OLT with mesh interconnection

Abstract

A system having OLTs with mesh interconnections.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This invention claims the benefit of U.S. Provisional Patent Application No. 63 / 396,567, filed August 9, 2022. [Background technology]

[0002] The subject matter of this application relates to OLTs with mesh interconnections.

[0003] Passive optical networks (PONs) are often used as access networks, or as part of a larger communications network. Communications networks typically have a high-capacity core section through which data or other information related to telephone calls, digital television, and Internet communications is transmitted over significant distances. The core section may have the ability to interact with other networks to complete the transmission of telephone calls, digital television, and Internet communications. In this way, the core section in combination with the passive optical network enables communications to and from subscribers (or devices associated with subscribers, customers, businesses, or otherwise).

[0004] The access network of a communications network extends from the core of the network to individual subscribers, such as those associated with a particular residence (e.g., business location). The access network may be wireless access, such as a cellular network, or fixed access, such as a passive optical network or a cable network.

[0005] Referring to FIG. 1, in a PON 10, a set of optical fibers and passive interconnection devices is used for most or all of the communications throughout the access network. A set of one or more optical network terminals (ONTs) 11 are devices typically located at subscriber residences (e.g., or business locations). The term "ONT" includes what are also referred to as optical network units (ONUs). There may be any number of ONTs associated with a single optical splitter 12. As an example, 32 or 64 ONTs are often associated with a single network optical splitter 12. The optical splitters 12 are interconnected with each ONT 11 by respective optical fibers 13, or otherwise by respective fibers within a fiber optic cable. Selected ONTs may be removed and / or added to the access network associated with the optical splitter 12 as needed. There may also be multiple optical splitters 12 arranged in a cascaded configuration.

[0006] The optical fiber 13 interconnecting the optical splitter 12 and the ONT 11 acts as an access (or "drop") fiber. The optical splitter 12 is typically located within a street cabinet or other structure in which one or more optical splitters 12 are located, each serving a respective set of ONTs. In some cases, an ONT may serve multiple subscribers, such as subscribers in multiple dwelling units (e.g., apartment buildings). In this way, a PON can be considered a point to multipoint topology, in which a single optical fiber serves multiple endpoints by using passive optical fiber splitters to divide the fiber bandwidth between the endpoints.

[0007] An optical line terminal (OLT) 14 is located in a central office that interfaces directly or indirectly with a core network 15. The interface 16 between the OLT 14 and the core network 15 may be one or more optical fibers or any other type of communication medium. The OLT 14 forms optical signals for transmission downstream to the ONTs 11 through feeder optical fibers 17 and receives optical signals from the ONTs 11 through the feeder optical fibers 17. The optical splitter 12 is typically a passive device that distributes signals received from the OLT 14 to the ONTs 11. Similarly, the optical splitter 12 receives optical signals from the ONTs 11 and provides optical signals to the OLT 14 through the feeder optical fibers 17. In this manner, a PON includes an OLT with multiple ONTs, which reduces the amount of fiber required compared to a point-to-point architecture.

[0008] As can be observed, an optical signal containing all of the data for the ONTs 11 is provided to the feeder fiber 17. Thus, all of the data provided to each of the ONTs is provided to all of the ONTs through the optical splitter 12. Each of the ONTs selects the portion of the received optical signal intended for that particular ONT and transmits the data to its subscribers while discarding the remaining data. Typically, data to the ONTs is broadcast to the feeder fiber 17 and provided to each of the ONTs.

[0009] Upstream transmissions from the ONTs 11 through their respective optical fibers 13 are typically transmitted in bursts according to a schedule provided to each ONT by the OLT. In this manner, each of the ONTs 11 transmits upstream optical data at different times. In some embodiments, the upstream and downstream transmissions are transmitted using different wavelengths of light so that they do not interfere with each other. In this manner, a PON may utilize wavelength division multiplexing, using one wavelength for downstream traffic and another wavelength for upstream traffic over a single-mode fiber.

