tailieunhanh - Kỹ thuật truyền dữ liệu 12

Tham khảo tài liệu 'kỹ thuật truyền dữ liệu 12', giáo dục - đào tạo, cao đẳng - đại học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | APTER 12 Local Area Networks A local area network LAN is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographic area. LANs are dominated by four architectures Ethernet Token Bus Token Ring and fiber distributed data interface FDDI . Ethernet Token Bus and Token Ring are standards of the IEEE and are part of its Project 802 FDDI is an ANSI standard. The data link control portion of the LAN protocols in use today are all based on HDLC. However each protocol has adapted HDLC to fit the specific requirements of its own technology. For example ring technology has different needs than star technology as we will see later in this chapter. Differences in the protocols are necessary to handle the differing needs of the designsX PROJECT 802 In 1985 the Computer Society of the IEEE started a project called Project 802 to set standards to enable intercommunication between equipment from a variety of manufacturers. Project 802 does not seek to replace any part of the OSI model. Instead it is a way of specifying functions of the physical layer the data link layer and to a lesser extent the network layer to allow for interconnectivity of major LAN protocols. In 1985 the Computer Society of the IEEE developed Project 802. It covers the first two layers of the OSI model and part of the third level. The relationship of IEEE Project 802 to the OSI model is shown in Figure . The IEEE has subdivided the data link layer into two sublayers logical link control LLC and medium access control MAC . The LLC is non-architecture-specific that is it is the same for all IEEE-defined LANs. The MAC sublayer on the other hand contains a number of distinct modules each carries proprietary information specific to the LAN product being used. 369 70 CHAPTER 12 LOCAL AREA NETWORKS Figure LAN compared with the OSl model Other layers Other layers Network Network Logical link control LLC Media access control MAC