Feature Description

Seamless handovers between LTE and Wi-Fi (S2b), for UEs that need continuity with their ongoing data session, is supported in the 5G UPF architecture.

When handover is initiated from LTE to Wi-Fi, the Delete Bearer Request (DBR) is sent over the LTE tunnel immediately when the Create Session Response (CSR) is sent on the Wi-Fi tunnel. This causes some packet loss because of the IPsec tunnel establishment delay at the ePDG. To address the issue of packet loss, a Delete Bearer Request is sent on LTE tunnel only on expiry of the configured handover timer. If the LTE tunnel is active, uplink and downlink data is exchanged on the LTE tunnel. When handover is complete, uplink and downlink data is exchanged on the Wi-Fi tunnel. This prevents packet loss. During Wi-Fi to LTE handover, if the Modify Bearer Request is received with HI=1, it initiates a tunnel switch from Wi-Fi to LTE as per the specification.

With this feature, the following benefits are seen:

  • Minimum packet loss during LTE to Wi-Fi (S2bGTP) handover and making the handover seamless (that is, MAKE before BREAK).

  • LTE procedures are handled gracefully over the LTE tunnel when both tunnels are established with the P-GW.

  • Wi-Fi procedures are handled gracefully over the Wi-Fi tunnel when both tunnels are established with the P-GW.

Important
  • In an LTE to Wi-Fi or Wi-Fi to LTE handover, a tunnel identifier is allocated for new access traffic type for experiencing seamless handover.