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Cisco ONS 15454 Reference Manual, R8.5.x
78-18106-01
Chapter 12 SONET Topologies and Upgrades
12.4 Dual-Ring Interconnect
12.4 Dual-Ring Interconnect
Dual-ring interconnect (DRI) topologies provide an extra level of path protection for circuits on
interconnected rings. DRI allows users to interconnect BLSRs, path protection configurations, or a path
protection with a BLSR, with additional protection provided at the transi tion nodes. In a DRI topology,
ring interconnections occur at two or four nodes.
The drop-and-continue DRI method is used for all ONS 15454 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 fai lure. 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 15454:
• A traditional DRI requires two pairs of nodes to interconnect two networks. Each pair of
user-defined primary and secondary nodes drops traffic over a pair of interconne ction links to the
other network.
• An integrated DRI requires one pair of nodes to interconnect two networks. The two interc onnected
nodes replace the interconnection ring.
For DRI topologies, a hold-off timer sets the amount of time before a selector switch occurs. It reduces
the likelihood of multiple switches, such as:
• Both a service selector and a path selector
• Both a line switch and a path switch of a service selector
For example, if a path protection DRI service selector switch does not restore traffic, then the path
selector switches after the hold-off time. The path protection DRI hold-off timer default is 100 ms. You
can change this setting in the Path Protection Selectors tab of the Edit Circuits window. For BLSR DRI,
if line switching does not restore traffic, then the service selector switches. The hold-off time delays the
recovery provided by the service selector. The BLSR DRI default hold-off time is 100 ms, but it can be
changed.

12.4.1 BLSR DRI

Unlike BLSR automatic protection switching (APS) protocol, BLSR-DRI is a path-level protection
protocol at the circuit level. Drop-and-continue BLSR-DRI requires a service selector in the primary
node for each circuit routing to the other ring. Service selectors monitor signal conditions from dual feed
sources and select the one that has the best signal quality. Same-side routing drops the traffic at primary
nodes set up on the same side of the connected rings, and opposite-side routing drops the traffic at
primary nodes set up on the opposite sides of the connected rings. For BLSR-DRI, primary and
secondary nodes cannot be the circuit source or destination.
Note A DRI circuit cannot be created if an intermediate node exists on the interconnecting link. However, an
intermediate node can be added on the interconnecting link after the DRI circuit is created.
DRI protection circuits act as protection channel access (PCA) circuits. In CTC, you set up DRI
protection circuits by selecting the PCA option when setting up primary and secondary nodes during DRI
circuit creation.