Difference Between Fast Ethernet and Gigabit Ethernet

Ethernet in computer networks refers to a collection of standards and components, which provides a media to communicate in a Local Area Network (LAN), between network devices. There are various standards developed during past decades, IEEE came with “IEEE 802.3 – Ethernet standard” under IEEE 802 protocol suite. Original Ethernet standard IEEE 802.3 supports a data rate of 10 megabits per second (Mbps).

With the development of technology, 10Mbps speed in LAN was not sufficient. IEEE improved the Ethernet to IEEE 802.3u “Fast Ethernet” standard, and later they came with IEEE 802.3z “Gigabit Ethernet” standard. 

What is Fast Ethernet? 

Fast Ethernet is an improvement of Ethernet, which provides 100Mbps speed. Speed improvement over Ethernet is achieved by reducing the bit time (time taken to transmit one bit) to 0.01 microseconds. IEEE uses 100BASE-Tx/Rx; as usual, “100” stands for 100Mbps speed and “Base” stands for Baseband signals. Following shows the physical media specifications.

100Base-T4 can use four different twisted pairs of category 3 UTP (Unshielded Twisted Pairs) cables; three pairs in both directions with one pair for CS/CD. It uses 25MHz signals with 8B/6T encoding. Inter frame time gap is reduced to 960 nanoseconds from 9.6 microseconds in Ethernet. Maximum distance between two stations is 200m with hub connected in the middle.

100Base-TX uses two pairs of twisted pair cables; one pair for transmission, and the other for reception.

100Base-FX is for Fiber optical medium; there are two cables for transmission and reception. It uses FDDI (Fiber Distributed Data Interface) technology to convert 4B/5B to NRZI code group streams into optical signals at 125MHz clock frequency. 

What is Gigabit Ethernet? 

With more improvements to the Ethernet and Fast Ethernet, IEEE announced IEEE 802.3z – Gigabit Ethernet in February 1997. Although Gigabit Ethernet uses the same CSMA/CD and Ethernet framing format, it shows significant differences like slot time. As its name implies, Gigabit Ethernet provides 1000Mbps transmission in full-duplex and half-duplex. Physical media specifications are listed below. 

1000Base-SX supports duplex links up to 275 meters, use 850nm laser wavelength with fiber channel technology. This can be used only in multimode fiber with 8B/10B encoding in 1.25Gbps line.

1000Base-LX differs only from longer wavelength of 1300nm and above.

1000Base-CX and 1000Base-T uses copper cabling and distances from 25m to 100m respectively.