| Protocol | rrc | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 38.331 | Spec Section | 5.2.2, 6.3.1 |
| Direction | gNB -> UE | Message Type | Broadcast System Information |
| Full message name | 5G NR - System Information |
|---|---|
| Protocol | RRC |
| Technology | 5G |
| Direction | gNB -> UE |
| Interface | Uu |
| Signaling bearer / channel | Broadcast transport / BCCH-DL-SCH |
| Typical trigger | Broadcast according to system-information scheduling when the UE needs SIBs beyond MIB and SIB1. |
| Main purpose | Delivers additional system information blocks after MIB and SIB1 so the UE can acquire the wider broadcast context needed for access, mobility, slicing, NTN, MBS, or other features. |
| Main specification | 3GPP TS 38.331, 5.2.2, 6.3.1 |
| Release added | Release 15 |
| Procedures where used | System Information Acquisition, Broadcast Context Expansion |
| Related timers | None highlighted |
System Information is the NR RRC broadcast container used to carry one or more SIBs or positioning SIBs with the same periodicity.
Delivers additional system information blocks after MIB and SIB1 so the UE can acquire the wider broadcast context needed for access, mobility, slicing, NTN, MBS, or other features.
System Information is the broadcast RRC container that carries SIBs beyond MIB and SIB1.
Call flow position: Broadcast after the UE has already acquired MIB and SIB1.
Typical state: UE is camped and extending its broadcast context.
Preconditions:
Next likely message: UE reads and applies the contained SIBs
Previous message(s): MIB, System Information Block 1 (SIB1)
Next message(s): Contained SIB processing, Initial Access, Paging monitoring, Mobility decisions
Security context: Broadcast information. It is cell-common and not protected by dedicated AS security.
SystemInformation ::= SEQUENCE {
criticalExtensions CHOICE {
systemInformation SystemInformation-IEs,
...
}
}
SystemInformation-IEs ::= SEQUENCE {
sib-TypeAndInfo SEQUENCE (SIZE (1..maxSIB)) OF CHOICE { ... },
lateNonCriticalExtension OCTET STRING OPTIONAL,
...
}
The practical task is to identify which SIBs the container carries and whether that matches the SI scheduling and the UE's needs.
BCCH-DL-SCH-Message
message: c1
systemInformation
criticalExtensions
systemInformation
sib-TypeAndInfo
sib3
sib4
| IE | Required | Description |
|---|---|---|
sib-TypeAndInfo | Yes | List of SIBs or related SI content carried in the current System Information message. |
lateNonCriticalExtension | Optional | Extension field for later release additions. |
sib-TypeAndInfoList of SIBs or related SI content carried in the current System Information message.
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.
lateNonCriticalExtensionExtension field for later release additions.
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.
Likely cause: The relevant SIB may not be included in the System Information message the UE reads.
What to inspect: Check the contained SIB list and SI scheduling.
Next step: Correlate the container with the specific missing SIB page.
SIB1 is a specific broadcast block with essential scheduling and access information, while System Information is the container that carries other SIBs.
It is the broadcast RRC container used to deliver one or more SIBs.
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.