5G NR - System Information Block 19 (SIB19)

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.2.2.4.20, 6.3.1
Direction	gNB -> UE	Message Type	Broadcast System Information

Full message name	5G NR - System Information Block 19 (SIB19)
Protocol	RRC
Technology	5G
Direction	gNB -> UE
Interface	Uu
Signaling bearer / channel	Broadcast transport / BCCH-DL-SCH
Typical trigger	Broadcast by an NTN-capable serving cell when UEs need NTN-specific system information for access, synchronization support, and NTN-aware mobility behavior.
Main purpose	Provides the NTN broadcast information the UE needs to access and operate on non-terrestrial NR cells, including parameters used for timing, mobility support, and NTN-specific access behavior.
Main specification	3GPP TS 38.331, 5.2.2.4.20, 6.3.1
Release added	Release 17
Procedures where used	System Information Acquisition, NTN Initial Access, NTN Mobility and Neighbor Awareness
Related timers	SIB19 does not use a dedicated UE-specific transaction timer, Interpretation depends on SI acquisition timing and the validity of the NTN-specific broadcast information
Related cause values	SIB19 does not carry reject causes, Problems are usually inferred from missing SI acquisition, wrong NTN parameter interpretation, or access behavior that does not match the broadcast configuration

What is System Information Block 19 (SIB19) in simple terms?

System Information Block 19 (SIB19) is an NR broadcast system information block used to provide NTN-specific parameters for the serving cell and, when present, neighboring NTN cells.

Provides the NTN broadcast information the UE needs to access and operate on non-terrestrial NR cells, including parameters used for timing, mobility support, and NTN-specific access behavior.

Why this message matters

SIB19 is the 5G NR broadcast block that gives the UE the NTN-specific information it needs to work correctly on satellite or other non-terrestrial NR cells.

Where this message appears in the call flow

System Information Acquisition

Call flow position: Read as additional broadcast information after MIB and SIB1 are already available.

Typical state: UE is camped and expanding the broadcast-information context for NTN access.

Preconditions:

MIB and SIB1 have been acquired.
The UE knows the scheduling for additional system information.
The serving cell supports NTN operation.

Next likely message: UE applies the NTN-specific broadcast parameters locally

NTN Initial Access

Call flow position: Used before or during access preparation when the UE needs NTN-specific parameters such as timing-related or ephemeris-related information.

Typical state: UE is preparing for NTN-aware access behavior rather than using only terrestrial assumptions.

Preconditions:

The UE supports NTN operation.
The serving cell broadcasts SIB19.

Next likely message: NTN-aware PRACH or later RRC access signaling

NTN Mobility and Neighbor Awareness

Call flow position: Relevant when the cell also broadcasts NTN-specific parameters for neighboring cells.

Typical state: UE has valid serving-cell broadcast information and may use the NTN neighbor context for mobility-related behavior.

Preconditions:

SIB19 has been acquired successfully.

Next likely message: No direct next RRC message is required; the information is consumed locally by the UE

Call flow position

Previous message(s): MIB, System Information Block 1 (SIB1), Initial Access

Next message(s): NTN-aware random access preparation, NTN timing and synchronization adjustment, RRC Setup Request

Message direction and transport

Sender and receiver: gNB -> UE

Interface: Uu

Domain: Access-side radio control and NTN broadcast 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

SIB19 is an NTN-focused broadcast block, not a generic terrestrial mobility or service-information SIB.
Its practical value is that it gives the UE the NTN-specific parameters needed to behave correctly in non-terrestrial access conditions.
For engineering work, SIB19 becomes especially important when NTN access, timing alignment, Doppler handling, or NTN mobility behavior does not match the deployment expectation.

ASN.1 for 5G NR - System Information Block 19 (SIB19)

BCCH-DL-SCH-Message ::= SEQUENCE {
  message CHOICE {
    c1 CHOICE {
      systemInformationBlockType1 SystemInformationBlockType1,
      systemInformation          SystemInformation,
      ...
    },
    ...
  }
}

SystemInformation ::= SEQUENCE {
  criticalExtensions CHOICE {
    systemInformation SystemInformation-IEs,
    ...
  }
}

SystemInformation-IEs ::= SEQUENCE {
  sib-TypeAndInfo SEQUENCE (SIZE (1..maxSIB)) OF CHOICE {
    sib19 SystemInformationBlockType19-r17,
    ...
  }
}

SystemInformationBlockType19-r17 ::= SEQUENCE {
  distanceThresh-r17    INTEGER OPTIONAL,
  ntn-Config-r17        NTN-Config-r17,
  ...
}

How to read this ASN.1

SIB19 is typically carried inside the broader SystemInformation container. In practice, the most important field is ntn-Config-r17, because that is where the serving cell exposes the NTN-specific parameters the UE needs.

