Juniper EX4200 Series, Руководство по оборудованию, Страница: 145 / 344

For instructions on connecting an EX4200 switch to a management console using an
Ethernet cable with an RJ-45 connector, see
“Connecting a Switch to a Management
Console” on page 187 .
Related
Documentation
Management Port Connector Pinout Information for an EX4200 Switch on page 127
•
•
Console Port Connector Pinout Information for an EX Series Switch on page 125
•
Rear Panel of an EX4200 Switch on page 12
Understanding EX Series Switches Fiber-Optic Cable Signal Loss, Attenuation, and
Dispersion
To determine the power budget and power margin needed for fiber-optic connections,
you need to understand how signal loss, attenuation, and dispersion affect transmission.
EX Series Switches use various types of network cable, including multimode and
single-mode fiber-optic cable.
•
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable on page 123
• Attenuation and Dispersion in Fiber-Optic Cable on page 123
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable
Multimode fiber is large enough in diameter to allow rays of light to reflect internally
(bounce off the walls of the fiber). Interfaces with multimode optics typically use LEDs
as light sources. However, LEDs are not coherent light sources. They spray varying
wavelengths of light into the multimode fiber, which reflects the light at different angles.
Light rays travel in jagged lines through a multimode fiber, causing signal dispersion.
When light traveling in the fiber core radiates into the fiber cladding (layers of lower
refractive index material in close contact with a core material of higher refractive index),
higher-order mode loss (HOL) occurs. Together, these factors reduce the transmission
distance of multimode fiber compared to that of single-mode fiber.
Single-mode fiber is so small in diameter that rays of light reflect internally through one
layer only. Interfaces with single-mode optics use lasers as light sources. Lasers generate
a single wavelength of light, which travels in a straight line through the single-mode fiber.
Compared to multimode fiber, single-mode fiber has a higher bandwidth and can carry
signals for longer distances. It is consequently more expensive.
Exceeding the maximum transmission distances can result in significant signal loss, which
causes unreliable transmission. For information about the maximum transmission distance
and supported wavelength range for the types of single-mode and multimode fiber-optic
cables that are used on different EX Series switches see
Pluggable Transceivers Supported
on EX Series Switches .
Attenuation and Dispersion in Fiber-Optic Cable
An optical data link functions correctly provided that modulated light reaching the receiver
has enough power to be demodulated correctly.
Attenuation is the reduction in strength
of the light signal during transmission. Passive media components such as cables, cable
splices, and connectors cause attenuation. Although attenuation is significantly lower
123 Copyright © 2015, Juniper Networks, Inc.
Chapter 8: Transceiver and Cable Specifications