5G/NR  - NAS  

 

 

 

LADN / DNN

LADN and DNN are new concept introduced in 5G. I have vague understanding about these that these concept replaces the concept of APN in LTE, but for long time the concept hasn't come clear to me.

Since these new concepts are introduced instead of using APN mainly to implement the concept of Network Slice, it would worth having some detailed picture of Network Slice. I wrote a separate note for Network Slicing.

What is LADN ?

LADN stands for Local Area Data Network, which is a feature in 5G networks that allows a local operator or enterprise to provide data services within a limited geographic area, such as a building, campus, or industrial site. It is a special type of data network in 5G that is accessible only within a specific geographical area (or areas) The LADN feature enables local operators or enterprises to provide their own 5G data services with their own network infrastructure, while still being connected to the wider 5G network.

With LADN, a local operator or enterprise can set up a private 5G network to provide specific services tailored to their needs, such as industrial automation, smart building systems, or high-speed data transfers within a limited area. The LADN can be connected to the wider 5G network through a gateway to provide access to external data services and resources.

LADN can be deployed in different modes, including standalone mode, where the LADN network is independent of the wider 5G network, and dual connectivity mode, where the LADN network is connected to the wider 5G network for seamless mobility and access to external resources. The LADN feature is defined in the 3GPP standards for 5G networks and is expected to play a significant role in enabling new use cases and applications for 5G.

Key Characteristics of LADN:

  • Localized Accessibility: A UE can only access the LADN when it is in the defined geographical area(s). Outside that area, the UE cannot use the LADN.
  • Reduced Latency & Cost: Because traffic remains local, LADN can reduce latency and potentially lower backhaul costs compared to routing traffic out to a distant data center or the public Internet.
  • Private Networking: LADNs are often used for private networks—for example, industrial IoT devices on a factory floor can connect to a local data center for real-time process control.
  • UE Registration: The UE is informed about the availability of a LADN through network signaling (e.g., the 5G core can provide the UE a list of LADNs that are accessible in the current location).

Use Cases for LADN

  • Enterprise Campus: Employees and IoT devices connect to a private enterprise LAN while on campus.
  • Smart Factories: Machines and robots communicate with on-premises edge servers for real-time control and monitoring.
  • Stadiums / Venues: High-bandwidth local services (like instant replays, local streaming) can be delivered locally, reducing load on the operator’s core network.
  • Retail / Malls: Local content delivery, loyalty programs, or AR/VR services running in a local edge network.

How it works:

  • Service Area Configuration: The 5G core predefines the geographic area(s) where the LADN is accessible (e.g., GPS coordinates or cell IDs).
  • UE Registration: When a UE enters the LADN service area:
    • The AMF (Access and Mobility Management Function) checks if the UE is authorized for the LADN.
    • The UE can establish a PDU session with the LADN DNN.
  • Outside the Service Area:
    • The UE cannot access the LADN, even if it requests it.
    • Existing LADN sessions may be suspended or terminated when the UE leaves the area.

Signaling of LADN

Key Signaling Procedures for LADN

  • LADN functionality is primarily managed during:
  • UE Registration (to inform the UE about available LADNs).
  • PDU Session Establishment (to connect to an LADN).
  • UE Mobility (to track if the UE enters/leaves an LADN service area).

