How LTE Stuff Works?: 5G NR: SIB6, SIB7 and SIB8

Introduction

NR connected to 5GC provides support for Public Warning Systems (PWS) by means of system information broadcasting.

NR is responsible for scheduling and broadcasting of the warning messages.

NR is also responsible for paging the UE to provide indication that the warning message is being broadcasted.

Earthquake and Tsunami Warning System (ETWS) is a public warning system developed to meet the regulatory requirements for warning notifications related to earthquake and/or tsunami events.

- ETWS warning notifications can either be a primary notification (short notification) or secondary notification (providing detailed information).

- ETWS Primary Notification shall:

· convey data which is small enough to be sent quickly on the network.

· convey small amount of data to indicate the imminent occurrence of Earthquake and Tsunami, etc.

· be delivered within 4 seconds to the UE in the Notification Area even under congestion situation.

- ETWS Secondary Notification may:

· convey a large amount of data in order to deliver text, audio to instruct what to do/where to get help, graphical data such as a map indicating the route from present position to evacuation site, timetable of food distribution etc.

· Secondary Notification is delivered to the users in the Notification Area even under congestion situation.

- ETWS Primary Notification has higher priority than Secondary Notification i.e., the notifications shall be able to be sequenced by the PLMN according to priority of notification in case that both notifications should exist at the same time in PLMN.

Commercial Mobile Alert System (CMAS) is a public warning system developed for the delivery of multiple, concurrent warning notifications. These messages include CMAS Presidential Level Alerts, CMAS Child Abduction Emergency (e.g. AMBER), Imminent Threat, Public Safety etc…

Paging is used to inform UEs about ETWS and CMAS indications. UE monitors ETWS/CMAS indications in its own paging occasion for RRC_IDLE and RRC_INACTIVE and in any paging occasion for RRC_CONNECTED.

Paging indicating ETWS/CMAS notification triggers acquisition of system information (without delaying until the next modification period).

Different SIBs are defined for ETWS primary notification, ETWS secondary notification and CMAS notification. The following table provides the summary;

SIB Type	SIB Contents
SIB6	ETWS primary notification
SIB7	ETWS secondary notification
SIB8	CMAS warning notification

General Information

5G NR system information in general is discussed in detail in the post 5G NR:System Information.

SIB6, SIB7 and SIB8 are mapped to BCCH logical channel and is either broadcast periodically on DL-SCH or broadcast on-demand on DL-SCH (i.e. upon request from UEs in RRC_IDLE or RRC_INACTIVE) or sent in a dedicated manner on DL-SCH to UEs in RRC_CONNECTED.

SIB6, SIB7 and SIB8 are carried in SystemInformation (SI) messages, which are transmitted on the DL-SCH. SIB1 contains scheduling information for SI-message carrying corresponding SIB. For more information about scheduling of SI-messages, refer to 5G NR: System Information.

SIB6, SIB7 and SIB8 can be configured to be cell specific or area specific, using an indication in SIB1. The cell specific SIB is applicable only within a cell that provides the SIB while the area specific SIB is applicable within an area referred to as SI area, which consists of one or several cells and is identified by systemInformationAreaID.

System Information Block 6 (SIB6)

SIB6 contains an ETWS primary notification. ETWS primary notifications are meant contain small data/information in order to facilitate quicker delivery.

Overview of SIB6 contents presented below;

*SIB6*
messageIdentifier	BIT STRING ( SIZE (16) )
serialNumber	BIT STRING ( SIZE (16) )
warningType	OCTET STRING ( SIZE (2) )

messageIdentifier identifies the source and type of ETWS notification using 16-bit string. Different message identifiers are defined for PWS in section 9.4.1.2.2 from 23.041. For example, hex value 1100 indicates Tsunami warning message, 1101 indicates Earthquake warning message, 1102 indicates Tsunami and Earthquake combined warning message and so on.

serialNumber identifies variations of an ETWS Primary Notification. This parameter identifies a particular ETWS Primary Notification message from the source and type indicated by the Message Identifier and is altered every time the ETWS Primary Notification message with a given Message Identifier is changed.

warningType identifies the warning type of the ETWS primary notification and provides information on emergency user alert and UE popup. It has three fields warning type value, emergency user alert and popup indications. The encoding of the Warning-Type parameter is as shown below.

Octet 1								Octet 2
7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0
Warning Type Value									Padding

					Emergency User Alert
					Popup

The warning type value field is expressed as 7-bit string. The following table shows the values and their corresponding warning types.

