A distributed protocol for fast and robust virtual path restoration

Broadband networks must be designed for survivability, otherwise serious failures threaten their integrity. That is why restoration strategies have previously been studied in some depth, first for SDH/SONET transport networks, and then for ATM trunk networks based on the virtual path (VP) concept. In terms of survivability, the characteristics of VPs can be exploited to permit cost effective preassigned restoration by allocating protection paths to working VP routes. This involves setting virtual path identifiers (VPIs) in translation tables of VP cross-connects of the protection route, as well as management of spare capacity reservations in network links. The purpose of this latter operation is twofold: first, spare capacity should be shared between protection paths activated due to different possible failures; second, any failure must not result in the aggregate protection path capacity of any link exceeding the reserved value. In devising a mechanism for activating restoration, the principal goal is to restore failed paths as quickly as possible. This paper describes a novel distributed protocol which enables rapid switching from working to protection routes in the event of serious physical layer failures. A further objective is to instill robustness into the restoration scheme such that adverse effects of less common failures (e.g. node or multiple span) do not degrade network performance