Method and apparatus are disclosed for calculating a target connection frame number (CFN) for a data frame in wireless communications. An update to an offset between the CFN and a radio access network frame number is computed. A target CFN variable is incremented in response to a received timer signal. The value of an update variable is checked to determine whether a new value of the offset has been received since a previous update to the offset. A new target CFN is calculated using a current target CFN and the new value of the offset on a condition that the new value of the offset has been received. The current target CFN is set equal to the new target CFN.