1. The European Emergency Number Association website. Overload of calls. https://eena.org/document/overload-of-calls/
2. Technion website. A Routing Policy for Call Centers Designed to Respond to Unexpected Overloads. http://iew.technion.ac.il/msom2010//msom.technion.ac.il/ confprogram/papers/MC/4/38.pdf
3. Lecture Notes in Computer Science;SN Stepanov,2019
4. Gans, N., Koole, M., Mandelbaum, A.: Telephone call-centers: tutorial, review and research prospects. Manuf. Serv. Manag. 5, 79–141 (2003)
5. Stolletz, R., Helber, S.: Perfomance analysis of an inbound call-center with skills-based routing. OR Spectr. 26, 331–352 (2004)