Juniper PTX10008 Hardware Manual page 184

Console Port Connector Pinouts for a PTX10000 | 190
Management Port Connector Pinouts for the PTX10000 Router | 192
Connecting a PTX10000 Router to a Management Console | 237
Connecting a PTX10000 to a Network for Out-of-Band Management | 237
Understanding PTX10000 Series Fiber-Optic Cable Signal Loss, Attenuation,
and Dispersion
IN THIS SECTION
Signal Loss in Multimode and Single-Mode Fiber-Optic Cables | 186
Attenuation and Dispersion in Fiber-Optic Cable | 187
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. The PTX10000 Series uses
various types of network cables, including multimode and single-mode fiber-optic cables.
Signal Loss in Multimode and Single-Mode Fiber-Optic Cables
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 reflect
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
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.
186