SONET/SDH-like resilience for IP networks: a survey of traffic protection mechanisms

Typically IP networks respond to a link failure by finding an alternate traffic path after the failure is discovered. This results in a convergence time during which traffic may be dropped at the failed link until an alternate path is found (e.g., through link state routing protocols like OSPF or IS-IS). While there has been steady progress in decreasing IP routing convergence times, these approaches are limited by the need to communicate among multiple routers. However, IP traffic can be protected using techniques below layer 3, which are not subject to this constraint. This article discusses mechanisms where a link failure can be protected locally, SONET/SDH-like, at sub-50-ms protection times. Descriptions of linear SONET automatic protection switching for routers, resilient packet ring protection, IP interface bundling, and MPLS fast reroute are covered. Protection triggers and coexistence of various protection methods are also discussed.