Free-run accuracy with Cordless DECT must be considered because the transmission equipment (DECT) requires an absolute accuracy of +/- 10 ppm for the entire temperature range and +/- 5 ppm for the limited temperature range. The small clock generator suffices as long as Telecom or any equivalent carrier supplies the system via digital interface. The standard clock generator should be used for "island" operation over a longer period of time. This is provided therefore for all OpenScape 4000 systems and the IPDAs.