Methods for air interface message transfer in fast call setup processes

A method for fast call setup for originating User Equipment (UE) and terminating User Equipment, comprising:

• Step 1:
• When the originating UE starts a service sensitive to call setup delay, NAS of the UE informing a RRC layer whether to start fast call setup procedure. If not, the RRC starts RRC connection request directly. If so, here goes Step 2;
• Step 2:
• RRC layer of UE encapsulates Service Request into Initial Direct Transfer (IDT). If it is successful, proceed to Step 3. Otherwise, RRC layer of UE proceed as usual, i.e., RRC sends RRC CONNECTION REQUEST directly.
• Step 3:
• RRC CONNECTION REQUEST undergoes the process of non-critical extension, and the encapsulated IDT is put into the extended part.
• RNC, after receiving the extended RRC CONNECTION REQUEST, take the IDT message from the extended RRC CONNECTION REQUEST, and then encapsulate the Service Request message from IDT and send it to CN.