Patent Application
20230188874
Access data networks which have nodes and links that are located outside of facilities which provide high availability power and protection against physical accidents and other means of causing failure of network components are fundamentally less reliable than similar networks in which nodes and links are contained within more secure and reliable facilities. These access networks connect hosts to core networks which employ sophisticated routing protocols and redundant connectivity to ensure that the network has high availability. Connectivity to the high-reliability core network is via one or more gateway nodes at the edge of that core network. To improve the availability of connections of end-hosts connected via access networks to the core network, a primary and secondary gateway node are often designated, with the access network providing connectivity paths to both. Mechanisms to select which gateway node is active at a given time exist, and the gateway nodes involved employ protocols such as Virtual Router Redundancy Protocol (VRRP) and Multi-Chassis LAG (ML-LAG) and other similar protocols to select which gateway node is the active connection point for a given end-host. These mechanisms require support of these protocols by the gateway nodes, which communicate between each other to determine which node is currently active. The nature of these protocols provide a minimum time required to change the active gateway host, and during this time, the end-host is not connected to the core network and this minimum time may be in excess of end-user application requirements. In order to avoid the requirement of these protocols for selecting the active gateway node, it is desired to have a mechanism to connect end-hosts to the core network which doesn't require the gateway nodes to select the active access node connection point, as well as not requiring any special functionality in the access network to support it.
A common architecture for access network employs Passive Optical Network (PON) technologies, such Gigabit PON (GPON) and 10-Ggabit symmetric PON (XGS-PON). PON-based architecture employ an access node containing the PON Optical Line Terminal (OLT) and an Optical Network Unit (ONU) (sometimes referred to as an Optical Network Termination, or ONT) at the customer location. High availability methods are defined for the Passive Optical Network (PON) technologies. These mechanisms are defined in ITU-T G.984 (GPON) and ITU-T G.9807 (XGS-PON) and similar documents and discussed further in ITU-T G.sup51. As described in ITU-T G.984.1, redundancy methods defined at the PON layer only protect the PON portion of the access network rather than the full path between the end-host and the gateway node(s). Type B protection is defined to use multiple OLTs but only a single ONT per subscriber. As a result, in involves considerable complexity to achieve rapid switchover, requiring that the primary and secondary OLTs coordinate their provisioning and operational states (e.g. connected ONTs, ranging information, etc.) so that this information doesn't have to be rediscovered during the switchover interval. This typically limits the speed at which network switching takes place. Type C protection avoids these complexities by using separate ONU/ONTs for the primary and secondary paths, allowing the OLT-ONT relationship to be constant across a switchover event.
The ITU-T supplements G.sup51 and G.sup54 additionally describe the use of Ethernet Linear Protection Switching (ELPS) to protect the path between a network ethernet switch and the splitter (Type B redundancy). Note that while a similar approach could be applied to Type-C redundancy, unlike the VRRP and MC-LAG approaches described above, the network-based switching element is a single device and represents a single point of failure, reducing the value of the protection switching mechanism. A method to realize Type C protection but avoid the single point of failure in the network ethernet switch is clearly desired.
The mechanism defined here achieves the above mentioned goals by pushing the responsibility for gateway node selection to a newly introduced protection switch edge node which sits beyond the access network, typically deployed on the end customer side of a conventional access network (e.g. customer side of the Optical Network Unit (ONU) or Optical Network Termination (ONT)). This node provides a mechanism to connect to two independent access networks, each with a primary connection point to the core network as shown in
Relative to the VRRP and MC-LAG approaches, this new methodology moves the functionality for selecting primary and secondary gateway nodes to each protection switch edge node and does not require coordination between the gateway nodes and protection switch edge nodes for selection (outside of fault detection) and does not require coordination between the gateway nodes. By only requiring a network maintenance entity group end point (e.g., MEP) on the gateway nodes, and no changes to the access nodes, this functionality can be added to virtually any network, simply by deploying redundant access networks. These redundant access networks may be configured to improve reliability by using separate physical paths from each end-node to the gateway nodes, though this is not required if only equipment redundancy (vs. full path redundancy) is desired. Furthermore, this mechanism allows the functionality to be added to networks where the gateway nodes do not employ mechanisms for choosing the active gateway node using protocols that require communication between the gateway nodes. The lack of dependence on such protocols extends the applicability of this mechanism to many deployment scenarios where the current method are excluded due to the functionality of existing deployed networks. With the new invention, the decision for which gateway node is active is not made by the gateway nodes, but rather by the newly invented protection switch edge node, allowing both faster switch over, and connectivity to gateway nodes which do not employ specialized protocols to select the active node. In doing so, such a mechanism will move the decision for choosing the gateway node for each end-host to a network device which performs this function for one or a few end-hosts that are located within a short physical proximity of each other. By pushing the decision to the edge of the access network, high-availability access to the core network is possible without employing complex protocols on the gateway nodes or the access network, which is between the protection switch edge node and the gateway nodes.
