The 1000BaseX (IEEE 802.3z) Gigabit Ethernet standard was ratified in June 1998, after more than two years of intense effort within the IEEE 802.3 Ethernet Committee. The key objective of the 802.3z Gigabit Ethernet Task Force was to develop a Gigabit Ethernet standard. The IEEE 802.3z Gigabit Ethernet standard includes three Physical Layer specifications: two for fiber optic media (1000BaseSX and 1000BaseLX), and one for shielded copper media (1000BaseCX). Another working group, the IEEE 802.3ab Task Force, is also defining the Physical Layer to run Gigabit Ethernet over the installed base of Category 5 UTP cabling. This 1000BaseT standards effort is still in progress. A fourth transceiver type, 1000BaseLH (not shown on the diagram), is a multivendor specification that defines optical transceivers that support distances greater than the 1000BaseLX specification.