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CBS (Cell Broadcast Service)

 

Just in terms of user experience, CBS may look like a kind of Short Message service(SMS) or USSD (your device would popup a notification signal or text string as it recieves CBS message). But if you gets into a little bit deeper, you would notice that CBS and SMS/USSD has completely different foundation.

 

First, you would see high level difference as follows :

  • SMS is one to one message and CBS is a message broadcast to many people simultaneously.
  • SMS can be bidirectional (you can send and receive the message) and CBS is usually unidirectional (subscribers can only receive the message).

More importantly, CBS and SMS/USSD are transmitted by completely different channel and mechanism. Whereas SMS/USSD is transmitted by DCCH->DPCH as normal signaling message, CBS is using its own independent channel (CTCH-> SCCPCH) as shown below. (Channel Configuration for CBS is configured in SIB5 or SIB5bis)

 

 

 

CBS Message parameter and an example is shown here.

 

 

Reference :

  • 25.324  Broadcast/Multicast Control BMC
  • 23.041 Technical realization of Cell Broadcast Service (CBS)