Fast ethernet

Fast Ethernet or High-Speed Ethernet is the name of a series of IEEE standards for 100 Mbps (megabits per second) Ethernet networks. The name Ethernet comes from the physical concept of ether. At the time the fast prefix was added to differentiate it from the original 10 Mbps Ethernet version.

Due to increased storage capacity and processing power, today's PCs are capable of handling high-quality graphics and complex multimedia applications. When these files are stored and shared on a network, transfers from one client to another result in heavy use of network resources.

Traditional networks operated between 4 and 16 Mbps. More than 40% of all PCs are connected to Ethernet. Traditionally Ethernet ran at 10 Mbps. At these speeds, since companies produce large files, they can experience long delays when sending the files over the network. These delays produce the need for greater speed in the networks.

Fast Ethernet is currently not the fastest version of Ethernet, with Gigabit Ethernet and 10 Gigabit Ethernet currently being the fastest.

3Com 3c905-TX 100BASE-TX PCI network interface card.

History

Traditional networks operated between 4 and 16 Mbps. More than 40% of all PCs are connected to Ethernet. Traditionally Ethernet worked at 10Mbps. At these speeds, since companies produce large files, they can experience long delays when sending the files over the network. These delays produce the need for greater speed in the networks.

Today, the following classification of Ethernet protocol networks can be made:

- Ethernet (also called original Ethernet): Up to 10 Mbps.
- Fast Ethernet: Up to 100 Mbps.
- Gigabit Ethernet: Up to 1000 Mbps.
- 10 Gigabit Ethernet.

The following factors were decisive in implementing Fast Ethernet:

• Increased speeds of processors
• Increased network users
• The new bandwidth intensive applications used in networks.

Each of these changes adds an increase in localized load on the network.

Fast Ethernet was introduced in 1995, and was the fastest version of Ethernet for another 3 years, until it was surpassed and replaced by the Gigabit Ethernet version.

At the time, two IEEE standards competed for the 100 Mbps local area network market. The first was IEEE 802.3 100Base-TX, commercially called Fast Ethernet, which uses the CSMA/CD access method with some degree of modification, the standards for which were announced in late 1994 or early 1995. The second was IEEE 802.12 100BaseVG, adapted from HP's 100VG-AnyLAN, which uses a demand priority method instead of CSMA/CD. For example, real-time voice and video could be given higher priority than other data. This latest technology did not prevail, leaving Fast Ethernet with almost the entire market.

General Characteristics

A fast Ethernet adapter can be logically divided into a Media Access Controller (MAC) part, which deals with availability issues, and a Physical Layer (PHY) zone.

The MAC layer communicates with the physical via a synchronous parallel 25 MHz 4-bit interface, known as MII.

The MII interface can have an external connection, but it is normal to make its connection through ICs in the network adapter.

The MII interface sets a maximum data bit rate of 100Mbit/s for all versions of fast Ethernet.

It can be seen that currently in real networks the amount of data sent per signal is below this theoretical maximum. This is due to the fact that headers and tails are added to each packet to detect possible errors, occasionally "packets are lost" due to noise, or the waiting time required for each packet to be received by the other terminal.

Support

Fast ethernet can work over fiber optics and copper wire. Each way of working has specific standards adapted to the required situation:

COPPER

• 100BASE-TX
• 100BASE-T4
• 100BASE-T2

FIBER OPTICS

• 100BASE-FX
• 100BASE-SX
• 100BASE-BX

Standards for copper

Depending on the type of standard used, the type of cable will belong to a different category with certain characteristics that follow the following table: 100BASE-T is a Fast Ethernet standard that uses a twisted copper pair. We can find the following categories of this standard:

 100BASE-TX (100 Mbit/s over 2 pairs of braided copper in category 5 or above)

 100BASE-T4 (100 Mbit/s over 4 pairs of braided copper category 3 or above)

 100BASE-T2 (100 Mbit/s over 2 pairs of braided copper category 3 or above)

The cable segment length for a 100Base-T type standard is limited to 100 meters. This is included in the IEEE 802.3 standard (approved in 1995)

100BASE-TX

The most common standard for this type of Ethernet is 100BaseTX, and it is supported by most Ethernet hardware in production today.

Uses 2 pairs of Category 5 or higher twisted copper (a Category 5 cable contains 4 pairs, so it can support 2 100BASE-TX links).

In a typical 100Base-TX configuration, one twisted pair of wires is used in each direction (full-duplex).
(See IEEE 802.3 for details)

Configuring a 100Base-TX network is very similar to a 10Base-T network. When we use this standard to create a local area network, the network components (computers, printers, etc.) are usually connected to a switch or a hub, creating a network with a star topology. Alternatively, it is possible to connect two components directly using a crossover cable.

As for the type of encoding, use 4B5B.

100BASE-T4

It was one of the first implementations of Fast Ethernet. Four pairs of twisted cable are required, but these can be category 3 instead of category 5, which is required by TX, allowing old installations to be amortized. Of the four pairs, one pair is reserved for transmitting, another for receiving, and both switch to send/receive so that communication is always established simultaneously through 3 pairs.

As for the type of encoding, it uses 8B6T.

100BASE-T2

In this standard, data is transmitted over two copper pairs, 4 bits per symbol. First, a 4-bit symbol is extended into two 3-bit symbols by a complicated coding procedure based on a linear feedback register (see the standard for more information). This is necessary to flatten the bandwidth and spectrum of the signal.

The original bitmap that represents the code is not constant in time and has a long period (it could be said that it appears with a random frequency).

Regarding the type of encoding, it uses PAM-5.

Standards for Fiber Optic

The fiber optic version of these standards achieves higher speed, as well as covering a larger area without the need for repeaters.

100BASE-FX

It is a version of Fast Ethernet over fiber optics. It uses a type of 1300 light (NIR; nm near-infrared) that is transmitted through two lines of multimode fiber optics (MMF), one for reception (RX) and the other for transmission (TX).

For these cases, the maximum length covered is 400 meters for half-duplex connections (to ensure collision detection) or 2 kilometers for full-duplex over multimode fiber optics (compared to 100 meters over cable coppermade).

Regarding the type of encoding used, 100BASE-FX uses the same 4B5B and NRZI encoding that 100BASE-TX used.

100BASE-SX

It uses two multimode fiber optic lines to receive and transmit. This is a lower cost alternative to 100BASE-FX as it uses a shorter wavelength, which is much less expensive than the long wavelength used in 100BASE-FX. 100BASE-SX can work at distances of up to 300 meters.

100BASE-SX uses the same wavelength as the fiber optic version 10BASE-FL. Due to the short wavelength used (850 nm), less expensive optical components (LEDs instead of lasers) are required, making it an attractive option for those upgrading from 10BASE-FL and those who do not demand long distances..

100BASE-BX

Works over a single fiber optic line (unlike 100BASE-FX, which uses a pair of fibers). Because we have only one line, a multiplexer is used that divides the signal into two different wavelengths, one to transmit, and one to receive.

100BASE-LX

100BASE-LX is a version of Fast Ethernet with two single-mode optical fibers. It has a nominal range of 10 km and a nominal wavelength of 1310 nm.

Advantages of Fast Ethernet

Fast Ethernet is based on the Ethernet standard, so it is compatible with any Ethernet network, regardless of its type, since network adapters (network cards) automatically adjust their speed to the slowest adapter, so that all the equipment can be connected (although at the cost of losing speed).

It can be installed on most current networks with almost no changes to the network infrastructure.

Finally, Fast Ethernet is low cost and the most widely adopted solution available on the market.