The basic principle of the
token ring network Each station of the token ring network is connected to the ring interface trunk coupler TCU through a cable. The main function of TCU: to pass all passing frames and provide an interface for the access station to send and receive data. Corresponding to this, there are two states of TCU: listening state and sending state. Data is always transmitted bit by bit from one TCU to the next in a specific direction, and each TCU regenerates and retransmits each bit.
令牌环网的媒体接入控制机制采用的是分布式控制模式的循环方法。在令牌环网中有一个令牌（Token）沿着环形总线在入网结点计算机间依次传递，令牌实际上是一个特殊格式的MAC控制帧，本身并不包含信息，仅控制信道的使用，确保在同一时刻只有一个结点能够独占信道。站点只有取到令牌后才能发送数据帧，因此令牌环网不会发生碰撞。由于令牌在网环上是按顺序依次传递的，因此对所有入网计算机而言，访问权是公平的。
