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what is PDU session in 5G/NR ?

PDU Session in 5G/New Radio (NR) refers to a communication session established between a user's device (referred to as UE or User Equipment) and the 5G network's data network (DN). A PDU Session is essentially the logical channel through which data packets are transmitted from the UE to the DN, facilitating internet access, voice over new radio (VoNR), and other data services. The concept of a PDU Session in 5G is crucial for understanding how data connectivity is managed and maintained within the network.

Each PDU Session supports a specific type of network protocol, such as IPv4, IPv6, or both, and is identified by a unique session ID. This ID is important for managing and distinguishing between multiple sessions that a single device might have with the network simultaneously.

The establishment, maintenance, and termination of a PDU Session involve various network functions within the 5G architecture, including:

  • AMF (Access and Mobility Management Function): Manages session mobility and ensures seamless connectivity as the UE moves.
  • SMF (Session Management Function): Handles session management tasks such as session establishment, modification, and release.
  • UPF (User Plane Function): Routes and forwards user data packets for the active PDU Session.

The PDU Session is a key component of the 5G network's service-based architecture (SBA), which enables flexible and efficient data service delivery. It allows for the deployment of multiple network slices, each catering to specific service requirements, ensuring that the network can meet diverse user and application demands.

Types of PDU Sessions

In 5G, a PDU Session can support different types of data units, known as PDU types. The main PDU types are:

  • IPv4: Supports only IPv4 addressing for user data.
  • IPv6: Supports only IPv6 addressing for user data.
  • IPv4v6: Supports both IPv4 and IPv6 addressing simultaneously.
  • Unstructured: Used for services that do not require IP addressing, such as Ethernet or non-IP data.
  • Ethernet: Supports Ethernet frames, enabling services like enterprise LAN connectivity over 5G.

PDU Session Lifecycle

  1. Establishment: The UE requests a new PDU Session by sending a request to the network. The network authenticates the UE, allocates resources, and assigns a unique PDU Session ID.
  2. Modification: During the session, parameters such as QoS (Quality of Service), network slice, or PDU type can be modified as needed.
  3. Release/Termination: When the session is no longer needed, it is released, freeing up network resources.

Quality of Service (QoS) in PDU Sessions

Each PDU Session can be associated with one or more QoS Flows, which define the level of service (such as latency, reliability, and bandwidth) for different types of traffic. This allows the network to prioritize critical applications (like emergency calls or real-time gaming) over less sensitive data.

Network Slicing and PDU Sessions

5G networks support network slicing, where multiple virtual networks are created on top of a shared physical infrastructure. Each PDU Session can be mapped to a specific network slice, ensuring that the session receives the appropriate resources and policies for its intended service (e.g., enhanced mobile broadband, ultra-reliable low-latency communications, or massive IoT).

Summary

In summary, a PDU Session in 5G is a fundamental concept that enables flexible, efficient, and secure data connectivity between user devices and the network. It supports multiple protocols, advanced QoS management, and network slicing, making it a cornerstone of the 5G service architecture.