Sun Microsystems 1.0 - Manual (Page 104)

78 SunFDDI/P 1.0 Adapter User’s Guide—May 1997
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The dual-ring, and the concentrators attached to it directly, are called the main
distribution frame. Only one main distribution frame per network is allowed.
The second level in the hierarchy is called the intermediate distribution frame and
consists of the root concentrators in each building, and any stations connected
to them directly.
The third level in the hierarchy is called the horizontal distribution frame and
consists of concentrators connected to distributed stations, usually through
wall boxes.
Advantages
The ring of trees configuration combines many of the advantages of the basic
dual-ring and the concentrator-based topologies. It offers good fault tolerance
and is a very flexible configuration.
Since only a few stations (the root concentrators) are attached to the dual ring,
optical bypass switches can be used to increase the reliability of the main
distribution frame, as described in “Optical Bypass Switches” on page 62. The
small number of stations and the increased reliability of the concentrators
means that the chances of having more than three adjacent stations bypassed at
one time are minimal.
The cumulative length of the network can be increased because the limitation
on distance occurs between the end-station and the nearest concentrator, and
not between the end-station and the root concentrator.
Disadvantages
Only the concentrators attached directly to the dual-ring benefit from its
inherent redundancy.