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How APN works in LTE ?

An Access Point Name (APN) acts as a gateway between a mobile network and another network, typically the Internet. It's a crucial setting on mobile devices for enabling access to the Internet and other services. Here's a detailed look at the APN's role in mobile telecommunications, including when a UE does not request a specific APN.

Case 1: UE Requests a Specific APN

When a user equipment (UE) requests a specific APN, it means the device is explicitly asking the network to connect using a particular gateway, often configured in the device's settings. This process allows the user or application to access certain services, such as corporate networks, private APNs, or specialized internet access, by specifying the APN name. The network then processes this request, verifies the APN, and establishes a data session accordingly.

  • Connection Request: The UE initiates a connection by sending a request to the network, including the APN name configured in its settings.
    • The UE sends a request to the network, including the APN name configured in its settings.
    • This request indicates the type of service or network the user wants to access (e.g., internet, corporate VPN).
  • APN Evaluation: The network checks the requested APN against its database to verify if it is valid and allowed for the subscriber.
    • The network checks the requested APN against its database to verify if it is valid and allowed for the subscriber.
    • Authorization and policy checks are performed to ensure the user can access the requested APN.
  • Gateway Routing: The network determines the correct gateway (P-GW) for the specified APN and routes data traffic accordingly.
    • The network determines the correct gateway (P-GW) for the specified APN.
    • Data traffic from the UE is routed through this gateway to reach the external network or service.
  • IP Address Allocation: The gateway assigns an IP address to the UE for communication during the session.
    • The gateway assigns an IP address to the UE for communication.
    • This IP address is used for all data sessions associated with the APN.
  • Data Session Establishment: The network establishes a data session (bearer) with settings based on the APN configuration.
    • The network establishes a data session (bearer) with settings based on the APN configuration.
    • Quality of Service (QoS) and other parameters are set according to the APN profile.
  • Data Transfer: The UE can now send and receive data through the established session, accessing the requested services.
    • The UE can now send and receive data through the established session.
    • Access to the requested internet services or private networks is enabled.

Case 2: UE Does Not Request a Specific APN

If the UE does not specify an APN during the network attachment process, the mobile network automatically assigns a default APN based on the subscriber's profile stored in the network's database. This ensures that the device can still access the internet and other services without manual configuration. The default APN is typically set by the operator to provide general internet access, and the session is established using this configuration.

  • UE Network Attachment and Default APN Selection: During network attachment, if no APN is specified, the network looks up the subscriber's profile and selects the default APN configured by the operator.
    • During network attachment, if no APN is specified, the network looks up the subscriber's profile.
    • The default APN configured by the operator is selected for the session.
  • Session Establishment with Default APN: The network initiates a data session using the default APN settings, applying appropriate session parameters.
    • The network initiates a data session using the default APN settings.
    • Data bearers are set up, and session parameters are applied based on the default APN.
  • IP Address Allocation: The P-GW associated with the default APN allocates an IP address to the UE for all data communication during the session.
    • The P-GW associated with the default APN allocates an IP address to the UE.
    • This IP address is used for all data communication during the session.
  • Accessing Services: With the default APN and data bearer active, the UE can access the internet and operator-provided services without manual APN configuration.
    • With the default APN and data bearer active, the UE can access the internet and operator-provided services.
    • No manual APN configuration is required for basic connectivity.

Further Readings