By Serkant Uluderya, Engineering Manager at Netsia and Linux Foundation Broadband VOLTHA TST Member
The concept of Fixed Access Network Sharing (FANS), as defined by the Broadband Forum (BBF) in its TR-370 specification, is revolutionizing the broadband industry by enabling multiple Virtual Network Operators (VNOs) to operate on a single infrastructure provider’s (InP) access network. This approach addresses the economic impracticality of every broadband provider deploying its own fiber access network and caters to the increasing demand for open access networks. The LF Broadband VOLTHA (Virtual OLT Hardware Abstraction) project plays a crucial role in facilitating this sharing by providing an open source, disaggregated, and multi-vendor solution for PON broadband access equipment.
Understanding Fixed Access Network Sharing (FANS) and TR-370
FANS, as introduced by the Broadband Forum, defines a model where a single infrastructure provider owns and manages the access network, while multiple Internet Service Providers (ISPs), acting as VNOs, leverage this shared infrastructure to deliver broadband services to their customers. This paradigm is akin to Mobile Virtual Network Operators (MVNOs) in the mobile telecommunications sector. A key driver for FANS is the elimination of duplicate networks and their associated costs, leading to significant economic benefits. Given the shared nature of passive optical networks (PONs), where a single active Optical Line Terminal (OLT) is owned and managed by the InP, FANS effectively meets the demand for open access networks.
The Broadband Forum’s TR-370 specification outlines different methodologies for managing shared access infrastructure. This includes exposing services that run on top of the infrastructure from the InP to the VNOs. Implementations of FANS often utilize a domain controller based on Software Defined Networking (SDN) principles, which exposes the network’s management layer to each individual VNO for service activation and monitoring.
LF Broadband VOLTHA: Enabling Disaggregated PON for FANS
VOLTHA is an open source initiative focused on PON broadband access equipment, promoting a multi-vendor, disaggregated, and “any broadband access as a service” model for the Central Office. Its core function is to provide an isolation layer between an abstract, vendor-agnostic PON management system and the diverse array of vendor-specific and white-box PON hardware devices.
VOLTHA’s architecture is particularly well-suited for FANS implementations due to its ability to present the PON network as a programmable Ethernet switch to an SDN controller via its northbound interface. On its southbound side, VOLTHA communicates with various PON hardware devices using vendor-specific protocols through OLT and ONU adapters. This abstraction layer is critical for enabling multi-vendor interoperability within a shared access network environment.
Key concepts within VOLTHA that align with FANS objectives include:
- Network as a Switch: VOLTHA transforms a set of connected access network devices into a single SDN-programmable switch. This simplifies network management for both the InP and VNOs.
- Evolution to Virtualization: VOLTHA’s design allows it to work with a wide range of access network technologies and devices, supporting the virtualization of the access layer.
- Unified OAM Abstraction: It provides a consistent, vendor- and technology-agnostic approach to device management tasks, encompassing service lifecycle, device lifecycle (including discovery and upgrades), system monitoring, alarms, troubleshooting, and security.
- Cloud/DevOps Bridge to Modernization: VOLTHA leverages a microservices architecture running on Docker and Kubernetes, facilitating modern cloud-native deployment and operational practices.
A typical VOLTHA and ONOS (SDN controller) deployment involves an infrastructure comprising storage (etcd or Redis), a message bus (Kafka), and the SDN controller, alongside multiple VOLTHA stacks. All VOLTHA components are containerized and deployed using Kubernetes, offering flexibility in deployment location, from a data center to the OLT box itself.
The VOLTHA stack itself contains several interacting components:
- VOLTHA core: This is the central component, receiving requests from the northbound interface, breaking them down for adapters, handling adapter registration, and storing configuration information for ONUs and OLTs. It also abstracts OLT and ONU pairs as a logical device.
- OLT adapter: Responsible for interacting with the physical OLT, reporting information and events to the core, and issuing requests from the core to the device. It abstracts the OLT’s technology (e.g., GPON, XGS-PON, EPON).
- ONU adapter: Manages interactions and commands towards the ONU via OMCI, including discovery, MIB upload, and T-CONT/GEM port configuration.
For aspects of OLT management not directly handled by VOLTHA, an optional Device Management Interface (DMI) can be deployed. This interface allows operator OSS/BSS systems to manage tasks like software upgrades and component inventory.
Practical Implementation of FANS with SDN and VOLTHA
One example is Netsia’s BB Suite, which offers a comprehensive FANS solution aligned with TR-370, leveraging both SDN and management system models. It supports various device types, including whitebox, BBF native, and legacy OLTs, and provides user-friendly interfaces for both InPs and VNOs. Netsia’s BB Suite ensures VNOs only see their own devices and profiles, while InPs maintain a system-wide view for network health monitoring. The BB Suite also supports standard northbound interfaces for integration with third-party OSS/BSS systems.
Conclusion
The LF Broadband VOLTHA project, by providing an open and disaggregated platform for PON broadband access, is a foundational element in realizing the vision of Fixed Access Network Sharing as defined by the Broadband Forum’s TR-370 specification. Through its abstract APIs, vendor-agnostic approach, and cloud-native architecture, VOLTHA empowers InPs to efficiently share their network infrastructure with multiple VNOs. This not only drives economic benefits by eliminating redundant deployments but also fosters a more open and competitive broadband market, ultimately benefiting end-customers with a wider array of service choices. The ongoing collaboration between organizations like the Broadband Forum and open source projects like VOLTHA is crucial for the continued evolution and widespread adoption of shared access networks.
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