This GTS specifies the stage 1 description of Explicit Call Transfer (ECT) from the service subscriber s and user s points of view, in particular: - the procedures for normal operation with successful outcome; - the action to be taken in exceptional circumstances; - the interaction with other Global System for Mobile communications (GSM) supplementary services. This TS does not deal with the Man-Machine Interface (MMI) requirements, but makes reference to the appropriate GSM Technical Specification and ETS. The charging principles applied to ECT are established in this standard in terms of the charging information required to be collected. Any subsequent charging implications are outside of the scope of this TS. This ETS is applicable to the digital cellular telecommunication system GSM. Any interactions with other networks not dealt with in Clause 9 are outside the scope of this TS.