[0010] A schedule from the OLT allocates upstream bandwidth to ONTs. Because the optical distribution network is shared, ONT upstream transmissions are likely to collide if they are transmitted at random times. ONTs are typically located at various distances from the OLT and / or optical splitter, resulting in different transmission delays for each ONT. The OLT measures the delay and sets registers in each ONT to equalize that delay with respect to other ONTs associated with the OLT. Once the delay is accounted for, the OLT transmits so-called grants to individual ONTs in the form of a grant map. A grant map is an authorization to use a defined time interval for upstream transmission. The grant map is dynamically recalculated periodically, such as for each frame. The grant map allocates bandwidth to all ONTs so that each ONT receives a timely bandwidth allocation for its service needs. Much data traffic, such as website browsing, tends to be bursty and fluctuates significantly over time. Dynamic bandwidth allocation (DBA) between different ONTs can cause a PON to be oversubscribed for upstream traffic. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows a network that includes a passive optical network. [Figure 2] Figure 2 shows a chassis-based OLT. [Figure 3] FIG. 3 shows a chassis-based OLT with a switch fabric. [Figure 4] FIG. 4 shows a single backplane-based OLT. [Figure 5] FIG. 5 shows multiple OLTs and a switch. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to FIG. 2, an optical line terminal typically includes multiple vertical cards (i.e., blades), each of which includes multiple ports providing interconnection to a PON access network, and each of the vertical cards is interconnected to a common backplane circuit board. The common backplane circuit board includes a series of traces thereon, along with various integrated circuits that distribute signals to each of the vertical cards via interconnects such as PCI slots. In this manner, a desired number of vertical cards may be added to the optical line terminal while still having a common backplane circuit board suitable for supporting additional vertical cards until the optical line terminal is fully populated. Furthermore, the optical line terminal includes power management for each potential line card it may support. In this manner, the optical line terminal is designed for the ability to support a significant number of ports across vertical cards, such as a minimum of 64 ports or more. Unfortunately, such OLTs tend to be burdensome to install in locations remote from the core network, such as remote enclosures in a distribution network, due to limited power availability and limited space availability in the remote enclosures. Additionally, backplanes with interfaces for vertical cards present a significant number of issues related to signal integrity and physical robustness over time, as the interfaces tend to corrode when used in uncontrolled humidity and temperature environments with dust and debris.

[0014] Referring also to Figure 3, vertical cards, removably interconnected to a backplane, are interconnected to each other via a leaf-spline switch fabric, all of which are enclosed and integrated within the housing for the optical line terminal (OLT). Leaf-spline switching provides an integrated approach to distributing data. As the bandwidth requirements of the access network increase over time, existing vertical cards are replaced with updated vertical cards that include increased capacity. However, the leaf-spline switch fabric often tends to be insufficient to support the bandwidth requirements of the updated vertical cards, thereby potentially necessitating the replacement of the entire OLT.

[0015] Referring to FIG. 4, a modified approach to OLT architecture is desirable for improved modularity, signal integrity, and robustness. The modified OLT 400 includes a single backplane circuit board 410 without blades having a PON port removably interconnected thereto. The circuit board 410 includes a network-side interface (NSI) port 420 that interconnects to a core network, such as using an Ethernet-based connection. The circuit board 410 includes electronic components 430, such as a processor and optical components, for transmitting and receiving data via the NSI port 420. The electronic components 430 on the circuit board 410 further format the data for transmission over the PON network through a selected one of multiple PON ports 440 using a PON transceiver (optical transmitter and optical receiver). The PON ports 440 are interconnected with respective ONTs using respective optical fibers using a PON-based protocol.

