Patent Publication Number: US-2016234582-A1

Title: Method and system for redundancy in a passive optical network

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/114,269 filed Feb. 10, 2015, the disclosure of which is incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention is related to optical networking and in particular, redundancy in a passive optical network. 
     BACKGROUND OF THE INVENTION 
     Passive optical networking (PON) is well known in the art to provide telecom services, such as video, voice and data. However, the use and requirements of telecom providers are very different than those of the enterprise. While telecom providers must are closed networks with very specialized and highly trained network engineers, enterprise users may run the gamut from knowledgeable to novices. Furthermore, building owners or operators may be concerned about network security in the PON deployments due to increased threats of placing network ports throughout a building. System uptime may also be a large concern. 
     A better paradigm for providing redundancy in a passive optical network is desired. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide an improved network topology including redundancy in passive optical networks. 
     In one aspect, the invention may reside in a networking data collector. The networking data collector may include a passive optical networking system and means for obtaining and storing network information from the at least one optical networking terminal. The PON system may include: at least one optical line terminal (OLT); a passive optical splitter; and at least one optical networking terminal (ONT). 
     In another aspect, the invention may reside in an analytics engine. The engine may include a passive optical network, means for collecting networking information from components in the passive optical network; identifying patterns in the network information; and notifying a user based on the patterns identified. 
     In another aspect, the present invention may reside in a networking data collector. The data collector may include: a passive optical networking system including: at least one optical line terminal (OLT); a passive optical splitter; and at least one optical networking terminal (ONT), means for obtaining and storing network information from the at least one optical networking terminal. The network information may, for each device at a particular ONT, include at least one of: destination address, source address, timing, amount of traffic, link-speed, timing, and traffic direction. 
     Alternately, the network information may include, for each device at a particular ONT, at least one of: return transit time (RTT), received signal strength indicators (RSSI), transmitted signal strength indicators (TSSI), current bias of the laser, temperature, and laser drift. 
     In another aspect, the present invention may reside in an analytics engine. The analytics engine may include: a passive optical network; means for collecting networking information from components in the passive optical network; identifying patterns in the network information; and notifying a user based on the patterns identified. In some embodiments, the pattern may be based on at least one of destination address, source address, timing, amount of traffic, link-speed, timing, and traffic direction. In other embodiments, the pattern may be based on PON parameters including at least one of return transit time (RTT), received signal strength indicators (RSSI), transmitted signal strength indicators (TSSI), current bias of the laser, temperature, and laser drift. 
     In some embodiments, the analytics engine creates a device signature for each device in the network. In other embodiments, the device signature may be based on heuristics over many devices of the same model or type or may be based on at least one of traffic profile, power profile and communication peers. In even further embodiments, the device signature may be based on the combination of traffic profile, power profile and communication peers. 
     In some preferred embodiments, the traffic profile may include the ratio of up/down traffic. Further, the analytics engine may identify a pattern for predicting a device failure. For example, the analytics engine may identify the pattern for device failure based on packet loss, timing. In some embodiments, the analytics engine may identify the pattern for device failure based on drifts in power consumption or based on a learning pattern of behaviour. In other embodiments, the pattern for device failure may be based on a combination of a learning pattern of behaviour and rules set by a device manufacturer. Similarly, the learning pattern may use at least one of heuristics and machine learning or may be selected from a change in MAC address, a change in power consumption, and a change in traffic profile. Alternately, in some embodiments the learning pattern may use at least one of time of day, seasonal changes, a weather almanac, business hours, and other forms of periodicity. 
     The pattern for a camera may change in response to commands sent to the camera. The command may be one of point, tilt, and zoom of the camera and may lead to changes in expected power consumption. 
     In a preferred embodiment, the analytics engine identifies a pattern for a network intrusion. Similarly, the analytics engine identifies a pattern for learning and tracking device behaviour over time. 
     Alternately, the analytics engine may identify a signature for every packet in the networking system. The analytics engine may identify a signature for every port in the networking system. The analytics engine may identify a signature for every device in the networking system. The analytics engine may identify a signature for every ONT in the networking system. 
     In yet another aspect, the invention may reside in a passive optical networking (PON) system implementing redundancy. Such a system may include a first optical line terminal (OLT), a second optical line terminal, a first optical networking terminal (ONT) including an optical port and at least one Ethernet port; and a first passive optical splitter. The first and the second OLT may include at least one Ethernet port and a first optical port having a transmit function and a receive function. 