There are many possible implementations of the above described invention, the detailed description of the invention will use the context of an access network employing Passive Optical Network (PON) technologies such as Gigabit PON (GPON) and 10-Ggabit symmetric PON (XGS-PON), but that should not be construed as limit the scope of the invention as it should be obvious to anyone skilled in the art that the applicability of the new method does not employ any protocol or mechanism that is specific to any PON protocol or technology. Furthermore, the fault-detection protocol described employs Y.1731 ethernet management protocols and peered point-to-point management paths, but that again should not be construed as a limiting implementation of the invention. Furthermore, the protection switching mechanism of the newly invented protection switch edge node is described as a modification of the ITU-T G.8031 Ethernet Linear Protection Switch (ELPS) protocol, a protocol that is defined to operate between peer nodes, with multiple paths of connectivity between them. The state machines defined in G.8031 assume a peer node at the far end. In our implementation, we employ a slightly modified ELPS state machine at only the protection switch edge node, and do not have a L2 peer node making similar decisions using the ELPS state machine or other similar mechanism. Therefore we refer to this newly defined mechanism as “Single-Ended ELPS”, but that should not be construed as limiting other implementations of the invention which do not employ a modified version of the ELPS state machine.
Additionally, once a protection switch event has been restored (e.g. the fault on the primary path has been repaired), the traffic may switch back to the primary path, or the traffic may remain on the secondary path. The path that is carrying traffic is typically called the active path, and the path that is not carrying traffic is typically called the standby path. Working and protection are other equivalent terms that can be used in place of primary and secondary.
In one embodiment, this specification relates to fast Type C GPON redundancy failover in a network. Type C PON provides protection between two aggregation switches and a CPE with two GPON uplinks to two distinct PONs (passive optical networks). To achieve desirable failover speeds the specification describes a novel use of ITU G.8031 1:1 ELPS (Ethernet Linear Protection Switching) in a single ended application to ensure path integrity through the network. ELPS is a standardized method for protection switching between two point-to-point paths through a network. During a failure on the working path, traffic will switch over to the protection path. In single ended 1:1 ELPS, a network device is configured with 1:1 ELPS and switches paths in the event of disruption of a working communication path. Fault detection and failover occurs without other underlying communication paths having knowledge of either the ELPS protocol or state machine.
A network may comprise multiple aggregation switches, multiple OLTs, and multiple CPEs (customer-premises equipment).
The disclosure herein describes solutions that leverage local decision making of ELPS path selection, without using a coordinated endpoint. The ELPS state machine is simplified in its operation because it does not coordinate with the opposite endpoint as defined by ITU-T G.8031. Moving the path decision making to the CPE allows for each individual CPE to make a determination as to the available path to use. This determination is done autonomously in the CPE without the need for additional user or software intervention. These changes are needed because G.8031 Standard 1:1 ELPS introduces a single point of failure, which is undesirable. For instance, the selector and bridge are coordinated between endpoints using state machines. APS packets are sent on the protect path and CCMs (continuity check messages) run on each path to determine path state.
For purposes of this disclosure, a communication path extends between an aggregation switch and a CPE. An aggregation switch generates CCMs and delineates the boundary of the ELPS protection domain. Network fault detection occurs through transmission of multiple Ethernet OAM (operations, administration and maintenance) CCMs per second, allowing for fast path failure detection. As one example, transmitting Ethernet OAM CCMs at 3.3 ms intervals allows path failure detection within approximately 11 ms according to the disclosure herein. RDI (remote defect indication) is used to determine path integrity and can detect unidirectional failures.
