HP 600 Series, Services And Applications

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Cabling
Optical fiber has many advantages over traditional copper cabling. Fiber
doesn’t emit electrical signals and is immune to electrical interference,
making it secure and reliable. It is easy to manipulate because it is light-
weight. Important specifications of fiber-optic cable are attenuation and the
optical signal wavelength the cable can carry.
Two types of transmission media are currently defined by the FDDI
standards: multimode fiber and single-mode fiber. Both operate at 100
Mbit/s. Multimode means that multiple rays of light can enter the fiber from
different angles. Multimode uses light-emitting diodes (LEDs) that convert
electrical signals into light and transmit the light into the fiber-optic cable.
Single mode means that only one ray of light is allowed to enter the fiber.
Single mode uses laser diodes (LDs) to convert electrical signals into light
and transmit the light into the fiber-optic cable. The HP routers do not
support single-mode fiber. They do support multimode fiber—only at 1300
nanoseconds.
Attenuation and Optical Budget
Signal attenuation through optical fiber is important with FDDI. It describes
the amount of energy (optical power) that is lost as the light signal travels
from the transmitter through the cable to the receiver. The longer the cable,
the higher the loss of optical power. Energy loss is denoted in decibels (dB),
an expression used to mathematically compare the power of two signals.
Attenuation is calculated by knowing the unit attenuation and the length of
the link. The maximum cable attenuation is the power loss in the cable as
well as any loss incurred by splices, connectors, and anything else
connected to the cable. PMD specifies an optical power budget between any
two stations of 11 dB. SMF-PMD allows for a range of power budgets that
extends from a minimum of 10 dB to a maximum of 32 dB.
Shining a Light on FDDI
How FDDI Works
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