     The passive optical splitter may include a first optical input optically coupled to the first optical port of the first OLT, a second optical input optically coupled to the first optical port of the second OLT, and a plurality of optical outputs, wherein a first optical output is optically coupled to the optical port of the first ONT. 
     In operation, the first ONT may be registered with the first OLT and the second OLT may have the transmit function of the first optical port turned off. The receive function of the first optical port on the second OLT may be turned on and may be listening to the communication between the first OLT and the first ONT. When the second OLT no longer receives a signal indicating that the first OLT is still registered with the first ONT, the second OLT may turn on the receive function of the first optical port and registers with the first ONT. 
     In yet another aspect, the present invention may reside in a passive optical networking (PON) system for implementing redundancy. The system may include a first optical line terminal (OLT) including at least one Ethernet port; a first optical port having a transmit function and a receive function; a second optical line terminal (OLT) including at least one Ethernet port; a first optical port having a transmit function and a receive function; a first optical networking terminal (ONT) including an optical port and at least one Ethernet port; a first passive optical splitter including: a first optical input optically coupled to the first optical port of the first OLT; a second optical input optically coupled to the first optical port of the second OLT; and a plurality of optical outputs, wherein a first optical output is optically coupled to the optical port of the first ONT; and wherein the first OLT cannot directly communicate with the second OLT through the first passive optical splitter. In operation, the first ONT is registered with the first OLT and the second OLT has the transmit function of the first optical port turned off, but the receive function turned on and is listening to the communication from the first ONT to the first OLT. When the second OLT no longer receives a signal indicating that the first OLT is still registered with the first ONT, the second OLT turns on the receive function of the first optical port and registers with the first ONT to allow the flow of traffic from the first ONT to the second OLT. 
     In yet another aspect, the present invention may reside in a state machine for implementing redundancy in a passive optical network. The passive optical network may include an optical line terminal (OLT) with multiple optical channels. The state machine includes an ACTIVE state, a PROTECT state and a STANDBY state. The ACTIVE state allows the OLT to register with at least one optical line terminal (ONT) and to pass traffic with the at least one ONT under normal operation. 
     The PROTECT state continuously monitors the RSSI of the at least one ONT connected to a different OLT in the ACTIVE state, where in the OLT in the PROTECT state has disabled its transmit capabilities and has enabled its receive capabilities. 
     Finally, the STANDBY state is used after initial STARTUP to ensure that the OLT does not immediately shine a laser and interfere with the different OLT in the ACTIVE state. 
     In yet another aspect, the present invention resides in a method for implementing redundancy in a passive optical network. The method may include optically coupling a first optical line terminal (OLT) and a second OLT to at least one optical networking terminal (ONT) through a two-to-many passive optical splitter. The first OLT may be optically coupled to the first input of the passive optical splitter and the second OLT may be optically coupled to the second input of the passive optical splitter, with traffic passing from the at least one ONT through the first OLT. The method may also include disabling the transmit function and enabling the receive function on the optical port of the second OLT. The method may also include monitoring the received signal strength indicator (RSSI) on the second OLT to create a takeover signal if the link between the at least one ONT and the first OLT is disconnected. The method may also include enabling the transmit function on the optical port of the second OLT and registering the second OLT with the at least one ONT on receipt of the takeover signal. The method may also include enabling the second OLT to takeover the role of passing traffic with the at least one ONT, from the first OLT; and the method may also include passing the traffic from the at least one ONT through the second OLT after the successful completion of the takeover. 
     Other devices, methods and machine-readable media are also described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is described by way of example with reference to the following accompanying drawings, wherein: 
         FIG. 1  shows a local area network in accordance with an embodiment of the present invention; 
         FIG. 2  shows a local area network implementing redundancy between two OLTs in accordance with an embodiment of the present invention; 
         FIG. 3  shows a local area network implementing redundancy between two OLTs in accordance with an embodiment of the present invention; 
         FIG. 4  shows a flowchart for a method for implementing redundancy in accordance with an embodiment of the present invention; and 
         FIG. 5  shows a state diagram for implementing redundancy in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the disclosure will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure. 
