Network Functions have traditionally been deployed as software packages inside virtual machines or containers. In order to make them cloud-native and exploit the lowcost, scalability and resiliency of the cloud, Network Functions need to be disaggregated. Such disaggregation enables flexible deployment and resource allocation policies for critical components of a Network Function. However, growing interest of vendor neutrality and interoperability from vendors and operators, requires standardisation of well-defined interfaces. In this paper, we propose an abstraction layer for the disaggregation of a broadband network gateway (BNG). In the proposed architecture, this layer abstracts the BNG functions, and provides a stable translation target for configuring and managing subscriber sessions by adding forwarding rules or specifying Quality of Service parameters.