Standards Supported By These Cables; Understanding Ex Series Switches Fiber-Optic Cable Signal Loss, Attenuation, And Dispersion; Signal Loss In Multimode And Single-Mode Fiber-Optic Cable - Juniper EX8208 Hardware Manual

Standards Supported by These Cables

The cables comply with the following standards:
SFP mechanical standard SFF-843— see ftp://ftp.seagate.com/sff/SFF-8431.PDF.
Electrical interface standard SFF-8432— see ftp://ftp.seagate.com/sff/SFF-8432.PDF.
SFP+ Multi-Source Alliance (MSA) standards
Understanding EX Series Switches Fiber-Optic Cable Signal Loss,
Attenuation, and Dispersion
IN THIS SECTION

Signal Loss in Multimode and Single-Mode Fiber-Optic Cable | 131

Attenuation and Dispersion in Fiber-Optic Cable | 132
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
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.
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