     Some portions of the detailed descriptions which follow are presented in terms of algorithms which include operations on data stored within a computer memory. An algorithm is generally a self-consistent sequence of operations leading to a desired result. The operations typically require or involve physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, can refer to the action and processes of a data processing system, or similar electronic device, that manipulates and transforms data represented as physical (electronic) quantities within the system&#39;s registers and memories into other data similarly represented as physical quantities within the system&#39;s memories or registers or other such information storage, transmission or display devices. 
     The present disclosure can relate to an apparatus for performing one or more of the operations described herein. This apparatus may be specially constructed for the required purposes such as an application specific integrated circuit (ASIC), or it may comprise a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a machine (e.g. computer) readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), erasable programmable ROMs (EPROMs), electrically erasable programmable ROMs (EEPROMs), flash memory, magnetic or optical cards, or any type of media suitable for storing electronic instructions, and each coupled to a bus. 
     A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (“ROM”); random access memory (“RAM”); magnetic disk storage media; optical storage media; flash memory devices; etc. 
     At least certain embodiments of the present disclosure include one or application programming interfaces (API) or drivers in an environment with user interface software interacting with a software application. Various function calls or messages are transferred via the application programming interfaces between the user interface software and software applications. Transferring the function calls or messages may include issuing, initiating, invoking or receiving the function calls or messages. Example application programming interfaces transfer function calls to implement scrolling, gesturing, and animating operations for a device having a display region. An API may also implement functions having parameters, variables, or pointers. An API or driver may receive parameters as disclosed or other combinations of parameters. In addition to the APIs or drivers disclosed, other APIs or drivers individually or in combination can perform similar functionality as the disclosed APIs or drivers. 
       FIG. 1  illustrates a local area network  10  (LAN) using fiber optic connections in accordance with an embodiment of the present invention. The LAN  10  includes an optical line terminal  12  (OLT), optical splitter  16 , and optical network terminal  100  (ONT) (shown in  FIG. 1  as ONT  100 A- 100 E). The OLT is coupled to the optical splitter  16  by a first fiber optic connection  14 . Furthermore, the passive optical splitter is coupled with the ONT  100  using a second fiber optic connection  22 . 
     The OLT  12  may be connected to one or more processors (illustrated as CPU  15 ) and a database (shown as DB  13 ). In some embodiments, the CPU  15  and DB  13  may be integrated with the OLT  12 . 
     The LAN  10  may be connected to external networks  2 , such as the internet. In some embodiments a router/switch  4  may be used. In a preferred embodiment, this may take the form of an external switch  4  which allows the two OLTs  12  to communicate with each other over an Ethernet connection. 
     The ONT  100  is coupled with a peripheral device  28  (seen in  FIG. 1  as peripheral devices  28 A- 28 E). Peripheral devices  28 A- 28 E may include any number of types of devices for inclusion within LAN  10 . For example, a peripheral device  28  may include a computer, a printer, a server and the like. In a preferred embodiment, the peripheral device  28  may be a camera, such as a security camera, connected in a LAN  10  which is designed to provide security coverage of a building, area and the like. 
     In some embodiments, an Ethernet cable (not shown) of the peripheral device  28  may be used to couple the peripheral device  28  to the ONT  100  over an Ethernet standard. For example, if the peripheral device is network enabled, the ONT  100  may connect to the peripheral device through the peripheral device&#39;s network jack. 
     In other embodiments, the ONT may be incorporated directly into the peripheral device  28 . For example, a network interface card (not shown) or proprietary connector and the like may be installed in the peripheral device  28  for coupling the ONT  100  to the peripheral device  28 . For example, a small form-factor pluggable transceiver (SFP) may be used. In this manner, the ONT  100  may be installed directly in the peripheral device  28  and may be operable to communicate with the peripheral device  28  over a bus (not shown) or other communication channel, as known in the art. 
     The OLT  12  is in communication with the ONT  100  using a passive optical networking (PON) standard. As known in the art, a passive optical network (PON) is a point-to-multipoint network architecture which uses passive (i.e. unpowered) optical splitters to connect to peripheral devices  28  over optical fiber. In this manner, an OLT  12  is operable to enable a single optical fiber to serve multiple peripheral devices  28 . Typical PON implementations have between  16 - 128  peripheral devices  28 . Architectures utilizing a PON reduce the amount of fiber and related infrastructure required to connect network in comparison to point-to-point architectures. 
