Ethernet Standards for Optical Fiber Networking

100BASE-FX

100BASE-FX is a version of Fast Ethernet over optical fiber. It uses a 1300 nm near-infrared (NIR) light wavelength transmitted via two strands of optical fiber, one for receive(RX) and the other for transmit(TX). Maximum length is 412 m (1350 feet) for half-duplex connections (to ensure collisions are detected), and 2 km (6600 feet) for full-duplex over multimode fiber (MMF). 100BASE-FX uses the same 4B5B encoding and NRZI line code that 100BASE-TX does. 100BASE-FX should use SC, ST, LC, MTRJ or MIC connectors with SC being the preferred option.

100BASE-FX is not compatible with 10BASE-FL, the 10-Mbps version over optical fiber. The 100BASE-FX standard specifies a network capable of 100-Mbps throughput that uses baseband transmission and fiber optic cabling. 100BASE-FX requires MMF containing at least two strands of fiber. In half-duplex mode, one strand is used for data transmission while the other strand is used for reception. In full-duplex implementations, both strands are used for sending and receiving data. The standard allows for a maximum of one repeater to connect segments. 100BASE-FX uses a star topology with its repeaters connected in a bus fashion.

100BASE-FX, like 100BASE-T, is also considered Fast Ethernet and is described in IEEE’s 802.3u standard. Organizations switching, or migrating, from UTP to fiber media can combine 100BASE-TX and 100BASE-FX within one network. To do this, transceivers in computers and connectivity devices must have both RJ-45 and SC, ST, LC, or MT-RJ ports. Alternatively, a 100BASE-TX to 100BASE-FX media converter may be used at any point in the network to interconnect the different media and convert the signals of one standard to signals that work the other standard.

Related products in Fiber-Mart: Fast Ethernet Media Converter

1000BASE-LX

IEEE has specified three different types of 1000BASE, or 1-Gigabit, Ethernet technologies for use over optical fiber in its 802.3z standard. 1000BASE-LX is a fiber optic gigabit Ethernet standard specified in IEEE 802.3 Clause 38 which uses a long wavelength laser (1270 to 1355 nm), and a maximum RMS spectral width of 4 nm. It is specified to work over a distance of up to 5 km over 10 µm single-mode fiber (SMF).

1000BASE-LX can also run over all common types of MMF with a maximum segment length of 550 m. For link distances greater than 300 m, the use of a special launch conditioning patch cord may be required. This launches the laser at a precise offset from the center of the fiber which causes it to spread across the diameter of the fiber core, reducing the effect known as differential mode delay which occurs when the laser couples onto only a small number of available modes in MMF.

Probably the most common 1-Gigabit Ethernet (GE) standard in use today is 1000BASE-LX. The 1000 stands for 1000-Mbps or 1 Gbps throughput. BASE stands for baseband transmission, and LX represents its reliance on long wavelengths of 1300 nm. 1000BASE-LX has a longer reach than any other GE technology available today. It relies on either SMF or MMF. The maximum segment length is 550 m with MMF, while used with SMF it can reach 5 km. 1000BASE-LX networks can use one repeater between segments. Because of its potential length, 1000BASE-LX is an excellent choice for long backbones connecting buildings in a MAN, e.g., or connecting an ISP with its telecommunications carrier.

1000BASE-SX

1000BASE-SX is also a fiber optic GE standard for operation over MMF using a 770 to 860 nm, NIR light wavelength. The standard specifies a distance capability between 220 m (62.5/125 µm fiber, i.e., OM1 with low modal bandwidth) and 550 m (50/125 µm fiber, i.e., OM2 with high modal bandwidth). In practice, with good quality fiber, optics, and terminations, 1000BASE-SX will usually work over significantly longer distances. This standard is highly popular for intra-building links in large office buildings, co-location facilities and carrier neutral internet exchanges.

1000BASE-SX is similar to 1000BASE-LX in that it has a maximum throughput of 1 Gbps. However, it relies on only MMF as its medium. This makes it less expensive to install than 1000BASE-LX. Another difference is that 1000BASE-SX uses short wavelengths of 850 nm. Thus, the SX, which stands for short. The maximum segment length for 1000BASE-SX depends on two things: the diameter of the fiber and the modal bandwidth used to transmit signals. Modal bandwidth is measure of the highest frequency of signal a MMF can support over a specific distance and is measured in MHz-km. It is related to the distortion that occurs when multiple pulses of light, although issued at the same time, arrive at the end of a fiber at slightly different times. The higher the modal bandwidth, the longer a MMF can carry a signal reliably.

When used with fibers whose diameters are 50 µm each, and with the highest possible modal bandwidth, the maximum segment length on a 1000BASE-SX network is 550 m. When used with fibers whose diameters are 62.5 µm each, and with the highest possible modal bandwidth, the maximum segment length is 275 m. Only one repeater may be used between segments. Therefore, 1000BASE-SX is best suited for shorter network runs than 1000BASE-LX, e.g., connecting a data center with a telecommunications closet in an office building.

Related products in Fiber-Mart: Gigabit Ethernet Media Converter

Reference: Fiber-Mart