Daisy-chaining remote OLTs

Abstract

A system that supports daisy-chaining of remote optical line terminals.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 397,306, filed August 11, 2022. [Background technology]

[0002] The subject matter of this application relates to daisy-chaining remote OLTs for passive optical networking.

[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. Summary of the Invention

[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 terminations (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 a respective optical fiber 13, or otherwise by a respective fiber 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] Optical fiber 13 interconnecting optical splitter 12 and ONT 11 acts as an access (or "drop") fiber. Optical splitter 12 is typically located within a 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., apartments). 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 at a central office, interfacing 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.

[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 including a passive optical network. [Figure 2] FIG. 2 shows a passive optical network with downstream data traffic. [Figure 3] FIG. 3 shows a passive optical network with upstream data traffic. [Figure 4] FIG. 4 shows a remote OLT. [Figure 5] Figure 5 shows a daisy-chained remote OLT. [Figure 6] Figure 6 shows the committed information rate for the ONT. [Figure 7] Figure 7 shows the use of reserved bandwidth for an ONT. DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring to Figure 2, a PON network is based on a point-to-multipoint downstream transmission arrangement. Data from the OLT is transmitted to all ONTs interconnected to it. The data from the OLT is transmitted in the form of one or more frames, with each frame containing data for one or more ONTs. For example, in GPON, a constant 125 μs frame is used, and each frame contains an allocation map that provides information about the slots assigned to the allocation ID (among other control information). Each frame is therefore divided into one or more time slots that are assigned to one of the corresponding selected ONTs.

[0014] Referring to Figure 3, a PON network is based on a multipoint-to-point upstream transmission arrangement using a time-division multiplexing access mechanism. The OLT allocates a time slot (BW) to each ONT for its upstream transmission, ensuring collision-free transmission. Data from each ONT is transmitted to the corresponding OLT interconnected to it. Data from an ONT is transmitted in the form of a portion of one or more frames, with each frame containing data from one or more ONTs. For example, GPON uses a reference frame of 125 μs, but this is not an absolute value because allocation rounds can span multiple upstream frames. GPON uses the Generic Encapsulation Method (GEM), which allows the transport, segmentation, and reassembly of Ethernet frames and legacy traffic (ATM or TDM). Thus, each frame is divided into one or more time slots that are assigned to one of the corresponding selected ONTs.

[0015] Referring to FIG. 4, in some installations, it is often desirable to locate an optical line terminal at a location remote from the core network, commonly referred to as a remote optical line terminal (OLT). A remote OLT may include one or more feeds from the core network to the remote OLT. The remote OLT may then distribute data to and receive data from multiple ONTs. Each ONT then provides and receives data from customer devices. A remote OLT typically has the capacity to serve hundreds to thousands of ONTs.

[0016] In some environments, a single remote OLT may not provide sufficient quality of service for its associated ONTs and / or may not have sufficient capacity to provide service to all ONTs. Referring to Figure 5, it may be desirable to include multiple remote OLTs for a portion of a network, at a particular location, or otherwise, to provide improved service and / or service capacity, where a first remote OLT 500 receives data from a core network 510 based on one or more feeds 512, typically using an Ethernet or other packet-based network.

[0017] The first remote OLT 500 includes a northbound interface 502. The first remote OLT 500 preferably separates data using an internal router intended for the ONT 504 to which the first remote OLT 500 directly provides data services. The first remote OLT 500 includes optical modulators (e.g., lasers) and optical sensors (e.g., photodiodes) that provide data services to the ONT 504 over one or more fibers 505 at a primary southbound interface 506 using a passive optical network-based protocol. The first remote OLT 500 provides remaining data to a secondary southbound interface 507 without passing through the optical modulator and / or optical sensor, where it is provided to one or more feeds 508. The interconnection to the secondary southbound interface 507 typically uses an Ethernet or other packet-based network. The secondary southbound interface 507 of the first remote OLT 500 also receives data from other devices from one or more feeds 508 and provides such data to another device to the northbound interface 502 on one or more feeds 512. As can be seen, the first remote OLT 500 separates the received southbound data using either a passive optical network-based protocol or another network protocol that is not a passive optical network-based protocol (e.g., Ethernet). As can be seen, the first remote OLT 500 receives data from a passive optical network-based protocol on one interface and a non-passive optical network-based protocol on another interface and provides the combined data on the non-passive optical network-based protocol (e.g., Ethernet) to the northbound interface.

