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What is CM SERVICE REQUEST?

In the air interface protocol stack, Layer 3 Network Layer is divided into three sub-layers: CM (connect management) MM (mobile management) RR (Radio resource management). The CM layer is divided into three parts: CC call control , SSS supplementary service, SMS SMS CM Service Request refers to the service request of CC or SSS or SMS, which expresses to the network that the mobile phone wants to do one of these three things.