SAFE AND EFFECTIVE ERROR RATE MONITORS FOR SS7 SIGNALING LINKS

This paper describes SS7 error monitor characteristics, discusses the existing SUERM (Signal Unit Error Rate Monitor), and develops the rece ntly proposed EIM (Error Interval Monitor) for higher speed SS7 links. A SS7 error monitor is considered safe if it ensures acceptable link quality and is considered effective if it is tolerant to short-term ph enomena. Formal criteria for safe and effective error monitors are for mulated in this paper. This paper develops models of changeover transi ents, the unstable component of queue length resulting from errors. Th ese models are in the form of recursive digital filters. Time is divid ed into sequential intervals. The filter's input is the number of erro rs which have occurred in each interval. The output is the correspondi ng change in transmit queue length. Engineered EIM's are constructed b y comparing an estimated changeover transient with a threshold T using a transient model modified to enforce SS7 standards. When this estima te exceeds T, a changeover will be initiated and the link will be remo ved from service. EIM's can be differentiated from SUERM by the fact t hat EIM's monitor errors over an interval while SUERM's count errored messages. EIM's offer several advantages over SUERM's, including the f act that they are safe and effective, impose uniform standards in link quality, are easily implemented, and make minimal use of real-time re sources.