Dual (SONET) ring interworking: High penalty cases and how to avoid them

Abstract

The Dual (that is, two-node) Ring Interworking (DRI) feature is required to guarantee sub-second demand restoration with multiple interconnected SONET rings. There is a capacity (and, indirectly, cost) penalty for implementing DRI, as rings with larger capacities will be required to canT the same set of demands with DRI than with single (that is, one-node) ring interworking (SRI). This paper considers in detail the DRI capacity penalty with a pair of interconnected rings. In this case, the DRI capacity penalty can range from 0% to 100%, and be higher than 1000% in a contrived example. The above observation also holds if we consider a chain of interconnected rings spanning a country and carrying primarily east-to-west or north-to-south traffic. This paper analyzes the components of this DRI penalty and outlines how this penalty can be reduced. The paper also shows that almost all of this penalty can be mitigated with Triple Ring Interworking (TRI). In TRI, the essential idea is to balance the inter-ring load across 2 links involving 3 nodes rather than a single link. Finally, in a large network of interconnected tings where each ring connects to multiple rings an extension of the TRI strategy to balance the total inter-ring load across multiple separate links involved in interworking between pairs of rings will be shown to be useful in reducing the DRI penalty.