363-206-285
Administration and Provisioning
8-56 Issue 3 June 2001
The OC-3/IS-3 lines between an OC-12 node and an OC-3 node connected in a
ring 0x1 fashion behave like the OC-3 lines between the nodes on an OC-3 ring
and do not perform line level protection switching. Instead, the OC-3 shelves
perform the normal path protection switching functions.
Some points to note for this application are:
â– 0x1 can be thought of as a "ring on ring" with many of the characteristics of
a single ring.
â– Pass-through cross-connections may be required at the VT and STS level.
â– The OC-3 ring can be composed of any three STSs in the OC-12.
â– An OC-12 STS may be the first STS in one extension, the second STS in
another, and the third STS in another.
Example Cross-Connections 8
The OC-12 (STS level) cross-connections are:
â– At CO: mb-1:a-3
mb-1 is dropped to the third STS in the OC-3 between CO and CO-1.
â– At RT1: mb-1:a-1
mb-1 is dropped to the first STS in the OC-3 between RT1 and RT1-1.
â– At RT2: mb-1:c-2
mb-1 is dropped to the second STS in the OC-3 between RT2 and RT2-2.
â– RT3 is an OC-3 shelf equipped with OC-12 optics. The 24G-U OLIUs
provide the ability to drop up to any three of the 12 STS-1s at this node.
The remaining STS-1s continue on the OC-12 ring.
â– At RT4: mb-1:mb-1
mb-1 is passed through RT4 at the STS level.
These cross-connections can be thought of as establishing one STS of an OC-3
ring embedded in the OC-12 system. This is sometimes referred to as a "ring on
ring." In the example, the OC-3 nodes are CO-1, RT1-1, and RT2-2. The STS
itself traverses all eight nodes. An "ordinary" STS (for example, one that carries a
DS3 from an originating node to a terminating node) can drop at only two
locations (terminate in two-way at the source and destination), and pass-through
cross-connections are needed at the intermediate nodes. There can be multiple
drop (ring 0x1) type cross-connections to optical extensions.
The VT cross-connections that follow drop or pass through individual VTs in the
STSs.ThisislikeanordinaryOC-3ring,exceptthat,thesameOC-12STScanbe
dropped to different STSs in the various OC-3s. In an ordinary ring, the same time
slot (for example m-1-1-1) is used all the way around the ring. In a ring-on-ring
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