| Protocol | rrc | Network | 5g |
|---|---|---|---|
| Spec | 3GPP TS 38.331 | Spec Section | 5.2.2.4.16, 6.3.1 |
| Direction | gNB -> UE | Message Type | Broadcast System Information |
| Full message name | 5G NR - System Information Block 15 (SIB15) |
|---|---|
| Protocol | RRC |
| Technology | 5G |
| Direction | gNB -> UE |
| Interface | Uu |
| Signaling bearer / channel | Broadcast transport / BCCH-DL-SCH |
| Typical trigger | Broadcast when the network needs to expose disaster roaming eligibility and disaster-related PLMN information. |
| Main purpose | Provides disaster-condition and disaster inbound roaming information so the UE can apply the correct access and network-selection behavior during disaster scenarios. |
| Main specification | 3GPP TS 38.331, 5.2.2.4.16, 6.3.1 |
| Release added | Release 17 |
| Procedures where used | System Information Acquisition, PLMN Selection and Disaster Roaming |
| Related timers | SIB15 does not use a dedicated UE-specific transaction timer |
| Related cause values | SIB15 does not carry reject causes |
System Information Block 15 (SIB15) is an NR broadcast system information block used to provide disaster roaming information for PLMNs sharing the cell.
Provides disaster-condition and disaster inbound roaming information so the UE can apply the correct access and network-selection behavior during disaster scenarios.
SIB15 is the 5G NR broadcast block that tells the UE about disaster roaming support and which PLMNs are affected.
Call flow position: Read as additional SI after MIB and SIB1 are already available.
Typical state: UE is camped and extending broadcast context for network selection behavior.
Preconditions:
Next likely message: UE applies the disaster roaming information locally
Call flow position: Used when the UE evaluates disaster-related PLMN and inbound roaming support.
Typical state: UE is in idle or pre-access selection behavior rather than a dedicated transaction.
Preconditions:
Next likely message: Network selection decision or later RRC access
Previous message(s): MIB, System Information Block 1 (SIB1)
Next message(s): PLMN selection using disaster roaming information, RRC Setup Request
Security context: Broadcast information. It is cell-common and not protected by dedicated AS security.
SystemInformation-IEs ::= SEQUENCE {
sib-TypeAndInfo SEQUENCE (SIZE (1..maxSIB)) OF CHOICE {
sib15-v1700 SIB15-r17,
...
},
...
}
SIB15-r17 ::= SEQUENCE {
commonPLMNs-r17 NULL OPTIONAL,
dedicatedPLMNs-r17 SEQUENCE (SIZE (1..maxPLMN)) OF PLMN-Identity OPTIONAL,
...
}
Engineers usually inspect SIB15 as a compact disaster-roaming broadcast container. The practical focus is which PLMNs the cell marks as disaster-related and how that maps to allowed inbound roaming behavior.
BCCH-DL-SCH-Message
message: c1
systemInformation
criticalExtensions
systemInformation
sib-TypeAndInfo
sib15
commonPLMNsWithDisasterCondition-r17: present
dedicatedPLMNs-r17: 001-01, 001-02
| IE | Required | Description |
|---|---|---|
commonPLMNsWithDisasterCondition-r17 | Optional | List of PLMNs for which disaster condition applies and disaster inbound roaming is accepted. |
dedicatedPLMNs-r17 | Optional | Per-network disaster inbound roaming PLMN list used when common PLMN handling is not enough. |
applicableDisasterInfoList | Yes | Maps the disaster roaming meaning to the PLMN or NPN identities advertised by the cell. |
commonPLMNsWithDisasterCondition-r17List of PLMNs for which disaster condition applies and disaster inbound roaming is accepted.
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.
dedicatedPLMNs-r17Per-network disaster inbound roaming PLMN list used when common PLMN handling is not enough.
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.
applicableDisasterInfoListMaps the disaster roaming meaning to the PLMN or NPN identities advertised by the cell.
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.
Likely cause: SIB15 may be missing or the disaster PLMN mapping may not match expectations.
What to inspect: Check whether SIB15 was broadcast and whether the expected PLMNs appear in the disaster information.
Next step: Compare SIB1 network identities with the disaster roaming information in SIB15.
SIB1 identifies the cell and access context, while SIB15 adds disaster-roaming behavior for those advertised networks.
SIB15 is System Information Block 15, used to broadcast disaster roaming information.
The gNB broadcasts SIB15 as additional system information.
It helps explain how the UE should behave for disaster-related PLMN selection and inbound roaming.
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.