Resource sharing strategies: Which sharing to better protect primary shortest paths?

With the widespread use of real-time applications (VoIP, IPTV, Video conference, etc.) in Internet, protection and resource optimization become increasingly desired. Network protection aims to decrease the interruption time of communications by precomputing backup paths capable to receive and route traffics of affected primary paths upon failures. Resource optimization is achieved by improving data routing and resource sharing: data routing is often optimized by following the shortest paths whereas resource sharing is applied between the backup paths protecting against different failure risks. Two strategies of resource sharing are defined in literature: (1) backup sharing which limits the resource sharing to the backup paths and (2) global sharing which extends the resource sharing to the primary and backup paths. In this paper, we compared the effects of resource sharing strategies on the resource utilization when the primary paths correspond to the shortest ones according to a static metric. With the single failure assumption, we show formally that the resource sharing between primary and backup paths is limited to some few links which cannot form a backup path. Thus, independently of the amount of resources (for instance: bandwidth) that can be shared between the primary and backup paths, the maximum number of backup paths is bounded. In our simulation, we comfort our formal result by showing that the two strategies have close acceptance rates of backup paths and protection bandwidth utilizations.