SECURITY MODE CONTROL OF THE RRC PROTOCOL IN CASE OF MULTI-RAB SR-VCC OR MDT INTER-RAT HANDOVERS TO UTRAN

摘要

The application relates to the RRC protocol as standardised in TS 25.331 and in particular addresses the problem that the Routing Area Update procedure does not work properly after the SRVCC with PS and CS RABs from E-UTRAN to UTRAN. Problematic Scenario: 1. CS CN and PS CN send Relocation Request for the handover to UTRAN due to PS + CS SRVCC triggered from E-UTRA 2. During the handover procedure, latest CN domain for which ciphering and integrity protection is configured for Signaling RAB is CS CN as specified in TS25.331 clause 8.3.6.3. 3. SRBs can have only one latest CN domain to which ciphering is configured. So it can be CS or PS and now it is CS (see step 2). This can mean there is no integrity protection started for the PS CN. This is not needed since SRB data is integrity protected, (according to TS 33.102 clause 6.5.4) "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." 4. UE triggers Routing Area Update and PS CN sends Routing Area Update Accept. 5.UE does not accept NAS messages from SGSN (i.e, Routing Area Update Accept) as it considers that PS integrity protection is not activated. To solve the problem explained above, following two possible solutions are proposed 1. Upon first SMC procedure after SRVCC HO, UE activates integrity protection using the integrity key of the key set used. If "RAB info" contains both CS and PS RABs, UE AS layer shall indicate to the upper layers of CS and PS domain, i.e. MM and GMM, that integrity protection is activated (315). 2. Upon SRVCC HO, UE adds an indicator in the RAU performed towards the SGSN to trigger "SMC" procedure for PS domain.