In 5G, SMF stands for “Session Management Function.” It is a core network element responsible for managing the sessions between user devices and the network.

Section 6.2.2 of 3GPP’s Technical Specification 23.501 provides a detailed description of the role and functions of SMF

• SMF is one of the key network functions in the 5G Core Network (5GC), responsible for session management and policy control.
• SMF interacts with other network functions such as User Plane Function (UPF), Access and Mobility Management Function (AMF), and Policy Control Function (PCF) to establish and manage sessions.
• SMF is responsible for providing QoS control and enforcement based on policies received from PCF. It also collects usage data and generates charging information for billing purposes.
• SMF supports the concept of network slicing, where multiple logical networks can be created on top of a single physical network infrastructure. SMF is responsible for managing the sessions and QoS control for each slice.
• SMF performs subscriber authentication and authorization, including the authentication of devices connecting to the network.
• SMF supports different session types, including data, voice, and video sessions.
• SMF is designed to be highly scalable and resilient, with the ability to handle a large number of sessions simultaneously and to provide redundancy and failover mechanisms for high availability.
• SMF can be implemented as a standalone function or as a combined function with other network functions such as PCF.

• SMF communicates with other network functions using the Service-Based Interface (SBI) and the Network Repository Function (NRF) for service discovery.
• SMF provides session continuity management, which allows for the seamless transfer of a session from one network node to another.
• SMF provides support for mobility management, including handovers between 5G cells and inter-system handovers between 5G and other access technologies.
• SMF is responsible for managing the allocation of IP addresses and for providing support for different types of addressing schemes.
• SMF provides support for different deployment scenarios, including centralized and distributed deployment models.
• SMF supports different types of traffic steering and traffic offloading mechanisms, including 3GPP-defined traffic steering and traffic offloading mechanisms as well as operator-specific mechanisms.
• SMF supports policy enforcement for edge computing and network function virtualization (NFV) deployments.
  
  

Some more functionalities come under SMF from 23.502-4.3.2

• SMF is responsible for session establishment, modification, and release, and for managing session state information.
• SMF is responsible for policy and charging control (PCC), including enforcing QoS policies and collecting usage data for billing purposes.
• SMF is responsible for subscriber authentication and authorization, including the authentication of devices connecting to the network.
• SMF is responsible for providing security functions such as encryption and decryption of user data, and for enforcing security policies.
• SMF interacts with other network functions such as AMF, PCF, and UPF to establish and manage sessions.
• SMF provides support for different types of sessions, including data sessions, voice sessions, and video sessions.
• SMF supports the concept of network slicing, where multiple logical networks can be created on top of a single physical network infrastructure. SMF is responsible for managing the sessions and enforcing QoS policies for each slice.
• SMF provides support for mobility management, including handovers between 5G cells and inter-system handovers between 5G and other access technologies.
• SMF is designed to be highly scalable and resilient, with the ability to handle a large number of sessions simultaneously and to provide redundancy and failover mechanisms for high availability.

Session Establishment Process

• The UE initiates a session request to the AMF.
• The AMF performs access authentication and authorization for the UE, and determines the SMF to be used for the session.
• The AMF initiates a session establishment request to the SMF, providing the QoS requirements for the session.
• The SMF performs policy and charging control (PCC) to determine if the UE is authorized to use the requested resources and if the requested QoS can be guaranteed.
• The SMF initiates a session establishment response to the AMF, providing the session establishment result and the QoS parameters.
• The AMF forwards the session establishment response to the UE, along with the QoS parameters.
• The UE acknowledges the session establishment response, and the session is established.

Reference 23.502 – Figure 4.3.2.2.1-1