Why segmentation is needed for ETWS secondary notification sometimes ?

Question

The ETWS msg from RRC send as primary and secondary notifications. Secondary notification size can be 9600 bytes at max so to handle such big size on radio interface between ENB and UE we are segmenting SIB 11. As per RRC spec we need to send paging, SIB1 along with SIB11 for secondary notification. As we are segmenting SIB 11 into number of segments for that do I need to send SIB1 for each segment or once?

Answer 1

The transmission of a warning message like ETWS to a mobile terminal in a mobile communication network is triggered by an emergency event. The mobile terminal is first made aware of the need to receive a warning message by reception of an emergency event notification.

ETWS message is divided into no. of message segments. Here each segment contains different Information which will enable the mobile terminal to discriminate between segments belonging to different warning messages.

Answer 2

ETWS is a kind of public warning system (PWS) to notify all the UEs in a specific area of emergency situation like Earthquake or Tsunami or something similar. The concept is very similar to Cell Broadcasting in WCDMA and GSM network.

In WCDMA, we used a special channel called CTCH (Common Traffic Channel) for this purpose, but in LTE we use a couple of SIB messages to periodically broadcast the warning information to all the UEs in a certain area simultaneously. The SIBs that carry the information about ETWS is SIB10 and SIB11.

When an emergency situation happens, network broadcast the details of the emergency via SIB 10/SIB11 and inform UE to let decode SIB10/11 by sending special Paging message. When UE recieves this Paging message, UE has to decode SIB10/11 and display the warning information on the screen.

In LTE, there are three main components getting involved in sending ETWS as follows.
i) Paging : ETWS Notification.
ii) SIB 10 : Secondary Notification
iii) SIB 11 : Primary Notification

Now coming to the main question why secondary notification is divided to segments, the reason is each segment contains different Information which will enable the mobile terminal to discriminate between segments belonging to different warning messages.