Cisco CISCO7201 Bedienungsanleitung PDF herunterladen (Seite 10)

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PA-A6 ATM Port Adapter Installation and Configuration

OL-2672-05

Chapter 1 Overview

Additional Information

Approximating the PA-A6 Power Margin

The LED used for a multimode transmission light source creates multiple propagation paths of light,

each with a different path length and time requirement to cross the optical fiber, causing signal

dispersion (smear). Higher-order mode loss (HOL) results from light from the LED entering the fiber

and being radiated into the fiber cladding. A worst-case estimate of power margin (PM) for multimode

transmissions assumes minimum transmitter power (PT), maximum link loss (LL), and minimum

receiver sensitivity (PR). The worst-case analysis provides a margin of error; not all of the parts of an

actual system will operate at the worst-case levels.

The power budget (PB) is the maximum possible amount of power transmitted. The following equation

lists the calculation of the power budget:

PB = PT – PR

PB = –20 dBm – (–30 dBm)

PB = 10 dBm

The power margin calculation is derived from the power budget minus the link loss, as follows:

PM = PB – LL

If the power margin is positive, as a rule, the link will work.

Table 1-8 lists the factors that contribute to link loss and the estimate of the link loss value attributable

to those factors.

After you calculate the power budget minus the data link loss, the result should be greater than zero.

Circuits with results that are less than zero may have insufficient power to operate the receiver.

The SONET specification requires that the signal must meet the worst-case parameters listed

in Table 1-9.

Table 1-8 Link Loss Factors and Values

Link Loss Factor Estimate of Link Loss Value

Higher-order mode losses 0.5 dB

Clock recovery module 1 dB

Modal and chromatic dispersion Dependent on fiber and wavelength used

Connector 0.5 dB

Splice 0.5 dB

Fiber attenuation 1 dB/km

Table 1-9 PA-A6 Port Adapter SONET Signal Requirements

Single Mode (SML) Single Mode (SMI) Multimode

PT –5 dBm –15 dBm –20 dBm

PR –34 dBm –31 dBm –30 dBm

PB 29 dBm 16 dBm 10 dB

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Cisco CISCO7201 Bedienungsanleitung Seite 10