coupled to the first input port of the channel-side interface for detecting whether the primary channel of the optical fiber transmits optical signals normally; and if yes, capable of generating a first opto-electro signal; (G) a second optical sensing module, which is coupled to the second reception port of the channel-side interface for detecting whether the backup channel of the optical fiber transmits the monitoring beam normally; and if yes, capable of generating a second opto-electro signal; and (H) a communication module, which is capable of responding to the first opto-electro signal and the second opto-electro signal by generating a corresponding switching control signal to activate the first optical switching module and the second optical switching module to perform a failover switching action from the failed primary channel to the backup channel. 
     The optical network transmission channel failover switching device according to the invention is characterized by the provision of a two-to-two (2×2) type of optical switch, a one-to-two (1×2) type of optical switch, and a monitoring beam generating module for providing a backup channel monitoring function that can be used to activate the switching action. This feature allows the utilization of the optical network system to have enhanced reliability, serviceability, and security. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
         FIG. 1A  is a schematic diagram showing the application of the optical network transmission channel failover switching device of the invention with a typical type of optical network system; 
         FIG. 1B  is a schematic diagram showing the application of the invention with an advanced type of optical network system having EDFA circuitry; and 
         FIG. 2  is a schematic diagram showing a modularized architecture of the optical network transmission channel failover switching device of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The optical network transmission channel failover switching device according to the invention is disclosed in full details by way of preferred embodiments in the following with reference to the accompanying drawings. 
       FIGS. 1A-1B  are two schematic diagrams used to illustrate the application of the optical network transmission channel failover switching device according to the invention (as the block indicated by the reference numeral  100 ) with an optical network system  10 . It is to be noted that in this application, two devices of the invention should be used.  FIG. 1A  shows the application of the invention with a typical optical network system, while  FIG. 1B  shows the application of the invention with an advanced type of optical network system that is equipped with EDFA (Erbium-Doped Fiber Amplifier) modules  50 . 
     As shown, the optical network system  10  is equipped with a local-side optical signal processing unit  20  and a remote-side optical signal processing unit  30  which are interconnected to each other via an optical fiber  40  having a primary channel  41  and a backup channel  42 . The backup channel  42  is used as a redundant backup for the primary channel  41 . In Internet applications, for example, the optical network system  10  can be a PON (Passive Optical Network) system, and the local-side optical signal processing unit  20  is an optical line terminal (OLT), while the remote-side optical signal processing unit  30  is an optical network unit (ONU). The local-side optical signal processing unit  20  and the remote-side optical signal processing unit  30  each have a beam emitting port TX 1 , TX 2  for emitting an optical signal beam to the opposite side and a beam reception port RX 1 , RX 2  for receiving the optical signal beam from the opposite side. 
     In practice, the primary channel  41  is used as the main transmission route for the local-side optical signal processing unit  20  and the remote-side optical signal processing unit  30  to exchange optical signals, i.e., the local-side optical signal processing unit  20  can output an optical signal from its beam emitting port TX 1  and transmit the outputted optical signal via the primary channel  41  of the optical fiber  40  to the beam reception port RX 2  of the remote-side optical signal processing unit  30 ; and vice versa, the remote-side optical signal processing unit  30  can output an optical signal from its beam emitting port TX 2  and transmit the outputted optical signal also via the primary channel  41  of the optical fiber  40  to the beam reception port RX 1  of the local-side optical signal processing unit  20 . In the event of a failure to the primary channel  41 , the two optical network transmission channel failover switching devices of the invention  100  will be simultaneously activated for failover switching to the backup channel  42 , such that under this condition, the local-side optical signal processing unit  20  and the remote-side optical signal processing unit  30  can nevertheless use the backup channel  42  for exchange of optical signals. 
     As shown in  FIG. 2 , the optical network transmission channel failover switching devices of the invention  100  each comprises: (A) an equipment-side interface  110 ; (B) a channel-side interface  120 ; (C) a first optical switching module  210 ; (D) a second optical switching module  220 ; (E) a monitoring beam generating module  230 ; (F) a first optical sensing module  240 ; (G) a second optical sensing module  250 ; and (H) a communication module  260 . Firstly, the respective attributes and behaviors of these modules are described in details in the following. 
     The equipment-side interface  110  is used for coupling to either the local-side optical signal processing unit  20  or the remote-side optical signal processing unit  30 , and which includes an input port IN and an output port OUT. As shown in  FIGS. 1A-1B , its input port IN is used for connection to either the beam emitting port TX 1  of the local-side optical signal processing unit  20  or the beam emitting port TX 2  the remote-side optical signal processing unit  30 , while its output port OUT is used for connection to the beam reception port RX 1 /RX 2  of the same. 
