APPENDIX A: BASIC FDDI NETWORKS
Connection Management (CMT) controls physical layer insertion and removal of stations. CMT has three main components:
•Entity Coordination Management (ECM) controls bypass switches and coordinates trace (recovery) functions.
•Configuration Management (CFM) controls PHY and MAC entity configuration within a node. Attaching or removing a station from the ring changes the logical structure of the ring.
•Physical Connection Management (PCM) controls the physical connection between adjacent PHYs. It tests the quality of the link and enforces connection rules, screens marginal connections, and supports maintenance activities.
A.5 FDDI Connection Rules
One of the primary functions of SMT Connection Management is to control physical connections among A, B, M, and S type ports. The following table summarizes the FDDI connection rules.
| A | B | S | M |
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A | V,U | V | V,U | V,P |
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B | V | V,U | V,U | V,P |
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S | V,U | V,U | V | V |
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M | V | V | V | X |
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V - valid connection
X - illegal connection
U - undesirable connection
P - valid, but when both A and B connect to M ports, only the B connection is active. Connecting A and B to M ports creates a dual homing configuration. Dual homing provides a redundant topology for concentrators. Figure
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