A.11 Use case for DRB retainability related KPI

28.5543GPP5G end to end Key Performance Indicators (KPI)Management and orchestrationRelease 18TS

DRB is the key and limited resource for 5GS to deliver services. Once a QoS flow reaches a gNB it will trigger setup of a new DRB or it will be mapped to an existing DRB. The decision on how to map QoS flows into new or existing DRBs is taken at the CU-CP. CU-CP also defines one set of QoS parameters (one 5QI) for the DRB. If a QoS flow is mapped to an existing DRB, the packets belonging to that QoS flow are not treated with the 5QI of the QoS flow, but they are treated with the mapped 5QI of the DRB.

The release of the DRB needs to be monitored, so that abnormal releases while the UE is considered in an active transfer shall be logged. DRB retainability is a key performance indicator of how often an end-user abnormally loses a DRB during the time the DRB is actively used. This key performance indicator is of great important to estimate the end users’ experiences. DRBs with bursty flow are considered active if any data (UL or DL) has been transferred during the last 100 ms. DRBs with continuous flow are seen as active DRBs in the context of this measurement as long as the UE is in RRC connected state. A particular DRB is defined to be of type continuous flow if the mapped 5QI is any of {1, 2, 65, 66}.

The key performance indicator shall monitor the DRB retainability for each used mapped 5QI value, as well as for the used S-NSSAI(s). DRBs used in 3GPP option 3 shall not be covered by this KPI. For the case when a DRB have multiple QoS flows mapped and active, when a QoS flow is released it will not be counted as a DRB release (DRB still active) in this KPI.