DDN Failure Scenario

  1. MME sends Release Access Bearer request to SGW-C to release downlink remote TEIDs of all the bearers for that UE.

  2. On arrival of Release Access Bearer request, SGW-C informs the same to SGW-U by updating FAR with Apply Action as BUFFER in Sx Modification Request for all the PDNs.

  3. SGW-U send Sx Modification response after applying Buffering in SGW-U for corresponding PDN.

  4. SGW-C sends Release Access Bearer response to MME.

  5. First Downlink data arriving in SGW-U triggers Sx Report Request (with Report Type as Downlink Data Report) toward SGW-C.

  6. On arrival of Sx Report Request message, the SGW-C initiates Downlink Data Notification request message toward MME.

  7. SGW-C sends Sx Report Response message toward SGW-U.

  8. If MME is not able to page UE then it can reject Downlink Data Notification Request with relevant cause.

    OR

    If MME accepts Downlink Data Notification Request. But later sends Downlink Data Notification Failure indication in order to indicate SGW-C that the UE did not respond to paging.

  9. SGW-C received DDN failure and hence to stop sending next DDN immediately , SGW-C starts DDN Failure Timer. SGW-C sends Sx Modification Request with DROBU flag to discard buffered packets and Apply Action as DROP to drop subsequent packets.

  10. SGW-U sends Sx Modification Response to SGW-C.

  11. On DDN Failure Timer Expiry SGW-C initiates Sx Modification with Apply Action as BUFFER in order to start buffering again.

Further steps are continued from Step 3 in the DDN Success Scenario call flow.