40GBase-SR4 is an interface for 40 Gigabit Ethernet. It is a fiber optic interface for multimode fiber of OM classes 3 and 4 with four parallel OM3/4 fibers in both directions. The interface designation SR, which stands for Short Reach, indicates that it is an interface for short wavelengths. The 40GBase SR4 is described in IEEE 802.3ba.
The 40GbE interface operates with 64B66B coding and the number 4 states that transmission is via a ribbon fiber with four multimode fibers in each direction. The wavelength range at 850 nm is used as the optical window.
The light signals are generated by VCSEL lasers. Transmission takes place at a data rate of 10 Gbit/s. The 64B66B coding results in a baud rate of 10.3125 GBaud. The bridgeable distance depends on the OM class of the multimode fiber and is 100 m for OM3 and 150 m for OM4. 40GBase-SR4 uses an MPO connector as the FOconnector.
The 40GbE optical interface for short distances uses a QSFP module (Quad Small Form Factor Pluggable) as transceivermodule.