This is the second Broadband Network Gateway (BNG) blog. The previous blog introduced the Capgemini Engineering software. We discussed how the Open BNG sub-group from the Telecom Infra Project (TIP) is promoting the deployment of disaggregated BNG. TIP has recently released a requirements document for open and disaggregated BNG. Here we take a closer look at BNG deployment options and the software features applicable in each deployment option.
The BNG has traditionally been deployed in a central office where subscriber sessions are terminated and subscriber traffic is routed towards the core network. The subscriber sessions are carried over a Layer 2 Tunneling Protocol (L2TP) or multiprotocol label switching over pseudowires (MPLS PW) to the BNG depending on the type of aggregation network. The Open BNG Technical Requirements v1.0 release by TIP envisions three categories of BNG deployment options described below. The Capgemini BNG network operating system (NOS) fully supports all three deployment options and corresponding features relevant to each deployment option.
Service-only BNG deployment
Typically, the BNG can service more than the minimum required 32,000 subscribers. In this model, it is necessary to scale a large number of subscribers, which means a large number of subscriber queues for differentiated services. Hardware selection is critical to support high-scale routing and more subscriber sessions, such as telemetry, lawful interception, and hierarchical QoS (H-QoS).
Figure 1. Service-only BNG deployment | Source: Telecom Infrastructure Project
In this option, the software is expected to support the core BNG features, including IPv4- and IPv6-based subscriber sessions. The Capgemini Engineering BNG network operating system fully supports the features required to deploy in a central office, including the following features:
- PPPoE and IPoE (IPv4 and IPv6) subscriber management
- Technical Report (TR) 101 support, which includes a proxy ARP, prevent ARP broadcast to subscribers and source IP spoofing
- Multicast service
- TR 177 including a neighbor discovery (ND) proxy and auto-spoofing protection
- H-QoS for subscribers that provides per-service policing and shaping, and hierarchical scheduling
- TR-146-based session management for IP address assignment, authentication, policy management, accounting, and user policies based on a subscriber service level agreement (SLA)
- Ensuring lawful intercept (LI) with the Communications Assistance for Law Enforcement Act (CALEA) and internal network interfaces INI1, INI2, and INI3
- Telemetry including sFLOW, NetFlow, IPFIX and per VLAN, port, flow, and subscriber
- Timing including PTP (G.8275.1, G8275.2) and SyncE
Fully distributed BNG
In this option, BNGs can be directly connected to access networks, optical loss test set (OLTS) and digital subscriber line access multiplexer (DSLAM), consumer electronic (CE) devices, and mobile backhaul networks. Hence, the BNG needs more than subscriber management features, as mentioned above. Choosing the right hardware platform may be challenging considering the variety of features that need to be supported in this deployment. (See the UfiSpace blog referenced below for hardware options and features that influence the choice of hardware for the full functionality and maximum distributed deployment.)
Figure 2. Fully distributed BNG | Source: Telecom Infrastructure Project
The BNG provides aggregation functionality towards business CE devices. Depending on the type of aggregation network, business services can be aggregated using Layer 2 VPN (VPLS/VPWS) or simple 802.1q or L3VPN. The mobile backhaul traffic is typically aggregated using an MPLS Level 3 VPN (L3VPN). The operators have a choice to terminate some of the subscriber sessions in this BNG, and some of the sessions are tunneled to the centralized BNG. Apart from the BNG features, Capgemini BNG NOS supports the following features that support multiservice.
- Layer 2 – 802.1q VLAN (single- and double-tagged), MEF 2.0/3.0 services (E-Line, E-LAN, E-Tree), LAG, LLDP, G.8032, IEEE 802.1ag/Y.1731
- Multicast – IGMP/MLD snoop, IGMPv2/v3/MLD, PIM-SM/SSM
- Layer 3 – Static IPv4, IPv6, OSPFv2,v3, IS-IS, BGP4, BGP6, RIP, VRRP, VRF
- MPLS – Static LSP, PW, LDP, T-LDP, RSVP-TE, L2VPN, L3VPN
- Segment Routing – OSPF, IS-IS extensions for SR, MPLS services using segment routing
- Multi-chassis LAG (MC-LAG)
Medium distributed BNG
In this model, BNG features are almost the same as a fully distributed BNG, except the number of subscribers that the model is required to support may be less than a fully distributed BNG. This type of BNG may form an integral part of the aggregation network. Multiple devices can be stacked in a daisy-chain model to form a single box BNG to support the higher number of subscribers. The Capgemini Engineering NOS supports multi-unit stacking where multiple white boxes can be stacked (up to eight) together to realize the scalability required by the operators. This gives operators greater flexibility to expand the number of devices as the number of subscribers grows. It is also possible that, like in the first option, the operator can choose to terminate a certain number of subscriber sessions, and the remaining sessions can be tunneled to a centralized BNG through an L2TP tunnel or using MPLS PW. Apart from the features mentioned in the previous two deployment options, the key features required in this option are:
- Multi-unit stacking
- L2TP tunnel
- MPLS PW
Director, Product Management, Networking Software Frameworks
Sathiya oversees the evolution and roadmap of networking products, specifically on cell site gateway and BNG at Capgemini Engineering. He has expertise in evolving networking products from conceptualization to development to deployment. His experience spans Layer2, MEF, OAM, and protection switching.
Blog post, “The Capgemini Engineering Broadband Network Gateway Solution,” Capgemini Engineering
“Open BNG Technical Requirements,” Telecom Infrastructure Project,
Will Chang, “Disaggregating the Broadband Network Gateway,” Jun. 6, 2021, UfiSpace