In July 1976, Metcalfe and Boggs published their foundational paper on Ethernet in Communications of the ACM. Their efficiency model -- E = (P/C)/(P/C + W*T) -- measures the fraction of Ether time carrying good forward packets under contention. For fifty years this model has framed how the community thinks about Ethernet performance. We argue it is silent on the question that matters for modern intra-rack interconnect: bilateral transaction efficiency -- the fraction of link time that produces committed agreements between sender and receiver. Metcalfe and Boggs themselves planted the seed in their EFTP "end-dally" protocol (Section 7.2.2), and the deeper anchor is older still: Abramson's Alohanet carried positive acknowledgments at the link layer -- a bilateral mechanism Metcalfe consciously removed in 1973 to obtain Ethernet's simple, ACK-free packet format. The result is a fifty-year bilateral zigzag: Aloha (bilateral) to Ethernet (unilateral) to the EFTP end-dally (bilateral) to TCP (unilateral-with-bilateral-above). We formalize bilateral efficiency, connect it to the back-to-back Shannon channel with Perfect Information Feedback, and -- scoping the claim explicitly to intra-rack distances of one meter or less -- describe how the Open Aethernet link recovers mutual knowledge at the link layer. The correction to Table 1 is not a different set of numbers. It is a different question.

翻译：1976年7月，Metcalfe 和 Boggs 在《ACM 通讯》上发表了关于以太网的奠基性论文。其效率模型——E = (P/C)/(P/C + W*T)——度量了在竞争条件下以太网传输有效前向数据包的时间占比。五十年来，该模型一直主导着学界对以太网性能的思考方式。我们认为，该模型对于现代机架内互连的关键问题——双边交易效率，即链路时间中用于产生发送方与接收方之间确认协议的时间占比——并未给出回答。Metcalfe 和 Boggs 本人在其 EFTP "端到端延迟"协议（第 7.2.2 节）中埋下了这一思想的种子，而其更深层的根源则更为久远：Abramson 的 Alohanet 在链路层携带了肯定确认——这是一种双边机制，Metcalfe 在 1973 年有意移除以获得以太网简单、无确认的数据包格式。其结果是五十年来双边机制的曲折演进：Aloha（双边）→ 以太网（单边）→ EFTP 端到端延迟（双边）→ TCP（单边-带-双边上层）。我们形式化了双边效率，将其与具有完美信息反馈的点对点香农信道联系起来，并——明确将论述范围限定在一米或更短的机架内距离——描述了开放以太网链路如何在链路层恢复互知知识。对表 1 的修正并非一套不同的数字，而是一个不同的问题。