Abstract
This paper characterizes the impact that the use of UDP versus TCP has on the performance and scalability of the OpenSER SIP proxy server. The Session Initiation Protocol (SIP) is an application-layer signaling protocol that is widely used for establishing Voice-over-IP (VoIP) phone calls. SIP can utilize a variety of transport protocols, including UDP and TCP. Despite the advantages of TCP, such as reliable delivery and congestion control, the common practice is to use UDP. This is a result of the belief that UDP