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Cisco ONS 15600 SDH Reference Manual, Release 9.0
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Chapter 8 SDH Topologies and Upgrades
8.5 Dual-Ring Interconnect
Figure 8-8
SNCP with a Fiber Break
Because each traffic path is transported around the entire ring, SNCP rings are best suited for networks
where traffic concentrates at one or two locations and is not widely distributed. SNCP capacity is equal
to its bit rate. Services can originate and terminate on the same SNCP, or they can be passed to an
adjacent access or interoffice ring for transport to the service-terminating location.
8.5 Dual-Ring Interconnect
Dual-ring interconnect (DRI) topology provides an extra level of path protection for circuits on
interconnected rings. DRI allows users to interconnect MS-SPRings, SNCP rings, or an SNCP ring with
an MS-SPRing, with additional protection provided at the transition nodes. In a DRI topology, ring
interconnections occur at two or four nodes.
The drop-and-continue DRI method is used for all ONS 15600 SDH DRIs. In drop-and-continue DRI, a
primary node drops the traffic to the connected ring and routes traffic to a secondary node within the
same ring. The secondary node also routes the traffic to the connected ring; that is, the traffic is dropped
at two different interconnection nodes to eliminate single points of failure. To route circuits on DRI, you
must choose the Dual Ring Interconnect option during circuit provisioning. Dual transmit is not
supported.
Two DRI topologies can be implemented on the ONS 15600 SDH:
•
A traditional DRI requires two pairs of nodes to interconnect two networks. Each pair of
user-defined primary and a secondary nodes drop traffic over a pair of interconnection links to the
other network.
Span 1
Span 2
Span 3
Span 4
Fiber
break
Source
Destination
159620
ONS 15600 SDH
Node 0
ONS 15454 SDH
Node 1
ONS 15600 SDH
Node 2
ONS 15454 SDH
Node 3
= Fiber 1 (working)
= Fiber 2 (protected)
