Analysis of the link error monitoring algorithms in the Signaling System Number 7 protocol

Link quality in the common channel signaling (CCS) network is monitored and reported by the Signaling System No.7 (SS7) protocol level 2 signaling link error monitoring procedures. The procedures include two algorithms: the signal unit error rate monitor (SUERM), which provides one of the criteria for taking the link out of service, and the alignment error rate monitor (AERM), which determines whether a link should be put into service. The authors, motivated by the excessive link status changes observed in some field operations of the CCS network provide a detailed analysis of the signaling link error monitoring algorithms and show that under current SS7 specifications of the error monitoring algorithms, the probability of a link oscillating in and out of service could be high for certain sustained error rates. While the risk to the existing network may not be high due to the light loads carried at present, there is still a need to study the error monitoring issues thoroughly