A tracheal tube comprising a nematic polymer or nematic elastomer, wherein an outer diameter of the tracheal tube changes in size in response to exposure of the tracheal tube to light or heat. The method includes generating duplicate data by using repetition coding, the duplicate data being the same as original data, shifting the phase of the duplicate data, and transmitting the original data and the phase-shifted duplicate data. The inclined surface extends from a starting point defined by a crossing point of a spherical recess of the inner roller and a short radius r of an elliptic cutout formed on the inner roller. Then, an approximated curve is obtained from the characteristic values. Following the call, the session key is converted into a new seed by application of a second function and the new seed is stored for use in the next call. The request for establishing a call path can also identify the called party.