     The channel-side interface  120  is used for coupling to the optical fiber  40 , and which includes a first transmission port OUT 1 , a second transmission port OUT 2 , a first reception port IN 1 , and a second reception port IN 2 . As shown in  FIGS. 1A-1B , the first transmission port OUT 1  is used for connection to the primary channel  41 , the second transmission port OUT 2  is used for connection to the backup channel  42 , the first input port IN 1  is used for connection to the primary channel  41 , and the second reception port IN 2  is used for connection to the backup channel  42 . 
     The first optical switching module  210  is a 2×2 (two-to-two) type of optical switch, which includes a first connecting port P 1 , a second connecting port P 2 , a third connecting port P 3 , and a fourth connecting port P 4 , and which is capable of providing a two-to-two optical switching function for selectively connecting the first connecting port P 1  and the second connecting port P 2  to the third connecting port P 3  and the fourth connecting port P 4 . In assembly, the first connecting port P 1  is connected to the input port IN of the equipment-side interface  110 ; the second connecting port P 2  is used for reception of a monitoring beam from the monitoring beam generating module  230 ; the third connecting port P 3  is connected via the first transmission port OUT 1  of the channel-side interface  120  to the primary channel  41  of the optical fiber  40 ; and the fourth connecting port P 4  is connected via the second transmission port OUT 2  of the channel-side interface  120  to the backup channel  42  of the optical fiber  40 . The switching action of the first optical switching module  210  is controlled by a switching control signal SW for selectively connecting the first connecting port P 1  and the second connecting port P 2  to the third connecting port P 3  and the fourth connecting port P 4 . 
     The second optical switching module  220  is a 1×2 (one-to-two) type of optical switch, which includes a first connecting port Q 1 , a second connecting port Q 2 , and a third connecting port Q 3 , and which is capable of providing a one-to-two optical switching function for selectively connecting the first connecting port Q 1  to either the second connecting port Q 2  or the third connecting port Q 3 . In assembly, the first connecting port Q 1  is connected to the output port OUT of the equipment-side interface  110 , the second connecting port Q 2  is used for connection via the first input port IN 1  of the channel-side interface  120  to the primary channel  41  of the optical fiber  40 , and the third connecting port Q 3  is used for connection via the second reception port IN 2  of the channel-side interface  120  to the backup channel  42  of the optical fiber  40 . The switching action of the second optical switching module  220  is also controlled by the above-mentioned switching control signal SW for connecting the first connecting port Q 1  selectively to either the second connecting port Q 2  or the third connecting port Q 3 . 
     The monitoring beam generating module  230  is preferably implemented with a laser diode (LD), which is capable of generating a laser beam for use to serve as a monitoring beam and emitting the monitoring beam to the second connecting port P 2  of the first optical switching module  210  for injection via the first optical switching module  210  into the backup channel  42  of the optical fiber  40 . When the laser beam is injected into the backup channel  42 , it serves as a monitoring beam for the backup channel  42  for detection of whether the backup channel  42  can work normally. 
     The first optical sensing module  240  is coupled to the first input port IN 1  of the channel-side interface  120  for detecting whether the primary channel  41  of the optical fiber  40  can transmit optical signals normally. If the primary channel  41  can work normally, the optical signal beam transmitting therein will be sensed by the first optical sensing module  240 , causing the generation of a first opto-electro signal I op1 . In practice, for example, this first optical sensing module  240  is implemented with an optical splitter  241  and a photo diode (PD)  242 ; wherein the optical splitter  241  is connected via the first input port IN 1  of the channel-side interface  120  to the primary channel  41  of the optical fiber  40  for intercepting the optical signal beam in the primary channel  41 ; while the photo diode  242  is capable of sensing the optical beam intercepted by the optical splitter  241  and responsively generating the first opto-electro signal I op1 . 
     The second optical sensing module  250  is coupled to the second reception port IN 2  of the channel-side interface  120  for detecting whether the backup channel  42  of the optical fiber  40  can transmit optical signals normally. If the backup channel  42  can work normally, the optical beam (i.e., the above-mentioned monitoring beam) transmitting therein will be sensed by the second optical sensing module  250 , thus causing the generation of a second opto-electro signal I op2 . In practice, for example, this second optical sensing module  250  is implemented with an optical splitter  251  and a photo diode (PD)  252 ; wherein the optical splitter  251  is connected via the second reception port IN 2  of the channel-side interface  120  to the backup channel  42  of the optical fiber  40  for intercepting the monitoring beam in the backup channel  42 ; while the photo diode  252  is capable of sensing the monitoring beam intercepted by the optical splitter  251  and responsively generating the second opto-electro signal I op2 . 
