5G NR - System Information Block 14 (SIB14)

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.2.2.4.15, 6.3.1
Direction	gNB -> UE	Message Type	Broadcast System Information

Full message name	5G NR - System Information Block 14 (SIB14)
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 UEs supporting V2X sidelink communication need the related SIB14 information.
Main purpose	Provides additional broadcast V2X sidelink communication information so the UE can apply the correct V2X sidelink behavior when the cell supports that feature set.
Main specification	3GPP TS 38.331, 5.2.2.4.15, 6.3.1
Release added	Release 16
Procedures where used	System Information Acquisition, V2X Sidelink Communication, Broadcast V2X Configuration Validation
Related timers	SIB14 does not use a dedicated UE-specific transaction timer, Interpretation depends on SI acquisition timing and the validity of the broadcast V2X sidelink information
Related cause values	SIB14 does not carry reject causes, Problems are usually inferred from missing acquisition, wrong V2X configuration application, or V2X behavior that does not match the broadcast information

What is System Information Block 14 (SIB14) in simple terms?

System Information Block 14 (SIB14) is an NR broadcast system information block used to provide information related to LTE SystemInformationBlockType26 for V2X sidelink communication.

Provides additional broadcast V2X sidelink communication information so the UE can apply the correct V2X sidelink behavior when the cell supports that feature set.

Why this message matters

SIB14 is the 5G NR broadcast block that gives the UE extra V2X sidelink communication information related to LTE SystemInformationBlockType26.

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 extending its broadcast-information context for V2X sidelink operation.

Preconditions:

MIB and SIB1 have been acquired.
The UE knows the scheduling for additional system information.
The UE supports the relevant V2X sidelink capability.

Next likely message: UE applies the SIB14 broadcast information locally

V2X Sidelink Communication

Call flow position: Used when the UE needs the additional broadcast information related to SystemInformationBlockType26 for V2X sidelink communication.

Typical state: UE is not necessarily in a dedicated UE-specific RRC transaction.

Preconditions:

The UE is V2X sidelink-capable.
The serving cell broadcasts SIB14.

Next likely message: UE uses the announced V2X sidelink settings during operation

Broadcast V2X Configuration Validation

Call flow position: Relevant when engineers compare broadcast V2X information with actual UE behavior.

Typical state: UE has valid broadcast SI and observed V2X behavior can be correlated with SIB14 content.

Preconditions:

SIB14 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), System Information Block 13 (SIB13)

Next message(s): V2X sidelink communication using the acquired broadcast configuration, Later RRC connection establishment if the wider scenario requires it, Ongoing V2X sidelink monitoring and operation

Message direction and transport

Sender and receiver: gNB -> UE

Interface: Uu

Domain: Access-side radio control and broadcast V2X sidelink 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

SIB14 is an NR broadcast block for additional V2X sidelink communication information, not a generic access or mobility SIB.
Its practical value is in scenarios where SIB13 alone is not enough and the UE also needs the information related to LTE SystemInformationBlockType26.
For engineering work, SIB14 becomes relevant when V2X sidelink behavior does not match the expected broadcast configuration.

ASN.1 for 5G NR - System Information Block 14 (SIB14)

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 {
    sib14 SIB14-r16,
    ...
  }
}

SIB14-r16 ::= SEQUENCE {
  sl-V2X-ConfigCommonExt-r16 OCTET STRING,
  lateNonCriticalExtension   OCTET STRING OPTIONAL,
  ...
}

How to read this ASN.1

SIB14 is usually carried inside the broader SystemInformation container. In practice, the main point is that it delivers the V2X sidelink information related to LTE SystemInformationBlockType26, and engineers usually interpret it together with SIB13.

