11-1 FRAMING成帧 The data link layer needs to pack bits into frames,so that each frame is distinguishable from another.Our postal system practices a type of framing.The simple act of inserting a letter into an envelope separates one piece of information from another;the envelope serves as the delimiter. 数据链路层需要将一组比特位组成帧，以便帧和帧之间 是可以识别的。邮局系统就实现了成帧方式，信封就是 一种分隔符。 Topics discussed in this section: Fixed-Size Framing固定长度成帧例如第18章的ATM信元 Variable-Size Framing可变长度成帧面向字符和面向比特位 11.3 11.3 11-1 FRAMING 成帧 The data link layer needs to pack bits into frames, so that each frame is distinguishable from another. Our postal system practices a type of framing. The simple act of inserting a letter into an envelope separates one piece of information from another; the envelope serves as the delimiter. 数据链路层需要将一组比特位组成帧，以便帧和帧之间 是可以识别的。邮局系统就实现了成帧方式，信封就是 一种分隔符。 Fixed-Size Framing 固定长度成帧 例如第18章的 ATM信元 Variable-Size Framing 可变长度成帧 面向字符和面向比特位 Topics discussed in this section: