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Cisco ONS 15454 Installation and Operations Guide
November 2001
Chapter5 SONET Topologies
Bidirectional Line Switched Rings
Figure5-4 A four-node, four-fiber BLSR
Four-fiber BLSRs provide span and ring switching:
•Span switching (Figure5-5) occurs when a working span fails. Traffic switches to the protect fibers
between the nodes (Node 0 and Node 1 in the Figure 5-5 example) and then retur ns to th e w or ki ng
fibers. Multiple span switches can occur at the same time.
•Ring switching (Figure 5-6) occurs when a span switch cannot recover tr affic, suc h as whe n both
the working and protect fibers fail on the same span. In a ring switch, traffic is routed to the prote ct
fibers throughout the full ring.
Node 0
Node 1
Node 2
Node 3
Span 1
Span 2Span 3
Span 4
Span 8
Span 7Span 6
Span 5
OC-48 Ring
= Working fibers
= Protect fibers
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