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.