光学 MSA：QSFP-DD 使 PAM4 信号处于主导地位

在 2018 年进行了大量演示和 alpha 模块测试之后，双密度版本的四通道小型可插拔 (QFSP) 多源协议 (MSA) 模块标准有望成为新线卡的规则。QSFP-DD 热潮的隐含意义不是模块本身的物理特性，而是转向先进信令方法的趋势。十年前，QSFP28 的问世预示着使用 NRZ 信令的 25Gbps 电通道即将占据主导地位。如今，QSFP-DD 及其更庞大的表亲 —— 八进制 SFP 或 OSFP ，都使用 PAM4 信令。其用得最多的是 50Gbps 通道。但 QSFP-DD 足够灵活，可以在各种实施中使用八通道接口：25G x 8 用于 200Gbit 以太网，50G x 8 用于 400Gbit 以太网，可能还有一些早期的 100G x 8 用于预标准 800Gbit 以太网。

嵌入式光学革命，还是插接式连接的合作伙伴？关于 COBO 的看法

Slow but steady advances were made in 2018 in on-board optical links for chip-to-chip and chip-to-module interfaces. The integrated-optics revolution, anticipated three years ago when the Consortium for On-Board Optics (COBO), of which Semtech is an associate member, was launched, has been replaced by a realization that only slow migration from traditional pluggable modules will serve the data center, whether within a single line card or server blade, or between cards and racks. Even as recent as a year ago, COBO members began rethinking and changing their tune to stress coexistence of pluggable MSA modules and the embedded on-board modules chosen by COBO as a de facto standard.