The mobile component of today’s end-to-end solution in virtually every national implementation around the worlds is based on a technology called Cell Broadcast. The cell broadcast service architecture is described in the 3GPP standard 23.041 and is supported over 2G, 3G and 4G networks in a similar manner, using one CBC (Cell Broadcast Center) which serves all these networks — the broadcast service’s basic functionality does not change when roaming from one network technology to another.
Cell Broadcast is defined by the European Telecommunications Standards Institute (ETSI) and is incorporated into the GSM 3GPP standards. It is a location-based mobile network service that mass-delivers text or binary messages to citizens’ phones within the range of the base station cell, group of base station cells, or the entire network
CB Messages need to go through a series of steps involving the following components: CBE (Cell Broadcast Entity) -The originator of the Cell Broadcast message being sent. It dictates the message text, message destination and the message scheduling. The Alert Aggregator that we will discuss shortly is a CBE.
CBC (Cell Broadcast Center) — This entity resides in the mobile operator’ core network. The CBC handles and manages the sending of a message received from the CBE; it routes it to the target cells through the RAN controllers (see below), and implements the interfaces connecting it to the RAN controllers.
RAN (Radio Access Network) Controller — The entity in the operator’s radio network that manages a group of cells. The RAN controller distributes the Cell Broadcast message to the target cells. (BSC, RNC and MME are the RAN Controllers for 2G, 3G and 4G networks respectively.)
Cell Antenna – The component that wirelessly sends the Cell Broadcast message to mobile devices
End-User Device – The end-user’s equipment (generally a mobile phone) that responds to the Cell Broadcast protocol to receive and present the message to the user.
CB messages appear in many ways to be similar to point to point SMS messages in that they are text-based, short, and used in mass-mailings. But whereas a standard text message can be sent – for instance, for non-urgent commercial purposes – in small batches to specific users around the clock, such an approach would not be effective for an emergency alert system text message.
When a country’s 50 million citizens need to be told immediately of an emergency situation, a single broadcast (called a load spike or mass call event) would first bottleneck the cellular networks, and eventually bring it down altogether. Especially in times of emergency, this is obviously not desirable. Instead, CB messages are sent out simultaneously to all mobile devices in a specified area connected to a set of cells.
This point-to-area approach means that the area is “blanketed” without having the devices confirm reception. Though newer phones generally come with the this ability turned on, and the messages are received anonymously, it is technically possible to disable the functionality.
A Cell Broadcast message page can use 93 characters and up to 15 of these pages may be combined into Cell Broadcast message. Each page uses the same message identifier (indicating the source of the message), and an identical same serial number. This way, the recipient mobile device can identify and ignore broadcasts of messages already received.