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RRC5GgNB -> UE3GPP TS 38.331
5G NR - System Information Block 9 (SIB9)
System Information Block 9 (SIB9) is an NR broadcast system information block used to convey time information such as UTC and GPS-related timing context to the UE.
Message Fact Sheet
Protocol
rrc
Network
5g
Spec
3GPP TS 38.331
Spec Section
5.2.1, 5.2.2, 6.3.1
Direction
gNB -> UE
Message Type
Broadcast System Information
Full message name
5G NR - System Information Block 9 (SIB9)
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 network provides time information services through NR system information.
Main purpose
Provides wall-clock and reference-time information so the UE can derive UTC, GPS time, and related local-time context when the network offers that capability.
Main specification
3GPP TS 38.331, 5.2.1, 5.2.2, 6.3.1
Release added
Release 15
Procedures where used
System Information Acquisition, Network Time Acquisition, Idle Operation, Connected Operation
Related timers
SIB9 does not use a dedicated UE-specific transaction timer, Time interpretation depends on SI acquisition timing and the validity of the broadcast reference
Related cause values
SIB9 does not carry reject causes, Problems are usually inferred from missing acquisition, stale time information, or wrong UTC / local time behavior at the UE
What is System Information Block 9 (SIB9) in simple terms?
System Information Block 9 (SIB9) is an NR broadcast system information block used to convey time information such as UTC and GPS-related timing context to the UE.
Provides wall-clock and reference-time information so the UE can derive UTC, GPS time, and related local-time context when the network offers that capability.
Why this message matters
SIB9 is the 5G NR broadcast block that mainly gives the UE network time information such as UTC and GPS-related timing context.
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 broadcast-information context beyond access and mobility.
Preconditions:
MIB and SIB1 have been acquired.
The UE knows the scheduling for additional system information.
Next likely message: UE applies the time information locally or continues normal operation using the new reference
Network Time Acquisition
Call flow position: Used when the UE needs network-broadcast time information such as UTC or GPS-related context.
Typical state: UE is not necessarily in a dedicated UE-specific RRC transaction.
Preconditions:
The network broadcasts SIB9.
The UE is capable of using the broadcast time information.
Next likely message: Local time derivation, GPS conversion, or service behavior using the broadcast timing reference
Idle / Connected Time Alignment
Call flow position: Provides time reference information that may be used by the UE outside a dedicated message transaction.
Typical state: UE may be camped, idle, inactive, or otherwise operating with valid broadcast SI.
Preconditions:
SIB9 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): Time synchronization usage in the UE, Idle or connected operation using network time context, Later access and service behavior using aligned time reference
Message direction and transport
Sender and receiver: gNB -> UE
Interface: Uu
Domain: Access-side radio control and broadcast system 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
SIB9 is not mainly about access or mobility. Its practical purpose is broadcast time transfer.
For engineering work, the main question is whether the network-broadcast time information is present, current, and interpreted correctly by the UE.
SIB9 becomes especially important when devices show wrong network time, wrong time zone behavior, or service issues tied to time alignment.
ASN.1 for 5G NR - System Information Block 9 (SIB9)
SIB9 is typically carried inside the broader SystemInformation container. The most important practical field is timeInfo, which conveys UTC and GPS-related timing context with broadcast semantics rather than UE-specific signaling.
UTC-related fields explain the wall-clock time the UE can derive from the network.
leapSeconds matters when converting between UTC and GPS-related time domains.
Local offset or DST-related fields, when present, help explain why displayed local time looks correct or incorrect.
Important Information Elements
IE
Required
Description
timeInfo
Yes
The core SIB9 payload. It carries time-related information used to derive UTC and related timing context.
utc-Time
Optional
Broadcast UTC-related information with the network-defined accuracy and interpretation rules.
leapSeconds
Optional
Helps the UE convert between UTC and GPS-related time domains correctly.
daylightSavingTime / local time offset context
Optional
Additional fields may help the UE derive local time behavior when that information is broadcast.
reference boundary context
Optional
Operationally important timing reference details that explain exactly which radio-frame or SI-window boundary the time refers to.
Detailed field explanation
timeInfo
The core SIB9 payload. It carries time-related information used to derive UTC and related timing context.
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.
utc-Time
Broadcast UTC-related information with the network-defined accuracy and interpretation rules.
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.
leapSeconds
Helps the UE convert between UTC and GPS-related time domains correctly.
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.
daylightSavingTime / local time offset context
Additional fields may help the UE derive local time behavior when that information is broadcast.
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.
reference boundary context
Operationally important timing reference details that explain exactly which radio-frame or SI-window boundary the time refers to.
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 SIB9 behavior.
Verify that the UE actually acquired the additional SI carrying SIB9.
Check whether timeInfo is present, current, and internally consistent.
Inspect leap-second and local offset related values when UTC and local time do not match expectations.
Correlate the SIB9 time reference with the radio-frame or SI-window timing context if the implementation exposes it.
If the UE shows incorrect time, compare SIB9 content with the device's applied time and time-zone state.
Common Issues and Troubleshooting
The UE shows the wrong network time.
Likely cause: SIB9 may be missing, stale, or carrying unexpected time or offset information.
What to inspect: Check timeInfo, utc-Time, leapSeconds, and any local-time offset related fields.
Next step: Compare the decoded SIB9 values with the final time shown on the device.
UTC looks correct but local time is wrong.
Likely cause: The issue may be in local offset or daylight-saving interpretation rather than the UTC base time itself.
What to inspect: Check any local offset or DST-related fields and how the UE applies them.
Next step: Separate UTC correctness from local-time derivation during debugging.
Time synchronization behavior is unstable or delayed.
Likely cause: The UE may not be reacquiring SIB9 consistently, or the broadcast reference may not align with expectations.
What to inspect: Check SI scheduling, reacquisition timing, and whether the UE is actually consuming the updated SIB9 content.
Next step: Correlate SIB9 acquisition timing with the observed user-visible time change.
LTE / 5G / Variant Comparison
SIB9 versus SIB5 to SIB8
SIB5 to SIB8 are mainly about inter-RAT mobility. SIB9 is mainly about broadcast time information.
SIB9 versus dedicated RRC
SIB9 is broadcast cell-common time information, not UE-specific connected-mode configuration.
FAQ
What is SIB9 in 5G NR?
SIB9 is System Information Block 9, an NR broadcast block used mainly to provide network time information such as UTC and GPS-related timing context.
Who sends SIB9?
The gNB broadcasts SIB9 as additional system information.
What is the main purpose of SIB9?
To provide broadcast time information that the UE can use to derive UTC, GPS-related time, and sometimes local time context.
On which channel is SIB9 sent?
SIB9 is carried in system information on BCCH-DL-SCH.
Why is SIB9 useful in troubleshooting?
Because it helps explain why a UE may show incorrect network time or inconsistent time alignment.
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.