This paper describes the usage of OPNET simulation tool to evaluate VoIP over MPLS networks which employs RSVP protocol as QoS mechanism with SIP or H.323 as signaling protocols for setting up VoIP calls over the Internet. The results showed that the H.323 with RSVP over MPLS networks produced minimal end-to-end delay than SIP protocol; making it a good choice as a signaling protocol with VoIP over MPLS networks for places requiring minimal end-to-end delay, while SIP reported lowest delay jitter with minimal call setup time
Azeddien M. Sllame, Asra Hema, Huda Alnajem(3-2018)

Virtual Private Network (VPN) technology provides a way of protecting information being transmitted over the Internet, by allowing users to establish a virtual private “tunnel” to securely enter an internal network, accessing resources, data and communications via an insecure network such as the Internet. A VPN is a communications environment in which access is controlled to permit peer connections only within a defined community of interest, and is constructed though some form of partitioning of a common underlying communications medium, where this underlying communications medium provides services to the network on a nonexclusive basis. arabic 6 English 50
Mariam Abojela Msaad, Amer R. Zerek, Hana H. saleh(1-2012)

This paper describes a comparative study of the performance of VoIP over wireless networks using OPNET tool. The simulation study is completed by running VoIP application in different network scenarios with IEEE 802.16 (UGS, ertPS) and IEEE 802.11 (b, g) with best effort service and interactive service The result clearly illustrated that the WiMax type ertPS has the best performance among all tested cases
Azeddien M. Sllame, Hana Soso, Mona Aown, Lamya Abdelmajeed(9-2016)