Patent Publication Number: US-2009238567-A1

Title: Electrical Ring Distribution Interface for an Optical Transceiver

Description:
RELATED APPLICATIONS 
     This application is a Continuation of a pending application entitled, OPTICAL TRANSCEIVER WITH ELECTRICAL RING DISTRIBUTION INTERFACE, invented by Miller et al., Ser. No. 11/395,858, filed Mar. 31, 2006, attorney docket no. applied — 161, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to digital communications and, more particularly, to a system for efficiently distributing electrical communications signals, converted from optical network communications, via a ring of optical network units (ONUs). 
     2. Description of the Related Art 
       FIG. 1  is a schematic block diagram depicting a “triple play” system for distributing optical communication signals to a customer premise (prior art). A optical line terminal (ONT) broadcasts a ITU-T G.984.3 PON (GPON) optical signal out to many ONUs, which are typically outside units, or to many optical network terminals (ONTs), which are typically indoor units. The ONUs (ONTs) convert the GPON optical signal into video, telephone, and Ethernet electrical signals for use in the customer premise. The responses back from the various ONUs (ONTs) are converted to a GPON optical signal and time division multiplexed (TDM) back to the OLT. A typical single-family unit (SFU) may have four Ethernet ports. 
     Additional issues are presented when an OLT is interfaced with a multi-dwelling unit (MDU), such as an apartment building. Currently, there are two methods of interfacing an OLT to an MDU. One option is place an ONU in each apartment, and run optical fiber to each ONU. This option is hardware expensive, because multiple copies of the optic fiber must be run in parallel to each ONU. Alternately, a single ONU is assigned to the MDU. However, the ONU must have a network processor and Ethernet switch to bring out multiple ports. This option is software expensive, because software must be written to configure the network processor and Ethernet switch. Further, a policing function must be enabled to guarantee each user a Service Level Agreement (SLA) that includes some measure of privacy protection. 
     It would be advantageous if an MDU could be interfaced to an OLT GPON optical signal with a minimum expenditure of software and hardware assets, and development costs. 
     SUMMARY OF THE INVENTION 
     The present invention presents an ONU device that can convert GPON optical signals to a GPON electrical signal, for distribution in a system of ring-connected ONUs. Each ONU has three high-speed connections. One interface transceives optical signals (e.g., 2.5 GPON). There are also a ring North Rx/Tx interface, and a ring South Rx/Tx interface for electrical signals. In this manner, an entire multi-dwelling unit can be interfaced to the OLT via a single optical connection to just one of the ONUs. A second optical line may be run to another of the ONUs, if additional (redundant) optical protection is desired. Otherwise, the converted optical signal is distributed through the ring via the ring North and/or ring South interfaces. 
     Accordingly, a ring connection method is provided for distributing signals in an optical-to-electrical interface. The method electrically connects a plurality of nodes in a series-connected ring, and receives an optical signal at a first node from a service provider. The method converts the optical signal to an electrical signal, and distributes the electrical signal via the ring. At each node, the electrical signal is supplied from a customer interface. Typically, each node has a plurality of customer interfaces. 
     In one aspect, ITU-T G.984.3 Giagbit-capable Passive Optical Network (GPON) optical signals are received and converted to a customer interface electrical signal such as an Ethernet, asynchronous transfer mode (ATM), or time division multiplexed (TDM) signal. 
     Electrically connecting the plurality of nodes in the series-connected ring includes: series connecting the nodes in a first (North) ring; and, series connecting the nodes in a second (South) ring, opposite in direction from the first ring. 
     In another aspect, the method receives a customer interface electrical signal from a customer interface at each node. The received customer interface electrical signals from each node are multiplexed, and the multiplexed signals are distributed via the ring. Then, the multiplexed signals are converted to an optical signal, and transmitted to the OLT service provider. 
