Cisco CISCO7201 Manual de usuario descargar pdf (Pagina 9)

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PA-A6 ATM Port Adapter Installation and Configuration

OL-2672-05

Chapter 1 Overview

Additional Information

Table 1-6 illustrates the overhead bytes of the SONET frame.

Power Budget

To design an efficient optical data link, evaluate the power budget. The power budget is the amount of

light available to overcome attenuation in the optical link and to exceed the minimum power that the

receiver requires to operate within its specifications. Proper operation of an optical data link depends on

modulated light reaching the receiver with enough power to be correctly demodulated.

Attenuation, caused by the passive media components (cables, cable splices, and connectors), is common

to both multimode and single-mode transmission.

The following variables reduce the power of the signal (light) transmitted to the receiver in multimode

transmission:

• Chromatic dispersion (spreading of the signal in time because of the different speeds of light

wavelengths)

• Modal dispersion (spreading of the signal in time because of the different propagation modes in the

fiber)

Attenuation is significantly lower for optical fiber than for other media. For multimode transmission,

chromatic and modal dispersion reduce the available power of the system by the combined dispersion

penalty. The power lost over the data link is the sum of the component, dispersion, and modal losses.

Table 1-7 lists the factors of attenuation and dispersion for typical fiber-optic cable.

Table 1-6 Overhead Bytes of the SONET Frame

Path Overhead

Section A1 Framing A2 Framing A3 Framing J1 Trace

Overhead B1 BIP-8 E1 Orderwire E1 User B3 BIP-8

D1 Data Com D2 Data Com D3 Data Com C2 Signal Label

H1 Pointer H2 Pointer H3 Pointer G1 Path Status

B2 BIP-8 K1 K2 F2 User Channel

Line D4 Data Com D5 Data Com D5 Data Com H4 Indicator

Overhead D7 Data Com D8 Data Com D9 Data Com Z3 Growth

D10 Data Com D11 Data Com D12 Data Com Z4 Growth

S1/Z1 Sync Status/Growth M0 or M1/Z2 REI-L Growth E2 Orderwire Z5 Tandem

Connection

Table 1-7 Typical Fiber-Optic Link Attenuation and Dispersion Limits

Limits Single Mode Multimode

Attenuation 0.5 dB/km 1.0 dB/km

Dispersion No limit 500 MHz/km

1. The product of bandwidth and distance must be less than 500 MHz/km.

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Cisco CISCO7201 Manual de usuario Pagina 9