[0016] As shown in FIG. 4 , the OLT 400 does not include a broad switch fabric, such as a leaf spline switch fabric, other than managing switching between ports 440 on the circuit board 410 and data transmission through the NSI ports 420, which may be implemented by an FPGA. Multiple NSI ports may be present as needed. Fewer or more PON ports may be present as needed. The OLT 400 is designed for the ability to support a limited number of PON ports, such as up to 16 ports, without supporting PON ports on any removable blades. Due to limitations arising from a single backplane circuit board 410, particularly with regard to scalability, it may be further desirable to include the ability to interconnect multiple OLTs 400 in parallel to a selected set of subscribers requiring more data capacity than a single OLT 400 can provide.

[0017] Referring to FIG. 5 , the modified architecture includes a modular approach that includes multiple OLTs 400, each based on a single backplane circuit board 410. Each OLT 400 is enclosed within its own housing and supports its own respective set of subscribers. Each OLT 400 is interconnected with a switch 500, with one or more NSI ports that are in turn interconnected to the core network. The switch 500 is enclosed within its own housing. The switch 500 is interconnected with each OLT by a respective set of one or more cables. In this modified architecture, the capacity to support a PON access network can be expanded by increasing the number of OLTs 400 interconnected with the switch 500. With each OLT interconnected in parallel to the switch 500, the bandwidth carried by the switch 500 increases correspondingly, up to the limit of the switch 500. Additionally, if the bandwidth requirements of an OLT 400 interconnected to a switch 500 exceed the capabilities of the switch 500, the switch 500 may be replaced with an updated switch 500 with increased bandwidth capabilities. As can be observed, the OLT 400 does not need to be replaced to update the capabilities of the switch 500.

[0018] The processing capabilities of each of the OLTs 400 may be relatively limited, often having only sufficient computational resources to provide PON-related processing for transmitting and receiving PON data to the PON network, without significant additional computational resources, in order to reduce the power requirements and possible resulting heat dissipation of the OLT.

[0019] With such limited overload processing available at the OLT, it may be desirable to virtualize some management features for the OLT to reduce the computational burden on the OLT. The virtualized management function may use computational resources on servers associated with the core network, which is easily scalable as desired. The virtualized management function may be used to provision each of the OLTs. The virtualized management function may be used to re-provision each of the OLTs when one or more subscribers are moved from one port of the same OLT to another port or to a port of a different OLT. The virtualized management function may be used to detect alarm conditions in one or more of the OLTs, for example, when an OLT becomes unavailable or otherwise fails.

[0020] In some cases, such as for subscribers requiring high availability, there may be redundancy in the ability to transmit data over the PON network to such subscribers. If an OLT becomes unavailable or otherwise fails, the system can automatically fail over to a backup OLT to continue providing PON data to the subscriber. The backup OLT may be interconnected to each of the fibers from the other ONTs, such as through an optical switch network. A virtualized management function may automatically redirect data traffic to the backup OLT.

[0021] Each OLT may contain a portion of the processing for management of the OLTs running on it, providing a balance of processing control traffic. If one or more of the OLTs fails, becomes unavailable, or otherwise does not have sufficient computing resources available, the processing for management of the OLTs running on it is redistributed among the surviving OLTs. Thus, OLT management is distributed across the OLTs and redistributed as needed.

[0022] Furthermore, each functional block or various features in each of the foregoing embodiments may be implemented or performed by a circuit, typically an integrated circuit or multiple integrated circuits. A circuit designed to perform the functions described herein may include a general-purpose processor, a digital signal processor (DSP), an application-specific or general-purpose integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, or discrete hardware components, or a combination thereof. A general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, controller, microcontroller, or state machine. The general-purpose processor or each circuit described above may be composed of digital circuits or analog circuits. Furthermore, as advances in semiconductor technology allow integrated circuits to replace multiple integrated circuits, integrated circuits based on this technology may also be used.

