IEEE 802.3bz, NBASE-T and MGBASE-T refer to standards for Ethernet over twisted pair at speeds of 2.5 Gbit/s and 5 Gbit/s. These represent intermediate speeds between Gigabit Ethernet and 10 Gigabit Ethernet, potentially allowing for faster speeds over existing cabling. The resulting standards are named 2.5GBASE-T and 5GBASE-T. They are both specified in Clauses 125 and 126 of the current IEEE 802.3 standard.
