Fast Ethernet

• Fast Ethernet uses the same frame formats and CSMA/CD technology as normal 10Mbps Ethernet. The difference is that the maximum delay for the signal across the segment is now 5.12 microseconds instead of 51.2 microseconds. This comes from the fact that the bit time (time to transmit one bit) is 0.01 microseconds and that the slot time for a frame is 512 bit times. The Inter-Packet Gap (IPG) for 802.3u is 0.96 microseconds as opposed to 9.6 microseconds for 10Mbps Ethernet.

• Fast Ethernet is the most popular of the newer standards and is an extension to 10BaseT, using CSMA/CD. The '100' denotes 100Mbps data speed and it uses the same two pairs as 10BaseT (1 and 2 for transmit, 3 and 6 for receive) and must only be used on Category 5 UTP cable installations with provision for it to be used on Type 1 STP. The Copper physical layer being based on the Twisted Pair-Physical Medium Dependent (TP-PMD) developed by ANSI X3T9.5 committee. The actual data throughput increases by between 3 to 4 times that of 10BaseT.