Introduction

Cell broadcast was orinally conceived as a commercial service in GSM and UMTS but, for various reasons, it failed to meet business expectations. As a consecuence, most mobile operators did not deploy it, and a few did very limited roll-outs.

The situation started to change in the first decade of the 2000's, when some countries like Japan, The Netherlands and the USA, started using cell broadcast for public warning and required to all the mobile operators in their territory to deploy CBCs. CBS rapidly became core for PWS in all standards bodies, including ATIS (for WEA), ETSI (for EU-Alert), Korea (for KPAS) and Japan (for ETWS). Cellular PWS solutions are now in place in many regions (e.g. article 110 of the EECC mandates that all EU member states must have cellular PWS working nationally by end of June 2022), which is forcing many MNOs for deploy CBCs inside their network.

This document attempts to describe a comprehensive list of functional test cases for acceptance testing of CBCs towards NEs in the southbound interface, as shown in the following figure.

Scope

Test cases:

Are organised per technology.
Include a description, list of pre-requisites, execution procedure and expected outcome. For most test cases, the description includes a high level flow of messages. Only what is relevant for each message is described (e.g. IEs that relate to the test).

Note My intention was to include sample traces for each test case. But I have not been able to get these traces so far.

The scope of all the test cases is the CBC. I.e. TC's only cover interactions of the CBC with direct peer NEs (RNCs, MMEs, AMFs). It does not cover further interactions of these peers with radio nodes (NBs, eNBs, gNBs) except for the cases in which failure response from radio nodes are due to incorrect behaviour of the CBC.

The CBE is out of the scope. In this TS, it is just a tool used to trigger
test cases, but it is not the focus of this work. Besides, the CBE - CBC interface is not really standardised in most regions, but is often proprietary to each CBC vendor. This interface is usually based on CAPv1.2 from Oasis.

Cell broadcast message

PWS alerts can only contain text messages. CBS messages are sent in pages of up to 82 octets and a message can contain up to 15 pages. This gives a maximum message length of 1230 octets.

Depending on the text encoding used, GSM7 or UCS2, each page can contain up to 93 or 41 characters respectively. For additional information about text encoding, check here.

Authorities should always try to send concise alert messages, since the more pages the message has, the longest it takes for a handset to receive it and the most likely it is to fail to receive it completely. Most handsets do not show partial messages, but wait to receive it completely before alerting the user.

Cell broadcast specifications

3GPP TS23.041 is the main specification for Cell Broadcast Service and it is the basis for this test specification. It is, however, a stage 2 document, even though it defines protocol details as well. The stage 3 (protocol) specifications for the different technologies are:

LTE: 3GPP TS29.168
5G: 3GPP TS29.518 and 3GPP TS38.413

Protocol specifications (stage 3) take precedence over stage 2 ones. If there is a conflict between descriptions in stage 2 and stage 3, then the stage 3 description shall be the one considered.

Note on 3GPP Relases

3GPP Rel16 is the basis for this work. I will jump into Rel17 if I see important CRs affecting the outcome.

Interworking with other NEs (MMEs, AMFs) using older versions might cause some test cases to fail and require customisation. It is up to the test engineers to identify and get these issues resolved with the CBC and the peer entity vendors.

CBE - CBC interface

CAPv1.2 is the base for this interface in most current national CBS roll-outs for PWS. However, standalone CAPv1.2 does not include all the support needed for CBS, for this reason some countries and organisations specify profiles to CAPv1.2. Such profiles:

Specifie how CAP shall be used for alerting. E.g. which elements are mandatory or how to use existing elements to send CBS specific information (e.g. for the CBC to derive the alert level).
Extend CAP with new elements to convey CBS specific information (e.g. the periodicity of alert broadcast over the radio channel).

A couple of examples of national profiles that have explicit hooks for CBS are:

IPAWS Profile by the USA Federal Emergency Management Agency (FEMA).
CAP-FR by the French Government (public version not available at the time of this writting). This profiles supports CBS and LB-SMS.

In USA, ATIS 0700008 is the standard protocol for the CBE - CBC interface, and it uses CAPv1.1 as its base.

The CBE - CBC interface is NOT in the scope of this TS. This TS uses vanilla CAPv1.2 for requests sent from CBE to CBC and assumes that this CAP has been extended somehow, e.g. via a national CAP profile, to include functionality that is missing in plain CAPv1.2. For example, it assumes that CAPv1.2 has been extended to:

Convey Alert level, when the level is not defined by the values of CAP parameters Severity, Urgency and Certainty as specified in 3GPP TS23.041 and shown in this table.
Provide all the information that the CBC needs to calculate the number of times that a message has to be broadcasted (Number of broadcasts) and the repetition period between broadcasts.
Provide means for the CBC to send asynchronous updates to the CBE (e.g. when a MME or AMF sends a WRITE-REPLACE-WARNING INDICATION to the CBC with information about broadcast failure in an eNB / gNB).

Alternatives to Cell Broadcast

Besides cell broadcast, another popular solution for PWS is Location Based SMS (LB-SMS). This solution is used in several countries, being Australia the one that has probably done the most serious deployment and used it most masively.

The key advantage of LB-SMS over CBS is pasive location. This functionality delivers situational awareness to the civil protection authorities that manage emergency events. For example, it allows them to know how many people is affected and how people is reacting to their notifications (e.g. a request for evacuation). With LB-SMS, the civil protection personnel managing an emergency also gets information about how many people is actually receiving the alert messages.

Obviously, LB-SMS is not as fast as CBS for large area events and it is sensitive to congestion in the network, which can be a serious issue specially in catastrophic events like earthquakes. This is, however, not an issue in more predictable major events such as bush fires, floods, tornados or even tsunamis.

Authorities shall consider complementing CBS with LB-SMS and passive location. Several countries, like France and Croatia, have done it and they are surely more prepared to cover adecuately all types of emergencies.