In the 802.3bm standard developed by the IEEE working group, 40 Gigabit Ethernet( 40GbE) and 100 Gigabit Ethernet( 100GbE) are standardized. Both variants are transmitted over eight multimode fibers - four in both directions.
With this concept, 802.3bm deviates from the previous version 802.3ba, in which 100GbE was transmitted over ten optical fibers in each of the two directions. In other words, 10 Gbit/s per fiber in each case. Since there was no simple migration path from 40GbE to 100GbE, 802.3bm transmits both Ethernet variants over eight optical fibers but at different data rates: 40GbE with 10 Gbit/s and 100GbE with 25Gbit/s and optical fiber.
The advantage of 802.3bm is the simpler cabling. For 100GbE, this version no longer requires two multi-fiber connectors for 12 fibers, like the MPO connector in Base-12 cabling, but can work with one connector and Base-8 cabling.