5G NR - System Information Block 13 (SIB13)

Message Fact Sheet

Protocol	rrc	Network	5g
Spec	3GPP TS 38.331	Spec Section	5.2.2.4.14, 6.3.1
Direction	gNB -> UE	Message Type	Broadcast System Information

Full message name	5G NR - System Information Block 13 (SIB13)
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 corresponding broadcast configuration.
Main purpose	Provides V2X sidelink communication-related broadcast configuration so the UE can support the intended V2X sidelink behavior when that functionality is delivered through NR system information.
Main specification	3GPP TS 38.331, 5.2.2.4.14, 6.3.1
Release added	Release 16
Procedures where used	System Information Acquisition, V2X Sidelink Communication, V2X Service Preparation
Related timers	SIB13 does not use a dedicated UE-specific transaction timer, Interpretation depends on SI acquisition timing and the validity of the broadcast V2X configuration
Related cause values	SIB13 does not carry reject causes, Problems are usually inferred from missing acquisition, wrong V2X resource use, or V2X sidelink behavior that does not match the broadcast configuration

What is System Information Block 13 (SIB13) in simple terms?

System Information Block 13 (SIB13) is an NR broadcast system information block used to provide V2X sidelink communication information aligned with the LTE SystemInformationBlockType21 behavior referenced by NR.

Provides V2X sidelink communication-related broadcast configuration so the UE can support the intended V2X sidelink behavior when that functionality is delivered through NR system information.

Why this message matters

SIB13 is the 5G NR broadcast block that mainly gives the UE the V2X sidelink communication configuration it needs when that feature is supported.

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 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 V2X sidelink-related broadcast configuration locally

V2X Sidelink Communication

Call flow position: Used when the UE needs cell-provided V2X sidelink communication configuration delivered by NR.

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

Preconditions:

The UE is V2X sidelink-capable.
The serving cell broadcasts SIB13.

Next likely message: UE uses the announced V2X sidelink resources and communication settings

V2X Service Preparation

Call flow position: Relevant when the UE prepares V2X communication using broadcast-provided sidelink information.

Typical state: UE may be camped, idle, or otherwise operating with valid broadcast SI.

Preconditions:

SIB13 has been acquired successfully.

Next likely message: No direct RRC next 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 12 (SIB12)

Next message(s): V2X sidelink communication preparation, V2X sidelink operation using the configured resources, Later RRC connection establishment if the wider scenario requires it

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

SIB13 is not a generic mobility or naming SIB. Its practical purpose is V2X sidelink communication configuration.
For engineering work, the main question is whether the V2X resource and communication information announced in SIB13 matches the intended deployment and the UE behavior.
SIB13 becomes especially important when V2X communication does not start, uses the wrong resource pool, or behaves inconsistently.

ASN.1 for 5G NR - System Information Block 13 (SIB13)

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 {
    sib13 SystemInformationBlockType13-r16,
    ...
  }
}

SystemInformationBlockType13-r16 ::= SEQUENCE {
  ...   -- V2X sidelink communication related information
}

How to read this ASN.1

SIB13 is typically carried inside the broader SystemInformation container. In practice, the key point is that it contains the V2X sidelink communication information referenced by NR, aligned with the LTE SIB21 style behavior for V2X communication.

Decoded Message Dump

BCCH-DL-SCH-Message
  message: c1
    systemInformation
      criticalExtensions
        systemInformation
          sib-TypeAndInfo
            sib13
              v2x-SL-Config
                commResourcePool: present
                txParameters: configured
                syncReference: provided

How to read this dump

The key practical block is the V2X sidelink communication configuration.
Resource-pool and transmission-parameter style fields help explain why V2X communication starts, fails, or uses unexpected resources.
If V2X behavior is wrong, the issue may be in SIB13 content, in UE capability, or in how the UE applies the broadcast configuration.

Important Information Elements

IE	Required	Description
`v2x sidelink configuration`	Yes	The core SIB13 payload. It carries the V2X sidelink communication information delivered through NR system information.
`resource pool related information`	Optional	Operationally important V2X resource configuration that explains how the UE should use sidelink communication resources.
`frequency or channel-use context`	Optional	Helps explain which V2X sidelink communication context applies on the serving system.
`communication-parameter set`	Optional	Useful for understanding why actual V2X communication behavior does or does not match the deployment expectation.

Detailed field explanation

`v2x sidelink configuration`

The core SIB13 payload. It carries the V2X sidelink communication information delivered through NR system information.

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.

`resource pool related information`

Operationally important V2X resource configuration that explains how the UE should use sidelink communication resources.

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.

`frequency or channel-use context`

Helps explain which V2X sidelink communication context applies on the serving system.

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.

`communication-parameter set`

Useful for understanding why actual V2X communication behavior does or does not match the deployment expectation.

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 SIB13 behavior.
Verify that the UE actually acquired the additional SI carrying SIB13.
Check whether the V2X sidelink communication configuration is present and complete.
Inspect resource-pool and transmission-related information against the observed V2X behavior.
If V2X communication does not start, verify that the UE is actually using the SIB13-provided configuration path.
Separate SIB13 broadcast configuration issues from higher-layer V2X application or service-trigger issues.

Common Issues and Troubleshooting

The UE does not start V2X sidelink communication.

Likely cause: SIB13 may be missing, incomplete, or not providing the expected V2X resource configuration.

What to inspect: Check the broadcast V2X configuration, resource-pool information, and whether the UE acquired SIB13 at all.

Next step: Compare the broadcast SIB13 content with the intended V2X deployment and UE capability set.

The UE uses unexpected V2X resources.

Likely cause: The resource-pool related information in SIB13 may differ from what the deployment expects.

What to inspect: Check the configured communication-resource information and how the UE applied it.

Next step: Correlate the decoded SIB13 content with actual V2X resource use seen in traces.

General sidelink works but V2X-specific behavior is wrong.

Likely cause: The issue may sit in SIB13 rather than the more generic sidelink broadcast information in SIB12.

What to inspect: Separate generic NR sidelink behavior from V2X-specific sidelink communication behavior.

Next step: Analyze SIB12 and SIB13 together only after separating the scenario.

LTE / 5G / Variant Comparison

SIB13 versus SIB12

SIB12 focuses on generic NR sidelink communication and discovery information. SIB13 focuses on V2X sidelink communication information.

SIB13 versus dedicated RRC

SIB13 is broadcast cell-common V2X sidelink information, not UE-specific connected-mode configuration.

FAQ

What is SIB13 in 5G NR?

SIB13 is System Information Block 13, an NR broadcast block used mainly to provide V2X sidelink communication information.

Who sends SIB13?

The gNB broadcasts SIB13 as additional system information.

What is the main purpose of SIB13?

To provide broadcast V2X sidelink communication configuration for supported UEs.

On which channel is SIB13 sent?

SIB13 is carried in system information on BCCH-DL-SCH.

Why is SIB13 useful in troubleshooting?

Because it helps explain why V2X sidelink communication may not start, may use the wrong resources, or may behave inconsistently.

Does SIB13 contain UE-specific information?

No. SIB13 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.