Section: 4.7.7c Change of the ciphering algorithm at PS Handover
Content: For PS handover to A/Gb mode (see subclause 10.5.1.14 and 3GPP TS 44.060[ None ]  [76]) the network shall either assign a GSM ciphering algorithm to be used in the target cell or deactivate ciphering in the target cell. The MS shall start to use the new GSM ciphering algorithm or deactivate ciphering upon an indication from the lower layers that the PS handover procedure has been successfully completed (see 3GPP TS 44.060[ None ]  [76]) After PS handover to Iu mode (see 3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]) the network shall activate integrity protection and shall either assign a ciphering algorithm to be used in the target cell or deactivate ciphering in the target cell, using the security mode control procedure (3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]). If the GSM ciphering algorithm is changed at PS handover and the routing area updating procedure triggered by the PS handover procedure is not accepted by the network, the MS shall delete any GPRS ciphering key sequence number and proceed as specified in subclauses 4.7.5.1.4 and 4.7.5.2.4. If the routing area updating procedure fails, because the radio resources assigned in the new cell are released before the MS receives a ROUTING AREA UPDATE ACCEPT message, the MS shall delete any GPRS ciphering key sequence number and proceed as specified in subclauses 4.7.5.1.5 item b and 4.7.5.2.5, respectively.