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Fiber Cables And 10/40/100 Gigabit Ethernet

The increase in required bandwidth has taken place at an accelerated rate, so that the demand for very high bit rate for computer networking has arrived. 10 GIGABIT cabling is being ordered, and installed in many large and small corporation computer rooms between servers, routers, switches and various communication equipment. 40/100 Gigabit Ethernet cabling systems are being researched and developed for up and coming requirements needing very high data bit rate to transfer increasingly large volumes of information.

10 Gigabit data can be transferred over various versions of presently available copper or fiber cables. The copper cables include Cat 6 UTP – up to 50 meters, Cat 6A – up to 100 meters, Cat 7 UTP – up to 100 meters. The most common multi-mode fiber cables transmitting 10 Gigabits and using 850nm lasers include OM3 fiber– up to 300 meters, and OM4 fiber- up to 550 meters. This is called 10GBase-SR. These cables are duplex, usually terminated in SC or LC connectors

10GBASE-LRM uses 1300nm lasers on multi-mode fiber cable and uses OM3 fiber-up to 220 meters. For long distances up to 10 kilometers such as for campus networks, singlemode fiber would be used at 1300 nm. This is called 10GBase-LR. The fiber cables are usually duplex fibers, often terminated in SC or LC connectors.

The IEEE published the 802.3ba 40G/100G Ethernet standards in June of 2010. This standard gives guidance for 40/100G transmission using multi-mode and singlemode fiber cables. OM3 and OM4 are the multi-mode fiber cables given in the standard. Multi-mode fiber cables use parallel optics transmission rather than serial transmission because of limits on the fiber speed at 850nm. A 40 Gigabit channel using multi-mode fibers require 8 fibers with 4 transmitting at 10 Gig and 4 receiving at 10 Gig. At 100 Gig, 10 fibers transmit at 10 Gig and 10 fibers receive at 10 Gig. 20 fibers are required. The fiber cables used are 12 fiber cables with MTP connectors. These cables and connectors are presently available.

Singlemode at 40/100G uses fiber wavelength division multiplexing (WDM) and serial transmission. For short cable runs multi-mode fiber cables would probably be utilized. A parallel optical interface is required where multiple multi-mode fibers are used to achieve the required speed (i.e. 40/100G ).

INSERTION LOSS- For the 40/100G Ethernet Standard using OM3 fiber over a 100 meter run, the maximum channel loss allowed is 1.9 db. This includes the 1.5 db total connector loss for the total cable run. The maximum channel loss using OM4 fiber over a 150 meter run is 1,5 db. This includes a 1.00-db total connector loss. Insertion loss is a very important requirement for the runs in a computer system. It determines that the system will handle the high data rate signals correctly, for the run distance. If multiple connectors are mated in the cable run, the losses have to be carefully considered to meet the required standards.

SKEW-Skew is the difference in transmission time of the light signals transmitted on different fibers for parallel signal transmission operation. The 802.3ab standard requires a limit on the light signal skew of 79 ns. Transmission errors can be caused by too much skew over the various channels in parallel operation. The lower the skew the better the quality of the fiber cable.