A.43 Monitor of DRB release

28.5523GPP5G performance measurementsManagement and orchestrationRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

DRB is the key and limited resource for NG-RAN 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 as:

– an abnormal release of the DRB will cause the call(/session) drop, which directly impacts the QoS and slice delivered by the network, and the satisfaction degree of the end user;

– a successfully released DRB can be used to setup other requested calls(/sessions). The DRB failed to be released will still occupy the limited resource and hence it can not be used to admit other requested calls(/sessions).

From a retainability measurement aspect, DRBs do not need to be released because they are inactive, they can be kept to give fast access when new data arrives.

To define (from a DRB release measurement point of view) if a DRB is considered active or not, the DRB can be divided into two groups:

For DRBs with bursty flow, a DRB is said to be active if there is user data in the PDCP queue in any of the directions or if any data (UL or DL) has been transferred during the last 100 ms.
For DRBs with continuous flow, the DRB is seen as being active in the context of this measurement as long as the UE is in RRC connected state, and the session time is increased from the first data transmission on the DRB until 100 ms after the last data transmission on the DRB.

A particular DRB is defined to be of type continuous flow if the mapped 5QI is any of {1, 2, 65, 66}.

Due to different priority and tolerance for different service type with different QoS level in the DRB, the measurement needs to be performed per mapped 5QI, to be able to judge the result.

Similarly, the abnormal and failed DRB releases will affect different Service Level Agreements in the networks. Therefore, each S-NSSAI needs to be monitored.

The DRB can be released by PDU Session Resource Release procedure, UE Context Release procedure, Reset procedure either initiated by NG-RAN or AMF and NG Path Switch procedure (see TS 38.413 [11]).

Therefore, performance measurements related to DRB Release (see TS 38.413 [11]) and UE Context Release (see TS 38.413 [11]) procedure for each QoS level (mapped 5QI) and each S-NSSAI are necessary to support the monitor of DRB release.