IEEE标准容限内以太网转发时延的测试与分析

Measurement and Analysis of Forwarding Delay in Ethernet Architecture Within Tolerances of the IEEE Specifications

本文在介绍以太网时延和以太网线速的基础上,对线速转发丢包问题进行分析.以测试交换机和Smartbits测试卡作为两个对接交换设备的模型,提出了时钟频偏是交换机转发时延的主要影响因素.推导了以太网交换机内部转发时延和频偏时延的计算公式,进行了以太网交换机一次、二次转发时延测试,理论计算和实验研究的结果验证了提出理论的正确性.

Based on ethemet delay and ethemet frame rate are briefly introduced, packet loss under the frame rate is analyzed in this paper. The model between a switch under tested （SUT） and a Smartbits card is presented and used for two interconnecting switches, this paper presents that clock frequency error （CFE） between a SUT and a Smartbits card is a leading factor of forwarding delay in an ethemet switch. The formulae of internal forwarding delay and forwarding delay caused by existing CFE are deduced. experimental measurement on primary Forwarding delay and secondary forwarding delay is implemented. Theoretical analysis and experimental study testify the accuracy of the above theory.