Decoded Message Dump

BCCH-DL-SCH-Message
  message: c1
    systemInformation
      criticalExtensions
        systemInformation
          sib-TypeAndInfo
            sib14
              sl-V2X-ConfigCommonExt-r16: present
              lateNonCriticalExtension: absent

How to read this dump

The key practical indicator is the presence of sl-V2X-ConfigCommonExt-r16.
SIB14 is often interpreted together with SIB13 when validating the full V2X broadcast configuration.
If the UE's V2X behavior is wrong, check not only whether SIB14 exists, but whether the decoded extension information matches the intended deployment.

Important Information Elements

IE	Required	Description
`sl-V2X-ConfigCommonExt-r16`	Yes	The core SIB14 payload. It carries the information related to LTE SystemInformationBlockType26 for V2X sidelink communication.
`V2X communication extension information`	Optional	Operationally important extension information that helps explain how V2X sidelink communication should behave in the serving cell.
`lateNonCriticalExtension`	Optional	Carries later non-critical extension information when relevant for the release and deployment.

Detailed field explanation

`sl-V2X-ConfigCommonExt-r16`

The core SIB14 payload. It carries the information related to LTE SystemInformationBlockType26 for V2X sidelink communication.

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.

`V2X communication extension information`

Operationally important extension information that helps explain how V2X sidelink communication should behave in the serving cell.

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.

`lateNonCriticalExtension`

Carries later non-critical extension information when relevant for the release and deployment.

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 SIB14 behavior.
Verify that the UE actually acquired the additional SI carrying SIB14.
Check whether sl-V2X-ConfigCommonExt-r16 is present.
Compare SIB14 with SIB13 to see whether the full V2X broadcast configuration is complete and internally consistent.
If V2X communication does not behave as expected, separate missing SIB14 acquisition from UE capability or application-layer issues.
Correlate the broadcast SIB14 content with the actual V2X sidelink resources and behavior seen in traces.

Common Issues and Troubleshooting

The UE does not apply the expected V2X sidelink behavior.

Likely cause: SIB14 may be missing, not acquired, or not aligned with the expected V2X configuration.

What to inspect: Check whether SIB14 was scheduled, acquired, and decoded successfully.

Next step: Compare SIB13 and SIB14 together before concluding that the issue is in the UE implementation.

V2X configuration looks incomplete in broadcast SI.

Likely cause: The serving cell may broadcast SIB13 without the additional SIB14 information needed for the scenario.

What to inspect: Check the presence of SIB14 and the sl-V2X-ConfigCommonExt-r16 field.

Next step: Validate whether the deployment is intended to use only SIB13 or both SIB13 and SIB14.

The UE decodes broadcast SI but V2X behavior still differs from expectation.

Likely cause: The broadcast V2X information may be valid syntactically but mismatched to the intended configuration or UE support.

What to inspect: Check the decoded SIB14 content together with UE capability assumptions and observed V2X behavior.

Next step: Correlate the decoded broadcast content with the actual trace behavior instead of checking SIB14 in isolation.

LTE / 5G / Variant Comparison

SIB14 versus SIB13

SIB13 carries information related to LTE SystemInformationBlockType21 for V2X sidelink communication. SIB14 carries information related to LTE SystemInformationBlockType26 for V2X sidelink communication.

SIB14 versus SIB12

SIB12 focuses on generic NR sidelink communication and discovery information, while SIB14 is specifically about additional V2X sidelink communication information.

FAQ

What is SIB14 in 5G NR?

SIB14 is System Information Block 14, an NR broadcast block used to carry information related to LTE SystemInformationBlockType26 for V2X sidelink communication.

Who sends SIB14?

The gNB broadcasts SIB14 as additional system information.

What is the main purpose of SIB14?

To provide additional broadcast V2X sidelink communication information needed by supported UEs.

On which channel is SIB14 sent?

SIB14 is carried in system information on BCCH-DL-SCH.

Why is SIB14 useful in troubleshooting?

Because it helps explain why V2X sidelink behavior may be incomplete, inconsistent, or different from the intended broadcast configuration.

Does SIB14 contain UE-specific information?

No. SIB14 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.