中文摘要：

研究带两个服务等级约束的3台同型机在线排序问题。工件和机器的服务等级为1或2，加工允许中断但不允许引入机器空闲时间，目标是最小化最大完工时间。该文首先证明任意在线算法的竞争比至少是3/2，接着对仅有1台机器等级为1的情形给出了竞争比为5/3的在线算法。

英文摘要：

We study online scheduling on three identical machines with two grades of service （GoS） levels. Each job , as well as each machine , is associated with a GoS level of either 1 or 2 .Preemption is allowed but machine idle times are forbidden .The objective is to minimize the maximum completion time of jobs .We first show that the competitive ratio of any online algorithm is no smaller than 3/2.Then, for the problem when only one machine has a GoS level of 1, we propose a 5/3-competitive algorithm.