5-7
Cisco ONS 15454 Installation and Operations Guide
November 2001
Chapter5 SONET Topologies
Bidirectional Line Switched Rings
5.2.3 BLSR Bandwidth
BLSR nodes can terminate traffic that is fed fr om e ith er si de of t he rin g. Th er ef or e, BL SRs are s uit e d
for distributed node-to-node traffic applications such as intero ffice net wor ks an d ac cess netwo rks.
BLSRs allow bandwidth to be reused around the ring and ca n carr y m or e t raffic tha n a ne twork wit h
traffic flowing through one central hub. BLSRs can also carry more traffic t han a UPSR operating at the
same OC-N rate. Table 5- 2 shows the bidirectional bandwidth capacities of two-fiber BLSRs. The
capacity is the OC-N rate divided by two, multiplied by the number of nodes in the ring minus the
number of pass-through STS-1 circuits. Tabl e 5-3 shows the bidirectional bandwidth capacities of
four-fiber BLSRs.
Figure 5-7 shows an example of BLSR bandwidth reuse. The same STS carries three dif ferent traffi c sets
simultaneously on different spans on the ring: one set from Node 3 to Node 1, one from Node 1 to Node
2, and another from Node 2 to Node 3.
Table5-2 Two-Fiber BLSR Capacity
OC Rate Working Bandwidth Protection Bandwidth Ring Capacity
OC-12 STS1-6 STS 7-12 6 x N1 - PT2
1. N equals the number of ONS 15454 nodes configured as BLSR nodes.
2. PT equals the number of STS-1 circuits passed through ONS 15454 nodes in the ring (capacity can vary
depending on the traffic pattern).
OC-48 STS 1-24 STS 25-48 24 x N - PT
OC-192 STS 1-96 STS 97-192 96 x N - PT
Table5-3 Four-Fiber BLSR Capacity
OC Rate Working Bandwidth Protection Bandwidth Ring Capacity
OC-48 STS 1-48 (Fiber 1) STS 1-48 (Fiber 2) 48 x N - PT
OC-192 STS 1-192 (Fiber 1) STS 1-192 (Fiber 2) 192 x N - PT