Importance

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Abstract

A state machine for data link control is implemented in the state management of a second layer protocol of a subscriber unit, which establishes message transmissions and management with an RP and an RPCU. In an acquiring state, the subscriber unit scans frequencies to find an available channel and downlinks information of system channels from the RPCU. The system channels include a first channel and a second channel. In a standby state, the subscriber unit keeps receiving the information, and the standby state includes an initial state, an idle state, and a time slot waiting state. The initial state is for determining and comparing the information and confirming whether the first channel is changed and whether the subscriber unit is registered. The idle state is to wait for a message that requests to establish a TC from the third layer protocol and to determine whether the second channel belongs to normal call messages, informing the third layer protocol to make a corresponding response. The time slot waiting state is to wait the RPCU to reply whether the TC is successfully established. The state machine enters the initial state when it searches and synchronizes with a specific channel in the acquiring state, enters the idle state after a complete first channel message is received in the initial state, and returns to the idle state if no TC establishment fails. Once the TC is successfully established in the time slot waiting state, the subscriber unit enters an active state.

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