     Additional details of the above-described method, a ring-connected ONU, and a system of ring-connected ONUs are provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram depicting a “triple play” system for distributing optical communication signals to a customer premise (prior art). 
         FIG. 2  is a schematic block diagram of a system of ring-connected optical network units (ONU) for distributing signals. 
         FIG. 3  is a schematic block diagram of a ring-connected ONU for distributing signals. 
         FIG. 4  is a schematic block diagram depicting downlink communication details of an exemplary ONU. 
         FIG. 5  is a schematic block diagram depicting uplink communication details of an exemplary ONU. 
         FIGS. 6A and 6B  are flowcharts illustrating a ring connection method for distributing signals in an optical-to-electrical interface. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a schematic block diagram of a system of ring-connected optical network units (ONU) for distributing signals. The system  200  comprises a plurality of ONUs. Shown are ONUs  202 ,  204 ,  206 , and  208 . In other aspects, up to 64 ONUs may be ring-connected. However, it should be understood that the system is not inherently limited to any particular number of ONUs. 
       FIG. 3  is a schematic block diagram of a ring-connected ONU for distributing signals. ONU  204  of  FIG. 2  is used as an example, however, the following description could also be applied to the other ONUs in the system. ONU  204  comprises an optical port on line  300  for transceiving optical signals. An optical-to-electrical translation module  302  has an interface connected to the optical port on line  300 , and an interface for transceiving electrical signals. 
     A first (North) ring port is connected to the translation module  302  on line  306  to transceive ring-connected electrical signals between a first ONU neighbor (i.e., ONU  202  of  FIG. 2 ). A second (South) ring port connected to the translation module  302  on line  308  to transceive ring-connected electrical signals between a second ONU neighbor (i.e., ONU  206  of  FIG. 2 ). A customer interface port on line  310  transceives customer interface electrical signals with a user. 
     Typically, a common downlink (downstream) signal is sent from the service provider (OLT) to all the users on line  300 . However, to control distribution of the signal, the signal is decrypted before it is provided to a user. For example, only customers paying a service charge to the service provider receive decrypted customer interface electrical signals. In this aspect, the translation module  302  converts an encrypted optical signal into an encrypted electrical signal. The encrypted electrical signal is distributed via the first and second ring ports, on lines  306  and  308 , respectively. A deframer module  312  has an interface connected to the translation module on line  314  and an interface on line  310  to supply a decrypted electrical signal to the customer interface. 
     In one aspect, the translation module  302  receives a ITU-T G.984.3 Giagbit-capable Passive Optical Network (GPON) signal on line  300  and converts the GPON optical signal into a GPON electrical signal, which is provided on lines  306 ,  308 , and  314 . The deframer module  312  converts the GPON electrical signal into a customer interface electrical signal. 
     Typically, there is a plurality of customer interfaces connected to the deframer module  312 , each transceiving customer interface electrical signals with a user. Shown are four customer interfaces ( 310 ,  316 ,  318 , and  320 ) per ONU. However, the ONU is not inherently limited to any particular number of customer interfaces. The deframer module  312  time division demultiplexes a GPON signal on line  314  into a customer interface electrical signal for each customer interface. For example, the customer interface electrical signal can be an Ethernet, asynchronous transfer mode (ATM), or time division multiplexing (TDM) signal. However, the deframer module  312  is not limited to any particular format or protocol. 
     In one aspect, each ONU further comprises a downlink multiplexer  321  having an interface connected to the ring ports on lines  306  and  308 , and the translation module on line  314  to receive (GPON) electrical signals. The downlink MUX  321  has an interface connected to the deframer  312  on line  323  to supply a multiplexed (GPON) electrical signal. 
     With respect to the uplink, a first multiplexer (MUX)  322  has an interface connected to the ring ports on lines  306  and  308 , as well as to the customer interface(s) (e.g.  310 ) to receive electrical signals. An interface is connected to the translation module  302  on line  324  to supply a multiplexed electrical signal. The translation module  302  converts multiplexed electrical signals into an optical signal, and transmits the optical signal on line  300 . 