[0023] It will be understood that the present invention is not limited to the particular embodiments described, and that changes can be made therein, as interpreted in accordance with the principles of prevailing law, including the doctrine of equivalents or any other doctrine that expands the scope of enforceable claims beyond their literal scope, without departing from the scope of the invention as defined in the appended claims. Unless the context indicates otherwise, a reference in a claim to the number of instances of an element, whether to a single instance or to multiple instances, requires at least the recited number of instances of the element, but is not intended to exclude from the scope of the claim structures or methods having more instances of that element than recited. As used in the claims, the term "comprise" or derivatives thereof are used in a non-exclusive sense, which is not intended to exclude the presence of other elements or steps in the claimed structure or method.

Claims

1. 1. A network architecture, comprising: (a) a first optical line terminal including a first single backplane circuit board that does not include any removably engageable cards, the first single backplane circuit board not including any cards that include PON ports on the engageable cards; (b) the first single backplane circuit board includes at least one first network-side interface for receiving data from a core network and providing data to the core network; (c) the first single backplane circuit board includes a plurality of PON ports for receiving data from an optical PON network and providing data to the optical PON network, and the first single backplane circuit board includes 16 or fewer of the PON ports; (d) the first single backplane circuit board supports a processor, at least one transmitter, and at least one optical sensor configured to provide and receive data to the plurality of PON ports and to provide and receive data from the at least one network-side interface; (e) a network architecture wherein the first single backplane, the processor, the at least one transmitter, and the at least one optical sensor are all enclosed within a first OLT housing.

2. 2. The network architecture of claim 1, further comprising: a second optical line terminal including a second single backplane circuit board that does not include any removably engageable cards, but no cards that include PON ports on the engageable cards, the second single backplane circuit board including at least one second network-side interface for receiving data from the core network and providing data to the core network, the second single backplane circuit board including a plurality of PON ports for receiving data from an optical PON network and providing data to the optical PON network, the second single backplane circuit board including 16 or fewer of the PON ports, the second single backplane circuit board supporting a processor, at least one transmitter, and at least one optical sensor configured to provide and receive data to the plurality of PON ports and to provide and receive data from the at least one network-side interface, the second single backplane, the processor, the at least one transmitter, and the at least one optical sensor all being enclosed within a second OLT housing.

3. (a) further comprising a switch enclosed within a switch housing, wherein the switch housing, the first OLT housing, and the second OLT housing are separate from one another; (b) the at least one first network-side interface is interconnected to at least one port of the switch by at least one cable; (c) the at least one second network-side interface is interconnected to at least one port of the switch by at least one cable; (d) the switch is interconnected to the core network; The network architecture of claim 2.

4. 4. The network architecture of claim 3, further comprising a server including a virtualized OLT, the virtualized OLT selectively provisioning the first optical line terminal and the second optical line terminal.

5. 4. The network architecture of claim 3, further comprising a server including a virtualized OLT, wherein the virtualized OLT selectively reprovisions the first optical line terminal and the second optical line terminal when a subscriber previously associated with the first optical line terminal is subsequently associated with the second optical line terminal.

6. The network architecture of claim 3 , further comprising a server including a virtualized OLT, said virtualized OLT detecting an alarm condition of said first optical line termination device.

7. 2. The network architecture of claim 1, further comprising: a second optical line terminal including a second single backplane circuit board that does not include any removably engageable cards, but no cards including PON ports on the engageable cards, wherein the second single backplane circuit board includes at least one second network-side interface for receiving data from the core network and providing data to the core network, the second single backplane circuit board includes a plurality of PON ports for receiving data from an optical PON network and providing data to the optical PON network, the second single backplane circuit board includes 16 or fewer of the PON ports, the second single backplane circuit board supports a processor, at least one transmitter, and at least one optical sensor configured to provide and receive data to the plurality of PON ports and to provide and receive data from the at least one network-side interface, the second single backplane, the processor, the at least one transmitter, and the at least one optical sensor are all enclosed within a second OLT housing, and the first optical line terminal and the second optical line terminal support the same set of the optical network terminal devices.

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