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4G/LTE - Basic Procedure |
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SIB(System Information Block) Modification/Notification
System Information Block does not changes as any other RRC messages, but it is not stay all the time like the print on a stone. SIB does changes in some cases. When the SIBs are changes, there should be some mechanism by which UE can be informed or can detect the changes and update the changed contents. In this page, I will talk about this process.
< How Network informs SIB changes >
When a Network changes some information in a SIB, it would do a sequence of procedure as follows. i) Transmit the modified SIB ii) Transmit the SIB1 with changed systemInfoValueTag value iii) Transmit a Paging message with systemInfoModification = true
< When UE tries checking SIB changes >
UE tries checking SIB changes in any of following cases i) detected systemInfoValueTag changes within a modification period specified by modificationPeriodCoeff in SIB2 ii) received Paging message with systemInfoModification = true
< 3GPP Description on SIB Changes and Notification >
Following is some of the clips (quotes) from 3GPP 36.331 about SIB changes and Notification. It may not sound very clear at the first glance, but I put these down to give you original source and formal descriptions.
36.331 - 5.2.1.3 System information validity and notification of changes
When the network changes (some of the) system information, it first notifies the UEs about this change, i.e. this may be done throughout a modification period. ... The Paging message is used to inform UEs in RRC_IDLE and UEs in RRC_CONNECTED about a system information change. If the UE is in RRC_CONNECTED or uses a DRX cycle shorter than or equal to the modification period, and receives a Paging message including the systemInfoModification, it knows that the system information will change at the next modification period boundary ... SystemInformationBlockType1 (or MasterInformationBlock-NB in NB-IoT) includes a value tag systemInfoValueTag, that indicates if a change has occurred in the SI messages. UEs may use systemInfoValueTag, e.g. upon return from out of coverage, to verify if the previously stored SI messages are still valid ....
The UE using a DRX cycle shorter than or equal to the modification period verifies that stored system information remains valid by either checking systemInfoValueTag in SystemInformationBlockType1 (or MasterInformationBlock-NB in NB-IoT) after the modification period boundary, or attempting to find the systemInfoModification indication at least modificationPeriodCoeff times during the modification period in case no paging is received, in every modification period. If no paging message is received by the UE during a modification period, the UE may assume that no change of system information will occur at the next modification period boundary.
36.331 - 5.3.2.3 Reception of the Paging message by the UE
Upon receiving the Paging message, the UE shall: ... 1> if the systemInfoModification is included; or 1> if the UE is configured with a DRX cycle longer than the modification period and the systemInfoModification-eDRX is included: 2> re-acquire the required system information using the system information acquisition procedure ...
Example 1 > SIB Modification - SIB1 Contents
In this example, I will show you a case where an IE (Information Elements) in SIB1 is changed. Since the changed IE and systemInfoValueTag is in the same SIB (SIB 1), eNB would trigger only two steps after the change as follows. i) transmit the changed SIB 1 with the modified systemInfoValueTag and modified contents ii) transmit Paging
< Original SIBs > ============================================
