Network Slice Admission Control Function (NSACF) is a network function that monitors and controls the number of registered user equipments (UEs) and established protocol data unit (PDU) sessions per network slice. It also provides information to an application function (AF) for analysis and further processing.
Network slicing is a technology that allows operators to provide customized networks with different functionalities for diverse services or groups of users with specific service requirements. For example, a network slice for enhanced mobile broadband (eMBB) may have different quality of service (QoS) requirements than a network slice for ultra-reliable low-latency communication (URLLC) or massive machine-type communication (mMTC).
To manage network slicing efficiently, admission control and resource allocation mechanisms are needed to ensure that the network slices can meet the QoS requirements of the users and the service providers. Admission control is the process of deciding whether to accept or reject a slice request based on the availability of resources and the service level agreement (SLA) of the slice. Resource allocation is the process of assigning resources to the accepted slice requests based on the QoS requirements and the optimization objectives of the network.
The NSACF is part of the admission control mechanism for network slicing in the 5G core network. It interacts with other network functions, such as the access and mobility management function (AMF), the session management function (SMF), and the unified data management (UDM).
The NSACF is responsible for the following functions:
• Monitoring the number of registered UEs and established PDU sessions per network slice and reporting it to the AF
• Controlling the number of registered UEs and established PDU sessions per network slice based on the SLA and the network slice selection policy
• Rejecting or terminating UEs or PDU sessions that exceed the limit of the network slice
• Supporting network slice specific authentication and authorization (NSSAA) procedures
• Supporting network slice specific policy control procedures
The NSACF is a logical function that can be implemented in different ways, depending on the deployment scenario and the operator’s preference. For example, the NSACF can be co-located with the AMF, or it can be deployed as a separate network function. The NSACF can also be shared by multiple AMFs, or it can be dedicated to a single AMF. The NSACF can also be deployed at different levels, such as PLMN level, shared slice level, or slice specific level.