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It is well known that for link-restoration in an optical mesh network, the lower bound on the ratio between protection capacity and working capacity is 1/(d-1) where d is the average node degree of the mesh topology. No similar bounds are known for shared backup path restoration in which backup paths share bandwidth on their links if their primary paths are link disjoint. Shared backup path restoration has recently received interest and is being deployed by carriers because of its reduced restoration capacity overhead. This paper presents a quantitative analytical model for the protection capacity requirement in an optical mesh networks with an end-to-end shared backup path based restoration scheme. This analytical model can be used for quick back-of-the-envelope calculations of restoration capacity overhead without explicit computation-intensive routing of primary and shared backup paths. We perform simulations of the efficiency of network utilization of path-based restoration, and in particular focus on the impact of sharing of wavelength channels for mesh-restored lightpaths. We also investigate the impact of sharing of wavelength channels for mesh-restored lightpaths on the increase in restoration latency, since cross-connects are soft-reserved during provisioning and need to be setup on the backup path after failure.