Inter-RAT (radio access technology) reestablishment enhancements in multi-RAT dual connectivity (MR-DC)

A network node, of a radio access network, RAN, configured to operate in dual connectivity towards a user equipment, UE together with a further network node in the RAN to establish a connection with a user equipment (UE) operating in dual connectivity (DC) with a master cell group (MCG) comprising a primary cell (PCell) served by a master node (MN), and with a secondary cell group (SCG) comprising a primary secondary cell (PSCell) served by a secondary node (SN), the network node comprising:

• interface circuitry operable to communicate with the UE and with at least the further network node in the RAN;
• and
• processing circuitry operably coupled to the interface circuitry, whereby the processing circuitry and the interface circuitry are configured to receive, from the UE, a re-establishment request message comprising:
• a plurality of parameters associated with the PSCell,
• a first message authentication code (MAC), and
• an indication of the UE's selection of a target cell served by a target node as a replacement for the PCell:
• the PCell utilizes a first radio access technology (RAT), and
• the PSCell and the target cell utilize a second RAT different from the first RAT;
• and
• verify integrity of the re-establishment request message based on the first MAC;
• determine a full UE context for the UE based on:
• the plurality of parameters associated with the PSCell, and
• a successful verification of the integrity of the re-establishment request message;
• establish a connection with the UE based on the full UE context, whereby the target cell served by the target node will serve as a PCell for DC;
• and
• the determining the full UE context comprises:
• based on the plurality of parameters associated with the PSCell, determining that the target node is different than the SN;
• sending, to the SN, a context request message including the plurality of parameters associated with the PSCell;
• and
• receiving, from the MN, a context response message including the full UE context.