[0018] The second remote OLT 520 includes a northbound interface 522. The second remote OLT 520 preferably separates data using an internal router intended for the ONT 524 to which the second remote OLT 520 directly provides data services. The second remote OLT 520 includes optical modulators (e.g., lasers) and optical sensors (e.g., photodiodes) that provide data services to the ONT 524 over one or more fibers 525 at a primary southbound interface 526 using a passive optical network-based protocol. The second remote OLT 520 provides the remaining data to a secondary southbound interface 527 without passing through the optical modulator and / or optical sensor, where it is provided to one or more feeds 528. The interconnection to the secondary southbound interface 527 typically uses an Ethernet or other packet-based network. The secondary southbound interface 527 of the second remote OLT 520 also receives data from other devices from one or more feeds 528 and provides such data to another device to the northbound interface 522 on one or more feeds 508. As can be seen, the second remote OLT 520 separates the received southbound data using either a passive optical network-based protocol or another network (e.g., Ethernet) that is not a passive optical network-based protocol. As can be seen, the second remote OLT 520 receives data from a passive optical network-based protocol on one interface and a non-passive optical network-based protocol on another interface and provides the combined data over a non-passive network-based protocol (e.g., Ethernet) to the northbound interface.

[0019] The third remote OLT 530 includes a northbound interface 532. The third remote OLT 530 preferably separates data using an internal router intended for the ONT 534 to which the third remote OLT 530 directly provides data services. The third remote OLT 530 includes optical modulators (e.g., lasers) and optical sensors (e.g., photodiodes) that provide data services to the ONT 534 over one or more fibers 535 at a primary southbound interface 536 using a passive optical network-based protocol. The third remote OLT 530 provides the remaining data to a secondary southbound interface 537 without passing through the optical modulator and / or optical sensor, where it is provided to one or more feeds 538. The interconnection to the secondary southbound interface 537 typically uses an Ethernet or other packet-based network. The secondary southbound interface 537 of the third remote OLT 530 also receives data from other devices from one or more feeds 538 and provides such data to another device to the northbound interface 532 on one or more feeds 528. As can be seen, the third remote OLT 530 separates the received southbound data using either a passive optical network-based protocol or another network (e.g., Ethernet) that is not a passive optical network-based protocol. As can be seen, the third remote OLT 530 receives data from a passive optical network-based protocol on one interface and a non-passive optical network-based protocol on another interface and provides the combined data over a non-passive network-based protocol (e.g., Ethernet) to the northbound interface.

[0020] As can be seen, the remote OLTs may be daisy-chained together, with data selectively provided to the ONTs based on a passive optical network-based protocol. Separation and combination of data at the remote OLTs between the corresponding ONTs and other devices may be implemented using any suitable internal device, such as, for example, an internal router. In this manner, digital data is provided to the PON optical elements for data transmission and reception. In another embodiment, separation and combination of data at the remote OLTs between the corresponding ONTs and other devices may be implemented using any suitable external device, such as, for example, an external router. In this case, the external router directs the data to the appropriate remote OLT for transmitting the data to the respective ONT, and to another external router, which in turn directs the data to the appropriate remote OLT for transmitting the data to the respective ONT. In this case, the remote OLT preferably includes only a single southbound interface (which may include multiple individual PON ports) for the associated PON device, and preferably includes only a single northbound interface (which may include multiple network ports).

[0021] As can be seen, if such remote OLTs are daisy-chained together in some manner, a hierarchy of remote OLTs may exist. Each Internet Protocol address and / or MAC address of the ONT may be associated with a respective OLT with its own Internet Protocol address and / or MAC address, preferably a range of Internet Protocol addresses and / or MAC addresses for each OLT. In this manner, for each data packet or set of data packets, the Internet Protocol address and / or MAC address may be used by a router or other device to determine whether the data should be provided to the associated remote OLT, or whether the data should otherwise be provided to the next router to be provided to the associated remote OLT, etc.

[0022] The core network, or other devices, may employ a discovery protocol using broadcast data packets, such that each respective remote OLT receives the broadcast data packet and, in response, provides a response data packet identifying itself as a remote OLT. The response data packets from multiple remote OLTs may be used to determine the logical relationships between the respective remote OLTs, such as which remote OLT is downstream from another remote OLT. In this manner, the hierarchy of the remote OLTs may be determined automatically, thereby reducing the possibility of operator error if such relationships were configured manually within the core network. Furthermore, if the network architecture changes, the discovery protocol may be used to rediscover the relative relationships between different remote OLTs. Furthermore, the results of the discovery protocol may be used to configure routers within the network so that data is forwarded to the appropriate device. Other techniques may also be used to determine the hierarchical relationships between various components of the network.

