容错状态下的时钟同步是 ATM系统中的重要问题。本文分析了 ATM用户连接的要求 ,提出了与业务类型相关的调度模型 ,它能够满足用户信元的实时传输、发送顺序和信元丢失要求。由于同时考虑了信元的优先级和时限 ,不同传输和丢弃优先级但有相同实时传输要求的信元连接可以同时得到服务。最后 ,根据容错实时系统的要求 ,本文提出了一种容错状态下实现同步的调度方案 ,可以在可容忍时钟精度范围内很好地解决时钟同步问题 Clock synchronization in fault-tolerant state is an important issue in ATM systems. This paper analyzes the requirements of ATM user connection, and proposes a scheduling model related to the service type. It can meet the real-time transmission, sending order and cell loss requirements of user cells. Due to the priority and timing of cells, both the different transmission and discard priorities but the same real-time transmission requirements for cell connectivity can be served at the same time. Finally, according to the requirements of fault-tolerant real-time system, this paper presents a scheduling scheme to achieve synchronization in fault-tolerant state, which can well solve the clock synchronization problem within the range of tolerable clock accuracy