S1-AP interface is defined kill procedure which is mainly used to ask eNodeB to stop an ongoing broadcast warning messages. Each warning message is uniquely identified by "Message Identifier" and "Serial Number".
When MME needs to stop broadcasting of any of the warning message, it prepares and sends "Kill Request" with this "Message Identifier" and "Serial number" and also it can include "Warning Area List" IE (optional) with the kill request message.
As soon as, eNodeB receives "Kill Request" message from an MME, it stops broadcasting of warning messages based on the information receives in request message. If "warning area list" is present then eNodeB considers that list to identify cells or tai's or emergency area ids to stop broadcasting of warning message else it stops warning message for all of its cells. Once this operation finishes, eNodeB prepares and sends "Kill Response" message to MME with the same identifiers "Message Identifier" and "Serial Number" and also it can send "Broadcast cancelled area list" (optional IE) in the response message.