This Standard specifies the 100BASE-X PMD (including MDI) and fiber optic medium for a short wavelength, multimode fiber, 100BASE-SX. In order to form a complete 100BASE-SX Physical Layer it shall be integrated with the 100BASE-X and PMA in accordance with clause 24 of IEEE Std. 802.3-1998, which is assumed incorporated by reference. As such, the 100BASE-SX PMD shall comply with the PMD service interface according to clause 24.4.1 of IEEE Std. 802.3-1998.

This Standard also specifies the Media Conversion Sublayer, which extends the Auto-Negotiation function defined in IEEE Std. 802.3-1998 to fiber optic media. With the introduction of the Media Conversion Sublayer, devices sharing a fiber optic link segment can configure automatically to take advantage of their full capabilities. By exchanging information during an initialization phase, the link partners determine the operational capabilities of each other, and choose one based on a priority resolution function defined in this Standard. The supported management capabilities allow enabling and disabling the Auto-Negotiation function. It also forces a specific operational data rate and duplex mode. The Media Conversion Sublayer extends the Parallel Detection function to the fiber optic environment. The Parallel Detection function allows for the recognition of 10BASE-FL and 100BASE-SX compatible devices, even when those devices do not include the Auto-Negotiation function. This Standard is intended for LED based systems only.