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5-5
Cisco ONS 15454 Installation and Operations Guide
November 2001
Chapter 5 SONET Topologies
Bidirectional Line Switched Rings
Figure 5-4 A four-node, four-fiber BLSR
Four-fiber BLSRs provide span and ring switching:
• Span switching (Figure 5-5) 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 returns to the working
fibers. Multiple span switches can occur at the same time.
• Ring switching (Figure 5-6) occurs when a span switch cannot recover traffic, such as when both
the working and protect fibers fail on the same span. In a ring switch, traffic is routed to the protect
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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