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Optical fiber update

In terms of performance, there are different types and grades that are recognized in the TIA/EIA-568-B.3 standard.

January 1, 2005  

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The TIA cabling standards specify a minimum set of performance re- quirements for op- tical fiber cabling.

These require-ments depend on the choice of optical fiber as well as the intended application for which it is used.

Optical fiber cabling is primarily used for interconnection between telecommunications equipment in the backbone and in data centers, but can also be used in the horizontal for centralized fiber cabling or fiber-to-the-desk implementations.

There are different types and grades of optical fiber that are recognized in TIA/EIA-568-B.3 standard.

These include 50/125 and 62.5/125 micrometer multimode fiber as well as singlemode fiber. For multimode fiber, the grade of performance is given by the maximum attenuation and the minimum information transmission capacity of the fiber.

For different applications, the max- imum supportable distance and the maximum channel attenuation will depend on the type and grade of fiber that is used. These are given in the table on the right for the 1 Gb/s and 10 Gb/s Ethernet application.

As can be seen from this table, the loss budget is quite restrictive for 10 Gigabit Ethernet (10 GbE) applications.

Let’s look at the example of a 10 GbE application using 50/125 mm laser-optimized fiber for a channel with two connections.

The fiber loss is 0.3 km *3.5 dB/km = 1.05 dB and the connector loss is 2*0.75 = 1.5 dB for a total of 2.55 dB.

This means that for worse case components as specified in TIA 568 B.3, we are limited to a maximum of two connections.

Better performance can be achieved in practice, since the connector loss is usually in the range of 0.3 dB to 0.5 dB. It is recommended to consult with the manufacturer of the connectivity hardware when using channels that include more than two connections.

As a final point, TIA has recently published TSB-140.

This TSB describes field-testing of length, optical attenuation and polarity for optical fiber cabling using an optical loss test set (OLTS), an optical time domain reflectometer (OTDR) or a visible light source such as a visual fault locator (VFL).

Its purpose is to clarify the test procedures and to identify the different tiers of testing that apply in the field. For multimode cabling, attenuation measurements are performed according to ANSI/TIA/EIA-526-14A, Method B.

For singlemode cabling, attenuation measurements are performed in accordance to ANSI/TIA/EIA-526-7, Method A.1.

Paul Kish is Director, IBDN Systems & Standards at Belden CDT Networking Division (NORDX). He is also vice chair of the TR-42 engineering committee.

Disclaimer: The information presented is the author’s view and is not official TIA correspondence.