Content for  TS 23.501  Word version:  19.1.0

The QoS Parameter Notification control indicates to the NG-RAN that notifications of "GFBR can no longer (or can again) be guaranteed" are requested when the NG-RAN determines that the GFBR, the PDB or the PER of the QoS profile cannot be fulfilled (or can be fulfilled again) for a QoS Flow (during the lifetime of the QoS Flow) and that the QoS Flow should be kept while the NG-RAN is not fulfilling the requested QoS profile. Notification control may be used for a GBR QoS Flow if the application traffic is able to adapt to the change in the QoS (e.g. if the AF is capable to trigger rate adaptation). The NG-RAN determination whether the GFBR, the PDB and the PER can be fulfilled or not, is done under consideration of the QoS parameters Averaging Window and MDBV (for a GBR QoS Flow using the Delay-critical resource type), which are either provided explicitly as part of the QoS profile or implicitly via the standardized 5QI QoS characteristics defined in clause 5.7.4. The SMF shall only enable Notification control when the QoS Notification Control parameter is set in the PCC rule (received from the PCF) that is bound to the QoS Flow. The Notification control parameter is signalled to the NG-RAN as part of the QoS profile.

If, for a given GBR QoS Flow, Notification control is enabled and the NG-RAN determines that the GFBR, the PDB or the PER of the QoS profile cannot be fulfilled, NG-RAN shall send a notification towards SMF that the "GFBR can no longer be guaranteed". Furthermore, the NG-RAN shall keep the QoS Flow (i.e. while the NG-RAN is not fulfilling the requested QoS profile for this QoS Flow), unless specific conditions at the NG-RAN require the release of the NG-RAN resources for this GBR QoS Flow, e.g. due to Radio link failure or RAN internal congestion. The NG-RAN should try to fulfil the GFBR, the PDB and the PER of the QoS profile again. Upon receiving a notification from the NG-RAN that the "GFBR can no longer be guaranteed", the SMF may forward the notification to the PCF, see TS 23.503. When the NG-RAN determines that the GFBR, the PDB and the PER of the QoS profile can be fulfilled again for a QoS Flow (for which a notification that the "GFBR can no longer be guaranteed" has been sent), the NG-RAN shall send a notification, informing the SMF that the "GFBR can again be guaranteed" and the SMF may forward the notification to the PCF, see TS 23.503. The NG-RAN shall send a subsequent notification that the "GFBR can no longer be guaranteed" whenever necessary. During a handover, the Source NG-RAN does not inform the Target NG-RAN about whether the Source NG-RAN has sent a notification for a QoS Flow that the "GFBR can no longer be guaranteed". The Target NG-RAN performs admission control rejecting any QoS Flows for which resources cannot be permanently allocated. The accepted QoS Flows are included in the N2 Path Switch Request or N2 Handover Request Acknowledge message from the NG-RAN to the AMF. The SMF shall interpret the fact that a QoS Flow is listed as transferred QoS Flow in the Nsmf_PDUSession_UpdateSMContext Request received from the AMF as a notification that "GFBR can again be guaranteed" for this QoS Flow unless the SMF is also receiving a reference to an Alternative QoS Profile for this QoS Flow (which is described in clause 5.7.2.4.2). After the handover is successfully completed, the Target NG-RAN shall send a subsequent notification that the "GFBR can no longer be guaranteed" for such a QoS Flow whenever necessary. If the SMF has previously notified the PCF that the "GFBR can no longer be guaranteed" and the SMF does not receive an explicit notification that the "GFBR can no longer be guaranteed" for that QoS Flow from the Target NG-RAN within a configured time, the SMF shall notify the PCF that the "GFBR can again be guaranteed".

If, for a given GBR QoS Flow, Notification control is enabled and the NG-RAN has received a list of Alternative QoS Profile(s) for this QoS Flow and supports the Alternative QoS Profile handling, the following shall apply:

1. If the NG-RAN determines that the GFBR, the PDB or the PER of the QoS profile cannot be fulfilled, NG-RAN shall send a notification towards SMF that the "GFBR can no longer be guaranteed". Before sending a notification that the "GFBR can no longer be guaranteed" towards the SMF, the NG-RAN shall check whether the GFBR, the PDB and the PER that the NG-RAN currently fulfils match any of the Alternative QoS Profile(s) in the indicated priority order. If there is a match, the NG-RAN shall indicate the reference to the matching Alternative QoS Profile with the highest priority together with the notification to the SMF.
   If there is no match, the NG-RAN shall send a notification that the "GFBR can no longer be guaranteed" towards the SMF indicating that the lowest Alternative QoS Profile cannot be fulfilled (unless specific conditions at the NG-RAN require the release of the NG-RAN resources for this GBR QoS Flow, e.g. due to Radio link failure or RAN internal congestion).
2. If a notification that the "GFBR can no longer be guaranteed" has been sent to the SMF and the NG-RAN determines that the currently fulfilled GFBR, PDB or PER are different (better or worse) from the situation indicated in the last notification, the NG-RAN shall send a notification (i.e. "GFBR can no longer be guaranteed" or "GFBR can again be guaranteed") to the SMF and indicate the current situation (unless specific conditions at the NG-RAN require the release of the NG-RAN resources for this GBR QoS Flow, e.g. due to Radio link failure or RAN internal congestion).
3. The NG-RAN should always try to fulfil the QoS profile and, if this is not possible, any Alternative QoS Profile that has higher priority.
4. Upon receiving a notification from the NG-RAN, the SMF may inform the PCF. If it does so, the SMF shall indicate the currently fulfilled situation to the PCF. See TS 23.503.
5. If the PCF has not indicated differently, the SMF uses NAS signalling (that is sent transparently through the RAN) to inform the UE about changes in the QoS parameters (i.e. 5QI, GFBR, MFBR) that the NG-RAN is currently fulfilling for the QoS Flow after Notification control has occurred.

