Network Router User Manual

Appendix D
Cable Specifications
■ Network Cable Specifications and Guidelines on page 183
■ Cable Specifications for Routing Engine Management Interfaces on page 187
Network Cable Specifications and Guidelines
The various PICs supported on the router accept different kinds of network cable,
including multimode and single-mode fiber-optic cable. For more information, see
the following sections:
■ Fiber Optic and Network Cable Specifications on page 183
■ Signal Loss in Multimode and Single-Mode Fiber-Optic Cable on page 183
■ Attenuation and Dispersion in Fiber-Optic Cable on page 184
■ Attenuation in SONET/SDH PICs on page 184
■ Calculating Power Budget for Fiber-Optic Cable on page 185
■ Calculating Power Margin for Fiber-Optic Cable on page 185
Fiber Optic and Network Cable Specifications
The router supports PICs that use various kinds of network cable, including multimode
and single-mode fiber-optic cable. For information about the type of cable used by
each PIC, see the M10i Internet Router PIC Guide.
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. LEDs are not coherent sources, however. 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,
higher-order mode loss (HOL) results. Together these factors limit the transmission
distance of multimode fiber compared to single-mode fiber.
Single-mode fiber is so small in diameter that rays of light can reflect internally
through one layer only. Interfaces with single-mode optics use lasers as light sources.
Network Cable Specifications and Guidelines ■ 183