Synchronous Optical Network (SONET)technology has made high-speed self-healing ring (SHR) architecturespractical and economical for the uses in many local exchange carriers’ intralocal access transport area telecommunication networks. This paperanalyses the K-terminal reliability, i.e., the probability that a subsetof k specific terminal stations of an SONET SHR can communicate, forfour types of SONET SHRs and derives their K-terminal reliabilityexpressions.