3com 2500 Quick Setup Guide
Single Mode Fiber Standards
D-5
The modal bandwidth specified in
on
page D-2 is 500 MHz • km, which allows the cable
plant to support end-to-end bandwidth of 250
MHz at the maximum 2 km distance. As a check,
use the following formula to verify that the
bandwidth of your fiber is within an acceptable
range:
plant to support end-to-end bandwidth of 250
MHz at the maximum 2 km distance. As a check,
use the following formula to verify that the
bandwidth of your fiber is within an acceptable
range:
n MHz • km/x km = y MHz
In this formula, n is the amount of bandwidth
available according to the fiber specification. Divide
this number by the total length of the fiber (x) in
kilometers. The result is the modal bandwidth (y),
measured in MHz.
available according to the fiber specification. Divide
this number by the total length of the fiber (x) in
kilometers. The result is the modal bandwidth (y),
measured in MHz.
If the result is lower than 250 MHz, the link may
increase bit errors. To reduce the likelihood of bit
errors, shorten the length of the fiber or use
different fiber until the result of the calculation
reaches 250 MHz.
increase bit errors. To reduce the likelihood of bit
errors, shorten the length of the fiber or use
different fiber until the result of the calculation
reaches 250 MHz.
Example
Cable with a modal bandwidth of 500 MHz • km
will have 250 MHz of bandwidth at 2 km:
will have 250 MHz of bandwidth at 2 km:
(500 MHz • km)/2 km = 250 MHz
The same cable would have 500 MHz of bandwidth
at 1 km. A fiber cable with a bandwidth
specifications of 200 MHz • km would have only
100 MHz of bandwidth at 2 km, which would not
support FDDI. In this case, another type of fiber
would be required.
at 1 km. A fiber cable with a bandwidth
specifications of 200 MHz • km would have only
100 MHz of bandwidth at 2 km, which would not
support FDDI. In this case, another type of fiber
would be required.
Single Mode Fiber Standards
The SMF-PMD standard defines the requirements for
an FDDI cable plant to support an interstation
distance of up to 14.4 kilometers (8.6 miles) of
single mode fiber. The cable plant includes all fiber
optic components between any two
communicating FDDI stations and their associated
“station-to-network” connectors at each end.
an FDDI cable plant to support an interstation
distance of up to 14.4 kilometers (8.6 miles) of
single mode fiber. The cable plant includes all fiber
optic components between any two
communicating FDDI stations and their associated
“station-to-network” connectors at each end.
To determine whether your cable plant complies
with the SMF-PMD standard, do the following:
with the SMF-PMD standard, do the following:
■
Compare the specifications of the fiber you are
using to standard specifications, as described in
using to standard specifications, as described in
.
■
If you mix equipment supporting Category 1 and
Category 2, verify the maximum attenuation
between the equipment, as described in
Category 2, verify the maximum attenuation
between the equipment, as described in
.
■
If your cables are not keyed for single mode
FDDI transceivers, modify the transceiver and
connector housing so that they fit together, as
described on page D-7 in
FDDI transceivers, modify the transceiver and
connector housing so that they fit together, as
described on page D-7 in
.”
The following sections describe each of these steps
and give examples.
and give examples.