Sign in Subscribe

5G SA Xn Handover Call flow

Last updated on 


The 5G Standalone (SA) Xn Handover Call Flow involves the transfer of a user's ongoing communication session from one cell to another within a 5G network. This process is known as handover or handoff and is crucial for maintaining seamless connectivity as a user moves through different coverage areas. The Xn interface is used for communication between gNBs (Next Generation NodeB) in the 5G network.

Below is a detailed technical explanation of the 5G SA Xn Handover Call Flow:

  1. Preparation for Handover:
    • The handover process typically begins when the source gNB (gNB1) decides that a handover is necessary. This decision may be based on factors such as the user's movement, signal quality, or load balancing considerations.
    • The source gNB evaluates potential target gNBs (gNB2) for the handover and selects the most suitable one.
  2. Handover Request:
    • The source gNB sends a Handover Request message to the target gNB. This message contains information about the ongoing session, radio resources, and other relevant parameters.
  3. Handover Preparation at Target gNB:
    • Upon receiving the Handover Request, the target gNB performs necessary preparations for the handover. This includes allocating radio resources, verifying the feasibility of the handover, and informing other network elements about the upcoming handover.
  4. Path Switch at UE:
    • The User Equipment (UE) is instructed to switch its radio connection from the source gNB to the target gNB. This may involve reconfiguring the radio parameters and establishing a new connection with the target gNB.
  5. Data Forwarding:
    • The source gNB starts forwarding the user's data to the target gNB to ensure continuity of the ongoing communication session.
  6. Data Forwarding Confirmation:
    • The target gNB acknowledges the successful reception of the user's data. This confirmation is essential to ensure that no data packets are lost during the handover process.
  7. Handover Completion:
    • The source gNB, having received the acknowledgment from the target gNB, can release the radio resources allocated for the UE. The handover is now considered complete.
  8. Bearer Update:
    • The core network (5G Core) updates the bearers associated with the UE to reflect the new connection through the target gNB.
  9. Path Confirmation at UE:
    • The UE confirms the successful handover and continues its communication through the target gNB.