With the increasing amount of software deployed in the common channel signaling networks (CCSNs) and its increasing complexity, software and its failure effects on the CCSNs have become a major concern. The software error contributing to the 1991 CCSN outages, which affected a large number of customer lines, has underscored the vulnerability of the CCSNs to software failures. The current mated pair signaling transfer point (STP) implementations in the CCSNs, with both STPs from the same supplier having the same software, make this architecture susceptible to common-cause software failure modes that might result in failures of both STPs simultaneously. To address these concerns, ways have been considered to achieve software diversity in the CCSNs by ensuring software failure mode independence among network nodes. Four potential alternatives are identified here: (i) multiple software developments in STPs; (ii) different software generics for backup; (iii) mixed-supplier STP pairs; and (iv) E-link sets to different supplier STPs. The advantages and disadvantages of these alternatives to ensure software diversity are examined in this paper and should be weighed by individual telecommunications network providers. concerns expressed in this paper are not exhaustive listings, but rather catalysts for further studies and discussions.
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