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vonr 5g call flow

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The 5G call flow involves a series of signaling and data transfer procedures between different network elements to establish and maintain a communication session. The following is a simplified overview of a 5G voice call flow, specifically focusing on the Non-Standalone (NSA) architecture, where 5G relies on existing 4G LTE infrastructure.

  1. Initial Registration and Attach Procedure:
    • The mobile device attaches to the LTE network initially.
    • The device registers with the LTE core network (EPC - Evolved Packet Core).
  2. Access to 5G NR (New Radio):
    • When 5G services are requested, the device accesses the 5G NR network through the existing LTE network. This is known as the LTE-to-5G handover.
  3. RRC Connection Setup in 5G:
    • The Radio Resource Control (RRC) connection is established between the device and the 5G base station (gNB - Next-Generation NodeB).
  4. Authentication and Key Agreement (AKA):
    • The device undergoes authentication and key agreement processes to ensure secure communication with the 5G network.
  5. Bearer Setup:
    • A dedicated communication channel, known as a bearer, is established between the device and the 5G core network (5GC).
  6. Session Management:
    • The 5G Session Management function in the 5G core network sets up a connection for the voice service. This involves the establishment of a Session Management (SM) context.
  7. Policy and Charging Control (PCC):
    • Policies for the user's data session and charging parameters are applied by the Policy and Charging Control (PCC) function in the 5GC.
  8. IMS Registration:
    • The device registers with the IP Multimedia Subsystem (IMS), which is responsible for voice and multimedia services.
  9. Establishment of PDU Session:
    • A Packet Data Unit (PDU) session is established for carrying IP-based services, including voice, in the 5G core.
  10. VoLTE Call Setup:
  • The Voice over LTE (VoLTE) call setup involves signaling between the IMS and the 5G core network to establish the voice session.
  1. Media Plane Establishment:
    • The media plane is established for the actual voice data transfer between the calling and receiving parties.
  2. Quality of Service (QoS) Handling:
    • QoS parameters are applied to ensure the desired quality of the voice call, including prioritization and allocation of resources.
  3. Handover (if needed):
    • If the device moves between different cells or network areas, handover procedures may be initiated to maintain the ongoing voice call.
  4. Call Release:
    • Once the call is complete, the necessary signaling is performed to release the resources and terminate the session.

This call flow provides a high-level overview, and each step involves numerous signaling messages and interactions between different network elements. The 5G architecture is designed to provide enhanced capabilities, including higher data rates, lower latency, and support for a diverse range of services beyond traditional voice calls.