This European Telecommunication Standard (ETS) specifies stage one of the Packet Data on Signalling channels service (PDS) which allows packet data transmission in GSM networks on dedicated channels. The PDS service is offered in two variants, PDSS1 and PDSS2; each variant may be supported by a mobile station independently. PDSS1 is subject to subscription in a GSM network, whereas PDSS2 may only be subject to subscription of an application (this however is out of the scope of the service description). The service is described from the service subscriber s and user s point of view: in particular: - the procedure for normal operation with successful outcome; - the action to be taken in exceptional circumstances; - the interaction with other GSM services and features. This specification does not deal with the Man-Machine Interface (MMI) requirements.