Unit 4 Research Project Report

Unit 4 Research Project Report IEEE802 standard series protocol, the data link layer includes a logical link control (LLC) sublayer and the media access control (MAC) sub-layer which is located between the MAC layer and the physical LLC, which allows adaptation to different LLC media access technology and physical media. MAC sublayer as a separate, they will not change the impact of the media access method and higher level protocols. MAC disassembly of data and media access management of two modules, the completion of the data frame encapsulation, re-opened send and receive functions. Ethernet frame encapsulation format as shown in Table 1, where the destination address, source address, length / type field and the data generated by the four layer protocol module when transmitting data frames, data encapsulation module automatically adding data to be transmitted in the first seven bytes of preamble and a delimiter byte and add at the end of the data transfer byte sent four cyclic redundancy check code, if the data length is less than 46 bytes , the data is automatically filled in order to achieve the minimum length required when receiving data frame, the data will be automatically discarded removable module preamble and delimiter two fields. Media access management module main CSMA / CD (carrier sense multiple access with collision detection) protocol. CSMA / CD is a distributed MAC protocol that enables multiple network stations (nodes) can be shared transmission medium. Sending data when the frame, the first node listens for a carrier, when the medium is idle starts when the transmission frame, if in conflict with other nodes in the transmission process, each node must be given is a 32-bit transmission blocking signals to enhance the size of the conflict, in order to inform the bus conflict has occurred on each site, and then re-random delay period contention medium, and then resend the data frame.