Larger-Scale Operations Can Be Accommodated With Broadband Network Gateways
Across the globe, telecommunications companies are making substantial investments in upgrading their fiber networks to expand broadband coverage and capacity. To take full advantage of faster access speeds and prevent potential bandwidth limitations further upstream, they must also design Broadband Network Gateways (BNGs) at the network’s edge to accommodate larger-scale operations.
The BNG serves as a crucial component within the network, overseeing subscriber access to broadband content and applications across the internet, private cloud environments, and content delivery networks. The Broadband Forum’s TR-101 specification outlines its role and specific requirements, encompassing subscriber authentication, IP address allocation, bandwidth management, and usage tracking. Over time, subsequent specifications have broadened its functionality to encompass both wired and fixed-wireless access aggregation, making the BNG an increasingly versatile and strategic platform for broadband service providers.
As the telecommunications industry transitions into the digital era characterized by 5G and cloud-based information and communication technologies (ICT), the Disaggregated Broadband Network Gateway (DBNG) represents the next significant milestone in the evolution of BNGs. The DBNG’s architecture is meticulously detailed in the Broadband Forum’s TR-459, segregating control plane and user plane functions through open and standardized interworking protocols. This innovative approach has the potential to simplify and unify BNG deployments for both wired and 4G/5G fixed-wireless access.
Why Separate The Control And User Plane Functions Of A BNG?
Traditionally, BNGs have been deployed as integrated systems where both the user and control plane functions coexist on a single routing appliance. While this deployment approach works well for many scenarios, it doesn’t always cater to the unique scaling requirements of each function. User plane functions primarily need to scale according to session bandwidth demands, whereas control plane functions demand more computational and storage resources and scale in relation to the number of connected user devices and active sessions.
When these functions are co-located, one often becomes over- or underutilized, potentially limiting scalability and adding unnecessary costs. While centralized BNGs are simpler to manage, in large networks with high subscriber densities, it’s more efficient to position BNG systems closer to subscribers to reduce backhaul costs and latency, particularly when content caches and compute resources are also distributed. However, as the BNG network footprint expands, so does the proliferation of subscriber management control points, leading to increased operational complexity and expenses.
This is where a disaggregated BNG with Control and User Plane Separation (CUPS) comes into play. CUPS enables the independent placement, scaling, and lifecycle management of Control Plane Functions (CPFs) and User Plane Functions (UPFs). CPFs can be virtualized and scaled using compute and storage servers in a data center to achieve optimal operational efficiency, while UPFs can be strategically distributed closer to subscribers to ensure optimal performance.
In essence, a distributed BNG with CUPS offers a solution that addresses the scalability challenge and provides operational advantages, streamlining the management and performance of broadband networks.
Separating and centralizing subscriber state and control processing offers several advantages, including more flexible and cost-effective redundancy models, streamlined and dynamic IP address space management, and simplified maintenance. Control plane functions involve software lifecycles, and user plane functions, with hardware-dependent life-cycles, often evolve at different rates and can be upgraded independently, enhancing maintenance efficiency.
Decoupling and virtualizing control plane functions also give network operators greater flexibility to customize and automate broadband service delivery. Historically, both operators and equipment vendors made numerous deployment-specific modifications to BNG control plane functions through vendor-specific RADIUS and DHCP attributes and custom-developed code, resulting in significant costs and resistance to change. However, a disaggregated BNG, combined with a standardized CUPS interface, allows for easier development of control plane extensions within a cloud-native IT environment while isolating user plane functions from these changes.
Simplified Evolution To A Multi-Access Edge
Moving towards a multi-access edge with 5G core interworking, a disaggregated BNG with CUPS also simplifies the evolution to a multi-access edge with converged wireline and fixed-wireless access, all operating under a unified 5G service-based architecture.
The Broadband Forum’s TR-459 specification achieves this by leveraging the same Packet Forwarding Control Protocol (PFCP) defined by the 3GPP working group for control and user plane separation in mobile gateways to manage subscriber session state on the DBNG. PFCP is complemented by a Control Packet Redirect Interface, enabling the disaggregated User Plane to forward subscriber signaling (e.g., DHCP and PPPoE) to the BNG Control Plane. By utilizing a well-established protocol like PFCP, product solutions’ development, testing, and integration become significantly more cost-effective and efficient.
This chosen strategy ensures interoperability between BNG control and user plane functions and provides a clear path for converged operators to seamlessly expand broadband services over 5G Fixed Wireless Access (FWA), enhancing the overall network’s capabilities and service offerings.
Nokia’s Multi-Access Gateway product solution effectively puts the TR-459 CUPS recommendations for disaggregated BNGs and FWA into practice. This solution’s Multi-Access Gateway controller (MAG-c) handles the virtualized control plane functions and can be hosted in regional data centers. Meanwhile, the user plane functions are on physical (7750 SR) or virtualized service routers at the broadband edge.
Established standards have laid the groundwork, and practical solutions are readily available. In May of this year, the Broadband Forum released the second iteration of the TR-459 BNG CUPS specification, incorporating further enhancements in terms of resiliency, scalability, and deployment efficiency. Nokia’s Multi-Access Gateway successfully implements the disaggregated BNG architecture with CUPS, and we are already witnessing the initial large-scale commercial deployments.
A DBNG featuring Control User Plane Separation empowers service providers to optimize the cost and coverage of service delivery by employing a unified control plane across physical and/or virtualized user plane instances for both wireline and 5G fixed-wireless access.
This approach grants users the freedom to connect to their preferred services and applications using any available broadband access technology in their vicinity, ensuring a swift and seamless broadband experience regardless of location.
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