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Maintenance Description
9-32 Issue 3 June 2001
Dual Ring Interworking (DRI) 9
The DDM-2000 OC-3 Multiplexers support DRI which provides end-to-end
protection from loss of service on traffic traveling over interconnected rings. This
is achieved by connecting the two rings at two dual-homing offices and by
provisioning the multiplexers at these nodes to "drop and continue" all necessary
paths. This provides a redundant path in case of a catastrophic failure at one of
the two DRI offices or one of the nodes in each DRI office. The end nodes perform
standard path protection switching on the signals from these two redundant paths.
Dual Ring Interworking (DRI) Path Protection
Scheme 9
Figure 9-16 shows DRI path protection switching. Note that the upper ring could
be an FT-2000 OC-48 Lightwave System bidirectional line switched ring. In the
receive direction, a DRI node that passes a signal between rings performs two
steps:
1. The VT1.5 and/or STS-1 signals to be passed between rings are "dropped
and continued." This means the signal is dropped at that node and
simultaneously copied into the OC-3 signal in the outgoing direction of the
same ring rotation.
2. The VT1.5 and/or STS-1 signal that was dropped in Step 1 and the
corresponding VT1.5 and/or STS-1 signal incoming from the other ring
direction are compared, and the signal with the highest quality is selected
as in single ring topologies.
In the transmit direction, a DRI node feeds VT1.5 or STS-1 signals in the direction
opposite to the "continue" portion of the drop and continue signal (Step 1
previously) to only one rotation of the ring as shown in Figure 9-13. This routing is
to only one rotation as distinguished from how an ordinary path switched ring
bridges incoming low-speed traffic onto both rotations.
The drop and continue routing necessary for DRI is established with a cross-
connection command.
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