[0023] In the hierarchical relationships determined between different connections in the network, each of the remote OLTs and / or routers may prioritize data traffic based on such relationships. For example, a remote OLT may prioritize data traffic from its respective ONT over data traffic from other remote OLTs. For example, a remote OLT may prioritize data traffic from other remote ONTs over data traffic from its respective ONT. For example, a router may prioritize data traffic from a corresponding OLT and its respective ONT over data traffic from other remote routers and / or remote OLTs. For example, a router may prioritize data traffic from other remote routers and / or remote OLTs over data traffic from its corresponding OLT and its respective ONT. In this manner, prioritization of data traffic may be based on the relationships between the hierarchical architectures of the remote OLTs and / or routers. In this manner, certain data traffic may be prioritized over other data traffic (e.g., transmitted first, transmitted earlier, not dropped, dropped, etc.). In this manner, certain data traffic may be dropped and / or prioritized based on prioritization when there is network congestion.

[0024] As an example, there may be queues of data in the remote OLT and / or router, and the data is queued before being transmitted to the next device in the network. The data may be tagged with priority tags, such as low priority, medium priority, and high priority. When data is dropped from any particular queue, low priority data is preferably dropped before medium priority and high priority data, and medium priority data is preferably dropped before high priority data. Also, data in any particular queue may be reordered based on the priority tags. For example, data with a high priority tag may be reordered to be transmitted before data with medium priority and low priority tags, and data with a medium priority tag may be reordered to be transmitted before data with a low priority tag. As an example, traffic in some passive optical networks may be prioritized based on the P bit.

[0025] As an example, there may be queues of data within the remote OLT and / or router, where the data is queued before being transmitted to the next device in the network. The data may be prioritized based on the customer's service level agreement associated with the data, such as low, medium, or high, or 0-7, where 7 is high and 0 is low. If data is dropped from any particular queue, device, or otherwise, preferably low SLA data is dropped before medium SLA data and high SLA data, and medium SLA data is dropped before high SLA data, even if based on a 0-7 service level agreement.

[0026] Referring to FIG. 6, after further consideration, it was determined that a technique should be implemented that provides a method for determining how to manage data traffic when data from different devices, such as different ONTs, both of which have the same highest service level agreement, should be prioritized in the event of contention. In such a case, for a limited and / or unlimited period of time, the system can assign a committed information rate (CIR) to each of the different ONTs with the highest service level agreements, particularly to ONTs that have recently experienced data contention. The committed information rate defines the guaranteed bandwidth provided by the network when delivering data frames from each ONT. While incorporating the committed information rate for selected ONTs may result in unused bandwidth because the bandwidth associated with the committed information rate cannot be used by other ONTs, it otherwise provides the desired data prioritization for the selected ONTs based on their highest service level agreements. The remaining bandwidth available after excluding the bandwidth associated with the committed information rate-based ONTs is then allocated from among the remaining ONTs. If it is determined that data contention has been suppressed or is otherwise not occurring regularly, the system can remove the committed information rate for the selected ONT.

[0027] Referring to FIG. 7, another technique for determining how to manage data traffic when data from different devices, such as different ONTs, should be prioritized when both have the same highest service level agreement includes reserving an additional portion of bandwidth, such as 10% of the bandwidth, for the ONT with the highest service level agreement, even if a data collision would otherwise occur, and not making this additional portion of bandwidth available to other ONTs among ONTs with lower service level agreements. For example, a first ONT with the highest service level agreement may use a first selected portion of bandwidth, which is always allocated to them in addition to their normal allocation. For example, a second ONT with the highest service level agreement may use a second selected portion of bandwidth, which is always allocated to them in addition to their normal allocation. If there is a potential collision for the ONT with the highest service level agreement, all or a portion of the additional portion of the reserved bandwidth may be used by the ONT in addition to its normal allocation of bandwidth. If one or more ONTs have the highest service level agreement, all or a portion of the additional portion of the reserved bandwidth may be used by the ONT in addition to its normal allocation of bandwidth. The reserved bandwidth may be modified depending on the conditions of the network.

