A bitmap manager, a method of allocating a bitmap memory, a method of generating an acknowledgement between network entities, and a network entity implementing the same. The bitmap manager may include a bitmap memory for storing a block acknowledge of received frames based on a bitmap, a bitmap management information controller for receiving a bitmap entry number and storing bitmap management information associated with the physical address of the bitmap memory, and a bitmap manager finite state machine (BM FSM), receiving an update or an extract request for the received frames, managing the bitmap management information, and updating or extracting the bitmap memory.