Section: P.4 Inter-system change between A/Gb mode and S1 mode
Content: An MS is required to perform routing area updating for IMS voice termination at inter-system change from S1 mode to A/Gb mode and tracking area updating for IMS voice termination at inter-system change from A/Gb mode to S1 mode if: 1) conditions 1 and 2 of annex P.3 are fulfilled; 2) the "IMS voice over PS session indicator" received for S1 mode has the value "IMS voice over PS session in S1 mode supported"; and 3) the voice domain preference for E-UTRAN as defined in 3GPP TS 24.167[ 3GPP IMS Management Object (MO); Stage 3 ]  [134] is not "CS voice only".