Section: 8.3 Bearer type change
Content: In MR-DC, all the possible bearer type change options are supported: - MCG bearer to/from split bearer; - MCG bearer to/from SCG bearer; - SCG bearer to/from split bearer. Bearer termination point change is supported for all bearer types, and can be performed with or without bearer type change: - MN terminated bearer to/from SN terminated bearer. For MR-DC: - when the security key is changed for a bearer due to a termination point change, the associated PDCP and RLC entities are re-established, while MAC behavior might depend on the solution selected by the network, e.g. MAC reset, change of LCID, etc. (see Annex A); - for MCG bearer, split bearer and SCG bearer, during MN security key change the MCG/SCG PDCP and RLC are re-established and MCG/SCG MAC is reset; - if a bearer type change happens together with MN security key change then for MCG bearer, split bearer and SCG bearer, the MCG/SCG PDCP and RLC are re-established and MCG/SCG MAC is reset; - if a bearer type change happens through SN change procedure, then SN terminated PDCP and SCG RLC are re-established and SCG MAC is reset. MCG RLC/MAC behavior depends on the solution selected by the network, see Annex A; - one step (direct) bearer type change between MN terminated bearer types without using the handover procedure is supported; - one step (direct) bearer type change between SN terminated bearer types without using the handover or SN change procedure is supported; - one step (direct) bearer type change from/to MN terminated bearer to/from SN terminated bearer without using the handover procedure is supported; - PDCP SN length change for an AM DRB or RLC mode change for DRB is performed using a release and add of the DRBs (in a single message) or full configuration; - One step (direct) bearer type change with PDCP version change (only applicable for EN-DC) is supported. For MR-DC with 5GC: - in a bearer termination point change of a DRB from a source NG-RAN node to a target NG-RAN node, for each DRB for which the source NG-RAN node provides QoS flow to DRB mapping information to the target NG-RAN node, the source NG-RAN node also offers the indicated DRB ID for usage at the target NG-RAN node. The target NG-RAN node informs the source NG-RAN node if it accepts the DRB offloading and takes the DRB ID into use. NOTE 1: In this clause the term "handover" refers to an E-UTRA handover or to an NR synchronous reconfiguration not necessarily implying a P(S)Cell change with or without security key change. NOTE 2: L2 handling for bearer type change in MR-DC is also summarized in Annex A (the table does not consider the cases that PDCP SN length is changed and avoiding reuse of COUNT).