REPLACING PRINTED WIRING WITH ENGINEERED CABLE SOLUTIONS FOR HIGH-SPEED APPLICATIONS JASON ELLISON, PRINCIPAL ENGINEER, AMPHENOL COMMUNICATIONS SOLUTIONS
Since networking equipment operating at 100G and 200G total data rate per port has become ubiquitous, network system development engineers have shifted their focus to 200G, 400G, and 800G port data rates, with 1.6T per port on the horizon. However, getting faster transmission through interconnects is not as simple as just turning up the speed with a dial. It requires adjustments to signal modulation and SerDes technology, as well as advancements in interconnectivity and IC packaging. Figure 1 relates data rate to the required bandwidth in gigahertz and illustrates some of the changes.
Assuming an OSFP (Octal Small Form-Factor Pluggable) IO solution, a data rate of 200G uses NRZ modulation — a two-level modulation. As the data rate increases from 200G to 400G, the channel frequency requirement stays almost the same. Instead of increasing bandwidth, the data rate is doubled by changing the modulation to PAM4 — a four-level modulation. Simply put, for every one bit sent with NRZ, two bits are sent through the channel with PAM4. As data rates increase to 800G, PAM4 remains, and the frequency required doubles.
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