The Wi-Fi Alliance certifies vendor equipment to ensure 802.11 products on the market follow the various 802.11 specifications. Consumer versions of Wi-Fi products have additionally maintained backward compatibility. For example, 802.11b, 802.11g, and 802.11n equipment all can communicate with each other, and mixed Wi-Fi networks with devices running multiple of these standards are commonly referred to as "802.11b/g/n" networks. 802.11ac too communicates with each of these others. The old 802.11a technology is not compatible with these others and has fallen out of mainstream usage as a result.