How It Works

This section provides an overview of how this feature works.

  • Buffering is supported at SAEGW-U.

  • Support of buffering starts when UE moves to IDLE state due to Release Access Bearer.

  • ACTIVE to IDLE transition:

    • When the UE moves to ECM-IDLE state, since the SAEGW supports buffering capability and decides to activate buffering in SAEGW-U for the session, the SAEGW-C informs the SAEGW-U through an Sx session modification.

    • After the buffering starts, when the first downlink packet arrives on any bearer, the SAEGW-U informs the SAEGW-C. The SAEGW-U sends an Sx reporting message to the SAEGW-C, unless specified otherwise, and identifies the S5/S8 bearer on which the downlink packet is received.

    • On receiving the reporting message, the SAEGW-C decides whether to send a DDN message to the MME, as defined in 3GPP TS 23.401 [2]. The DDN notification is sent with the Sx-Usage-Report.

  • IDLE to ACTIVE transition:

    • At the UE transition to ECM-CONNECTED state, the SAEGW-C updates the SAEGW-U through Sxa interface with the F-TEIDu of the eNodeB/RNC/SGSN. The buffered data packets, if any, are then forwarded to the eNodeB/RNC/SGSN by the SAEGW-U.

  • If the Apply Action is BUFFER, and SGW-U recovers, the SGW-U initiates Sx Report (with DLDR Report Type) on arrival of the downlink data packet.

  • In SGW-U, a timer is implemented that starts after each Sx Report (with DLDR report Type) is sent. If the Apply Action is not changed, then on timer expiry, Sx Report (with DLDR Report Type) gets initiated again.

  • ARP of the bearer is included in the DDN message.

  • In a multi-PDN session, if the DDN is initiated for one PDN and then data is received on another PDN, wherein the bearer has higher priority, then the DDN is initiated again with the higher priority ARP value.