Below are the steps how do UE read when there is a modification of sib from NW side.
This we can get from below test case according 3GPP spec TS-36.523-1
8.1.1.2 RRC / Paging for notification of BCCH modification in idle mode
According the Test Case Below is the steps included for the Test case,
Main Steps in this test cases are 1,5,6,7 and 7a.
Step 1 verifies whether the UE is able respond to paging or not after the attach which is without any SI modification. In-fact this during this attach whatever SI has been transmitted are the scale to determine about the SI changes done by NW.
Step 5 NW transmits a paging like below,
Air Message: AIR_MSG_TYPE_PCCH   
        paging  Paging 
          systemInfoModification PagingsystemInfoModification_true  
          pagingRecordList_exist         0  
          systemInfoModification_exist 1  
          etws_Indication_exist                 0  
          nonCriticalExtension_exist         0 
As this is applicable to all the UE on that eNB so this kind of Paging doesn't include any UE identity.
Step 6 ensures that UE receive's the changed system information.
         This will be done by in this test scenario,
          First UE will go and read SIB1 - which will have SystemInfoValueTag as 1 in this case.
          Then UE will go and read SIB2 according scheduling Info provided by the new SIB1.
           This test case includes only PRACH CONFIG INDEX changed in SIB2 as below,
Previously:
prach_ConfigIndex
 3
  
Now:
prach_ConfigIndex
 10
  
Step 7  and 7a is just for checking whether UE is able to setup RRC Connection with NW or not?
         This steps will not be happening in case of live NW.
          Here NW pages (
Step 7) UE with Paging message as below with S-Tmsi and UE establishes Rrc Connection Successfully (
Step 7a).
Air Message: AIR_MSG_TYPE_PCCH   
  
          pagingRecordList_exist         1  
          systemInfoModification_exist 0  
          etws_Indication_exist                 0  
          nonCriticalExtension_exist         0 
        pagingRecordList[0]  PagingRecord 
            ue_Identity  PagingUE_Identity_ 
              s_TMSI  S_TMSI 
                mmec  MMEC 
                  buff[0..0] 01   
                TMSI  S_TMSIm_TMSI 
                  buff[0..3] c2 34 56 78   
 
        
 
  
St 
 | 
  
Procedure 
 | 
  
Message Sequence 
 | 
  
TP 
 | 
  
Verdict 
 | 
 
  
  
 | 
  
  
 | 
  
U - S 
 | 
  
Message 
 | 
  
  
 | 
  
  
 | 
 
  
1 
 | 
  
The SS transmits a Paging message including
  a matched identity. 
 | 
  
<-- 
 | 
  
Paging 
 | 
  
- 
 | 
  
- 
 | 
 
  
2 
 | 
  
Check: Does the UE transmit an RRCConnectionRequest
  message? 
 | 
  
--> 
 | 
  
RRCConnectionRequest 
 | 
  
1 
 | 
  
P 
 | 
 
  
3 
 | 
  
The SS transmits an RRCConnectionSetup
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionSetup 
 | 
  
- 
 | 
  
- 
 | 
 
  
3A 
 | 
  
The UE transmits an RRCConnectionSetupComplete
  message. 
This message includes a SERVICE REQUEST
  message. 
 | 
  
--> 
 | 
  
RRCConnectionSetupComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
3B 
 | 
  
The SS transmits a SecurityModeCommand
  message. 
 | 
  
<-- 
 | 
  
SecurityModeCommand 
 | 
  
- 
 | 
  
- 
 | 
 
  
3C 
 | 
  
The UE transmits a SecurityModeComplete
  message. 
 | 
  
--> 
 | 
  
SecurityModeComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
3D 
 | 
  
The SS transmits an RRCConnectionReconfiguration
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionReconfiguration 
 | 
  
- 
 | 
  
- 
 | 
 
  
3E 
 | 
  
The UE transmits an RRCConnectionReconfigurationComplete
  message. 
 | 
  
--> 
 | 
  
RRCConnectionReconfigurationComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
3F 
 | 
  
The SS transmits an RRCConnectionRelease
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionRelease 
 | 
  
- 
 | 
  
- 
 | 
 
  
3G 
 | 
  
Wait for 5 s for the UE to enter E-UTRA
  RRC_IDLE state. 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
 
  
4 
 | 
  
The SS changes the prach-ConfigIndex in
  the system information 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
 
  
5 
 | 
  
The SS transmits a Paging message including a systemInfoModification. 
 | 
  
<-- 
 | 
  
Paging 
 | 
  
- 
 | 
  
- 
 | 
 
  
6 
 | 
  
Wait for 15s for the UE to receive system
  information. 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
 
  
7 
 | 
  
The SS transmits a Paging message
  including a matched identity. 
 | 
  
<-- 
 | 
  
Paging 
 | 
  
- 
 | 
  
- 
 | 
 
  
7A 
 | 
  
Check: Does the UE re-transmit a random access
  using prach-ConfigIndex given in step 4? 
 | 
  
- 
 | 
  
- 
 | 
  
1 
 | 
  
P 
 | 
 
  
8 
 | 
  
The UE transmit an RRCConnectionRequest
  message. 
 | 
  
--> 
 | 
  
RRCConnectionRequest 
 | 
  
- 
 | 
  
- 
 | 
 
  
9 
 | 
  
The SS transmits an RRCConnectionSetup
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionSetup 
 | 
  
- 
 | 
  
- 
 | 
 
  
9A 
 | 
  
The UE transmits an RRCConnectionSetupComplete
  message. 
This message includes a SERVICE REQUEST
  message. 
 | 
  
--> 
 | 
  
RRCConnectionSetupComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
9B 
 | 
  
The SS transmits a SecurityModeCommand
  message. 
 | 
  
<-- 
 | 
  
SecurityModeCommand 
 | 
  
- 
 | 
  
- 
 | 
 
  
9C 
 | 
  
The UE transmits a SecurityModeComplete
  message. 
 | 
  
--> 
 | 
  
SecurityModeComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
9D 
 | 
  
The SS transmits an RRCConnectionReconfiguration
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionReconfiguration 
 | 
  
- 
 | 
  
- 
 | 
 
  
9E 
 | 
  
The UE transmits an RRCConnectionReconfigurationComplete
  message. 
 | 
  
--> 
 | 
  
RRCConnectionReconfigurationComplete 
 | 
  
- 
 | 
  
- 
 | 
 
  
9F 
 | 
  
The SS transmits an RRCConnectionRelease
  message. 
 | 
  
<-- 
 | 
  
RRCConnectionRelease 
 | 
  
- 
 | 
  
- 
 | 
 
  
9G 
 | 
  
Wait for 5 s for the UE to enter E-UTRA
  RRC_IDLE state. 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
  
- 
 | 
 
  
10 
 | 
  
Check: Does the test result of generic
  test procedure in TS 36.508 subclause 6.4.2.2 indicate that the
  UE is in E-UTRA RRC_IDLE state on Cell 1? 
 | 
  
- 
 | 
  
- 
 | 
  
1 
 | 
  
- 
 |