100 Мбит/с Ethernet стандарты

Ethernet standards that carry data at the nominal rate of 100 Mbit/s

In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE TX is by far the most common. Fast Ethernet was introduced in 1995 as the IEEE 802.3u standard and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet. The acronym GE/FE is sometimes used for devices supporting both standards.

The 100 in the media type designation refers to the transmission speed of 100 Mbit/s, while the BASE refers to baseband signaling. The letter following the dash (T or F) refers to the physical medium that carries the signal (twisted pair or fiber, respectively), while the last character (X, 4, etc.) refers to the line code method used. Fast Ethernet is sometimes referred to as 100BASE X, where X is a placeholder for the FX and TX variants.

Fast Ethernet is an extension of the 10 megabit Ethernet standard. It runs on twisted pair or optical fiber cable in a star wired bus topology, similar to the IEEE standard 802.3i called 10BASE T, itself an evolution of 10BASE5 (802.3) and 10BASE2 (802.3a). Fast Ethernet devices are generally backward compatible with existing 10BASE T systems, enabling plug and play upgrades from 10BASE T. Most switches and other networking devices with ports capable of Fast Ethernet can perform autonegotiation, sensing a piece of 10BASE T equipment and setting the port to 10BASE T half duplex if the 10BASE T equipment cannot perform auto negotiation itself. The standard specifies the use of CSMA/CD for media access control. A full duplex mode is also specified and in practice, all modern networks use Ethernet switches and operate in full duplex mode, even as legacy devices that use half duplex still exist. A Fast Ethernet adapter can be logically divided into a media access controller (MAC), which deals with the higher level issues of medium availability, and a physical layer interface (PHY). The MAC is typically linked to the PHY by a four bit 25 MHz synchronous parallel interface known as a media independent interface (MII), or by a two bit 50 MHz variant called reduced media independent interface (RMII). In rare cases, the MII may be an external connection but is usually a connection between ICs in a network adapter or even two sections within a single IC. The specs are written based on the assumption that the interface between MAC and PHY will be an MII but they do not require it. Fast Ethernet or Ethernet hubs may use the MII to connect to multiple PHYs for their different interfaces. The MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s. The information rate actually observed on real networks is less than the theoretical maximum, due to the necessary header and trailer (addressing and error detection bits) on every Ethernet frame, and the required interpacket gap between transmissions.

100BASE TX is the predominant form of Fast Ethernet, and runs over two pairs of wire inside a Category 5 or above cable. Cable distance between nodes can be up to One pair is used for each direction, providing full duplex operation at 100 Mbit/s in each direction. Like 10BASE T, the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6. Since a typical Category 5 cable contains four pairs and the performance requirements of 100BASE TX do not exceed the capabilities of even the worst performing pair, one typical cable can carry two 100BASE TX links with a simple wiring adaptor on each end. Cabling is conventionally wired to one of ANSI/TIA 568's termination standards, T568A or T568B. 100BASE TX uses pairs 2 and 3 (orange and green). The configuration of 100BASE TX networks is very similar to 10BASE T. When used to build a local area network, the devices on the network (computers, printers etc.) are typically connected to a hub or switch, creating a star network. Alternatively, it is possible to connect two devices directly using a crossover cable. With today's equipment, crossover cables are generally not needed as most equipment supports auto negotiation along with auto MDI X to select and match speed, duplex and pairing. With 100BASE TX hardware, the raw bits, presented 4 bits wide clocked at 25 MHz at the MII, go through 4B5B binary encoding to generate a series of 0 and 1 symbols clocked at a 125 MHz symbol rate. The 4B5B encoding provides DC equalization and spectrum shaping. Just as in the 100BASE FX case, the bits are then transferred to the physical medium attachment layer using NRZI encoding. However, 100BASE TX introduces an additional, medium dependent sublayer, which employs MLT 3 as a final encoding of the data stream before transmission, resulting in a maximum fundamental frequency of 31.25 MHz. The procedure is borrowed from the ANSI X3.263 FDDI specifications, with minor changes.

In 100BASE T1 the data is transmitted over a single copper pair, 3 bits per symbol, each transmitted as code pair using PAM3. It supports full duplex transmission. The twisted pair cable is required to support 66 MHz, with a maximum length of 15 m. No specific connector is defined. The standard is intended for automotive applications or when Fast Ethernet is to be integrated into another application. It was developed as Open Alliance BroadR Reach (OABR) before IEEE standardization.

Proposed and marketed by Hewlett Packard, 100BaseVG was an alternative design using category 3 cabling and a token concept instead of CSMA/CD. It was slated for standardization as IEEE 802.12 but it quickly vanished when switched 100BASE TX became popular.

100BASE FX is a version of Fast Ethernet over optical fiber. The 100BASE FX physical medium dependent (PMD) sublayer is defined by FDDI's PMD, so 100BASE FX is not compatible with 10BASE FL, the 10 Mbit/s version over optical fiber. 100BASE FX is still used for existing installation of multimode fiber where more speed is not required, like industrial automation plants. running on 1310 nm wavelength. The signal attenuation per km at 1300 nm is about half the loss of 850nm.

100BASE SX is a version of Fast Ethernet over optical fiber standardized in TIA/EIA 785 1 2002. It is a lower cost, shorter distance alternative to 100BASE FX. Because of the shorter wavelength used (850 nm) and the shorter distance supported, 100BASE SX uses less expensive optical components (LEDs instead of lasers). Because it uses the same wavelength as 10BASE FL, the 10 Mbit/s version of Ethernet over optical fiber, 100BASE SX can be backward compatible with 10BASE FL. Cost and compatibility makes 100BASE SX an attractive option for those upgrading from 10BASE FL and those who do not require long distances.

100BASE LX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah 2004 clause 58. It has a 10 km reach over a pair of single mode fibers.

100BASE BX10 is a version of Fast Ethernet over optical fiber standardized in 802.3ah 2004 clause 58. It uses an optical multiplexer to split TX and RX signals into different wavelengths on the same fiber. It has a 10 km reach over a single strand of single mode fiber.

100BASE EX is very similar to 100BASE LX10 but achieves longer distances up to 40 km over a pair of single mode fibers due to higher quality optics than a LX10, running on 1310 nm wavelength lasers. 100BASE EX is not a formal standard but industry accepted term. It is sometimes referred to as 100BASE LH (long haul), and is easily confused with 100BASE LX10 or 100BASE ZX because the use of LX(10), LH, EX, and ZX is ambiguous between vendors.

100BASE ZX is a non standard but multi vendor term to refer to Fast Ethernet transmission using 1,550 nm wavelength to achieve distances of at least 70 km over single mode fiber. Some vendors specify distances up to 160 km over single mode fiber, sometimes called 100BASE EZX. Ranges beyond 80 km are highly dependent upon the path loss of the fiber in use, specifically the attenuation figure in dB per km, the number and quality of connectors/patch panels and splices located between transceivers.