The present invention relates to a wireless communication system having protocol architecture for reducing latency of a cellular system. In the protocol architecture of the wireless communication system in the cellular system, a physical layer supports wireless transmission of the cellular system and estimates a radio channel condition. A data link layer determines a data transmission mode based on a QoS of user data and the radio channel condition estimated by the physical layer and performs segmentation and assembly of the packet data, and a network layer establishes and releases a radio bearer for transmitting packet data transmitted from the data link layer and a control command. A control service access point is provided for control information transmission between the data link layer and the physical layer.