the method according to the invention relates in general to transmission in cellular telecommunication systems and in particular to optimization of the data transfer mode . in the method according to the invention the data transfer mode is controlled using the downlink quality measured by the mobile station and the uplink quality measured by the base station . for transparent connections it can be determined a desired maximum threshold for the rxqual value , and when the uplink or downlink rxqual exceeds that maximum threshold , a more error - tolerant channel coding of a lower transmission speed is taken into use and the channel resources available are increased e . g . by growing the number of time slots to keep the user data transmission rate constant .