Call Flow - Handover (Mobility)

Call Flow - Handover (Mobility)

To provide a seamless connectivity to the users during RRC connected mode, network triggers a procedure called handover so that UE remains connected to the cell with the best radio conditions (signal strength/quality).

Handover procedure/flow comprises of three phases -

• Handover preparation phase : is the phase when the source RAN(eNB) request the target RAN(eNB) to prepare and accommodate the UE. The target RAN performs admission control and reserves cell resources required by the UE.

• Handover execution phase : starts when the source RAN command the UE to make a handover. The source RAN performs packet forwarding to target RAN during the execution phase. The phase ends when the UE access the target RAN and confirms new connection towards the target cell.

• Handover completion phase : Here, user data path to the Serving gateway (SGW) is switched over to the target RAN. The handover complete phase starts when target RAN intimates MME and SGW about the handover. Then MME/SGW switches the bearer from source RAN to target RAN. The target RAN informs the source RAN that the handover is completed. The source RAN then releases UE resources. (Ref - 3GPP)

There are multiple events occurred during this Intra-freq. HO (A1,2,3,4,5), which will be discussed in next post).

👉 This Lecture belongs to the complete course on RAN Engineering course and link for the course is - https://www.itelcotech.com/learningpath/ran-engineer-4g-and-5g