$$R_{\mathrm{line}} = 2\,R_{\mathrm{baud}}$$

Equation 11 · Datacenters

How AI Datacenter Interconnects Actually Work

This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.

Modern high-rate Ethernet lanes use PAM4 modulation: instead of encoding one bit per symbol as ordinary NRZ signaling does, PAM4 uses four distinct voltage levels to encode two bits per symbol, so a lane’s bit rate runs at twice its baud (symbol) rate rather than matching it one for one. Writing $R_{\mathrm{baud}}$ for the symbol rate and $R_{\mathrm{line}}$ for the resulting line rate, $R_{\mathrm{line}} = 2\,R_{\mathrm{baud}}$. which is exactly the relationship documented for real 400G optics: a 26.5625 Gbaud lane carries 53.125 Gb/s in an eight-lane configuration, and a 53.125 Gbaud lane carries 106.25 Gb/s in a four-lane configuration [ 8 ] . That doubling is not free. Four voltage levels packed into the same…

Meanings in this article

• $R_{\mathrm{baud}}$: the writing.

Equation guide → · Article →