Dual node ring interworking
Overview
Dual node ring interworking (DRI) is a configuration that provides path-level protection for selected STS-N circuits that are being carried through two UPSRs. Protection for the route between the two rings is provided by interconnecting the rings at two places (see Figure 3-33, Dual ring interworking protection.
Each circuit that is provisioned with DRI protection is dual-homed, meaning it is duplicated and subsequently passed-through at two different nodes on a ring. The two interconnecting nodes in each ring do not need to be adjacent.
DRI protection
The self-healing mechanisms of the two UPSRs remain independent and together protect against simultaneous single failures on both rings (not affecting the interconnections). The DRI configuration additionally protects against failures in either of the interconnections between the rings, whether the failure is in a facility or an interconnection node.
Ring interworking
All Alcatel-Lucent 1665 DMX tributary SONET interfaces (OC-3, OC-12, and OC-48) support DRI. The Alcatel-Lucent 1665 DMX high-speed ring can be an OC-12/48/192 UPSR. An Alcatel-Lucent 1665 DMX ring supports DRI with UPSRs, including rings using the following products:
Additionally, there can be intermediate network elements in the interconnection routes between the two rings.
UPSR-to-UPSR interworking
In the UPSR to UPSR interworking both UPSR DRI nodes select the better of two paths travelling in the drop direction and pass traffic to one rotation of the ring in the add direction.
UPSR drop and continue
Alcatel-Lucent 1665 DMX supports the drop and continue method of DRI, in which both UPSR DRI nodes select the better of two paths travelling in the drop direction and pass traffic to one rotation of the ring in the add direction. Each node drops the circuit in the direction of the other ring and a pass-through circuit to the other DRI node is made. The best of the 2 resulting signals is dropped at the terminating node of the new ring.
UPSR to UPSR protection switching example
The figure below illustrates a failure of the interconnection to a DRI node at the point labeled "X" in the figure. A failure in the route from Node A to Node Z results in a path switch at the surrounding nodes adjacent to the failure. The DRI nodes themselves will only perform the protection switch if they are the nodes adjacent to the failure. As you can see, while all nodes and lines remain fully functional, DRI functions as described in the section above. Both DRI nodes in the top ring select the best of the 2 signals received from that ring, and transmit them to the DRI nodes in the lower ring. The best of the signals received at the terminating node is dropped.
A path protection switch in an Alcatel-Lucent 1665 DMX occurs in <50 milliseconds (not counting the detection time) at the nodes adjacent to any failure.
Figure 3-33: Dual ring interworking protection
