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12.8 SIGNALING BETWEEN MOBILE AND NETWORK 377(Section 12.9.1). The network then assigns a SDCCH and returns an IMMEDIATEASSIGNMENT message (Section 12.9.1). At this point, the MS and BSS tune theirtransmitter and receiver to the SDCCH.The MS next sends a CM SERVICE REQUEST (Section12.9.2), indicating that itwishes to originate a call. The network then decides whether to execute or skip theMS authentication. If the MS has ciphering capability, they ciphering mode isstarted by command from the network.The call-control messages that follow are similar to the correspondingQ.931messages of Digital Subscriber Signaling System No. 1 (Section 10.3.2).The MS sends a SETUP message (Section 12.9.3) that includes the called partynumber, bearer capability, and other information. The network acknowledges with aCALL PROCEEDING message (Section 12.9.3). It then allocates a TACH, sends anASSIGNMENT COMMAND (Section 12.9.1), and then releases SDCCH. Onreceipt of the command, the MS sends an ASSIGNMENT COMPLETE (Section12.9.1) message tunes to TACH. From this point, the signaling is on the SACCHto TACH.When the network receives an indication from the fixed network that the calledparty is being alerted, it sends an ALERTING message (Section 12.9.3), and the MSnotifies its user.When the called party answers, the network sends a CONNECT message(Section 12.9.3), and the MS returns a CONNECT ACKNOWLEDGE (Section12.9.3). The conversation can now begin.12.8.6 Connection Setup for Call Terminating at MSIn Fig. 12.8-3, a MS is active and idle, and listening to the P AGCH of its cell. Whenthe mobile network receives a call for the MS, it transmits PAGING REQUEST inall cells of the MS location area (Section 12.9.1). The called MS is identified byTMSI or IMSI. When recognizing that it is being paged, the MS sends aCHANNEL REQUEST (Section 12.9.1) message. The network then allocates aSDCCH and returns an IMMEDIATE ASSIGNMENT message (Section 12.9.1).The MS acknowledges the paging request with a PAGING RESPONSE message(Section 12.9.1). The network then decides Whether to execute or skip the MSauthentication. If the MS has ciphering capability, the network initiates the cipheredmode on SDCCH.The message sequence that follows is similar to that of Section 12.8.5, except thatfor some messages the roles of the MS and the network are reversed. The networkstarts with a SETUP message (Section 12.9.3), and the MS acknowledges with aCALL CONFIRMED message (Section 12.9.3).At this point, the network allocates a TACH and sends an ASSIGNMENTCOMMAND (Section 12.9.1). The MS acknowledges with an ASSIGNMENTCOMPLETE (Section 12.9.3.1) message and then tunes to TACH. The networkthen releases SDCCH, and signaling for the rest of the call is on the SACCH orFACCH of TACH.