New standards for 400-Gb/s Ethernet will operate over 4- and 8-fiber-pair constructions of multimode fiber, leveraging PAM-4 signaling. The IEEE is introducing 400GBASE-SR4.2 and 400BBase-SR8 to support the short reach application space inside the data center. Both use PAM-4 signaling to provide for higher transmission speeds over MMF using VCSELs.

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