p-Cycles are a new protection technique for optical (or MPLS) transport networks, using preconnected cycles of spare capacity to restore failed working traffic. We offer five new contributions to the field, beginning with the first comprehensive survey of p-cycle literature to date. While considering Hamiltonian p-cycles, we illustrate that they are not always cheaper than a multiple-cycle design, but by using such a p-cycle in a "semi-homogeneous" way, a lower bound on efficiency can be achieved. When we included p-cycles in a multi-method design, it was found that combined optimization can lead to a modest cost savings, but moreover, can allow a better quality of service for many demands. After designing p-cycle networks with accurate path length restrictions (and showing a threshold hop-limit effect), we concluded that the normal circumference-limiting technique is an effective substitute. Finally, our study of accurately distributed p-cycle preselection showed promising (although variable) capacity cost results.
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