Section: 6.5.5 Integrity key selection
Content: There may be one IK for CS connections (IKCS), established between the CS service domain and the user and one IK for PS connections (IKPS) established between the PS service domain and the user. The data integrity of radio bearers for user data is not protected. The signalling radio bearers are used for transfer of signalling data for services delivered by both CS and PS service domains. These signalling radio bearers are data integrity protected by the IK of the service domain for which the most recent security mode negotiation took place. This may require that the integrity key of an (already integrity protected) ongoing signalling connection has to be changed, when a new connection is established with another service domain, or when a security mode negotiation follow a re-authentication during an ongoing connection. This change should be completed by the RNC within five seconds after receiving the security mode command from the VLR/SGSN. NOTE: For the behaviour of the terminal regarding key changes see section 6.4.5.