There is described a method of providing a positioning service for plural terminals operating in a communication network which may, for example be a GSM telephone network. The terminals have receivers for receiving signals from transmission sources. In the method measurements of the signals received from one or more of the transmission sources by the receivers are made and the measurements transferred to one or more data nodes. At the data node(s) one or more records of one or more of the measurements are created and at least some of the records are transferred to one or more computing nodes. At the computing node(s) a table of the records transferred to the computing node is maintained and a computation is carried out, using at least part of the table, from which the positions or states of motion or relative positions or relative states of motion of said plural terminals and the transmission time offsets of the transmission sources are extractable.