[0028] Another technique for determining how to manage data traffic when data from different devices, such as different ONTs, should be prioritized when both have the same maximum service level agreement includes synchronizing frames between different ONTs that have the same maximum service level agreement. For multiple different ONTs that receive data service from the same remote OLT, different assigned time slots are provided for each of the different ONTs. For multiple different ONTs that receive data service from different remote OLTs, different assigned time slots are provided for each of the different ONTs with respect to other assigned time slots for the OLTs. The different assigned time slots between the different OLTs may be adjusted to account for differences in transmission time between the different OLTs so that data from two different assigned time slots at each device remains non-overlapping. Thus, from a time perspective, subframes of frames from different ONTs that receive the same maximum service level agreement are aligned in a non-overlapping manner between the different OLTs, including taking into account data travel time, timing of transmissions from any queues, time traversing one or more interconnections, and other time adjustments. In this way, bandwidth allocation for these different OLTs may depend on a centralized allocation of bandwidth that takes into account the hierarchical structure of remote OLTs in the network.

[0029] In additional embodiments, one or more queues in the network may include a separate queue for the highest service level agreement, such as service level 7. Queues with data corresponding to ONTs with the highest service level agreement may be removed from the queue and transmitted more frequently than other queues that do not correspond to the highest service level agreement.

[0030] As mentioned above, when multiple highest service level agreement ONTs exist, there is preferably coordination between what occurs on passive optical network-based devices (e.g., PON-based data traffic) and what occurs on non-passive optical network-based devices (e.g., packet-based Ethernet data traffic), which may reduce data contention.

[0031] If desired, the core network (or other method) may include a collaborative dynamic bandwidth allocation technique that allocates bandwidth among multiple remote OLTs to increase the overall efficiency of data transmission. The collaborative dynamic bandwidth allocation technique may further take into account the hierarchy of the remote OLTs, timing between different OLTs and / or routers, transmission times, etc.

[0032] 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.

[0033] It will be understood that the present invention is not limited to the particular embodiments described, and that changes may be made therein as interpreted in accordance with the principles of prevailing law, including the doctrine of equivalents, or any other principle 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. An access network, comprising: (a) a first optical line terminal capable of receiving digital data and, in response, providing first transmitted optical digital data to a first plurality of optical network termination devices, the first optical line terminal capable of receiving first received optical digital data from the first plurality of optical network termination devices and, in response, providing digital data; (c) a first routing device associated with the first optical line terminal that receives first digital data, provides a first portion of the first digital data as the received digital data of the first optical line terminal that is provided as first transmitted optical digital data, and provides a second portion of the first digital data to a second routing device; (d) a second optical line terminal capable of receiving the digital data and, in response, providing second transmitted optical digital data to a second plurality of optical network termination units, the second optical line terminal capable of receiving second received optical digital data from the second plurality of optical network termination units and, in response, providing digital data; (c) a second routing device associated with the second optical line terminal that receives the second portion of the first digital data as second digital data, provides the first portion of the second digital data as the received digital data of the second optical line terminal that is provided as second transmitted optical digital data, and provides the second portion of the second digital data to another device.

2. 2. The access network of claim 1, further comprising: each of said first plurality of optical network termination units capable of receiving said first optical digital data from said first optical line termination unit from an optical fiber connection and providing optical digital data from said optical fiber connection to said first optical line termination unit.

3. 3. The access network of claim 2, further comprising each of said second plurality of optical network termination units receiving said second optical digital data from said second optical line termination unit from an optical fiber connection and providing optical digital data from said optical fiber connection to said second optical line termination unit.

4. 2. The access network of claim 1, wherein at least one of the first routing device and the first optical line terminal prioritizes data packets based on a hierarchical relationship of the first optical line terminal and the second optical line terminal.

5. 2. The access network of claim 1, wherein the first routing device prioritizes data packets between the first optical line terminal and the second optical line terminal.

6. 2. The access network of claim 1, wherein at least one of the first routing device and the first optical line terminal prioritizes the data packets based on a service level agreement associated with each of the data packets.

7. 2. The access network of claim 1, wherein at least one of the first routing device and the first optical line terminal prioritizes the data packets based on a highest service level agreement associated with each of the data packets.

8. The access network of claim 7 , wherein the prioritization is based on a committed information rate of the data packet having the highest service level agreement associated therewith.

9. The access network of claim 7 , wherein the prioritization is based on a reserved portion of bandwidth for the data packet having the highest associated service level agreement.

10. 2. The access network of claim 1, wherein (1) at least one of the first routing device and the first optical line terminal, and (2) at least one of the second routing device and the second optical line terminal, prioritize the data packets based on a highest service level agreement associated with each of the data packets from (1) at least one of a first plurality of optical network devices and (2) at least one of a second plurality of optical network devices, and wherein the data packets are synchronized in time with respect to each other in a non-overlapping manner.

Images