同步通信终端

The standards specify several types of end user access circuits, each of which involves one or more B channels and one D channel. The B channels are for circuit-switched user communications, and the D channels are primarily for signaling and control (e.g., on-hook and off-hook signaling, ringing signals, performance monitoring, synchronization and error control).

该标准详细列出了几种终端用户电路类型，每一种类型包含一个或多个B信道以及1个D信道。B信道用于电路交换用户通信，D信道主要用于信令和控制（例如挂和摘机机信令、振铃信号、性能监控、同步以及错误控制）。

Breath, muscle contraction of the buttocks; arch body, as far as possible to hold his head, right leg straight towards the ceiling (peg-leg knee in order to avoid muscle tension).

呼气，收缩臀部肌肉；拱起身体，尽量抬起头来，右腿伸直朝向天花板（膝微屈，以避免肌肉紧张）。

The cost of moving grain food products was unchanged from May, but year over year are up 8%.

粮食产品的运输费用与5月份相比没有变化，但却比去年同期高8％。