     In another aspect, a second multiplexer  326  has an interface connected to the ring ports  306  and  308  and the customer interface(s) (e.g.  310 ) to receive electrical signals. The second multiplexer  326  has an interface connected to supply multiplexed electrical signal to the first ring port on line  306 . Likewise, a third multiplexer  328  has an interface connected to the ring ports  306  and  308  and the customer interface(s) (e.g.,  310 ) to receive electrical signals. An interface is connected to supply multiplexed electrical signal to the second ring port on line  308 . 
     The uplink messages to the OLT (service provider) are typically originated by the user. Therefore, security and eavesdropping protection from other users is a desirable feature. In one aspect, a framer module  330  has an interface to accept a plurality of customer interface electrical signals from a plurality of customer interfaces (e.g.,  310 ,  316 ,  318 , and  320 ). Again the framer module  330  is not limited to any particular number of customer interfaces. The framer module  330  has interface connected to the first, second, and third multiplexers on line  332  to supply the plurality of customer interface electrical signals framed into a GPON signal. In the event of an evolution in the GPON standard, or the use of a different optical standard, the framer module  330  can also be used to encrypt the customer interface electrical signals. 
     Note, although ONU  204  is shown with a connected and operating optical interface  300 . Other ONUs in the ring-connected system (e.g.  202 , see  FIG. 2 ) need not necessarily have a connected optical interface to receive optical signals. That is, an ONU with an optical connection can receive converted optical signals from ONU  204  communicated via the ring connection. In another aspect, an ONU (i.e., ONU  206 , see  FIG. 2 ) may be connected to a backup line which can be selectively engaged is the main optical line develops a fault. Alternately, the protection optical line may continually send optical signals, but the ONU&#39;s translation module is selectively enabled to only convert optic/electrical signals in the event that the main optical line fails or ONU  204  fails. 
     Functional Description 
     Returning briefly to  FIG. 2 , each ONU has three potential high-speed interfaces: the optical (2.5 GPON) interface, the ring North interface, and the ring South interface. For the multi-dwelling case, a first ONU chip on a system board is hooked to the optical interface. A second ONU chip can be hooked to an optics line if optical protection is necessary. Otherwise, converted optical communications are distributed via the ring North and ring South interfaces. The system of  FIG. 2  utilizes two types of protection. The main and protection lines provide 1+1 Optical protection, while the bidirectional rings provide protection from an ONU malfunction. 
     In the downlink direction, the OLT controls how much bandwidth each user receives. From the point of view of the OLT, the OLT cannot determine if it is communicating with a plurality of single family units (SFUs) or one Multi-Dwelling unit equipped with a ring-connected ONU system. Thus, the software used in both the OLT and ONT need not be modified, and the need for multiple optical receivers is eliminated. 
       FIG. 4  is a schematic block diagram depicting downlink communication details of an exemplary ONU. Note that the ring input and output can combined either before, or after decryption. Typically, there is only a single key per ONU, however in other aspects, a separate decryption key can be used for each of the four Ethernet ports. The ring connections easily support 1+1 optical protection. Because the ONU&#39;s are in a ring, every ONU can “see” the protection signal after it has switched over from the main optical signal. This architecture permits each Ethernet customer interface port to have a dedicated protected bandwidth. 
       FIG. 5  is a schematic block diagram depicting uplink communication details of an exemplary ONU. The uplink (upstream) bandwidth is assigned by the OLT using a bandwidth map. The bandwidth map allocates a certain number of upstream timeslots to each traffic container (TCONT). In this manner, the OLT can control the uplink bandwidth assigned to each Ethernet customer interface port. 