c1: systemInformationBlockType1 (1) ------------------------------------------------ systemInformationBlockType1 cellAccessRelatedInfo plmn-IdentityList: 1 item Item 0 PLMN-IdentityInfo plmn-Identity ... cellReservedForOperatorUse: notReserved (1) trackingAreaCode: 0001 cellIdentity: 00000000 cellBarred: notBarred (1) intraFreqReselection: notAllowed (1) .... ..0. csg-Indication: False cellSelectionInfo q-RxLevMin: -110dBm (-55) p-Max: 23dBm freqBandIndicator: 4 schedulingInfoList: 2 items Item 0 SchedulingInfo si-Periodicity: rf16 (1) sib-MappingInfo: 0 items Item 1 SchedulingInfo si-Periodicity: rf32 (2) sib-MappingInfo: 1 item Item 0 SIB-Type: sibType3 (0) si-WindowLength: ms20 (5) systemInfoValueTag: 0 nonCriticalExtension nonCriticalExtension ims-EmergencySupport-r9: true (0)
c1: systemInformation (0) ------------------------------------------------ systemInformation criticalExtensions: systemInformation-r8 (0) systemInformation-r8 sib-TypeAndInfo: 1 item Item 0 sib-TypeAndInfo item: sib2 (0) sib2 radioResourceConfigCommon rach-ConfigCommon ... maxHARQ-Msg3Tx: 4 bcch-Config modificationPeriodCoeff: n4 (1) pcch-Config defaultPagingCycle: rf128 (2) nB: oneT (2) prach-Config ... pdsch-ConfigCommon referenceSignalPower: 18dBm p-b: 0 pusch-ConfigCommon .... pucch-ConfigCommon ... soundingRS-UL-ConfigCommon: release (0) release: NULL uplinkPowerControlCommon ... ul-CyclicPrefixLength: len1 (0) ue-TimersAndConstants t300: ms1000 (5) t301: ms1000 (5) t310: ms1000 (5) n310: n1 (0) t311: ms1000 (0) n311: n1 (0) freqInfo additionalSpectrumEmission: 1 timeAlignmentTimerCommon: infinity (7)
c1: systemInformation (0) ------------------------------------------------ systemInformation criticalExtensions: systemInformation-r8 (0) systemInformation-r8 sib-TypeAndInfo: 1 item Item 0 sib-TypeAndInfo item: sib3 (1) sib3 cellReselectionInfoCommon q-Hyst: dB0 (0) cellReselectionServingFreqInfo s-NonIntraSearch: 16dB (8) threshServingLow: 16dB (8) cellReselectionPriority: 4 intraFreqCellReselectionInfo q-RxLevMin: -110dBm (-55) p-Max: 23dBm s-IntraSearch: 16dB (8) .... ...0 presenceAntennaPort1: False neighCellConfig: No MBSFN subframes are present... t-ReselectionEUTRA: 0s
< After SIB Changes > ============================================
c1: systemInformationBlockType1 (1) ------------------------------------------------ systemInformationBlockType1 cellAccessRelatedInfo plmn-IdentityList: 1 item Item 0 PLMN-IdentityInfo plmn-Identity .... cellReservedForOperatorUse: notReserved (1) trackingAreaCode: 0001 cellIdentity: 00000000 cellBarred: notBarred (1) intraFreqReselection: notAllowed (1) .... ..0. csg-Indication: False cellSelectionInfo q-RxLevMin: -120dBm (-60) p-Max: 23dBm freqBandIndicator: 4 schedulingInfoList: 2 items Item 0 SchedulingInfo si-Periodicity: rf16 (1) sib-MappingInfo: 0 items Item 1 SchedulingInfo si-Periodicity: rf32 (2) sib-MappingInfo: 1 item Item 0 SIB-Type: sibType3 (0) si-WindowLength: ms20 (5) systemInfoValueTag: 1 nonCriticalExtension nonCriticalExtension ims-EmergencySupport-r9: true (0)
c1: paging (0) ------------------------------------------------ paging systemInfoModification: true (0)
Example 2 > SIB Modification - SIB2 Contents
In this example, I will show you a case where an IE (Information Elements) in SIB2 is changed. Since the changed IE and systemInfoValueTag are in different SIBs (SIB 1 and SIB2), eNB would trigger three steps after the change as follows. i) transmit the changed SIB2 ii) transmit SIB 1 with the modified systemInfoValueTag iii) transmit Paging
< Original SIBs > ============================================
