Dynamic Routing of Locally Restorable Bandwidth Guaranteed Tunnels Using Aggregated Link Usage Information

This paper presents new algorithms for dynamic routing of locally restorable bandwidth guaranteed paths. Dynamic routing implies routing of requests that arrive one-by-one with no a priori knowledge of future arrivals, and so necessitating use of on-line algorithms. Local restorability means that upon a link or node failure, the first node upstream from the failure must be able to switch the path to an alternate preset outgoing link so that path continuity with bandwidth guarantees is restored by a strictly local decision. The motivation for use of local restoration is that it is much faster than path restoration because failure information does not have to propagate to the source. Local restoration implies that to successfully route a path set-up request an active (primary) path, and a bypass backup path for every link and node used by the active path must be determined . This locally restorable on-line routing problem is becoming particularly important in optical networks and in MPLS (Multi Protocol Label Switching) based networks due to the trend toward dynamic provisioning of bandwidth guaranteed or wavelength paths. To prevent excessive resource usage for backup paths, and to satisfy the implicit service provider requirement of optimizing network resource utilization so as to increase the number of potential future demands that can be routed, it is desirable to judiciously share backup paths while still maintaining local restorability. The best sharing performance is achieved if the routing of every path in progress in the network is known to the routing algorithm at the time of a new path set-up. However, this requires maintenance of non-aggregated or per-path information which is not often desirable particularly when distributed routing is preferred. We show that a partial information scenario which uses only aggregated and not per-path information provides sufficient information for efficient dynamic routing of locally restorable bandwidth guaranteed paths. In this partial information scenario the routing algorithm only knows what fraction of each link’s bandwidth, is currently used by active paths, and is currently used by backup paths. Obtaining this information is feasible using proposed traffic engineering extensions to routing protocols. We develop efficient dynamic routing algorithms for bandwidth guaranteed paths that are locally restorable under single link or node failure. The routing is done using a sequence of shortest path computations, and it permits sharing of backup paths between requests as well as between the backup paths for different network elements for the same request. We compare the routing performance of our algorithm to other known restoration schemes. Our partial information based locally restorable algorithm performs very well in terms of the number of rejected requests and total bandwidth usage.