数据链路层在自动化环境中的设备之间提供基本的时间关键型消息通信。 该协议为所有参与的数据链路实体提供通信机会 a） 根据预先建立的时间表，以同步启动的循环方式，以及b）按照这些数据链路实体中的每个周期的请求，以循环或非循环异步方式。 因此，该协议可以被描述为一个异步提供循环和非循环访问的协议，但每个循环都有一个同步重启。交叉引用:ISO/IEC/IEEE 8802-3:2017ISO/IEC 10731IEEE标准802。 1IEEE标准802.1QISO/IEC 7498-1ISO/IEC 7498-3IEC 61158-1:2019BS EN IEC 61158-1:2019购买本文件时，所有当前可用的修订版均包含在购买本文件中。

The data-link layer provides basic time-critical messaging communications between devices in an automation environment. This protocol provides communication opportunities to all participating data-link entities a) in a synchronously-starting cyclic manner, according to a pre-established schedule, andb) in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those data-link entities. Thus this protocol can be characterized as one which provides cyclic and acyclic access asynchronously but with a synchronous restart of each cycle.Cross References:ISO/IEC/IEEE 8802-3:2017ISO/IEC 10731IEEE Std 802.1DIEEE Std 802.1QISO/IEC 7498-1ISO/IEC 7498-3IEC 61158-1:2019BS EN IEC 61158-1:2019All current amendments available at time of purchase are included with the purchase of this document.