5G/NR  - Access Control  

 

 

 

UAC(Unified Access Control)

UAC is a set of mechanism (algorithm) to determine whether to allow the UE for a specific services or state changes. UAC is a pretty complicated algorithm that get many factors involved at each point of decision making process. Overall concept similar to LTE Access Control, but I think the related parameters are more dispersed here and there... causing more confusion -:).  In LTE, Access control is mainy controlled by RRC(SIBs) but it seems NAS has more control ever Access Control in NR seems.

Factors for UAC mechanism

The rough categories of factors affecting UAC is illustarated below and main framework is specified in 24.501-4.5, but you may refer to additional specification like 38.331 and USIM specification for further details.

Factors

Description

RRC

NAS

USIM

Triggers for Checking UAC

Triggers for UAC check is specified in 24.501-4.5.1 and can be summarized as follows.

Trigger

Description

NAS State Change
  • 5GMM-IDLE --> 5GMM-CONNECTED

Service Request (in 5GMM-CONNECTED)
  • MO-MMTEL-voice-call-started indication
  • MO-MMTEL-video-call-started indication
  • MO-SMSoIP-attempt-started
  • MO SMS over NAS
  • UL NAS TRANSPORT message for PDU session establishment (except for the purpose of IDLE -> CONNECTED NAS State change)
  • UL NAS TRANSPORT message for PDU session modification (except for the purpose of IDLE -> CONNECTED NAS State change)
  • Request to re-establish the user-plane resources for an existing PDU session
  • Notification for an uplink user data packet to be sent for a PDU session with suspended user-plane resources

RRC Information for UAC

SIB1 ::=        SEQUENCE {

    cellSelectionInfo                   SEQUENCE {

        q-RxLevMin                          Q-RxLevMin,

        q-RxLevMinOffset                    INTEGER (1..8)      OPTIONAL,   -- Need R

        q-RxLevMinSUL                       Q-RxLevMin          OPTIONAL,   -- Need R

        q-QualMin                           Q-QualMin           OPTIONAL,   -- Need R

        q-QualMinOffset                     INTEGER (1..8)      OPTIONAL    -- Need R

    }    OPTIONAL,   -- Need S

    cellAccessRelatedInfo               CellAccessRelatedInfo,

    connEstFailureControl               ConnEstFailureControl   OPTIONAL,   -- Need R

    si-SchedulingInfo                   SI-SchedulingInfo       OPTIONAL,   -- Need R

    servingCellConfigCommon             ServingCellConfigCommonSIB    OPTIONAL,   -- Need R

    ims-EmergencySupport                ENUMERATED {true}             OPTIONAL,   -- Need R

    eCallOverIMS-Support                ENUMERATED {true}             OPTIONAL,   -- Cond Absent

    ue-TimersAndConstants               UE-TimersAndConstants         OPTIONAL,   -- Need R

 

    uac-BarringInfo                     SEQUENCE {

        uac-BarringForCommon                UAC-BarringPerCatList     OPTIONAL,   -- Need S

        uac-BarringPerPLMN-List             UAC-BarringPerPLMN-List   OPTIONAL,   -- Need S

        uac-BarringInfoSetList              UAC-BarringInfoSetList,

        uac-AccessCategory1-SelectionAssistanceInfo CHOICE {

            plmnCommon                      UAC-AccessCategory1-SelectionAssistanceInfo,

            individualPLMNList              SEQUENCE (SIZE (2..maxPLMN))

                                               OF UAC-AccessCategory1-SelectionAssistanceInfo

        }   OPTIONAL

    }     OPTIONAL,   -- Need R

 

    useFullResumeID                     ENUMERATED {true}    OPTIONAL,   -- Need N

    lateNonCriticalExtension            OCTET STRING         OPTIONAL,

    nonCriticalExtension                SEQUENCE{}           OPTIONAL

}

 

UAC-AccessCategory1-SelectionAssistanceInfo ::= ENUMERATED {a, b, c}

 

UAC-BarringInfoSetList ::= SEQUENCE (SIZE(1..maxBarringInfoSet)) OF UAC-BarringInfoSet

 

UAC-BarringInfoSet ::= SEQUENCE {

    uac-BarringFactor              ENUMERATED {p00, p05, p10, p15, p20, p25, p30, p40,

                                               p50, p60, p70, p75, p80, p85, p90, p95},

    uac-BarringTime                ENUMERATED {s4, s8, s16, s32, s64, s128, s256, s512},

    uac-BarringForAccessIdentity   BIT STRING (SIZE(7))

}

 

RRCSetupRequest ::= SEQUENCE {

   rrcSetupRequest                        RRCSetupRequest-IEs

}

RRCSetupRequest-IEs ::= SEQUENCE {

    ue-Identity                          InitialUE-Identity,

    establishmentCause                   EstablishmentCause,

    spare                                BIT STRING (SIZE (1))

}

 

InitialUE-Identity ::= CHOICE {

   ng-5G-S-TMSI-Part1                    BIT STRING (SIZE (39)),

   randomValue                           BIT STRING (SIZE (39))

}

 

EstablishmentCause ::= ENUMERATED {

   emergency,

   highPriorityAccess,

   mt-Access,

   mo-Signalling,

   mo-Data,

   mo-VoiceCall,

   mo-VideoCall,

   mo-SMS,

   mps-PriorityAccess,

   mcs-PriorityAccess,

   spare6, spare5, spare4, spare3, spare2, spare1}

USIM Information for UAC

EFUAC_AIC (UAC Access Identities Configuration) : 31.102-4.4.11.7

EFUAC_ACC (Access Control Class) : 31.102-4.2.15

How to determine Access Identity ?

Basically Access Identity is determined by a few parameters in UICC as described in the following table.

< 24.501-Table 4.5.2.1: Access identities >

What kind of service can be provided for a access category ?

< 24.501-Table 4.5.2.2: Mapping table for access categories >

 

Mapping between access categories/access identities and RRC establishment cause

< 24.501 - Table 4.5.6.1: Mapping table for access identities/access categories and RRC establishment cause when establishing N1 NAS signalling connection via NR connected to 5GCN >

 

< 24.501 - Table 4.5.6.2: Mapping table for access identities/access categories and RRC establishment cause when establishing N1 NAS signalling connection via E-UTRA connected to 5GCN >

Reference

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