1. Hannu Hietalahti Kevin Holley Stephen Hayes Brian Daly
IETF #79, 7 – 12 Dec, 2010, Beijing, China
PWS
Public Warning System
Hannu Hietalahti
Kevin Holley
Stephen Hayes
Brian Daly

2. Contents Cell Broadcast Service Overview Current status of PWS
PWS Service requirements
Cell Broadcast Service
PWS Technical overview
Use case
Details
Extensibility
Message Identifiers
Regional Standards
CMAS architecture and call flow example
Summary

3. Current status of Public Warning System
PWS comprises public alert services in 3GPP
Earthquake and Tsunami Warning System ETWS (Rel-8)
Commercial Mobile Alert System CMAS (Rel-9)
EU-Alert requirements are being studied (Rel-11)
Global service
Warning categories must be defined globally
Detection of the warning categories must be global for roaming users
Applicable in 3GPP systems over GSM, UTRAN and LTE radio
Specification references
Stage 1 in 3GPP TS (Requirements)
Stage 2 in 3GPP TS (CBS, Message Identifier coding)
Stage 3 in 3GPP TS , , , , , (Radio interface)

4. Service requirements (from 3GPP TS 22.268)
Broadcast Warning Notifications to multiple users simultaneously
Geographical notification area is specified by the Warning Notification Provider
Roaming subscribers must be supported
Concurrent broadcast of multiple Warning Notifications
with no acknowledgement required
PWS capable terminals in idle mode shall be able to receive broadcast warnings
User may opt-out from certain alert categories
Warning Notifications languages are determined by regulatory requirements
Warning Notifications are processed by PWS on a first in, first out basis, subject to regulatory requirements
Reception and presentation of Warning Notifications to the user shall not pre-empt an active voice or data session.
Current implementation requirement is up to 90 7-bit characters
Typical contents of the warning:
Event Description
Area Affected
Recommended Action
Expiration Time (with time zone)
Sending Agency

5. Cell Broadcast Service (CBS)
CBS is defined in 3GPP TS23.041
CBS can cover different services that are independent of each other
PWS uses CBS in GSM and UTRAN
In LTE the messages are encoded according to CBS rules, but distribution at the radio interface is LTE specific
Unacknowledged broadcast to all CBS-capable mobiles within a particular region
defined geographical areas known as cell broadcast areas
may comprise of one or more cells, up to the entire network
CBS messages may originate from a number of Cell Broadcast Entities (CBEs) through an operator’s Cell Broadcast centre (CBC)
CBS messages are sent from the CBC to the cells, in accordance with the CBS's coverage requirements
Maximum capacity ranges from GSM 93 7-bit characters to LTE 316 characters
Message segmentation is possible (15 – 64 segments)
A CBS message is identified by a message identifier and serial number
Can be used by the mobile to “screen” which messages are received
Also to identify and ignore re broadcasts of already received messages
3GPP manages the message identifiers
CBS messages may be broadcast cyclically by the cell at a frequency and for a duration agreed between the operator and the information provider

6. Technical overview, use case (Figure from 3GPP TS 22.268)
Key points:
Interface provided to Government authority to submit alert messages
Government authority is responsible for interface to and authentication of alert originators
Security against fake alarms, operator must authenticate alert issuer at interface C
Support for all terminals in the affected geographical area, including roaming users and terminals sourced from other countries
Distribution mechanisms at radio interface differ between GSM, UTRAN, LTE but are all based on broadcast mechanisms

7. Technical overview, details
Radio procedures for broadcasting in 3GPP radio access technologies
Common paging or SysInfo change or CBS
Distribution area
Geographical selectivity is based on network topology
Alert codes are globally defined
Detection of alert categories is not restricted to physical distribution channel at radio interface but part of PWS service
Paging to wake up the terminal to listen to broadcast information
Mutual authentication to avoid MiM and playback attacks
Data coding scheme is critical for compatibility and mobility
Message Identifier corresponds with alert category
Message Identifiers to be received can be pre-configured on USIM or by the user
Language code
Default 7-bit coding with several language specific extensions or 16-bit UCS2 coding for other languages
Sequencing to distinguish between different messages

