Architect's TL;DR: SR4 is the budget king for intra-rack links; CWDM4 is the efficiency workhorse for campus-scale 2km spans; LR4 is the premium choice for 10km DCI where stability is non-negotiable. Lowest CAPEX; leverages high-density MPO trunks. Continuing our discussion on 100G optical modules, let's explore the essential 100G transmission standards—SR4, DR1, DR4, BiDi SR, LR4, CWDM4, SWDM4, ER, and ZR. These standards often cause confusion when selecting the right module for your needs. Each of these modules offers distinct features and advantages that cater to various network requirements. Before diving into a detailed comparison, let's briefly introduce. This definitive guide cuts through the confusion, exploring all major 100G QSFP28 options – from SR4 and LR4 to CWDM4, Single Lambda, and beyond – helping you make an informed decision for your high-speed connectivity needs. 📝 What is a QSFP28 Optical Module? The QSFP28 (Quad Small Form-factor. Selecting the wrong 100G optical module is a silent killer of data center ROI, leading to cascading failures in port density, thermal headroom, and cabling lifecycle. Technically speaking, while all three deliver 100Gbps, their underlying physical layers—ranging from 850nm parallel VCSELs to 1310nm.
