Overlay Ring Circuits - Cisco ONS 15600 Reference Manual

Chapter 8 SDH Topologies and Upgrades

8.9 Overlay Ring Circuits

An overlay ring configuration consists of a core ring and subtended rings
Ring Circuit routes traffic around multiple rings in an overlay ring configuration, passing through one
or more nodes more than once. This results in multiple cross-connections on the nodes connecting the
core ring to the subtended rings. For example, a customer having a core ring with cross-connects
provisioned using TL1 can create create cross-connects on subtended rings, due to a business need,
without having to hamper the existing cross-connects on the core ring. This circuit can be either
protected or unprotected.
A typical path protected overlay ring configuration is shown in
the nodes B, D, and F twice resulting in two cross-connections on these nodes for the same circuit. In
Figure
drop nodes by provisioning a primary and secondary destination, making it a path protected circuit.
Figure 8-21 Overlay Ring Circuit
Overlay ring supports circuit sizes; STS-1, 3c, 6c, 9c, 12c, 24c, 36c, 48c, and 192cs. Both unidirectional
and bidirectional circuits are supported. Overlay ring circuits are contiguous concatenated (CCAT) and
not virtual concatenated (VCAT) circuits.
Manual routing is mandatory while provisioning the overlay ring circuit. Overlay ring circuits created
using Transaction Language 1 (TL1) are discovered by CTC and the status "DISCOVERED" is
displayed.
If the overlay ring circuit is deleted, the cross-connects on the core ring and subtended rings get deleted.
Cross-connects on a subtended ring can be deleted through TL1 but would reflect as a partial overlay
ring circuit in CTC, i.e. core ring will continue having cross-connects.
78-18400-01
8-21, the circuits on the OC-12 path are unprotected. The DS3 drop traffic is protected on the
Node A Node B
OC-3
Path
Protection
Subtended
Rings
DS3 PASS-THRU
Node C
OC-12
Path Protection
Node F
OC-3
Path
Protection
Node G
DS3 DROP
Cisco ONS 15600 SDH Reference Manual, Release 9.0
8.9 Overlay Ring Circuits
(Figure 8-21). An Overlay
Figure 8-21, where the circuit traverses
Node D Node E
OC-3
Path
Protection
Core Subtended
Ring Ring
DS3 CIRCUIT
OC-3 OVERLAY RING
8-23