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C-2 A
PPENDIX
C: ATM M
ODULE
T
ECHNICAL
S
PECIFICATIONS
Maximum attenuation includes attenuation and the
loss induced by other components such as
connectors, splices, and the mating of unlike fiber
types. Although some 2km (1.25 miles) cables have a
total attenuation of less than 11dB, the 2km (1.25
miles) inter-station distance must be maintained to
comply with modal bandwidth requirements.
The maximum attenuation value in this table is based
on a cable diameter of 62.5, 80 or 100mm.
Table C-3 shows the alternative Multi-Mode fiber
types that can be used.
If you are using fiber with a diameter of 50mm and
have IBM 8271 Nways Ethernet LAN Switch
equipment at both ends of the link, substitute 8.0dB
for the maximum attenuation. If IBM 8271 Nways
Ethernet LAN Switch equipment is only at one end,
substitute 6.0dB for the maximum attenuation value.
If you are using equipment at the end of the link from
a vendor other than IBM, you must perform a
separate loss budget analysis. Contact the vendor(s)
for values to use in your analysis.
Does the Cable Provide Sufficient Bandwidth?
Bandwidth for multi-mode fiber is referred to as
modal bandwidth because it varies with the modal
field (or core diameter) of the fiber.
Modal bandwidth is specified in units of MHz.km,
which indicates the amount of bandwidth supported
by the fiber for a 1km (0.625 miles) distance. Your
cable must have a Modal bandwidth of 500MHz,
which allows the cable to support end-to-end
bandwidth of 250MHz at the maximum 2km (1.25
miles) distance.
Table C-2
Standard Multi-mode Cable Specifications
Specification Description
Core 62.5
µ
m diameter
Cladding 125
µ
m diameter nominal
122
µ
m minimum
128
µ
m maximum
Numerical aperture 0.275
Maximum attenuation 11dB (including 1dB allowed for
reflection and dispersion penalties)
Modal bandwidth 500 MHz.km
Maximum distance between
nodes
2km (1.25 miles)
Output power (from transceiver) -20dB minimum
-14dB maximum
Receiver power -31dB minimum sensitivity
-14dB maximum sensitivity
Table C-3
Alternative Multi-mode Cable Specifications
Core ( m) Cladding ( m) Numerical Aperture
50 125 0.20
50 125 0.22
85 125 0.28
100 140 0.29