In event of path failure detection, if the path that has failed is currently being used as the active path, the ELPS state machine forces a failover to the standby path, if it is valid. Each CPE has its own MEG. Upstream traffic from the CPE to the aggregation switch moves over as soon as the ELPS state machine changes the path. Upon ELPS failover, the CPE shall send a gratuitous ARP (address resolution protocol) message to ensure management traffic fails over. The aggregation switch learns the MAC (media access control) address on the new port and allows downstream management (e.g. control) traffic to flow.
The disclosure herein scales across any number of CPEs and is limited only by the Ethernet OAM generation rate of the aggregation switches. Thus, the solutions provided herein horizontally scale by using multiple aggregation switches.
There are many advantages of the solutions described in this disclosure. For instance the solutions provide rapid switching between working and protect paths upon detection of a network failure and reduces single point of failure in the network. The solutions require no participation from the OLTs in the communication paths and thereby reduce complexity, command and control traffic, processing latency, and the like. Likewise, no additional or unique protocols are needed to maintain the ELPS state machines for the ELPS protection groups. In addition, this solution allows for redundancy of OLT and ONU equipment, whereas previous disclosures provided redundancy of only the OLT. For instance, the solutions described herein provide geographic redundancy of the network equipment and provide two fully redundant OLT and ONU links. Moreover, this solution does not unnecessarily failover paths that are not in the fault state. Instead, each CPE is free to failover individually and independently of the other CPEs on the same PON.
As one of skill in the art will appreciate, the solutions described herein combine several protocols and functions into a single novel solution that provides horizontally scalable resilient transport agnostic path protection.
The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.
Like reference numbers and designations in the various drawings indicate like elements.
Methods and systems for Rapid Type C GPON Redundancy Failover are discussed throughout this document. As will be discussed in more detail with reference to the figures, redundant communication paths exist between a CPE and a network. Network access is via one or more aggregation switches. These redundant communication paths can be viewed as an ELPS protection group whose connectivity is protected from network failures through the use of a unique form of Single Ended 1:1 ELPS processing. Unlike traditional ELPS processing, only one endpoint is directly involved in fault detection and there is no coordination between the two endpoints using APS messages. The network fault detection and rapid failover scheme described herein also decouples the control and data planes. The solution separates the control and data planes such that the control plane is monitored using the unique Single Ended 1:1 ELPS while the data plane uses ELAN resiliency. Thus, as is disclosed herein, the network can individually or collectively control failover, as appropriate. As one example, CCMs associated with one VLAN could detect network faults causing failovers in different VLANs.
Per ELPS, between two network entities, traffic traverses one of two paths: a working path or a protection path. A given path has two states: active or standby. These two paths and their associated traffic and services, running on VLANs, form an ELPS (Ethernet linear protection switching) group. In normal operation, the traffic and services will traverse the working path, as it is active while the protection path is standby. However, in a fault state, the ELPS group fails over from the active working path such that its traffic and services now traverse the newly active protection path. The ELPS group may revert the active path to the working path when the failure has been corrected, however this is not required.
As described in the standard, G.8031 1:1 ELPS uses selectors and bridges at upstream and downstream network elements (EAST and WEST endpoints) that are coordinated using state machines tracking the active and standby status of the working transport entity (TE) and the protection transport entity (TE). To detect faults on the working and protection TEs, CCM traffic is sent over both paths. When a fault is detected, APS packets are sent on the protection TE. For clarity, the term working TE and working path refer to the same element, and the term protection TE and protection path refer to the same element.
G.8031 can be advantageously modified by replacing the selector and bridge at the WEST endpoint with an Ethernet switch. CCM messages are communicated on each of the working and protect paths to monitor path health. CCM endpoints detect network faults and determine the path fault domain. The Ethernet switch generates CCM messages on the working and the protect paths that will inform the CPE of their status and integrity, and ultimately allow it to make a decision as to which path to use. The EAST endpoints then choose which of the working or protect path should be designated the active path. Among the ports assigned to the working and protect paths, the active port of the WEST Ethernet switch is determined to be that port with a MAC address known to the system (e.g., through ARP tables, IP to MAC address mappings, etc.). Unlike G.8031 defined in the standard, no APS packets are used. In other words, this solution can be implemented independent of APS packets.