Key Signaling Messages and IEs

  • A. During UE Registration
    • When a UE registers with the 5G core network, the AMF (Access and Mobility Management Function) informs the UE about the LADNs it is authorized to access.
    • Registration Accept (NAS Message)
      • Message: Sent by the AMF to the UE during registration.
      • Relevant IE:
        • LADN Information : Contains the list of LADNs (DNNs) the UE can access, along with their service areas (e.g., tracking areas, cell IDs, or geographic coordinates).
      • Purpose: The UE uses this information to determine when it is within an LADN service area.
  • B. During PDU Session Establishment : When a UE requests a PDU session for an LADN:
    • PDU Session Establishment Request (NAS Message)
      • Message: Sent by the UE to the AMF.
      • Relevant IE:
        • DNN : Specifies the LADN the UE wants to connect to (e.g., factory-ladn).
    • Nsmf_PDUSession_CreateSMContext Request (HTTP/2)
      • Message: Sent by the AMF to the SMF (Session Management Function) to trigger session setup.
      • Relevant IEs:
        • DNN
        • LADN Service Area (preconfigured in the SMF/UDM) : Validates if the UE’s current location is within the LADN’s allowed geographic area.
    • Nudm_SDM_Get (HTTP/2)
      • Message: The SMF retrieves LADN subscription data from the UDM (Unified Data Management).
      • Relevant IEs:
        • LADN Configuration : Includes the DNN, service area, and associated policies (e.g., QoS).
    • PDU Session Establishment Accept/Reject
      • Reject Cause: If the UE is outside the LADN service area, the SMF rejects the request with a cause code (e.g., LADN not available)
  • C. During Mobility Management : When the UE moves in/out of an LADN service area:
    • Service Request or Periodic Registration Update
      • The AMF tracks the UE’s location using UE Location Reporting.
      • If the UE enters an LADN service area, the AMF updates the SMF/UPF to enable LADN access.
    • N2 Message (AMF to RAN)
      • Includes LADN Indication to prioritize traffic or configure localized routing.

Example Workflow

  • UE Registration:
    • AMF sends Registration Accept with LADN Information (e.g., DNN=factory-ladn, service area=GPS coordinates).
  • UE Enters LADN Zone:
    • AMF detects UE is within the LADN service area via location reporting.
  • PDU Session Request:
    • UE sends PDU Session Establishment Request with DNN=factory-ladn.
  • SMF Validation:
    • SMF checks UE location against LADN Service Area (from UDM).
  • Session Setup:
    • If valid, SMF configures UPF for localized routing (e.g., to an on-site edge server).

What is DNN ?

DNN can also refer to the Data Network Name, which is a new feature in 5G networks that is used to support network slicing

Network slicing is a technique used in 5G to divide a physical network infrastructure into multiple virtual networks, each with its own resources and quality of service (QoS) requirements. Each virtual network is identified by a unique Data Network Name (DNN), which is used by the 5G core network to route traffic to the appropriate network slice.

For example, a mobile operator can create a dedicated network slice for a particular enterprise customer with specific QoS requirements, and assign a unique DNN to that network slice. This enables the enterprise customer to have a dedicated and secure network that is customized to their specific needs.

A DNN identifies which external data network the UE (user device) should connect to. Examples of common data networks include:

  • The public Internet.
  • A private enterprise network.
  • A cloud application network or content delivery network.

Key Points about DNN:

  • Identification: The DNN is used by the 5G core network to determine the packet data network or service to which the user wants to connect.
  • Policy & Charging: Different DNNs might be subject to different QoS (Quality of Service), charging policies, or traffic handling rules.
  • Network Slice Association: In 5G, a DNN can also be coupled with a Network Slice to provide a customized set of network resources for specific services.

Signaling of LADN

Key Procedures Involving DNN

  • DNN is primarily used in:
    • PDU Session Establishment: To select the external data network.
    • UE Registration: To inform the UE about allowed/supported DNNs.
    • SMF Selection: To route traffic to the correct network.

Signaling Messages and IEs for DNN

  • PDU Session Establishment : The DNN is a critical IE during session setup:
    • PDU Session Establishment Request (NAS Message)
      • Sent by: UE → AMF
      • IE: DNN : Specifies the data network the UE wants to connect to (e.g., internet, ims).
    • Nsmf_PDUSession_CreateSMContext Request (HTTP/2)
      • Sent by: AMF → SMF
      • IE: DNN : Used by the SMF to select session policies, UPF, and external network.
    • Nudm_SDM_Get (HTTP/2)
      • Sent by: SMF → UDM
      • IE: DNN : The SMF retrieves subscription data (e.g., QoS profiles) tied to the DNN.
    • PDU Session Establishment Accept (NAS Message)
      • Sent by: SMF → UE (via AMF)
      • IE: DNN : Confirms the DNN for the established session.
  • UE Registration
    • Registration Request (NAS Message)
      • Sent by: UE → AMF
      • IE: Requested DNN (optional) : The UE may request specific DNNs during registration.
    • Registration Accept (NAS Message)
      • Sent by: AMF → UE
      • IE: Allowed DNN List (optional) : Indicates DNNs the UE is authorized to use (e.g., internet, enterprise-vpn).
  • Service Request : When modifying or resuming a PDU session:
    • Service Request (NAS Message)
      • IE: DNN (implicitly tied to the PDU session ID).