     Any suitable version of a PON standard may be used. For example, the PON standard may be the Gigabit Passive Optical Networks (GPON) standard developed by the International Telecommunication Union (ITU) or the Ethernet Passive Optical Networks (EPON) standard developed by the Institute of Electrical and Electronics Engineers (IEEE). Other flavours of PON such as APON, 10G-PON, 10G-EPON, SPON and the like may also be used. 
     Packets may be passed in the LAN  10  amongst the peripheral devices  28 . In this manner, the OLT behaves as a layer 2 (L2) switch (i.e. data link layer) in the Open Systems Interconnection (OSI) model, while providing the benefits of an optical infrastructure including long reach, smaller and lighter cables, fewer cables, and resistance to lightning and electrostatic discharge (ESD). 
     In addition, using an OLT  12  with fiber optic transmission paths to implement the LAN  10  is desirable in that optical fiber is expected to become cheaper than unshielded twisted pair (UTP) cabling, as the cost of metals and other natural resources required by Ethernet cabling and the like increases. 
     As also shown in  FIG. 1 , the LAN  10  may include a powered patch panel  18  or unpowered patch panel  20  coupled to the passive optical splitter  16 . The patch panels  18 / 20  may be coupled between the passive optical splitter  160  and one or more of the ONT  100 . The patch panels  18 / 20  are configured to allow a plurality of ONT  100  to be plugged and unplugged into the LAN  100  over a plurality of second fiber optic connections  22 . 
     In other embodiments, a patch panel  18 / 20  is not required. ONTs  100  may be directly connected to the optical splitter  16  without requiring a patch panel  18 / 20 . 
     Data Collector 
     In a preferred embodiment, the PON system  1  may include an analytical engine to run analytics on the network. The analytics may improve the functioning on the PON system  1 . For the analytics to run, a networking data collector be created to collect and store network information available in the PON system. For example, a PON system  1  incorporating a data collector may include an optical line terminal (OLT  12 ), a passive optical splitter  16  and at least one optical networking terminal (ONT  100 ). 
     In a preferred embodiment, there may be one or more means for obtaining and storing network information from the at least one optical networking terminal  100 . For example, there may be a processor  15  or standalone computer or server capable of collecting and storing the network information. For example, the server may have a database  13  or other software for storing the information. In larger systems, a cloud-based solution may be used to gather and store the network information. The information may be stored in a proprietary or open source database  13 . 
     In a preferred embodiment, the network information may be for each device at a particular ONT  100 . The network information may include destination address, source address, timing, amount of traffic, link-speed, timing, and traffic direction. The network information may be some combination of these attributes. 
     In other embodiments, the networking data collector return transit time (RTT), received signal strength indicators (RSSI), transmitted signal strength indicators (TSSI), current bias of the laser, temperature, and laser drift. In certain embodiments one or more combinations of parameters may be used. 
     Analytics 
     Using data collected and stored by the data collector, the PON system may include an analytics engine capable of extracting useful insights from the data collected. In a preferred embodiment, an analytics engine may include a passive optical network, means for collecting networking information from components in the passive optical network, identifying patterns in the network information and notifying a user based on the patterns identified. 
     Analytics—PON Patterns 
     Different types of patterns can be extracted from the data collected. In a preferred embodiment, the pattern is based on at least one of destination address, source address, timing, amount of traffic, link-speed, timing, and traffic direction. In other embodiments, the pattern is based on PON parameters. For example, in some embodiments, the patters may be based on return transit time (RTT), received signal strength indicators (RSSI), transmitted signal strength indicators (TSSI), current bias of the laser, temperature, and laser drift. 
     Analytics—Device Signatures 
     In a preferred embodiment, a device signature for each device in the network may be created. For example, the device signature may be based on heuristics comprising data taken from many devices of the same model or type. In others, the device signature may be based on one or more of traffic profile, power profile and communication peers. A communication peer may be a similar device such as a camera, sensor and the like. Device signatures may also be formed by one or more combinations of parameters. In a preferred embodiment, the device signature may be formed from traffic profile including the ratio of up/down traffic. 
