In a packet switched wireless communications network, a parameter of a communication channel request indicates that the communication channel is to be used to transfer call related control messages. Upon receipt of the communication channel request, a network element sends a request to a radio access network that a part of the communication channel should be setup to transfer call related control messages. Another network element sets filtering information to allow only specific messages to be transferred on the communication channel. Specifically, the filtering information is set such that only call related control messages may be transferred on the communication channel. The other network element then sends the filtering information to the user equipment (UE). The UE derives the uplink filtering information from the received filtering information.