TCH指配知识.doc

及早指配，早指配，晚指配 Mobile originating call establishment The mobile station initiates immediate assignment, service request using the CM SERVICE REQUEST message, and contention resolution. The network may initiate authentication and may start the ciphering mode setting. After sending the CIPHERING MODE COMPLETE message, the mobile station initiates call establishment by sending the SETUP message to the network. The network answers with a CALL PROCEEDING message. a) Non-OACSU option (early assignment) With this option the network allocates a traffic channel to the mobile station before it initiates call establishment in the fixed network. 早指配：ALERTING 之前已经指配TCH信道。 If call queuing is applied, it may cause variable delay in the traffic channel assignment. When user alerting has been initiated at the called side, an ALERTING message is sent to the mobile station. The network may optionally instruct the MS to attach the user connection at this stage of the call, by means of the progress indicator information element set to the value #1 or #8(if the ringing tone will be sent by the remote end) in the ALERTING message. In that case, an alerting ringing tone has to be generated by the network. NOTE: The speech codec is transparent for supervisory tones. A CONNECT message and its acknowledgement CONNECT ACKNOWLEDGE complete the call establishment when the called party has answered. The mobile originating call setup with early assignment is shown in figure 7.10a/GSM?04.08. b) OACSU option (late assignment) The network determines when the traffic channel is to be assigned. The assignment may be performed at any time after call establishment has been initiated in the fixed network. In the following the case is considered where the network will only allocate a traffic channel after the called party has answered the call (late assignment). 晚指配：ALERTING 之后指配TCH信道。 As in a) an ALERTING message is sent to the mobile station when user alerting has been initiated at the called side.