[9]Henning Schulzrinne and Knarig Arabshian“Providing Emergency Services in Internet Telephony” Department of Computer Science Columbia University, New York, NY, MAY,JUNE 2002.
Elbayoumy, A. D., & Shepherd, S. (2007). A Comprehensive Secure VoIP Solution. International Journal of Network Security, 5(2), 233-240. https://doi.org/10.6633/IJNS.200709.5(2).17