*Warning typeValue*	*Warning type*
0 0 0 0 0 0 0	Earthquake
0 0 0 0 0 0 1	Tsunami
0 0 0 0 0 1 0	Earthquake and Tsunami
0 0 0 0 0 1 1	Test
0 0 0 0 1 0 0	Other
0 0 0 0 1 0 1 — 1 1 1 1 1 1 1	Reserved for future use

The fields for emergency user alert and popup indications are type binary. They are used to command UEs to activate emergency user alert and message popup in order to alert the users upon the reception of ETWS primary notification (e.g. paging message). The fields are as shown below;

*Value*	Instruction to the UE
*Value*	*Emergency User Alert*	*Popup*
0	No instruction as to Emergency alert	No instruction as to Popup
1	Activate Emergency user alert	Activate Popup on the display

System Information Block 7 (SIB7)

SIB7 contains an ETWS secondary notification. ETWS secondary notification convey a large amount of data in order to deliver text, audio to instruct what to do/where to get help, graphical data such as a map indicating the route from present position to evacuation site, timetable of food distribution etc.

Overview of SIB7 contents presented below;

*SIB7*
messageIdentifier	BIT STRING ( SIZE (16) )
serialNumber	BIT STRING ( SIZE (16) )
warningMessageSegmentType	ENUMERATED {notLastSegment, lastSegment}
warningMessageSegmentNumber	INTEGER (0 … 63)
warningMessageSegment	OCTET STRING
dataCodingScheme	OCTET STRING ( SIZE (1) )

serialNumber identifies variations of an ETWS Secondary Notification. This parameter identifies a particular ETWS Secondary Notification message from the source and type indicated by the Message Identifier and is altered every time the ETWS Secondary Notification message with a given Message Identifier is changed.

warningMessageSegmentNumber provides the segment number of the ‘ETWS warning message segment’ contained in the SIB. A segment number ‘zero’ corresponds to the first segment, a segment number ‘one’ corresponds to the second segment, and so on.

warningMessageSegment carries a segment of the actual Warning Message Contents IE.

warningMessageSegmentType indicates whether the included ETWS warning message segment is the last segment or not.

dataCodingScheme identifies the alphabet/coding and the language applied variations of an ETWS notification. One octet long Data Coding Scheme indicates the intended handling of the message at the MS, the character set/coding, and the language (when applicable). The field is mandatorily present in the first segment of SIB7 and is absent otherwise.

System Information Block 8 (SIB8)

SIB8 contains a Commercial Mobile Alert Service (CMAS) notification. Overview of SIB8 contents presented below;

*SIB8*
messageIdentifier	BIT STRING ( SIZE (16) )
serialNumber	BIT STRING ( SIZE (16) )
warningMessageSegmentType	ENUMERATED {notLastSegment, lastSegment}
warningMessageSegmentNumber	INTEGER (0 … 63)
warningMessageSegment	OCTET STRING
dataCodingScheme	OCTET STRING ( SIZE (1) )
warningAreaCoordinatesSegment	OCTET STRING

messageIdentifier identifies the source and type of CMAS notification using 16-bit string. Different message identifiers are defined for PWS in section 9.4.1.2.2 from 23.041.

serialNumber identifies variations of CMAS Notifications. This parameter identifies a particular CMAS notification message from the source and type indicated by the Message Identifier and is altered every time the CMAS Notification message with a given Message Identifier is changed.

warningMessageSegmentNumber is the segment number of the CMAS warning message segment contained in the SIB. A segment number ‘zero’ corresponds to the first segment, ‘one’ corresponds to the second segment, and so on. If warning area coordinates are provided for the warning message, then this field applies to both warning message segment and warning area coordinates segment.

warningMessageSegment carries a segment, with one or more octets, of the Warning Message Contents IE defined in 38.413. The first octet of the Warning Message Contents IE is equivalent to the first octet of the CB data IE defined in and encoded according to section 9.4.2.2.5 of 23.041, and so on.

warningMessageSegmentType indicates whether the included CMAS warning message segment is the last segment or not. If warning area coordinates are provided for the warning message, then this field applies to both warning message segment and warning area coordinates segment.

warningAreaCoordinatesSegment: If present, this field carries a segment, with one or more octets, of the geographical area where the CMAS warning message is valid. The first octet of the first warningAreaCoordinatesSegment is equivalent to the first octet of Warning Area Coordinates IE defined in and encoded according to 23.041 and so on.

dataCodingScheme identifies the alphabet/coding and the language applied variations of a CMAS notification. One octet long Data Coding Scheme indicates the intended handling of the message at the MS, the character set/coding, and the language (when applicable). The field is mandatorily present in the first segment of SIB8 and is absent otherwise.

Reference: 3GPP TS 38.331, 22.268, 38.413 and 23.041