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Sepam Ethernet GuideNetwork architectureCablingCopper CablingDE80686Twisted pair cablesThe modern copper implementations of Ethernet use twisted pair cables, and most oftenthe Unshielded Twisted Pair (UTP). Twisted pair cabling is a common form of wiring inwhich 2 conductors are wound around each other to cancel electromagnetic interference(crosstalk).RJ45 plug.Cables categoriesLAN cables are identified with a category rating. The American National StandardsInstitute/Electronic Industries Association (ANSI/EIA) standard 568 is one of severalstandards that specify categories of twisted pair cabling systems (wires, junctions, andconnectors) in terms of the data rates that they can sustain effectively. The specificationsdescribe the cable material and the types of connectors needed to conform to a category.Standard Cable Connector Max cable lengthHalf-Duplex Full-Duplex10BASE-T UTP Cat 3 or better (2 pairs used) RJ45 100 m (328 ft) 100 m (328 ft)100BASE-TX UTP Cat 5 or better (2 pairs used) RJ45100 m (328 ft) 100 m (328 ft)DE80687.DE80688Straight and crossover cablesEthernet cables route transmitted signals from one device to another. Depending onthese devices, 2 types of cable are used:b Straight cables (drop cables) connect an end device to an infrastructure device.b Crossover cables are installed between 2 end devices that communicate with eachother directly, or between 2 infrastructure devices.These cables differ in the way individual wires are connected to the RJ45 plugs. Thefollowing schematics apply to the widely used EIA/TIA 568B cables.Signal(end device)TX+RJ45pin1RJ45 Signalpin (infrastructure device)white/orange1 RX+TX-2orange2RX-RX+unusedunusedRX-3456white/greenbluewhite/bluegreen3456TX+unusedunusedTX-unused7white/brown7unusedCategory 5e UTP Ethernet cable.unused8brownStraight cable (otherwise called patch cable).8unusedDE80689Signal RJ45(end device) pinTX+ 1TX- 2RX+ 3unused 4unused 5RXunused76unused 8RJ45 Signalpin (end device)white/greengreenwhite/orange12TX+TXblue3 RX+white/blue4 unusedorange5 unusedwhite/brown6 RXunusedbrown78 unusedCrossover cable.Note: This crossover cable layout is not suitable for 1000Base-T operation (all 4 pairs should be crossed).MDI/MDI-XToday most of the devices offered on the market support the medium dependent interfaceMDI/MDI-X functionality in their Ethernet ports. This functionality allows the autoswitchingof transmit and receive wire pairs. To connect this type of device, use eitherstraight or crossover cable; the device senses and accommodates the TX/RX pairs.16 SEPED310018EN - 10/2010
Sepam Ethernet GuideNetwork architectureCablingFiber optic cablingFiber optic cable has the ability to transmit signals over longer distances and at fasterspeeds than copper cable. Also, because fiber optic cable transmits light, it does notpresent the problems of electromagnetic interference associated with copper cabling.It is ideal for harsh environments and outside connections due to its high immunity tomoisture, as well as to lightning.Parts of a fiber cableTypically, a fiber optic cable consists of 3 parts:b core: thin ultra-pure glass (silica) or plastic center of the fiber that transmits lightb cladding: outer optical material that surrounds the core and reflects light back intothe coreb buffer jacket: outer plastic jacket or coating that protects the fiber from damage andmoisture.A light signal can propagate through the core of a fiber along a single path (calledsingle-mode fiber) or multiple paths (called multimode fiber).DE80691Single mode.Single-mode fibersSingle-mode fiber has a small core diameter (about 9 μm) and transmits infraredlaser light (wavelength = 1300 to 1550 nm). It provides only one optical mode thatforces light along a linear path through the cable end and causing much lowerdispersion and attenuation than multimode.Single mode fiber is more expensive and harder to handle. It is only used when itssignificantly highest bandwidth and distance ratings are of interest.DE80690DE80793Step index multimode.DispersionDispersionMultimode fibersThere are 2 types of multimode cable:b Step-index: has an abrupt change between core and cladding. It is limited to about 50Mb/s.b Graded-index: has a gradual change between core and cladding. It is limited to 1Gb/s.When cable is graded, the amount of refraction is reduced gradually outward from thecore. Because light travels faster when refraction is lower, light travelling through theouter material travels faster than light at the center of the core. The propagationdispersion is then reduced.Multimode fiber has a large core diameter (typically 50, 62.5 or 100 μm) and transmitsinfrared light (wavelength = 850 to 1300 nm) from light-emitting diodes (LEDs). Thecladding diameter is usually 125 μm.Fiber size is commonly indicated by the core diameter followed by a slash and thecladding diameter, without units (eg: 62.5/125).DE80692DE80693Graded index multimode.ST connector.The following table synthesizes some of the most common optical standards.Standard Cable type Wawelength (nm) Preferred Minimummin - max (typical) connector range10BASE-FL MM 62.5/125 770-860 (850) ST 2000 m (6550 ft)or MM 50/125100BASE-FX MM 62.5/125 1270-1355 (1300) SC 2000 m (6550 ft)or MM 50/1251000BASE-SX MM 62.5/125 770-860 (850) SC 220 m (720 ft)or MM 50/1251000BASE-LX MM 62.5/125 1270-1355 (1300) SC 550 m (1800 ft)or MM 50/1251000BASE-LX SM 9/125 1270-1355 (1310) SC 5000 m (16400 ft)or SM 8/125The real range of a fiber optic link can deviate considerably from the typical valuesindicated in the table:b It can be higher, depending on the devices transmit and receive characteristicsb It can also be shorter, due to poor fiber quality or cabling losses (mainly due tobending and intervening connections).A precise optical budget calculation should be made in every case, unless thedistance is very short.SC connector.SEPED310018EN - 10/201017
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