GSM Handset Arch

我一直对手机软硬件的全貌不是很清楚，经常听到什么L1,L2,MMI一类的词，所以仔细的google了一下，从一篇叫GSM Handset Vulnerabilities的文章中得到了比较完善的解答：

A basic handset is shown below, which illustrates both hardware and software components.

Control software resides in Layer 3 and is responsible for all control functions, such as call setup, mobility tracking, and handover activity. The man machine interface (MMI) and subscriber ID module (SIM) operations are also managed, yet they can be considered as applications sitting above the stack. Layer 2 is responsible for control-message flow control and retransmission. Layer 1 manages the airlink and controls the RF hardware in response to network messages and airlink conditions. Additionally, all audio functions are handled by this layer in support of voice traffic.