This article helps network and facilities engineers compare PAM4 modulation optical transceiver options versus NRZ modulation, using practical constraints from leaf-spine fabrics, real switch compatibility realities, and measured optical behaviors. When a data center upgrades from 100G to 200G or expands 400G links, the transceiver choice often becomes the hidden bottleneck: link budgets, power per port, optics sourcing, and failure modes. Understanding the lifespan of an ONU is crucial for network operators and users alike. PAM4 sends two bits in each symbol. This makes data move twice as fast as NRZ. It receives optical signals from an Optical Line Terminal (OLT) at the provider's central office and converts them into electrical signals for devices such as routers, PCs, and. This paper presents a comprehensive review of methods aimed at improving the energy efficiency (EE) of wired access passive optical networks (PONs) and active optical networks (AONs). The comparison has also been drawn among the proposed EPON link with NRZ and RZ modulation scheme.
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