8. PWS extensibility
Message identifier ranges are assigned for different broadcast use cases
MI 0 – 999 are defined by GSMA for Flash messages, weather reports, traffic reports, date & time, etc
MI are defined by 3GPP for specific services, among them PWS
MI values 1100 – 18FF are reserved for PWS use
More than 2000 code points not assigned yet
ME application configures the reception of the MIs related with the service
Reception of any MI can be configured on USIM by the HPLMN operator
Legacy terminal processing of unforeseen data is normatively specified and thus predictable
alert category, character set, broken sequence, etc.
All alert categories shall be globally unique
National or regional exceptions cannot change the meaning of alert code
Japanese Tsunami alert code cannot be re-used for avalanche warning in Switzerland
CMAS Presidential Level Alert code point can be re-used for EU-Alert 1
Additions to existing codes are possible
National extensions must be defined globally

9. Message Identifiers (3GPP TS 34.041)
Decimal
Hex
Meaning
0 – 999
0000 – 03E7
Allocated by GSMA (see GSMA PRD SE.15  )
... …
4352
1100
ETWS CBS Message Identifier for earthquake warning message.
4353
1101
ETWS CBS Message Identifier for tsunami warning message.
4354
1102
ETWS CBS Message Identifier for earthquake and tsunami combined warning message.
4355
1103
ETWS CBS Message Identifier for test message.
Normal UE silently discards this message. Test UE may may display its contents.
4356
1104
ETWS CBS Message Identifier for messages related to other emergency types.
4357 – 4359
ETWS CBS Message Identifier for future extension.
Intended for standardization in future versions of this document. These values shall not be transmitted by networks that are compliant to this version of this document. If a Message Identifier from this range is in the "search list", the ME shall attempt to receive this CBS message.
4370
1112
CMAS CBS Message Identifier for Presidential Level Alerts. Not settable by MMI.
4371
1113
CMAS CBS Message Identifier for Extreme Alerts with Severity of Extreme, Urgency of Immediate, and Certainty of Observed. Settable by MMI as per CMAS subscriber opt-out requirements
111F-112F
CMAS CBS Message Identifier for future extension.
1130 – 18FF
CBS Message Identifier for future PWS use. These values shall not be transmitted by networks that are compliant to this version of this document. If a Message Identifier from this range is in the "search list", the ME shall attempt to receive this CBS message.
6400 – 40959
1900 – 9FFF
Intended for standardization in future versions of this document . These values shall not be transmitted by networks that are compliant to this version of this document. If a Message Identifier from this range is in the "search list", the ME shall attempt to receive this CBS message.

10. Regional Standards ETWS, CMAS, EU-Alert
ETWS requirements are defined by Japanese requlator, but not normatively referenced from 3GPP specifications
3GPP TS captures the 3GPP system requirements for ETWS
CMAS is defined under FCC CFR 47 Part 10 Rules in the U.S.
CMAS Standards developed by ATIS and TIA:
J-STD-100, J-STD-101, ATIS , ATIS , ATIS , ATIS
EU-Alert requirements are specified in ETSI ETS

11. CMAS architecture E-UTRAN Access specific broadcast procedures UTRAN
Public
authority
E-UTRAN
Network
Operator
UTRAN
Access specific broadcast procedures
GERAN 11

12. CMAS Call Flow Example
CMSP Gateway in the operator network receives the CMAS alert from the government entity
The alert is passed to the operator’s cell broadcast centre (CBC) which identifies the cell site(s) to broadcast the alert
The alert is broadcast using 3GPP PWS

13. Summary
PWS was designed by 3GPP as a global solution for issuing public warnings over 3GPP mobile systems
PWS is designed to allow extendable set of national and regional specific alerts while maintaining global uniqueness
PWS is a service for alerting and updating the user of emergency situations in a timely, secure, and geographically selective manner
PWS architecture
provides interface towards public authorities who generate and authorize the warnings
uses common PWS broadcast and message coding capabilities
uses radio specific cell broadcast procedures in GSM, UMTS and LTE
is extendable in future 3GPP enhancements