WASET
    Sa’ed Abed and  Mohammad H. Al Shayeji and  Ovais Ahmed and  Sahel Alouneh,  Formal Specification and Description Language and Message Sequence Chart to Model and Validate Session Initiation Protocol Services.   journal   = {International Journal of Computer and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    February 2016, vol. 111(3). 534 - 542
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/10004038.