BNG / vBNG

A BNG sits at the boundary between the access network (fiber, DSL or wireless) and the ISP core, creating a session for every subscriber. The role is described in Broadband Forum architecture documents such as TR-101 and TR-178. It combines PPPoE or IPoE (DHCP) session termination, authentication via RADIUS, IPv4 address and IPv6 prefix assignment, per-subscriber QoS and rate limiting, access control lists and lawful-intercept interfaces in one place. It is the evolution of what used to be called a BRAS (Broadband Remote Access Server).

A vBNG (virtual BNG) runs the same functions as software on standard x86 servers instead of dedicated hardware. With fast packet-processing techniques such as DPDK, a single server can carry tens of thousands of subscriber sessions and tens of Gbit/s of traffic. In the CUPS (Control and User Plane Separation) architecture defined in Broadband Forum TR-459, session management runs in a central control plane. Forwarding happens on user-plane nodes that scale horizontally, so capacity can be added as the subscriber base grows.

When sizing a BNG, concurrent sessions, busy-hour traffic, per-subscriber queueing, the IPv4 address pool and, if needed, CGNAT capacity must be evaluated together. In fiber networks, subscribers usually reach the BNG over VLANs handed off by the OLT. Session data flows to billing and subscriber management through RADIUS accounting. In networks that use CGNAT, the NAT mapping logs also matter for legal retention obligations.