Which Ethernet standard was introduced in 1999 and supports 5 GHz and 54 Mbit/s?

The correct choice is 802.11a, which was introduced in 1999 and is noteworthy for operating at the 5 GHz frequency band and offering data rates of up to 54 Mbit/s. This standard was one of the early advancements in wireless networking technologies.

When 802.11a was developed, it focused on providing higher data rates and less interference compared to the 2.4 GHz frequency band, which was already crowded due to other devices and standards like 802.11b. The 5 GHz band allows for a larger number of non-overlapping channels, which can provide better performance in terms of speed and reliability when used in environments with many networks.

The other standards mentioned were introduced around the same time or later and have different characteristics. For example, 802.11b, which emerged shortly after, operates at the 2.4 GHz frequency and offers speeds of up to 11 Mbit/s. Meanwhile, 802.11g, released in 2003, operates on both 2.4 GHz and supports data rates up to 54 Mbit/s, but it wasn't introduced until several years after 802.11a. Lastly, 802.11n, which came out in