A method of operation of a Master Next Generation - Radio Access Network, NG-RAN, node in a cellular communications network , comprising: deciding , by the Master NG-RAN node , to split an existing Protocol Data Unit, PDU, session that includes a current uplink tunnel information; setting up , by the Master NG-RAN node , resources for the PDU session to be split by: sending , by the Master NG-RAN node , an S-Node Modification Request including the current uplink tunnel information for the PDU session to be split to a Secondary NG-RAN node in the cellular communications network ; and receiving , by the Master NG-RAN node , a newly added additional downlink tunnel information for the PDU session to be split from the Secondary NG-RAN node ; sending , by the Master NG-RAN node , a PDU Session Resource Modify Indication to a Fifth Generation Core, 5GC, node in the cellular communications network , where the PDU Session Resource Modify Indication comprises a current downlink tunnel information for the PDU session to be split and the newly added additional downlink tunnel information for the PDU session to be split; receiving , by the Master NG-RAN node , a newly added additional uplink tunnel information for PDU session to be split from the 5GC node; and sending, by the Master NG-RAN node , an S-Node Modification Request including the newly added additional uplink tunnel information for the PDU session to be split to the Secondary NG-RAN node . deciding , by the Master NG-RAN node , to split an existing Protocol Data Unit, PDU, session that includes a current uplink tunnel information; setting up , by the Master NG-RAN node , resources for the PDU session to be split by: sending , by the Master NG-RAN node , an S-Node Modification Request including the current uplink tunnel information for the PDU session to be split to a Secondary NG-RAN node in the cellular communications network ; and receiving , by the Master NG-RAN node , a newly added additional downlink tunnel information for the PDU session to be split from the Secondary NG-RAN node ; sending , by the Master NG-RAN node , a PDU Session Resource Modify Indication to a Fifth Generation Core, 5GC, node in the cellular communications network , where the PDU Session Resource Modify Indication comprises a current downlink tunnel information for the PDU session to be split and the newly added additional downlink tunnel information for the PDU session to be split; receiving , by the Master NG-RAN node , a newly added additional uplink tunnel information for PDU session to be split from the 5GC node; and sending, by the Master NG-RAN node , an S-Node Modification Request including the newly added additional uplink tunnel information for the PDU session to be split to the Secondary NG-RAN node . sending , by the Master NG-RAN node , an S-Node Modification Request including the current uplink tunnel information for the PDU session to be split to a Secondary NG-RAN node in the cellular communications network ; and receiving , by the Master NG-RAN node , a newly added additional downlink tunnel information for the PDU session to be split from the Secondary NG-RAN node ; sending , by the Master NG-RAN node , a PDU Session Resource Modify Indication to a Fifth Generation Core, 5GC, node in the cellular communications network , where the PDU Session Resource Modify Indication comprises a current downlink tunnel information for the PDU session to be split and the newly added additional downlink tunnel information for the PDU session to be split; receiving , by the Master NG-RAN node , a newly added additional uplink tunnel information for PDU session to be split from the 5GC node; and sending, by the Master NG-RAN node , an S-Node Modification Request including the newly added additional uplink tunnel information for the PDU session to be split to the Secondary NG-RAN node . <EOS>