A wireless communications system includes a core packet network coupled to multiple base transceiver stations, each station providing wireless services to mobile units. In an embodiment, the stem packing assembly can have a leakage rate according to ISO 15848-1 of less than 1\xd710\u22124 mgs\u22121m\u22121 for at least 500 cycles at 160\xb0 C. Based on the latter and a set of measured values of input variables of an extended model of the system, a prediction of output variables of the model is produced. Second processing means cooperate with a second drum provided with a second curve formed by a second groove which is being traced by a second projection connected with the second processing means so as to arrange that by its movement along the periphery of the second drum the second processing means is positioned in its operational position with reference to the poultry.