计算机专业解析ppt,计算机专业英语课件解析.ppt
计算机专业英语课件解析
* 计算机专业英语 * 4.2 The OSI Reference Model The OSI reference model, sometimes also called ISO or 7 layers reference model for communication. This model describes the principles for interconnection of computer systems in an Open System Interconnection environment. The general principle which leads to the definition of the OSI standard was to allow connection and communication between any computer systems as long as they comply with this “open” standard. * 计算机专业英语 * The major principles A layer should be created where a different level of abstraction is needed. Each layer should perform a well-defined function. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. The layer boundaries should be chosen to minimize the information flow across the interfaces. The number of layers should be large enough so that distinct functions need not be put together in the same layer without necessity, and small enough so that the architecture will not become out of control. * 计算机专业英语 * The OSI Reference Model * 计算机专业英语 * The Physical Layer The physical layer defines network transmission media, signaling methods, bit synchronization, architecture (such as Ethernet or Token Ring), and cabling topologies. The physical layer is concerned with transmitting raw bits over a communication channel. The design issues here largely deal with mechanical, electrical and procedural interfacing to the subnet. * 计算机专业英语 * The Data Link Layer The task of the data link layer is to obtain a raw transmission facility and to transform it into a line that appears free of transmission errors to the network later. It accomplished this task by breaking the input data up into data frames, transmitting the frames sequentially, and processing the acknowledgment frames sent back by the receiver. * 计算机专业英语 * The Network Layer The network layer controls the operation of subnet. It determines the chief characteristics of the node-host interface, and how