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RRC5GgNB -> UE3GPP TS 38.331
5G NR - System Information Block 11 (SIB11)
System Information Block 11 (SIB11) is an NR broadcast system information block used to provide idle and inactive measurement configuration for the UE.
Message Fact Sheet
Protocol
rrc
Network
5g
Spec
3GPP TS 38.331
Spec Section
5.2.1, 5.2.2, 6.3.2
Direction
gNB -> UE
Message Type
Broadcast System Information
Full message name
5G NR - System Information Block 11 (SIB11)
Protocol
RRC
Technology
5G
Direction
gNB -> UE
Interface
Uu
Signaling bearer / channel
Broadcast transport / BCCH-DL-SCH
Typical trigger
Broadcast by the cell as additional system information when the UE needs idle or inactive measurement configuration from system information.
Main purpose
Provides measurement-related configuration so the UE can perform idle or inactive measurements in line with the serving cell's broadcast policy.
Main specification
3GPP TS 38.331, 5.2.1, 5.2.2, 6.3.2
Release added
Release 16
Procedures where used
System Information Acquisition, Idle Measurements, Inactive Measurements, Cell Reselection
Related timers
SIB11 does not use a dedicated UE-specific transaction timer, Measurement behavior depends on the validity and refresh of the broadcast measurement configuration
Related cause values
SIB11 does not carry reject causes, Problems are usually inferred from missing acquisition, missing measurements, or mobility behavior that does not match the configured measurement policy
What is System Information Block 11 (SIB11) in simple terms?
System Information Block 11 (SIB11) is an NR broadcast system information block used to provide idle and inactive measurement configuration for the UE.
Provides measurement-related configuration so the UE can perform idle or inactive measurements in line with the serving cell's broadcast policy.
Why this message matters
SIB11 is the 5G NR broadcast block that mainly tells the UE what to measure while it is idle or inactive.
Where this message appears in the call flow
System Information Acquisition
Call flow position: Read as additional broadcast information after the essential access layer is already available.
Typical state: UE is camped and expanding the measurement-related broadcast-information context.
Preconditions:
MIB and SIB1 have been acquired.
The UE knows the scheduling for additional system information.
Next likely message: UE applies the measurement configuration locally for idle or inactive operation
Idle / Inactive Measurements
Call flow position: Used when the UE needs measurement configuration from broadcast SI rather than a dedicated connected-mode message.
Typical state: UE is not in a dedicated measurement-control RRC transaction.
Preconditions:
The UE supports the measurement behavior signaled through system information.
The network broadcasts SIB11.
Next likely message: Measurement results influence reselection, search, or mobility decisions
Cell Reselection and Mobility Support
Call flow position: Provides measurement support information that contributes to later mobility decisions.
Typical state: UE may be idle, inactive, or otherwise operating with valid broadcast SI.
Preconditions:
SIB11 has been acquired successfully.
Next likely message: No direct RRC next message is required; the information is consumed locally by the UE
Next message(s): Idle measurement execution, Inactive measurement execution, Cell reselection or mobility decisions using the acquired measurement results
Message direction and transport
Sender and receiver: gNB -> UE
Interface: Uu
Domain: Access-side radio control and broadcast measurement information
Signaling bearer: Broadcast transport
Logical channel: BCCH-DL-SCH
Transport / encapsulation: RRC system information carried on BCCH-DL-SCH after the UE has acquired the essential system information and the scheduling for additional SI
Security context: Broadcast information. It is cell-common and not protected by dedicated AS security.
Message Structure Overview
SIB11 is not mainly about access, identity, or time. Its practical purpose is broadcast measurement configuration.
For engineering work, the main question is whether the idle or inactive measurement setup matches the operator's mobility design and the UE behavior seen in the field.
SIB11 becomes especially important when reselection, search, or idle/inactive mobility looks wrong even though other broadcast SIBs decode correctly.
ASN.1 for 5G NR - System Information Block 11 (SIB11)
SIB11 is typically carried inside the broader SystemInformation container. The most important practical field is measIdleConfigSIB-r16, which provides idle or inactive measurement configuration rather than dedicated connected-mode measurement control.