Decoded Message Dump

BCCH-DL-SCH-Message
  message: c1
    systemInformation
      criticalExtensions
        systemInformation
          sib-TypeAndInfo
            sib19
              distanceThresh-r17: 20
              ntn-Config-r17
                epochTime-r17: present
                kOffset-r17: present
                ta-Info-r17: present

How to read this dump

The key practical block is ntn-Config-r17.
distanceThresh-r17 is useful when engineers are validating NTN location-based measurement or behavior triggers.
If NTN access or synchronization is wrong, first confirm that the UE actually decoded the expected SIB19 content.

Important Information Elements

IE	Required	Description
`ntn-Config-r17`	Yes	The core SIB19 payload. It carries the NTN-specific parameters needed by the UE for NTN access and operation.
`distanceThresh-r17`	Optional	Used for position-based behavior in idle or inactive NTN-related measurements and operation.
`neighborCellConfig-r17`	Optional	Optional NTN-specific parameters for neighboring cells when the deployment broadcasts them.
`epoch and ephemeris-related information`	Optional	Operationally important NTN context used to support timing, synchronization, and satellite-aware behavior.

Detailed field explanation

`ntn-Config-r17`

The core SIB19 payload. It carries the NTN-specific parameters needed by the UE for NTN access and operation.

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.

`distanceThresh-r17`

Used for position-based behavior in idle or inactive NTN-related measurements and operation.

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.

`neighborCellConfig-r17`

Optional NTN-specific parameters for neighboring cells when the deployment broadcasts them.

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.

`epoch and ephemeris-related information`

Operationally important NTN context used to support timing, synchronization, and satellite-aware behavior.

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 SIB19 behavior.
Verify that the UE actually acquired the additional SI carrying SIB19.
Check whether ntn-Config-r17 is present and complete.
Inspect timing-related, epoch-related, or NTN synchronization-related fields against observed UE behavior.
If NTN access fails, separate missing SIB19 acquisition from PRACH, RF, or core-network issues.
Where neighbor NTN information is broadcast, compare serving-cell and neighbor-cell NTN assumptions with the trace behavior.

Common Issues and Troubleshooting

The UE cannot access the NTN cell correctly.

Likely cause: SIB19 may be missing, incomplete, or not decoded correctly, so the UE lacks the NTN-specific parameters it needs.

What to inspect: Check that SIB19 was scheduled, acquired, and decoded, especially ntn-Config-r17.

Next step: Correlate the SIB19 content with PRACH, timing-advance, and synchronization behavior.

The UE sees the NTN cell but timing or synchronization behavior is unstable.

Likely cause: The NTN-specific timing context from SIB19 may be missing, stale, or inconsistent with the deployment.

What to inspect: Check epoch-related and timing-related SIB19 fields against the observed UE behavior.

Next step: Verify the broadcast NTN parameters before assuming the issue is only RF or implementation-related.

NTN neighbor behavior or mobility assumptions look wrong.

Likely cause: Optional neighboring-cell NTN information may be absent or not aligned with the intended network configuration.

What to inspect: Check whether SIB19 includes the relevant NTN neighbor-cell information.

Next step: Compare the broadcast neighbor assumptions with the actual NTN cell behavior in traces.

LTE / 5G / Variant Comparison

SIB19 versus terrestrial broadcast SI

Unlike the classic terrestrial SIBs, SIB19 focuses on NTN-specific parameters needed for non-terrestrial operation.

SIB19 versus MIB and SIB1

MIB and SIB1 give the UE the essential access and scheduling context. SIB19 adds NTN-specific broadcast parameters needed for correct NTN behavior.

FAQ

What is SIB19 in 5G NR?

SIB19 is System Information Block 19, an NR broadcast block used to carry NTN-specific parameters for the serving cell and optionally neighboring NTN cells.

Who sends SIB19?

The gNB or NTN-capable serving cell broadcasts SIB19 as additional system information.

What is the main purpose of SIB19?

To provide NTN-specific broadcast information needed for correct access, synchronization, and NTN-aware UE behavior.

On which channel is SIB19 sent?

SIB19 is carried in system information on BCCH-DL-SCH.

Why is SIB19 useful in troubleshooting?

Because it helps explain why NTN access, timing, synchronization, or neighbor-cell behavior may not match expectations.

Does SIB19 contain UE-specific information?

No. SIB19 is broadcast cell-common information.

Related message pages

Related Procedures

5G Initial Registration

Related Tools

Use This Reference in Practice

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.