Protocols within the stack perform data encapsulation by adding a header—and, in some cases, a footer—to the information received from an upper-layer protocol. -data encapsulation occurs when the transmitting systems protocol stack packages information as its passed down from one layer to the next, preparing it for transmission across the network. the encapsulation process is performed by the sending hosts protocol stack. each protocol layer on the sending host adds a header with control information as its passed down the stack in preparation for transmission on the network. protocols use special codes, like a cyclical redundancy check (crc), to allow for error checking. protocol identification specifies the protocol thats carried in a frame. both the crc and the protocol identification are included in the fields of information that are added during the encapsulation process. user data is the original raw information that must be encapsulated prior to transmission across the network.