基于Nak-Only握手协议的WUSB系统的设计

摘要

在WUSB系统的设计中,针对ACK等短数据包在物理层是定长数据包时会浪费带宽的问题,提出了一种Nak-Only握手协议,其主要思想是通过一种消极等待机制来代替ACK的传输,从而节省了过长握手包造成的带宽浪费.这种方案在实现中需要WUSB物理层的收发转换延迟具有良好的稳定性,但在收发转换延迟跳动较大的情况下,也可以用发送端缓存3个数据包的方法来避免数据包丢失.通过仿真验证了Nak-Only握手协议会对WUSB带来吞吐率上的提升,效果可以接近物理层支持理想变长数据包时的性能.%A Nak-Only handshake protocol is brought out to reduce the waste of bandwidth when short data packet such as ACK transmitting in a PHY-layer packet with specific length. It keeps the receiver negatively waiting instead of sending the ACK packet, so that the waste of bandwidth could be reduced. This program requires a stable TX-RX switching time in the PHY-layer. But if the switching time sometimes exceeds the limit, packet lost could also be avoided by buffering 3 data packets in the transmitter. It can be proved from the simulation that Nak-Only handshake protocol improves the throughput rate of WUSB, and the effect is close to the ideal case that packet length could be freely specified in PHY-layer.