Alignment server for hitless path switching in ATM networks

The vast amounts of information carried over broadband networks requires careful design of the network with regard to survivability and fault tolerance. A non-disruptive operation, where hitless path switching is provided, would be very useful. On the other hand, it increases system complexity. This paper presents a novel technique that allows hitless switching of asynchronous transfer mode (ATM) paths on-demand. In order to allow hitless path switching in ATM networks without major modifications to the existing ATM node concepts, a VP/VC alignment server (VAS) is introduced. This server can subsequently be shared by all ATM connections that need to be switched from one transmission system to another. A novel method is presented to gradually equalize the delay difference. The granularity of changes in the delay is determined by the delay requirements of the service. Finally, we present results obtained from performance studies that indicate the time needed for alignment and subsequent hitless switchover per connection.