     Analytics—Device Failures 
     In a preferred embodiment, the analytics engine may identify a pattern that can be used predict a device failure. For example, the pattern for device failure may be based on packet loss or timing. In some embodiments, the analytics engine identifies the pattern for device failure is based on drifts in power consumption. In others, the pattern for device failure is based on a learning pattern of behaviour. In a most preferred embodiment, the pattern for device failure is based on a combination of a learning pattern of behaviour and rules set by a device manufacturer. The learning pater may use both heuristics and machine learning. The learning pattern may include at least one of time of day, seasonal changes, a weather almanac, business hours, and other forms of periodicity. 
     Analytics—Network Intrusions 
     The analytics engine may be used to identify security threats. Users can be notified of the threats in real time using messaging services. Intrusion detection may be quick based on or more packets. In other embodiments, learned behaviour is required and it may take time for a network intrusion to be detected by the analytics engine. 
     In a preferred embodiment, the pattern identifying the network intrusion is due to a change in MAC address. In others, a change in power consumption or a change in traffic profile indicates a threat to the PON system. Furthermore, the change in traffic profile may include changes in reporting time, length, payload size and traffic behaviour. 
     The analytics engine may identifies a pattern for learning and tracking device behaviour over time. Sometimes, the pattern for a camera changes in response to commands sent to the camera. For example, a command to point, tilt, and zoom a camera may lead a camera to actualize the command. Such actualization may lead to changes in power consumption, which may be measured by the PON system. 
     In a preferred embodiment, the analytics engine identifies a signature for every packet in the networking system. Or, the analytics engine may identify a signature for every port in the networking system. Signatures for every device in the networking system may also be used or signatures for every ONT in the networking system. 
     Redundancy 
     Uptime is an important part of a networking system. This is particular true in a building network, where devices connected directly deal with tenant comfort and building efficiency. In a preferred embodiment, redundancy may be accomplished between two OLT  12 , without requiring a direct connection or heartbeat between the first and the second OLT  12 . 
     Such a system such as shown in  FIGS. 2 and 3  may include a first optical line terminal (OLT  12 ), a second OLT  12 , a two-to-many passive optical splitter  16  and at least one optical networking terminal (ONT  100 ). The first and the second OLT  12  may each include an Ethernet port  12 ETH and an optical port  12 OPT having a transmit function and a receive function. 
     The ONT  100  may also include an optical port  100 OPT and at least one Ethernet port  100 ETH. Devices  28  within the building network would then be connected to the Ethernet ports  100 ETH on the ONT  100 . Devices may include cameras, building automation system devices and the like. 
     The passive optical splitter  16  includes two inputs  16 IN and multiple outputs  16 OUT. The first optical input  16 IN is optically coupled to the first optical port  12 OPT of the first OLT  12 . The second optical input  16 IN is optically coupled to the first optical port  12 OPT of the second OLT  12 . The first optical output  16 OUT of the passive optical splitter  16  is optically coupled to the optical port  100 OPT of the ONT  100 . 
     In operation, the ONT  100  may be registered with either the first OLT  12  or the second OLT  12  using a PON standard, as is known in the art. In operation, one of the OLT  12  will be in an ACTIVE state to pass traffic between the ONT  100  and the OLT  12  and the other OLT  12  will be in a PROTECT state or redundancy mode. The second OLT  12  has the transmit function of the first optical port  12 OPT turned off. However, the second OLT  12  leaves the receive function of the first optical port  12 OPT enabled such that it can listen to communications of the ONT  100  which travel upstream to both the first and the second OLT  12  through the passive optical splitter  16 . Any signal which travels upstream through any of the outputs  16 OUT of the passive optical splitter  16 , travel through both optical inputs  16 IN. Similarly, any signal which travels down through either the first input  16 IN or the second input  16 IN of the passive optical splitter is sent to all optical outputs  16 OUT of the passive optical splitter  16 . In this manner, the second OLT  12  may listen to the communications between the first ONT  100  (or any ONT  100 ) and the first OLT  12 , without interfering with their communications. 
     In certain situations or failures, the communication between the first OLT  12  and one or more ONT  100  may be interrupted. For example, if there is a cable cut between the first input  16 IN of the passive optical splitter  16  and the first OLT  12  or if the first optical port  12 OPT of the first OLT  12  is faulty, then communication between the ONT  100  and the first OLT  12  will be interrupted. If this occurs, the second OLT  12  no longer receives a signal to indicate that the first OLT  12  is still registered or communicating with the first ONT  100 . In this situation, the second OLT  12  may turn on the transmit function of the first optical port  12 OPT knowing that the first OLT  12  is no longer registered with the ONT  100  and force the ONT  100  to register with the second OLT  12 . 
