Narendra M. Shekokar and  Satish R. Devane,  A Novel Approach to Avoid Billing Attack on VOIP System.   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    February 2010, vol. 38(2). 340 - 344
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/4447.