Section: 4.7.8 Inter-UE QoS for NB-IoT UEs using Control Plane CIoT EPS Optimisation
Content: To allow the E-UTRAN to prioritise resource allocation between different NB-IoT UEs when some of the UEs are using the Control Plane CIoT EPS Optimisation, the eNodeB may request, based on configuration, the MME to supply the eNodeB with the negotiated QoS profile for any UE that is using the Control Plane CIoT EPS Optimisation. The QoS profile sent to the eNodeB by the MME consists of the E-RAB Level QoS Parameter in the E-RAB to be Setup List IE (see TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ]  [36]). In order to reduce signalling load on the MME, the eNodeB may be configured to request the QoS profile from the MME by using the UE's S-TMSI as identifier, e.g., when the eNodeB's NB-IoT load exceeds certain threshold(s) or when the eNodeB needs to cache the QoS profile. If the UE has more than one EPS bearer active, the MME sends QoS profile for only one EPS bearer to the eNodeB. In this case the MME uses local configuration (e.g. considering table 6.1.7 in TS 23.203[ Policy and charging control architecture ]  [6], the MME chooses the non-GBR EPS bearer with the QCI corresponding to the highest Priority Level) to determine which EPS bearer's QoS to send to the eNodeB. If the MME has no EPS bearers active for the UE, then this fact is indicated to the eNodeB. The eNodeB can use the QoS profile to assist with resource prioritisation decisions between different NB-IoT UEs (irrespective of whether the UE/eNodeB is using the Control Plane CIoT EPS Optimisation, or, the User Plane CIoT EPS Optimisation).