Specifications

B.7 FDDI Connection Rules
B–12 FDDI Overview
B.7 FDDI Connection Rules
B.7.1 Predictability
FDDI connection rules can seem complex and sometimes confusing, however, once
clarified and understood, one can easily see how the applied rules prevent the forma-
tion of non-useful topologies that can disrupt communications among stations in the
ring. FDDI connection rules also ensure that the ring always converges to a pre-
defined topology.
For example, as shown in Figure B–6, if Port A (DAC 1) is connected to Port B
(DAC 2), and then Port B (DAC 1) is connected to an M-port of (DAC 3), Port A
(DAC 1) breaks its connection to Port B (DAC 2).
This behavior is referred to as taking the tree connection over the ring connection.
This particular rule ensures that the same tree topology is always formed, indepen-
dent of the order in which the physical connections are made.
Figure B–6 FDDI Connection Rules
LKG-10100-96F
Dual Ring
DAS DAS DAS
DAS DAS DAC 3
M
Tree
DAC 2
B
DAC 1
A
B
Rejected Dual Ring Connection