Taking load distribution} which refers to the ability

Taking into account the previous scenario and bringing up the discussion of the tasks from a virtual BRAS function, is necessary to define extra operation functionalities that allow us to provide a higher spectrum of operational and functional tasks that are able to fit the requirements of the given scenario. Thus, an evaluation and comparison of the functionalities can be performed on each of the different approaches presented later on.The first of the additional functionalities considered to fit the scenario for a BRAS virtualized function is the extit{access services creation decentralization}. It refers to the ability to turn a service creation point system into multiple systems that are able to provide the same services and can be distributed along the provider’s network using a low-cost-effective implementation.  The next extra functional task is the extit{service load distribution} which refers to the ability of a multi-platform system to chose and enable one or multiple platforms in a network path to collaborate in the execution of a defined virtualized network function.

In the case of a virtualized function of a BRAS system, the extit{service load distribution} entails the use of platforms in the subscriber path able to distribute the processes that provide access service creation. extit{Load balancing} relates to the distribution of the workload towards two or more platforms that enable the same services functionalities. For instance, in the context of a virtual BRAS function, that uses separated servers to provide layer 3 address assignment and policy configuration, when service requests are received from different end users, they may be relayed in an equitable or desired fashion to each of the available servers. The extit{flow distribution} also considered in this context as extit{traffic balancing} is the intended distribution of flows across different data path platforms. For a VNF of a BRAS system, extit{flow distribution} involves at least two forwarding platforms which according to a balancing/distribution algorithm or to a predefined configuration, a preferred platform is chosen to process and forward the incoming traffic. As a remark, the extit{flow distribution} is not involved in the distribution of traffic at the moment of the access services creation process rather the distribution of the traffic for already operative users.

extit{Session control} is a characteristic of a virtual BRAS network function that aims to gather the subscriber’s current session state and session identification information, in order to for example enable further capabilities such as session migration.In an NFV architecture, the extit{scale in/out} functionality refers to add or remove data path elements from a specific system in order to expand or reduce the delivered service capacity whose service purpose and operational behaviour is exactly the same and whose only objective is to scale the services provided for the initial running implementation. For the particular case of a BRAS as a virtualized network function, it is assumed as the addition or removal of data path elements to increase or reduce the number of supported sessions or more specifically the number of flows installed in the initial data path elements.The extit{session migration} functional task enables the migration of sessions between different virtual machines or physical platforms based on the session control information. Usually, this functionality in the access service creation context is oriented towards the improvement of the resilience and reliability based on the availability of the sessions for end users.Some additional functionalities described before are shown in figure ef{fig:Additional_functionalities} in order to provide a visual explanation of access services characteristics that lay down in the virtualization environment and that give a clear differentiation between each other.