     In this manner, the PON system  1  can implement redundancy with the second OLT  12  taking over communications with the ONT  100 . If the databases  13  are synced between the first OLT  12  and the second OLT  12 , the ONTs  100  will be properly registered and configured during the registration process with the second OLT  12 . Syncing is required between the first OLT  12  and the second OLT  12  to ensure any network configurations are consistent between the first OLT  12  and the second OLT  12 . If not, when a takeover occurs, the network pathways will not allow for the proper configuration of the redundant network. For example, configuration information may include VLAN information, port information, port enabled information, ONU information and communication information. 
     To initiate the takeover procedure, a signal must be created to indicate to the second OLT  12  that it should take over. In a preferred embodiment, the signal indicating to the second OLT  12  that the first OLT  12  is no longer registered with the first ONT  100  is a received signal strength indicator. When the received signal strength indicator falls below a threshold for a certain period of time, the second OLT  12  can assume that the first OLT  12  is no longer registered with the first ONT  100  and may turn on the transmit function of the first optical port  12 OPT to take over. The ONTs  100  that were previously registered with the first OLT  12  can now register with the second OLT  12  and traffic can resume passing through the PON system  1 . 
     The receive function on the optical port of the second OLT  12  may be configured to obtain an absolute measurement of different values. For example, the receive function may take a reading from the RSSI of a single ONT  100 . If this single ONT  100  is no longer registered, the second OLT  12  may consider that a failure condition has occurred and use this as a signal that a takeover is required. In alternative embodiments, a combination of the RSSI from many or all of the registered ONT  100  for that optical port  12 OPT can be used. In this manner, the second OLT  12  is not reliant on the RSSI of a single ONT  100  and a takeover only occurs if all of the ONT  100  optically coupled to the optical port fail. In other words, the second OLT  12  will only initiate takeover proceedings if the optical port  12 OPT of the first OLT  12  is no longer optically coupled or registered to any ONT  100 . In this manner, the PON system  1  can ensure that there is a systemic failure requiring a redundancy takeover and not a problem caused by a single ONT  100 . 
     In another preferred embodiment, the second OLT  12  may wait for an extended period of time to ensure the RSSI reading obtained by the second OLT  12  indicates that no ONT  100  are still registered with the first OLT  12 . For example, a period of  10  seconds to a minutes, with a preferred time between  20  and  30  seconds, may be enough for the second OLT  12  to decide that the first OLT  12  is no longer receiving any signal from any ONT  100 . Only once this period of time has passed with no RSSI reading above the threshold will a takeover procedure occur. In this way, the second OLT  12  may takeover for the first OLT  12  with no direct communication with the first OLT  12 . Instead, a period of low RSSI below a threshold is used to indicate to the second OLT  12  to begin the takeover procedure. 
     When the second OLT  12  takes over, any traffic previously passing from the first or any ONT  100  through the first OLT  12  and through the external switch  4  is now rerouted after the takeover through the second OLT  12  and then through the external switch  4 . This process enables redundancy between the two OLT  12 . As mentioned, the first OLT  12  and the second OLT  12  do not require any direct communication for the second OLT  12  to takeover when a failure in the first OLT  12  occurs. A failure may include the first optical port  12 OPT of the first OLT  12  failing or a cut in the optical fibre between the first OLT  12  and the first ONT  100 . 
     In some embodiments, a direct Ethernet link  4 A between the first OLT  12  and the second OLT  12  allows the handover to occur immediately after the signal indicating the first OLT  12  is registered with the first ONT  100  is no longer received. When contacted by the second OLT  12 , the first OLT  12  can determine whether communication to the ONT  100  has been lost and, if so, tell the second OLT  12  to immediately take over. 
