When there is a change in the network, (e.g. Addition/deletion of a node), STP is invoked. One main concern with STP is the convergence time of 30-50 seconds. In a carrier-class network, network downtime of a few seconds would be unacceptable. This convergence time can be restricted to few 100s of milliseconds by using Rapid Spanning Tree Protocol (RSTP). RSTP is an evolution of the STP and provides for faster spanning tree convergence after a topology change. In the 2004 edition of 802.1D, STP is superseded by the RSTP.
While RSTP was primarily intended to provide a loop-free environment, it can also be used to provide for protection in an Ethernet-switched network. The convergence times of 100s of milliseconds may be a far-cry from the gold standard of 50-ms, but is often sufficient in non-voice networks.
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