曼彻斯特编码和以太网协议
这里的理论问题是——[一般]以太网协议使用 8 字节前导码，除了最后一个字节外，具有（几乎）全 10101010 位模式。这样做的目的之一是为了发送器/接收器同步。
由于曼彻斯特编码本质上可以同步发送方和接收方，您认为前导码是必要的还是多余的开销？我认为这是多余的，但指示帧的开始/结束可能很重要。
Theoretical question here -- the [general] Ethernet protocol uses an 8 byte preamble with an (almost) all 10101010 bit pattern, save for the very last byte. One purpose of this is for sender/receiver synchronization.
Since Manchester Encoding can inherently sync the sender and receiver, do you think that the preamble is necessary or redundant overhead? I would argue that it is redundant, but that it may be important to indicate the start / end of frames.
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曼彻斯特编码将在位级别上同步，但您还需要获得更高级别的同步。特别是，您需要字节级和帧级同步：字节是因为这样您实际上可以传输完全可以理解的数据，帧是因为这样您可以理解整个消息。通过拥有该标头，它可以为以太网硬件提供足够的时间来开始侦听后面的真实消息并正确确定该消息的开始位置；它不必捕获前导码的第一部分即可工作，因此更可靠。可靠性好。
The Manchester Encoding will synch things up at the bit level, but you also need to get higher level synchronization in place too. In particular, you need byte level and frame level synch: bytes because then you can actually transfer data that can be understood at all, and frames because then you can comprehend the overall message. By having that header, it gives the Ethernet hardware enough time to start listening for the real message that follows and to correctly determine where that message starts; it doesn't have to capture the first bit of the preamble to work, and so is more reliable. Reliability is Good.
原来的以太网已经完全可以了吗？被 802.3 取代，这说明了第 8 个八位位组 (SFD) 的差异。前导码的目的是在数据到达之前使发送方和接收方保持同步。如果没有它，数据的前几个字节可以使用曼彻斯特编码中的固有时钟来同步，但它们可能会丢失。
根据当前的技术水平，可能会使用更短的前导码。就此而言，我们实际上也不需要在现代有线网络中进行冲突检测。
但正如他们所说，如果它没有坏，就不要修理它。
The original Ethernet has been totally? replaced by 802.3 which accounts for the difference in the 8th octet (SFD). The purpose of the preamble is to get the sender and receiver in sync, before the data arrives. Without it the first few bytes of the data could use the inherent clock in Manchester Encoding to get in sync, but they might be lost.
Based on the current state of the art, a shorter preamble could likely be used. For that matter we don't really need collision detection in modern wired networks either.
But as they say, if it ain't broke don't fix it.