The cable buffer is one of two types:loose buffer or tight buffer.The loose buffer uses a hard plastic tube being in an inside diameter several times that of the fiber.One or more fibers lie within the buffer tube.The tube isolates the fiber from the rest of the cable and the mechanical forces operating in it.The tight buffer has a plastic directly applied over the fiber coating.This construction provides better crush and impact resistance.It does not,however,protect the fibre as well from the stresses of temperature variations.
When a table contains several layers of jacketing and protective material,the outer layers are often called the sheath.The jacket becomes the layer directly protecting fibers,and the sheath refers to additional layers.This terminology is particularly common in the telephone industry.
Cables for indoor applications include the following:
- Simplex cables
- Duplex cables
- Multiplier cables
- Hey-,light-,and plenum-duty cables
- Breakout cables
- Ribbon cables
Although these categories overlap,they represent the common ways of referring to fibers.Figure 7-5 shows cross sections of several typical cable types.
Simplex cables contain single fiber. “Simplex”is a term used in electronics to indicate one-way transmission.Since a fiber carries signals in only one direction,from transmitter to receiver,a simplex cable allows only one-way communication.
Duplex cables contain two optical two optical fibers. Duplex relates to two-way communication.One fiber carries signals in one direction;the other fiber carries signals in the other direction.(Of course,duplex operation is possible with two simplex cables.) Figure compares simplex and duplex operations.
In appearance,duplex cables resemble two simplex cables whose jackets have been bonded together,similar to the jacket of common lamp cords.Ripcord constructions,which allows the two cables to be easily separated,are popular.
Duplex cable is used instead of two simplex cables for aesthetics and convenience, it is easier to handle a single duplex cable,there is less chance of the two channels becoming confused,and the appearance is more pleasing.Remember,the power cord from your lamps is a duplex cable that could easily be two separate wires.Make a single duplex cord in the lamp not make better sense? The same reasoning prevails with fiber optic cables.
Most Outdoor Fiber Optic Cables contain many fibers.The strength member is usually a large steel or fiberglass rod in the center,although small steel strands in the outer sheath are also used, most high-fiber count cables divide the fibers among several buffer tubes.
In cables containing many fibers,not all the fibers are always used at first.Some are kept as spares to replace fibers that fail in the future.Others are saved for future expansion,as the demands for additional capacity dictate,In stalling a cable can be expensive.Having extra fibers in place when they are needed saves future installation costs of additional fibers and cables.It pays to think ahead.