Cisco CISCO7201 Manual de usuario descargar pdf (Pagina 11)

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PA-A6 ATM Port Adapter Installation and Configuration

OL-2672-05

Chapter 1 Overview

Additional Information

Multimode Power Budget Example with Sufficient Power for Transmission

The following is a sample multimode power budget calculated based on the following variables:

Length of multimode link = 3 kilometers (km)

Four connectors

Three splices

Higher-order mode loss (HOL)

Clock recovery module (CRM)

Estimate the power budget as follows:

PB = 10 dB – 3 km (1.0 dB/km) – 4 (0.5 dB) – 3 (0.5 dB) – 0.5 dB (HOL) – 1 dB (CRM)

PB = 10 dB – 3 dB – 2 dB – 1.5 dB – 0.5 dB – 1 dB

PB = 2 dB

The positive value of 2 dB indicates that this link would have sufficient power for transmission.

Multimode Power Budget Example of Dispersion Limit

Following is an example with the same parameters as the previous example, but with a multimode link

distance of 4 km:

PB = 10 dB – 4 km (1.0 dB/km) – 4 (0.5 dB) – 3 (0.5 dB) – 0.5 dB (HOL) – 1 dB (CRM)

PB = 10 dB – 4 dB – 2 dB – 1.5 dB – 0.5 dB – 1 dB

PB = 1 dB

The value of 1 dB indicates that this link would have sufficient power for transmission. But due to the

dispersion limit on the link (4 km x 155.52 MHz > 500 MHz/km), this link would not work with

multimode fiber. In this case, single-mode fiber would be the better choice.

Single-Mode Transmission

The single-mode signal source is an injection laser diode. Single-mode transmission is useful for longer

distances, because there is a single transmission path within the fiber and smear does not occur. In

addition, chromatic dispersion is also reduced because laser light is essentially monochromatic.

The receiver for single-mode intermediate reach (SMI) cannot be overloaded by the SMI transmitter and

does not require a minimum fiber cable length or loss. The maximum receive power for single-mode long

reach (SML) is –10 dBm, and the maximum transmit power is 0 dBm. The SML receiver can, therefore,

be overloaded when short lengths of fiber are used. Overloading the receiver will not damage the receiver

but can cause unreliable operation. To prevent overloading an SML receiver connected with short fiber

links, insert a minimum 10-dB attenuator on the link between any single-mode long-reach transmitter

and the receiver.

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Cisco CISCO7201 Manual de usuario Pagina 11