     In a preferred alternate embodiment, the first OLT  12  and the second OLT  12  may be connected together via an external switch  4  to improve upon the redundancy performance. Rather than wait for the timeout period to expire, a direct connection  4 A between the first OLT  12  and the second OLT  12  may hasten the takeover by the second OLT  12 . When the received signal strength indicator falls below the threshold, the second OLT  12  can query the first OLT  12  about whether communications to the ONT  100  has been lost. If so indicated, the first OLT  12  can indicate this to the second OLT  12  and hasten the takeover without waiting for the timeout period. This may improve the task of a takeover by reducing the required time to ensure the takeover occurs correctly. In an alternate embodiment, a mixture of a timeout period and a communication request and acknowledgement to force a takeover may improve the performance of the takeover procedure. 
     In operation in at least one embodiment of the present invention, the invention resides in a method for implementing redundancy in a passive optical network as shown in  FIG. 5 . As shown in BLOCK  510 , the method  500  may include optically coupling a first optical line terminal (OLT) and a second OLT to at least one optical networking terminal (ONT) through a two-to-many passive optical splitter. Any number of splits output splits may be used so long as there is adequate amount of optical power at the output of the passive optical splitter to allow an ONT to register with the OLT. 
     In operation, the first OLT is optically coupled to the first input of the passive optical splitter and the second OLT is optically coupled to the second input of the passive optical splitter. In this manner traffic can theoretically flow between the first OLT and the ONT or the second OLT and the ONT. As shown in  FIGS. 3 and 4 , no traffic can flow directly from the first OLT and the second OLT through an optical channel as the passive optical splitter only allows traffic to flow in an upstream or downstream direction, with traffic passing from the one or more ONT through either the first OLT or the second OLT. 
     At any time, the ONT is only capable of registering and passing traffic with a single OLT. However, since both the first and the second OLT are optically coupled or connected with the ONT and thereby capable of registering with the ONT, one of the OLT must be disabled or prevented from registering or communicating with the ONT so as to not affect the behaviour of the ONT and the other OLT. In order to accomplish this, when the ONT is registered and communicating with the first OLT, the transmit function of the optical port on the second OLT must be disabled as shown in BLOCK  520 . In this manner no light from the second OLT is able to interfere with the normal operation of the first OLT and the one or more ONT that the first OLT is registered and communicating with. 
     At the same time, it may be desirable to enable the receive function of the optical port on the second OLT. In this manner, the second OLT is capable of monitoring the communication between the one or more ONT and the first OLT without interfering with the operation or communication of the one or more ONT registered with the first OLT. It can then use this capability for monitoring purposes. 
     In BLOCK  530 , the second OLT may monitor the received signal strength indicator (RSSI) on communications from the one or more ONT to the first OLT. The second OLT may use this information to create a takeover signal if the link between the at least one ONT and the first OLT is broken. For example, the RSSI may drop below a minimum threshold if no ONT are registered with the first OLT or if the fibre between the one or more ONT and the first OLT is broken. In a preferred embodiment, the minimum threshold is less than −25 dBm. In another preferred embodiment, the RSSI minimum is at the most −30 dBm. Such may be the case if this is a fiber cut between the one or more ONT and the first OLT. 
     In a preferred embodiment, the takeover signal may include waiting for the RSSI to be below a minimum threshold for a predetermined period of time. For example, the predetermined period of time may be between 10 and 30 seconds. However, other time periods may be used to increase reliability or for faster switchovers. 
     While not necessary, the takeover signal in BLOCK  530  may further include an acknowledgement message from the first OLT to the second OLT to initiate the takeover role. In a preferred embodiment, this acknowledgement message may be in direct response to a request from the second OLT. For example, upon the completion of the predetermined period of time of low RSSI, the second OLT may ask the first OLT whether it has lost communications with the at least one ONT. If the first OLT responds in the affirmative, the second OLT may then generate the takeover signal and initiate the takeover 
     On receipt of the takeover signal as shown in BLOCK  540 , the second OLT may enable the transmit function of its optical port. In this manner, it may be enabled to both transmit and receive information through its optical port. 
     Furthermore, the second OLT may be enabled to now register with the at least one ONT as shown in BLOCK  550 . Once registered with the at least one ONT, the second OLT will then be capable of passing traffic with the at least one ONT through the passive optical splitter. 
