Safe and effective error rate monitors for SS7 signaling links

Abstract

This paper describes SS7 error monitor characteristics, discusses the existing SUERM (signal unit error rate monitor), and develops the recently 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 phenomena. Formal criteria for safe and effective error monitors are formulated. This paper develops models of changeover transients, the unstable component of queue length resulting from errors. These models are in the form of recursive digital filters. Time is divided into sequential intervals. The filter's input is the number of errors which have occurred in each interval. The output is the corresponding change in transmit queue length. Engineered EIMs are constructed by comparing an estimated changeover transient with a threshold T using a transient model modified to enforce SS7 standards. When this estimate exceeds T, a changeover will be initiated and the link will be removed from service. EIMs can be differentiated from SUERM by the fact that EIMs monitor errors over an interval while SUERMs count errored messages. EIM offer several advantages over SUERMs, including the fact that they are safe and effective, impose uniform standards in link quality, are easily implemented, and make minimal use of real-time resources. >