Functions of the cdma2000 Signaling Services Layer
The Signaling Services Layer processes all messages exchanged between the mobile and the base station. These messages control such things as call setup and tear down, hand offs, feature activation, system configuration, registration and authentication.
In the mobile, the Signaling Services Layer is also responsible for maintaining the mobile’s call processing states:
  Mobile Station Initialization State
  Mobile Station Idle State
  System Access State
  Mobile Station Control on the Traffic Channel State