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 defined how the networking community thinks about Ethernet performance. We argue that the model, while correct for its intended purpose, measures only the forward channel and is silent on the question that matters for modern distributed systems: bilateral transaction efficiency -- the fraction of link time that produces committed agreements between sender and receiver. We show that Metcalfe and Boggs themselves understood this distinction intuitively. Their EFTP "end-dally" protocol (Section 7.2.2 of the original paper) is a three-phase bilateral handshake that attempts to achieve mutual knowledge of transfer completion -- precisely the property that their efficiency model cannot capture. We connect this observation to the Open Atomic Ethernet's bilateral transaction primitive, to the back-to-back Shannon channel formulation with Perfect Information Feedback, and to the Two-State Vector Formalism (TSVF) from physics, which provides the theoretical framework for understanding why both boundary conditions -- sender and receiver -- must be specified for a transaction to have definite value. The correction to Table 1 of Metcalfe and Boggs is not a different set of numbers. It is a different question.

翻译：1976年7月，梅特卡夫和博格斯在《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)——衡量在竞争条件下以太网传输有效数据包的时间占比。五十年来，这一模型定义了网络学界对以太网性能的认知。我们认为，尽管该模型在其预期用途上正确无误，但它仅衡量前向信道，而未能触及现代分布式系统关注的关键问题：双边事务效率——即链路时间中用于产生发送方与接收方之间确定协议的部分。我们证明，梅特卡夫和博格斯本人直观地理解了这一区别。他们的EFTP“端延迟”协议（原始论文第7.2.2节）是一种三阶段双边握手协议，旨在实现传输完成的互知——而这一特性恰好是其效率模型无法捕捉的。我们将这一观察与开放原子以太网的双边事务原语、具有完美信息反馈的背靠背香农信道公式，以及物理学的二态矢量形式（TSVF）相联系——后者为理解为何必须同时指定事务的边界条件（发送方和接收方）才能赋予事务确定值提供了理论框架。对梅特卡夫和博格斯论文中表1的修正并非一组不同的数字，而是一个不同的问题。