Specifications

B.5 Physical Topologies
FDDI Overview B–9
B.5.3 Tree Topologies
FDDI also allows for the creation of tree topologies. Tree topologies start with a
stand-alone concentrator at the top of the tree. Stations (DAS or SAS) or other con-
centrators (DACs) connect to this concentrator, and branch out from the top of the
tree.
• How to Identify Trees
The distinguishing feature of a tree topology is the connection to an M port.
Single attachment stations (S ports) typically connect to a concentrator, but
Dual Attachment Stations (A and B ports) can also connect to the M ports.
• Benefit
A major advantage of the use of trees built with concentrators is the ability
of the concentrator to electronically disconnect stations from the ring in case
of failure, or, by management control.t
B.5.4 Dual Ring of Trees Topology
The third, and most common, FDDI configuration (see Figure B–4) is referred to as
the Dual Ring of Trees. This configuration type is a very robust topology and is a
hybrid of the Dual Ring and Tree topologies.
Dual Attachment Concentrators (DACs) and Dual Attachment Stations (DASs)
attach together in a dual ring, with treed stations connected to the concentrators’ M
ports. The concentrator connects stations attached to these M ports into the flow of
the primary ring.