Example Workflow

  • UE Request:
    • UE sends PDU Session Establishment Request with DNN=enterprise-vpn.
  • SMF Selection:
    • AMF forwards the DNN to SMF via Nsmf_PDUSession_CreateSMContext.
  • Subscription Check:
    • SMF queries UDM with Nudm_SDM_Get to validate DNN=enterprise-vpn.
  • Session Setup:
    • SMF selects UPF and policies based on the DNN.

How a DNN is related to LADN ?

The terms DNN (Data Network Name) and LADN (Local Area Data Network) are related concepts that are used to support network slicing and provide customized services to different types of users and devices.

A LADN is a virtual network slice that is optimized for use within a specific geographical area, such as a building, campus, or factory. It is designed to provide low-latency, high-bandwidth connectivity to local devices and applications, and can be customized with specific QoS requirements.

A DNN, on the other hand, is a unique identifier used by the 5G core network to route traffic to a specific network slice. In the context of a LADN, the DNN would be used to identify and route traffic to the LADN network slice.

For example, a factory might require a dedicated LADN network slice to support real-time monitoring and control of machines and devices on the factory floor. The LADN could be customized with specific QoS requirements to ensure low-latency, high-bandwidth connectivity, and a unique DNN would be assigned to the LADN to enable efficient routing of traffic to and from the factory.

Overall, the DNN and LADN are related concepts that are used in 5G to provide customized network services and support efficient use of network resources.

Following is brief highlights on how DNN and LADN work together.

  • DNN Selection
    • When a UE attaches to the 5G network, it may request one or more data network connections (PDU Sessions). Each PDU Session is associated with a specific DNN.
    • The 5G core network uses the requested DNN to determine the appropriate Session Management Function (SMF) and User Plane Function (UPF) to route user traffic to the intended network.
  • Local vs. Non-Local DNN
    • A standard DNN might be something like “internet” or “operator.default,” giving the user a general connection to the internet or to their service provider’s network.
    • A Local Area DNN (LADN) is a specialized DNN accessible only in a restricted region. If the UE is within that region, the network notifies the UE that LADN service is available. The UE can then establish a PDU Session to that LADN if needed.
  • UE Notification of LADN Availability
    • Broadcast or Signaling: When the UE registers with the 5G core, the core identifies that the UE is in the local area served by the LADN and can send a notification that LADN is available.
    • Policy Control: The 5G core (e.g., PCF – Policy Control Function) ensures that the user is allowed to access that LADN and enforces any local policies or QoS parameters.
  • Session Establishment
    • If the UE needs to communicate with the local data network, it sets up a PDU Session using the LADN’s DNN.
    • The SMF in the 5G core selects a local UPF which connects directly to the on-premises or local data network.
  • Mobility Implications
    • If the user device moves away from the local area where LADN is offered, the 5G core may tear down the LADN session or keep it dormant until the UE returns to the coverage area. The exact behavior depends on operator policies.

How a DNN can be compared to APN ?

In LTE, APN (Access Point Name) is used as an identifier for a specific network operator's packet data network. It is used by the mobile device to connect to the packet data network and access the internet and other services.

In 5G, the DNN (Data Network Name) is the counterpart of APN in LTE. It is used to identify and route traffic to a specific network slice, which can be customized with specific QoS requirements for different services and applications.

Like the APN, the DNN enables efficient routing of traffic within the 5G network, and allows for customized network services to be provided to different users and devices. However, the DNN goes beyond the functionality of the APN by enabling dynamic allocation of network resources to different network slices based on their specific QoS requirements, which enables more efficient use of network resources and better performance for different services and applications.

Reference