Protocol testing for various applications real world applications can be analyzed using several methods, i.e. measurement, simulation and emulation. The first method from several method is live network testing. The second method is network simulation (simulation using Network Simulator) and the last method is emulation method (Emulab Testbed, DETER Testbed, and NIST Net). Emulation Method in network is the method which combines real elements of network application that has been deployed. For example an end host and protocol implementation, with synthetic elements, simulated or abstracted, such as network link, intermediate node, and background traffic. This paper shows the result of our experiment and testing of a Voice over Internet Protocol (VoIP) application using Session Initiation Protocol (SIP). VoIP testing is conducted using an open source network emulation software tool called NIST Net. VoIP that using SIP can be deployed in network that has been established. The network parameters used in our experiments are bandwidth and drop packets. The result shows the bandwidth and jitter characteristic during the experiment. The quality of VoIP depends on the number of drop packet. It can be summarized that the quality of VoIP depends on bandwidth, Jitter, and drop packet.