NT1310 Physical Networking

NT1310 Physical Networking Unit 10

Key Concept 1: Fiber-Optics System Design and Installation

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Installation Specifications

Bend Radius

Optical fiber depends on the maintenance of total internal reflection to carry an optical signal. Macrobends, or very small radius bends in the optical fiber, can change the light’s angle of incidence enough to cause some or a majority of the light to pass into the cladding, severely attenuating the signal or cutting it off completely.

Tensile Rating

The job of the strength member is to ensure that no tensile stress is placed on the optical fiber during and after installation. The strength member does have physical limitations. Tensile forces that exceed the physical limitations the cable was designed to handle can damage the cable and possibly break the optical fiber.


Installation Hardware

• Pulling eye – specially designed to attach to the cable’s strength member at one end and a pulling line at the other, to feed cable through a wall, conduit or other inaccessible space.

• Pull box – installed after long straight runs in the conduit to reduce the tensile load as a cable is pulled through

• Splice enclosures – protects a mechanical or fusion splice from exposure and strain

• Patch panels - interconnection point for fiber-optical cables, allowing signals to be routed from cable to cable with a patch cord or jumper


Installation Methods

• Tray and Duct – optical fiber rests in trays or horizontal ductwork

• Conduit – fiber runs through dedicated conduit, which is then run through structures or underground

• Direct Burial – run a suitable cable directly in the ground, or inside a protective pipe or conduit which is then placed in the ground

• Aerial – strung along a series of poles, similar to power lines

• Blown Fiber – ideal for new construction:

• Install the special tubing or conduit

• Blow the optical fiber through the tubes from location to location

• Terminate the optical fiber

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Basic Fiber-Optic System Design Considerations

• How much data needs to be moved today?

• How much data will need to be moved in the future?

• What is the transmission distance?


Fiber vs. Copper

Advantages of Fiber

• Higher bandwidth

• Lower attenuation

• No EMI

• Much less space needed

• High security of data

• No risk of electrical hazards

Advantages of Copper

• Cheaper

• Already installed many places

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Questions?

NT1310 Physical Networking Unit 10

Key Concept 2: Fiber-Optic Testing and Troubleshooting

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Testing Equipment

• Continuity Tester – low-cost tool that allows you to quickly verify the continuity of an optical fiber

• Visual Fault Locator – expensive tool that allows you to quickly identify breaks or macrobends in the fiber, and identify a poor fusion splice in multimode or single-mode optical fiber

• Fiber Identifier – by placing a slight macrobend in an optical fiber, it can detect infrared light traveling through the fiber and deterimne the direction of light travel

• Optical Return Loss Test Set – measures the amount of optical light energy that is reflected back to the transmit end of the fiber-optic cable

• Optical Time-Domain Reflectometer – provides the most information about the cable. It can be used to evaluate the loss and reflectance of interconnections and splices. It will also measure attenuation rate of a fiber and locate faults


Troubleshooting

Inspection and Evaluation

• Connector Inspection – weakest link in any fiber-optic installation is likely the connector. Make every effort possible to ensure the connector is kept clean.

• Connector Endface Evaluation – can only be properly evaluated with an inspection microscope. Slight indent or score marks are acceptable.

• Receptacle/Mating Sleeve Inspection and Cleaning – many ways to cleanse an endface, including a cleaning stick and a tape type cleaner.


Restoration

The first step in any restoration is to ask the customer three questions:

• What do they believe the problem is?

• When do they believe the problem first occurred?

• What was the last thing done to the system?

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Questions?

Documents

NT1310 Physical Networking