Abstract: According to some real time sensitive network require for common data throughput, an adaptive p persistent CSMA/CD protocol for reducing the delay effectively is proposed. Firstly, the monitoring variables reflecting the network status will be found out, based on the monitoring values, the network status is classified into four types, the light load status, the relative light load status, the relative heavy load status and the heavy load status. Then the sending possibility p and the maximum back-off threshold [Bm] will be adjusted dynamically based on the judged network status. Finally, the delay and throughput and bus utilization of networks are simulated. The result shows that the adaptive p persistent CSMA/CD protocol can effectively reduce delay and jitter.

Key words: delay, back-off threshold, Carrier Sense Multiple Access with Collision Detection（CSMA/CD）, adaptive

摘要： 针对一些对实时性要求较高而数据吞吐量不高的网络服务，提出一种有效减小时延的自适应p-坚持CSMA/CD协议算法。依据与网络性能相关的关键参数之间的关系，提炼出能有效反映网络负载的状态监测量，基于对监测量的联合判断结果，将网络分为轻负载、较轻负载、较重负载和重负载四种状态，并针对不同负载状态调整发送概率[p]和最大避退上限值[Bm]。通过对协议的时延、吞吐量和总线利用率进行仿真，与一般的p-坚持CSMA/CD协议相比，自适应p-坚持CSMA/CD协议能较有效降低时延、减小抖动。

关键词: 时延, 避退上限, CSMA/CD协议, 自适应