A reliability analysis of Double-Ring topologies with Dual Attachment using p-cycles for optical metro networks

The distribution of multicast traffic (e.g. IPTV or business point-to-multipoint) in the metropolitan environment requires highly resilient network infrastructures. Currently-deployed fibre ducts in the metropolitan area are typically based on ring topologies interconnected by the dual homing approach. In this study, an easy evolution towards meshed topologies is proposed, based on Double Rings with Dual Attachments (DRDA). This work analyses in detail the resilience capabilities of DRDAs and the two dual p-cycles defined over them. It is shown that, just by ensuring service repair rates of 12 h, large service availability values can be achieved (of the order of four to five-nines). Additionally, the amount of backup capacity required to recover from link failures is further calculated in this paper. Furthermore, this work gives a mathematical framework or reference to all those network operators who are willing to deploy highly resilient metropolitan area networks at a moderate cost. The five-nines service availability degree is easily achieved provided sufficiently small service repair times (in the range of 12 h). Additionally, large service availability values are obtained with little extra backup capacity (about three-nines with only doubling capacity).