Traffic characteristics and modeling of emergency calls at the PSAP

In the recent years Voice over IP (VoIP) telephony started to migrate from research to the market. In the future, All-IP networks will substitute the classical Public Switched Telephone Networks (PSTNs). Nowadays, there is no All-IP network yet, but many VoIP-providers already enable calls from VoIP to a PSTN and vice versa. By doing so, critical infrastructures within the PSTN like Public Safety Answering Points (PSAP), are accessible from the VoIP network (e.g. the Internet). Thus, there is a need for reliable performance modeling and evaluation. One aspect of particular interest e.g. for the performance evaluation of intrusion detection architectures for emergency call services is the characterization and modeling of emergency call length and frequency. In this paper, we provide a detailed analysis of traces from different PSAPs. Our work is based on empirical long-time measurements at two PSAPs. Based on these traces we characterize the load's interarrival times and call lengths concerning variation of the load, dependencies, and scalability. Furthermore, we provide fittings of the empirical data to standard probability distributions.