Evaluation of Security Protocols for the Session Initiation Protocol

Despite the popularity of VoIP these clays, this method of communication may present significant security challenges in terms of privacy and accounting. Authentication and message encryption are considered essential mechanisms in VoIP for it to be comparable to PSTN. SIP is responsible for setting up a secure call in VoIP. SIP employs TLS, DTLS or IPSec, combined with TCP, UDP or SCTP, as a security protocol in VoIP. These security mechanisms may introduce additional overheads into SIP performance. However, these overheads have not been understood in detail by the technical community. In this paper we demonstrate the effect of a security protocol on the performance of SIP by comparing the call setup delays that occur with various security protocols. We simulate the various combinations of three security protocols and three transport-layer protocols suggested for SIP. UDP with any combination of security protocols performs much better than the combination of TCP. TLS over SCTP may have more impact on performance on average. The reasons for the differences in SIP performances are given.