Protocol Overhead

E文文档中，经常出现Protocol Overhead一词。

现摘录维基中的解释：

Protocol overhead refers to characteristics of computer communications schemes. An application which transfers data across a network can not expect to use the full of the communications medium, since some data is necessary for routing of the message, describing the information content of the message, and other protocol needs. This extra data is referred to as overhead, since it does not contribute to the information in the content of the message.

Thus, protocol overhead, expressed as a percentage, is the number of non-application (protocol and ) divided by the total number of bytes in the message

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在金山词霸《英汉通信科技名词》词典中，对overhead有如下解释：

不属于用户信息的辅助比特。在传输通道的发送端,按规定的时间间隔被附加于数字信号,在接收端再被去掉,主要用于代码检错和传输控制等。