Four standardizedphysical implementations of Ggigabit Ethernet exist:

1000BSE-SX--A fiber optic implementation for a pair of multimode fiber.SX corresponds to short wavelength,lasers transmitting light at a wavelength of 850 nanometers are used.

1000BASE-LX--A fiberoptic implementation for a pair of single-mode or multimode fibers,LX corresponds to the long wavelength, lasers transmitting light at a wavelength of 1300nm are used.

1000BASE-CX--A short shielded copper cable used in wiring closets and equipment rooms.CX corresponds to copper.

1000BASE-T-- An unshielded twisted-pair implementation that operates across four pairs of Category 5 twisted-pair cabling.

Gigabit Ethernet runs on multimode and single-mode optical fiber.Some differences exist between the fiber optic transceivers used for Gigabit Ethernet and the ones that were used only for 10Mbps and Ethernet.

Although lasers were used for transmission across long-distance 10Mbps and 100Mbps Etherenet single-mode links,less expensive light emitting diodes (LEDs) were used for 10Mbs and 100Mbs transmission across shorter multi-mode fiber lines.However,LEDs cannot operate at 100Mps.At gigabyte speed,lasers are required for multimode fiber as well as single-mode fiber.

Fortunately,there is a type of laser at hand that is quite inexpensive and can be used with multimode fiber:the Vertical Cavity Surface Emitting Laser.VCSEL emitters transmitting light whose wavelength is 850nm can support gigabyte transmission across cables that are hundreds of miters in length.850nm laser transceivers are utilized in the short wavelength implementations.

The more costly lasers used for data transmission across single-mode fiber are operated at a wavelength for 1300nm for the long wavelength implementation. LX lasers are used with both multimode and single-mode cables.However,even with long wavelength lasers,multimode cable lengths are restricted to at most 550 meters. contrast,1000BASE-LX single-mode cables can be thousands of meters in length.

LX transmission across multimode fiber requires the help of a special mode conditioning patch cord.This type of patch cord is described in the LC LC Fiber Patch Cord ,after the discussion of fiber optic connectors that follows.

The recommended plug for 1000BASE-SX and 1000BASE-LX is LC-SC Patch Cord connetor,depicted in Figure 9.2.It is used for both multimode and single mode fiber optic gigabyte installations,this connector also is used for 1000BASE-LE.

A problem arises when a LX laser source is aimed at the center of the cord of a multimedia fiber.Multiple overlapping signals are created,and the receiver may not be able to interpreting incoming signals correctly. It turns out that offsetting the beam from the center of the multimode core solves the problem,An LX laser transmitter is connected to a special mode -conditioning patch cord that consists of a single mode fiber spliced to an off center position on a multimode fiber,the light beam is aimed into the LC-LC Single Mode Patch Cord end of the splice fiber.

The type of multimode fiber that is used in the patch cord must be the same ones type that is used in the attached cable run.

Posted by: mikofy at 06:04 AM | No Comments | Add Comment
Post contains 479 words, total size 4 kb.