When starting with protocols that work at the upper layers of the network models, each set of data is wrapped inside the next lower layer protocol, similar to wrapping letters inside an envelope. The application creates the data, then the transport l

正交幅度调制，即QAM。现有的协议，如802.11b无线以太网（Wi-Fi）协议和数字视频广播（DVB）协议都使用了64-QAM调制。-Quadrature amplitude modulation, i.e. QAM. Existing protocols, such as 802.11b wireless Ethernet (Wi-Fi) protocol, and Digital Video Broadcasting (DVB) protocols are used in 64-QAM m