Section: 5.2 Call establishment procedures
Content: Establishment of a call is initiated by request of upper layer in either the mobile station or the network; it consists of: - the establishment of a CC connection between the mobile station and the network; - the activation of the codec or interworking function. Whenever it is specified in the present document clause 5 that the mobile station shall attach the user connection, this means that the mobile station shall activate the codec or interworking function as soon as an appropriate channel is available. The mobile station shall de-activate the codec or interworking function whenever an appropriate channel is no longer available. As soon as an appropriate channel is (again) available, the codec or interworking function shall be re-activated. If a new order to attach the user connection is received, the new order shall supersede the previous one. A channel shall be considered as appropriate if it is consistent with the possibly negotiated bearer capability applicable for the actual phase of the call. The mobile station shall not consider a channel as not appropriate because the type of the channel (full rate/half rate) is not the preferred one. If: - the user connection has to be attached but no appropriate channel is available for a contiguous time of 30 seconds; or if - the codec or interworking function is de-activated for a contiguous time of 30 seconds; then the mobile station may initiate call clearing. Upon request of upper layers to establish a call, restricting conditions for the establishment of the call are examined. These restricting conditions concern the states of parallel CC entities and are defined elsewhere. If these restricting conditions are fulfilled, the call establishment is rejected. Otherwise a CC entity in state U0, "null", is selected to establish the call. It initiates the establishment by requesting the MM sublayer to establish an MM connection. In Iu mode, if the lower layers indicate the release of a radio access bearer, whereas the corresponding call is still active, the MS shall not automatically initiate the release of that call.