During handover, the prioritized list of Alternative QoS Profile(s) (if available) is provided to the Target NG-RAN per QoS Flow in addition to the QoS profile. If the Target NG-RAN is not able to guarantee the GFBR, the PDB and the PER included in the QoS profile and if Alternative QoS Profiles are provided to the Target NG-RAN and the Target NG-RAN supports Alternative QoS Profiles, the Target NG-RAN checks whether the GFBR, the PDB and the PER values that it can fulfil match any of the Alternative QoS Profile(s) taking the priority order into account. If there is a match between one of the Alternative QoS Profiles and the GFBR, the PDB and the PER values that Target NG-RAN can fulfil, the Target NG-RAN shall accept the QoS Flow and indicate the reference to that Alternative QoS Profile to the Source NG-RAN. If there is no match to any Alternative QoS Profile, the Target NG-RAN rejects QoS Flows for which the Target NG-RAN is not able to guarantee the GFBR, the PDB and the PER included in the QoS profile. After the handover is completed and a QoS Flow has been accepted by the Target NG-RAN based on an Alternative QoS Profile, the Target NG-RAN shall treat this QoS Flow in the same way as if it had sent a notification that the "GFBR can no longer be guaranteed" with a reference to that Alternative QoS Profile to the SMF (as described in clause 5.7.2.4.1b). If a QoS Flow has been accepted by the Target NG-RAN based on an Alternative QoS Profile, the reference to the matching Alternative QoS Profile is provided from the Target NG-RAN to the AMF (which forwards the message to the SMF) during the Xn and N2 based handover procedures as described in TS 23.502. After the handover is completed successfully, the SMF shall send a notification to the PCF that the "GFBR can no longer be guaranteed" for a QoS Flow (see TS 23.503 for details) if the SMF has received a reference to an Alternative QoS Profile and this reference indicates a change in the previously notified state of this QoS Flow. If the PCF has not indicated differently, the SMF shall also use NAS signalling (that is sent transparently through the RAN) to inform the UE about the QoS parameters (i.e. 5QI, GFBR, MFBR) corresponding to the new state of the QoS Flow. If a QoS Flow has been accepted by the Target NG-RAN based on the QoS Profile, the SMF shall interpret the fact that a QoS Flow is listed as transferred QoS Flow in the message received from the AMF as a notification that "GFBR can again be guaranteed" for this QoS Flow. After the handover is successfully completed, the Target NG-RAN performs as described in clause 5.7.2.4.1b. If the SMF has previously notified the PCF that the "GFBR can no longer be guaranteed" and the SMF does not receive an explicit notification that the "GFBR can no longer be guaranteed" for that QoS Flow from the Target NG-RAN within a configured time, the SMF shall notify the PCF that the "GFBR can again be guaranteed". If a QoS Flow has been accepted by the Target NG-RAN and SMF did not receive from the Target NG-RAN a reference to any Alternative QoS Profile and the SMF has previously informed the UE about QoS parameters corresponding to any of the Alternative QoS Profile(s), the SMF shall use NAS signalling to inform the UE about the QoS parameters corresponding to the QoS Profile.

During QoS Flow establishment and modification, a prioritized list of Alternative QoS Profile(s) can be provided to the NG-RAN for the QoS Flow in addition to the QoS profile. If the NG-RAN is not able to guarantee the GFBR, the PDB and the PER included in the QoS profile and if Alternative QoS Profiles are provided to the NG-RAN and the NG-RAN supports Alternative QoS Profiles, the NG-RAN shall check whether the GFBR, the PDB and the PER values that it can fulfil match at least one of the Alternative QoS Profile(s) taking the priority order into account. If there is a match between one of the Alternative QoS Profiles and the GFBR, the PDB and the PER values that the NG-RAN can fulfil, the NG-RAN shall accept the QoS Flow and indicate the reference to that Alternative QoS Profile to the SMF. If there is no match to any Alternative QoS Profile, the NG-RAN shall reject the QoS Flow establishment or modification. After a successful QoS Flow establishment or modification during which the NG-RAN indicated that the currently fulfilled QoS matches one of the Alternative QoS Profiles, the NG-RAN shall treat this QoS Flow in the same way as if it had sent a notification that the "GFBR can no longer be guaranteed" with a reference to that Alternative QoS Profile to the SMF (as described in clause 5.7.2.4.1b). If the SMF has received a reference to an Alternative QoS Profile during QoS Flow establishment and modification the SMF may inform the PCF about it (as described in TS 23.503). If the PCF has not indicated differently, the SMF shall use NAS signalling (that is sent transparently through the RAN) to inform the UE about the QoS parameters (i.e. 5QI, GFBR, MFBR) corresponding to the referenced Alternative QoS Profile.