A method of controlling selection of a data transmission network node, such as a base station, node B, eNodeB, GGSN or LTE PDN-GW, for a mobile device in a telecommunications network is disclosed. The mobile telecommunications network includes a plurality of mobility management nodes, such as SGSN and LTE MME. When the mobile terminal moves from a first one of the mobility management nodes to a second of the nodes, it is determined at the second node whether to cause the mobile terminal to re-select a data transmission network node. The determining step may be performed in response to a periodic routing area/periodic tracking area update request generated by the mobile terminal or in response to the mobile terminal being in an idle communication state. When the data transmission network node is re-selected, a data transmission network node that is relatively geographically near to the mobile terminal is selected.