Cognitive radio technology is an effective method to improve the utilization and efficiency of radio spectrum. Cognitive radio technology solves spectrum scarcity problem by allowing cognitive users to use spectrum holes when primary users are absent. Cognitive radio networks are classified according to the infrastructure into: (A) centralized cognitive radio networks and (B) cognitive radio ad-hoc networks. The cognitive media access control (MAC) protocols are the master key of designing cognitive radio network. These allow cognitive users to identify and use the available frequency spectrum in a manner constrains the levels of interference to the primary users. Cognitive radio MAC protocols can be classified into: (A) random access control protocol (B) time slotted control protocols (C) hybrid protocols. In this paper, the dynamic open spectrum sharing (DOSS) MAC protocol is proposed as an example for random access control protocol. Due to the collision among users, the network throughput will be reduced. In order to enhance the performance of DOSS protocol, a back-off algorithm (BOA) will be executed and analyzed to enhance the network throughput. An optimum number of data retransmissions that decrease blocking and dropping ratio are investigated. Moreover, two accessing channels techniques for the proposed algorithm will be presented: fixed channel allocation (FCA) and dynamic channel allocation (DCA) schemes. DCA scheme allows to users to choose the control channel in a dynamic manner. The dynamic behavior decreases the limitation of control channel saturation. So, it can increase the network throughput. The performance analysis of the FCA and DCA schemes for the proposed protocol will be simulated. Finally, the performance analysis of DCA scheme of DOSS mac protocol with BOA will be investigated.