     The communication module  260  is capable of responding to the first opto-electro signal I op1  and the second opto-electro signal I op2  by generating a corresponding switching control signal SW to activate the first optical switching module  210  and the second optical switching module  220  to perform a failover switching action between the primary channel  41  and the backup channel  42  of the optical fiber  40 . In practice, the switching control signal SW can be implemented in such a manner that when the light intensity at the first input port IN 1  is higher than a threshold value (indicating that the primary channel  41  can operate normally), then SW=0 and thus no failover switching action is activated; and when the light intensity at the first input port IN 1  isn&#39;t only lower than the threshold value (indicating that the primary channel  41  fails to work normally) but the light intensity at the second reception port IN 2  is higher than the threshold value (indicating that the backup channel  42  can work normally), then SW=1 and a failover switching action is enabled. In practice, for example, the communication module  260  is integrated to an ERC (Embedded Remote Communication) circuit. Moreover, if the light intensity at the second reception port IN 2  is lower than the threshold value, it indicates that the backup channel  42  also fails to work normally, and the communication module  260  will responsively generate a backup-channel failure notifying message FAIL and display the FAIL message on a network workstation (not shown) or directly on the local-side optical signal processing unit  20  or the remote-side optical signal processing unit  30  with a flashing light or beep to notify the network management personnel to perform maintenance work on the optical fiber  40 . 
     The following is a detailed description of a practical application example of the optical network transmission channel failover switching devices of the invention  100  during actual operation. 
     At start of operation, the optical network transmission channel failover switching devices of the invention  100  are preset to connect both the local-side optical signal processing unit  20  and the remote-side optical signal processing unit  30  to the primary channel  41  of the optical fiber  40 ; i.e., initially, the first optical switching module  210  is preset to connect its first connecting port P 1  to the third connecting port P 3  and its second connecting port P 2  to the fourth connecting port P 4 , while the second optical switching module  220  is preset to connect its first connecting port Q 1  to the second connecting port Q 2 . This connection state allows the local-side optical signal processing unit  20  and the remote-side optical signal processing unit  30  to exchange optical signals via the primary channel  41 . At the same time, the monitoring beam generating module  230  is activated to generate a laser beam which is then injected by way of the first optical switching module  210  (i.e., 2×2 optical switch) into the backup channel  42  for use to serve as a monitoring beam in the backup channel  42 . 
     When the primary channel  41  operates normally, the optical signal beam transmitting therein will be intercepted by the optical splitter  241  of the first optical sensing module  240  and then sensed by the photo diode  242 . If the light intensity is higher than a preset threshold value, it causes the photo diode  242  to generate a first opto-electro signal I op1 . In this case, the communication module  260  responsively outputs SW=0, which causes no switching action to the first optical switching module  210  and the second optical switching module  220 . Therefore, the first optical switching module  210  and the second optical switching module  220  still connect the primary channel  41  for transmission of optical signal beams. 
     On the other hand, in the event of a failure to the primary channel  41 , the light intensity at the first input port IN 1  drops below the threshold value, which then causes the output of I op1  from the photo diode  242  to be interrupted. In this case, if the backup channel  42  is still in good condition, the monitoring beam transmitting inside the backup channel  42  can be detected by the photo diode  252  of the second optical sensing module  250  (i.e., the light intensity at the second reception port IN 2  is higher than the threshold value). This causes the communication module  260  to output SW=1 to enable a switching action to the first optical switching module  210  and the second optical switching module  220 . In response, the first optical switching module  210  switches its first connecting port P 1  for redirected connection to the fourth connecting port P 4  and its second connecting port P 2  for redirected connection to the third connecting port P 3 ; and concurrently, the second optical switching module  220  switches its first connecting port Q 1  for redirected connection to the third connecting port Q 3 . At the same time, this switching control signal SW is also transmitted via the backup channel  42  to the opposite side for the optical network transmission channel failover switching device of the invention  100  on the opposite side to perform a similar switching action, i.e., causing the first optical switching module  210  to switch its first connecting port P 1  to the fourth connecting port P 4  and its second connecting port P 2  to the third connecting port P 3 ; and concurrently, causing the second optical switching module  220  to switch its first connecting port Q 1  to the third connecting port Q 3 . As a result, the primary channel  41  is failover switched to the backup channel  42 . 
     However, if the light intensity at the second reception port IN 2  is also lower than the threshold value, it indicates that the backup channel  42  also fails to work normally, and the communication module  260  will responsively generate a backup-channel failure notifying message FAIL and display the FAIL message on a network workstation (not shown) or directly on the local-side optical signal processing unit  20  or the remote-side optical signal processing unit  30  with a flashing light or beep to notify the network management personnel to perform maintenance work on the optical fiber  40 . 
     In conclusion, the invention provides an optical network transmission channel failover switching device which is designed for use with an optical network for providing the optical network with a transmission channel failover switching function, and which is characterized by the provision of a two-to-two (2×2) type of optical switch, a one-to-two (1×2) type of optical switch, and a monitoring beam generating module for providing a backup channel monitoring function that can be used to activate the switching action. This feature allows the utilization of the optical network system to have enhanced reliability, serviceability, and security. The invention is therefore more advantageous to use than the prior art. 
     The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.