Section: 8.12.2 NSA IAB Integration procedure
Content: The IAB integration procedure for NSA is shown in Figure 8.12.2-1. Figure 8.12.2-1: Signalling flow for IAB integration procedure in NSA Phase 1-1. IAB-MT part setup with E-UTRAN. In this phase, the IAB-MT part connects to the LTE network as a UE, by performing RRC connection setup procedure with an eNB, authentication with the EPC, IAB-node’s access traffic-related radio bearer configuration at the E-UTRAN side, and optionally, OAM connectivity establishment by using the IAB-MT’s PDN connection. The IAB-node can select the IAB-supporting eNB based on an over-the-air indication from eNB (transmitted in SIB1). To indicate its IAB capability, the IAB-MT includes the IAB-node indication in RRCConnectionSetupComplete message, to assist the eNB to select an MME supporting IAB. The eNB then configures the IAB-MT part with an NR measurement configuration in order to perform discovery, measurement and measurement reporting of candidate gNBs. To enable the eNB choose an en-gNB which supports IAB function, the IAB capability of neighbour gNBs can be pre-configured in the eNB (e.g. by OAM). NOTE: Other ways to enable the eNB know the IAB capability of neighbour gNBs are not precluded. Phase 1-2. SgNB addition. In this phase, the IAB-MT part connects to the parent node IAB-DU and IAB-donor-CU via the EN-DC SgNB Addition procedure. The procedure defined in clause 8.4.1 is reused. The eNB includes “IAB Node Indication” in SGNB ADDITION REQUEST message to inform the IAB-donor-CU that the request is for an IAB-node. In addition, SRB3 can be set up for the IAB-MT, to transmit RRC message between the IAB-MT and the IAB-donor-CU via the NR links directly. Phase 2-1: BH RLC channel establishment. This phase is the same as Phase 2-1 in the standalone IAB integration procedure (refer to the Phase 2-1 in clause 8.12.1). This step may occur in Phase 1-2. Phase 2-2: Routing update. This phase is the same as Phase 2-2 in the standalone IAB integration procedure (refer to the Phase 2-2 in clause 8.12.1), except that the IP traffic on the F1-C interface may be transmitted via the MeNB. Phase 3. IAB-DU part setup. This phase is the same as Phase 3 in the standalone IAB integration procedure (refer to the Phase 3 in clause 8.12.1), except that the IP traffic on the F1-C interface may be transmitted via the MeNB. The IAB-donor-CU decides to only configure LTE leg, or only to configure NR leg, or to configure both LTE leg and NR leg, to be used for F1-C traffic transfer. The configuration may be performed before IAB-DU part setup. IAB-donor-CU may also change the configuration after IAB-DU part setup. In case the configuration is not performed before IAB-DU part setup, the IAB node uses the NR leg as the default one. When both LTE leg and NR leg are configured, it is up to the implementation to select the leg for F1-C traffic transfer.