Protection using rings has been the common method of reducing downtime on SONET/SDH based telecommunication networks. With the trend towards IP over DWDM, there is a need for IP based protection and restoration mechanisms. In this paper, the mechanisms being developed at several standards organizations including OIF, IETF, and ITU are described. These mechanisms are in some sense more powerful than the previous SONET/SDH based mechanisms and protect against not only link and node failures but also against domain failures. Here domain refers to an entire region of the network. In particular, Shared Risk Group (SRG) concepts being developed at IETF and OIF is explained.
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