Cisco Systems 15454 SDH 11.4 Dual Ring Interconnect

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Cisco ONS 15454 SDH Reference Manual, R5.0

April 2008

Chapter11 SDH Topologies and Upgrades

11.4 Dual Ring Interconnect

11.4 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, SNCPs, or an SNCP 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 15454 SDH DRIs. In drop-an d-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 SDH:

•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 SNCP DRI service selector switch does not restore traffic, then the path selector

switches after the hold-off time. The SNCP DRI hold-off timer default is 100 ms. You can change this

setting in the SNCP Selectors tab of the Edit Circuits window. For MS-SPRing 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 MS-SPRing DRI default hold-off time is 100 ms and cannot be

changed.

Unlike MS-SPRing automatic protection switching (APS) protocol, MS-SPRing DRI is a path-level

protection protocol at the circuit level. Drop-and-continue MS-SPRing D RI requires a service selector

in the primary node for each circuit routing to the other ring. Se rvice 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 ring s, and opposite-side routing drops

the traffic at primary nodes set up on the opposite sides of the connected ri ngs. For MS-SPRing 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.