5.2.6 Start of ciphering

23.0343GPPHigh Speed Circuit Switched Data (HSCSD)Release 17Stage 2TS

In A/Gb mode, in order to start ciphering, the RR Encryption procedure is controlled by the main signalling link, only. The encryption information for secondary HSCSD channel is forwarded to the corresponding TCH/F in initial channel activation or later in the channel reactivation or Mode modify message.

The change of ciphering modes for separate channels within the HSCSD connection might not be perfectly synchronized.

In GERAN Iu mode, the Security mode control procedure is used to start ciphering (see 3GPP TS 44.118 [21]).