3.4.7a Selective Ciphering of Downlink SACCH

3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 17TS

Selective Ciphering of Downlink SACCH, when ciphering is started between the network and the mobile station in dedicated mode or dual-transfer mode, refers to the mechanism used by the network in downlink to cipher or not to cipher any given individual SACCH block selectively according to its content; and to the ability of the mobile station to decode downlink SACCH blocks whether any given individual SACCH block is ciphered or not.

The use of Selective Ciphering of Downlink SACCH is under control of the network. The network may use Selective Ciphering of Downlink SACCH only if supported by the mobile station, as indicated in the MS Classmark 3 IE (see 3GPP TS 24.008). The network shall ensure that when Selective Ciphering of Downlink SACCH is used, it is used as long as ciphering is active during the RR connection.

If Selective Ciphering of Downlink SACCH is used, the network shall ensure that:

– a SACCH block shall not be ciphered if it contains any of the following RR messages: SYSTEM INFORMATION TYPE 5, SYSTEM INFORMATION TYPE 5bis, SYSTEM INFORMATION TYPE 5ter, SYSTEM INFORMATION TYPE 6, SYSTEM INFORMATION TYPE 14, MEASUREMENT INFORMATION, EXTENDED MEASUREMENT ORDER; and

– a SACCH block shall be ciphered if it contains SAPI 3 data (SMS), see 3GPP TS 44.006, optionally it should not be ciphered if carrying a CP-Ack message (see 3GPP TS 24.011).

A mobile station that supports Selective Ciphering of Downlink SACCH may use the above information to deter mine if Selective Ciphering of Downlink SACCH is used or not.