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一、CSMA/CD CSMA/CD是广泛用于总线或树形局部网络的一种访问协议。在基带系统中,最早采用这种访问协议的是著名的原型以太网(1976年);最早采用此类访问协议的宽带系统是MITRENET(1979年)。其基本思想起源于ALOHA系统,ALOHA方式具体可分为纯ALOHA和时间片ALOHA两种形式,最大吞吐量分别只有18.4%和36.8%。造成ALOHA方式信道效率低的根本原因是节点的发送意图与信道状态无关。为克服此弱点,CSMA方式应运而生,其主要改进是增添了“讲前先听”的功能。它具体可分为三种形式:断续监听式、1—持续监听式和P—持续
First, CSMA / CD CSMA / CD is an access protocol widely used for bus or tree local network. In baseband systems, the earliest adopters of such access protocols were the well-known Prototype Ethernet (1976); the earliest adopters of such access protocols were MITRENET (1979). Its basic idea originated in the ALOHA system. The ALOHA method can be divided into pure ALOHA and time slice ALOHA. The maximum throughput is only 18.4% and 36.8% respectively. The fundamental reason for the low efficiency of the channel caused by the ALOHA method is that the transmission intention of the node is not related to the channel state. To overcome this weakness, the CSMA approach came into being, with the major improvement being the addition of the “listen before speaking” function. It can be divided into three specific forms: intermittent listening type, 1-continuous monitoring and P-continued