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10: Ethernet - Fast Ethernet over copper & fiber optics part 3



Fast Ethernet
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In 1995, 100BASE-T, a more advanced version of Ethernet, was released, but this time it is called Fast Ethernet rather than Ethernet for the reason that  it carries traffic at the rate of 100Mb/s, which is much faster than the previous versions. It was introduced by IEEE as 802.3u standard. This version remained the fastest one until the emergence of Gigabit Ethernet. Interestingly, this standard keeps all of the old frame formats, interfaces and procedural rules. 100BASE-T is an umbrella term which includes other standards that are also considered to be part of Fast Ethernet. These standards can be divided into two parts, Fiber and Copper.

Copper standards, which appeared before fiber optics, were released in this order: 100BASE-TX, 100BASE-T4, 100BASE-T2, 100BASE-T1, 100BASE-VG, whereas Fiber standards were introduced in the following order : 100BASE-FX, 100BASE-SX, 100BASE-BX, 100BASE-LX10.

Fast Ethernet over copper

To start with 100BASE-TX, which is the predominant form of Fast Ethernet , this standard supports data transfer rates up to 100 Mb/s running over Category 5 copper cable with two twisted pairs. 4B5B MLT-3 is the encoding  method used for data transmission.
The next standard is 100BASE-T4. Though it was not widely used, it had some interesting features.  data are carried at the rate of 100 Mb/s requiring four twisted copper pairs in CAT 3 rather than CAT 5 required by TX. One pair serves to transmit while the other pair is used for reception. Three pairs are used to transmit data in each direction, either for receiving or transmitting not both, and one pair is reserved for collision detection. Thus, all that makes 100BASE-T4 inherently half-duplex.  This standard is able to be implemented with CAT 3, 4 , 5 UTP (unshielded twisted pair) or STP cables (shielded twisted pair).

Then we have 100BASE-T2, which is standardized in IEEE 802.3y. This standard was not also widely used, however it served as the ground for the development of other standards such as 1000BASE-T. Data are transmitted over two copper pairs using CAT 3. two pairs are used for simultaneously transmitting and receiving, thus allowing full-duplex operation.

Afterwards we have 100BASE-T1, which is standardized in IEEE 802.3bw-2015 Clause 96. It allows data transmission only over a single pair. It support only full-duplex.

Finally, the 100BaseVG standard was proposed by HP (Hewlett Packard ) company, and planned to be later standardized as IEEE 802.12. As soon as the 100BASE-TX came into existence, this standard vanished to the extent that it dit not endure any short time. It  uses CAT 3 cabling and token concept rather than CSMA/CD. Therefore, it can be inferred that 100BASE-TX is the most popular and the widely used Fast Ethernet standard.

Fast Ethernet over fiber

Optical fiber is another strong and fast cabling system that was developed during the time of Fast Ethernet. This type of cabling is characterized by high speed. In today’s networks, countries are connected together by means of optical fiber for the reason of its quality and the speed of data transmission. The following is a list of fiber optics standards :

100BASE-FX is the famous Fast Ethernet version of fiber optics. In full-duplex communication over multi-mode ( means several waves are transmitted at a time) optical fiber, the cable can reach up to 2 Km, whereas in half-duplex connections the maximum length is 412 metres. The cable consists of two strands of optical fiber, one for transmit (TX) and the for receive (RX). By means of  this cable, 1300 nm (0.000000001 m) near-infrared (NIR) light wavelength is carried.

100BASE-SX is another version of Fast Ethernet over optical fiber. The cable can be stretched up to 550 metres. This version also has two strands of multi-mode fiber optics allowing the operation of transmit and receive. This version might be resorted to on the grounds of its lower cost compared to 100BASE-FX. It uses shorter wavelength (850 nm) than 100BASE-FX (1300 nm). This version is backward-compatible because it uses the same wavelength as 10 Mbit/s Ethernet over optical fiber (10BASE-FL). Significantly, 100BASE-FX is not backward-compatible. Thus, 100BASE-SX may seem appealing to those who do not require long distances. It is very significant to mention that this standard is not part of IEEE 802.3 ones, it was rather invented by an other company.

100BASE-BX10 is a Fast Ethernet version over a single strand of fiber optics, unlike 100BASE-FX and 100BASE-SX which use two strands of fiber optics. The wavelengths are unequally used, 1310 nm is used for transmit and 1550 nm for receive.

100BASE-LX10 is another interesting Fast Ethernet version over single-mode fiber optics. This version was designed for long distances reaching about 10 km. The wavelength is nearly the same as 100BASE-BX10 version – 1310 nm.

The next lesson is a sequel to this one
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10: Ethernet - Fast Ethernet over copper & fiber optics part 3 Reviewed by BOUFTIRA on 2:54:00 PM Rating: 5

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