Section: 6.6.5 Cipher key selection
Content: There is one CK for CS connections (CKCS), established between the CS service domain and the user and one CK for PS connections (CKPS) established between the PS service domain and the user. The radio bearers for CS user data are ciphered with CKCS. The radio bearers for PS user data are ciphered with CKPS. 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 ciphered by the CK of the service domain for which the most recent security mode negotiation took place. This may require that the cipher key of an (already ciphered) ongoing signalling connection has to be changed, when a new connection is established with another service domain, or when a security mode negotiation follows 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.