NR and E-UTRA carrier lists help explain what the UE is expected to measure while idle or inactive.
If the UE does not search or measure the expected frequencies, SIB11 is one of the first broadcast messages to check.
Important Information Elements
IE
Required
Description
measIdleConfigSIB-r16
Yes
The core SIB11 payload. It carries the idle or inactive measurement configuration broadcast by the network.
measIdleCarrierListNR-r16
Optional
NR carrier measurement list used when the UE should monitor additional NR frequencies while idle or inactive.
measIdleCarrierListEUTRA-r16
Optional
E-UTRA carrier measurement list used when the UE should perform idle or inactive measurements on LTE frequencies.
measurement thresholds and search configuration
Optional
Operationally important measurement settings that influence what the UE looks for and when.
serving / neighbor measurement scope
Optional
Helps engineers understand which frequencies or RATs the UE should monitor in idle or inactive.
Detailed field explanation
measIdleConfigSIB-r16
The core SIB11 payload. It carries the idle or inactive measurement configuration broadcast by the network.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
measIdleCarrierListNR-r16
NR carrier measurement list used when the UE should monitor additional NR frequencies while idle or inactive.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
measIdleCarrierListEUTRA-r16
E-UTRA carrier measurement list used when the UE should perform idle or inactive measurements on LTE frequencies.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
measurement thresholds and search configuration
Operationally important measurement settings that influence what the UE looks for and when.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
serving / neighbor measurement scope
Helps engineers understand which frequencies or RATs the UE should monitor in idle or inactive.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
What to check in logs and traces
Confirm MIB and SIB1 were decoded successfully before reviewing SIB11 behavior.
Verify that the UE actually acquired the additional SI carrying SIB11.
Check whether measIdleConfigSIB-r16 is present and complete.
Inspect the NR and E-UTRA carrier lists against the expected measurement and mobility plan.
If the UE is not measuring expected frequencies, compare SIB11 content with actual idle or inactive search behavior.
Separate broadcast measurement configuration issues from connected-mode dedicated measurement-control issues.
Common Issues and Troubleshooting
The UE does not measure the expected neighboring frequencies in idle or inactive.
Likely cause: SIB11 may be missing, incomplete, or not aligned with the intended measurement plan.
What to inspect: Check measIdleConfigSIB-r16 and the configured carrier lists.
Next step: Compare the broadcast measurement configuration with the observed UE search behavior.
Cell reselection behavior looks wrong even though SIB3 and SIB4 look reasonable.
Likely cause: The UE may not be measuring the right carriers because SIB11 configuration is incomplete or missing.
What to inspect: Check the measurement scope and configured NR / E-UTRA carrier lists.
Next step: Analyze SIB11 together with SIB3 and SIB4 instead of treating measurement and reselection separately.
Idle and inactive mobility behavior differs unexpectedly.
Likely cause: The measurement policy broadcast in SIB11 may not match what the deployment expects for those states.
What to inspect: Check whether the UE is actually applying the intended idle/inactive measurement configuration.
Next step: Correlate SIB11 acquisition timing with the observed state-specific mobility behavior.
LTE / 5G / Variant Comparison
SIB11 versus SIB3 and SIB4
SIB3 and SIB4 focus on reselection policy. SIB11 focuses on the measurement configuration that may feed those later mobility decisions.
SIB11 versus dedicated RRC measurement control
SIB11 is broadcast measurement information for idle or inactive behavior, not a UE-specific connected-mode measurement-control message.
FAQ
What is SIB11 in 5G NR?
SIB11 is System Information Block 11, an NR broadcast block used mainly to provide idle and inactive measurement configuration.
Who sends SIB11?
The gNB broadcasts SIB11 as additional system information.
What is the main purpose of SIB11?
To provide measurement configuration the UE can use while idle or inactive.
On which channel is SIB11 sent?
SIB11 is carried in system information on BCCH-DL-SCH.
Why is SIB11 useful in troubleshooting?
Because it helps explain why a UE may not measure expected frequencies or may behave unexpectedly during idle or inactive mobility.
Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.