Juniper Networks M5 - Manual (Page 68)

Network Cable Specifications and Guidelines
connecting the DC power and grounding cables during initial installation, see “Connect
Power to a DC-Powered Router” on page 66. For instructions on replacing the cables on an
operating router, see “Disconnect and Connect DC Power” on page 108.
Power cords and cables must not block access to router components or
drape where people could trip on them.
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 48
•
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable on page 48
•
Attenuation and Dispersion in Fiber-Optic Cable on page 49
•
Calculating Power Budget for Fiber-Optic Cable on page 49
•
Calculating Power Margin for Fiber-Optic Cable on page 50
•
Attenuate to Prevent Saturation at SONET/SDH PICs on page 51
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 M5 and M10 Internet Routers 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. Lasers generate a
single wavelength of light, which travels in a straight line through the single-mode fiber.
48 M5 and M10 Internet Routers Hardware Guide