A method of operation in a gateway node that is coupled to a core network of a wireless communication network , the method comprising: determining that data is available for sending to a wireless device that accesses the wireless communication network via a radio cell provided by a radio node that is coupled to the core network of the wireless communication network via the gateway node ; generating service data units corresponding to the data, based on processing the data according to an upper portion of a radio protocol stack , wherein the radio protocol stack is split between the gateway node , which implements the upper portion of the radio protocol stack, and the radio node , which implements a remaining, lower portion of the radio protocol stack ; establishing an intra-stack Internet Protocol, IP, link with the radio node , communicatively coupling the upper portion of the radio protocol stack at the gateway node with the lower portion of the radio protocol stack at the radio node , and sending Service Data Units, SDUs, from the upper portion of the radio protocol stack , as implemented in the gateway node , to the lower portion of the radio protocol stack , as implemented in the radio node , via the intra-stack IP link , wherein the radio protocol stack includes as said upper portion a Packet Data Convergence Protocol, PDCP, layer, and a Radio Resource Control, RRC, layer and includes as said lower portion a Radio Link Control, RLC, protocol layer below the PDCP layer, a Medium Access Control, MAC, protocol layer below the RLC protocol layer, and a Physical, PHY, protocol layer below the MAC protocol layer, and characterised in that the intra-stack IP link communicatively couples the gateway node to the RLC protocol layer at the radio node . determining that data is available for sending to a wireless device that accesses the wireless communication network via a radio cell provided by a radio node that is coupled to the core network of the wireless communication network via the gateway node ; generating service data units corresponding to the data, based on processing the data according to an upper portion of a radio protocol stack , wherein the radio protocol stack is split between the gateway node , which implements the upper portion of the radio protocol stack, and the radio node , which implements a remaining, lower portion of the radio protocol stack ; establishing an intra-stack Internet Protocol, IP, link with the radio node , communicatively coupling the upper portion of the radio protocol stack at the gateway node with the lower portion of the radio protocol stack at the radio node , and sending Service Data Units, SDUs, from the upper portion of the radio protocol stack , as implemented in the gateway node , to the lower portion of the radio protocol stack , as implemented in the radio node , via the intra-stack IP link , wherein the radio protocol stack includes as said upper portion a Packet Data Convergence Protocol, PDCP, layer, and a Radio Resource Control, RRC, layer and includes as said lower portion a Radio Link Control, RLC, protocol layer below the PDCP layer, a Medium Access Control, MAC, protocol layer below the RLC protocol layer, and a Physical, PHY, protocol layer below the MAC protocol layer, and characterised in that the intra-stack IP link communicatively couples the gateway node to the RLC protocol layer at the radio node . <EOS>