A Comparison of SIP and H.323 for Internet Telephony

Two standards have recently emerged for signaling and control for Internet Telephony. One is ITU Recommendation H.323, and the other is the IETF Session Initiation Protocol (SIP). These two protocols represent very different approaches to the same problem: H.323 embraces the more traditional circuit-switched approach to signaling based on the ISDN Q.931 protocol and earlier H-series recommendations, and SIP favors the more lightweight Internet approach based on HTTP. In this paper, we compare SIP and H.323 on complexity, extensibility, scalability, and features. I. INTRODUCTION In order to provide useful services, Internet telephony requires a set of control protocols for connection establishment, capabilities exchange, and conference control. Currently, two protocols exist to meet this need. One is ITU-T H.323, and the other is the IETF Session Initiation Protocol (SIP). In this paper, we compare the two protocols on complexity, extensibility, scalability, and services. The ITU H.323 ...