c1: systemInformationBlockType1 (1) ------------------------------------------------ systemInformationBlockType1 cellAccessRelatedInfo plmn-IdentityList: 1 item Item 0 PLMN-IdentityInfo plmn-Identity ... cellReservedForOperatorUse: notReserved (1) trackingAreaCode: 0001 cellIdentity: 00000000 cellBarred: notBarred (1) intraFreqReselection: notAllowed (1) .... ..0. csg-Indication: False cellSelectionInfo q-RxLevMin: -110dBm (-55) p-Max: 23dBm freqBandIndicator: 4 schedulingInfoList: 2 items Item 0 SchedulingInfo si-Periodicity: rf16 (1) sib-MappingInfo: 0 items Item 1 SchedulingInfo si-Periodicity: rf32 (2) sib-MappingInfo: 1 item Item 0 SIB-Type: sibType3 (0) si-WindowLength: ms20 (5) systemInfoValueTag: 0 nonCriticalExtension nonCriticalExtension ims-EmergencySupport-r9: true (0)
c1: systemInformation (0) ------------------------------------------------ systemInformation criticalExtensions: systemInformation-r8 (0) systemInformation-r8 sib-TypeAndInfo: 1 item Item 0 sib-TypeAndInfo item: sib2 (0) sib2 radioResourceConfigCommon rach-ConfigCommon ... maxHARQ-Msg3Tx: 4 bcch-Config modificationPeriodCoeff: n4 (1) pcch-Config defaultPagingCycle: rf128 (2) nB: oneT (2) prach-Config ... pdsch-ConfigCommon referenceSignalPower: 18dBm p-b: 0 pusch-ConfigCommon .... pucch-ConfigCommon ... soundingRS-UL-ConfigCommon: release (0) release: NULL uplinkPowerControlCommon ... ul-CyclicPrefixLength: len1 (0) ue-TimersAndConstants t300: ms1000 (5) t301: ms1000 (5) t310: ms1000 (5) n310: n1 (0) t311: ms1000 (0) n311: n1 (0) freqInfo additionalSpectrumEmission: 1 timeAlignmentTimerCommon: infinity (7)
c1: systemInformation (0) ------------------------------------------------ systemInformation criticalExtensions: systemInformation-r8 (0) systemInformation-r8 sib-TypeAndInfo: 1 item Item 0 sib-TypeAndInfo item: sib3 (1) sib3 cellReselectionInfoCommon q-Hyst: dB0 (0) cellReselectionServingFreqInfo s-NonIntraSearch: 16dB (8) threshServingLow: 16dB (8) cellReselectionPriority: 4 intraFreqCellReselectionInfo q-RxLevMin: -110dBm (-55) p-Max: 23dBm s-IntraSearch: 16dB (8) .... ...0 presenceAntennaPort1: False neighCellConfig: No MBSFN subframes are present... t-ReselectionEUTRA: 0s
< After SIB Changes > ============================================
c1: systemInformationBlockType1 (1) ------------------------------------------------ systemInformationBlockType1 cellAccessRelatedInfo plmn-IdentityList: 1 item Item 0 PLMN-IdentityInfo plmn-Identity .... cellReservedForOperatorUse: notReserved (1) trackingAreaCode: 0001 cellIdentity: 00000000 cellBarred: notBarred (1) intraFreqReselection: notAllowed (1) .... ..0. csg-Indication: False cellSelectionInfo q-RxLevMin: -110dBm (-55) p-Max: 23dBm freqBandIndicator: 4 schedulingInfoList: 2 items Item 0 SchedulingInfo si-Periodicity: rf16 (1) sib-MappingInfo: 0 items Item 1 SchedulingInfo si-Periodicity: rf32 (2) sib-MappingInfo: 1 item Item 0 SIB-Type: sibType3 (0) si-WindowLength: ms20 (5) systemInfoValueTag: 1 nonCriticalExtension nonCriticalExtension ims-EmergencySupport-r9: true (0)
c1: systemInformation (0) ------------------------------------------------ systemInformation criticalExtensions: systemInformation-r8 (0) systemInformation-r8 sib-TypeAndInfo: 1 item Item 0 sib-TypeAndInfo item: sib2 (0) sib2 ac-BarringInfo ...1 .... ac-BarringForEmergency: True ac-BarringForMO-Signalling ac-BarringFactor: p00 (0) ac-BarringTime: s4 (0) ac-BarringForSpecialAC: f8 ac-BarringForMO-Data ac-BarringFactor: p00 (0) ac-BarringTime: s4 (0) ac-BarringForSpecialAC: f8 radioResourceConfigCommon rach-ConfigCommon ... bcch-Config modificationPeriodCoeff: n4 (1) pcch-Config defaultPagingCycle: rf128 (2) nB: oneT (2) prach-Config ... pdsch-ConfigCommon referenceSignalPower: 18dBm p-b: 0 pusch-ConfigCommon ... pucch-ConfigCommon ... soundingRS-UL-ConfigCommon: release (0) release: NULL uplinkPowerControlCommon ... ul-CyclicPrefixLength: len1 (0) ue-TimersAndConstants t300: ms1000 (5) t301: ms1000 (5) t310: ms1000 (5) n310: n1 (0) t311: ms1000 (0) n311: n1 (0) freqInfo additionalSpectrumEmission: 1 timeAlignmentTimerCommon: infinity (7)
c1: paging (0) ------------------------------------------------ paging systemInfoModification: true (0)
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