In and data services. It also frames the

In the previous section, we describe the goals and metrics required for the design of our BRAS system. To fulfill them a system architecture is proposed. It involves the planes and the modules which are the base to develop the design of the BRAS system. The interoperability between those modules defines the hierarchical way that the system uses to provide services both internally and externally. Therefore, those relationships shape the way in which the system handles the control and data services. It also frames the structure of the system and consequently determines its a behavior with respect to the discussed functionalities.  The proposed architecture is presented in figure
ef{fig:3_plane_system_architecture}. In principle, the whole system is composed of three planes namely the data plane, the control plane, and the management plane. An overview of the plane interactions and the main functional blocks within each plane is exhibited. Table
ef{tab:System_architecture} present the module specifications corresponding to each of the planes. Although the management plane offers important functions for the system administration, they do not affect directly the creation of access services, but rather improve the administrative part of the system which at this point of the design is seen as an additional-valued characteristic of the system. Therefore, this thesis will focus on the design and implementation of the BRAS virtualized network function depicted in the figure
ef{fig:3_plane_system_architecture} with a dashed line since the management modules require additional characteristics and research that due to time constraints will be omitted and are suggested later on as future work. The components of the BRAS virtualized network function are used in next sections as a reference for the design of the functionalities of the system. Notice that in the description presented in table
ef{tab:System_architecture} for the modules of the management plane, they are not considered as fundamental required services to attend the creation of services for subscribers.The previously presented plane/module-based system represents the high-level definition of the system design envisioned for the virtual BRAS network function. It requires making use of an environmental structure that enables the communication with adjacent systems (access and core devices). To define such environment, it is important to assess parallel architectures that approach a residential function virtualization problem. Therefore, this work broaches the central office re-architected as a data center (CORD) citep{peterson2016central}, in which a two-step transformation process is defined. First, disaggregation and virtualization of the devices and second, insert the disaggregated elements into a service framework that offers orchestration of the elements. We consider CORD as an attractive approach because of it has developed a specific orientation for the creation of access services for residential networks and the design of our system architecture adapts therefrom various characteristics which allow us setting a concrete system architecture. Furthermore, since the virtual BRAS network function presents a scale-out strategy that implies an increase in management complexity, through applying the management approach presented by CORD, it can be considerably attenuated.The need for additional networking resources can be supplied through scale out of virtual or physical machines which yield to new compute resources with available networking capacity. Replication of session information to a new virtual or physical machine is not the only need that a scaling out mechanism have to be considered, but also the physical interfaces that the system presents to all other adjacent systems that compose the provider’s network. The system must deal with the physical interfaces that are presented towards both the access network or the core network. These physical configurations can be caused by different reasons, e.g. physical limitation of the platforms that are connected to the system or special requirements that internal elements present and using the scale-out property the saturated resources of the original platform can be relieved. Consequently, and just like the management complexity reduction, we use CORD to define the network environment as a base for the design of the functionalities provided by the BRAS system.After a preliminary overview of the system architecture and defining the requirements for the BRAS function virtualization, the next section encompasses the design process for the Virtual BRAS network function by adapting scale in and scale out capabilities. We state here that, the design and implementation of basic functionalities for a BRAS over NFV platforms have already been addressed by citep{ruckert2014flexible}, citep{bifulco2013rethinking}. Therefore, the design steps for those functionalities are omitted