Default-Bearer QoS Handling for 5G Sessions

The following procedure explains how the SMF handles the modification of authorized QoS for the default bearer in a 5G session.

  1. The SMF receives SmPolicyUpdateNotify from PCF with changed 5QI in AuthorizedDefaultQoS and/or a different session AMBR value.

  2. The SMF initiates N1N2MessageTransfer procedure with AMF to send N1 PDU Session Modification Command and N2 PDU Session Resource Modify Request Transfer IE in this message.

    1. In the N1 message, the default QoS flow is modified in Authorized QoS Flow Description IE to update the 5QI value.

    2. In the N1 message, the Mapped EPS Bearer Context IE is modified to update the QCI of the default bearer.

    3. In the N2 message, the QoS flow level QoS parameter for the default flow is modified to update the 5QI value.

  3. The SMF accepts the SMContextUpdate Request from AMF with the responses for the N1 and N2 requests sent in N1N2Message Transfer message.

  4. On the N4 interface, the following changes are done:

    1. New instance of the BearerLvlInfo IE is included with the changed 5QI to QFI mapping.

    2. Update PDR is sent for all PDRs which are a part of default flow to reflect the association with the new BearerLvlInfo IE.

    3. Forwarding Action Rule (FAR) associated with all PDRs in the default flow is updated with the new DSCP marking value if the 5QI-DSCP mapping configuration has a different value for the changed 5QI.