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1.1.1 Call Release

If the calling party hangs up first, the MS sends disconnect message to MSC throughFACCH. After receiving this message, the MSC sends release message to informthe called party to terminate the communication. The end-to-end connection is over.

ut the call is not complete, !ecause certain tas"s such as sending charge indicationare performed. #hen the connection to the MS is no longer necessary, the systemsends a $%&%AS% message to the MS and starts T'(). After receiving thismessage, the MS sends a $%&%AS% C*M+&%T% message to the system and thecall is over. The MS stops the T'() after receiving the $%&%AS% C*M+&%T%message. Similarly, if the called party hangs up first, it sends a $%&%AS% messageto the calling party. The MSC sends the calling party a ISC*%CT message afterreceiving the $%&%AS% message. If the call is terminated in an a!normal ay, thismessage further indicates the cause for that.

#hen the MSC receives the $%&%AS% C*M+&%T% message from the MS, it sendsa C&%A$ C*MMA message to SC to release all the signaling lin"s. Thismessage contains the cause for the call clearance, such as handover complete orlocation updating complete. The call connection release is over. If the a!normal

release occurs !ecause of radio lin" failure or device failure, the SC sends aC&%A$ $%/0%ST message to the MSC.

After receiving the C&%A$ $%/0%ST message, SC sends a CHA%& $%&%AS%message to the MS and starts T'1(2 to sho that all the loer layer lin"s arereleased. Meanhile, it re3uires the MS to enter the idle mode. #hen the MSreceives the CHA%& $%&%AS% message, it removes the uplin" signaling lin" 4tostop sending the measurement report of uplin" channel associated signaling onSACCH5. The MS sends ISC message to TS and starts T'11(. After receivingthis message, The TS sends 0A to MS and the $%&%AS% IICATI* to theSC. #hen the T'11( times out or the MS receives the 0A frame, it enters the idlemode.

Figure 1.1 Call release

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In order to ensure the timely removal of the uplin" and donlin", hen the SCsends the CHA%& $%&%AS% message to the MS for the uplin" removal, it alsosends a deactivate SACCH 4SACCH5 to the TS re3uiring for the release of thedonlin" signaling 4to stop the signaling connection !eteen the to parties5. Afterreceiving this message, the TS stops the transmission of the donlin" SACCHframe and sends the deactivate SACCH ac"noledgement to the MSC.

After receiving the $%&%AS% IICATI* message, SC resets the T'1(2 andstarts the T'111, and sends $F CHA&% $%&%AS% to the TS 4the T'111 is resetat the same time5, re3uiring for the release of TCH resources. #hen the SCreceives the $F CHA&% $%&%AS% ac"noledgement message from the TS, itsends a C&%A$ C*M+&%T% message to the MSC, indicating that the radio lin"clearance is over and the channel is availa!le for reallocation.

After receiving the C&%A$ C*M+&%T% message, the MSC releases the SCC+connection !y sending $&S and receiving $&C. The hole MS originating call flois over.