     Without this architecture, an Ethernet switch would be required for the multi-dwelling scenario, which would require the addition of hardware to control how much uplink bandwidth is assigned to each customer interface port. However, if the ONU chips are ring-connected as shown in  FIGS. 2 and 5 , then each Ethernet customer interface port gets it&#39;s own traffic container. From the point of view of the OLT, the OLT cannot determine if it is connected to four transmitting SFU&#39;s, or one MDU enabled with a ring-connected system with four ONUs. Thus, the ONU and OLT software need not be changed to accommodate the ring-connected ONU system. Note,  FIG. 5  shows only a single MUX with an output connected to the optical interface. In other aspects, MUXs having the same inputs as the displayed MUX are used, one MUX for each ring connection (see  FIG. 3 ). 
       FIGS. 6A and 6B  are flowcharts illustrating a ring connection method for distributing signals in an optical-to-electrical interface. Although the method is depicted as a sequence of numbered steps for clarity, the numbering does not necessarily dictate the order of the steps. It should be understood that some of these steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of sequence. The method starts at Step  600 . 
     Step  602  electrically connects a plurality of nodes in a series-connected ring. Step  604  receives an optical signal at a first node from a service provider (OLT). Step  606  converts the optical signal to an electrical signal. Step  608  distributes the electrical signal via the ring. Step  610  supplies the electrical signal from a customer interface at each node. In one aspect, Step  610  supplies a plurality of customer interface electrical signals from a corresponding plurality of customer interface ports at each node. 
     In one aspect, receiving the optical signal from the service provider in Step  604  includes receiving a ITU-T G.984.3 Giagbit-capable Passive Optical Network (GPON) signal. Then, converting the optical signal to the electrical signal in Step  606  includes converting to a customer interface electrical signal such as an Ethernet, ATM, or TDM signal. Typically, Step  610  time division demultiplexes the GPON signal into the plurality of customer interface electrical signals. 
     In another aspect, electrically connecting the plurality of nodes in the series-connected ring in Step  602  includes substeps. Step  602   a  series connects the nodes in a first (North) ring. Step  602   b  series connects the nodes in a second (South) ring, opposite in direction from the first ring. 
     In a different aspect, converting the optical signal to the electrical signal in Step  606  includes converting an encrypted optical signal into an encrypted electrical signal. Then, supplying the electrical signal from the customer interface in Step  610  includes selectively decrypting the encrypted electrical signal at each node. In another aspect, Step  610  multiplexes customer interface electrical signals that are supplied from ring-connected nodes. If the node (e.g. the first node) happens to be directly connected to the optical interface, as opposed to being indirectly connected via the bidirectional ring interface, then the converted optical signal is multiplexed together with the electrical signals supplied by the ring-connected nodes. A multiplexed customer interface electrical signal is then supplied to a customer interface. 
     In one aspect, Step  603   a  accepts a first (Working) optical signal at the first node. Step  603   b  accepts a second (Protection) optical signal at a second node. Then, receiving the optical signal from the service provider in Step  604  includes substeps. Step  604   a  initially converts the first optical signal to an electrical signal. Step  604   b  converts the second optical signal to the electrical signal in the event of an optical line fault. 
     In another aspect, Step  612  receives a customer interface electrical signal from a customer interface. At each node, Step  614  multiplexes the received customer interface electrical signals from each node. Step  616  distributes the multiplexed electrical signals via the ring. Step  618  converts the multiplexed electrical signals into an optical signal. Step  620  transmits the optical signal to the service provider. 
     In one aspect, receiving the electrical signal from the customer interface at each node (Step  612 ) includes substeps. Step  612   a  accepts a plurality of customer interface electrical signals from a plurality of customer interfaces. Step  612   b  frames the plurality of customer interface electrical signals into a GPON signal. 
     An optical/electrical interface system and method have been provided for the ring connection distribution of electrical signals. Some examples of particular subcircuits, circuit connections, and communication protocols have been given to illustrate the invention. However, the invention is not limited to merely these examples. Other variations and embodiments of the invention will occur to those skilled in the art.