     Finally, as shown in BLOCK  560 , the second OLT has assumed control of passing the traffic from the at least one ONT. Because of the failure in the communication path between the first OLT and the at least one ONT, a takeover has successfully occurred where traffic is now enabled to continuing flowing through the second OLT. If the first and second OLT are communicatively coupled to an external switch through their respective Ethernet ports, this traffic can continue to flow upon the successful takeover. In this manner, the second OLT is configured to takeover handling all of the traffic from the first OLT, if the first OLT fails or a fibre cut occurs between the optical port of the first OLT and one of the two inputs of the passive optical splitter which is optically coupled to the first OLT. 
     In operation in at least one additional embodiment of the present invention, a state machine may be configured on each OLT  12  to maintain which OLT is operating to pass traffic from the connected and registered ONTs  100 . A state machine  200  in accordance with one embodiment of the present invention is shown in  FIG. 4 . The state machine  200  is configured to operate the redundancy checks required to place and keep the first OLT  12  and the second OLT  12  into their respective states. When there are multiple optical channels for each OLT  12 , a single state machine  200  may be used for both or all optical channels. In some embodiments, the state machine  200  covers the operation of multiple optical channels and a takeover occurs if a failure is detected in a single optical channel  12 OPT. In alternate embodiments, a separate state machine  200  may be used for each channel. As known in the art, each optical channel corresponds to a separate optical port  12 OPT. In the following description, reference to a specific OLT  12  refers to a specific optical port  12 OPT on the OLT  12 . It should be understood that where there are multiple optical ports  12 OPT, the following references to first OLT  12  and second OLT  12  should make reference to their respective or specific optical ports  12 OPT. 
     As seen in  FIG. 4 , the state machine includes a STANDBY  210  state and an ONLINE  220  state. The STANDBY state is used after initial STARTUP to ensure that the OLT  12  does not immediately shine a laser when entering the ONLINE state. Otherwise, this may interfere with the operation of a second OLT  12  already in operation. The ONLINE state is composed of further sub-states INIT  230 , DETECT  240 , PROTECT  250 , TAKEOVER  260  and ACTIVE  270 . 
     When the first OLT  12  (i.e. an optical port  12 OPT on the first OLT  12 ) is registered with ONT  100  over the optical port  12 OPT, it is considered to be in the ACTIVE state. An OLT  12  in the ACTIVE state is fully functioning and is configured to register and to pass traffic with an ONT  100 . An OLT  12  in the ACTIVE state is capable of operating normally within a PON system. 
     When a second OLT  12  (i.e. an optical port  12 OPT on the second OLT  12 ) is listening to the activity of the first OLT  12  and the ONT  100 , the second OLT  12  is considered to be in the PROTECT state. An OLT  12  in the PROTECT state has the OLT&#39;s transmit function disabled. However, it is still capable of receiving light from the optically coupled ONTs  100 . When in the PROTECT state, the second OLT  12  is not transmitting through the optical port  12 OPT; instead, it is only receiving information in the DETECT state such as the RSSI of the one or more ONT  100 , and measuring the RSSI to indicating when a failure occurs. When a failure occurs a takeover signal will be generated and push the OLT  12  into the TAKEOVER state. 
     In operation, the second OLT  12  in the PROTECT state may be continuously monitoring the RSSI of the ONT  100  connected to the optical port  12  OPT. If the second OLT  12  determines that the RSSI falls below a threshold, the second OLT  12  may begin counting using a timer. This may be within the PROTECT state itself or cycling through a number of states as shown in  FIG. 4 . If the RSSI is below the threshold for a pre-determined period of time, the second OLT  12  may start the takeover process by moving into the TAKEOVER state. As discussed above, this may include sending a message to the first OLT  12  to see if the first OLT  12  is still there. A response from the first OLT  12  may include a message not to take over. Alternatively, the response from the first OLT  12  may include a message to hasten takeover. If this occurs, the second OLT  12  may initiate the takeover process and enable the transmit function of its optical port  12 OPT. Once enabled, the second OLT  12  may then register with all the ONT  100  that it is optically coupled with. 
     In alternate embodiments, the second OLT  12  may receive no message from the first OLT  12 . This may occur if the first OLT  12  has lost power or has otherwise crashed or is unresponsive. In these situations, the second OLT  12  may wait for a predetermined period of time before taking over communication with the ONT  100 . During this predetermined period of time, the second OLT  12  may continue to request a response from the first OLT  12 , in case the first OLT  12  comes out of its indeterminate state. 
     In the foregoing specification, the disclosure has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader scope of the disclosure as set forth in the following claims. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.