Expansion - FDDI
10-2
FDDI Workgroups
If, for example, we wished to add another five FDDI single-attached stations to
the first chassis we designed in Chapter 7, we would first have to examine the
available chassis slots. The current design leaves three slots of the chassis free: the
first, half-sized slot and two full sized slots. As there are no FDDI modules which
fit in the first slot of the MMAC chassis, we have two slots available for the
addition of FDDI modules. Looking at the modules already in the chassis, we add
one FDCMIM-28 module to the current design. This concentrator module will
provide eight RJ45 ports which meet the FDDI TP-PMD standard for UTP cabling.
This module fills the need for five connections and leaves three ports available for
future expansion.
When an FDDI network is expanded to include more connections or stations, it is
important to remember that all stations on an FDDI network share the available
bandwidth. Any station that is added to an existing ring, regardless of wether it is
dual-attached or single-attached, is added to the overall total number of stations.
If the total number of FDDI stations exceeds 500, or if the sum of the cabling
between FDDI devices in the network exceeds 100 Km, the FDDI network will be
out of specification, and difficulties, errors, and faults may arise.
Adding Dual Attached Concentrators
While it is usually not economical or beneficial to place more than one FDMMIM
in a single chassis, the relatively small number of FDDI stations that can be
supported by a single MMAC (due to low port densities on FDDI concentrator
modules) often require that new DACs be added to the overall FDDI ring. These
new DACs are added to the network by setting up a new MMAC chassis with an
FDMMIM module and whatever other networking modules you require. Simply
follow the procedures for designing an FDDI network as outlined in Chapter 7,
FDDI
.
The MMAC designs for locations 2 and 3 of the example FDDI design in Chapter
7 each incorporate two MMAC chassis in order to meet the station requirements
for those locations. Each MMAC chassis first establishes a managed connection to
the dual FDDI ring by placing an FDMMIM management module in the first
full-sized slot in the chassis.
Again, when adding dual-attached concentrators to the FDDI ring, it is important
to calculate the station count and total ring length in order to ensure that the
maximums of the standard are not exceeded. A table of the basic maximums
associated with the ANSI X3T9.5 standard for FDDI may be found in Appendix A.
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