In one implementation, the CPEs only transmit and receive on the active path while monitoring both paths using CCMs. The aggregation switches are agnostic to the ELPS group. However, the aggregation switches contain MEPs to generate CCMs to each CPE. The CPEs make the decision as to which path to use based on the CCMs received from the switch, and trigger path changes in the ELPS state machine accordingly. For instance, the absence of received CCM traffic on a MEP of the CPE indicates a network fault on that communication path. On failover, the aggregation switches relearn the traffic MAC addresses on the newly active path as the traffic starts to flow through it, such as through ARP messaging for management or through upstream data packets. Accordingly, rapid fault detection and failover can occur in many embodiments.
Because the WEST endpoint does not use the ELPS protocol or state machine, it's functionality can be split between multiple aggregation switches, providing additional redundancy.
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An ELPS protection group is established 530 comprising the working path and the protection path. Communication proceeds over the ELPS protection group 540. As communication proceeds over the ELPS protection group 540, CCM traffic is monitored 550 for fault detection 560. A fault on a working path can be detected 560 based on the absence of CCM traffic at a MEP, of a CPE device, associated with the working path. For example, if CCM traffic persists, no fault is indicated 565. If CCM traffic is absent, a fault is detected 570. When a fault is detected 570, the CPE may send an RDI notification to the aggregation switch over the protect path. RDI notifications can be sent over either the working or the protect path, depending on which has the fault. When a fault is detected 570 on the working path, the protection path is promoted to an active state and becomes the active path for that ELPS protection group 580. Communications continue on that ELPS protection group 540 and CCM traffic continues to be monitored 550. For instance, once the protection path is made active, the CPE switches upstream traffic to the aggregation switch from the working communication path to the protection communication path. For downstream traffic, the aggregation switches learn a MAC address of a port coupled to the active path at the CPE. The aggregation switches may learn this MAC address by sending a gratuitous ARP message. The CPE sends a gratuitous ARP for the aggregation switch to learn its management MAC address. Upstream traffic flowing through the CPE causes the aggregation switch to learn other MAC addresses. Once the MAC address of the port coupled to the active path at the CPE is learned, the aggregation switches send downstream traffic on the active path to the port at the CPE.
An ELPS protection group is established 630 comprising the working path and the protection path. Communication proceeds over the ELPS protection group 640. As communication proceeds over the ELPS protection group 640, CCM traffic is monitored 650 for fault detection 560. A fault on both the active and the standby paths can be detected 660 based on the absence of CCM traffic at a MEP, of a CPE device, associated with the working path. For example, if CCM traffic persists, no fault is indicated 665. If CCM traffic is absent, a fault is detected 670. When a fault is detected 670, the CPE may send an RDI notification to the aggregation switch over the protect path. RDI notifications can be sent over either the working or the protect path, depending on which has the fault. When a fault is detected 670 on both the active and the standby paths, the working path is promoted to an active state and becomes the active path for that ELPS protection group 680. Communications continue on that ELPS protection group 640 and CCM traffic continues to be monitored 650. For instance, once the protection path is made active, the CPE switches upstream traffic to the aggregation switch from the working communication path to the protection communication path. For downstream traffic, the aggregation switches learn a MAC address of a port coupled to the active path at the CPE. The aggregation switches may learn this MAC address by sending a gratuitous ARP message. The CPE sends a gratuitous ARP for the aggregation switch to learn its management MAC address. Upstream traffic flowing through the CPE causes the aggregation switch to learn other MAC addresses. Once the MAC address of the port coupled to the active path at the CPE is learned, the aggregation switches send downstream traffic on the active path to the port at the CPE.
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CPE (customer-premises equipment) generally refers to devices such as telephones, routers, network switches, residential gateways, set-top boxes, fixed mobile convergence products, home networking adapters and Internet access gateways that enable consumers to access communication providers' services and distribute them in a residence or business over a local area network.
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.
Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products, or a single hardware product or multiple hardware products, or any combination thereof.
Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.
This application claims priority to U.S. Provisional Application Ser. No. 63/288,403, filed on Dec. 10, 2021, the entire contents of which are hereby referenced in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63288403 | Dec 2021 | US |
